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Sample records for ca sr substitution

  1. Magnetic characterization of Ca substituted Ba and Sr hexaferrites

    NASA Astrophysics Data System (ADS)

    Asti, G.; Carbucicchio, M.; Deriu, A.; Lucchini, E.; Slokar, G.

    1980-04-01

    A magnetic characterization has been worked out for the solid solution from Ba and Sr hexaferrites (BaFe 1 2O 1 9, SrFe 1 2O 1 9) towards CaO- xFe 2O 3 (2 ⪕ x ⪕5.5). Measurements of Curie temperature, saturation magnetization, magnetic anisotropy, together with Mössbauer characterization indicate that the intrinsic properties of the studied compounds do not change appreciably with increasing Ca content. These results, together with the X-ray data, are consistent with the formation of an undistorted M-type cell with a low content of iron and oxygen vacancies.

  2. Proton Matrix ENDOR Studies on Ca2+-depleted and Sr2+-substituted Manganese Cluster in Photosystem II.

    PubMed

    Nagashima, Hiroki; Nakajima, Yoshiki; Shen, Jian-Ren; Mino, Hiroyuki

    2015-11-20

    Proton matrix ENDOR spectra were measured for Ca(2+)-depleted and Sr(2+)-substituted photosystem II (PSII) membrane samples from spinach and core complexes from Thermosynechococcus vulcanus in the S2 state. The ENDOR spectra obtained were similar for untreated PSII from T. vulcanus and spinach, as well as for Ca(2+)-containing and Sr(2+)-substituted PSII, indicating that the proton arrangements around the manganese cluster in cyanobacterial and higher plant PSII and Ca(2+)-containing and Sr(2+)-substituted PSII are similar in the S2 state, in agreement with the similarity of the crystal structure of both Ca(2+)-containing and Sr(2+)-substituted PSII in the S1 state. Nevertheless, slightly different hyperfine separations were found between Ca(2+)-containing and Sr(2+)-substituted PSII because of modifications of the water protons ligating to the Sr(2+) ion. Importantly, Ca(2+) depletion caused the loss of ENDOR signals with a 1.36-MHz separation because of the loss of the water proton W4 connecting Ca(2+) and YZ directly. With respect to the crystal structure and the functions of Ca(2+) in oxygen evolution, it was concluded that the roles of Ca(2+) and Sr(2+) involve the maintenance of the hydrogen bond network near the Ca(2+) site and electron transfer pathway to the manganese cluster. PMID:26438823

  3. Partial substitution of calcium in Bi-Sr-Ca-Cu-O superconductor

    NASA Astrophysics Data System (ADS)

    Sýkorová, D.; Smrková, O.; Michna, E.

    2006-09-01

    Chemical substitutions may change structural and physical parameters in HTS. Substituents influence formation of Bi-2223 phase, pinning centers, intergrain connection and change hole carrier concentration. Bulk samples with partial substitution of calcium in Bi3.2Pb0.8Sr4Ca5-yMxCu7Oy by 5 B elements (M = V, Nb, Ta), x = 0-0.8 were prepared by solid state reaction in air. Resistivity and magnetic susceptibility measurements evaluated superconducting properties. Phase composition was checked by X-ray diffraction

  4. Influence of SrO substitution for CaO on the properties of bioactive glass S53P4.

    PubMed

    Massera, Jonathan; Hupa, Leena

    2014-03-01

    Commercial melt-quenched bioactive glasses consist of the oxides of silicon, phosphorus, calcium and sodium. Doping of the glasses with oxides of some other elements is known to affect their capability to support hydroxyapatite formation and thus bone tissue healing but also to modify their high temperature processing parameters. In the present study, the influence of gradual substitution of SrO for CaO on the properties of the bioactive glass S53P4 was studied. Thermal analysis and hot stage microscopy were utilized to measure the thermal properties of the glasses. The in vitro bioactivity and solubility was measured by immersing the glasses in simulated body fluid for 6 h to 1 week. The formation of silica rich and hydroxyapatite layers was assessed from FTIR spectra analysis and SEM images of the glass surface. Increasing substitution of SrO for CaO decreased all characteristic temperatures and led to a slightly stronger glass network. The initial glass dissolution rate increased with SrO content. Hydroxyapatite layer was formed on all glasses but on the SrO containing glasses the layer was thinner and contained also strontium. The results suggest that substituting SrO for CaO in S53P4 glass retards the bioactivity. However, substitution greater than 10 mol% allow for precipitation of a strontium substituted hydroxyapatite layer. PMID:24338267

  5. Electrical conductivity of cobalt-titanium substituted SrCaM hexaferrites

    NASA Astrophysics Data System (ADS)

    Eraky, M. R.

    2012-03-01

    A series of polycrystalline M-type hexagonal ferrites with the composition Sr0.5Ca0.5CoxTixFe12-2xO19 (where x=0.0-0.8) were prepared by the conventional ceramic technique. The electrical conductivity has been measured from 300 to 590 K. The dc conductivity, σdc, exhibited a semiconductor behavior. The negative sign of thermoelectric power coefficient S reveals that all samples are n-type semiconductors. Both σdc and mobility, μd, increases with the substitution of Co2+ and Ti4+ ions, reach maximum at x=0.4 and start decreasing at x>0.4. Many conduction mechanisms were discussed to explain the electric conduction in the system. It was found that the hopping conduction is the predominant conduction mechanism. For samples with compositional parameter x=0.0 and 0.8, the band conduction mechanism shares in electric conduction beside the hopping process.

  6. Ca-for-Sr substitution in the thermoelectric [(Sr,Ca){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}] misfit-layered cobalt-oxide system

    SciTech Connect

    Yamauchi, Hisao; Karvonen, Lassi; Egashira, Takayuki; Tanaka, Yoshiaki; Karppinen, Maarit

    2011-01-15

    Calcium-for-strontium substituted samples of the misfit-layered cobalt-oxide system, [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}], were successfully synthesized up to x=0.2 with a sample-encapsulation technique originally developed for the x=0 end phase. While the x=0 sample has a commensurate match between the two layer blocks (i.e. q=0.5), isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q>0.5). At the same time the Seebeck coefficient gets increased, but the increase in resistivity results in suppressing the thermoelectric power factor. The magnetic anomaly in the x=0 sample gets released upon the Ca substitution for the x=0.2 sample to exhibit an almost Curie-Weiss behavior. It is concluded that with increasing x in [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}] the properties smoothly evolve towards those previously reported for the x=1.0 end member, [Ca{sub 1.7}O{sub 2.1}H{sub 2.4}]{sub 0.58}[CoO{sub 2}]. -- Graphical abstract: In the misfit-layered [(Sr{sub 1-x}Ca{sub x}){sub 2}(O,OH){sub 2}]{sub q}[CoO{sub 2}] (0.0{<=}x{<=}0.2) system the x=0 phase has a commensurate match between the two layer blocks (i.e. q=0.5), while isovalent Ca-for-Sr substitution induces lattice misfit (i.e. q>0.5). At the same time Seebeck coefficient gets increased. Simultaneous increase in resistivity however outweighs this benefit, and accordingly the thermoelectric power factor is decreased. Display Omitted

  7. Observation of low-temperature magnetic ordering in mixed-phase Sr-Ca-Cu-O superconductors substituted by iron

    NASA Astrophysics Data System (ADS)

    Sklyarova, A.; Shinoda, S.; Nagumo, T.; Chizhik, V. I.; Matveev, V. V.; Suematsu, H.

    2016-08-01

    The series of unsubstituted Sr2CaCu2O6 and iron-substituted Sr2CaCu2‑x Fe x O6 (x=0.1,x=0.05) materials were produced by a high-pressure synthesis route and characterized using X-ray diffraction and SQUID magnetometry. The change of contained phase ratio was found at different substituent concentrations in the samples synthesized under the same conditions: unexpected growth of 0201 and CuO phase with decrease of iron content was observed. Synthesis temperature-dependence of obtained phase fractions was found for the samples with x=0.05. The superconductivity transition was found for all obtained samples and the highest critical temperature was around 103 K. From the SQUID measurements distortions of the magnetic susceptibility curves were found; these were explained by the magnetic ordering arising at low temperatures. This magnetic ordering was associated with the magnetic moment appearing in iron-doped 0201 phase.

  8. Microstructure and magnetic properties of Ca-substituted M-type SrLaCo hexagonal ferrites

    NASA Astrophysics Data System (ADS)

    Huang, Xin; Liu, Xiansong; Yang, Yujie; Huang, Kai; Niu, Xiaofei; Jin, Dali; Gao, Shang; Ma, Yuqi; Huang, Feng; Lv, Farui; Feng, Shuangjiu

    2015-03-01

    M-type strontium hexaferrites with chemical composition of Sr0.80-xCaxLa0.20Fe11.85Co0.15O19 (x=0-0.15) were prepared by the ceramic process. The samples were sintered at temperatures of 1175, 1185 and 1195 °C for 2 h in air. Effects of the substituted amount x of Ca2+ on the ferrites microstructure and magnetic properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and B-H hysteresis curve measurements. As a result, at x≤0.12, all samples are single phase after the Ca substitution. At x=0.15, another phase of hematite (α-Fe2O3) is present. In addition, the maximum values of the remanence (Br) and maximum energy product ((BH)max) for the magnets have been obtained at x=0.08 for sintering temperature=1185 °C. The maximum value of the intrinsic coercive force (Hcj) for the magnets has been obtained at x=0.12 when the magnets were sintered at 1185 °C.

  9. Ti doping-induced magnetic and morphological transformations in Sr- and Ca-substituted BiFeO3

    NASA Astrophysics Data System (ADS)

    Khomchenko, V. A.; Paixão, J. A.

    2016-04-01

    The investigation focuses on the crystal structure, microstructure, local ferroelectric and magnetic properties of the Bi0.9Sr0.1Fe1-x Ti x O3-δ (x  =  0.05, 0.1, 0.15; δ  =  (0.1  -  x)/2) multiferroics prepared by a solid-state reaction method. All the samples have been found to be isostructural with the pure BiFeO3 (the material crystallizes in a polar rhombohedral structure belonging to the space group R3c). It has been shown that the pattern of changes in the lattice parameters of the Bi0.9Sr0.1Fe1-x Ti x O3-δ samples can be interpreted as consistent with the doping-driven elimination of anion vacancies at x  ⩽  0.1 and the formation of cation vacancies at x  >  0.1. The readjustment of the defect structure associated with the mechanism of charge compensation in the aliovalent-substituted BiFeO3 is accompanied by correlated changes in the morphology, ferroelectric/ferroelastic domain structure and magnetic properties of the materials. In particular, it has been found that the deviation from the ideal (δ  =  0) cation-anion stoichiometry in the Bi0.9Sr0.1Fe1-x Ti x O3-δ system leads to a significant decrease in the average size of crystal grain and ferroelectric domains and gives rise to an antiferromagnetic-weak ferromagnetic transformation. Results of this study have been compared with those obtained for equally substituted samples of the Bi0.9Ca0.1Fe1-x Ti x O3-δ series (Khomchenko and Paixão 2015 J. Phys.: Condens. Matter 27 436002) to demonstrate how the variation in the chemical pressure introduced by the partial replacement of Bi3+ with bigger (Sr2+) and smaller (Ca2+) ions can affect the multiferroic behavior of Ti-doped bismuth ferrites.

  10. Ti doping-induced magnetic and morphological transformations in Sr- and Ca-substituted BiFeO3.

    PubMed

    Khomchenko, V A; Paixão, J A

    2016-04-27

    The investigation focuses on the crystal structure, microstructure, local ferroelectric and magnetic properties of the Bi0.9Sr0.1Fe1-x Ti(x)O(3-δ) (x  =  0.05, 0.1, 0.15; δ  =  (0.1  -  x)/2) multiferroics prepared by a solid-state reaction method. All the samples have been found to be isostructural with the pure BiFeO3 (the material crystallizes in a polar rhombohedral structure belonging to the space group R3c). It has been shown that the pattern of changes in the lattice parameters of the Bi0.9Sr0.1Fe(1-x)Ti(x)O(3-δ) samples can be interpreted as consistent with the doping-driven elimination of anion vacancies at x  ⩽  0.1 and the formation of cation vacancies at x  >  0.1. The readjustment of the defect structure associated with the mechanism of charge compensation in the aliovalent-substituted BiFeO3 is accompanied by correlated changes in the morphology, ferroelectric/ferroelastic domain structure and magnetic properties of the materials. In particular, it has been found that the deviation from the ideal (δ  =  0) cation-anion stoichiometry in the Bi0.9Sr0.1Fe(1-x)Ti (x)O(3-δ) system leads to a significant decrease in the average size of crystal grain and ferroelectric domains and gives rise to an antiferromagnetic-weak ferromagnetic transformation. Results of this study have been compared with those obtained for equally substituted samples of the Bi0.9Ca0.1Fe(1-x)Ti(x)O(3-δ) series (Khomchenko and Paixão 2015 J. Phys.: Condens. Matter 27 436002) to demonstrate how the variation in the chemical pressure introduced by the partial replacement of Bi(3+) with bigger (Sr(2+)) and smaller (Ca(2+)) ions can affect the multiferroic behavior of Ti-doped bismuth ferrites. PMID:27009357

  11. Control of the superconducting properties of Sr{sub 2−x}Ca{sub x}VO{sub 3}FeAs through isovalent substitution

    SciTech Connect

    Corkett, Alex J.; Free, David G.; Cassidy, Simon J.; Ramos, Silvia; Clarke, Simon J.

    2014-08-15

    The effect of the isovalent substitution of Sr{sup 2+} by Ca{sup 2+} on the structure and superconducting properties of Sr{sub 2−x}Ca{sub x}VO{sub 3}FeAs is described in the compositional range 0≤x≤0.5. SQUID magnetometry measurements reveal that after an initial increase in T{sub c}, which is maximised at 29.5 K in Sr{sub 1.95}Ca{sub 0.05}VO{sub 3}FeAs, a rapid suppression of superconductivity is observed with increasing x. XANES spectra of Sr{sub 2−x}Ca{sub x}VO{sub 3}FeAs collected on the Fe and V absorption K-edges show that the position of both edges are invariant with composition within the experimental uncertainty. A combination of synchrotron X-ray powder diffraction and neutron powder diffraction techniques is used to rationalise the observed changes in T{sub c} with x, in terms of changes to the structure of the FeAs layer upon partial Ca substitution. These findings demonstrate that superconductivity in the Fe-based superconductors is extremely sensitive to the crystal structure with T{sub c} maximised in samples with regular FeAs{sub 4}-tetrahedra. - Graphical abstract: Superconducting transition temperature is controlled by structural parameters in Sr{sub 2−x}Ca{sub x}VO{sub 3}FeAs. - Highlights: • Substitution of Sr by Ca in the superconductor Sr{sub 2}VO{sub 3}FeAs is isovalent. • Relationship between superconducting T{sub c} and structural parameters is demonstrated. • Linear dependence of T{sub c} on structural parameters rather than composition.

  12. AC Dielectric Properties and Positron Annihilation Study on Co and Ti Substitution Effect on Ca-Sr M-Hexaferrites

    NASA Astrophysics Data System (ADS)

    Mahmoud, K. R.; Eraky, M. R.

    2016-06-01

    The dependence of AC conductivity σ AC, dielectric constant έ, and dielectric loss tangent tan δ on frequency and composition have been investigated at room temperature for polycrystalline Ca0.5Sr0.5Co x Ti x Fe12 - 2 x O19 (where 0.0 ≤ x ≤ 0.8) hexaferrites. It was found that the parameters σ AC, ɛ ', and tan δ have maximum values at x = 0.4 of the Co and Ti substitution. The behavior of σ AC, ɛ ', and tan δ with frequency and composition was explained on the basis of the hopping conduction mechanism and the Koops model. Positron annihilation lifetime spectroscopy (PALS) was used to investigate the defects and changes in electron density for hexaferrite samples. The PAL parameters ( τ 1, I 1, τ 2, I 2, and mean lifetime) show that altering the doping percentage of the Co and Ti ions affects the size and concentration of defects. The results reveal that there are some large voids in the studied samples. The obtained results indicate the high sensitivity of the PALS technique to the enhanced structure changes with changing composition of the investigated samples and correlate the results with the measured electrical parameters.

  13. Ab-initio study of the magnetism, structure and spin dependent electronic states of Ti substituted MO (M = Mg, Ca, Sr)

    NASA Astrophysics Data System (ADS)

    Jaiganesh, G.; Jaya, S. Mathi

    2015-06-01

    The magnetism, structure and spin polarized electronic structure of Ti substituted MO (M = Mg, Ca, Sr) are studied using the ab-initio techniques within the framework of the density functional theory. Appropriately constructed supercell along with the full structural optimization of these cells is used for studying the influence of Ti substitution on the magnetism and electronic structure of these compounds. We find from our calculations that the Ti substituted MO compounds energetically favor magnetically ordered state. The Ti concentration is found to be important in deciding the magnetic order and we have observed antiferromagnetic order for the Ti concentration of 0.25. The Ti substituted MO compounds are thus an interesting class of materials that deserve further studies.

  14. Ab-initio study of the magnetism, structure and spin dependent electronic states of Ti substituted MO (M = Mg, Ca, Sr)

    SciTech Connect

    Jaiganesh, G. Jaya, S. Mathi

    2015-06-24

    The magnetism, structure and spin polarized electronic structure of Ti substituted MO (M = Mg, Ca, Sr) are studied using the ab-initio techniques within the framework of the density functional theory. Appropriately constructed supercell along with the full structural optimization of these cells is used for studying the influence of Ti substitution on the magnetism and electronic structure of these compounds. We find from our calculations that the Ti substituted MO compounds energetically favor magnetically ordered state. The Ti concentration is found to be important in deciding the magnetic order and we have observed antiferromagnetic order for the Ti concentration of 0.25. The Ti substituted MO compounds are thus an interesting class of materials that deserve further studies.

  15. Microstructural and transport properties in substituted Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}-modulated compounds

    SciTech Connect

    Autret-Lambert, C. . E-mail: cecile.autret@univ-tours.fr; Pignon, B.; Gervais, M.; Monot-Laffez, I.; Ruyter, A.; Ammor, L.; Gervais, F.; Bassat, J.M.; Decourt, R.

    2006-06-15

    X-ray powder diffraction and resistivity measurements were performed on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} ceramics substituted by Y and Zn for Ca and Cu sites, respectively. X-ray diffraction patterns show an incommensurate modulated structure along the b-axis. The structural refinements were carried out using the four-dimensional space group Bbmb(0{beta}1)000. From the X-ray peak profiles analysis, an anisotropic line-shape broadening was observed. The use of the ''Williamson and Hall'' method allows distinguishing the origin of broadening as mainly due to microstrains. A large transition from a metallic to semiconductor behaviour is observed on the resistivity curves at x{approx}0.4 for Bi{sub 2}Sr{sub 2}Ca{sub 1-x}Y{sub x}Cu{sub 2}O{sub 8+{delta}} and at x{sup '}{approx}0.36 for Bi{sub 2}Sr{sub 2}Ca{sub 1-x}Y{sub x}Cu{sub 1.94}Zn{sub 0.06}O{sub 8+{delta}}, which can be also correlated to the defects. Oppositely to the metallic behaviour, which satisfies the Mathiessen's rule, the semiconducting one can be modelled by a variable range hopping process.

  16. Effect of cation substitution on structural transition: synthesis, characterization and theoretical studies of NaCa4B3O9, NaCaBO3, NaSrBO3 and Li4CaB2O6.

    PubMed

    Yang, Yun; Su, Xin; Pan, Shilie; Yang, Zhihua

    2015-10-21

    Single crystals of NaCa4B3O9, NaCaBO3, NaSrBO3 and Li4CaB2O6 have been successfully synthesized through conventional high-temperature solid-state reactions. They are structurally characterized by single crystal X-ray diffraction and exhibit three-dimensional crystal structures consisting of isolated planar BO3 as fundamental building blocks. Interestingly, for the centrosymmetric crystal structure of NaCaBO3 (Na3Ca3B3O9), as 2/3 of the Na(+) ions are substituted by Ca(2+) ions, NaCa4B3O9 is obtained and crystallizes in the noncentrosymmetric space group Ama2 (crystal class mm2). A second harmonic generation (SHG) test of the title compound by the Kurtz-Perry method shows that NaCa4B3O9 can be phase matchable with an effective SHG coefficient approximately one-half that of KH2PO4 (KDP). Studies of their optical properties as well as band structure calculations based on density functional theory methods have been also performed. NaCa4B3O9 possesses a moderate birefringence of about 0.05 at 1064 nm. To explain the difference in optical nonlinearity we compared the electronic structures of NaCa4B3O9, KCa4B3O9 and KSr4B3O9 crystals, in particular at the bottom of the conduction band (CB) and the top of the valence band (VB), since they are known to play a primary role in SHG. These electronic structures are responsible for the optical-nonlinearity of NaCa4B3O9, KCa4B3O9 and KSr4B3O9 crystals. PMID:26387438

  17. Crystal structure refinement, dielectric and magnetic properties of Ca/Pb substituted SrFe12O19 hexaferrites

    NASA Astrophysics Data System (ADS)

    Hooda, Ashima; Sanghi, Sujata; Agarwal, Ashish; Dahiya, Reetu

    2015-08-01

    SrFe12O19 (SFO), Sr0.5Ca0.5Fe12O19 (SCFO) and Sr0.5Pb0.5Fe12O19 (SPFO) hexaferrites have been synthesized by a conventional solid state reaction technique. Powder X-ray diffraction and Rietveld refinement confirm the presence of M-type hexagonal phase in prepared samples. However in SCFO, secondary phase was also present with main phase. Analysis of Nyquist's plots of SFO hexaferrite revealed the contribution of many electrically active regions corresponding to bulk mechanism, distribution of grain boundaries and electrode processes also. Both conductivity and electric modulus formalisms have been employed to study the relaxation dynamics of charge carriers. A perfect overlapping of the normalized plots of modulus isotherms on a single 'super curve' for all the studied temperatures reveals a temperature independence of dynamic processes involved in conduction and for relaxation. In SPFO sample coercivity is reduced effectively but accompanied with increase in magnetization, which is requirement for hexaferrites to be used as magnetic recording media.

  18. Effect of diamagnetic Ca, Sr, Pb, and Ba substitution on the crystal structure and multiferroic properties of the BiFeO3 perovskite

    NASA Astrophysics Data System (ADS)

    Khomchenko, V. A.; Kiselev, D. A.; Vieira, J. M.; Jian, Li; Kholkin, A. L.; Lopes, A. M. L.; Pogorelov, Y. G.; Araujo, J. P.; Maglione, M.

    2008-01-01

    In this work, we studied the effect of heterovalent Ca, Sr, Pb, and Ba substitution on the crystal structure, dielectric, local ferroelectric, and magnetic properties of the BiFeO3 multiferroic perovskite. Ceramic solid solutions with the general formula Bi0.7A0.3FeO3 (A is a doping element) were prepared and characterized by x-ray diffraction, dielectric, piezoresponse force microscopy (PFM), and magnetic measurements. It is shown that the crystal structure of the compounds is described within the space group R3c, permitting the spontaneous polarization, whose existence was confirmed by the PFM data. Magnetic properties of the solid solutions are determined by the ionic radius of the substituting element. Experimental results suggest that the increase in the radius of the A-site ion leads to the effective suppression of the spiral spin structure of BiFeO3, resulting in the appearance of net magnetization.

  19. Isovalent Ca and Ba substitutions in thermoelectric layer-structured oxyselenide Sr2CoO2Cu2Se2

    NASA Astrophysics Data System (ADS)

    Chou, T. L.; Mustonen, O.; Tripathi, T. S.; Karppinen, M.

    2016-01-01

    Multilayered compounds typically present exotic functionalities, and some of them have been suggested as potential materials for thermoelectric conversion owing to their unique capability to decouple electronic and heat transport. Here we report new [CoO2] and [Cu2Se2] layered A 2CoO2Cu2Se2 compounds in which Sr at the intervening alkaline-earth A site is partially replaced with Ca or Ba. The parent Sr2CoO2Cu2Se2 phase is a direct gap p-type semiconductor, and density functional theory (DFT) calculations indicate its topmost valence band consists of Cu 3d-Se 4p states. Upon the isovalent cation substitution the lattice modification in the ab plane is constrained by the stiff [CoO2] layer such that the lattice shrinkage/expansion mainly happens along the c axis. Substitution of Sr with the heavier and larger Ba significantly enhances the thermopower but more hole states would be required to optimize the thermoelectric performance. Thermal stability is related to the inter-oxide-selenide-layer interaction, and our thermogravimetric measurement data reveal that the A 2CoO2Cu2Se2 materials could operate in the intermediate temperature region.

  20. Isovalent Ca and Ba substitutions in thermoelectric layer-structured oxyselenide Sr2CoO2Cu2Se2.

    PubMed

    Chou, T L; Mustonen, O; Tripathi, T S; Karppinen, M

    2016-01-27

    Multilayered compounds typically present exotic functionalities, and some of them have been suggested as potential materials for thermoelectric conversion owing to their unique capability to decouple electronic and heat transport. Here we report new [CoO2] and [Cu2Se2] layered A2CoO2Cu2Se2 compounds in which Sr at the intervening alkaline-earth A site is partially replaced with Ca or Ba. The parent Sr2CoO2Cu2Se2 phase is a direct gap p-type semiconductor, and density functional theory (DFT) calculations indicate its topmost valence band consists of Cu 3d-Se 4p states. Upon the isovalent cation substitution the lattice modification in the ab plane is constrained by the stiff [CoO2] layer such that the lattice shrinkage/expansion mainly happens along the c axis. Substitution of Sr with the heavier and larger Ba significantly enhances the thermopower but more hole states would be required to optimize the thermoelectric performance. Thermal stability is related to the inter-oxide-selenide-layer interaction, and our thermogravimetric measurement data reveal that the A2CoO2Cu2Se2 materials could operate in the intermediate temperature region. PMID:26702873

  1. Substitution of chromium for univalent copper in superconducting Pb{sub 2}Sr{sub 2}(Ca, Y)Cu{sub 3}O{sub 8-{delta}}

    SciTech Connect

    Seshadri, R.; Maignan, A.; Hervieu, M.

    1996-11-15

    Following considerations of geometry and the similarity between chromate and carbonate groups in terms of size and charge, the authors have investigated the possibility of replacing the two-coordinate Cu{sup I} in superconducting lead cuprates of the general formula Pb{sub 2}Sr{sub 2}(Ca, Y)Cu{sub 3}O{sub 8} by Cr. A high-resolution electron microscopy study coupled with energy dispersive X-ray analysis on small crystals of the title phases suggests that between 10 and 15% of the Cu{sup 1} can be replaced by Cr. While from the present structural study using HRTEM and Rietveld refinement of X-ray powder data the authors are unable to precisely obtain the oxidation state and oxygen coordination of Cr, the authors suggest in analogy with Cr substitution in other similar cuprates that in the title phases Cu{sup I}O{sub 2} rods are partially replaced by tetrahedral CrO{sub 4}{sup 2-} groups. Infrared spectroscopy supports the presence of CrO{sub 4}{sup 2-} groups. The phases Pb{sub 1.75}Sr{sub 2}Ca{sub 0.2}Y{sub 0.8}Cu{sub 3}O{sub 8-{delta}} and Pb{sub 1.75}Sr{sub 2}Ca{sub 0.2}Y{sub 0.8}Cu{sub 2.85}Cr{sub 0.15}O{sub 8-{delta}} are superconducting as-prepared, but the substitution of Cr for Cu{sup I} results in a decrease of the T{sub C} as well as the superconducting volume fraction.

  2. Computational insights on crystal structures of the oxygen-evolving complex of photosystem II with either Ca²⁺ or Ca²⁺ substituted by Sr²⁺

    SciTech Connect

    Vogt, Leslie; Ertem, Mehmed Z.; Pal, Rhitankar; Brudvig, Gary W.; Batista, Victor S.

    2015-01-15

    The oxygen-evolving complex of photosystem II can function with either Ca²⁺ or Sr²⁺ as the heterocation, but the reason for differing turnover rates remains unresolved despite reported X-ray crystal structures for both forms. Using quantum mechanics/molecular mechanics (QM/MM) calculations, we optimize structures with each cation in both the resting state (S₁) and in a series of reduced states (S₀, S₋₁, and S-₂). Through comparison with experimental data, we determine that X-ray crystal structures with either Ca²⁺ or Sr²⁺ are most consistent with the S-₂ state, Mn₄[III,III,III,II] with O4 and O5 protonated. As expected, the QM/MM models show that Ca²⁺/Sr²⁺ substitution results in elongation of the heterocation bonds and displaces terminal waters W3 and W4. The optimized structures also show that hydrogen-bonded W5 is displaced in all S states with Sr²⁺ as the heterocation, suggesting that this water may play a critical role during water oxidation.

  3. Effect of Hf substitutions on the formation and superconductivity of Tl-1212 type phase TlSr{sub 2}(Ca{sub 1−x}Hf{sub x})Cu{sub 2}O{sub 7−δ}

    SciTech Connect

    Al-Sharabi, Annas; Abd-Shukor, R.

    2013-11-27

    The TlSr{sub 2}(Ca{sub 1−x}Hf{sub x})Cu{sub 2}O{sub 7−δ} (Tl-1212) superconductor for x = 0.0 to 0.4 has been prepared by the solid state reaction method and studied by powder X-ray diffraction method, electrical resistance and scanning electron microscope (SEM). Most of the samples showed the Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Hf-substitution (x ≤ 0.15 or x ≤ 0.25) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature (T{sub c} {sub onset}) between 38 and 47 K for Hf substitution.

  4. Computational insights on crystal structures of the oxygen-evolving complex of photosystem II with either Ca²⁺ or Ca²⁺ substituted by Sr²⁺

    DOE PAGESBeta

    Vogt, Leslie; Ertem, Mehmed Z.; Pal, Rhitankar; Brudvig, Gary W.; Batista, Victor S.

    2015-01-15

    The oxygen-evolving complex of photosystem II can function with either Ca²⁺ or Sr²⁺ as the heterocation, but the reason for differing turnover rates remains unresolved despite reported X-ray crystal structures for both forms. Using quantum mechanics/molecular mechanics (QM/MM) calculations, we optimize structures with each cation in both the resting state (S₁) and in a series of reduced states (S₀, S₋₁, and S-₂). Through comparison with experimental data, we determine that X-ray crystal structures with either Ca²⁺ or Sr²⁺ are most consistent with the S-₂ state, Mn₄[III,III,III,II] with O4 and O5 protonated. As expected, the QM/MM models show that Ca²⁺/Sr²⁺ substitutionmore » results in elongation of the heterocation bonds and displaces terminal waters W3 and W4. The optimized structures also show that hydrogen-bonded W5 is displaced in all S states with Sr²⁺ as the heterocation, suggesting that this water may play a critical role during water oxidation.« less

  5. Anisotropic scattering rate in Fe-substituted Bi2Sr2Ca(Cu1-xFex)2O8+δ

    DOE PAGESBeta

    Naamneh, M.; Lubashevsky, Y.; Lahoud, E.; Gu, G.; Kanigel, A.

    2015-05-27

    We measured the electronic structure of Fe substituted Bi2212 using Angle Resolved Photoemission Spectroscopy (ARPES). We find that the substitution does not change the momentum dependence of the superconducting gap but induces a very anisotropic enhancement of the scattering rate. A comparison of the effect of Fe substitution to that of Zn substitution suggests that the Fe reduces Tc so effectively because it supresses very strongly the coherence weight around the anti-nodes.

  6. Effect of Sr and Ca solid-solution behaviour on superconductive properties as determined by microstructure analysis

    NASA Astrophysics Data System (ADS)

    Hong, Zhanglian; Wang, Minquan; Xiong, Guohong; Fan, Xianping

    1997-02-01

    The effects of the Sr and Ca composition and site-selection in a solid solution of a Bi-system superconductor on the superconductive properties were studied. Results showed that the Sr and Ca solid-solution behaviour had a remarkable effect on the superconductive properties. Further analysis indicated that this effect originated from varied hole concentration which was determined by the content of Sr atoms substituting for Bi atoms within the BiO layers. This substitution was influenced by the Sr and Ca solid-solution behaviour. This result offers a new mechanism for clarifying why the bivalent Sr and Ca cations affect the superconductive properties.

  7. Hydrothermal synthesis and characterization of Si and Sr co-substituted hydroxyapatite nanowires using strontium containing calcium silicate as precursors.

    PubMed

    Zhang, Na; Zhai, Dong; Chen, Lei; Zou, Zhaoyong; Lin, Kaili; Chang, Jiang

    2014-04-01

    In the absence of any organic surfactants and solvents, the silicon (Si) and strontium (Sr) co-substituted hydroxyapatite [Ca10(PO4)6(OH)2, Si/Sr-HAp] nanowires were synthesized via hydrothermal treatment of the Sr-containing calcium silicate (Sr-CS) powders as the precursors in trisodium phosphate (Na3PO4) aqueous solution. The morphology, phase, chemical compositions, lattice constants and the degradability of the products were characterized. The Si/Sr-HAp nanowires with diameter of about 60nm and up to 2μm in length were obtained after hydrothermal treatment of the Sr-CS precursors. The Sr and Si substitution amount of the HAp nanowires could be well regulated by facile tailoring the Sr substitution level of the precursors and the reaction ratio of the precursor/solution, respectively. The SiO4 tetrahedra and Sr(2+) ions occupied the crystal sites of the HAp, and the lattice constants increased apparently with the increase of the substitution amount. EDS mapping also suggested the uniform distribution of Si and Sr in the synthetic nanowires. Moreover, the Si/Sr-substitution apparently improved the degradability of the HAp materials. Our study suggested that the precursor transformation method provided a facile approach to synthesize the Si/Sr co-substituted HAp nanowires with controllable substitution amount, and the synthetic Si/Sr-HAp nanowires might be used as bioactive materials for hard tissue regeneration applications. PMID:24582251

  8. Characterization of Sr-substituted hydroxyapatite thin film by sputtering technique from mixture targets of hydroxyapatite and strontium apatite.

    PubMed

    Ozeki, K; Goto, T; Aoki, H; Masuzawa, T

    2014-01-01

    Sr-substituted hydroxyapatite thin films were prepared by sputtering technique from mixture targets of hydroxyapatite (HA) and strontium apatite (SrAp). The HA and SrAp powders were mixed at 0-100% Sr/(Sr+Ca) target ratios. The coated films were recrystallized by a hydrothermal treatment to reduce film dissolution. The films were then characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and inductively coupled plasma atomic emission spectrometry (ICP). The osteocompatiblity of the films was also evaluated by the size of the bone formation area in osteoblast cells.In the XRD patterns, peaks shifted to lower 2θ values with increasing Sr/(Sr+Ca) target ratios, which indicated Sr incorporation into the HA lattice. In the SEM observation of the hydrothermally treated films, the surface was covered with globular particles, and the size of the globular particles increased from Sr0 to Sr40, and then the size decreased from Sr60 to Sr100. The ICP analysis showed that the Sr/(Sr+Ca) film ratios were almost the same as the target ratios. In the cell culture, the bone formation area on the Sr-substituted HA films increased with increasing Sr concentration, and saturated at Sr60. PMID:24642972

  9. Photoluminescence Properties of Efficient Blue-Emitting Phosphor α-Ca1.65Sr0.35SiO4:Ce(3+): Color Tuning via the Substitutions of Si by Al/Ga/B.

    PubMed

    Li, Kai; Shang, Mengmeng; Lian, Hongzhou; Lin, Jun

    2015-08-17

    A series of Ce(3+)-doped α-Ca1.65Sr0.35SiO4 (CSSO) phosphors without and with the substitutions of Si by Al/Ga/B were synthesized via the high-temperature solid-state reaction process. X-ray diffraction patterns and Rietveld refinements were used to demonstrate the successful incorporations of Al/Ga/B into CSSO:Ce(3+). Without Al/Ga/B, the Ce(3+) singly doped CSSO phosphors present intense blue emission, which correspond to the broad emission bands in visible region with the wavelength range from 360 to 580 nm upon 350 nm excitation. The optimal emission intensity occurs in CSSO:0.05Ce(3+) sample with the emission peak wavelength at 436 nm. With the introduction of Al/Ga/B into the CSSO:0.05Ce(3+), the emission peak shifts from 436 to 457/465/446 nm under 365 nm excitation, respectively. The red shift of Ce(3+) emission is attributed to the polyhedral distortion of the cations, resulting in the enhancement of crystal field spitting due to the variations of the adjacent (Al/Ga/B,Si)O4 polyhedron. Moreover, the temperature-dependent photoluminescence was determined to be of light impact to CSSO:Ce(3+) with the introduction of Al/Ga/B. This research is useful for enriching the emission colors of Ce(3+)-activated phosphors. PMID:26247562

  10. Electronic structure of Ca, Sr, and Ba under pressure.

    NASA Technical Reports Server (NTRS)

    Animalu, A. O. E.; Heine, V.; Vasvari, B.

    1967-01-01

    Electronic band structure calculations phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure electronic band structure calculations for fcc phase of Ca, Sr and Ba over wide range of atomic volumes under pressure

  11. Regional and interspecific variation in Sr, Ca, and Sr/Ca ratios in avian eggshells from the USA.

    PubMed

    Mora, Miguel A; Brattin, Bryan; Baxter, Catherine; Rivers, James W

    2011-08-01

    To examine regional variation in strontium (Sr), which at high concentrations may reduce eggshell quality, increase egg breakage and reproductive failure, we analyzed Sr, and calcium (Ca) concentrations and Sr/Ca ratios in eggshells from 20 avian species from California, Texas, Idaho, Kansas, and Michigan. In addition, we included data previously reported from Arizona to expand the regional comparisons and to better establish patterns of Sr, and Sr/Ca ratios in bird species across the United States. We found Sr concentrations varied significantly among regions, among species, and among foraging guilds; this variability is strongly influenced by the Sr/Ca ratios in surface water from locations close to the region where the eggshells were collected. Sr concentrations and Sr/Ca ratios were significantly higher in bird eggshells from the Volta wildlife region in the San Joaquin Valley, California and in various locales from Arizona. Sr concentrations and Sr/Ca ratios in bird eggshells from other locations in the USA were lower than those detected in these two regions. Among foraging guilds, invertivores had the highest Sr concentrations and Sr/Ca ratios and carnivores had the lowest. In general, the Sr/Ca ratio increased strongly with increasing Sr concentrations (R(2) = 0.99, P < 0.0001). There was a significant correlation (R(2) = 0.58, P < 0.0001) between Sr/Ca ratios in water and the average Sr/Ca ratios in eggshells suggesting that these values could be determined from Sr/Ca ratios in water. Eggshell thickness was poorly correlated with Sr (R(2) = 0.03) but had a significant and positive correlation with Ca and was more properly correlated by a quadratic equation (R(2) = 0.50, Thickness = 2.13 - 0.02Ca - 3.07 * 10(-5)Ca(2)). Our study provides further evidence that Sr accumulates significantly in the avian eggshell, in some regions at concentrations which could be of concern for potential negative effects on reproduction. We suggest that when assessing the effects

  12. Lattice site location and annealing behavior of implanted Ca and Sr in GaN

    NASA Astrophysics Data System (ADS)

    De Vries, B.; Vantomme, A.; Wahl, U.; Correia, J. G.; Araújo, J. P.; Lojkowski, W.; Kolesnikov, D.

    2006-07-01

    We report on the lattice location of ion-implanted Ca and Sr in thin films of single-crystalline wurtzite GaN. Using the emission channeling technique the angular distributions of β- particles emitted by the radioactive isotopes 45Ca (t1/2=163.8 d) and 89Sr (t1/2=50.53 d) were monitored with a position-sensitive detector following 60 keV room-temperature implantation. Our experiments give direct evidence that ˜90% of Ca and >60% of Sr atoms were occupying substitutional Ga sites with root mean square displacements of the order of 0.15-0.30 Å, i.e., larger than the expected thermal vibration amplitude of 0.074 Å. Annealing the Ca implanted samples at 1100-1350 °C in high-pressure N2 atmosphere resulted in a better incorporation into the substitutional Ga site. The Sr implanted sample showed a small decrease in rms displacements for vacuum annealing up to 900 °C, while the substitutional fraction remained nearly constant. The annealing behavior of the rms displacements can explain why annealing temperatures above 1100 °C are needed to achieve electrical and optical activations, despite the fact that the majority of the acceptors are already located on Ga sites immediately after ion implantation.

  13. Allometric constraints on Sr/Ca and Ba/Ca partitioning in terrestrial mammalian trophic chains.

    PubMed

    Balter, Vincent

    2004-03-01

    In biological systems, strontium (Sr) and barium (Ba) are two non-essential elements, in comparison to calcium (Ca) which is essential. The Sr/Ca and Ba/Ca ratios tend to decrease in biochemical pathways which include Ca as an essential element, and these processes are termed biopurification of Ca. The quantitative pathway of the biopurification of Ca in relation to Sr and Ba between two biological reservoirs ( Rn and R(n -1)) is measured with an observed ratio (OR) expressed by the (Sr/Ca) Rn /(Sr/Ca)( Rn-1) and (Ba/Ca) Rn /(Ba/Ca)( Rn-1) ratios. For a mammalian organism, during the whole biopurification of Ca starting with the diet to the ultimate reservoir of Ca which is the bone, the mean values for ORSr and ORBa are 0.25 and 0.2, respectively. In this study, published Sr/Ca and Ba/Ca ratios are used for three sets of soils, plants, and bones of herbivorous and carnivorous mammals, each comprising a trophic chain, to illustrate the biopurification of Ca at the level of trophic chains. Calculated ORSr and ORBa of herbivore bones in relation to plants and of bones of carnivores in relation to bones of herbivores give ORSr=0.30+/-0.08 and ORBa=0.16+/-0.08, thus suggesting that trophic chains reflect the Sr/Ca and Ba/Ca fluxes that are prevalent at the level of a mammalian organism. The slopes of the three regression equations of log(Sr/Ca) vs. log(Ba/Ca) are similar, indicating that the process of biopurification of Ca with respect to Sr and Ba is due to biological processes and is independent of the geological settings. Modifications of the logarithmic expression of the Sr/Ca and Ba/Ca relationship allow a new formula of the biopurification process to be deduced, leading to the general equation ORBa=ORSr(1.79+/-0.33), where the allometric coefficient is the mean of the slopes of the three regression equations. Some recent examples are used to illustrate this new analysis of predator-prey relations between mammals. This opens up new possibilities for the

  14. Biocompatibility and biodegradability of Mg-Sr alloys: the formation of Sr-substituted hydroxyapatite.

    PubMed

    Bornapour, M; Muja, N; Shum-Tim, D; Cerruti, M; Pekguleryuz, M

    2013-02-01

    Magnesium is an attractive material for use in biodegradable implants due to its low density, non-toxicity and mechanical properties similar to those of human tissue such as bone. Its biocompatibility makes it amenable for use in a wide range of applications from bone to cardiovascular implants. Here we investigated the corrosion rate in simulated body fluid (SBF) of a series of Mg-Sr alloys, with Sr in the range of 0.3-2.5%, and found that the Mg-0.5 Sr alloy showed the slowest corrosion rate. The degradation rate from this alloy indicated that the daily Sr intake from a typical stent would be 0.01-0.02 mg day⁻¹, which is well below the maximum daily Sr intake levels of 4 mg day⁻¹. Indirect cytotoxicity assays using human umbilical vascular endothelial cells indicated that Mg-0.5 Sr extraction medium did not cause any toxicity or detrimental effect on the viability of the cells. Finally, a tubular Mg-0.5 Sr stent sample, along with a WE43 control stent, was implanted into the right and left dog femoral artery. No thrombosis effect was observed in the Mg-0.5 Sr stent after 3 weeks of implantation while the WE43 stent thrombosed. X-ray diffraction demonstrated the formation of hydroxyapatite and Mg(OH)₂ as a result of the degradation of Mg-0.5 Sr alloy after 3 days in SBF. X-ray photoelectron spectroscopy further showed the possibility of the formation of a hydroxyapatite Sr-substituted layer that presents as a thin layer at the interface between the Mg-0.5 Sr alloy and the corrosion products. We believe that this interfacial layer stabilizes the surface of the Mg-0.5 Sr alloy, and slows down its degradation rate over time. PMID:22871640

  15. Structural investigations of (Ca,Sr)ZrO3 and Ca(Sn,Zr)O3 perovskite compounds

    NASA Astrophysics Data System (ADS)

    Tarrida, Martine; Larguem, H.; Madon, M.

    2009-07-01

    (Ca x ,Sr1- x )ZrO3 and Ca(Sn y ,Zr1- y )O3 solid solutions were synthesized by solid-state reaction at high temperature before to be studied by powder X-ray diffraction and Raman Spectroscopy. Diffraction data allow the distortion of the ABO3 perovskite structure to be investigated according to cations substitution on A and B-sites. It is shown that distortion, characterized by Φ, the tilt angle of BO6 octahedra, slightly increases with decreasing y content in Ca(Sn y ,Zr1- y )O3 compounds and strongly decreases with decreasing x content in (Ca x ,Sr1- x )ZrO3 compounds. Such results are discussed in view of the relative A and B cation sizes. Raman data show that vibrational spectra are strongly affected by the cation substitution on A-site; the frequencies of most vibrational modes increase with increasing x content in (Ca x ,Sr1- x )ZrO3 compounds, i.e. with the decreasing mean size of the A-cation; the upper shift is observed for the 358 cm-1 mode (∂ ν/∂r = -60.1 cm-1/Å). On the other hand, the cation substitution on B-sites, slightly affect the spectra; it is shown that in most cases, the frequency of vibrational modes increases with increasing y content in Ca(Sn y ,Zr1- y )O3 compounds, i.e. with the decreasing mean size of the B-cation, but that two modes (287 and 358 cm-1) behave differently: their frequencies decrease with the decreasing mean size of the B-cation, with a shift respectively equal to +314 and +162 cm-1/Å. Such results could be used to predict the location of different elements such as trivalent cations or radwaste elements on A- or B-site, in the perovskite structure.

  16. Negative feedback from CaSR signaling to aquaporin-2 sensitizes vasopressin to extracellular Ca2.

    PubMed

    Ranieri, Marianna; Tamma, Grazia; Di Mise, Annarita; Russo, Annamaria; Centrone, Mariangela; Svelto, Maria; Calamita, Giuseppe; Valenti, Giovanna

    2015-07-01

    We previously described that high luminal Ca(2+) in the renal collecting duct attenuates short-term vasopressin-induced aquaporin-2 (AQP2) trafficking through activation of the Ca(2+)-sensing receptor (CaSR). Here, we evaluated AQP2 phosphorylation and permeability, in both renal HEK-293 cells and in the dissected inner medullary collecting duct, in response to specific activation of CaSR with NPS-R568. In CaSR-transfected cells, CaSR activation drastically reduced the basal levels of AQP2 phosphorylation at S256 (AQP2-pS256), thus having an opposite effect to vasopressin action. When forskolin stimulation was performed in the presence of NPS-R568, the increase in AQP2-pS256 and in the osmotic water permeability were prevented. In the freshly isolated inner mouse medullar collecting duct, stimulation with forskolin in the presence of NPS-R568 prevented the increase in AQP2-pS256 and osmotic water permeability. Our data demonstrate that the activation of CaSR in the collecting duct prevents the cAMP-dependent increase in AQP2-pS256 and water permeability, counteracting the short-term vasopressin response. By extension, our results suggest the attractive concept that CaSR expressed in distinct nephron segments exerts a negative feedback on hormones acting through cAMP, conferring high sensitivity of hormone to extracellular Ca(2+). PMID:25977473

  17. Sr / Ca and Mg / Ca ratios in polygenetic carbonate allochems from a Michigan marl lake

    NASA Astrophysics Data System (ADS)

    Treese, Thomas N.; Owen, Robert M.; Wilkinson, Bruce H.

    1981-03-01

    Rapid accumulation of CaCO 3 is occurring in Littlefield Lake, a marl lake located in central Michigan. The sediment, which is 95% CaCO 3, primarily consists of eight different genetic groups of carbonate allochems. These include calcite muds, sands, algal oncoids and Chara encrustations, as well as the dominant aragonitic gastropods Valvota tricarinota. Gyraulus deflectus and Amnicola integra. and the dominant aragonitic pelecypod Sphaerium partumeium. Samples of each of these groups were analyzed for Ca, Sr and Mg. Molar Mg/Ca ratios are primarily controlled by allochem mineralogy, with calcitic forms having Mg/Ca ratios 5-10 times larger than aragonitic (shelled) forms. The Sr/Ca ratios are primarily controlled by biochemical fractionation, and are significantly lower than Sr/Ca ratios of inorganically precipitated aragonite from other settings. Partition coefficients were determined for both Sr and Mg for each carbonate allochem group and, based on comparisons with results reported by other workers, the partition coefficients determined here are generally considered 'typical' or representative values for biogeneous freshwater carbonates. An analysis of variance of the data indicates that most genera and species of carbonate-secreting organisms in marl lakes have highly characteristic Sr/Ca and Mg/Ca ratios. These ratios can potentially serve as geochemical tracers in future investigations of lacustrine carbonate diagenesis. Both Sr and Mg are influenced by grain size and/or surface area, probably due to the presence of these elements in non-lattice-held (exchangeable) positions.

  18. Structural and optical properties of Bi1-xAxFeO3 (A = Sr, Ca; 0.40 ⩽ x ⩽ 0.55)

    NASA Astrophysics Data System (ADS)

    Thakur, Samita; Pandey, O. P.; Singh, K.

    2014-09-01

    The effect of Sr2+ and Ca2+ cation substitution on BiFeO3-type (Bi1-xAxFeO3; A = Sr, Ca; 0.40 ⩽ x ⩽ 0.55) ceramics are investigated for structural and optical properties. X-ray diffraction patterns confirmed that Ca2+/Sr2+ substitution facilitates the formation of tetragonal phase instead of rhombohedral phase as observed in undoped BiFeO3 (BFO). The iodometric titration results show that substitution of Sr2+ has higher tendency to form oxygen vacancies than Ca2+ substituted samples. On the other hand, Ca2+ substitution shows opposite trend. The FT-IR and Raman spectra show shift in the peak positions towards higher wavenumber and diffused bands with the increasing concentration of substituent. The parameters like band gap energy, Urbach energy has been calculated from the UV-visible spectra. Sr2+ substituted samples show higher structural distortion and low optical band gap values which can be correlated to the higher oxygen vacancies and low Fe4+ content as compared to Ca2+ substituted samples.

  19. Anisotropic scattering rate in Fe-substituted Bi2Sr2Ca(Cu1-xFex)2O8+δ

    SciTech Connect

    Naamneh, M.; Lubashevsky, Y.; Lahoud, E.; Gu, G.; Kanigel, A.

    2015-05-27

    We measured the electronic structure of Fe substituted Bi2212 using Angle Resolved Photoemission Spectroscopy (ARPES). We find that the substitution does not change the momentum dependence of the superconducting gap but induces a very anisotropic enhancement of the scattering rate. A comparison of the effect of Fe substitution to that of Zn substitution suggests that the Fe reduces Tc so effectively because it supresses very strongly the coherence weight around the anti-nodes.

  20. The influence of SrO and CaO in silicate and phosphate bioactive glasses on human gingival fibroblasts.

    PubMed

    Massera, J; Kokkari, A; Närhi, T; Hupa, L

    2015-06-01

    In this paper, we investigate the effect of substituting SrO for CaO in silicate and phosphate bioactive glasses on the human gingival fibroblast activity. In both materials the presence of SrO led to the formation of a CaP layer with partial Sr substitution for Ca. The layer at the surface of the silicate glass consisted of HAP whereas at the phosphate glasses it was close to the DCPD composition. In silicate glasses, SrO gave a faster initial dissolution and a thinner reaction layer probably allowing for a continuous ion release into the solution. In phosphate glasses, SrO decreased the dissolution process and gave a more strongly bonded reaction layer. Overall, the SrO-containing silicate glass led to a slight enhancement in the activity of the gingival fibroblasts cells when compared to the SrO-free reference glass, S53P4. The cell activity decreased up to 3 days of culturing for all phosphate glasses containing SrO. Whereas culturing together with the SrO-free phosphate glass led to complete cell death at 7 days. The glasses containing SrO showed rapid cell proliferation and growth between 7 and 14 days, reaching similar activity than glass S53P4. The addition of SrO in both silicate and phosphate glasses was assumed beneficial for proliferation and growth of human gingival fibroblasts due to Sr incorporation in the reaction layer at the glass surface and released in the cell culture medium. PMID:26099346

  1. A systematic study of superconductivity in BiPb(Sn)-Sb Sr-Ca-Cu-O systems

    NASA Technical Reports Server (NTRS)

    Akbar, Sheikh A.; Botelho, M. J.; Wong, M. S.; Alauddin, M.

    1990-01-01

    Superconducting transition above 160 K has been reported in the Bi-Pb-Sb-Sr-Ca-Cu-O system. Results of a systematic study emphasizing the correlations between the type and amount of dopant, and superconducting transition is presented. The effect of Sn (instead of Pb) substitution is also highlighted.

  2. Theoretical electric quadrupole transition probabilities for Ca, Sr and Ba

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.; Langhoff, S. R.; Jaffe, R. L.; Partridge, H.

    1984-01-01

    The 1D-1S quadrupole transition probabilities for Ca, Sr and Ba have been computed using extended GTO and STO valence basis sets and configuration-interaction wavefunctions that include the important core-valence correlation effects. For Ba and Sr, the relativistic contraction of the core orbitals was accounted for in the GTO calculations by a relativistic effective-core potential. The computed Einstein coefficient for Ca of 39.6/s is in excellent agreement with the recent experimental value of 40 + or - 8/s. The best Einstein coefficients for Sr (44.7/s) and Ba (2.98/s) imply increasing quadrupole line strengths down the column. Relativistic effects substantially increase the quadrupole Einstein coefficient for Ba.

  3. Synthesis of BiPbSrCaCuO superconductor

    DOEpatents

    Hults, William L.; Kubat-Martin, Kimberly A.; Salazar, Kenneth V.; Phillips, David S.; Peterson, Dean E.

    1994-01-01

    A process and a precursor composition for preparing a lead-doped bismuth-strontium-calcium-copper oxide superconductor of the formula Bi.sub.a Pb.sub.b Sr.sub.c Ca.sub.d Cu.sub.e O.sub.f wherein a is from about 1.7 to about 1.9, b is from about 0.3 to about 0.45, c is from about 1.6 to about 2.2, d is from about 1.6 to about 2.2, e is from about 2.97 to about 3.2 and f is 10.+-.z by reacting a mixture of Bi.sub.4 Sr.sub.3 Ca.sub.3 Cu.sub.4 O.sub.16.+-.z, an alkaline earth metal cuprate, e.g., Sr.sub.9 Ca.sub.5 Cu.sub.24 O.sub.41, and an alkaline earth metal plumbate, e.g., Ca.sub.2-x Sr.sub.x PbO.sub.4 wherein x is about 0.5, is disclosed.

  4. Synthesis of BiPbSrCaCuO superconductor

    DOEpatents

    Hults, W.L.; Kubat-Martin, K.A.; Salazar, K.V.; Phillips, D.S.; Peterson, D.E.

    1994-04-05

    A process and a precursor composition for preparing a lead-doped bismuth-strontium-calcium-copper oxide superconductor of the formula Bi[sub a]Pb[sub b]Sr[sub c]Ca[sub d]Cu[sub e]O[sub f] wherein a is from about 1.7 to about 1.9, b is from about 0.3 to about 0.45, c is from about 1.6 to about 2.2, d is from about 1.6 to about 2.2, e is from about 2.97 to about 3.2 and f is 10[+-]z by reacting a mixture of Bi[sub 4]Sr[sub 3]Ca[sub 3]Cu[sub 4]O[sub 16[+-]z], an alkaline earth metal cuprate, e.g., Sr[sub 9]Ca[sub 5]Cu[sub 24]O[sub 41], and an alkaline earth metal plumbate, e.g., Ca[sub 2[minus]x]Sr[sub x]PbO[sub 4] wherein x is about 0.5, is disclosed.

  5. Ge/Si, Ca/Sr and 87Sr/86Sr tracers of biogeochemical sources and cycling of Si and Ca at the Shale Hills CZO

    NASA Astrophysics Data System (ADS)

    Derry, L. A.; Meek, K.; Sparks, J. P.

    2014-12-01

    Plant uptake and cycling of nutrients is commonly the largest flux of nutrients in terrestrial ecosystems. Hydrologic and other losses are offset by inputs from atmospheric deposition and weathering. We measured elemental and isotopic compositions from soil solution, soil exchange complex, leaves and sapwater from two canopy species, soil and rock samples, and stream and ground waters at the Shale Hills CZO. Xylem fluid and leaf samples have similar Ge/Si < 1 μmo/mol, consistent with fractionation at the root-soil water interface. Ge/Si in soil waters is higher Ge/Si near the surface and increases over the growing season, indicating preferential uptake of Si. Ca/Sr in leaves of Quercus are significantly higher (450±150) than for Acer (200±100), and Ca/Sr is generally higher in leaves than in xylem, consistent with Ca uptake during transpiration. 87Sr/86Sr in both are similar for a given site, implying that the trees access similar pools of Sr and Ca, although there are site-to-site differences. Data on litterfall rates and transpiration rates yield similar estimates of plant cycling of Ca and Si. 87Sr/86Sr in soil solutions from ridgtop and swale sites are well explained by mixing Sr derived from shale and atmospheric deposition. Valley bottom soil solutions and stream and groundwater samples include Sr and Ca derived from dissolution of diagenetic carbonates, found in drill cuttings. A preliminary estimate of the Sr and Ca stream fluxes and isotopic mass balances imply propagation of a carbonate weathering front of ca. 200 m/Ma, faster than previously reported regolith weathering advance rates based on on cosmogenic nuclides and U series (Jin et al., 2010; Ma et al., 2010). These rates are not strictly comparable and differences are at least in part consistent with the greater depth of the carbonate weathering front (Brantley et al, 2013). The data for Ca, Sr, Si and Ge in soil, soil solutions and stream waters reflects the interaction of slower weathering

  6. Quantifying Saline Groundwater Discharge to the Rio Grande using 87Sr/86Sr and [Ca]/[Sr] Ratios

    NASA Astrophysics Data System (ADS)

    Hogan, J. F.; Phillips, F. M.; Mills, S. K.; Ruiz, J.; Chesley, J. T.

    2002-12-01

    Issues of water quality, especially salinity, limit the use of water resources from the Rio Grande. Identification and quantification of salinity sources is critical for improved river management. We have conducted winter and summer synoptic sampling of the Rio Grande from the headwaters in Colorado to south of El Paso, Texas. The total dissolved solids content (TDS) of the Rio Grande increases from less than 50 mg/L in headwater regions of Colorado to greater than 2000 mg/L south of El Paso, Texas. Increases in salinity are not a simple function of distance downriver, but rather occur in a series of steps. Many of these increases are located at the lower end of sedimentary basins leading to the hypothesis that they are the result of discharge of deep, saline, groundwaters. Of particular interest is the Albuquerque and Socorro basins where, in three distinct steps, the TDS of the river doubles from ~ 150 mg/L to ~ 300 mg/L. With little change in river discharge for this reach, this represents a significant increase in the solute burden of the river. We have used 87Sr/86Sr and [Ca]/[Sr] ratios to "fingerprint" and quantify saline groundwater discharge. The Rio Grande entering the Albuquerque basin has an 87Sr/86Sr ratio of 0.7096and a [Ca]/[Sr] ratio of 80. These values are consistent with a mixture of atmospheric deposition and weathering of basalt rock found upstream. Traveling through the Albuquerque and Socorro basin the Rio Grande shifts to a 87Sr/86Sr ratio of 0.7102 and a [Ca]/[Sr] ratio of 30, values which are consistent with saline groundwater discharge. Mixing relationships indicate only two solute sources are required, and that a total saline groundwater discharge rate of ~ 50 cfs is sufficient to explain the observed salinity increases.

  7. Growth rate effects on Mg/Ca and Sr/Ca ratios constrained by belemnite calcite

    NASA Astrophysics Data System (ADS)

    Vinzenz Ullmann, Clemens

    2016-04-01

    Multiple temperature proxies from single species are important to achieve robust palaeotemperature estimates. Besides the commonly employed oxygen isotope thermometer, also Mg/Ca and Sr/Ca ratios perform well as proxies for calcification temperature in the shells of some species. While salinity changes affect the ratios of earth alkaline elements much less than the δ18O thermometer, metabolic effects may exert a strong control on the expression of element ratios. Such effects are hard to study because biomineralization experiments have to overcome large intraspecific variability and can hardly ever isolate the controls of a single parameter on shell geochemistry. The unique geometry of the belemnite rostrum constitutes an exception to this rule. Its shape, large size, and the visibility of growth increments as bands enable the analysis of multiple, correlatable, high resolution geochemical profiles in a single fossil. The effects of the growth rate variability amongst these profiles on Mg/Ca and Sr/Ca ratios has been tested here. Within a specimen of Passaloteuthis bisulcata (Early Toarcian, Cleveland Basin, UK), Mg/Ca and Sr/Ca data were obtained from four profiles. With respect to growth rate in the first profile, which was taken as a reference, the relative growth rates in the remaining three profiles varied by a factor of 0.9 to 2.7. Results suggest that relative growth rate is linearly correlated with Mg/Ca and Sr/Ca, with a decrease of Mg/Ca by 8 % and increase of Sr/Ca by 6 % per 100 % increase in relative growth rate. The observed trends are consistent with abiogenic precipitation experiments and suggest that crystal precipitation rate exerts a significant, predictable control on the element distribution in biogenic calcite.

  8. Sr/Ca and Ba/Ca variations in environmental and biological sources: A survey of marine and terrestrial systems

    NASA Astrophysics Data System (ADS)

    Peek, Stephanie; Clementz, Mark T.

    2012-10-01

    The relative concentrations of strontium to calcium (Sr/Ca) and barium to calcium (Ba/Ca) in mammalian bioapatite are common biogeochemical indicators for trophic level and/or dietary preferences in terrestrial foodwebs; however, similar research in marine foodwebs is lacking. This study combined environmental and biological Sr/Ca and Ba/Ca data from both terrestrial and marine settings from 62 published books, reports, and studies along with original data collected from 149 marine mammals (30 species) and 83 prey items (18 species) and found that variations in Sr/Ca and Ba/Ca ratios of biological and environmental samples are appreciably different in terrestrial and marine systems. In terrestrial systems, environmental sources account for most of the variations in Sr/Ca and Ba/Ca ratios. In contrast, environmental sources in marine systems (i.e., seawater) are comparatively invariant, meaning most of the variations in Sr/Ca and Ba/Ca ratios originate from biological processes. Marine consumers, particularly non-mammalian and mammalian vertebrates, show evidence of biopurification of Ca relative to Sr and Ba, similar to what is observed in terrestrial systems; however, unlike terrestrial systems, variations in Sr/Ca and Ba/Ca ratios of environmental sources are overprinted by bioaccumulation of Sr and Ba at the base of marine foodwebs. This demonstrates that in marine systems, spatial or temporal differences may have little to no effect on Sr/Ca and Ba/Ca ratios of marine vertebrates, making Sr/Ca, and to a lesser extent Ba/Ca, potentially useful global proxies for trophic level and dietary preferences of marine vertebrates.

  9. Temperature Dependent Sr-Isotope (δ 88Sr) and Ca-Isotope (δ 44Ca) Fractionation in Carbonate Precipitates and Corals

    NASA Astrophysics Data System (ADS)

    Eisenhauer, A.; Fietzke, J.; Gussone, N.; Böhm, F.; Bock, B.; Nägler, T.

    2003-12-01

    The knowledge of the influence of temperature and other environmental factors on isotope fractionation of divalent cations like Ca2+ and Sr2+ during inorganic and biogenic controlled precipitation of calcium carbonate is crucial for their interpretation as paleo proxies. In order to extend our earlier studies on Ca-isotope fractionation (e.g. Gussone et al., 2003), we determined δ 88Sr isotope ratios on seawater and on corals. We define the stable Sr isotope ratio as δ 88Sr=((88Sr/86Sr)Sample/(88Sr/86Sr)Standard -1)*1000; Sr Standard is NBS 987. First measurements of the IAPSO seawater standard result in δ 88Sr of 0.38+/-0.02 ‰ . Coral CaCO3 precipitated from seawater in a temperature range from about 22° C to about 27° C correspond to δ 88Sr-values ranging from 0.17 ‰ to about 0.32 ‰ indicating that carbonate precipitated from seawater is isotopically lighter than seawater itself. The slope of 0.027 ‰ /° C for the temperature-δ 88Sr relationship in corals is about a factor of 1.7 larger than the slope of δ 44Ca ratios in inorganically precipitated aragonite. However, the fractionation α (T)=((88Sr/86Sr)CaCO3)/(88Sr/86Sr)Seawater) at a given temperature is about one order of magnitude less for Sr-isotopes relative to Ca-isotopes. The larger temperature-δ 88Sr gradient in comparison to the Ca-isotopes is interpreted to reflect the smaller ion potential and the correspondingly smaller mass of the associated Sr2+-aquocomplex. The observation that δ 88Sr and δ 44Ca are positively correlated with temperature points to the likelihood that kinetic or equilibrium fractionation effects and the mass of the associated acquocomplex control the degree of divalent cation isotope fractionation during CaCO3-precipitation. Reference: Gussone N., Eisenhauer A., Heuser A., Dietzel M., Bock B., Böhm F., Spero H., Lea D. W., Bijma J., and Nägler T. F. (2003) Model for Kinetic Effects on Calcium Isotope Fractionation (δ 44Ca) in Inorganic Aragonite and Cultured

  10. Processing & properties La{sub 1-x}A{sub x}Co{sub 1-y}Fe{sub y}O{sub 3}(A = Sr, Ca) perovskites

    SciTech Connect

    Stevenson, J.W.; Armstrong, T.R.; Pederson, L.R.

    1995-04-01

    Selected compositions within the system La{sub 1-x}A{sub x}Co{sub 1-y}Fe{sub y}O{sub 3-{delta}}(A = Sr, Ca) were prepared by combustion synthesis and characterized by XRD, TGA, electrical conductivity, and oxygen permeation measurements. Substantial weight loss (due to loss of lattice oxygen) was observed in some compositions at high temperatures. For Sr containing materials, this weight loss increased with increasing Sr content. A substantial decrease in electronic conductivity was observed at high temperatures in Sr doped materials; this decrease was related to the decreased oxygen stoichiometry at these temperatures. In Sr doped compositions, oxygen flux increased with increasing Sr content. Calculated values of ionic conductivity were greater than the conductivity of yttria stabilized zirconia. Substitution of Ca for Sr resulted in substantially lower fluxes.

  11. La and Sr substituted Pr{sub 2}NiO{sub 4+{delta}}: Oxygenation and electrical properties

    SciTech Connect

    Allancon, C.; Odier, P.; Loup, J.P.; Bassat, J.M.

    1997-06-01

    We report herein results concerning the solid solutions Pr{sub 2-x}M{sub x}NiO{sub 4+{delta}}, M = La, Sr. These two cations are larger than praseodymium and lead to a structural stabilization. The oxygen excess {delta} decreases with x for La and Sr substituted Pr{sub 2}NiO{sub 4+{delta}}. Both cases suggest that structural strain is a leading factor for the oxygenation ability of the title compounds. From the evolution of cell parameters, we suggest a phase transition for La substituted compounds occurring for x {approximately} 1-1.2. Surprisingly, this transition has a negligible effect on transport properties. On the other hand, a charge localization linked to the presence of praseodymium is observed. Owing to charge compensation, the Sr substituted compounds have a quasi-constant hole concentration (formally 50%) for x < 0.5. The Pr{sub 2-x}Sr{sub x}NiO{sub 4+{delta}} solid solution shows an anomalous behavior for x = 0.5 corresponding to Ni{sup 2+}/Ni{sup 3+} = 1. This anomaly combines an enhancement of the c/a ratio, a larger resistivity, and a peak for the activation energy of the resistivity versus T.

  12. CaCO3 and SrCO3 bioprecipitation by fungi isolated from calcareous soil.

    PubMed

    Li, Qianwei; Csetenyi, Laszlo; Paton, Graeme Iain; Gadd, Geoffrey Michael

    2015-08-01

    The urease-positive fungi Pestalotiopsis sp. and Myrothecium gramineum, isolated from calcareous soil, were examined for their properties of CaCO3 and SrCO3 biomineralization. After incubation in media amended with urea and CaCl2 and/or SrCl2 , calcite (CaCO3 ), strontianite (SrCO3 ), vaterite in different forms [CaCO3 , (Cax Sr1-x )CO3 ] and olekminskite [Sr(Sr,Ca)(CO3 )2 ] were precipitated, and fungal 'footprints' were observed on mineral surfaces. The amorphous precipitate mediated by Pestalotiopsis sp. grown with urea and equivalent concentrations of CaCl2 and SrCl2 was identified as hydrated Ca and Sr carbonates by Fourier transform infrared spectroscopy. Liquid media experiments showed M. gramineum possessed the highest Sr(2+) removal ability, and ∼ 49% of supplied Sr(2+) was removed from solution when grown in media amended with urea and 50 mM SrCl2 . Furthermore, this organism could also precipitate 56% of the available Ca(2+) and 28% of the Sr(2+) in the form of CaCO3 , SrCO3 and (Cax Sr1-x )CO3 when incubated in urea-amended media and equivalent CaCl2 and SrCl2 concentrations. This is the first report of biomineralization of olekminskite and coprecipitation of Sr into vaterite mediated by fungi. These findings suggest that urease-positive fungi could play an important role in the environmental fate, bioremediation or biorecovery of Sr or other metals and radionuclides that form insoluble carbonates. PMID:26119362

  13. Trace element proxies (Sr/Ca, Ba/Ca and Pb/Ca) in Bivalve shells: environmental signals or not?

    NASA Astrophysics Data System (ADS)

    Gillikin, D. P.; Dehairs, F.; Steenmans, D.; Meng, L.; Haifeng, T.; Navez, J.; Andre, L.; Baeyens, W.; Keppens, E.; Calmars Group,.

    2004-12-01

    Coral and sclerosponge skeletons have both been used as recorders of their environment. Sr/Ca, Ba/Ca and Pb/Ca have all shown to be useful in these substrates, giving insight into the past environment in which the skeleton grew (e.g., Lea et al., 1989, Nature 340, 373-376; Beck et al., 1992, Science 257, 644-647; Lazareth et al., 2000, Geology 28, 515-518; Rosenheim et al., 2004, Geology 32, 145-148). Although bivalves have not been studied as extensively as corals, these proxies are apparently not as reliable in bivalves (e.g., Vander Putten et al., 2000, GCA 64, 997-1011). We therefore investigate Sr/Ca and Pb/Ca in two species of aragonitic clams (Mercenaria mercenaria and Saxidomus giganteus) and Ba/Ca in the calcite layer of the mussel Mytilus edulis. Results indicate that Sr/Ca is primarily controlled by growth rate in S. giganteus whereas there was no relationship between these parameters in M. mercenaria. Pb/Ca is somewhat reproducible between specimens of S. giganteus, however long-term Pb/Ca records (1949-2003) in the shell of M. mercenaria did not show the expected curve of anthropogenically introduced lead, indicating that they are not recording environmental Pb concentrations. Therefore, Sr/Ca and Pb/Ca incorporation seem to be regulated by biological processes and not directly by environmental parameters. Ba/Ca in M. edulis shells on the other hand, does seem to be directly linked to the environment. Shells grown under laboratory and natural conditions both show the same linear relationship between dissolved Ba/Ca and shell Ba/Ca. Experiments involving manipulations of dissolved and particulate (i.e. food) Ba/Ca, suggest that the dominant pathway of barium into the shell is from the dissolved phase via the hemolymph. We were unable to explain the large peaks noted in the Ba/Ca profiles, however, they did not seem linked to phytoplankton blooms as has been previously suggested (Stecher et al., 1996, GCA 60, 3445-3456; Vander Putten et al., 2000

  14. Improvements of magnetic properties of Sr ferrite magnets by substitutions of La and Co

    SciTech Connect

    Ogata, Yasunobu; Kubota, Yutaka; Takami, Takashi; Tokunaga, Masaaki; Shinohara, Tadashi

    1999-09-01

    Recently, it is intensively required to improve the magnetic properties of Sr ferrite magnets in order to decrease the weight of motors used in automobiles and to improve the efficiency of motors used in electric appliances such as air conditioners. The effect of the simultaneous partial substitution of Co{sup 2+} for Fe{sup 3+} and of La{sup 3+} for Sr{sup 2+} ion in Sr ferrite on the magnetic properties of anisotropic Sr ferrite magnets was investigated. It was found that the coercive force of Sr ferrite magnets is increased without significant decrease in residual flux density by La-Co substitution. Temperature coefficients of coercive force were found to be also improved by La-Co substitution.

  15. Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite

    NASA Astrophysics Data System (ADS)

    Zougrou, I. M.; Katsikini, M.; Brzhezinskaya, M.; Pinakidou, F.; Papadopoulou, L.; Tsoukala, E.; Paloura, E. C.

    2016-08-01

    Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy.

  16. Ca L2,3-edge XANES and Sr K-edge EXAFS study of hydroxyapatite and fossil bone apatite.

    PubMed

    Zougrou, I M; Katsikini, M; Brzhezinskaya, M; Pinakidou, F; Papadopoulou, L; Tsoukala, E; Paloura, E C

    2016-08-01

    Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L 2,3-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca(1) and Ca(2) sites in the unit cell gives rise to specific spectral features. Moreover, Ca L 2,3-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L 2,3-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca(1) or Ca(2) sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. PMID:27379398

  17. Analysis of coupled Sr/Ca and 87Sr/ 86Sr variations in enamel using laser-ablation tandem quadrupole-multicollector ICPMS

    NASA Astrophysics Data System (ADS)

    Balter, Vincent; Telouk, Philippe; Reynard, Bruno; Braga, José; Thackeray, Francis; Albarède, Francis

    2008-08-01

    We present in this study results obtained with a laser-ablation coupled with both a quadrupole and a multi-collector ICPMS. The simultaneous in situ Sr/Ca and 87Sr/ 86Sr measurements along growth profiles in enamel allows the concomitant diet and migration patterns in mammals to be reconstructed. Aliquots of the powdered international standard NIST "SRM1400 Bone Ash" with certified Sr and Ca contents, was sintered at high pressure and temperature and was adopted as the reference material for external reproducibility and calibration of the results. A total of 145 coupled elemental and isotopic measurements of herbivores enamel from the Kruger National Park, South Africa, gives intra-tooth Sr/Ca and 87Sr/ 86Sr variations that are well larger than external reproducibility. Sr/Ca profiles systematically decrease from the dentine-enamel junction to the outer enamel whereas 87Sr/ 86Sr profiles exhibit variable patterns. Using a simple geometric model of hypsodont teeth growth, we demonstrate that a continuous recording of the 87Sr/ 86Sr variations can be reconstructed in the tooth length axis. This suggests that the mobility of a mammal can be reconstructed over a period of more than a year with a resolution of a ten of days, by sampling enamel along growth profiles. Our geometric model of hypsodont teeth growth predicts that an optimal distance between two successive profiles is equal to the enamel thickness. However, this model does not apply to the Sr/Ca signal which is likely to be altered during the enamel maturation stage due to differential maturation processes along enamel thickness. Here, the observed constant decreases of the Sr/Ca ratios in the ungulates of Kruger National Park suggests that they did not changed of diet, while some of them were migrating.

  18. Late INa increases diastolic SR-Ca2+-leak in atrial myocardium by activating PKA and CaMKII

    PubMed Central

    Fischer, Thomas H.; Herting, Jonas; Mason, Fleur E.; Hartmann, Nico; Watanabe, Saera; Nikolaev, Viacheslav O.; Sprenger, Julia U.; Fan, Peidong; Yao, Lina; Popov, Aron-Frederik; Danner, Bernhard C.; Schöndube, Friedrich; Belardinelli, Luiz; Hasenfuss, Gerd; Maier, Lars S.; Sossalla, Samuel

    2015-01-01

    Aims Enhanced cardiac late Na current (late INa) and increased sarcoplasmic reticulum (SR)-Ca2+-leak are both highly arrhythmogenic. This study seeks to identify signalling pathways interconnecting late INa and SR-Ca2+-leak in atrial cardiomyocytes (CMs). Methods and results In murine atrial CMs, SR-Ca2+-leak was increased by the late INa enhancer Anemonia sulcata toxin II (ATX-II). An inhibition of Ca2+/calmodulin-dependent protein kinase II (Autocamide-2-related inhibitory peptide), protein kinase A (H89), or late INa (Ranolazine or Tetrodotoxin) all prevented ATX-II-dependent SR-Ca2+-leak. The SR-Ca2+-leak induction by ATX-II was not detected when either the Na+/Ca2+ exchanger was inhibited (KBR) or in CaMKIIδc-knockout mice. FRET measurements revealed increased cAMP levels upon ATX-II stimulation, which could be prevented by inhibition of adenylyl cyclases (ACs) 5 and 6 (NKY 80) but not by inhibition of phosphodiesterases (IBMX), suggesting PKA activation via an AC-dependent increase of cAMP levels. Western blots showed late INa-dependent hyperphosphorylation of CaMKII as well as PKA target sites at ryanodine receptor type-2 (-S2814 and -S2808) and phospholamban (-Thr17, -S16). Enhancement of late INa did not alter Ca2+-transient amplitude or SR-Ca2+-load. However, upon late INa activation and simultaneous CaMKII inhibition, Ca2+-transient amplitude and SR-Ca2+-load were increased, whereas PKA inhibition reduced Ca2+-transient amplitude and load and additionally slowed Ca2+ elimination. In atrial CMs from patients with atrial fibrillation, inhibition of late INa, CaMKII, or PKA reduced the SR-Ca2+-leak. Conclusion Late INa exerts distinct effects on Ca2+ homeostasis in atrial myocardium through activation of CaMKII and PKA. Inhibition of late INa represents a potential approach to attenuate CaMKII activation and decreases SR-Ca2+-leak in atrial rhythm disorders. The interconnection with the cAMP/PKA system further increases the antiarrhythmic potential of late

  19. The Sr/Ca-temperature relationship in coralline aragonite: Influence of variability in (Sr/Ca)[sub seawater] and skeletal growth parameters

    SciTech Connect

    de Villiers, S.; Shen, G.T.; Nelson, B.K. )

    1994-01-01

    This paper provides an evaluation of two of the most likely pitfalls of Sr/Ca thermometry, i.e., the effect of biogenic cycling of Sr vs. Ca in the surface ocean and the effect of variable extension rate on Sr incorporation in coralline aragonite. The authors also report calibration of the Sr/Ca-temperature relationship for three coral species, Porites lobata, Pocillopora eydouxi, and Pavona clavus, collected for the Hawaiian and Galapagos islands. Analyses of seawater samples show significant spatial and depth variability in the Sr:Ca ratio. The uncertainty introduced by this effect is estimated to be <0.2[degrees]C for corals located in tropical oligotrophic waters, and potentially larger for corals located in upwelling areas. Sr/Ca along two different growth axes of a Galapagos Pavona clavus, with annual extension rates of [approximately]6 and 12 mm/y, respectively, indicate an offset of 1-2[degrees]C, with higher Sr/Ca values associated with slower extension rates. The offset observed between the two growth axes may be the result of variations in extension and/or calcification rate. These results are important in determining past sea surface temperatures for reconstruction of paleoclimates.

  20. Determination of Sr and Ca sources in small tropical catchments (La Selva, Costa Rica) - A comparison of Sr and Ca isotopes

    NASA Astrophysics Data System (ADS)

    Wiegand, B. A.; Schwendenmann, L.

    2013-04-01

    SummaryA comparative study of Sr and Ca isotopes was conducted to assess solute sources and effects of biogeochemical processes on surface water and groundwater in four small tropical catchments located at La Selva Biological Station, Costa Rica. Variable concentrations of dissolved Sr2+ and Ca2+ in the catchments are related to mixing of waters from different origin. Three catchments are influenced by high-solute bedrock groundwater, while another catchment is primarily supplied by local recharge. 87Sr/86Sr ratios were employed to discriminate contributions from mineral weathering and atmospheric sources. Solutes in bedrock groundwater have a predominant geogenic origin, whereas local recharge is characterized by low-solute inputs from rainwater and minor in situ weathering releases from nutrient-depleted soils. Bedrock groundwater contributes more than 60% of dissolved Sr2+ to surface discharge in the Salto, Saltito, and Arboleda catchments, whereas the Taconazo catchment receives more than 95% of dissolved Sr2+ from rainwater. δ44/40Ca values of dissolved Ca2+ vary greatly in the catchments, mainly as a result of heterogeneous Ca isotope compositions of the contributing sources. Based on differences in δ44/40Ca values, two distinct bedrock groundwaters discharging at the Salto and the Arboleda catchments are suggested. Effects of biological processes in the plant-soil system on solute generation in the catchments are indicated by variable Ca/Sr ratios. However, these effects cannot clearly be assessed by Ca isotopes due to the strong heterogeneity of δ44/40Ca values of Ca2+ sources and high Ca2+ concentrations in bedrock groundwater.

  1. Planktonic Foram Sr/Ca Indicates Long-Term Stability of Carbonate Saturation State and Seawater Sr/Ca during the Cenozoic

    NASA Astrophysics Data System (ADS)

    Caves, J. K.; Opdyke, B.; Owens, R.

    2012-12-01

    Changes in ocean chemistry are poorly understood over timescales of tens of millions of years; yet, such changes reflect the interplay of fundamental Earth processes, such as the long-term carbon-cycle, evolution, tectonics, and weathering. Simultaneously constraining two ocean chemical parameters could help deconvolve these processes and improve our understanding of the marine response to anthropogenic perturbations to the carbon cycle. We use a multi-proxy and modeling approach, utilizing planktonic foram Sr/Ca, calcite cements, and box-modeling to produce a first-attempt at a Cenozoic carbonate saturation state (Ω) curve and to improve estimates of long-term seawater Sr/Ca variability. Evidence from both culturing studies and glacial-interglacial records indicate that foram Sr/Ca is dominantly sensitive to Ω, suggesting that foram Sr/Ca can be used to reconstruct Ω if seawater Sr/Ca can be constrained. We apply this new proxy to an updated Cenozoic planktonic foram Sr/Ca record, comprising 1680 records from 18 publications. Our foram Sr/Ca record is largely constant during the Cenozoic, with a minimum at the Miocene-Pliocene boundary and a pronounced shift at 38Mya, corresponding to a major planktonic foram overturning event, which we interpret as a species offset. To constrain seawater Sr/Ca, we use both trace element data from calcite cements and a box-model linked to the 87Sr/86Sr record. Both the model and calcite cement data suggest seawater Sr/Ca has remained relatively stable, with slightly higher values during the Paleogene, a minimum during the mid-Miocene, and variability driven by changes in carbonate deposition and mineralogy. Relative to calcite, Ω was low (~4) during much of the Paleogene, but increased during the Oligocene, reaching a maximum during the mid-Miocene. Ω declined to a local minimum at the Miocene-Pliocene boundary, and has since increased to pre-industrial values of 5-6. This record helps explain the lag between the aragonite

  2. Sr/Ca and Mg/Ca in Aragonitic Bivalves: Do They Record Temperature?

    NASA Astrophysics Data System (ADS)

    Gillikin, D. P.; Ulens, H.; Dehairs, F.; Baeyens, W.; Navez, J.; Andre, L.; Keppens, E.; Calmars Group,.

    2003-12-01

    The chemical or isotopic composition of calcareous skeletons have long been recognized as archives of past and present environmental conditions. Oxygen isotopes (d18O) of biogenic carbonates are a powerful proxy of SST, however, although usually dominated by SST, salinity (SSS) also significantly effects the oxygen isotopic signal recorded in the carbonate. This has led researchers to explore new proxies, which are independent of SSS. Generally, Sr/Ca and Mg/Ca of seawater remains unchanged above salinities of 10 and marine animals will commonly live in habitats that do not fluctuate below this salinity. To solve the issue of SSS complicating paleotemperature records, these "new" proxies must be at least as reliable as d18O. If an environmental control is dominant, the proxies should be reproducible between specimens growing under the same field conditions. Both Sr and Mg have been used as paleotemperature proxies in corals and foraminifera, whereas a fewer attempts have been made to use these proxies in bivalves. Some report a clear seasonal periodicity in Sr/Ca profiles of bivalves, which covaries with d18O (i.e., temperature), whereas others have found no clear periodicity. We test the robustness of these proxies by analyzing the shell material from three species of aragonitic clams from around the world using a LA-ICP-MS. Three individuals of M. mercenaria from North Carolina, USA, three individuals of Saxidomus giganteus from Washington, USA and one Arctica islandica from Norway have been analyzed. As expected, there is excellent reproducibility of d18O between specimens (both M. mercenaria and S. giganteus) indicating external environmental conditions control this proxy (i.e. SST and SSS). Preliminary data analysis show that Sr and Mg are not reproducible between specimens from the same site nor do they exhibit a clear seasonal cyclicity, indicating individual metabolic effects (i.e., vital effects) dominate the incorporation of these elements. A. islandica

  3. Sr heterogeneity in textit{Arctica islandica} shells and the potential use of Sr/Ca ratios as paleotemperature proxies

    NASA Astrophysics Data System (ADS)

    Radermacher, Pascal; Schöne, Bernd R.; Nunn, Elizabeth V.; Zengjie, Zhang

    2010-05-01

    Quantifiable paleotemperature data can help to verify predictions made by numerical climate models. Traditionally, paleotemperature estimates are based on δ18O values of biogenic hard parts. However, oxygen isotope values not only reflect changes in ambient temperature, but also changes in δ18Owater, i.e. driven by freshwater influx, evaporation etc. Information regarding the δ18Owater value of past environments is limited for the geological past. The validity of published δ18O paleotemperature data can be tested using element-to-calcium ratios of bivalve shells such as the long-lived ocean quahog, Arctica islandica. Preliminary investigations suggest that Sr/Ca ratios of this species may provide more reliable paleotemperature data. However, contemporaneously deposited shell portions within the outer shell layer demonstrate at least a 30% variability in the Sr/Ca value. This study presents Sr/Ca ratios measured by ICP-OES wet-chemical analyses. Significantly different distributions of Sr/Ca ratios were recorded from the shell surface (over 1330 ppm), through the interior (850 ppm) and to the inner shell surface (1860 ppm). Furthermore, this study showed that different shell crystal fabrics incorporate different amounts of Sr into the CaCO3 lattice of the A. islandica shell. Disparate Sr distribution could potentially be explained either by postdepositional diagenetic processes or syndepositional processes during biomineralization (i.e. different amounts of Sr incorporated into the shell). Understanding the mechanism of the observed Sr heterogeneity is essential if Sr/Ca ratios are to be used confidently in paleotemperature reconstructions.

  4. Surface characterization, in vitro and in vivo biocompatibility of Mg-0.3Sr-0.3Ca for temporary cardiovascular implant.

    PubMed

    Bornapour, M; Mahjoubi, H; Vali, H; Shum-Tim, D; Cerruti, M; Pekguleryuz, M

    2016-10-01

    Magnesium-based alloys are attractive candidate materials for medical applications. Our earlier work showed that the ternary Mg-0.3Sr-0.3Ca alloy exhibits slower degradation rates than both binary Mg-Sr and Mg-Ca alloys. The ternary alloy immersed in simulated body fluid (SBF) forms a compact surface layer of corrosion products that we hypothesized to be a Sr-substituted hydroxyapatite (HA). The main objectives of the current work are to understand the bio-degradation mechanism of Mg-0.3Sr-0.3Ca, to identify the exact nature of its protective layer and to evaluate the in vitro and in vivo biocompatibility of the alloy for cardiovascular applications. To better simulate the physiological environment, the alloy was immersed in SBF which was daily refreshed. Raman spectroscopy and X-Ray photoelectron spectroscopy (XPS) confirmed the formation of a thin, Sr-substituted HA layer at the interface between the alloy and the corrosion products. In vitro biocompatibility evaluated via indirect cytotoxicity assays using HUVECs showed no toxicity effect and ions extracted from Mg-0.3Sr-0.3Ca in fact increased the viability of HUVECs after one week. In vivo tests were performed by implanting a tubular Mg-0.3Sr-0.3Ca stent along with a WE43 control stent into the right and left femoral artery of a dog. Post implantation and histological analyses showed no thrombosis in the artery with Mg-0.3Sr-0.3Ca stent after 5weeks of implantation while the artery implanted with WE43 stent was extensively occluded and thrombosed. Microscopic observation of the Mg-0.3Sr-0.3Ca implant-tissue interface confirmed the in situ formation of Sr-substituted HA on the surface during in vivo test. These results show that the interfacial layer protects the surface of the Mg-0.3Sr-0.3Ca alloy both in vitro and in vivo, and is the key factor in the bio-corrosion resistance of the alloy. PMID:27287101

  5. Strong biological controls on Sr/Ca ratios in aragonitic marine bivalve shells

    NASA Astrophysics Data System (ADS)

    Gillikin, David Paul; Lorrain, Anne; Navez, Jacques; Taylor, James W.; André, Luc; Keppens, Eddy; Baeyens, Willy; Dehairs, Frank

    2005-05-01

    It is well known that skeletal remains of carbonate secreting organisms can provide a wealth of information about past environments. Sr/Ca ratios have been successfully used as a temperature proxy in corals and sclerosponges. Previous work on aragonitic bivalve shells has not been conclusive but suggests a major control of growth rate on Sr/Ca ratios. As many studies have used bivalve growth rates to determine temperature, we tested if Sr/Ca ratios could predict temperature through its relationship with growth rate. Shells from the two species of clams from the same family (veneroidea) studied here, Saxidomus giganteus and Mercenaria mercenaria, show vastly different seasonal Sr/Ca profiles. A strong relationship between average annual Sr/Ca ratios and annual growth rate was found in S. giganteus shells from both Washington (R2 = 0.87) and Alaska (R2 = 0.64), USA, but not in M. mercenaria shells from North Carolina, USA. Furthermore, the Sr/Ca-growth rate relationship was also evident upon a more detailed inspection of subannual growth rates in S. giganteus (R2 = 0.73). Although there were significant positive correlations between Sr/Ca ratios and temperature in S. giganteus shells, the correlations were weak (0.09 < R2 < 0.27), and thus Sr/Ca ratios cannot be used as a reliable temperature proxy in these species of aragonitic bivalves. It is clear from this study that Sr/Ca ratios are not under thermodynamic control in either clam species, since thermodynamics predict a negative correlation between Sr/Ca ratios and temperature in aragonite. This points toward dominance of biological processes in the regulation of Sr2+. This is also reflected by the largely differing Sr/Ca partition coefficients (DSr) in these shells (DSr ≈ 0.25), when compared to inorganic, coral, and sclerosponge studies (DSr ≈ 1), all of which show a negative dependence of Sr/Ca on temperature. We suggest that caution be taken when using Sr/Ca in any biogenic aragonite as a temperature proxy

  6. Review of high-temperature superconductivity and the effect of chemical modifications on Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10. Technical report

    SciTech Connect

    Jones, T.E.; McGinnis, W.C.; Boss, R.D.

    1991-08-01

    Perform chemical modifications to existing materials that may enhance their superconducting properties and provide insight into the mechanisms responsible for high-temperature superconductivity. This report presented a review of high-temperature superconductivity. An overview of superconductivity from its original discovery to the present is also given. Synthesized two sets of samples. One set was based on the structure Bi2Sr2CaCu2O8 and the other on Bi2Sr2Ca2Cu3O10. In both cases, the copper was partially replaced with elements from the first transition row of elements. The replacement was at the level of 5 mol.-% of the transition element for copper. The transition elements used were vanadium (V), manganese (Mn), titanium (Ti), nickel (Ni), zinc (Zn), cobalt (Co), and iron (Fe) and determined the effect of the substitutions on the crystal structure.

  7. Climate proxies from Sr/Ca of coccolith calcite: calibrations from continuous culture of Emiliania huxleyi

    NASA Astrophysics Data System (ADS)

    Stoll, Heather M.; Rosenthal, Yair; Falkowski, Paul

    2002-03-01

    Continuous culture of the coccolithophorid Emiliania huxleyi reveals that coccolith Sr/Ca ratios depend on temperature and growth rate. At a constant temperature of 18°C, coccolith Sr/Ca ratios increased nearly 15% as growth rate increased from 0.1 to 1.5 divisions per day and calcification rate increased from 1.5 to 50 pg calcite per cell per day. When temperature increased from 7 to 26°C, Sr/Ca ratios increased by more than 25% (i.e., 1%/1°C), although the range in growth and calcification rates was the same as for experiments at constant temperature. The temperature dependence of Sr/Ca ratios in coccoliths is consistent with that observed in planktonic foraminifera and abiogenic calcites, suggesting that it is controlled by thermodynamic processes. However, the positive correlation of coccolith Sr/Ca with temperature contrasts with field studies in the equatorial Pacific, where Sr/Ca ratios are highest at the locus of maximum upwelling and productivity despite depressed temperatures. This paradox may reflect different calcification rate effects between E. huxleyi and the other species dominating assemblages in the equatorial Pacific sediments, which may be resolved by new techniques for separation of monospecific coccolith samples from sediments. Models of crystal growth indicate that kinetic effects on Sr partitioning in calcite due to surface enrichment could explain the Sr/Ca variations observed in constant temperature experiments but not the larger amplitude calcification rate effects observed in equatorial Pacific sediments. Despite the dual influence of temperature and growth rate on coccolith Sr/Ca, coccolith Sr/Ca correlates with "b," the slope of the dependence of carbon isotope fractionation in biomarkers (ɛ p) on CO 2(aq) at a range of growth rates and temperatures. Consequently, using coccolith Sr/Ca in combination with alkenone ɛ p may improve paleo-CO 2 determinations.

  8. Mechanical, thermal and laser properties of Yb:(Sr 1- xCa x) 3Y(BO 3) 3 (Yb:CaBOYS) for 1 μm laser applications

    NASA Astrophysics Data System (ADS)

    Gaumé, R.; Viana, B.; Vivien, D.; Roger, J. P.; Fournier, D.; Souron, J. P.; Wallez, G.; Chénais, S.; Balembois, F.; Georges, P.

    2003-10-01

    Yb:Sr 3Y(BO 3) 3 also known as Yb:BOYS has recently demonstrated very attractive laser properties, but a drawback with this material is its brittleness. It could break into small pieces, even under weak thermal loading. This behavior is attributed to its very large thermal expansion anisotropy: αc/ αa˜4. This ratio can be lowered to ˜1.7 by replacing 50% of Sr 2+ by Ca 2+ in the structure, which strengthen the crystal lattice and allows to reduce the brittleness. However, the thermal properties are affected by the Sr/Ca substitution as the thermal conductivity decreases by around 20 at.% for a 30 at.% calcium containing material. Laser characteristics under diode pumping with Yb 3+:(Sr 0.7Ca 0.3) 3Y(BO 3) 3 crystals (containing 15% Yb) remain comparable to those obtained with Yb:BOYS.

  9. STIM1 enhances SR Ca2+ content through binding phospholamban in rat ventricular myocytes

    PubMed Central

    Zhao, Guiling; Li, Tianyu; Brochet, Didier X. P.; Rosenberg, Paul B.; Lederer, W. J.

    2015-01-01

    In ventricular myocytes, the physiological function of stromal interaction molecule 1 (STIM1), an endo/sarcoplasmic reticulum (ER/SR) Ca2+ sensor, is unclear with respect to its cellular localization, its Ca2+-dependent mobilization, and its action on Ca2+ signaling. Confocal microscopy was used to measure Ca2+ signaling and to track the cellular movement of STIM1 with mCherry and immunofluorescence in freshly isolated adult rat ventricular myocytes and those in short-term primary culture. We found that endogenous STIM1 was expressed at low but measureable levels along the Z-disk, in a pattern of puncta and linear segments consistent with the STIM1 localizing to the junctional SR (jSR). Depleting SR Ca2+ using thapsigargin (2–10 µM) changed neither the STIM1 distribution pattern nor its mobilization rate, evaluated by diffusion coefficient measurements using fluorescence recovery after photobleaching. Two-dimensional blue native polyacrylamide gel electrophoresis and coimmunoprecipitation showed that STIM1 in the heart exists mainly as a large protein complex, possibly a multimer, which is not altered by SR Ca2+ depletion. Additionally, we found no store-operated Ca2+ entry in control or STIM1 overexpressing ventricular myocytes. Nevertheless, STIM1 overexpressing cells show increased SR Ca2+ content and increased SR Ca2+ leak. These changes in Ca2+ signaling in the SR appear to be due to STIM1 binding to phospholamban and thereby indirectly activating SERCA2a (Sarco/endoplasmic reticulum Ca2+ ATPase). We conclude that STIM1 binding to phospholamban contributes to the regulation of SERCA2a activity in the steady state and rate of SR Ca2+ leak and that these actions are independent of store-operated Ca2+ entry, a process that is absent in normal heart cells. PMID:26261328

  10. Reconstructing past seawater Mg/Ca and Sr/Ca from mid-ocean ridge flank calcium carbonate veins.

    PubMed

    Coggon, Rosalind M; Teagle, Damon A H; Smith-Duque, Christopher E; Alt, Jeffrey C; Cooper, Matthew J

    2010-02-26

    Proxies for past seawater chemistry, such as Mg/Ca and Sr/Ca ratios, provide a record of the dynamic exchanges of elements between the solid Earth, the atmosphere, and the hydrosphere and the evolving influence of life. We estimated past oceanic Mg/Ca and Sr/Ca ratios from suites of 1.6- to 170-million-year-old calcium carbonate veins that had precipitated from seawater-derived fluids in ocean ridge flank basalts. Our data indicate that before the Neogene, oceanic Mg/Ca and Sr/Ca ratios were lower than in the modern ocean. Decreased ocean spreading since the Cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early Tertiary may explain the recent rise in these ratios. PMID:20133522

  11. Synthesis and study of Sr-substituted misfit layer sulfides

    SciTech Connect

    Grippa, A.Yu. . E-mail: grippa@icr.chem.msu.ru; Lidin, S.; D'yachenko, O.G.; Rupasov, D.P.; Antipov, E.V.

    2005-01-04

    Two series of [(Ln{sub 1/3}Sr{sub 2/3}S){sub 1.5}]{sub 1.15}NbS{sub 2} (1.5Q/1H) and (Ln{sub 1-x}Sr{sub x}S){sub 1+y}NbS{sub 2} (1Q/1H) misfit layer sulfides have been synthesised and studied by X-ray powder and single crystal diffraction, EDX-analysis and magnetic measurements. For the early lanthanides (Ln = La, Ce) only the (Ln{sub 1-x}Sr{sub x}S){sub 1+y}NbS{sub 2} (x < 0.40-0.45, y = 0.15-0.17) compounds were formed whereas for late lanthanides (Ln = Pr, Nd, Sm, Gd-Er, Yb, Lu), and yttrium, both types of phases can be obtained. The crystal structure of (Pr{sub 0.55}Sr{sub 0.45}S){sub 1.15}NbS{sub 2} has been refined on the basis of X-ray single crystal data using the superspace approach. It consists of double layers [Pr{sub 0.55}Sr{sub 0.45}S] of NaCl-type (Q-part: a = 5.799(3) A, b = 5.810(2) A, c = 23.331(9) A, z = 4) and NbS{sub 2}-sandwiches (H-part: a = 3.332(3) A), z = 8, yielding a q-vector q = ({alpha} 0 0), {alpha} = 0.74) alternating along the c-direction. The superspace group pair is Fm2m ({alpha} 0 0):Fm2m ({alpha} 0 0) (No. 42.7). The refinement converged to R{sub w(obs)} = 0.069. According to the structure refinement and EDX-analysis data in the [Pr{sub 0.55}Sr{sub 0.45}S]-slab almost half of the Pr-atoms are randomly replaced by Sr. The minimal formal value of charge transfer from the Q- to the H-part of the structure necessary to stabilise the misfit Nb-based layer sulfides has been estimated as about 0.6 e per Nb atom.

  12. Magnetic excitations in the S = {1/2} quasi-one-dimensional magnet Sr{sub 14{minus}x}Ca{sub x}Cu{sub 24}O{sub 41}

    SciTech Connect

    Matsuda, M.; Katsumata, K.; Shapiro, S.M.; Shirane, G.

    1998-08-20

    Neutron scattering experiments have been performed on Sr{sub 14{minus}x}Ca{sub x}Cu{sub 24}O{sub 41} (x = 3 and 6), which consists of CuO{sub 2} chains and CuO{sub 2}O{sub 3} ladders, in order to study the effect of Ca substitution on the dimerized state in the chains. The Ca substitution broadens the excitation peak although the excitation energy is almost unchanged. The effects of Ca and Y substitution on the dimerized state are compared.

  13. The Unusual Metal-Insulator Transition in Ca(2-x)Sr(x)RuO(4)

    NASA Astrophysics Data System (ADS)

    Rice, T. Maurice

    2002-03-01

    The isoelectronic compounds Ca_2-xSr_xRuO4 offer a rare opportunity to follow the evolution of the electronic structure from a multiband metal, Sr_2RuO_4, to a Mott insulator, Ca_2RuO_4. The evolution is not at all monotonic but proceeds through a series of intermediate regions with unexpected behavior [1]. Sr_2RuO4 is a good metal with the 4 electrons in the t_2g-subshell of the Ru^4+-ions distributed equally in 3 bands. These in turn separate into a d_xy-band which disperses in both directions in the RuO_2-planes and d_xz/d_yz-bands dispersing only in one direction. The hybridization between these components occurs only through very weak interplanar processes. Substituting Ca for Sr leads to band narrowing through a rotation of the RuO_4-octahedra. A series of electronic structure calculations [2] using the LDA+DMFT method to incorporate strong correlations, predict an unusual state with 3 electrons localizing in the narrower d_xz/d_yz bands while the last electron remains itinerant in the broader d_xy-band. The observation of a strongly enhanced and temperature dependent spin susceptibility in the metallic state at x=0.5 is attributed to the S=1/2 local moments of the localized hole in the d_xz/d_yz-orbitals. The superexchange interaction between the local moments is strongly dependent on the specific orbital occupation and so glassy behavior in the orbital ordering can account for the glassy behavior observed in the susceptibility in the range 0.2 < x < 0.5. The final transition to a Mott insulator at x < 0.2 is driven by a compression of the RuO_4-octahedra and a switch to an electronic configuration with a filled d_xy-orbital and 2 electrons in the d_xz/d_yz orbitals which has a S=1 local moment expected for a Ru^4+-ion. [1] S. Nakatsuji and Y. Maeno, Phys. Rev. Lett. 84, 2666 (2000). [2] V.I. Anisimov, I.A. Nekrasov, D.E. Kondakov, T.M. Rice, and M. Sigrist, cond-mat0107095 and Eur. Phys. Jour. B (in press).

  14. Migration and rearing histories of chinook salmon (Oncorhynchus tshawytscha) determined by ion microprobe Sr isotope and Sr/Ca transects of otoliths

    USGS Publications Warehouse

    Bacon, C.R.; Weber, P.K.; Larsen, K.A.; Reisenbichler, R.; Fitzpatrick, J.A.; Wooden, J.L.

    2004-01-01

    Strontium isotope and Sr/Ca ratios measured in situ by ion microprobe along radial transects of otoliths of juvenile chinook salmon (Oncorhynchus tshawytscha) vary between watersheds with contrasting geology. Otoliths from ocean-type chinook from Skagit River estuary, Washington, had prehatch regions with 87Sr/86Sr ratios of ???0.709, suggesting a maternally inherited marine signature, extensive fresh water growth zones with 87Sr/86Sr ratios similar to those of the Skagit River at ???0.705, and marine-like 87Sr/86Sr ratios near their edges. Otoliths from stream-type chinook from central Idaho had prehatch 87Sr/86Sr ratios ???0.711, indicating that a maternal marine Sr isotopic signature is not preserved after the ???1000- to 1400-km migration from the Pacific Ocean. 87Sr/86Sr ratios in the outer portions of otoliths from these Idaho juveniles were similar to those of their respective streams (???0.708-0.722). For Skagit juveniles, fresh water growth was marked by small decreases in otolith Sr/Ca, with increases in Sr/Ca corresponding to increases in 87Sr/86Sr with migration into salt water. Otoliths of Idaho fish had Sr/Ca radial variation patterns that record seasonal fluctuation in ambient water Sr/Ca ratios. The ion microprobe's ability to measure both 87Sr/86Sr and Sr/Ca ratios of otoliths at high spatial resolution in situ provides a new tool for studies of fish rearing and migration. ?? 2004 NRC Canada.

  15. The Effect of Algal Symbionts on the Accuracy of Sr/Ca Paleotemperatures from Coral

    NASA Astrophysics Data System (ADS)

    Cohen, Anne L.; Owens, Kathryn E.; Layne, Graham D.; Shimizu, Nobumichi

    2002-04-01

    The strontium-to-calcium ratio (Sr/Ca) of reef coral skeleton is commonly used as a paleothermometer to estimate sea surface temperatures (SSTs) at crucial times in Earth's climate history. However, these estimates are disputed, because uptake of Sr into coral skeleton is thought to be affected by algal symbionts (zooxanthellae) living in the host tissue. Here, we show that significant distortion of the Sr/Ca temperature record in coral skeleton occurs in the presence of algal symbionts. Seasonally resolved Sr/Ca in coral without symbionts reflects local SSTs with a temperature sensitivity equivalent to that of laboratory aragonite precipitated at equilibrium and the nighttime skeletal deposits of symbiotic reef corals. However, up to 65% of the Sr/Ca variability in symbiotic skeleton is related to symbiont activity and does not reflect water temperature.

  16. Re-examination of the structural properties of solid solutions Sr {sub x}Ca{sub 1-x}CO{sub 3}

    SciTech Connect

    Lucas-Girot, Anita . E-mail: anita.lucas@univ-rennes1.fr; Hernandez, Olivier; Oudadesse, Hassane

    2007-06-05

    We have re-examined the evolution of orthorhombic cell parameters as a function of the substitution parameter x in solid solutions Sr {sub x}Ca{sub 1-x}CO{sub 3} in order to clarify contradictory results found in the literature. Calcium carbonate has been synthesized in the presence of Sr{sup 2+} ions (Sr/Ca molar ratio ranging from 10{sup -2} to 1), using experimental conditions that previously allowed us to obtain monophasic aragonite. The precipitates obtained have been analysed using powder X-ray diffractometry (XRD) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The powder XRD data confirm the occurrence of purely monophasic strontian-aragonites. Moreover, the cell parameters as well as the substitution parameter x have been refined for 0 < x < 0.5 against powder XRD data through Rietveld refinement. On the other hand, x was deduced from chemical analysis by ICP-AES. The agreement between both techniques is very satisfactory. The evolution of the cell parameters as a function of x is found to be linear within the studied range, this feature being confirmed for the overall domain (0 {<=} x {<=} 1) if one takes into account the cell parameters of aragonite CaCO{sub 3} and strontionite SrCO{sub 3}. This result, that is consistent with the existence of continuous solid solutions obeying the Vegard's law in the Sr {sub x}Ca{sub 1-x}CO{sub 3} system, contradicts previously published assertions.

  17. Cenozoic Seawater Sr/Ca ratios: Implications for coral reef development through ocean de-acidification

    NASA Astrophysics Data System (ADS)

    Sosdian, S. M.; Grossman, E. L.; Lear, C. H.; Tao, K.; Rosenthal, Y.

    2010-12-01

    Records of seawater chemistry help constrain the temporal variation in geochemical processes that impact the global carbon cycle and global climate across Earth’s history. To date, various attempts to reconstruct Cenozoic seawater Sr/Ca ratios have produced markedly different results, with estimated Paleogene seawater Sr/Ca ranging from ~50% higher than today to 70% lower. We reconstruct seawater Sr/Ca using Eocene to Pliocene fossil mollusks collected from US Gulf Coast (Mississippi, Alabama, and Florida). We use Conus spp. and Turritella, taxa for which the Sr/Ca distribution coefficients have been determined as a function of temperature in modern specimens [1, 2]. Specimens were serially sampled perpendicular to growth to produce seasonal records of Sr/Ca. Fossil Conus shells show pronounced seasonal Sr/Ca cycles with a strong inverse correlation between Sr/Ca and δ18O, similar to those observed in modern specimens [1]. The fossil Turritella also show similar Sr/Ca cyclicity as modern specimens [2]. We calculate seawater Sr/Ca ratios using our Sr/Ca record, modern Sr/Ca-temperature calibrations for Conus and Turritella [1, 2], and a paleotemperature record based on oxygen isotopes from the same samples [3]. Seawater Sr/Ca increased from ~11.5 to 13.9 mmol/mol between the mid-Eocene (42 Ma) and early Oligocene (33 Ma) and decreased substantially from the mid-Miocene (11 mmol/mol) to the Pliocene (9 mmol/mol) and modern (8.5 mmol/mol). A mass balance model of variations in seawater Sr concentrations suggests a long-term decrease through the Neogene, which we attribute to a significant increase in the proportion of aragonite versus calcite deposition in shallow waters. The largest change is coincident with the proliferation of coral reefs, which occurred after the calcite-aragonite sea transition, and was likely ultimately driven by ocean de-acidification. [1] Sosdian et al. (2006) Geochemistry, Geophysics, Geosystems (G3) 7, Q11023, doi:10.1029/2005GC001233; [2

  18. Evidence for the non-influence of salinity variability on the coral Sr/Ca paleothermometer

    NASA Astrophysics Data System (ADS)

    Moreau, M.; Corrège, T.; Dassié, E. P.; Le Cornec, F.

    2014-04-01

    The influence of salinity in the incorporation of trace elements in the skeleton of calcareous organisms is still poorly known. Studies on foraminiferal Mg/Ca thermometry have suggested a bias due to Sea Surface Salinity (SSS) variations, leading to potential erroneous estimation of Mg/Ca-based Sea Surface Temperature (SST). Culture experiments seem to indicate that in three coral species (not including the widely used Porites genus), salinity does not influence the Sr/Ca thermometer. In this study, we test the salinity effect on coral Sr/Ca-based SST reconstructions at monthly and interannual timescales in open-ocean environmental conditions, using a large spatial compilation of published coral data (mainly based on the Porites genus) originating from the Western Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the China Sea and the Red Sea and adding a new Eastern Pacific coral Sr/Ca record from the Clipperton atoll. We use simple and multiple regressions between Sr/Ca on one hand and SST and SSS on the other hand at the various sites. We find no evidence for a salinity bias on the Sr/Ca SST proxy for the two studied timescales. This study reinforces the use of coral Sr/Ca as a reliable paleothermometer.

  19. Epithelial CaSR Deficiency Alters Intestinal Integrity and Promotes Proinflammatory Immune Responses

    PubMed Central

    Cheng, Sam X.; Lightfoot, Yaíma L.; Yang, Tao; Zadeh, Mojgan; Tang, Lieqi; Sahay, Bikash; Wang, Gary P.; Owen, Jennifer L.; Mohamadzadeh, Mansour

    2014-01-01

    The intestinal epithelium is equipped with sensing receptor mechanisms that interact with luminal microorganisms and nutrients to regulate barrier function and gut immune responses, thereby maintaining intestinal homeostasis. Herein, we clarify the role of the extracellular calcium-sensing receptor (CaSR) using intestinal epithelium-specific Casr−/− mice. Epithelial CaSR deficiency diminished intestinal barrier function, altered microbiota composition, and skewed immune responses towards proinflammatory. Consequently, Casr−/− mice were significantly more prone to chemically induced intestinal inflammation resulting in colitis. Accordingly, CaSR represents a potential therapeutic target for autoinflammatory disorders, including inflammatory bowel diseases. PMID:24842610

  20. Mesures conjointes des rapports Sr/Ca et δ 18O effectuées sur Acropora nobilis et Pontes lutea: le paléothermomètre Sr/Ca est-il toujours fiable?

    NASA Astrophysics Data System (ADS)

    Boiseau, Muriel; Cornu, Hélène; Turpin, Laurent; Juillet-Leclerc, Anne

    1997-11-01

    We measured the Sr/Ca and 18O/ 16O ratios in Acropora nobilis and Porites lutea, from the Mayotte lagoon. As the variations of δ 18O seawater are negligible, coral δ 18O aragonite reflects only seasonal temperature variations. While there is a good agreement between the Sr/Ca ratio and δ 18O for Acropora nobilis, it is not the case for Porites lutea. Coral biological and environmental parameters cannot explain the discrepancies between Sr/Ca ratios and isotopic measurements. However, transport mechanisms of Sr 2+ and Ca 2+ and the presence of two mineralogical structures of strontium may affect the Sr/Ca ratio.

  1. (Ca/Sr)Au xCd 1- x: Stacking variants of the CrB-FeB series

    NASA Astrophysics Data System (ADS)

    Harms, Wiebke; Dürr, Ines; Daub, Michael; Röhr, Caroline

    2010-01-01

    The structural chemistry of binary 1:1 alkaline earth metallides AIIM ( M=p-block or late transition element) is dominated by planar M zig-zag chains, which are stacked in different orientations (CrB ( c) to FeB ( h) type) and with variable stacking distances (types I and II). As a case study of the electronic influences, the substitution of Au against Cd in the respective Ca and Sr aurides was examined by means of experimental, crystallographic and computational methods. Starting from CaAu, up to 11% of Au can be substituted by Cd without a change in the CrB structure type (orthorhombic, space group Cmcm, a=398.2(1), b=1122.6(6), c=460.9(2) pm, Z=4, R1=0.0303). Starting from SrAu (stacking sequence (hc)2(h2c)2), depending on the proportion of the Cd substitution a successive change to structures with increased hexagonality is observed: In SrAu0.93Cd0.07 (monoclinic, space group P21/m, a=621.3(4), b=472.4(2), c=1216.1(9) pm, β=96.97(5)∘, Z=6, R1=0.0467) the stacking sequence is h2 c, i.e. the hexagonality is 66.67%. A slightly more increased Cd content in SrAu0.78Cd0.22 (orthorhombic, space group Pnma, a=3243.3(8), b=474.17(8), c=626.20(9) pm, Z=16, R1=0.0682) drives the hexagonality to 75%, with a (h3c)2 stacking sequence known from several rare earth nickel compounds. Further Cd substitution is not possible. However, in the Cd-rich section of the two series, where the CsCl/β-brass structure type occurs for both alkaline earth elements, a small Au substitution, as determined from powder data by Rietveld refinements, is possible. The substitution limit and the stability ranges of the CsCl and the CrB type can be rationalized from the calculated band structures. Geometrical and electronic criteria are used to compare and discuss the stability ranges in a structural map.

  2. Ambient pressure structural quantum critical point in the phase diagram of (Ca(x)Sr(1-x))(3)Rh(4)Sn(13).

    PubMed

    Goh, S K; Tompsett, D A; Saines, P J; Chang, H C; Matsumoto, T; Imai, M; Yoshimura, K; Grosche, F M

    2015-03-01

    The quasiskutterudite superconductor Sr_{3}Rh_{4}Sn_{13} features a pronounced anomaly in electrical resistivity at T^{*}∼138  K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centered around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of T^{*} as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (i.e., x_{c}=0.9). This establishes the (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13} series as an important system for exploring the physics of structural quantum criticality without the need of applying high pressures. PMID:25793843

  3. Effects of low-level Ag doping on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}

    SciTech Connect

    Deis, T.A.; Eror, N.G.; Krishnaraj, P.; Prorok, B.C.; Lelovic, M.; Balachandran, U.

    1995-07-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} has been doped with silver, up to 10,000 ppm, in three ways: excess additions, substitution of Ag for Bi, and substitution of Ag for Sr. Effects of doping on the c-axis lattice parameter and critical temperature ({Tc}) were measured. Effects from doing were only observed in slow-cooled [10{degree}/hr] oxygen equilibrated samples. Doping by excess additions caused a small decrease in {Tc} and an increase in the c-axis length of the lattice. Doping by substitution, compared to excess Ag additions, caused a larger decrease in {Tc} and higher c-axis values for doping levels up to 1,000 ppm. Doping by substitution at higher levels (1,000--10,000 ppm) caused {Tc} to increase and the c-axis to decrease. Samples with similar substitutional doping levels exhibited comparable {Tc} values and samples with Ag substituted for Sr consistently exhibited higher c-axis values than samples that had equivalent amounts of Ag substituted for Bi.

  4. Large enhancement of superconducting transition temperature of SrBi3 induced by Na substitution for Sr

    PubMed Central

    Iyo, Akira; Yanagi, Yousuke; Kinjo, Tatsuya; Nishio, Taichiro; Hase, Izumi; Yanagisawa, Takashi; Ishida, Shigeyuki; Kito, Hijiri; Takeshita, Nao; Oka, Kunihiko; Yoshida, Yoshiyuki; Eisaki, Hiroshi

    2015-01-01

    The Matthias rule, which is an empirical correlation between the superconducting transition temperature (Tc) and the average number of valence electrons per atom (n) in alloys and intermetallic compounds, has been used in the past as a guiding principle to search for new superconductors with higher Tc. The intermetallic compound SrBi3 (AuCu3 structure) exhibits a Tc of 5.6 K. An ab-initio electronic band structure calculation for SrBi3 predicted that Tc increases on decreasing the Fermi energy, i.e., on decreasing n, because of a steep increase in the density of states. In this study, we demonstrated that high-pressure (~ 3 GPa) and low-temperature ( < 350 °C) synthesis conditions enables the substitution of Na for about 40 at.% of Sr. With a consequent decrease in n, the Tc of (Sr,Na)Bi3 increases to 9.0 K. A new high-Tc peak is observed in the oscillatory dependence of Tc on n in compounds with the AuCu3 structure. We have shown that the oscillatory dependence of Tc is in good agreement with the band structure calculation. Our experiments reaffirm the importance of controlling the number of electrons in intermetallic compounds. PMID:25965162

  5. Mg/Ca, Sr/Ca and Ca isotope ratios in benthonic foraminifers related to test structure, mineralogy and environmental controls

    NASA Astrophysics Data System (ADS)

    Gussone, Nikolaus; Filipsson, Helena L.; Kuhnert, Henning

    2016-01-01

    We analysed Mg/Ca, Sr/Ca and Ca isotope ratios of benthonic foraminifers from sediment core tops retrieved during several research cruises in the Atlantic Ocean, in order to improve the understanding of isotope fractionation and element partitioning resulting from biomineralisation processes and changes in ambient conditions. Species include foraminifers secreting tests composed of hyaline low magnesium calcite, porcelaneous high magnesium calcite as well as aragonite. Our results demonstrate systematic isotope fractionation and element partitioning patterns specific for these foraminiferal groups. Calcium isotope fractionation is similar in porcelaneous and hyaline calcite tests and both groups demonstrate the previously described anomaly with enrichment of heavy isotopes around 3-4 °C (Gussone and Filipsson, 2010). Calcium isotope ratios of the aragonitic species Hoeglundina elegans, on the other hand, are about 0.4‰ lighter compared to the calcitic species, which is in general agreement with stronger fractionation in inorganic aragonite compared to calcite. However, the low and strongly variable Sr content suggests additional processes during test formation, and we propose that transmembrane ion transport or a precursor phase to aragonite may be involved. Porcelaneous tests, composed of high Mg calcite, incorporate higher amounts of Sr compared to hyaline low Mg calcite, in agreement with inorganic calcite systematics, but also porcelaneous tests with reduced Mg/Ca show high Sr/Ca. While calcium isotopes, Sr/Ca and Mg/Ca in benthonic foraminifers primarily appear to fractionate and partition with a dominant inorganic control, δ44/40Ca temperature and growth rate dependencies of benthonic foraminifer tests favour a dominant contribution of light Ca by transmembrane transport relative to unfractionated seawater Ca to the calcifying fluid, thus controlling the formation of foraminiferal δ44/40Ca and Sr/Ca proxy signals.

  6. Extracellular calcium and CaSR drive osteoinduction in mesenchymal stromal cells.

    PubMed

    González-Vázquez, Arlyng; Planell, Josep A; Engel, Elisabeth

    2014-06-01

    Bone is the main store of calcium and progenitor cells in the body. During the resorption process, the local calcium concentration reaches 8-40mM, and the surrounding cells are exposed to these fluctuations in calcium. This stimulus is a signal that is detected through the calcium sensing receptor (CaSR), which modulates chemotactic and proliferative G protein-dependent signaling pathways. The objective of the present work is to evaluate the roles of extracellular calcium ([Ca(2+)]o) and the CaSR in osteoinduction. Rat bone marrow mesenchymal stromal cells (rBMSCs) were stimulated with 10mM of Ca(2+). Several experiments were conducted to demonstrate the effect of [Ca(2+)]o on chemotaxis, proliferation and differentiation on the osteoblastic lineage. It was found that [Ca(2+)]o induces rBMSCs to migrate and proliferate in a concentration-dependent manner. Real-time polymerase chain reaction and immunofluorescence also revealed that 10mM Ca(2+) stimulates overexpression of osteogenic markers in rBMSCs, including alkaline phosphatase (ALP), bone sialoprotein, collagen Ia1 and osteocalcin. Functional assays determining ALP activity and mineralization tests both corroborate the increased expression of these markers in rBMSCs stimulated with Ca(2+). Moreover, CaSR blockage inhibited the cellular response to stimulation with high concentrations of [Ca(2+)]o, revealing that the CaSR is a key modulator of these cellular responses. PMID:24525034

  7. Study of the superconducting properties of the Bi-Ca-Sr-Cu-O system

    NASA Technical Reports Server (NTRS)

    Khan, Musheer H.; Naqvi, S. M. M. R.; Zia-Ul-haq, S. M.

    1991-01-01

    High Temperature Superconductivity in the Bi-Ca-Sr-Cu-O System has been observed and has attracted considerable attention in 1988. The 80 K superconductivity phase has been identified to have a composition of Bi2CaSr2Cu2Ox, while the 110 K phase as reported in the literature has a possible composition of Bi2Ca2Sr2Cu3O(x). Researchers present here a study of the electrical properties of bulk samples of the slowly cooled and rapidly quenched 2:1:2:2 system. The samples used in this study were prepared from appropriate amounts of Bi2O3, CuO, SrCO3, CaCO3.

  8. Study of the superconducting properties of the Bi-Ca-Sr-Cu-O system

    NASA Technical Reports Server (NTRS)

    Khan, Musheer H.; Qidwai, A. A.; Zia-Ul-haq, S. M.; Binsaif, Rashid

    1990-01-01

    High Temperature Superconductivity in the Bi-Ca-Sr-Cu-O System has been observed and has attracted considerable attention in 1988. The 80 K superconductivity phase has been identified to have a composition of Bi2CaSr2Cu2Ox, while the 110 K phase as reported in the literature has a possible composition of Bi2Ca2Sr2Cu3Ox. Researchers present here a study of the electrical properties of bulk samples of the slowly cooled and rapidly quenched 2:1:2:2 system. The samples used in this study were prepared from appropriate amounts of Bi2O3, CuO, SrCO3, CaCO3.

  9. Sintering of bulk high- Tc superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B. ); Nash, A.S. )

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  10. Sintering of bulk high-{Tc} superconductors: Bi-Sr-Ca-Cu-O

    SciTech Connect

    Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B.; Nash, A.S.

    1992-05-01

    Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) superconductors have orthorhombic crystal structures. They form platelike grains that at high temperatures grow primarily in the a-b planes and not in the c direction. The diffusional properties of Bi-Sr-Ca-Cu-O superconductors are so anisotropic that 2212 and 2223 cannot, in general, be densified by solid-state sintering. Improved densification can be achieved by application of pressure or by use of transient liquid phases. Most useful bulk Bi-Sr-Ca-Cu-O superconductors are composites that contain Ag. The Ag lowers the melting points of the superconductors, which has significant effects on microstructural development. The results of disparate sintering studies are presented and discussed.

  11. Floating zone growth of Ba-substituted ruthenate Sr2-xBaxRuO4

    NASA Astrophysics Data System (ADS)

    Li, Z. W.; Liu, C.-F.; Skoulatos, M.; Tjeng, L. H.; Komarek, A. C.

    2015-10-01

    We report on the exploration to synthesize Sr2-xBaxRuO4, the large volume variant of the unconventional superconductor Sr2RuO4. We have succeeded in growing single crystals for x-values up to 0.4 by making use of the traveling solvent floating zone method. The quality of the obtained crystals is confirmed by X-ray and neutron diffraction measurements and the properties of these Ba-substituted ruthenates were studied with magnetic and electrical transport measurements.

  12. Characteristics (Delta44/40Ca, Mg/Ca and Sr/Ca) of Mytilus edulis and Arctica islandica Shells formed in a Temperature-Salinity Matrix

    NASA Astrophysics Data System (ADS)

    Hiebenthal, C.; Eisenhauer, A.; Wahl, M.

    2008-12-01

    We investigated the influence of temperature (5°C to 15°C (A. islandica) resp. 25°C (M. edulis)) and salinity (15 to 35 psu) regimes on the calcium (Ca) isotope fractionation (Δ44/40Ca) and on Mg/Ca and Sr/Ca in cultured bivalves (Mytilus edulis and Arctica islandica). In an orthogonal 2-factorial (temperature vs. salinity) experiment, the bivalves were allowed to grow for 15 weeks under tightly controlled conditions and then probed and analysed by thermal ionisation mass spectrometry (TIMS) and optical emission spectrometry (ICP-OES). Several interactions between the factors temperature and salinity with respect to their influence on bivalve shell parameters could be found. However, with the exception of Sr/Ca data, the variation of measured shell characteristics between individual bivalves was high. The Sr/Ca - salinity proxy seems to be the most reliable (linear. regression, M. edulis: Sr/Ca = -0.0283*sal + 1.7967, R2 = 0.81, p < 0.001), even though, in A. islandica shells, it can be blurred by temperature effects at low salinities (lin. regr. at 5°C: p > 0.05, at 10°C: Sr/Ca = - 0.061*sal + 3.13, R2 = 0.93, p < 0.001, at 15°C: Sr/Ca = -0.066*sal + 3.34, R2 = 0.92, p < 0.001). In M. edulis shells Mg/Ca ratios related well with seawater temperature (lin. regr.: Mg/Ca = 0.642*t - 0.107, R2 = 0.81, p < 0.001). Ca isotope ratios only in A. islandica related significantly with temperature (lin. regr.: Δ44/40Ca = 0.016*t - 1.26, R2 = 0.29, p < 0.01) but due to an interacting salinity effect at 10°C (lin. regr.: Δ44/40Ca = -0.0148*sal - 0.738, R2 = 0.62, p = 0.002) the temperature model can only explain a limited part of the variation. Overall, the calcitic shells of M. edulis appear to provide the better element ratio proxies (Mg/Ca for temperature and Sr/Ca for salinity) and the aragonitic shells of A. islandica have the better Ca isotope - temperature proxy.

  13. Kinetic control of skeletal Sr/Ca in a symbiotic coral: Implications for the paleotemperature proxy

    NASA Astrophysics Data System (ADS)

    Cohen, Anne L.; Layne, Graham D.; Hart, Stanley R.; Lobel, Phillip S.

    2001-02-01

    Modeling of past climates is critically dependent on estimates of past sea surface temperatures (SSTs), for which one of the principal techniques used is the measurement of Sr/Ca ratios in corals [Guilderson et al., 1994; McCulloch et al., 1999; Hughen et al., 1999]. The link between coral Sr/Ca and SST is not well-understood and there have been a number of discrepant observations [de Villiers et al., 1995; Alibert, 1998]. Corals with symbiotic zooxanthellae are known to show large diurnal fluctuations in calcification rate associated with the photosynthetic activity of their symbionts. Using detailed measurements with the ion microprobe, we compared the Sr/Ca content of discrete daytime and nighttime skeletal structures in the massive hermatypic coral Porties lutea over the course of 1 year and a seasonal temperature range of 4°C. The Sr/Ca content of daytime skeleton is always lower than that of adjacent nighttime skeleton. While the slope of the nighttime Sr/Ca-SST correlation is close to that seen in inorganic aragonite precipitates, that of the daytime correlation is >4 times as steep. We attribute these differences to the role of photosynthesis in calcification and conclude that bulk Sr/Ca is related principally to daytime calcification rate rather than directly to SST. More reliable estimates of past SST may be arrived at through selective analysis of nighttime skeleton.

  14. Phase, Microstructure, and Microwave Dielectric Properties of NaCa4- x Sr x Nb5O17 ( x = 0 to 4) Ceramics

    NASA Astrophysics Data System (ADS)

    Iqbal, Y.; Muhammad, R.

    2013-03-01

    A series of A5B5O17-type NaCa4- x Sr x Nb5O17 ( x = 0 to 4) compounds were processed through a solid-state mixed-oxide route. All the compositions formed dense single-phase ceramics within the detection limit of an in-house x-ray diffraction facility when sintered at 1300°C. The substitution of Sr for Ca changed the crystal symmetry from monoclinic ( x = 0) to orthorhombic ( x = 1 to 4) along with a slight increase in molar cell volume due to the relatively larger ionic radius of Sr. The relative permittivity ( ɛ r) and temperature coefficient of resonance frequency (TCF) increased from 46 to 84 and from -117 ppm/°C to +377 ppm/°C, respectively, while the quality factor ( Q × f) decreased from 11,063 GHz to 559 GHz with an increase in x from 0 to 4. Optimum properties were achieved for NaCa3SrNb5O17, which exhibited ɛ r = 57, Q × f = 4628 GHz, and TCF = -41 ppm/°C. Compounds in the NaCa4- x Sr x Nb5O17 series exhibited high ɛ r and Q × f with adjustable TCF; however, further work is required for simultaneous optimization of all three properties.

  15. Loparite, a rare-earth ore (Ce, Na, Sr, Ca)(Ti, Nb, Ta, Fe+3)O3

    USGS Publications Warehouse

    Hedrick, J.B.; Sinha, S.P.; Kosynkin, V.D.

    1997-01-01

    The mineral loparite (Ce, NA, Sr, Ca)(Ti, Nb, Ta, Fe+3)O3 is the principal ore of the light-group rare-earth elements (LREE) in Russia. The complex oxide has a perovskite (ABO3) structure with coupled substitutions, polymorphism, defect chemistry and a tendency to become metamict. The A site generally contains weakly bonded, easily exchanged cations of the LREE, Na and Ca. The B site generally contains smaller, highly charged cations of Ti, Nb or Fe+3. Mine production is from Russia's Kola Peninsula. Ore is beneficiated to produce a 95% loparite concentrate containing 30% rare-earth oxides. Loparite concentrate is refined by either a chlorination process or acid decomposition process to recover rare-earths, titanium, niobium and tantalum. Rare-earths are separated by solvent extraction and selective precipitation/dissolution. The concentrate is processed at plants in Russia, Estonia and Kazakstan.

  16. High-pressure densified solid solutions of alkaline earth hexaborides (Ca/Sr, Ca/Ba, Sr/Ba) and their high-temperature thermoelectric properties

    SciTech Connect

    Gürsoy, M.; Takeda, M.; Albert, B.

    2015-01-15

    Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB{sub 6}, SrB{sub 6}, BaB{sub 6} and the ternary hexaborides Ca{sub x}Sr{sub 1−x}B{sub 6}, Ca{sub x}Ba{sub 1−x}B{sub 6}, Sr{sub x}Ba{sub 1−x}B{sub 6} (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB{sub 6} (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process. - Highlights: • Solid solutions of alkaline earth hexaborides were synthesized. • High-temperature thermoelectric properties of mixed calcium borides are excellent. • Spark plasma source densification results in high ZT values. • Borides are rare-earth free and refractory materials.

  17. Synchrony of Cardiomyocyte Ca2+ Release is Controlled by t-tubule Organization, SR Ca2+ Content, and Ryanodine Receptor Ca2+ Sensitivity

    PubMed Central

    Øyehaug, Leiv; Loose, Kristian Ø.; Jølle, Guro F.; Røe, Åsmund T.; Sjaastad, Ivar; Christensen, Geir; Sejersted, Ole M.; Louch, William E.

    2013-01-01

    Recent work has demonstrated that cardiomyocyte Ca2+release is desynchronized in several pathological conditions. Loss of Ca2+ release synchrony has been attributed to t-tubule disruption, but it is unknown if other factors also contribute. We investigated this issue in normal and failing myocytes by integrating experimental data with a mathematical model describing spatiotemporal dynamics of Ca2+ in the cytosol and sarcoplasmic reticulum (SR). Heart failure development in postinfarction mice was associated with progressive t-tubule disorganization, as quantified by fast-Fourier transforms. Data from fast-Fourier transforms were then incorporated in the model as a dyadic organization index, reflecting the proportion of ryanodine receptors located in dyads. With decreasing dyadic-organization index, the model predicted greater dyssynchrony of Ca2+ release, which exceeded that observed in experimental line-scan images. Model and experiment were reconciled by reducing the threshold for Ca2+ release in the model, suggesting that increased RyR sensitivity partially offsets the desynchronizing effects of t-tubule disruption in heart failure. Reducing the magnitude of SR Ca2+ content and release, whether experimentally by thapsigargin treatment, or in the model, desynchronized the Ca2+ transient. However, in cardiomyocytes isolated from SERCA2 knockout mice, RyR sensitization offset such effects. A similar interplay between RyR sensitivity and SR content was observed during treatment of myocytes with low-dose caffeine. Initial synchronization of Ca2+ release during caffeine was reversed as SR content declined due to enhanced RyR leak. Thus, synchrony of cardiomyocyte Ca2+ release is not only determined by t-tubule organization but also by the interplay between RyR sensitivity and SR Ca2+ content. PMID:23601316

  18. [Spectra characteristics of LiM (M = Ca, Sr, Ba) BO3 : Tb3+ phosphor].

    PubMed

    Wang, Zhi-Jun; Li, Pan-Lai; Yang, Zhi-Ping; Guo, Qing-Lin

    2009-11-01

    LiM (M = Ca, Sr, Ba) BO3 : Tb3+ phosphors were synthesized by solid state reaction. The starting materials CaCO3, SrCO3, BaCO3, H3 BO3, Li2 CO3, Na2 CO3, K2 CO3 and Tb4 O7 (99.99% in mass) in appropriate stoichiometric ratio were mixed in the alumina crucible, then the mixed powders were calcined at 700 degrees C for 2 h, and LiCaBO3 : Tb3+, LiSrBO3 : Tb3+ and LiB-aBO3 : Tb3+ phosphors were obtained. The emission and excitation spectra were measured by a Shimadzu RF-540 ultraviolet spectrophotometer. All the photoluminescence properties of these phosphors were measured at room temperature. The emission spectra of LiM (M = Ca, Sr, Ba) BO3 : Tb3+ phosphors show several bands, and the main emission peaks correspond to the 5D4 --> 7F6(486, 486, 488 nm), 5D4 --> F5 (544, 544, 544 nm), 5D4 --> 7F4 (590, 595, 593 nm) and 5D4 --> 7F3 (620, 620, 616 nm) typical transitions of Tb3+, and the typical transitions of Tb3+ happens to split because of the effects of LiM (M = Ca, Sr, Ba) BO3 crystals field. The excitation spectra for the 544 nm green emission of LiM (M = Ca, Sr, Ba)BO3 : Tb3+ phosphors illuminate that these kinds of phosphors can be effectively excited by ultraviolet (350-410 nm) light, and emit green light, therefore, they are promising phosphors for white light emitting diodes. Effects of activation and charge compensation on the luminescence intensities of LiM (M = Ca, Sr, Ba) BO3 : Tb3+ phosphors were studied, and the results show that the intensities were obviously effected. PMID:20101952

  19. Hanford 100N Area Apatite Emplacement: Laboratory Results of Ca-Citrate-PO4 Solution Injection and Sr-90 Immobilization in 100N Sediments

    SciTech Connect

    Szecsody, James E.; Burns, Carolyn A.; Moore, Robert C.; Fruchter, Jonathan S.; Vermeul, Vincent R.; Williams, Mark D.; Girvin, Donald C.; McKinley, James P.; Truex, Michael J.; Phillips, Jerry L.

    2007-10-01

    This report summarizes laboratory scale studies investigating the remediation of Sr-90 by Ca-citrate-PO4 solution injection/infiltration to support field injection activities in the Hanford 100N area. This study is focused on experimentally testing whether this remediation technology can be effective under field scale conditions to mitigate Sr-90 migration 100N area sediments into the Columbia River. Sr-90 is found primarily adsorbed to sediments by ion exchange (99% adsorbed, < 1% in groundwater) in the upper portion of the unconfined aquifer and lower vadose zone. Although primarily adsorbed, Sr-90 is still considered a high mobility risk as it is mobilized by seasonal river stage increases and by plumes of higher ionic strength relative to groundwater. This remediation technology relies upon the Ca-citrate-PO4 solution forming apatite precipitate [Ca6(PO4)10(OH)2], which incorporates some Sr-90 during initial precipitation and additionally slowly incorporates Sr-90 by solid phase substitution for Ca. Sr substitution occurs because Sr-apatite is thermodynamically more stable than Ca-apatite. Once the Sr-90 is in the apatite structure, Sr-90 will decay to Y-90 (29.1 y half-life) then Zr-90 (64.1 h half-life) without the potential for migration into the Columbia River. For this technology to be effective, sufficient apatite needs to be emplaced in sediments to incorporate Sr and Sr-90 for 300 years (~10 half-lives of Sr-90), and the rate of incorporation needs to exceed the natural groundwater flux rate of Sr in the 100N area. A primary objective of this study is to supply an injection sequence to deliver sufficient apatite into subsurface sediments that minimizes initial mobility of Sr-90, which occurs because the injection solution has a higher ionic strength compared to groundwater. This can be accomplished by sequential injections of low, then high concentration injection of Ca-citrate-PO4 solutions. Assessment of low concentration Ca-citrate-PO4, citrate-PO4

  20. Structure electronic and ionic conductivity study versus Ca content in Ca{sub 10-x}Sr{sub x}(PO{sub 4}){sub 6}F{sub 2} apatites

    SciTech Connect

    Sghir, B.; Hlil, E.K.; Laghzizil, A.; Boujrhal, F.Z.; Cherkaoui El Moursli, R.; Fruchart, D.

    2009-07-01

    Substitution effect on the crystallographic structure in Ca{sub 10-x}Sr{sub x}(PO{sub 4}){sub 6}F{sub 2} solid solution are studied by X-ray diffraction patterns and Rietveld refinements. Full potential electronic structure calculations based on LCAO (linear combination atomic orbital) are also performed using the obtained crystallographic parameters. DOS modification and the charge transfer are estimated versus the calcium content. According to the complex impedance method, ionic conductivity changes are explained.

  1. Large Magnetothermopower Effect in Dirac Materials (Sr/Ca)MnBi2

    SciTech Connect

    Petrovic C.; Wang, K.; Wang, L.

    2012-03-12

    We report temperature and magnetic field dependence of the thermal transport properties in single crystals of (Sr/Ca)MnBi2 with linear energy dispersion. In SrMnBi2 thermopower is positive, indicating hole-type carriers and the magnetic field enhances the thermopower significantly. The maximum change of thermopower is about 1600% in 9 T field and at 10 K. A negative thermopower is observed in CaMnBi2 with dominant electron-type carriers, and, in contrast, the magnetic field suppresses the absolute value of thermopower. First-principle band structure shows that the chemical potential is close to the Dirac-cone-like points in linear bands. The magnetic field suppresses the apparent Hall carrier density of CaMnBi2 below 50 K. The large magnetothermopower effect in (Sr/Ca)MnBi2 is attributed to the magnetic field shift of chemical potential.

  2. Catalytic partial oxidation of n-tetradecane using pyrochlores: Effect of Rh and Sr substitution

    SciTech Connect

    Haynes, D.; Berry, D.; Shekhawat, D.; Spivey, J.

    2008-01-01

    The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2 y)O(7-j,) (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2 x)SrxRhyZr(2 y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had

  3. Catalytic Partial oxidation of n-Tetradecane Using Pyrochlores: Effect of Rh and Sr Substitution

    SciTech Connect

    Haynes, D.J.; Berry, D.A.; Shekhawat, Dushyant; Spivey, J.J.

    2008-07-31

    The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2 y)O(7-j,) (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2 x)SrxRhyZr(2 y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had

  4. Is otolith microchemistry (Sr: Ca and Ba:Ca ratios) useful to identify Mugil curema populations in the southeastern Caribbean Sea?

    PubMed

    Avigliano, E; Callicó-Fortunato, R; Buitrago, J; Volpedo, A V

    2015-11-01

    The aim of the present study was to evaluate the potential use of otolith microchemistry (Sr:Ca and Ba:Ca ratios) to identify silver mullet, Mugil curema, populations in Southeastern Caribbean Sea. Fish samples were collected in 7 areas of Nueva Esparta State (Venezuela). The otolith Sr:Ca and Ba:Ca ratios and water Sr:Ca were determined (by ICP-OES and EDTA volumetric method). Otoliths Sr:Ca and Ba:Ca ratios and Sr:Ca partition coefficient of mullets in Cubagua island (south of the State) were significantly different from ratios in La Guardia (north of the State). A discriminant analysis of otolith Sr:Ca and Ba:Ca ratios separated Cubagua Island from La Guardia values. These results suggest the existence of different mullet groups in the Southeastern Caribbean Sea. For this, the simultaneous use of Sr:Ca and Ba:Ca ratios could be a potential tool to identify populations in the study area. PMID:26628220

  5. Sr, Ca, and C isotope systematic in small tropical catchments, La Selva, Costa Rica

    NASA Astrophysics Data System (ADS)

    Wiegand, B. A.; Schwendenmann, L.

    2010-12-01

    Sr, Ca, and C isotopes were analyzed to assess sources and biogeochemical processes affecting surface and groundwater composition of four small catchments located at La Selva Biological Station, Costa Rica. 87Sr/86Sr ratios were employed to quantify inputs from mineral weathering and atmospheric sources. δ13C values of dissolved organic carbon (DOC) and δ44Ca values provide information on biological processes that affect water chemistry. Sr2+ and Ca2+ concentrations of surface and groundwater show large variations due to intermixture of bedrock groundwater with local groundwater [1]. Low 87Sr/86Sr ratios suggest weathering of volcanic rocks as the primary solute source in bedrock groundwater, while atmospheric and in situ weathering contributions are predominant in local groundwater. Contributions of bedrock groundwater constitute > 60 % in the Salto, Saltito and Arboleda catchments, whereas the Taconazo catchment receives atmospheric inputs of > 95 % in addition to local weathering contributions. Surface water and groundwater wells show δ13C-DOC values between -24 ‰ and -30 ‰ due to transfer of organic carbon from the soil zone. δ44Ca values of dissolved Ca2+ in surface and groundwater are considerably fractionated from the input sources rainwater and bedrock groundwater. Light δ44Ca values are preferentially distributed in stream water and shallow groundwater horizons and contrast with heavy Ca isotopes in deeper groundwater wells. Biological processes including plant uptake and decomposition in combination with cation exchange processes in the soils may explain the fractionation of Ca isotopes. [1]Genereux et al., 2009. Water Resour. Res, 45, W08413, doi:10.1029/2008WR007630

  6. Sr2+/Ca2+ and 44Ca/40Ca fractionation during inorganic calcite formation: III. Impact of salinity/ionic strength

    PubMed Central

    Tang, Jianwu; Niedermayr, Andrea; Köhler, Stephan J.; Böhm, Florian; Kısakürek, Basak; Eisenhauer, Anton; Dietzel, Martin

    2012-01-01

    In order to apply Sr/Ca and 44Ca/40Ca fractionation during calcium carbonate (CaCO3) formation as a proxy to reconstruct paleo-environments, it is essential to evaluate the impact of various environmental factors. In this study, a CO2 diffusion technique was used to crystallize inorganic calcite from aqueous solutions at different ionic strength/salinity by the addition of NaCl at 25 °C. Results show that the discrimination of Sr2+ versus Ca2+ during calcite formation is mainly controlled by precipitation rate (R in μmol/m2/h) and is weakly influenced by ionic strength/salinity. In analogy to Sr incorporation, 44Ca/40Ca fractionation during precipitation of calcite is weakly influenced by ionic strength/salinity too. At 25 °C the calcium isotope fractionation between calcite and aqueous calcium ions (Δ44/40Cacalcite-aq = δ44/40Cacalcite − δ44/40Caaq) correlates inversely to log R values for all experiments. In addition, an inverse relationship between Δ44/40Cacalcite-aq and log DSr, which is independent of temperature, precipitation rate, and aqueous (Sr/Ca)aq ratio, is not affected by ionic strength/salinity either. Considering the log DSr and Δ44/40Cacalcite-aq relationship, Sr/Ca and δ44/40Cacalcite values of precipitated calcite can be used as an excellent multi-proxy approach to reconstruct environmental conditions (e.g., temperature, precipitation rate) of calcite growth and diagenetic alteration. PMID:22347722

  7. Ca-Mg-Sr-Nd Isotopes in Granitic Rocks of the Lhasa Terrane, Southern Tibet

    NASA Astrophysics Data System (ADS)

    Peterson, B. T.; Simon, J. I.; Depaolo, D. J.; Christensen, J. N.; Harrison, T. M.

    2010-12-01

    Magnesium (Mg) and Calcium (Ca) isotopes are fractionated by aqueous precipitation and incongruent silicate weathering, resulting in sedimentary reservoirs with characteristic isotopic compositions. Limestones and dolomites are isotopically light in both elements, whereas shales/pelites can have heavy Mg and light Ca. The isotopic character of these reservoirs may persist through anatexis (Shen, et al., PNAS 106(49), 2009). Mg and Ca isotopes could therefore be used to gain new insights into the sources of granitic magmas and hence the mechanisms by which the continental crust forms and evolves. Radiogenic 40Ca gives additional information about the K/Ca ratios of magma sources, and Sr and Nd isotopes provide complementary age and lithology information. To evaluate the potential of Ca and Mg isotopes for studying granite petrogenesis we made measurements on a suite of granitic intrusive rocks of Jurassic to Miocene age in southern Tibet that exhibit large variations in Nd (ɛNd = +5 to -12) and Sr isotopes (87Sr/86Sr = 0.704 to 0.722). Our samples represent a transect northward from the Indus-Yalu Suture (IS), west of Lhasa. Rocks close to the IS have mantle-like Nd and Sr isotopic compositions, whereas those farther to the north have low ɛNd and higher 87Sr/86Sr, and include Mesozoic, Paleogene and Neogene peraluminous (2-mica) granites (DePaolo, et al., Goldschmidt, 2008; Kapp, et al., JGR 110, 2005; Hou et al., EPSL 220, 2004). Radiogenic 40Ca is detectable in peraluminous (2-mica) granites and correlates with high 87Sr/86Sr, but does not correlate with Nd isotopes, indicating that 2-mica granite magmas come from both low-K and high-K sources. Stable isotopes of both Ca and Mg show substantial variation. Relative to bulk silicate Earth (BSE, which we define as δ=0 for discussion) δ44Ca values vary from 0 to -0.7, and δ26Mg varies from -0.3 to +0.6. Thus to first order Ca is light and Mg is heavy relative to BSE. For samples with mantle-like Nd and Sr, δ44Ca

  8. Physical properties of Rh substituted CaFe2As2 tuned by annealing/quenching

    NASA Astrophysics Data System (ADS)

    Ran, Sheng; Bud'Ko, Sergey; Canfield, Paul

    2014-03-01

    Our previous work on CaFe2As2 single crystal grown out of FeAs flux has shown that a process of annealing and quenching can be used as an additional control parameter which can tune the ground state of CaFe2As2 systematically. We have also shown that CaFe2As2 is very pressure sensitive. Therefore, unlike the BaFe2As2 system, the effect of 4d transition metal substitution on CaFe2As2 is expected to be largely different from that of 3d transition metal substitution (e.g. cobalt or nickel substitution). In this talk we will present results of measurements on a Rh substituted CaFe2As2 system with different annealing/quenching temperatures. Phase diagrams with substitution level and annealing/quenching temperature as independent parameters are constructed and compared with that of other transition metal substitutions. Supported by the U.S. Department of Energy Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

  9. Enhancement of the critical current density in single-crystal Bi2Sr2CaCu2O8 superconductors by chemically induced disorder.

    PubMed Central

    Wang, Y L; Wu, X L; Chen, C C; Lieber, C M

    1990-01-01

    The effect of metal substitution on the critical current densities of single-crystal PbxBi2-xSr2CaCu2O8 (x = 0 or x = 0.7) superconductors has been investigated. Substitution of lead was found to increase the average critical current density from 1 x 10(5) A/cm2 to 2 x 10(6) A/cm2 at 5 K in an applied magnetic field of 10 kilooersteds (1 oersted = 80 A/m). The order of magnitude increase in the critical current density was observed for temperatures up to the flux vortex lattice melting point; the flux lattice melting point was also found to increase to 30 K (from 22 K) in the lead-substituted materials. Diffraction and microscopy investigations of the structural parameters indicate that the fundamental atomic lattices are virtually the same for both materials. Scanning tunneling microscopy images demonstrate, however, that lead substitution causes significant disorder (or defects) in the one-dimensional superstructure found in Bi2Sr2CaCu2O8. Since crystal defects can increase the critical current density by pinning the motion of flux vortices, it is likely that this lead-induced disorder enhances vortex pinning. The lead-induced disorder is specific to the nonsuperconducting Bi-O layers, and thus our results suggest that chemical substitutions may be utilized to control selectively flux pinning and the critical current density in these materials. Images PMID:11607103

  10. Measurement of Ca, Zn and Sr in enamel of human teeth by XRF

    SciTech Connect

    Wielopolski, L.; Featherstone, J.D.B.; Cohn, S.H.

    1984-01-01

    Energy dispersive x-ray fluorescence (EDXRF) has been employed to measure Ca, Zn, and Sr in enamel of human teeth. The calibration of the EDXRF system was performed by comparing Sr/Ca ratios with values obtained by atomic absorption analysis of acid etched biopsies of the enamel surface. Two calibration lines were obtained, one line for untreated teeth and the second line for teeth immersed (treated) in solutions containing Sr. A simple analytical model demonstrated that the two calibration lines were the result of the difference in the depth of the enamel sampled by EDXRF and by the acid-etched biopsy. The multi-elemental, non-destructive and quantitative aspects of EDXRF permit the sequential monitoring of the effects of Sr and Zn ions on the mineralization and demineralization processes in human enamel. The portability of the system and adaptability to non-invasive measurements makes it suitable for field studies. 26 references, 4 figures.

  11. Preparation and characterisation of nanophase Sr, Mg, and Zn substituted hydroxyapatite by aqueous precipitation.

    PubMed

    Cox, Sophie C; Jamshidi, Parastoo; Grover, Liam M; Mallick, Kajal K

    2014-02-01

    Hydroxyapatite (HA) substituted with 2 mol% Sr, 10 mol% Mg, and 2 mol% Zn were precipitated under identical alkaline conditions (pH 11) at 20°C from an aqueous solution. As-synthesised materials were confirmed to be phase pure by XRD and samples prepared in air contained surface adsorbed CO2 as observed by FTIR. SEM studies revealed a globular morphology and agglomeration behaviour, typical of precipitated nHA. EDS spectra confirmed nominal compositions and substitution of Sr, Mg and Zn. At the levels investigated cationic doping was not found to radically influence particle morphology. An indication of the potential in-vivo bioactivity of samples was achieved by analysing samples immersed in SBF for up to 28 days by interferometry and complementary SEM micrographs. Furthermore, a live/dead assay was used and confirmed the viability of seeded MC3T3 osteoblast precursor cells on HA and substituted HA substrates up to 7 days of culture. PMID:24411358

  12. Sr isotopic fractionation in Ca-Al inclusions from the Allende meteorite

    USGS Publications Warehouse

    Patchett, P.J.

    1980-01-01

    True relative Sr isotopic compositions, determined by double spiking on Ca-Al inclusions from the Allende meteorite show up to 1.5??? per mass unit mass fractionation relative to the Earth and bulk chondrites. All abnormal inclusions are light-isotope enriched. A lack of isotopically heavy Sr in inclusions would place constraints on the time, place and mechanism of origin of these objects. ?? 1980 Nature Publishing Group.

  13. Sr/Ca in Coral Aragonite: Is Night Carbonate a Good Indicator of Sea Surface Temperatures?

    NASA Astrophysics Data System (ADS)

    Allison, N.; Finch, A. A.

    2002-12-01

    Sr/Ca in coral skeletons has potential as an indicator of past seawater conditions but exhibits geochemical heterogeneity on a small spatial scale (<100 μm) that does not reflect variations in sea surface temperature (SST) or chemistry. Skeletal Sr/Ca is affected by variations in skeletal calcification rate which may be dependent on the photosynthetic activity of the zooxanthellae in coral tissue. The skeleton deposited at night may be unaffected by these variations and may be a more reliable indicator of SST (Cohen et al. 2001). We used secondary ion mass spectrometry with a 10 μm diameter analysis spot to construct records of Sr/Ca in a Porites lobata specimen from Lanakai, Oahu, Hawaii. Analyses were performed on sections cut perpendicular to the growth surface of the coral skeleton, spanning annual bands. Parallel tracks were analysed following fasciculi (composed of acicular crystals deposited during the day) and centres of calcification (composed of fusiform crystals deposited at night). The Sr/Ca of the day and night material follow similar seasonal trends but are offset with night carbonate typically enriched by 0.3-0.4 mmol mol-1. Both profiles are characterised by large Sr fluctuations of 0.4-0.5 mmol mol-1, which are deposited approximately days apart and are superimposed on the general Sr seasonal trend. These fluctuations do not reflect variations in SST but may relate to daily variations in coral calcification or linear extension rate both of which can vary markedly during the day and night. We conclude that night carbonate is affected by kinetic processes and that there are similar challenges in reconstructing SST records from night carbonate as from day carbonate. Cohen AL et al., Kinetic control of skeletal Sr/Ca in a symbiotic coral: implications for the palaeotemperature proxy, Paleoceanography, 16, 20-26, 2001.

  14. As-grown superconducting Bi-Sr-Ca-Cu-O thin films by coevaporation

    SciTech Connect

    Satoh, T.; Yoshitake, T.; Miura, S.; Fujita, J.; Kubo, Y.; Igarashi, H.

    1989-08-14

    Superconducting Bi-Sr-Ca-Cu-O thin films have been prepared on (100) MgO substrates at about 600 /degree/C by coevaporation. The /ital c/-axis lattice constant of this system was controlled to the values of 24--43 A by changing film composition. Superconducting transition temperatures of these films were affected by substrate temperature and by a post-deposition annealing at a low temperature. The highest zero resistance temperature (/ital T//sub /ital c/, zero/) of the as-grown Bi/sub 2/(Sr,Ca)/sub 3/Cu/sub 2/O/sub /ital x// film was 79 K. The best Bi/sub 2/(Sr, Ca)/sub 4/Cu/sub 3/O/sub /ital x// film showed an onset temperature of 105 K and /ital T//sub /ital c/, zero/ zero of 78 K after annealing at 400 /degree/C for 1 h.

  15. K-Ca and Rb-Sr Dating of Lunar Granite 14321 Revisited

    NASA Technical Reports Server (NTRS)

    Simon, Justin I.; Shih, C.-Y.; Nyquist, L. E.

    2011-01-01

    K-Ca and Rb-Sr age determinations were made for a bulk feldspar-rich portion of an Apollo rock fragment of the pristine lunar granite clast (14321,1062), an acid-leached split of the sample, and the leachate. K-Ca and Rb-Sr data were also obtained for a whole rock sample of Apollo ferroan anorthosite (FAN, 15415). The recent detection [1] of widespread intermediate composition plagioclase indicates that the generation of a diversity of evolved lunar magmas maybe more common and therefore more important to our understanding of crust formation than previously believed. Our new data strengthen the K-Ca and Rb-Sr internal isochrons of the well-studied Apollo sample 14321 [2], which along with a renewed effort to study evolved lunar magmas will provide an improved understanding of the petrogenetic history of evolved rocks on the Moon.

  16. Effects of Eu substituting positions and concentrations on luminescent, dielectric, and magnetic properties of SrTiO3 ceramics

    NASA Astrophysics Data System (ADS)

    Jiang, Chunge; Fang, Liang; Shen, Mingrong; Zheng, Fengang; Wu, Xinglong

    2009-02-01

    The structural, luminescent, dielectric, and magnetic properties of multifunction Eu3+-doped SrTiO3 (STO) ceramics were investigated at room temperature. Three different charge compensation mechanisms were realized by substituting Eu ion at different sites. It was found that the multifunction properties of the samples strongly depended on the substituting positions of Eu ion. Compared with Eu substitution at Sr or Ti site samples, the photoluminescence intensities and dielectric constant of both Sr and Ti sites substituted samples were obviously enhanced, mainly ascribed to the small lattice distortion and unique charge compensation mechanism. A linear magnetization-magnetic field behavior revealed the paramagnetic nature of the Eu3+ doped STO and was sensitive to the Eu doping concentrations.

  17. Properties of doped and undoped (Ca,Sr)CuO{sub 2} thin films

    SciTech Connect

    Norton, D.P.; Chakoumakos, B.C.; Budai, J.D.; Jones, E.C.; Christen, D.K.; Lowndes, D.H.

    1993-12-01

    The authors have studied the transport and structural properties of (Ca,Sr)CuO{sub 2}, Sr{sub 1{minus}y}Nd{sub y}CuO{sub 2}, and Sr{sub 1{minus}x}CuO{sub 2{minus}{delta}} thin films grown by pulsed-laser deposition. Stoichiometric {open_quotes}infinite layer{close_quotes} (Ca,Sr)CuO{sub 2} thin films grown over a large range of growth conditions are insulators, while superconductivity is observed in Sr{sub 1{minus}y}Nd{sub y}CuO{sub 2} films with {Tc}(onset) {approximately}28 K for y = 0.10. A Nd solubility limit of y = 0.10 is observed with the appearance of a new phase with c {approximately} 0.37 nm for y > 0.10. In addition, the transport and structural properties of Sr{sub 1{minus}x}CuO{sub 2{minus}{delta}} thin films grown by pulsed-laser deposition support the contention that the tetragonal phase is capable of accommodating a significant density of alkaline-earth deficiencies up to x {le} 0.3. Resistivity measurements indicate a significant change in the carrier density of the CuO{sub 2} planes as Sr vacancies are introduced. In addition, an enigmatic anomaly in resistivity at 185 K is observed for Sr{sub 0.85}CuO{sub 2{minus}{delta}} thin films. Magnetic measurements on these samples indicate that, although a significant drop in resistivity at 185 K is observed, it is not due to a superconducting transition. Hall measurements, as well as changes in resistivity with film growth conditions, suggest that the majority carriers in these Sr{sub 1{minus}x}CuO{sub 2{minus}{delta}} thin films are electrons even with the Sr-vacancies present.

  18. Influence of carbonate ion in the crystallization medium on the formation and chemical composition of CaHA-SrHA solid solutions

    NASA Astrophysics Data System (ADS)

    Nikolaev, Anton; Kuz'mina, Maria; Frank-Kamenetskaya, Olga; Zorina, Maina

    2015-06-01

    The study of the influence of carbonate ions in a solution to Sr-distribution in system «solution-crystal» and to ion substitutions and the non-stoichiometry of formed CaHA-SrHA solid solutions was carried out. The CaHA-SrHA solid solutions were synthesized by precipitation from aqueous solutions with the atomic C/P ratio equal to 0, 0.05 and 0.1 at T = 90 °C. Resulting precipitates were studied using various methods including X-ray powder diffraction, infrared spectroscopy and different chemical analyses. The results of the study have shown that in the range of values of (Ca + Sr)/P in the water solution from 40% to 85%, the presence of carbonate ions (C/P = 0.05-0.1) promotes the incorporation of strontium in the apatite. Crystalline apatite solid solutions formed from water solutions of such composition are more defective compared to apatites that are mainly calcium or strontium. They are characterized by a smaller size coherence scattering domain length along [0 0 1] direction and a greater number of carbonate ions, water molecules and vacancies at the Ca-sites.

  19. Superconductivity in the high-Tc Bi-Ca-Sr-Cu-O system - Phase identification

    NASA Technical Reports Server (NTRS)

    Hazen, R. M.; Prewitt, C. T.; Angel, R. J.; Ross, N. L.; Finger, L. W.

    1988-01-01

    Four phases are observed in superconducting Bi-Ca-Sr-Cu-O samples. The superconducting phase, with onset temperature near 120 K, is a 15.4-A-layered compound with composition near Bi2Ca1Sr2Cu2O9 and an A-centered orthorhombic unit subcell 5.41 x 5.44 x 30.78 A. X-ray diffraction and electron microscopy data are consistent with a structure of alternating perovskite and Bi2O2 layers. High-resolution transmission electron microscopy images reveal a b-axis superstructure of 27.2 A, numerous (001) stacking faults, and other defects.

  20. Synthesis of highly phase pure (Bi, Pb)-Sr-Ca-Cu-O superconductor

    DOEpatents

    Dorris, Stephen E.; Poeppel, Roger B.; Prorok, Barton C.; Lanagan, Michael T.; Maroni, Victor A.

    1994-01-01

    An article and method of manufacture of (Bi,Pb)-Sr-Ca-Cu-O superconductor. The superconductor is manufactured by preparing a first powdered mixture of bismuth oxide, lead oxide, strontium carbonate, calcium carbonate and copper oxide. A second powdered mixture is then prepared of strontium carbonate, calcium carbonate and copper oxide. The mixtures are calcined separately with the two mixtures then combined. The resulting combined mixture is then subjected to a powder in tube deformation and thermal processing to produce a substantially phase pure (Bi,Pb)-Sr-Ca-Cu-O superconductor.

  1. Synthesis of highly phase pure (Bi, Pb)-Sr-Ca-Cu-O superconductor

    DOEpatents

    Dorris, S.E.; Poeppel, R.B.; Prorok, B.C.; Lanagan, M.T.; Maroni, V.A.

    1994-10-11

    An article and method of manufacture of (Bi,Pb)-Sr-Ca-Cu-O superconductor are disclosed. The superconductor is manufactured by preparing a first powdered mixture of bismuth oxide, lead oxide, strontium carbonate, calcium carbonate and copper oxide. A second powdered mixture is then prepared of strontium carbonate, calcium carbonate and copper oxide. The mixtures are calcined separately with the two mixtures then combined. The resulting combined mixture is then subjected to a powder in tube deformation and thermal processing to produce a substantially phase pure (Bi,Pb)-Sr-Ca-Cu-O superconductor. 5 figs.

  2. Photoluminescence of A- and B-site Eu3+-substituted (SrxBa1-x)2CaWyMo1-yO6 phosphors

    NASA Astrophysics Data System (ADS)

    Sletnes, M.; Lindgren, M.; Valmalette, J. C.; Wagner, N. P.; Grande, T.; Einarsrud, M.-A.

    2016-05-01

    The photoluminescence of two series of A- and B-site Eu3+ substituted (SrxBa1-x)2CaWyMo1-yO6 double perovskite phosphor materials, (SrxBa1-x)1.96Eu0.02K0.02CaWyMo1-yO6 and (SrxBa1-x)2Ca0.96Eu0.02Li0.02WyMo1-yO6 (x and y=0, 0.25, 0.50, 0.75, and 1), were studied systematically as a function of stoichiometry and crystal structure. The Eu3+ lattice sites controlled by co-doping with either K or Li were confirmed by Raman spectroscopy. The variation in integrated emission intensity and emission colour over the experimental matrix was examined using statistical tools, and the observed trends were rationalized based on the physical and electronic structure of the phosphors. Phosphors with Eu on B-site with maximum Sr content had remarkably higher emission intensities than all other materials, but the emission was more orange than red due to domination of the 5D0-7F1 (595 nm) transition of Eu3+. The relative intensities of the 5D0-7F2 (615 nm) and 5D0-7F1 transitions of Eu3+, and thus the red-shift of the emission, decreased linearly with increasing Sr content in the A-site Eu-substituted phosphors, and reached a maximum for Sr1.96Eu0.02K0.02CaW0.25Mo0.75O6. A maximum external quantum efficiency of 17% was obtained for the phosphor Sr2Ca0.7Eu0.15Li0.15W0.5Mo0.5O6 with Eu on B-site.

  3. Measurements of Sr/Ca in bones to evaluate differences in temperature

    NASA Astrophysics Data System (ADS)

    Santos, P. R.; Added, N.; Aburaya, J. H.; Rizzutto, M. A.

    2008-04-01

    Analysis of aragonite from sea shells and coral skeletons showed a clear correlation between the strontium and calcium concentrations for these crystals (Sr/Ca ratio) and seawater temperature obtained by satellites and ship readings. In this work we present the results of a study that correlates Sr/Ca ratio with formation temperature of another calcium crystal, the hydroxyapatite (Ca10(PO4)6(OH)2), main mineral compound of teeth and bones from vertebrates. These animals, independent of its thermoregulation pattern (endothermic or ectothermic) have variations of internal temperature along the body. One interesting application of this work is to differentiate warm-blooded animals from cold-blooded ones just by measuring Sr/Ca ratio in their bones. Bones from a crocodile from Caiman yacare species and two dogs, a poodle and a non defined race, were analyzed using PIXE technique and thick target correction. A 1.78 (18) MeV external proton beam was used in LAMFI-USP with an accumulated charge of about 10 μC for probing the samples. Emitted X-rays were collected using Si-PIN detectors (140 keV for Fe). As in coral skeletons, the Sr/Ca ratio of animals is lower in the body's warmer parts and higher in colder parts.

  4. Comparison of equatorial Pacific sea surface temperature variability and trends with Sr/Ca records from multiple corals

    NASA Astrophysics Data System (ADS)

    Alpert, Alice E.; Cohen, Anne L.; Oppo, Delia W.; DeCarlo, Thomas M.; Gove, Jamison M.; Young, Charles W.

    2016-02-01

    Coral Sr/Ca is widely used to reconstruct past ocean temperatures. However, some studies report different Sr/Ca-temperature relationships for conspecifics on the same reef, with profound implications for interpretation of reconstructed temperatures. We assess whether these differences are attributable to small-scale oceanographic variability or "vital effects" associated with coral calcification and quantify the effect of intercolony differences on temperature estimates and uncertainties. Sr/Ca records from four massive Porites colonies growing on the east and west sides of Jarvis Island, central equatorial Pacific, were compared with in situ logger temperatures spanning 2002-2012. In general, Sr/Ca captured the occurrence of interannual sea surface temperature events but their amplitude was not consistently recorded by any of the corals. No long-term trend was identified in the instrumental data, yet Sr/Ca of one coral implied a statistically significant cooling trend while that of its neighbor implied a warming trend. Slopes of Sr/Ca-temperature regressions from the four different colonies were within error, but offsets in mean Sr/Ca rendered the regressions statistically distinct. Assuming that these relationships represent the full range of Sr/Ca-temperature calibrations in Jarvis Porites, we assessed how well Sr/Ca of a nonliving coral with an unknown Sr/Ca-temperature relationship can constrain past temperatures. Our results indicate that standard error of prediction methods underestimate the actual error as we could not reliably reconstruct the amplitude or frequency of El Niño-Southern Oscillation events as large as ± 2°C. Our results underscore the importance of characterizing the full range of temperature-Sr/Ca relationships at each study site to estimate true error.

  5. Monthly Sr/Ca oscillations in symbiotic coral aragonite: Biological effects limiting the precision of the paleotemperature proxy

    NASA Astrophysics Data System (ADS)

    Meibom, A.; Stage, M.; Wooden, J. L.; Constantz, B. R.; Dunbar, R. B.; Owen, A.; Grumet, N.; Bacon, C. R.; Chamberlain, C. P.

    2003-04-01

    In thermodynamic equilibrium with sea water the Sr/Ca ratio of aragonite varies predictably with temperature and the Sr/Ca ratio in coral have thus become a frequently used proxy for past Sea Surface Temperature (SST). However, biological effects can offset the Sr/Ca ratio from its equilibrium value. We report high spatial resolution ion microprobe analyses of well defined skeletal elements in the reef-building coral Porites lutea from Watamu, Kenya. Our data reveal distinct monthly oscillations in the Sr/Ca ratio, with an amplitude in excess of ten percent. These extreme Sr/Ca variations, which likely result from metabolic changes synchronous with the lunar cycle, introduce variability in Sr/Ca measurements based on conventional sampling techniques well beyond the analytical precision. Monte Carlo simulations show that under such conditions the precision of the Sr/Ca paleo-thermometer can be limited to about 2oC. Aragonite precipitated during periods of reduced growth rate have relatively small biological effects. Thus, Sr/Ca-based temperature reconstructions from massive scleractinian corals, such as Porites, would become more precise if the corals are preferentially sampled in low growth-rate regions of the skeleton. We therefore recommend a re-analysis of existing Sr/Ca records based on knowledge of temperature impacts on growth rates. If the biological effects observed in the Porites corals studied by us are confirmed in other Porites specimens from which long SST records have been derived on the basis of the Sr/Ca paleothermometer, it may invalidate conclusions based on inferred SST variations of less than 2oC. Our results also may help explain the notorious difficulties involved in obtaining an accurate and consistent calibration of the Sr/Ca vs. SST relationship.

  6. [Structure and photoluminescence of ASnO3 (A = Ca, Sr and Ba) : Eu nanocrystalline].

    PubMed

    Fu, Xiao-Yan; Niu, Shu-Yun; Zhang, Hong-Wu; Xin, Qin

    2007-09-01

    The present paper reports the photoluminescence properties of nanocrytalline ASnO3 (A = Ca, Sr and Ba) : 1% Eu phosphor synthesized by the Pechini-type sol-gel method. The powder was characterized by X-ray diffraction (XRD), UV-Vis absorption spectra, transmission electron microscopy (TEM) and photoluminescence measurements. The experimental results show that BaSnO3 has the ideal cubic peroskite structure, while SrSnO3 and CaSnO3 are both distorted from cubic symmetry by an octahedral tilting distortion. The difference of structure in induced the different spectral properties of ASnO3 : 1% Eu. On the other hand, when A2+ changes from Ca2+ to Ba2+, the luminescence intensity becomes weak. So CaSnO3 : 1% Eu seems to be a good candidate for new phosphors. PMID:18051556

  7. Catalytic partial oxidation of n-tetradecane on Rh and Sr substituted pyrochlores

    SciTech Connect

    Haynes, D.J.; Berry, D.A.; Shekhawat, Dushyant; Gardner, T.H.; Spivey, J.J.

    2007-10-01

    Catalyst deactivation by high levels of sulfur and aromatics limits the catalytic partial oxidation (CPOX) of diesel fuel into a H2-rich stream for fuel cells. These species poison traditional supported metal catalysts because they adsorb strongly to electron dense metal clusters and promote the formation of carbon on the surface. In this work, Rh + Sr are substituted into lanthanum zirconate (LZ) pyrochlore (La2Zr2O7) to give an La(2-x)SrxRhyZr(2-y)O(7- î) (LSRZ) catalyst. The resistance to deactivation and carbon formation were examined by the CPOX of a mixture of 5 wt% 1-methylnaphthalene + 1000 ppmw dibenzothiophene in n-tetradecane. The results were compared to a commercial Rh/ã-Al2O3 catalyst. In the presence of these contaminants, the activity of the LSRZ was only kinetically inhibited, which is thought to be attributable to the oxygen-ion conductivity that results from Sr substitution into the pyrochlore structure. Rh/ã-Al2O3 was deactivated, likely due to significant carbon accumulation on/near the Rh metal

  8. Coprecipitation of Sr, Ni and U with CaCO{sub 3}: An experimental study

    SciTech Connect

    Carlsson, T.; Aalto, H.

    1996-08-01

    At the Finnish candidate sites for a nuclear waste repository, calcite (CaCO{sub 3}) is a common fracture mineral that may participate in coprecipitation processes. The objective of this preliminary work was to study the coprecipitation of the trace elements Sr, Ni, and U with CaCO{sub 3} under controlled conditions. The experiments were made in a titration vessel at room temperature under pure N{sub 2} or a 0.1% CO{sub 2}/N{sub 2} mixture. The water phase contained CaCl{sub 2} (0.01M) and NaCl (0.05 M) to which trace amounts of Ni{sup 2+}, Sr{sup 2+} and UO{sub 2}{sup 2+} were initially added. CaCO{sub 3} was precipitated by the addition of Na{sub 2}CO{sub 3} and the use of CaCO{sub 3} seed crystals. When about 10{sup {minus}4} mol of precipitate had formed, the solution and solid phases were analyzed with ICP-MS. The results seem to indicate that Ni coprecipitated with CaCO{sub 3} under the experimental conditions, while U did not. In the case of Sr, further data are needed in order to make any conclusions from the experiments.

  9. Crystal structure of new Li + ion conducting perovskites: Li 2 xCa 0.5- xTaO 3 and Li 0.2[Ca 1- ySr y] 0.4TaO 3

    NASA Astrophysics Data System (ADS)

    Pham, Quoc Nghi; Crosnier-Lopez, Marie-Pierre; Le Berre, Françoise; Fauth, François; Fourquet, Jean-Louis

    2004-09-01

    Two new solid solutions—Li 2 xCa 0.5- xTaO 3 (0.05⩽ x⩽0.25) and Li 0.2[Ca 1- ySr y] 0.4TaO 3 (0< y⩽0.15)—based on the A defective ABO 3 perovskite structural type, are synthesized. The crystal structures of these Li + ion conducting compounds are solved from synchrotron radiation and conventional X-ray powder diffraction data. The unit cells exhibit a classical orthorhombic distortion of the cubic perovskite model (space group Pnma No. 62) with parameters close to 2a p, 2 ap, 2a p ( ap, primitive cubic cell parameter). The distortion of the cubic aristotype arises from the three tilts system a+b-b- of the TaO 6 octahedra. For the same lithium content ( x=0.10), the Sr 2+ substitution to Ca 2+ is found to enhance the electrical conductivity by quasi-one order of magnitude (at 200 °C, bulk dc conductivity values are close to 2.3×10 -6 and 1.1×10 -5 S cm -1 for Li 0.2Ca 0.4TaO 3 and Li 0.2[Ca 0.9Sr 0.1] 0.4TaO 3, respectively).

  10. Superconducting glass-ceramics in the Bi-Sr-Ca-Cu-O system

    NASA Technical Reports Server (NTRS)

    De Guire, Mark R.; Kim, Cheol J.; Bausal, Narottam P.

    1990-01-01

    Differential thermal analysis, XRD, SEM, and resistivity measurements, have been used to study the recrystallization during various heat treatments of a Bi1.5SrCaCu2O(z) glass obtained by rapid quenching from the melt. Heating at 450 C formed the Bi(2+x)Sr(2-x)-CuO(z) solid solution designated 'R'. Between 765 and 845 C, R reacts slowly with the glass to form the 80 K superconductor Bi2(Sr,Ca)3Cu2O(z), together with CuO. Heating for 7 days at the higher temperature, followed by slow cooling, raised the temperature of zero resistance to 77 K.

  11. Preparation of Bi-Sr-Ca-Cu-O superconductors from oxide-glass precursors

    DOEpatents

    Hinks, David G.; Capone, II, Donald W.

    1992-01-01

    A superconductor and precursor therefor from oxide mixtures of Ca, Sr, Bi and Cu. Glass precursors quenched to elevated temperatures result in glass free of crystalline precipitates having enhanced mechanical properties. Superconductors are formed from the glass precursors by heating in the presence of oxygen to a temperature below the melting point of the glass.

  12. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr.

    PubMed

    Li, H F; Xie, X H; Zheng, Y F; Cong, Y; Zhou, F Y; Qiu, K J; Wang, X; Chen, S H; Huang, L; Tian, L; Qin, L

    2015-01-01

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

  13. Development of biodegradable Zn-1X binary alloys with nutrient alloying elements Mg, Ca and Sr

    PubMed Central

    Li, H. F.; Xie, X. H.; Zheng, Y. F.; Cong, Y.; Zhou, F. Y.; Qiu, K. J.; Wang, X.; Chen, S. H.; Huang, L.; Tian, L.; Qin, L.

    2015-01-01

    Biodegradable metals have attracted considerable attentions in recent years. Besides the early launched biodegradable Mg and Fe metals, Zn, an essential element with osteogenic potential of human body, is regarded and studied as a new kind of potential biodegradable metal quite recently. Unfortunately, pure Zn is soft, brittle and has low mechanical strength in the practice, which needs further improvement in order to meet the clinical requirements. On the other hand, the widely used industrial Zn-based alloys usually contain biotoxic elements (for instance, ZA series contain toxic Al elements up to 40 wt.%), which subsequently bring up biosafety concerns. In the present work, novel Zn-1X binary alloys, with the addition of nutrition elements Mg, Ca and Sr were designed (cast, rolled and extruded Zn-1Mg, Zn-1Ca and Zn-1Sr). Their microstructure and mechanical property, degradation and in vitro and in vivo biocompatibility were studied systematically. The results demonstrated that the Zn-1X (Mg, Ca and Sr) alloys have profoundly modified the mechanical properties and biocompatibility of pure Zn. Zn-1X (Mg, Ca and Sr) alloys showed great potential for use in a new generation of biodegradable implants, opening up a new avenue in the area of biodegradable metals. PMID:26023878

  14. Microstructure and properties of Bi-Sr-Ca-Cu-O with nanometer-scale alumina additions.

    SciTech Connect

    Goretta, K. C.

    1998-09-11

    Al{sub 2}O{sub 3} particles {approx}30 nm is size were added to Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} in a 1:4 molar ratio. For comparison, 0.3 and {approx}3 pm Al{sub 2}O{sub 3} particles were added to separate batches. All materials were partial-melt processed. The Al{sub 2}O{sub 3} reacted during melting to primarily form stable compounds of approximate composition (Sr,Ca){sub 2}AlO{sub 4}. All additions caused slight decreases in the T{sub c} and melting point of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}. The submicrometer Al{sub 2}O{sub 3} additions induced large expansions in magnetic-hysteresis width at 6 K. Electron microscopy examinations strongly suggested that the hysteresis expansion was related to alloying of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} matrix rather than to pinning by volume defects.

  15. Tracing thermal aquifers of El Chichón volcano-hydrothermal system (México) with 87Sr/ 86Sr, Ca/Sr and REE

    NASA Astrophysics Data System (ADS)

    Peiffer, L.; Taran, Y. A.; Lounejeva, E.; Solís-Pichardo, G.; Rouwet, D.; Bernard-Romero, R. A.

    2011-08-01

    The volcano-hydrothermal system of El Chichón volcano, Chiapas, Mexico, is characterized by numerous thermal manifestations including an acid lake, steam vents and boiling springs in the crater and acid and neutral hot springs and steaming ground on the flanks. Previous research on major element chemistry reveals that thermal waters of El Chichón can be divided in two groups: (1) neutral waters discharging in the crater and southern slopes of the volcano with chloride content ranging from 1500 to 2200 mg/l and (2) acid-to-neutral waters with Cl up to 12,000 mg/l discharging at the western slopes. Our work supports the concept that each group of waters is derived from a separate aquifer (Aq. 1 and Aq. 2). In this study we apply Sr isotopes, Ca/Sr ratios and REE abundances along with the major and trace element water chemistry in order to discriminate and characterize these two aquifers. Waters derived from Aq. 1 are characterized by 87Sr/ 86Sr ratios ranging from 0.70407 to 0.70419, while Sr concentrations range from 0.1 to 4 mg/l and Ca/Sr weight ratios from 90 to 180, close to average values for the erupted rocks. Waters derived from Aq. 2 have 87Sr/ 86Sr between 0.70531 and 0.70542, high Sr concentrations up to 80 mg/l, and Ca/Sr ratio of 17-28. Aquifer 1 is most probably shallow, composed of volcanic rocks and situated beneath the crater, within the volcano edifice. Aquifer 2 may be situated at greater depth in sedimentary rocks and by some way connected to the regional oil-gas field brines. The relative water output (l/s) from both aquifers can be estimated as Aq. 1/Aq. 2-30. Both aquifers are not distinguishable by their REE patterns. The total concentration of REE, however, strongly depends on the acidity. All neutral waters including high-salinity waters from Aq. 2 have very low total REE concentrations (< 0.6 μg/l) and are characterized by a depletion in LREE relative to El Chichón volcanic rock, while acid waters from the crater lake (Aq. 1) and acid

  16. The comparative kinetics of Ca, Sr, And Ra in a freshwater turtle, Trachemys scripta

    SciTech Connect

    Hinton, T.G.

    1989-01-01

    The accumulation of {sup 45}Ca, {sup 47}Ca, {sup 88}Sr, and {sup 226}Ra was studied in the yellow-bellied slider, a common freshwater turtle of the Southeastern US. The author was particularly interested in testing the hypothesis of competitive inhibition, a concept whereby decreasing the intake of a stable dietary element increases the absorption and retention of chemically similar radionuclides. He established four specific hypotheses and examined the processes of absorption and elimination as a function of stable dietary calcium (2 and 20 mg g{sup {minus}1}), season (summer, fall, winter and spring), and age and sex of the animals (hatchlings, juveniles, adult males, adult females, and gravid females). Turtles were gavaged with radionuclides and the gamma-emitting isotopes were detected during serial whole-body counts performed on the live animals for up to 480 d. The analysis of the beta-emitting {sup 45}Ca was accomplished by chemical separation procedures. Data were fit to a two-component exponential retention model by nonlinear regression. The 10-fold reduction in dietary Ca did not affect the elimination rate constants, and increased the assimilation of Sr and Ra only within juveniles. For all animals the absorption of Ca was significantly greater than Sr, and likewise, Sr was greater than Ra. Mean absorptions were generally higher than values reported for other organisms. Unlike many other organisms, absorption rates did not decline at maturity. He suspects that high Ca demands in constructing and maintaining the massive shell, necessitated by the turtle's survival strategy, may contribute to the high absorption, as well as the lack of a decline at maturity. Elimination rate constants were greatest in the summer and declined to levels that were generally not distinguishable from zero in the spring, winter, and fall seasons.

  17. Synthesis, structural and vibrational properties of Bi{sub 0.8}La{sub 0.15}A{sub 0.05}FeO{sub 3} (A = Ca, Sr)

    SciTech Connect

    Sharma, Poorva E-mail: poorva.aks@gmail.com; Kumar, Ashwini; Varshney, Dinesh E-mail: poorva.aks@gmail.com

    2015-06-24

    The polycrystalline Bi{sub 0.8}La{sub 0.15}A{sub 0.05}FeO{sub 3} (A = Ca, Sr) was synthesized by solid state reaction route to study the structural and vibrational properties. X-ray diffraction patterns confirmed the formation of single-phase perovskite structure. Rietveld–refined crystal structure parameters revealed the existence of rhombohedral R3c symmetry in the prepared sample. The blue shift of phonon modes is attributed to lower atomic mass of La{sup 3+} and A = (Ca, Sr) substitution at Bi site in BiFeO{sub 3}.

  18. Catalytic partial oxidation of n-tetradecane using Rh and Sr substituted pyrochlores: Effects of sulfur

    SciTech Connect

    Haynes, D.; Berry, D.; Shekhawat, D. Spivey, J.

    2009-01-01

    The presence of high levels of organosulfur compounds hinders the catalytic partial oxidation (CPOX) of logistic fuels into a H2-rich gas stream for fuel cells. These species poison traditional supported metal catalysts because the sulfur adsorbs strongly to electron dense metal clusters and promotes the formation of carbon on the surface. To minimize deactivation by sulfur, two substituted lanthanum zirconate (LZ) pyrochlores (La2Zr2O7), identified in a previous study [D.J. Haynes, D.A. Berry, D. Shekhawat, J.J. Spivey, Catal. Today 136 (2008) 206], were investigated: (a) La–Rh–Zr (LRZ) and La–Sr– Rh–Zr (LSRZ). Using unsubstituted lanthanum zirconate and a conventional 0.5 wt% Rh/g-Al2O3 as comparisons, these four catalysts were exposed to a feed containing 1000 ppmw dibenzothiophene (DBT) in n-tetradecane (TD). DBT rapidly deactivated both the 0.5 wt% Rh/g-Al2O3 and LZ. The LRZ catalyst experienced a gradual deactivation, suggesting that Rh substitution into the pyrochlore structure, by itself, cannot completely eliminate deactivation by sulfur. However, the additional substitution of Sr stabilized yields of H2 and CO in the presence of DBT at levels only slightly below those observed without sulfur in the feed. After sulfur was removed from the feed, each catalyst was able to recover some activity. The recovery appears to be linked to carbon formed on active sites. The 0.5 wt% Rh/g-Al2O3, LZ, and LRZ all had comparable amounts of carbon formed on the surface: 0.90, 0.80 and 0.86 gcarbon/gcat, respectively. Of these three catalysts, only the LRZ was able to recover a significant portion of initial activity, suggesting that the carbon formed indiscriminately on the surface, and not solely on the active sites. LSRZ was able to regain almost its initial activity once sulfur was removed from the feed, and had the least amount of carbon on the surface (0.30 gcarbon/gcat). It is hypothesized that oxygen-ion mobility, which results from Sr substitution

  19. Magnetic properties of Fe substituted SrRuO3 thin films and SrRuO3/Fe2O3 superlattices

    NASA Astrophysics Data System (ADS)

    Chmaissem, Omar; Kolesnik, Stanislaw; Dabrowski, Bogdan; Choi, Yongseong; Haskel, Daniel

    2010-03-01

    In recent years, SrRuO3 thin films have received considerable interest because of their potential for use as electrodes in oxide-based spintronic applications. SrRuO3 bulk materials are known to exhibit good room temperature thermal and electrical conductivity, a stable perovskite crystal structure, and itinerant ferromagnetic properties at temperatures below 163 K. To the best of our knowledge, attempts to enhance the magnetic properties of SrRuO3 through chemical substitutions of transition metal elements (e.g., Fe, Co, Mn, Cu, Zn, Ti, Cr, etc) at the Ru site, all failed except for the case of Cr substitutions in which TC was successfully raised to 190 K. In this work, we will demonstrate the drastically different effects of Fe on the magnetic properties of SrRuO3 bulk materials and thin films. We will also show and discuss the magnetic properties of SrRuO3/Fe2O3 superlattices. Work supported by the NSF (DMR-0706610) and the DOE-Office of Science (DEAC-02-06CH11357).

  20. Regulation of plant immunity through ubiquitin-mediated modulation of Ca(2+) -calmodulin-AtSR1/CAMTA3 signaling.

    PubMed

    Zhang, Lei; Du, Liqun; Shen, Chenjia; Yang, Yanjun; Poovaiah, B W

    2014-04-01

    Transient changes in intracellular Ca(2+) concentration are essential signals for activation of plant immunity. It has also been reported that Ca(2+) signals suppress salicylic acid-mediated plant defense through AtSR1/CAMTA3, a member of the Ca(2+) /calmodulin-regulated transcription factor family that is conserved in multicellular eukaryotes. How plants overcome this negative regulation to mount an effective defense response during a stage of intracellular Ca(2+) surge is unclear. Here we report the identification and functional characterization of an important component of ubiquitin ligase, and the associated AtSR1 turnover. The AtSR1 interaction protein 1 (SR1IP1) was identified by CytoTrap two-hybrid screening. The loss-of-function mutant of SR1IP1 is more susceptible to bacterial pathogens, and over-expression of SR1IP1 confers enhanced resistance, indicating that SR1IP1 acts as a positive regulator of plant defense. SR1IP1 and AtSR1 act in the same signaling pathway to regulate plant immunity. SR1IP1 contains the structural features of a substrate adaptor in cullin 3-based E3 ubiquitin ligase, and was shown to serve as a substrate adaptor that recruits AtSR1 for ubiquitination and degradation when plants are challenged with pathogens. Hence, SR1IP1 positively regulates plant immunity by removing the defense suppressor AtSR1. These findings provide a mechanistic insight into how Ca(2+) -mediated actions are coordinated to achieve effective plant immunity. PMID:24528504

  1. Confounding effects of coral growth and high SST variability on skeletal Sr/Ca: Implications for coral paleothermometry

    NASA Astrophysics Data System (ADS)

    Grove, Craig A.; Kasper, Sebastian; Zinke, Jens; Pfeiffer, Miriam; Garbe-SchöNberg, Dieter; Brummer, Geert-Jan A.

    2013-04-01

    Massive corals offer continuous records of climate locked within their skeleton, with the most commonly applied paleo-thermometer being Sr/Ca. Recently, however, problems with Sr/Ca thermometry indicate that the intrinsic variance of single-core Sr/Ca time series differs between cores. Here, we compare the Sr/Ca records and growth parameters of two Porites lutea colonies sampled from the same reef zone, 0.72 km apart, with two gridded SST datasets, ERSST and HadISST, off NE Madagascar. Specifically, we address seasonal and interannual variability as well as trend differences between records over the same 43 year period. The two gridded SST datasets showed strong seasonality and weak positive ENSO anomalies on a slow 43 year warming trend at significantly different rates. Both the coral Sr/Ca records showed the same clear seasonality and similar amplitudes in SST. However, on interannual timescales, they displayed diverging 43 year Sr/Ca trends and opposite responses to weak ENSO anomalies. Moreover, their growth response also differed as one coral showed increasing extension/calcification rates and Sr/Ca ratios (cooling) over the 43 years, while the other coral showed decreasing extension/calcification rates and Sr/Ca ratios (warming). Further, during positive ENSO events, the calcification rates of the two corals were negatively correlated, while skeletal density anomalies were opposite. Possible explanations to why these corals are so different may be related to the corals growth response to SST changes. The growth response of individual corals to increasing SST seems to be opposite, which in turn are likely related to biological factors. Consequently, coral growth responses explain much of the inter-colony Sr/Ca variability.

  2. Two-dimensional incommensurately modulated structure of (Sr0.13Ca0. 87)2CoSi2O7 crystals.

    PubMed

    Bagautdinov, B; Hagiya, K; Kusaka, K; Ohmasa, M; Iishi, K

    2000-10-01

    The incommensurate structure of (Sr(0.13)Ca(0.87))(2)CoSi(2)O(7) at room temperature has been determined from single-crystal X-ray diffraction data. The compound has a non-centrosymmetric tetragonal basic cell of a = 7.8743 (4) and c = 5.0417 (2) A with the space group P4;2(1)m. The refinements of the basic structure converged to R = 0.038 for 757 main reflections. The two-dimensional incommensurate structure is characterized by the wavevectors q(1) = 0.286 (3)(a* + b*) and q(2) = 0.286 (3)(-a* + b*), where a*, b* are the reciprocal lattice vectors of the basic structure. With the (3 + 2)-dimensional superspace group P(p4mg)(P4;2(1)(m)), the refinements converged to R = 0.071 for 1697 observed reflections (757 main and 940 satellite reflections). The structure is described in terms of displacement of the atoms, rotation, distortion of CoO(4) and SiO(4) tetrahedra, and the partial ordering of the Sr and Ca atoms accompanied with the modulation. Correlated evolution of these features throughout the crystal gives rise to various oxygen coordination around Ca/Sr. Comparison of the derived modulated structure to that of Ca(2)CoSi(2)O(7) clarified that the partial substitution of Ca by large alkaline-earth atoms such as Sr should decrease the distortion of the polyhedra around the cations. PMID:11006557

  3. Optical and microwave detection using Bi-Sr-Ca-Cu-O thin films

    NASA Technical Reports Server (NTRS)

    Grabow, B. E.; Sova, R. M.; Boone, B. G.; Moorjani, K.; Kim, B. F.; Bohandy, J.; Adrian, F.; Green, W. J.

    1990-01-01

    Recent progress at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in the development of optical and microwave detectors using high temperature superconducting thin films is described. Several objectives of this work have been accomplished, including: deposition of Bi-Sr-Ca-Cu-O thin films by laser abation processing (LAP); development of thin film patterning techniques, including in situ masking, wet chemical etching and laser patterning; measurements of bolometric and non-bolometric signatures in patterned Bi-Sr-Ca-Cu-O films using optical and microwave sources, respectively; analysis and design of an optimized bolometer through computer simulation, and investigation of its use in a Fourier transform spectrometer. The focus here is primarily on results from the measurement of the bolometric and non-bolometric response.

  4. Optical and microwave detection using Bi-Sr-Ca-Cu-O thin films

    NASA Technical Reports Server (NTRS)

    Grabow, B. E.; Sova, R. M.; Boone, B. G.; Moorjani, K.; Kim, B. F.; Bohandy, J.; Adrian, F.; Green, W. J.

    1991-01-01

    Recent progress at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) in the development of optical and microwave detectors using high temperature superconducting thin films is described. Several objectives of this work have been accomplished, including: deposition of Bi-Sr-Ca-Cu-O thin films by laser abation processing (LAP); development of thin film patterning techniques, including in situ masking, wet chemical etching, and laser patterning; measurements of bolometric and non-bolometric signatures in patterned Bi-Sr-Ca-Cu-O films using optical and microwave sources, respectively; analysis and design of an optimized bolometer through computer simulation; and investigation of its use in a Fourier transform spectrometer. The focus here is primarily on results from the measurement of the bolometric and non-bolometric response.

  5. Antiferromagnetic Metallic State And Spin Valve Effect in Doped (Ca1-x Ax)3Ru2O7 (A = Sr, Ba) Single Crystals

    NASA Astrophysics Data System (ADS)

    Chikara, S.; Korneta, O. B.; Qi, T. F.; Parkin, S.; Cao, G.; Song, W. P.; Crummett, W. P.

    2009-03-01

    Bilayered Ca3Ru2O7 is a highly anisotropic system [1] characterized by orbitally-driven colossal magnetoresistance^2 and an unusual antiferromagnetic metallic (AFM-M) state [2]. We report transport and thermodynamic properties of (Ca1-x Ax)3Ru2O7 (A = Sr, Ba) single crystals as a function of temperature and applied magnetic field. While Ba doping shows a far stronger impact, both Sr and Ba substitution for Ca induce a large array of interesting phenomena. Among them, a bulk spin-valve effect occurs in the AFM-M range, which is largely broadened due to the doping. This effect in bulk crystals is a novel phenomenon first observed in Ca3(Ru1-xCrx)2O7 single crystals [3]. The spin-valve effect in (Ca1-xAx)3Ru2O7 single crystals opens new avenues to understand the underlying physics and realize the potential of spin valves in practical devices.[0pt] [1] G. Cao et al., PRL 78, 1751 (1997)[0pt] [2] X. N. Lin et al., PRL 95, 017203 (2005)[0pt] [3] G. Cao et al., PRL 100, 016604 (2008)

  6. Kinetics on Demand Is a Simple Mathematical Solution that Fits Recorded Caffeine-Induced Luminal SR Ca2+ Changes in Smooth Muscle Cells

    PubMed Central

    Perez-Rosas, Norma C.; Gomez-Viquez, Norma L.; Dagnino-Acosta, Adan; Santillan, Moises; Guerrero-Hernandez, Agustín

    2015-01-01

    The process of Ca2+ release from sarcoplasmic reticulum (SR) comprises 4 phases in smooth muscle cells. Phase 1 is characterized by a large increase of the intracellular Ca2+ concentration ([Ca2+]i) with a minimal reduction of the free luminal SR [Ca2+] ([Ca2+]FSR). Importantly, active SR Ca2+ ATPases (SERCA pumps) are necessary for phase 1 to occur. This situation cannot be explained by the standard kinetics that involves a fixed amount of luminal Ca2+ binding sites. A new mathematical model was developed that assumes an increasing SR Ca2+ buffering capacity in response to an increase of the luminal SR [Ca2+] that is called Kinetics-on-Demand (KonD) model. This approach can explain both phase 1 and the refractory period associated with a recovered [Ca2+]FSR. Additionally, our data suggest that active SERCA pumps are a requisite for KonD to be functional; otherwise luminal SR Ca2+ binding proteins switch to standard kinetics. The importance of KonD Ca2+ binding properties is twofold: a more efficient Ca2+ release process and that [Ca2+]FSR and Ca2+-bound to SR proteins ([Ca2+]BSR) can be regulated separately allowing for Ca2+ release to occur (provided by Ca2+-bound to luminal Ca2+ binding proteins) without an initial reduction of the [Ca2+]FSR. PMID:26390403

  7. Effect of doping in the Bi-Sr-Ca-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Akbar, S. A.; Wong, M. S.; Botelho, M. J.; Sung, Y. M.; Alauddin, M.; Drummer, C. E.; Fair, M. J.

    1991-01-01

    The results of the effect of doping on the superconducting transition in the Bi-Sr-Ca-Cu-O system are reported. Samples were prepared under identical conditions with varying types (Pb, Sb, Sn, Nb) and amounts of dopants. All samples consisted of multiple phases, and showed stable and reproducible superconducting transitions. Stabilization of the well known 110 K phase depends on both the type and amount of dopant. No trace of superconducting phase of 150 K and above was observed.

  8. Influence of chemical substitution on the photoluminescence of Sr(1-x)PbxWO4 solid solution

    NASA Astrophysics Data System (ADS)

    Hallaoui, A.; Taoufyq, A.; Arab, M.; Bakiz, B.; Benlhachemi, A.; Bazzi, L.; Villain, S.; Valmalette, J.-C.; Guinneton, F.; Gavarri, J.-R.

    2015-07-01

    The solid solution Sr1-xPbxWO4 based on luminescent tungstates SrWO4 and PbWO4 has been synthesized by solid-state reaction for all compositions 0≤x≤1. Using Rietveld method, the structural data of all polycrystalline samples have been refined and crystal cell parameters exhibited a linear behavior as a function of x. All substituted structures are of scheelite type. Scanning electron microscopy showed that a high level of crystallization characterized the samples, with modifications in sizes and shapes depending on composition x. Infrared and Raman spectroscopy have been performed to characterize the evolution of vibrational modes with substitution rate. Finally, a systematic study of luminescence under X-ray excitation has been performed: in the composition range x=0.2 to 0.4, intensities of emission exhibited increased values. The luminescence profiles have been interpreted in terms of four Gaussian components, two of them depending on substitution rate.

  9. Ca, Sr and Ba stable isotopes reveal the fate of soil nutrients along a tropical climosequence

    USGS Publications Warehouse

    Bullen, Thomas D.; Chadwick, Oliver A.

    2016-01-01

    Nutrient biolifting is an important pedogenic process in which plant roots obtain inorganic nutrients such as phosphorus (P) and calcium (Ca) from minerals at depth and concentrate those nutrients at the surface. Here we use soil chemistry and stable isotopes of the alkaline earth elements Ca, strontium (Sr) and barium (Ba) to test the hypothesis that biolifting of P has been an important pedogenic process across a soil climosequence developed on volcanic deposits at Kohala Mountain, Hawaii. The geochemical linkage between these elements is revealed as generally positive site-specific relationships in soil mass gains and losses, particularly for P, Ba and Ca, using the ratio of immobile elements titanium and niobium (Ti/Nb) to link individual soil samples to a restricted compositional range of the chemically and isotopically diverse volcanic parent materials. At sites where P is enriched in surface soils relative to abundances in deeper soils, the isotope compositions of exchangeable Ca, Sr and Ba in the shallowest soil horizons (< 10 cm depth) are lighter than those of the volcanic parent materials and trend toward those of plants growing on fresh volcanic deposits. In contrast the isotope composition of exchangeable Ba in deeper soil horizons (> 10 cm depth) at those sites is consistently heavier than the volcanic parent materials. The isotope compositions of exchangeable Ca and Sr trend toward heavier compositions with depth more gradually, reflecting increasing leakiness from these soils in the order Ba < Sr < Ca and downward transfer of light biocycled Ca and Sr to deeper exchange sites. Given the long-term stability of ecosystem properties at the sites where P is enriched in surface soils, a simple box model demonstrates that persistence of isotopically light exchangeable Ca, Sr and Ba in the shallowest soil horizons requires that the uptake flux to plants from those near-surface layers is less than the recycling flux returned to the surface as

  10. Structural and magnetic properties of La–Co substituted Sr–Ca hexaferrites synthesized by the solid state reaction method

    SciTech Connect

    Yang, Yujie; Liu, Xiansong Jin, Dali; Ma, Yuqi

    2014-11-15

    Graphical abstract: The change of the remanence (B{sub r}) and intrinsic coercivity (H{sub cj}) with La content (x) and Co content (y) of hexagonal ferrite Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} magnets. - Highlights: • Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} hexaferrites were synthesized by the solid state reaction method. • B{sub r} continuously increases with increasing dopant contents. • H{sub cb}, H{sub cj} and (BH){sub max} for the magnets first increases and then decreases with an increase in the La–Co contents. - Abstract: Hexagonal ferrite Sr{sub 0.7−x}Ca{sub 0.3}La{sub x}Fe{sub 12−y}Co{sub y}O{sub 19} (x = 0.05–0.50; y = 0.04–0.40) magnetic powders and magnets were synthesized by the solid state reaction method. X-ray diffraction was employed to determine the phase compositions of the magnetic powders. There is a single magnetoplumbite phase in the magnetic powders with the substitution of La (0.05 ≤ x ≤ 0.15) and Co (0.04 ≤ y ≤ 0.12) contents. For the magnetic powders containing La (x ≥ 0.20) and Co (y ≥ 0.16), magnetic impurities begin to appear in the structure. A field emission scanning electron microscope was used to characterize the micrographs of the magnets. The magnets have formed hexagonal structures. Magnetic properties of the magnets were measured by a magnetic properties test instrument. The remanence continuously increases with increasing dopant contents. Whereas, the magnetic induction coercivity, intrinsic coercivity and maximum energy product for the magnets first increases and then decreases with an increase in the La–Co contents.

  11. Formation of infinite-layered (Ca{sub 1{minus}x}Sr{sub x})CuO{sub 2} and NaCuO{sub 2}-type (Ca{sub 1{minus}y}Na{sub y}){sub 0.85}CuO{sub 2} in tartrate route

    SciTech Connect

    Kikkawa, Shinichi; Kato, Namie; Taya, Noriko; Tada, Masakazu; Kanamuru, Fumikazu

    1995-05-01

    Both NaCuO{sub 2}-type Ca{sub 0.85}CuO{sub 2} and infinite-layered (Ca{sub 1{minus}x}Sr{sub x})CuO{sub 2} could be prepared much more easily by firing the dried solids from mixed acetate aqueous solutions titrated with tartaric acid than by normal calcination. The presence of a narrow solid-solution composition range of 0.10 < x < 0.16 was confirmed in infinite-layered (Ca{sub 1{minus}x}Sr{sub x})CuO{sub 2} in the presentation using the tartrate route. The calcium could also be substituted by sodium in a range of y < 0.15 in NaCuO{sub 2}-type (Ca{sub 1{minus}y}Na{sub y}) {sub 0.85} CuO{sub 2} using the same route. Further substitution of Ca{sup 2+} with Y{sup 3+} might also be possible in infinite-layered (Ca{sub 1{minus}x}Sr{sub x})CuO{sub 2}, but resulted in the NaCuO{sub 2}-type compound in the substitution with Na{sup +}.

  12. 110K Bi-Sr-Ca-Cu-O superconductor oxide and method for making same

    DOEpatents

    Veal, B.W.; Downey, J.W.; Lam, D.J.; Paulikas, A.P.

    1992-12-22

    A superconductor is disclosed consisting of a sufficiently pure phase of the oxides of Bi, Sr, Ca, and Cu to exhibit a resistive zero near 110K resulting from the process of forming a mixture of Bi[sub 2]O[sub 3], SrCO[sub 3], CaCO[sub 3] and CuO into a particulate compact wherein the atom ratios are Bi[sub 2], Sr[sub 1.2-2.2], Ca[sub 1.8-2.4], Cu[sub 3]. Thereafter, heating the particulate compact rapidly in the presence of oxygen to an elevated temperature near the melting point of the oxides to form a sintered compact, and then maintaining the sintered compact at the elevated temperature for a prolonged period of time. The sintered compact is cooled and reground. Thereafter, the reground particulate material is compacted and heated in the presence of oxygen to an elevated temperature near the melting point of the oxide and maintained at the elevated temperature for a time sufficient to provide a sufficiently pure phase to exhibit a resistive zero near 110K. 7 figs.

  13. 110K Bi-Sr-Ca-Cu-O superconductor oxide and method for making same

    DOEpatents

    Veal, Boyd W.; Downey, John W.; Lam, Daniel J.; Paulikas, Arvydas P.

    1992-01-01

    A superconductor consisting of a sufficiently pure phase of the oxides of Bi, Sr, Ca, and Cu to exhibit a resistive zero near 110K resulting from the process of forming a mixture of Bi.sub.2 O.sub.3, SrCO.sub.3, CaCO.sub.3 and CuO into aparticulate compact wherein the atom ratios are Bi.sub.2, Sr.sub.1.2-2.2, Ca.sub.1.8-2.4, Cu.sub.3. Thereafter, heating the particulate compact rapidly in the presence of oxygen to an elevated temperature near the melting point of the oxides to form a sintered compact, and then maintaining the sintered compact at the elevated temperature for a prolonged period of time. The sintered compact is cooled and reground. Thereafter, the reground particulate material is compacted and heated in the presence of oxygen to an elevated temperature near the melting point of the oxide and maintained at the elevated temperature for a time sufficient to provide a sufficiently pure phase to exhibit a resistive zero near 110K.

  14. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn

    NASA Astrophysics Data System (ADS)

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-02-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis.

  15. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn.

    PubMed

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-01-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis. PMID:26907515

  16. Preliminary results of Sr:Ca ratios of Coilia nasus in otoliths by micro-PIXE

    NASA Astrophysics Data System (ADS)

    Zhong, L.; Guo, H.; Shen, H.; Li, X.; Tang, W.; Liu, J.; Jin, J.; Mi, Y.

    2007-07-01

    Coilia nasus, distributed in Changjiang River as well as northwest Pacific, has a high economic value owing to its delicacy and nutritional value. Recently, the fishing yields in Changjiang River have decreased dramatically due to excessive fishing and changes in the aquatic ecology. In order to prevent excessive fishing effectively, the life history pattern of C. nasus should be known in detail. Ootoliths contain much information about a fish's life history, because elemental concentrations remain unaltered after deposition, and can be analysed. C. nasus collected from Jing Jiang (lower reaches of the Changjiang River) and Jiu Duan Sha (the estuary of the Changjiang River) were studied by measuring Sr:Ca ratios in their otoliths using micro-PIXE. On average, the Sr:Ca ratios of estuarine C. nasus were found to be higher. The Sr:Ca ratios were higher in the core regions and lower in the outermost marginal regions, and shows fluctuations in certain regions. Possible corresponding life history patterns are discussed.

  17. Unique antitumor property of the Mg-Ca-Sr alloys with addition of Zn

    PubMed Central

    Wu, Yuanhao; He, Guanping; Zhang, Yu; Liu, Yang; Li, Mei; Wang, Xiaolan; Li, Nan; Li, Kang; Zheng, Guan; Zheng, Yufeng; Yin, Qingshui

    2016-01-01

    In clinical practice, tumor recurrence and metastasis after orthopedic prosthesis implantation is an intensely troublesome matter. Therefore, to develop implant materials with antitumor property is extremely necessary and meaningful. Magnesium (Mg) alloys possess superb biocompatibility, mechanical property and biodegradability in orthopedic applications. However, whether they possess antitumor property had seldom been reported. In recent years, it showed that zinc (Zn) not only promote the osteogenic activity but also exhibit good antitumor property. In our present study, Zn was selected as an alloying element for the Mg-1Ca-0.5Sr alloy to develop a multifunctional material with antitumor property. We investigated the influence of the Mg-1Ca-0.5Sr-xZn (x = 0, 2, 4, 6 wt%) alloys extracts on the proliferation rate, cell apoptosis, migration and invasion of the U2OS cell line. Our results show that Zn containing Mg alloys extracts inhibit the cell proliferation by alteration the cell cycle and inducing cell apoptosis via the activation of the mitochondria pathway. The cell migration and invasion property were also suppressed by the activation of MAPK (mitogen-activated protein kinase) pathway. Our work suggests that the Mg-1Ca-0.5Sr-6Zn alloy is expected to be a promising orthopedic implant in osteosarcoma limb-salvage surgery for avoiding tumor recurrence and metastasis. PMID:26907515

  18. The interaction of Ag with Bi-Pb-Sr-Ca-Cu-O superconductor

    NASA Astrophysics Data System (ADS)

    Dou, S. X.; Song, K. H.; Liu, H. K.; Sorrell, C. C.; Apperley, M. H.; Gouch, A. J.; Savvides, N.; Hensley, D. W.

    1989-10-01

    Bi-Pb-Sr-Ca-Cu-O superconductor compounds have been doped with up to 30 wt% Ag, sintered under variable oxygen partial pressure, and characterised in terms of the electrical and crystallographic behaviour. In contrast to previous reports that claim that Ag is the only metal non-poisoning to the superconductivity of Bi-Sr-Ca-Cu-O (BSCCO), it has been found that Ag additions to Bi-Pb-Sr-Ca-Cu-O depress Tc and Jc drastically and cause a large decrease in lattice parameters when samples are treated in air or pure oxygen. However, the lattice parameters, Tc and Jc remain unaffected by Ag additions when samples are heat treated in 0.030-0.067 atm oxygen. It is clear that the Ag reacts with and destabilises the superconducting phase when the samples are treated in air or pure oxygen while, when the samples are heat treated in low oxygen partial pressures, the Ag remains as an isolated inert metal phase that improves the weak links between the grains. This discovery clearly shows the feasibility of Ag-clad superconductor wire. For Ag-clad superconductor tape of 0.1 mm 2 cross sectional area heat treated in air, Jc was measured to be 54 A/cm 2. The same specimen sintered in 0.067 atm oxygen showed that the Jc increased to 2078 A/cm 2.

  19. Europium substitution into intermetallic phases grown in Ca/Zn flux

    SciTech Connect

    Stojanovic, Milorad; Latturner, Susan E.

    2009-08-15

    Replacement of calcium with europium in the phases Ca{sub 21}Ni{sub 2}Zn{sub 36} and CaNi{sub 2}Zn{sub 3} was attempted to explore the possibility of substitution in metal flux reactions and potential magnetic interactions between closely spaced Eu{sup 2+} ions. Limited substitution occurs when Eu is added to the reaction of nickel in a Ca/Zn flux mixture, up to stoichiometries of Eu{sub 5.8(3)}Ca{sub 15.2(3)}Ni{sub 2}Zn{sub 36} and Eu{sub 0.42(8)}Ca{sub 0.58(8)}Ni{sub 2}Zn{sub 3}. Structural characterization and magnetic susceptibility studies on Eu{sub x}Ca{sub 21-x}Ni{sub 2}Zn{sub 36} phases indicate that the Eu and Ca ions do not form an even solid solution on their sites, but instead segregate in separate regions of the crystals. The europium-rich regions of the samples order ferromagnetically, with T{sub C} dependent on the size of the clusters. If the concentration of Eu in the flux is raised above 20 mol%, a new compound Eu{sub 1.63(1)}Ca{sub 1.37(1)}Ni{sub 2}Zn{sub 3} (Cmcm, a=4.1150(5) A, b=16.948(2) A, c=10.302(1) A, Z=4, R{sub 1}=0.0396) is produced. - Graphical abstract: Exploration of europium substitution into intermetallic compounds grown in Ca/Zn flux has yielded analogs of Eu{sub x}Ca{sub 21-x}Ni{sub 2}Zn{sub 36} with unusual magnetic properties due to segregation of europium in the crystals; high concentrations of Eu in the flux trigger the growth of Eu{sub 1.63(1)}Ca{sub 1.37(1)}Ni{sub 2}Zn{sub 3} with a new structure type.

  20. Seasonal dripwater Mg/Ca and Sr/Ca variations driven by cave ventilation: Implications for and modeling of speleothem paleoclimate records

    NASA Astrophysics Data System (ADS)

    Wong, Corinne I.; Banner, Jay L.; Musgrove, MaryLynn

    2011-06-01

    A 4-year study in a central Texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites. We monitored cave-air compositions, in situ calcite growth, dripwater composition and drip rate every 4-6 weeks. Three groups of drip sites are delineated (Groups 1-3) based on geochemical variations in dripwater composition. Quantitative modeling of mineral-solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions. The covariation of Mg/Ca (and Sr/Ca) and Sr isotopes is key in delineating whether Mg/Ca and Sr/Ca variations are dictated by water-rock interaction (i.e., calcite or dolomite recrystallization) or prior calcite precipitation (PCP). Group 1 dripwater compositions reflects a narrow range of the extent of water-rock interaction followed by varying amounts of prior calcite precipitation (PCP). Group 2 dripwater compositions are controlled by varying amounts of water-rock interaction with little to no PCP influence. Group 3 dripwater compositions are dictated by variable extents of both water-rock interaction and PCP. Group 1 drip sites show seasonal variations in dripwater Mg/Ca and Sr/Ca, whereas the other drip sites do not. In contrast to the findings of most previous dripwater Mg/Ca-Sr/Ca studies, these seasonal variations (at Group 1 drip sites) are independent of changes in water flux (i.e., rainfall and/or drip rate), and instead significantly correlate with changes in cave-air CO 2 concentrations. These results are consistent with lower cave-air CO 2, related to cool season ventilation of the cave atmosphere, enhancing calcite precipitation and leading to dripwater geochemical evolution via PCP. Group 1 dripwater Mg/Ca and Sr/Ca seasonality and evidence for PCP as a mechanism that can account for that seasonality, have two implications for many other regions where seasonal ventilation of

  1. High precision glacial-interglacial benthic foraminiferal Sr/Ca records from the eastern equatorial Atlantic Ocean and Caribbean Sea

    NASA Astrophysics Data System (ADS)

    Shen, Chuan-Chou; Hastings, David W.; Lee, Typhoon; Chiu, Chin-Hsin; Lee, Meng-Yang; Wei, Kuo-Yen; Edwards, R. Lawrence

    2001-08-01

    Glacial-interglacial variation in the marine Sr/Ca ratio has important implications for coral Sr thermometry [J.W. Beck et al., Science 257 (1992) 644-647]. A possible variation of 1-3% was proposed based on ocean models [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 1107-1118]. Subsequently, studies have used fossil foraminifera to test this prediction [P.A. Martin et al., Geochem. Geophys. Geosyst. 1 (1999); H.M. Stoll et al., Geochim. Cosmochim. Acta 63 (1999) 3535-3547; H. Elderfield et al., Geochem. Geophys. Geosyst. 1 (2000)]. But whether some component of foraminiferal Sr/Ca variation can be uniquely ascribed to seawater Sr variation is still not clear. To address this question, we developed cleaning and analysis techniques and measured Sr/Ca ratios on individual shells of the modern benthic foraminifer Cibicidoides wuellerstorfi. We showed that different size shells have different Sr/Ca ratios; however, samples with shell sizes of 355-500 μm appear to have normally distributed Sr/Ca ratios (1σ=1.8%). For multi-shell measurements (with estimated errors of 0.12-0.39%), the ratio varied by as much as 7.2±0.5% during the last glaciation for two Caribbean records at the same site and by 3.7±0.5% over the past 40,000 yr for one record from the Sierra Leone Rise in the eastern equatorial Atlantic. The two Caribbean records are very similar indicating that the behavior of shell Sr uptake was identical locally and that the shell Sr/Ca ratio faithfully reflects the local environment. The Atlantic record differs from the Caribbean records by as much as several percent. Thus, the foraminiferal Sr/Ca changes cannot be solely due to changes in seawater Sr/Ca unless the glacial deep ocean had spatial variation in Sr/Ca well in excess of the modern ocean. Certain similarities between the three records do exist. Notably, the rate of change of Sr/Ca is similar between 9 and 0 ka (-0.25%/kyr) and between 25 and 16 ka (+0.16%/kyr). This suggests that

  2. Growth of Nucleation Sites on Pd-doped Bi_2Sr_2Ca1 Cu_2O_8+δ

    NASA Astrophysics Data System (ADS)

    Kouzoudis, D.; Finnemore, D. K.; Xu, Ming; Balachandran

    1996-03-01

    Enviromental Scanning Electron Microscope has shown evidence that during the growth of Bi_2Sr_2Ca_2Cu_3O_10+δ from mixed powders of Pb-doped Bi_2Sr_2Ca_1Cu_2O_8+δ and other oxides, a dense array of hillocks or mesas grow at the interface between an Ag overlay and Pb doped Bi_2Sr_2Ca_1Cu_2O_8+δ grains. These hillocks develop a texture that looks like ''chicken pox'' during the ramp up to the reaction temperature starting at about 700^circ C and they are about 500 to 1000 nm across and are spaced at about 500 to 1000 nm. If there is no Ag, this texture does not develop. Preliminary measurments indicate that the hillocks are re-crystallization of (Bi,Pb)_2Sr_2Ca_1Cu_2O_8+δ and are definetely not a Pb rich phase

  3. An apparent "vital effect" of calcification rate on the Sr/Ca temperature proxy in the reef coral Montipora capitata

    USGS Publications Warehouse

    Kuffner, Ilsa; Jokiel, Paul L.; Rodgers, Kuulei; Andersson, Andreas; Mackenzie, Fred T.

    2012-01-01

    Measuring the strontium to calcium ratio in coral skeletons reveals information on seawater temperatures during skeletal deposition, but studies have shown additional variables may affect the ratio. Here we measured Sr/Ca in the reef coral, Montipora capitata, grown in six mesocosms continuously supplied with seawater from the adjacent reef flat. Three mesocosms were ambient controls, and three had seawater chemistry simulating "ocean acidification" (OA). We found that Sr/Ca was not affected by the OA treatment, and neither was coral calcification for these small colonies (larger colonies did show an OA effect). The lack of OA effects allowed us to test the hypothesis that coral growth rate can affect Sr/Ca using the natural range in calcification rates of the corals grown at the same temperature. We found that Sr/Ca was inversely related to calcification rate (Sr/Ca = 9.39 - 0.00404 mmol/mol * mg day-1 cm-2, R2 = 0.32). Using a previously published calibration curve for this species, a 22 mg day-1 colony-1 increase in calcification rate introduced a 1°C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9, with mean 26.6 ± 0.9°C SD. Our results lend support to hypotheses invoking kinetic processes and growth rate to explain vital effects on Sr/Ca. However, uncertainty in the slope of the regression of Sr/Ca on calcification and a low R-squared value lead us to conclude that Sr/Ca could still be a useful proxy in this species given sufficient replication or by including growth rate in the calibration.

  4. A first principles study on newly proposed (Ca/Sr/Ba)Fe2Bi2 compounds with their parent compounds

    NASA Astrophysics Data System (ADS)

    Sundareswari, M.; Jayalakshmi, D. S.; Viswanathan, E.

    2016-02-01

    The structural, electronic, bonding and magnetic properties of newly proposed iron-based compounds viz., CaFe2Bi2, SrFe2Bi2, BaFe2Bi2 with their Fermi surface topology are reported here for the first time by means of first principles calculation. All these properties of newly proposed compounds are compared and analysed along with their respective parent compounds namely (Ca,Sr,Ba)Fe2As2.

  5. Relationship between coccolith Sr/Ca ratios and coccolithophore production and export in the Arabian Sea and Sargasso Sea

    NASA Astrophysics Data System (ADS)

    Stoll, Heather M.; Ziveri, Patrizia; Shimizu, Nobumichi; Conte, Maureen; Theroux, Susanna

    2007-03-01

    Coccolithophore CaCO 3 production can account for 20-80% of biogenic carbonate exported from the photic zone, and coccoliths are a dominant biogenic carbonate in many deep-sea sediments. A new method for picking individual coccoliths from sediment traps and sediments for analysis using Secondary Ion Mass Spectrometry (ion probe) allows us to make precise Sr/Ca and Mg/Ca determinations on coccoliths from single species even in samples where material is limited. There are large biological effects in Sr/Ca partitioning in coccoliths that have been related to variations in coccolithophore productivity. In sediment traps from the Sargasso Sea at Bermuda and Arabian Sea in the Somali Basin, we can identify Sr/Ca variations in several species that are consistent with inferred seasonal variations in coccolithophore productivity in surface waters. In the Arabian Sea, coccolith Sr/Ca ratios in Calcidiscus leptoporus and Helicosphaera carteri are lowest during the nonproductive intermonsoon. They are highest during the upwelling of southwest monsoon and during the nutrient entrainment from strong winds of the northeast monsoon. These Sr/Ca variations match seasonal trends in coccolith export flux. Furthermore, Sr/Ca variations in C. leptoporus are larger, and this species also has the greater variation in export flux between southwest monsoon and intermonsoon seasons. At Bermuda, a 1996 fall bloom, driven by passage of a warm mode water eddy, induced a large increase in Sr/Ca of C. leptoporus coincident with an increase of C. leptoporus export. Over an annual series for 2004, highest Sr/Ca ratios of C. leptoporus in the summer months match the typical summer peak in surface standing stock of this species and the stimulation of its productivity by mesoscale cyclonic eddies and eddy-eddy interactions. High Sr/Ca did not coincide with the highest export of C. leptoporus coccoliths, likely because cyclonic eddies, unlike mode-water eddies, are dominated by small phytoplankton

  6. Identifying weathering sources and processes in an outlet glacier of the Greenland Ice Sheet using Ca and Sr isotope ratios

    NASA Astrophysics Data System (ADS)

    Hindshaw, Ruth S.; Rickli, Jörg; Leuthold, Julien; Wadham, Jemma; Bourdon, Bernard

    2014-11-01

    Chemical and isotope data (ε40Ca, δ44/42Ca, 87Sr/86Sr, δ18O) of river water samples were collected twice daily for 28 days in 2009 from the outlet river of Leverett Glacier, West Greenland. The water chemistry data was combined with detailed geochemical analysis and petrography of bulk rock, mineral separates and sediment samples in order to constrain the mineral weathering sources to the river. The average isotopic compositions measured in the river, with 2SD of all the values measured, were ε40Ca = +4.0 ± 1.4, δ44/42Ca = +0.60 ± 0.10‰ and 87Sr/86Sr = 0.74243 ± 0.00327. Based on changes in bulk meltwater discharge, the hydrochemical data was divided into three hydrological periods. The first period was marked by the tail-end of an outburst event and was characterised by water with decreasing suspended sediment concentrations (SSC), ion concentrations and pH. During the second hydrological period, discharge increased whilst 87Sr/86Sr decreased from 0.74550 to 0.74164. Based on binary mixing diagrams using 87Sr/86Sr with Na/Sr, Ca/Sr and ε40Ca, this is interpreted to reflect an increase in reactive mineral weathering, in particular epidote, as the water residence time decreases. The decrease in water residence time is a result of the evolution from a distributed (long water residence time) to a channelised (short water residence time) subglacial drainage network. The third hydrological period was defined as the period when overall discharge was decreasing. This hydrological period was marked by prominent diurnal cycles in discharge. During this period, significant correlations between δ44/42Ca and SSC and δ18O were observed which are suggestive of fractionation during adsorption. This study demonstrates the potential of radiogenic Ca to both identify temporally changing mineral sources in conjunction with 87Sr/86Sr values and to separate source and fractionation effects in δ44/42Ca values.

  7. Theoretical investigation of superconductivity in SrPd2Ge2 , SrPd2As2 , and CaPd2As2

    NASA Astrophysics Data System (ADS)

    Karaca, Ertuǧrul; Tütüncü, H. M.; Uzunok, H. Y.; Srivastava, G. P.; Uǧur, Ş.

    2016-02-01

    Ab initio pseudopotential calculations have been performed to investigate the structural, electronic, and vibrational properties of SrPd2Ge2 , SrPd2As2 , and CaPd2As2 crystallizing in the ThCr2Si2 -type body-centered tetragonal structure. Our electronic results show that the density of states at the Fermi level is mainly dominated by the strong hybridization of Pd d states and Ge (or As) p states. The linear response method and the Migdal-Eliashberg approach have been used to calculate the Eliashberg spectral function for all these compounds. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter (λ ) is found to be 0.74 for SrPd2Ge2 , 0.66 for SrPd2As2 , and 0.72 for CaPd2As2 . Using the calculated values of λ and the logarithmically averaged phonon frequency ωln the superconducting critical temperature (Tc) values for SrPd2Ge2 , SrPd2As2 , and CaPd2As2 are found to be 3.20, 2.05, and 2.48 K, respectively, which are in acceptable agreement with the corresponding experimental values. The relative differences in the Tc values between the Ge and As compounds have been explained in terms of some key physical parameters.

  8. Plant uptake of cations under nutrient limitation: An environmental tracer study using Ca/Sr and K/Rb ratios

    NASA Astrophysics Data System (ADS)

    Shi, Z.; Keller, C. K.; Stacks, D.; Grant, M.; Harsh, J. B.; Letourneau, M.; Gill, R. A.; Balogh-Brunstad, Z.; Thomashow, L.; Dohnalkova, A.

    2012-12-01

    Vascular plant growth builds soils and ecosystem nutrient capital by sequestering and partitioning atmospheric CO2 into organic matter and continental runoff and driving terrestrial water and energy balances. Plant root-system functions, e.g. nutrient mobilization and uptake, are altered by environmental stress. However, the stress-response relationships are poorly understood. Chemical tracers have potential for assessing contributions of nutrients from various nutrient pools. Our objective is to quantitatively study how varying degrees of nutrient limitation (and corresponding needs to extract base cations from mineral sources) influence Ca and K uptake functions in a plant-root-mineral system. We are studying plant-driven mineral weathering in column experiments with red pine (Pinus resinosa) seedlings. The columns contain quartz sand amended with anorthite and biotite that constitute the sole mineral sources of Ca and K. These minerals also contain known amounts of Sr and Rb, which exhibit chemical behavior similar to Ca and K, respectively. The solution source of Ca and K was varied by adding 0% (no dissolved Ca and K), 10%, 30%, or 100% of a full strength Ca and K nutrient solution through irrigation water in which both Sr and Rb concentrations were negligible. Selected columns were destructively sampled at 3, 6 and 9 months to harvest biomass and measure plant uptake of cations. We used Ca/Sr and K/Rb ratio results to estimate the contributions of Ca and K from mineral and solution sources. For the 0% nutrient treatment, the Ca/Sr and K/Rb ratios in total biomass at 3 months, compared with those in the mineral phases, suggested preferential uptake of Ca and K over Sr and Rb, respectively, and allowed us to determine uptake discrimination factors for both cations. The K/Rb ratios in total biomass increased with greater K availability in the solution source, as expected, but Ca/Sr ratios did not show any dependence on Ca availability in the solution source

  9. Ca(2+) function in photosynthetic oxygen evolution studied by alkali metal cations substitution.

    PubMed

    Ono, T; Rompel, A; Mino, H; Chiba, N

    2001-10-01

    Effects of adding monovalent alkali metal cations to Ca(2+)-depleted photosystem (PS)II membranes on the biochemical and spectroscopic properties of the oxygen-evolving complex were studied. The Ca(2+)-dependent oxygen evolution was competitively inhibited by K(+), Rb(+), and Cs(+), the ionic radii of which are larger than the radius of Ca(2+) but not inhibited significantly by Li(+) and Na(+), the ionic radii of which are smaller than that of Ca(2+). Ca(2+)-depleted membranes without metal cation supplementation showed normal S(2) multiline electron paramagnetic resonance (EPR) signal and an S(2)Q(A)(-) thermoluminescence (TL) band with a normal peak temperature after illumination under conditions for single turnover of PSII. Membranes supplemented with Li(+) or Na(+) showed properties similar to those of the Ca(2+)-depleted membranes, except for a small difference in the TL peak temperatures. The peak temperature of the TL band of membranes supplemented with K(+), Rb(+), or Cs(+) was elevated to approximately 38 degrees C which coincided with that of Y(D)(+)Q(A)(-) TL band, and no S(2) EPR signals were detected. The K(+)-induced high-temperature TL band and the S(2)Q(A)(-) TL band were interconvertible by the addition of K(+) or Ca(2+) in the dark. Both the Ca(2+)-depleted and the K(+)-substituted membranes showed the narrow EPR signal corresponding to the S(2)Y(Z)(+) state at g = 2 by illuminating the membranes under multiple turnover conditions. These results indicate that the ionic radii of the cations occupying Ca(2+)-binding site crucially affect the properties of the manganese cluster. PMID:11566758

  10. Electronic structure, chemical bonding, and geometry of pure and Sr-doped CaCO3.

    PubMed

    Stashans, Arvids; Chamba, Gaston; Pinto, Henry

    2008-02-01

    The electronic structure, chemical bonding, geometry, and effects produced by Sr-doping in CaCO(3) have been studied on the basis of density-functional theory using the VASP simulation package and molecular-orbital theory utilizing the CLUSTERD computer code. Two calcium carbonate structures which occur naturally in anhydrous crystalline forms, calcite and aragonite, were considered in the present investigation. The obtained diagrams of density of states show similar patterns for both materials. The spatial structures are computed and analyzed in comparison to the available experimental data. The electronic properties and atomic displacements because of the trace element Sr-incorporation are discussed in a comparative manner for the two crystalline structures. PMID:17654648

  11. Comparison of Equatorial Pacific Sea Surface Variability and Trends with Sr/Ca Records from Multiple Corals

    NASA Astrophysics Data System (ADS)

    Alpert, A.; Cohen, A. L.; Oppo, D.; Gove, J.; Young, C.; Decarlo, T. M.

    2015-12-01

    The short duration of instrumental SST records makes it difficult to reliably separate anthropogenic-related trends from natural variability, especially in the tropical Pacific. The Sr/Ca ratio of massive corals has been used to lengthen the record and fill data gaps but its reliability has been questioned because different coral colonies on the same reef can have different Sr/Ca-temperature relationships and yield opposing derived SST trends. We exploited a unique multi-year dataset of in situ temperature data to assess whether inter-colony differences are attributable to small-scale oceanographic variability or "vital effects" and to quantify the effect of these differences on temperature estimates and uncertainties. Sr/Ca records from four massive Porites colonies growing on the east and west sides of Jarvis Island, central equatorial Pacific, were compared with temperature data from in situ loggers also placed on the east and west sides. In general, Sr/Ca captured - albeit inconsistently - the occurrence of inter-annual SST events but their amplitude was not consistently recorded by any of the corals. However, the Sr/Ca-temperature regressions derived from the four different colonies were statistically distinct. Assuming these relationships represent the full range of Sr/Ca-temperature calibrations in Jarvis Porites, we assessed how well Sr/Ca of a fossil coral with an unknown Sr/Ca-temperature relationship can constrain past temperatures. Our results indicate that the standard error of prediction methods underestimate the actual error as we could not reliably reconstruct the amplitude or frequency of ENSO events as large as ±2°C. Further, Sr/Ca of one coral implied a statistically significant cooling trend while that of its neighbor implied a warming trend whereas no long-term trend was identified in the instrumental data. This observation of a derived trend where none exists is consistent with observations made independently at other coral reef sites in the

  12. Trace metal (Mg/Ca and Sr/Ca) analyses of single coccoliths by Secondary Ion Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Prentice, Katy; Jones, Tom Dunkley; Lees, Jackie; Young, Jeremy; Bown, Paul; Langer, Gerald; Fearn, Sarah; EIMF

    2014-12-01

    Here we present the first multi-species comparison of modern and fossil coccolith trace metal data obtained from single liths. We present both trace metal analyses (Sr, Ca, Mg and Al) and distribution maps of individual Paleogene fossil coccoliths obtained by Secondary Ion Mass Spectrometry (SIMS). We use this data to determine the effects of variable coccolith preservation and diagenetic calcite overgrowths on the recorded concentrations of strontium and magnesium in coccolith calcite. The analysis of coccoliths from deep-ocean sediments spanning the Eocene/Oligocene transition demonstrates that primary coccolith calcite is resistant to the neomorphism that is common in planktonic foraminifera from similar depositional environments. Instead, where present, diagenetic calcite forms distinct overgrowths over primary coccolith calcite rather than replacing this calcite. Diagenetic overgrowths on coccoliths are easily distinguished in SIMS analyses on the basis of relatively higher Mg and lower Sr concentrations than co-occurring primary coccolith calcite. This interpretation is confirmed by the comparable SIMS analyses of modern cultured coccoliths of Coccolithus braarudii. Further, with diagenetic calcite overgrowth being the principle source of bias in coccolith-based geochemical records, we infer that lithologies with lower carbonate content, deposited below the palaeo-lysocline, are more likely to produce geochemical records dominated by primary coccolith calcite than carbonate-rich sediments where overgrowth is ubiquitous. The preservation of primary coccolith carbonate in low-carbonate lithologies thus provides a reliable geochemical archive where planktonic foraminifera are absent or have undergone neomorphism.

  13. Luminescence Properties of SrCaS:Cu Thin Film Phosphors

    NASA Astrophysics Data System (ADS)

    Mohammed, Edris; Park, Won; Tong, Wusheng; Stock, Stuart; Summers, Chris

    2000-03-01

    Luminescence Properties of SrxCa1-xS:Cu Thin Film Phosphors E. Mohammed, W. Park, W. Tong, S. Stock and C. J. Summers Phosphor Technology Center of Excellence Georgia Institute of Technology, Atlanta, GA 30332-0560 The luminescence properties of MBE grown thin film SrCaS:Cu phosphors are investigated. 10K photoluminescence (PL) results showed a broad emission band of Cu that shifted between 2.98eV and 2.58eV, with a large increase in linewidth ranging from 0.36eV for CaS:Cu to 0.49eV as the Sr composition was increased. The significant increase in linewidth suggested that the broad emission band of Cu was composed of two closely spaced bands suggesting a possible spin-orbit or Jahn-Teller splitting of the emitting level. Curve fitting of the 10K PL showed that the splitting varied from 100meV for x=0 to 240 meV for x=0.98. In the excitation spectra, the optical absorption edge shifted from 5.1eV to 4.7eV while the energies of the two direct excitation bands of Cu shifted from 4.4 to 4.8eV and 4.0 to 4.2eV respectively. The crystal field parameter 10Dq obtained from experiments showed a linear as the composition of Sr was varied between x=0 to x=0.98 and the result was in excellent agreement with crystal field calculations.

  14. Improved thermoelectric property of cation-substituted CaMnO3

    NASA Astrophysics Data System (ADS)

    Kumar, Pradeep; Kashyap Subhash, C.; Sharma Vijay, Kumar; Gupta, H. C.

    2015-09-01

    Single-phase pristine and cation-substituted calcium manganite (Ca1-xBixMn1-yVyO3-δ) polycrystalline samples were synthesized by the solid state reaction technique. Their thermoelectric properties were measured by a set up that was designed and assembled in the laboratory. The Ca1-xBixMn1-yVyO3-δ sample with x = y = 0.04 has shown a power factor (S2σ) of 176 μW/m/K2 at 423 K, which is nearly two orders of magnitude higher than that of the pristine sample (2.1 μW/m/K2). The power factor of the substituted oxide remains almost temperature independent as the Seebeck coefficient increases monotonically with temperature, along with the simultaneous decrease in electrical resistivity which is attributed to enhanced electron density due to co-doping of bismuth and vanadium and grain boundary scattering. These cation-substituted calcium manganites can be used as a potential candidate for an n-type leg in a thermoelectric generator (module).

  15. CO sub 2 -laser ablation of Bi-Sr-Ca-Cu oxide by millisecond pulse lengths

    SciTech Connect

    Meskoob, M.; Honda, T.; Safari, A.; Wachtman, J.B.; Danforth, S. ); Wilkens, B.J. )

    1990-03-15

    We have achieved ablation of Bi-Sr-Ca-Cu oxide from single targets of superconducting pellets by CO{sub 2}-laser pulses of l ms length to grow superconducting thin films. Upon annealing, the 6000-A thin films have a {ital T}{sub {ital c}} (onset) of 90 K and zero resistance at 78 K. X-ray diffraction patterns indicate the growth of single-phase thin films. This technique allows growth of uniform single-phase superconducting thin films of lateral area greater than 1 cm{sup 2}.

  16. Directly-coupled dc-SQUID magnetometers made of Bi-Sr-Ca-Cu oxide films

    SciTech Connect

    Matsuda, M.; Murayama, Y.; Kiryu, S.; Kasai, N.; Kashiwaya, S.; Koyanagi, M.; Endo, T. ); Kuriki, S. . Research Inst. of Applied Electricity)

    1991-03-01

    This paper reports on all high-T{sub c} dc- SQUID magnetometers made of Bi-Sr-Ca-Cu oxide films that were designed and fabricated. A directly-coupled scheme where a SQUID loop and a pick-up loop are connected directly in parallel was chosen to avoid fabricating the multi-layered structure. The flux noise which was measured in FLL operation at 4.2K increased in a form of 1/f as the frequency decreased below 20Hz.

  17. Gamma-ray shielding properties of CaO-SrO-B 2O 3 glasses

    NASA Astrophysics Data System (ADS)

    Singh, Kulwant; Singh, Harvinder; Sharma, Gopi; Gerward, Leif; Khanna, Atul; Kumar, Rajesh; Nathuram, Rohila; Sahota, Hari Singh

    2005-02-01

    Mass attenuation coefficients, effective atomic numbers and effective electron densities have been determined experimentally for the glass system xCaO·(0.3- x)SrO·0.7B 2O 3 at photon energies 511, 662, 1173, and 1332 keV. The results are compared with theoretical calculations. In addition, the molar volume of the glasses has been derived from density measurements, and the excess volume has been determined as a function of composition. The reported data should be useful for potential applications of these glasses in radiation shielding.

  18. Flux creep in Bi2Sr2Ca1Cu2O(8+x) single crystals

    NASA Technical Reports Server (NTRS)

    Agostinelli, E.; Fiorani, D.; Testa, A. M.; Tejada, J.

    1991-01-01

    Dissipative effects were investigated in Bi2Sr2Ca1Cu2O(8+x) single crystals by critical current and magnetic relaxation measurements. Activation energies for the flux motion were determined from the temperature dependence of the critical current and from the time decay of the zero field cooled and the remanent magnetization. The effective activation energy was found to increase with temperature, in agreement with the existence of a distribution of activation energies (E sub o 20 meV at 4.2 K for H + 10 kOe applied parallel to the c-axis.).

  19. Magnetic-field-induced microwave losses in epitaxial Bi-Sr-Ca-Cu-O films

    SciTech Connect

    Silva, E.; Giura, M.; Marcon, R.; Fastampa, R. ); Balestrino, G.; Marinelli, M.; Milani, E. )

    1992-06-01

    Magnetic-field-induced microwave losses in epitaxial {ital c}-axis-oriented Bi-Sr-Ca-Cu-O films have been observed. At low magnetic field, the behavior of the absorption is qualitatively analogous to that already observed in granular samples. The dominant part is attributed to the dephasing of a network of Josephson junctions. A structural analysis shows evidence of such a network. The dependence of the absorption on the angle between the magnetic field and the {ital a}-{ital b} plane is consistent with this model.

  20. Flux pinning by precipitates in the Bi-Sr-Ca-Cu-O system

    DOEpatents

    Shi, Donglu

    1992-01-01

    A fundamental pinning mechanism has been identified in the Bi-Sr-Ca-Cu-O system. The pinning strength has been greatly increased by the introduction of calcium- and copper-rich precipitates into the sample matrix. The calcium and copper are supersaturated in the system by complete melting, and the fine calcium and copper particles precipitated during subsequent crystallization anneal to obtain the superconducting phases. The intragrain critical current density has been increased from the order of 10.sup.5 A/cm.sup.2 to 10.sup.7 A/cm.sup.2 at 5 T.

  1. TiO2 controlling photoluminescence of AWO4 (A =Ca,Sr,Ba) nanofilms

    NASA Astrophysics Data System (ADS)

    Jia, Runping; Zhang, Guoxin; Wu, Qingsheng; Ding, Yaping

    2006-07-01

    AWO4 (A =Ca,Sr,Ba) nanofilms are prepared by a self-inventive technique using collodion to disperse nanoparticles and form film, and their photoluminescence (PL) properties are controlled by a nano-TiO2 doping method. This cannot only reach the results of uniform film and PL enhancement, but also realize a PL increase/decrease shift effect. The PL behaviors of AWO4 nanofilms doped by TiO2 are in good agreement with Gaussion function relation. In addition, there is a positive correlation between the critical concentrations of TiO2 in AWO4-TiO2 nanofilm series and A's ionic potential.

  2. Rare gases and Ca, Sr, and Ba in Apollo 17 drill-core fines

    NASA Technical Reports Server (NTRS)

    Pepin, R. O.; Dragon, J. C.; Johnson, N. L.; Bates, A.; Coscio, M. R., Jr.; Murthy, V. R.

    1975-01-01

    Trapped gas isotopic compositions and spallation gas concentrations as functions of depth in the Apollo 17 drill core were determined from mass spectrometer studies by means of correlation techniques. The distribution of He, Ne, Ar, Kr, and Xe as well as Ca, Sr, and Ba was investigated, and rare-gas spallation and neutron capture profiles are compared with attention to proposed depositional models for the Taurus-Littrow regolith. The data exclude a sedimentation pattern similar to that found at the Apollo 15 site but are possibly compatible with long-term continuous accretion models or models of very recent rapid accumulation of regolith.

  3. First-principles study on the structural, electronic, and optical properties of Ca1- x Sr x Se alloys

    NASA Astrophysics Data System (ADS)

    Ahmadian, F.; Salary, A.

    2016-01-01

    The structural, electronic, and optical properties of binary CaSe and SrSe compounds and Ca1- x Sr x Se alloys were studied by using the full potential linearized augmented plane wave (FPLAPW) method within density functional theory (DFT). The band structure calculations showed that the CaSe and the SrSe binary compounds in the rocksalt (RS), zinc-blende (ZB) and wurtzite (WZ) phases were semiconductors while they had a metallic characteristic in the CsCl phase. The lattice constant and bulk modulus values for the Ca1- x Sr x Se alloys in the RS and the ZB phases at different concentrations were calculated and compared with those obtained by using Vegard's law. The energy band gap values in the RS and the ZB phases were estimated for different x values by using both define acronyms the Perdew, Burke, and Ernzerhof (PBE-GGA) and the Engel and Vosko (EV-GGA) schemes, and the results were compared with those obtained by using the empirical electronegativity expression. The band gap bowing parameters were calculated by using quadratic functions and the procedure of Bernard and Zunger to fit the non-linear variation of the band gaps. The static dielectric constant ɛ 1(0) was calculated at different concentrations. The energy loss function L( ω) for the Ca1- x Sr x Se alloys in the RS and the ZB phases has a main peak corresponding to the plasmon frequency. The values of the static refractive index ( n(0)) for the Ca1- x Sr x Se alloys were calculated and compared with the values predicted by using the Moss, Ravindra, and Vandamme models. Finally, the extinction indic incident photon energies. es ( k( ω)) and the reflectivities ( R( ω)) for the Ca1- x Sr x Se alloys were calculated within a wide range of incident photon energies.

  4. Photoluminescence in the Ca{sub x}Sr{sub 1-x}WO{sub 4} system at room temperature

    SciTech Connect

    Porto, S.L.; Longo, E.; Simoes, L.G.P.; Lima, S.J.G.; Ferreira, J.M.; Soledade, L.E.B.; Espinoza, J.W.M.; Cassia-Santos, M.R.; Maurera, M.A.M.A.; Paskocimas, C.A.; Santos, I.M.G. Souza, A.G.

    2008-08-15

    In this work, a study was undertaken about the structural and photoluminescent properties, at room temperature, of powder samples from the Ca{sub x}Sr{sub 1-x}WO{sub 4} (x=0-1.0) system, synthesized by a soft chemical method and heat treated between 400 and 700 deg. C. The material was characterized using Infrared, UV-vis and Raman spectroscopy and XRD. The most intense PL emission was obtained for the sample calcined at 600 deg. C, which is neither highly disordered (400-500 deg. C), nor completely ordered (700 deg. C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO{sub 4} or SrWO{sub 4}, but for Ca{sub 0.6}Sr{sub 0.4}WO{sub 4}. The PL emission spectra could be separated into two Gaussian curves. The lower wavelength peak is placed around 530 nm, and the higher wavelength peak at about 690 nm. Similar results were reported in the literature for both CaWO{sub 4} and SrWO{sub 4}. - Graphical abstract: The structural and room temperature photoluminescence of Ca{sub x}Sr{sub 1-x}WO4 synthesized by a soft chemical method was studied. The most intense PL emission was obtained for the sample calcined at 600 deg. C, that is neither highly disordered (400-500 deg. C), nor completely ordered (700 deg. C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO{sub 4} or SrWO{sub 4}, but for Ca{sub 0.6}Sr{sub 0.4}WO{sub 4}.

  5. Local atomic configuration and Auger Valence Electron Spectra in BiSrCaCuO single crystals

    SciTech Connect

    Fujiwara, Y.; Hirata, S.; Nishikubo, M.; Kobayashi, T. ); Nakayama, H.; Fujita, H. . Faculty of Engineering)

    1991-03-01

    This paper reports on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (2212) and Ca-doped Bi{sub 2}Sr{sub 2}CuO{sub y} (2201) single crystals systematically investigated by Auger Valence Electron Spectroscopy (AVES). In AVES measurements on two kinds of crystals, a drastic difference was observed in the spectral shape of Ca(2p,3p,3p), reflecting a difference in spin-orbit splitting induced by local atomic configuration in the vicinity of Ca atoms. Furthermore, Ca(2p,3p,4s) spectrum appeared in both the crystals, which indicates that the real valency of Ca atoms is deviated from + 2 in the crystals. These results suggest that AVES is a promising probe for characterizing local atomic configuration and valence electron states of the constituent elements.

  6. Structural and magnetic properties of Ca-substituted barium W-type hexagonal hexaferrites

    NASA Astrophysics Data System (ADS)

    Huang, Kai; Liu, Xiansong; Feng, Shuangjiu; Zhang, Zhanjun; Yu, Jiangying; Niu, Xiaofei; Lv, Farui; Huang, Xing

    2015-04-01

    A series of W-type hexagonal ferrites with the composition Ba1-xCaxCo2Fe16O27 (x=0, 0.1, 0.3, 0.4 and 0.5) were synthesized using a sol-gel method. The effects of doping on structural and magnetic properties are studied by X-ray diffraction, thermal analyzer, scanning electron microscopy, vibrating sample magnetometer and vector network analyzer, respectively. The X-ray diffraction analysis shows that the samples belong to the W-type hexagonal ferrite. The lattice constants a and c decreases as Ca contents increases. The grains exhibit well defined hexagonal shape. The saturation magnetization and the intrinsic coercive force increases with the increase of the Ca substitution amount. The real part of complex permittivity (ε‧) and imaginary part (ε″) increase with more addition of Ca2+ amount. The imaginary part of complex permittivity (μ‧) increases and the real part (μ‧‧) goes down after Ca2+ is doped. Furthermore, the Ca2+ ions doped in the ferrite improved microwave absorbency.

  7. Coupled magnetic and elastic properties in LaPr(CaSr)MnO manganites

    NASA Astrophysics Data System (ADS)

    Eslava, G. G.; Parisi, F.; Bernardo, P. L.; Quintero, M.; Leyva, G.; Cohen, L. F.; Ghivelder, L.

    2016-09-01

    We investigate a series of manganese oxides, the La0.225Pr0.4(Ca1-xSrx)0.375MnO3 system. The x = 0 sample is a prototype compound for the study of phase separation in manganites, where ferromagnetic and charge ordered antiferromagnetic phases coexist. Replacing Ca2+ by Sr2+ gradually turns the system into a homogeneous ferromagnet. Our results show that the material structure plays a major role in the observed magnetic properties. On cooling, at temperatures below ∼ 100 K, a strong contraction of the lattice is followed by an increase in the magnetization. This is observed both through thermal expansion and magnetostriction measurements, providing distinct evidence of magneto-elastic coupling in these phase separated compounds.

  8. Sr/Ca ratios in cold-water corals - a 'low-resolution' temperature archive?

    NASA Astrophysics Data System (ADS)

    Rüggeberg, Andres; Riethdorf, Jan-Rainer; Raddatz, Jacek; López Correa, Matthias; Montagna, Paolo; Dullo, Wolf-Christian; Freiwald, André

    2010-05-01

    One of the basic data to understand global change and past global changes is the measurement and the reconstruction of temperature of marine water masses. E.g. seawater temperature controls the density of seawater and in combination with salinity is the major driving force for the oceans circulation system. Geochemical investigations on cold-water corals Lophelia pertusa and Desmophyllum cristagalli indicated the potential of these organisms as high-resolution archives of environmental parameters from intermediate and deeper water masses (Adkins and Boyle 1997). Some studies tried to use cold-water corals as a high-resolution archive of temperature and salinity (Smith et al. 2000, 2002; Blamart et al. 2005; Lutringer et al. 2005). However, the fractionation of stable isotopes (delta18O and delta13C) and element ratios (Sr/Ca, Mg/Ca, U/Ca) are strongly influenced by vital effects (Shirai et al. 2005; Cohen et al. 2006), and difficult to interpret. Nevertheless, ongoing studies indicate the potential of a predominant temperature dependent fractionation of distinct isotopes and elements (e.g. Li/Ca, Montagna et al. 2008; U/Ca, Mg/Ca, delta18O, Lòpez Correa et al. 2008; delta88/86Sr, Rüggeberg et al. 2008). Within the frame of DFG-Project TRISTAN and Paläo-TRISTAN (Du 129/37-2 and 37-3) we investigated live-collected specimens of cold-water coral L. pertusa from all along the European continental margin (Northern and mid Norwegian shelves, Skagerrak, Rockall and Porcupine Bank, Galicia Bank, Gulf of Cadiz, Mediterranean Sea). These coral samples grew in waters characterized by temperatures between 6°C and 14°C. Electron Microprobe investigations along the growth direction of individual coral polyps were applied to determine the relationship between the incorporation of distinct elements (Sr, Ca, Mg, S). Cohen et al. (2006) showed for L. pertusa from the Kosterfjord, Skagerrak, that ~25% of the coral's Sr/Ca ratio is related to temperature, while 75% are influenced

  9. Structural chemistry of M2Si5N8:Eu2+ (M = Ca, Sr, Ba) phosphor via structural refinement.

    PubMed

    Kim, Yong-Il; Kim, Kwang Bok; Lee, Yun-Hee; Kim, Ki-Bok

    2012-04-01

    Structural refinement using X-ray powder diffraction data and geometry energy calculations using quantum mechanics were used to investigate the preferential substitution sites and the amount of Eu2+ ions in the host lattice of alkaline earth elements co-doped M2Si5N8:Eu2+ (M = Ca, Sr, and Ba), which is a red color-emitting nitride phosphor prepared via a carbothermal reaction method. Of the possible preferential sites, the preferential site proposed by the structural refinement results, in which the Eu2+ ions might preferentially occupy nine coordinated sites with nitrogen in M2Si5N8:Eu2+, was confirmed via geometry energy calculations using a first-principle based on the density-functional theory. The final converged weighted R factor (R(wp)) and the goodness-of-fit indicator [S(= R(wp)/R(e))] were 9.51% and 1.77, respectively. Each occupancy of Eu2+ ions for the two non-equivalent M sites, M(1) and M(2), was 0.10(2) and 0.04(2), respectively. The final refined model described the crystal structure in a space group Pmn2, (No. 31) with Z = 2, a = 5.7424(1) angstroms, b = 6.8837(1) angstroms, c = 9.3586(1) angstroms, and alpha(= beta= gamma)= 90 degrees. PMID:22849142

  10. Multiple Magnetic Transitions and Magnetocaloric Effect in (La,Pr,M)MnO3 (M = Ca, Sr, Ba) Mixed Phase Manganites

    NASA Astrophysics Data System (ADS)

    Lampen, P. J.; Bingham, N. S.; Phan, M. H.; Srikanth, H. S.; Phan, T. L.; Yu, S. C.; Cheong, S. W.

    2012-02-01

    The manganite compound (La,Pr,Ca)MnO3 is a well-studied system that is known to exhibit a complex phase diagram featuring ``strain liquid'' and ``strain glass'' regions in combination with competing ferromagnetic (FM) and charge-ordered antiferromagnetic (CO/AFM) phases. The balance of these phases is sensitive to various perturbations including magnetic and electric field, strain, bandwidth, and A-site cation disorder. The A-site disorder and bandwidth of this compound can be tuned through the replacement of Ca with larger Sr and Ba ions. We report here a systematic study of the influence of cation substitution on the magnetic and magnetocaloric properties of La0.35Pr0.275M0.375MnO3 (M = Ca, Sr, Ba). Structural properties, including lattice parameters and Mn--O--Mn bond angles, were determined from X-ray diffraction patterns. DC magnetometry studies reveal multiple magnetic transitions in each sample which are probed by magnetocaloric effect (MCE) and transverse susceptibility (TS) experiments. Increasing the average A-site cationic radius is found to strongly impact the magnetic properties and phase behavior of the system.

  11. A coral Sr/Ca calibration and replication study of two massive corals from the Gulf of Mexico

    USGS Publications Warehouse

    DeLong, Kristine L.; Flannery, Jennifer A.; Maupin, Christopher R.; Poore, Richard Z.; Quinn, Terrence M.

    2011-01-01

    This study examined the variations in the ratio of strontium-to-calcium (Sr/Ca) for two Atlantic corals (Montastraea faveolata and Siderastrea siderea) from the Dry Tortugas National Park (centered on 24.7°N, 82.8°W) in the Gulf of Mexico. Cores from coral colonies in close proximity (10s of meters) and with the same environmental conditions (i.e., depth and water chemistry) were micro-sampled with approximately monthly resolution and the resulting Sr/Ca variations were calibrated with local sea surface temperature (SST) records. Replication tests for coral Sr/Ca variations found high agreement between intra-colony variations and between individual colonies of S. siderea (a single M. faveolata colony was sampled). Regression analysis of monthly variations in coral Sr/Ca and local SST revealed significant correlation on monthly and inter-annual timescales. Verification of the calibration on different timescales found coral Sr/Ca–SST reconstructions in S. siderea were more accurate than those from M. faveolata, especially on inter-annual timescales. Sr/Ca–SST calibration equations for the two species are significantly different (cf., Sr/Ca = -0.042 SST + 10.070, S. siderea; Sr/Ca = -0.027 SST + 9.893, M. faveolata). Mean linear extension for M. faveolata is approximately twice that of S. siderea (4.63, 4.31, and 8.31 mm year−1, A1, F1, and B3, respectively); however, seasonal Sr/Ca variability in M. faveolata is less than S. siderea (0.323, 0.353, and 0.254 mmol mol−1, A1, F1, and B3, respectively). The reduced slope for M. faveolata is attributed to physical sampling issues associated with complex time-skeletal structure of M. faveolata, i.e., a sampling effect, and not a growth effect since the faster growing M. faveolata has the reduced Sr/Ca variability.

  12. Relation Between Simultaneous Ca and Sr Transport Rates in Isolated Segments of Vetch, Barley, and Pine Roots 1

    PubMed Central

    Hutchin, Maxine E.; Vaughan, Burton E.

    1968-01-01

    Root segments of vetch, barley, and pine were exposed to a nutrient solution containing 85Sr and 45Ca tracers. Translocation was measured from solutions containing stable ions at concentrations of 2.5 mm Ca, and at either 0.5 mm or 2.5 mm Sr. Polar transport was established between 12 and 18 hr in barley, and between 16 and 22 hr in vetch. Acropetal transport remained below 5% of basipetal transport of tracer during these intervals. Transport in both vetch and barley usually declined before an elapsed time of 24 hr unlike corn, which maintained its steady state beyond 24 hr. Pine was radically different in that it showed no difference between acropetal and basipetal transport rates and had very low rates. Sr transport in all plants studied to date paralleled that of Ca and the ratio Sr:Ca transported was equal to the ratio Sr:Ca in the nutrient. In vetch, stable Ca transport was reduced to one-fifth when Sr concentration was increased from 0.5 mm to 2.5 mm. Yet stable Sr transport did not change, indicating that the effect on transport was not due to competitive inhibition. A similar effect was less pronounced in barley, but could not be detected in pine. The magnitude of the transport rates varied considerably among the various species, corn having the greatest followed by barley, vetch, and pine in decreasing order. Transport did not correlate with root weight or surface area; it amounted to from 0.03 to 0.60 nanomoles per hr in these experiments as compared to 7 nanomoles per hr previously established in corn (in all cases, 55 mm segments, sectioned 10 mm from apex). Images PMID:5725599

  13. Influence of cetyltrimethylammonium bromide on the morphology of AWO 4 (A = Ca, Sr) prepared by cyclic microwave irradiation

    NASA Astrophysics Data System (ADS)

    Thongtem, Titipun; Kaowphong, Sulawan; Thongtem, Somchai

    2008-09-01

    AWO 4 (A = Ca, Sr) was prepared from metal salts [Ca(NO 3) 2·4H 2O or Sr(NO 3) 2], Na 2WO 4·2H 2O and different moles of cetyltrimethylammonium bromide (CTAB) in water by cyclic microwave irradiation. The structure of AWO 4 was characterized by X-ray diffraction (XRD) and selected area electron diffraction (SAED). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed the presence of nanoparticles in clusters with different morphologies; spheres, peaches with notches, dumb-bells and bundles, influenced by CTAB. Six Raman vibrational peaks of scheelite structure were detected at 908, 835, 793, 399, 332 and 210 cm -1 for CaWO 4 and 917, 833, 795, 372, 336 and 192 cm -1 for SrWO 4, which are assigned as ν1(A g), ν3(B g), ν3(E g), ν4(B g), ν2(A g) and νf.r.(A g), respectively. Fourier transform infrared (FTIR) spectra provided the evidence of W-O stretching vibration in [WO 4] 2- tetrahedrons at 793 cm -1 for CaWO 4 and 807 cm -1 for SrWO 4. The peaks of photoluminescence (PL) spectra were at 428-434 nm for CaWO 4, and 447-451 nm for SrWO 4.

  14. Biogeochemistry of stable Ca and radiogenic Sr isotopes in a larch-covered permafrost-dominated watershed of Central Siberia

    NASA Astrophysics Data System (ADS)

    Bagard, Marie-Laure; Schmitt, Anne-Désirée; Chabaux, François; Pokrovsky, Oleg S.; Viers, Jérôme; Stille, Peter; Labolle, François; Prokushkin, Anatoly S.

    2013-08-01

    Stable Ca and radiogenic Sr isotope compositions were measured in different compartments (stream water, soil solutions, rocks, soils and soil leachates and vegetation) of a small permafrost-dominated watershed in the Central Siberian Plateau. The Sr and Ca in the area are supplied by basalt weathering and atmospheric depositions, which significantly impact the Sr isotopic compositions. Only vegetation significantly fractionates the calcium isotopes within the watershed. These fractionations occur during Ca uptake by roots and along the transpiration stream within the larch trees and are hypothesised to be the result of chromatographic processes and Ca oxalate crystallisations during Ca circulation or storage within plant organs. Biomass degradation significantly influences the Ca isotopic compositions of soil solutions and soil leachates via the release of light Ca, and organic and organo-mineral colloids are thought to affect the Ca isotopic compositions of soil solutions by preferential scavenging of 40Ca. The imprint of organic matter degradation on the δ44/40Ca of soil solutions is much more significant for the warmer south-facing slope of the watershed than for the shallow and cold soil active layer of the north-facing slope. As a result, the available stock of biomass and the decomposition rates appear to be critical parameters that regulate the impact of vegetation on the soil-water system in permafrost areas. Finally, the obtained δ44/40Ca patterns contrast with those described for permafrost-free environments with a much lower δ44/40Ca fractionation factor between soils and plants, suggesting specific features of organic matter decomposition in permafrost environments. The biologically induced Ca isotopic fractionation observed at the soil profile scale is not pronounced at the scale of the streams and large rivers in which the δ44/40Ca signature may be controlled by the heterogeneity of lithological sources.

  15. Ferromagnetism in 2212 phase Bi-Sr-Ca-Cu-O nano-superconductors

    NASA Astrophysics Data System (ADS)

    Baqiya, Malik A.; Widodo, Henry; Rochmawati, Lidya; Darminto, Adachi, Tadashi; Koike, Yoji

    2012-06-01

    Superconductors are characterized by zero resistance and Meissner effect. At below critical temperature (Tc), these materials exhibit diamagnetic properties. On the other hand, materials in nano-crystal size have specific properties that differ from bulk state. Nanomaterials are characterized by surface effect which influences physical and chemical properties of the materials. Combining these two mayor fields, it can be obtained superconductors in nano-crystal size (below 200 nm) using simple method (called as nano-superconductors). Generally, ceramic-oxides in nano-crystal size, even in cuprate-superconductors, may have ferromagnetic behavior at room temperature. In this research, Bi and Bi, Pb-based nano-superconductors synthesized by wet mixing technique have Tc ˜80 K for 2212 (Bi2Sr2CaCu2O8-δ and Bi1,6Pb0,4Sr2CaCu2O8-δ) phases. They also exhibit ferromagnetism effect and hysteresis curve although at well above Tc. This is unusual phenomenon because superconductor materials are generally diamagnetic at below Tc and paramagnetic at normal state. This phenomenon is possibly due to magnetic moments which may possibly come from oxygen vacancies of the nanoparticles surface.

  16. Anomalous phonon properties in the silicide superconductors CaAlSi and SrAlSi

    NASA Astrophysics Data System (ADS)

    Kuroiwa, S.; Hasegawa, T.; Kondo, T.; Ogita, N.; Udagawa, M.; Akimitsu, J.

    2008-11-01

    Lattice-dynamical properties of CaAlSi and SrAlSi with a similar layer structure to MgB2 have been first investigated by both Raman-scattering and ab initio calculations. All Raman-active phonons with E' symmetry have been clearly observed for both compounds. Their line shapes are asymmetric but their linewidths are ˜10cm-1 , which is very narrower than that of MgB2 . In addition to the Raman-active modes, several extra peaks have been observed below 160cm-1 . These low-energy extra modes can be assigned to the out-of-plane vibrations of Al perpendicular to Al-Si basal plane. Since these peak intensities are strongly affected by the incident energy (resonance Raman process), the electronic state is important for them. Moreover, in both crystals of CaAlSi and SrAlSi, we point out the energy difference for the different propagation directions along the c axis and the c plane, in spite of the very close wave vector to the Brillouin-zone center. This energy difference cannot be explained by a usual Raman-scattering scenario at this stage.

  17. Acropora interbranch skeleton Sr/Ca ratios: Evaluation of a potential new high-resolution paleothermometer

    NASA Astrophysics Data System (ADS)

    Sadler, James; Nguyen, Ai D.; Leonard, Nicole D.; Webb, Gregory E.; Nothdurft, Luke D.

    2016-04-01

    The majority of coral geochemistry-based paleoclimate reconstructions in the Indo-Pacific are conducted on selectively cored colonies of massive Porites. This restriction to a single genus may make it difficult to amass the required paleoclimate data for studies that require deep reef coring techniques. Acropora, however, is a highly abundant coral genus in both modern and fossil reef systems and displays potential as a novel climate archive. Here we present a calibration study for Sr/Ca ratios recovered from interbranch skeleton in corymbose Acropora colonies from Heron Reef, southern Great Barrier Reef. Significant intercolony differences in absolute Sr/Ca ratios were normalized by producing anomaly plots of both coral geochemistry and instrumental water temperature records. Weighted linear regression of these anomalies from the lagoon and fore-reef slope provide a sensitivity of -0.05 mmol/mol °C-1, with a correlation coefficient (r2 = 0.65) comparable to those of genera currently used in paleoclimate reconstructions. Reconstructions of lagoon and reef slope mean seasonality in water temperature accurately identify the greater seasonal amplitude observed in the lagoon of Heron Reef. A longer calibration period is, however, required for reliable reconstructions of annual mean water temperatures.

  18. Polarization Domain Switching of Improper Hybrid Ferroelectric (Ca,Sr)3Ti2O7 Crystals

    NASA Astrophysics Data System (ADS)

    Lim, Seong Joon; Gao, Bin; Kim, Jaewook; Huang, Fei-Ting; Cheong, Sang-Wook; RCEM Team

    The observation of switchable polarization loops at room temperature in (Ca,Sr)3Ti2O7, induced by improper hybrid ferroelectricity, has drawn much attention. Since the ferroelectric polarization directly couples with structural distortions (oxygen octahedral tilting and rotation) in hybrid improper ferroelectrics, the energy barrier for polarization switching is predicted to be large, and the observation of ferroelectric polarization loops was a surprise. Furthermore, the observed complexity of the domain wall configuration in (Ca,Sr)3Ti2O7 may complicate the domain wall motion or the domain nucleation for polarization switching. Thus, it is imperative to understand the mechanism and dynamics of polarization domain switching. Particularly, it has to be clarified if polarization switching occurs through 90° or 180° switching. Comparing piezoresponse force microscope and polarized optical microscope images before and after applying electric fields consecutively, we explored the mechanism and dynamics of polarization domain switching. This work is funded by the Gordon and Betty Moore Foundation's EPiQS Initiative through Grant GBMF4413 to the Rutgers Center for Emergent Materials.

  19. Epitaxial growth of Ca(x)Sr(1-x)F2 layers on CaF2 by vacuum evaporation

    NASA Astrophysics Data System (ADS)

    Norton, Nicholas G.; Knight, K. S.

    The evaporation and epitaxial growth on single crystal CaF2 substrates of CaF2/SrF2 mixtures are investigated. The evaporated films are studied with X-ray diffraction and optical microscopy. The X-ray diffraction results show that the evaporation of yCaF2(+) (1 - y)srF2 mixtures from a single boat, with y in the range 0 to 1, result in single phase, mixed crystals of composition CaxSr1-xF2. If Vegard's law is assumed to apply it is found experimentally that the film composition is the same as that of the source. For the evaporation of CaF2 and SrF2 onto cleaved CaF2 crystals it is shown that the best quality epitaxial films are obtained at substrate temperatures of 400 C. Over 400 C there is broadening of the X-ray diffraction spots from the overlayer compared with those from the substrate. Below 400 C there is a tendency for the epitaxial films to delaminate from the substrate.

  20. Sr/Ca ratios in cold-water corals - a 'low-resolution' temperature archive?

    NASA Astrophysics Data System (ADS)

    Rüggeberg, Andres; Riethdorf, Jan-Rainer; Raddatz, Jacek; López Correa, Matthias; Montagna, Paolo; Dullo, Wolf-Christian; Freiwald, André

    2010-05-01

    One of the basic data to understand global change and past global changes is the measurement and the reconstruction of temperature of marine water masses. E.g. seawater temperature controls the density of seawater and in combination with salinity is the major driving force for the oceans circulation system. Geochemical investigations on cold-water corals Lophelia pertusa and Desmophyllum cristagalli indicated the potential of these organisms as high-resolution archives of environmental parameters from intermediate and deeper water masses (Adkins and Boyle 1997). Some studies tried to use cold-water corals as a high-resolution archive of temperature and salinity (Smith et al. 2000, 2002; Blamart et al. 2005; Lutringer et al. 2005). However, the fractionation of stable isotopes (delta18O and delta13C) and element ratios (Sr/Ca, Mg/Ca, U/Ca) are strongly influenced by vital effects (Shirai et al. 2005; Cohen et al. 2006), and difficult to interpret. Nevertheless, ongoing studies indicate the potential of a predominant temperature dependent fractionation of distinct isotopes and elements (e.g. Li/Ca, Montagna et al. 2008; U/Ca, Mg/Ca, delta18O, Lòpez Correa et al. 2008; delta88/86Sr, Rüggeberg et al. 2008). Within the frame of DFG-Project TRISTAN and Paläo-TRISTAN (Du 129/37-2 and 37-3) we investigated live-collected specimens of cold-water coral L. pertusa from all along the European continental margin (Northern and mid Norwegian shelves, Skagerrak, Rockall and Porcupine Bank, Galicia Bank, Gulf of Cadiz, Mediterranean Sea). These coral samples grew in waters characterized by temperatures between 6°C and 14°C. Electron Microprobe investigations along the growth direction of individual coral polyps were applied to determine the relationship between the incorporation of distinct elements (Sr, Ca, Mg, S). Cohen et al. (2006) showed for L. pertusa from the Kosterfjord, Skagerrak, that ~25% of the coral's Sr/Ca ratio is related to temperature, while 75% are influenced

  1. Crystal structure of the (Pb, Hg)Sr 2(Ca, Y)Cu 2O 7- δ superconductor

    NASA Astrophysics Data System (ADS)

    Liu, R. S.; Hu, S. F.; Chen, D. H.; Shy, D. S.; Jefferson, D. A.

    1994-03-01

    Bulk superconductivity up to 90 K has been achieved in the Hg containing cuprate (Pb, Hg)Sr 2(Ca 1- xY x)Cu 2O 7- δ when x=0.3, which has the highest Tc among the Pb based materials. The crystal structure of the newly discovered Hg containing Pb based 1212 phase has been investigated by Rietveld analysis of X-ray powder diffraction (XRD) data, selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM). We have identified the phase responsible for superconductivity in the so-called 1212 phase with a space group of P4/mmm and lattice constants of a=3.8166(1) Å and c=11.9484(4) Å for the x=0.5 sample. A disordering of the hole reservoir layer (Pb, Hg) due to the displacement of the oxygen ions and Pb/ Hg ions from their ideal positions of (0.5, 0.5, 0) to (0.39, 0.5, 0) and from (0, 0, 0) to (0.044, 0, 0), respectively, was found in the XRD refinement of the x=0.5 sample. This displacement may have given rise to the appearance of superlattice spots along the [104] ∗ direction with a commensurate modulation factor of 8 in the electron-diffraction pattern viewed down [010]. Moreover, mutual substitutions of cations (≈19% Cu in the Pb/Hg sites and ≈9% Hg in the Ca/Y sites) have been found in the sample.

  2. Experimentally determined Mg/Ca and Sr/Ca ratios in juvenile bivalve calcite for Mytilus edulis: implications for paleotemperature reconstructions

    NASA Astrophysics Data System (ADS)

    Wanamaker, Alan D., Jr.; Kreutz, Karl J.; Wilson, Tiffany; Borns, Harold W., Jr.; Introne, Douglas S.; Feindel, Scott

    2008-10-01

    To further evaluate the potential use of Mg/Ca and Sr/Ca ratios as a paleothermometer in the shell carbonate of the blue mussel Mytilus edulis, we grew juvenile mussels (˜15 mm shell height; <2 years old) collected from Maine, USA, in controlled environments for 4 months. The four-by-three factorial design consisted of four circulating temperature baths (7, 11, 15 and 19°C), and three salinity ranges (23, 28, and 32). During the experiment, water Mg/Ca and Sr/Ca molar ratios were monitored weekly, and showed little variation across all salinity and temperature ranges. Data from sampled shells including all salinity treatments yielded relatively poor relationships between shell elemental chemistry and water temperatures. However, if only the low salinity treatment data (23) are used, the relationships between shell elemental chemistry and water temperature improve moderately. Based on the data presented here, it may be possible to use Mg/Ca and Sr/Ca ratios from the shell carbonate of juvenile M. edulis to reconstruct paleotemperatures in estuarine settings (salinity below 24) with a corresponding RMSE (root mean squared error; 95% confidence interval) of ±2.4°C and ±2.8°C, respectively. In order for this methodology to be statistically meaningful, water temperature changes must be rather large, as the errors associated with using Mg/Ca and Sr/Ca ratios from the shell material of M. edulis are substantial. Further work is required to determine if the findings presented here can be duplicated, and if the potential salinity effect is pervasive.

  3. Barium and strontium as calcium substitutes for contractile responses in the rat tail artery.

    PubMed

    Ebeigbe, A B; Aloamaka, C P

    1985-01-01

    The ability of Ba2+ and Sr2+ to substitute for Ca2+ in contractile responses of the rat tail artery has been examined. Both Ba2+ and Sr2+ caused comparable contractions in Ca-depleted NA-stimulated, or K+-depolarized strips. Ba2+ and Sr2+ substitute poorly for Ca2+ at noradrenaline-sensitive membrane sites. At high concentrations, the three divalent cations stabilize the membrane in the order: Ca2+ greater than Sr2+ greater than Ba2+. The relaxation rates following high-K+ contractions were similar for all three divalent cations, suggesting a common mechanism for sequestration/extrusion. PMID:2414057

  4. Solid-state combinatorial screening of (Sr,Ca,Ba, Mg)₂Si₅N₈:Eu(2+) phosphors.

    PubMed

    Lee, Bonghyun; Lee, Sangjun; Jeong, Hyung Gon; Sohn, Kee-Sun

    2011-03-14

    We employed a solid-state combinatorial chemistry technique to screen 4 ternary phosphor systems: (Sr,Ca,Ba)(2)Si(5)N(8):Eu(2+), (Sr,Ca,Mg)(2)Si(5)N(8):Eu(2+), (Sr,Mg,Ba)(2)Si(5)N(8):Eu(2+), and (Ca,Ba,Mg)(2)Si(5)N(8):Eu(2+). The current pure nitride-based system did not allow for the use of conventional liquid solution-based high-throughput experimentation, so that a specially designed solid-state high-throughput powder-dispensing synthesis technique was employed. As a result, four well-defined ternary combinatorial libraries were developed in terms of photoluminescent (PL) intensity and color chromaticity with no skipped compositions, which provided a quantitative relationship between PL properties and the composition of AE(2)Si(5)N(8):Eu(2+) (AE = alkaline earth elements) phosphors. PMID:21275428

  5. Stimulatory effects of the degradation products from Mg-Ca-Sr alloy on the osteogenesis through regulating ERK signaling pathway.

    PubMed

    Li, Mei; He, Peng; Wu, Yuanhao; Zhang, Yu; Xia, Hong; Zheng, Yufeng; Han, Yong

    2016-01-01

    The influence of Mg-1Ca-xwt.% Sr (x = 0.2, 0.5, 1.0, 2.0) alloys on the osteogenic differentiation and mineralization of pre-osteoblast MC3T3-E1 were studied through typical differentiation markers, such as intracellular alkaline phosphatase (ALP) activity, extracellular collagen secretion and calcium nodule formation. It was shown that Mg-1Ca alloys with different content of Sr promoted cell viability and enhanced the differentiation and mineralization levels of osteoblasts, and Mg-1Ca-2.0Sr alloy had the most remarkable and significant effect among all. To further investigate the underlying mechanisms, RT-PCR and Western Blotting assays were taken to analyze the mRNA expression level of osteogenesis-related genes and intracellular signaling pathways involved in osteogenesis, respectively. RT-PCR results showed that Mg-1Ca-2.0Sr alloy significantly up-regulated the expressions of the transcription factors of Runt-related transcription factor 2 (RUNX2) and Osterix (OSX), Integrin subunits, as well as alkaline phosphatase (ALP), Bone sialoprotein (BSP), Collagen I (COL I), Osteocalcin (OCN) and Osteopontin (OPN). Western Blotting results suggested that Mg-1Ca-2.0Sr alloy rapidly induced extracellular signal-regulated kinase (ERK) activation but showed no obvious effects on c-Jun N terminal kinase (JNK) and p38 kinase of MAPK. Taken together, our results demonstrated that Mg-1Ca-2.0Sr alloy had excellent biocompatibility and osteogenesis via the ERK pathway and is expected to be promising as orthopedic implants and bone repair materials. PMID:27580744

  6. Stimulatory effects of the degradation products from Mg-Ca-Sr alloy on the osteogenesis through regulating ERK signaling pathway

    PubMed Central

    Li, Mei; He, Peng; Wu, Yuanhao; Zhang, Yu; Xia, Hong; Zheng, Yufeng; Han, Yong

    2016-01-01

    The influence of Mg-1Ca-xwt.% Sr (x = 0.2, 0.5, 1.0, 2.0) alloys on the osteogenic differentiation and mineralization of pre-osteoblast MC3T3-E1 were studied through typical differentiation markers, such as intracellular alkaline phosphatase (ALP) activity, extracellular collagen secretion and calcium nodule formation. It was shown that Mg-1Ca alloys with different content of Sr promoted cell viability and enhanced the differentiation and mineralization levels of osteoblasts, and Mg-1Ca-2.0Sr alloy had the most remarkable and significant effect among all. To further investigate the underlying mechanisms, RT-PCR and Western Blotting assays were taken to analyze the mRNA expression level of osteogenesis-related genes and intracellular signaling pathways involved in osteogenesis, respectively. RT-PCR results showed that Mg-1Ca-2.0Sr alloy significantly up-regulated the expressions of the transcription factors of Runt-related transcription factor 2 (RUNX2) and Osterix (OSX), Integrin subunits, as well as alkaline phosphatase (ALP), Bone sialoprotein (BSP), Collagen I (COL I), Osteocalcin (OCN) and Osteopontin (OPN). Western Blotting results suggested that Mg-1Ca-2.0Sr alloy rapidly induced extracellular signal-regulated kinase (ERK) activation but showed no obvious effects on c-Jun N terminal kinase (JNK) and p38 kinase of MAPK. Taken together, our results demonstrated that Mg-1Ca-2.0Sr alloy had excellent biocompatibility and osteogenesis via the ERK pathway and is expected to be promising as orthopedic implants and bone repair materials. PMID:27580744

  7. Average and local structure of the Pb-free ferroelectric perovskites (Sr,Sn)TiO3 and (Ba,Ca,Sn)TiO3

    DOE PAGESBeta

    Laurita, Geneva; Page, Katharine; Suzuki, Shoichiro; Seshadri, Ram

    2015-12-16

    The characteristic structural off -centering of Pb2+ in oxides, associated with its 6s2 lone pair, allows it to play a dominant role in polar materials, and makes it a somewhat ubiquitous component of ferroelectrics. In this work, we examine the compounds Sr0.9Sn0.1TiO3 and Ba0.79Ca0.16Sn0.05TiO3 using neutron total scattering techniques with data acquired at di erent temperatures. In these compounds, previously reported as ferroelectrics, Sn2+ appears to display some of the characteristics of Pb2+. We compare the local and long-range structures of the Sn2+-substituted compositions to the unsubstituted parent compounds SrTiO3 and BaTiO3. Lastly, we find that even at these smallmore » substitution levels, the Sn2+ lone pairs drive the local ordering behavior, with the local structure of both compounds more similar to the structure of PbTiO3 rather than the parent compounds.« less

  8. Significantly enhanced ferroelectricity and magnetic properties in (Sr0.5Ca0.5)TiO3-modified BiFeO3 ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Liu, Xiao Qiang; Chen, Xiang Ming

    2015-05-01

    BiFeO3 multiferroic ceramics were modified by introducing (Sr0.5Ca0.5)TiO3 to form solid solutions. The single phase structure was easy to be obtained in Bi1-x(Sr0.5Ca0.5)xFe1-xTixO3 (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi1-x(Sr0.5Ca0.5)xFe1-xTixO3 ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the present solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with Mr = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe3+ by Ti4+, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.

  9. The structure of molten CaSiO3: A neutron diffraction isotope substitution and aerodynamic levitation study.

    SciTech Connect

    Skinner, Lawrie; Benmore, Chris J; Weber, Richard; Santodonato, Louis J; Tumber, Sonia; Neuefeind, Joerg C; Lazareva, Lena; Du, Jincheng; Parise, John B

    2012-01-01

    We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO3, to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a re-distribution of Ca-O bond lengths, especially towards longer distances in the liquid. The first order neutron difference function provides a rigorous test of recent molecular dynamics simulations and supports the model of the presence of short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO3.

  10. Biological responses of brushite-forming Zn- and ZnSr- substituted beta-tricalcium phosphate bone cements.

    PubMed

    Pina, S; Vieira, S I; Rego, P; Torres, P M C; da Cruz e Silva, O A B; da Cruz e Silva, E F; Ferreira, J M F

    2010-01-01

    The core aim of this study was to investigate zinc (Zn)- and zinc and strontium (ZnSr)-containing brushite-forming beta-tricalcium phosphate (TCP) cements for their effects on proliferation and differentiation of osteoblastic-like cells (MC3T3-E1 cell line) as well as for their in vivo behaviour in trabecular bone cylindrical defects in a pilot study. In vitro proliferation and maturation responses of MC3T3-E1 osteoblastic-like cells to bone cements were studied at the cellular and molecular levels. The Zn- and Sr-containing brushite cements were found to stimulate pre-osteoblastic proliferation and osteoblastic maturation. Indeed, MC3T3-E1 cells exposed to the powdered cements had increased proliferative rates and higher adhesiveness capacity, in comparison to control cells. Furthermore, they exhibited higher alkaline phosphatase (ALP) activity and increased Type-I collagen secretion and fibre deposition into the extracellular matrix. Proliferative and collagen deposition properties were more evident for cells grown in cements doped with Sr. The in vivo osteoconductive propertiesof the ZnCPC and ZnSrCPC cements were also pursued. Histological and histomorphometric analyses were performed at 1 and 2 months after implantation, using carbonated apatite cement (Norian SRS) as control. There was no evidence of cement-induced adverse foreign body reactions, and furthermore ZnCPC and ZnSrCPC cements revealed better in vivo performance in comparison to the control apatite cement. Additionally, the presence of both zinc and strontium resulted in the highest rate of new bone formation. These novel results indicate that the investigated ZnCPC and ZnSrCPC cements are both biocompatible and osteoconductive, being good candidate materials to use as bone substitutes. PMID:20821372

  11. High-T(c) superconducting films of Bi-Pb-Sr-Ca-Cu oxide prepared by plasma spraying

    NASA Astrophysics Data System (ADS)

    Yoshida, Yuji; Kitahara, Shigeru; Togano, Kazumasa; Yuyama, Michinari; Inoue, Kiyoshi

    1989-04-01

    Superconducting properties and microstructures of the Bi-Pb-Sr-Ca-Cu oxide films prepared by plasma spraying have been studied. Films with a thickness of about 150 microns have been prepared from Bi(1.52)Pb(0.48)Sr(1.66)Ca(1.18)Cu(2.31)O(x) powders. The as-sprayed films, deposited on nickel substrate, are amorphous and not superconductive. After annealing in air at 840 C the films exhibit a zero-resistance temperature of 107 K (zero field) with a transition width of about 11 K.

  12. Introduction of artificial pinning centres in Bi2Sr2CaCu2O8 ceramics

    NASA Technical Reports Server (NTRS)

    Majewski, P.; Elschner, S.; Bestgen, H.; Aldinger, F.

    1995-01-01

    Considering the phase equilibrium diagram of the system Bi203-SrO-CaO-CuO, single phase 'Bi2Sr2CaCu208' ceramics have been transformed by a simple annealing procedure into multiphase samples. The transformation results in the formation of second phases and in an increase of the intra-grain critical current density at 1 T of five times. This increase is believed to express improved pinning properties of the superconducting crystals. The prepared pinning centers are believed to be e.g. coherent precipitates (Guinier-Preston-zones) within the superconducting crystals.

  13. The effect of replacement of Sr by Ca on the structural and luminescence properties of the red-emitting Sr{sub 2}Si{sub 5}N{sub 8}:Eu{sup 2+} LED conversion phosphor

    SciTech Connect

    Li, Y.Q.; With, G. de; Hintzen, H.T.

    2008-03-15

    The influence of the replacement of Sr by Ca on structural and luminescence properties of Eu{sup 2+}-doped Sr{sub 2}Si{sub 5}N{sub 8} is reported. The Rietveld refinement of the powder X-ray diffraction data shows that the Ca{sup 2+} ion preferentially occupies the larger Sr site in Sr{sub 2}Si{sub 5}N{sub 8}:Eu{sup 2+}. Although the excitation spectrum is hardly modified, the position of the emission band of Eu{sup 2+} can be tailored through partial replacement of Sr by Ca in Sr{sub 2}Si{sub 5}N{sub 8}:Eu{sup 2+}, resulting in red-emission shifting from 620 to 643 nm. Furthermore, (Sr, Ca){sub 2}Si{sub 5}N{sub 8}:Eu{sup 2+} shows high potential as a conversion phosphor for white-light LED applications due to similar absorption, conversion efficiency and thermal quenching behaviour for 465 nm excitation after the introduction of the Ca ion. - Graphical abstract: The temperature dependence of the luminescence efficiency of M{sub 1.9}Eu{sub 0.1}Si{sub 5}N{sub 8} (M=Ca, Sr, Ba) and Sr{sub 1.3}Ca{sub 0.6}Eu{sub 0.1}Si{sub 5}N{sub 8} ({lambda}{sub exc}=465 nm)

  14. Optical Properties of Blue-Light-Emitting (Ca,Sr)Mg2Si3O9:Eu2+ Phosphor

    NASA Astrophysics Data System (ADS)

    Lee, Hyun Ju; Choi, Sung Hwan; Kim, Kyung Pil; Shin, Hyun Ho; Yoo, Jae Soo

    2010-10-01

    For light-emitting diode (LED) excitation at 400 nm, the optical properties of a Eu2+-activated CaO-SrO-MgO-SiO2 material system were investigated. All the materials were synthesized by solid state reaction. In particular, (Ca,Sr)Mg2Si3O9:Eu2+, which has the same crystal structure as CaMgSi2O6, was found to be promising as a blue-light-emitting phosphor for near UV LED application. The luminance intensity was optimized by controlling the Eu2+ concentration and the composition of the host lattice. The ratio of calcium ions to strontium ions was a convenient parameter for adjusting the maximum excitation peak to 400 nm, which is favorable for near UV LED excitation. The highest luminance intensity of Ca1-x-ySryMg2Si3O9:Eux2+ under 405 nm excitation was achieved at the Eu2+ concentration of x=0.01 and a Sr2+ concentration of y=0.3. The luminance intensity of (Ca,Sr)Mg2Si3O9:Eu2+ was found to be superior to that of a commercial blue-light-emitting BaMgAl10O17:Eu2+ phosphor, which is used for near-UV LED excitation.

  15. Magnetoresistance and thermoelectric power of the Bi-Sr-Ca-Cu-O system

    SciTech Connect

    Mandal, P.; Poddar, A.; Das, A.N.; Chakraborty, A.; Ghosh, B.; Choudhury, P.; Lahiri, S.K.

    1988-11-01

    We report measurements of the electrical resistance, magnetoresistance, upper critical field, and thermoelectric power of Bi/sub 1/Sr/sub 1/Ca/sub 1/Cu/sub 2/O/sub x/. In the mixed-phase sample, the magnetoresistance is negligible above 120 K. It starts increasing at 116 K, passes through a maximum at about 103 K, and is followed by a sharp increase around 85 K. The thermoelectric power is positive and the hole concentration obtained from the room-temperature value of thermoelectric power is 0.165, which is in good agreement with the value 0.15 obtained by Tarascon et al. from titration and thermogravimetric-analysis experiments.

  16. Preparation of Bi-Sr-Ca-Cu-O thin film by coevaporation and its thermal stability

    SciTech Connect

    Yoshitake, T.; Fujita, J.; Kubo, Y.; Igarashi, H.; Satoh, T.

    1989-02-06

    Thin film with a high T/sub c/ single phase was prepared on a (100)MgO substrate at a substrate temperature of about 620 /sup 0/C by coevaporation of Bi/sub 2/O/sub 3/, Sr, Ca, and Cu metal. The resistive superconducting transition with onset T/sub c/ of 80 K was observed for this film. By post-deposition annealing at 850 /sup 0/C, the high T/sub c/ phase was transformed into a low T/sub c/ phase, while films annealed at a higher temperature such as 890 /sup 0/C maintained the high T/sub c/ phase. These results indicated that the high T/sub c/ phase can exist only at the high-temperature region (approx.890 /sup 0/C) while the stable phase existing at the low-temperature region (approx.850 /sup 0/C) is the low T/sub c/ phase.

  17. Transport in atomically engineered BiSrCaCuO multilayers

    SciTech Connect

    Bozovic, I.; Eckstein, J.N.

    1995-10-01

    The authors have utilized atomic layer deposition to synthesize single crystal thin films of cuprate superconductors, as well as a variety of superlattices and multilayer heterostructures with atomically abrupt interfaces. For example, they made trilayer structures with the top and the bottom BiSrCaCuO electrodes separated by titanate barriers that were only 4 {angstrom} thick and yet free of pinholes over macroscopic areas. This unique synthetic capability made it possible to study transport in the c-axis direction under controlled and systematically varied conditions. Taken together, these experiments provide a picture of the c-axis transport in 2201, 2212, and various heterostructures under study. In particular, they suggest presence of a large density of localized states near the Fermi level and thus support a two-component description of the electron system in these compounds.

  18. Axial anisotropy of intergrain critical current in Bi-Pb-Sr-Ca-Cu-O

    NASA Astrophysics Data System (ADS)

    Umemura, Toshio; Egawa, Kunihiko; Wakata, Mitsunobu; Yoshizaki, Kiyoshi; Ni, Baorong; Matsushita, Teruo

    1990-08-01

    The intergrain critical current densities, J c, parallel and perpendicular to c-axis were measured as a function of the magnetic field at 4.2 and 77.3K by an ac inductive method for the fairly oriented Bi 1.6Pb 0.4Sr 2Ca 2Cu 3O y specimens. The J c's perpendicular to c-axis were higher than those parallel c-axis, about ten times within 5T at 4.2K, and about three times within 0.1T at 77.3K. Our results suggect the orientation of each grain to be especially worthwhile for performing the high J c at the low temperature.

  19. Fabrication and characterization of (Bi,Pb)-Sr-Ca-Cu-O (2223) bars

    SciTech Connect

    Chudzik, M.P.; Polzin, B.J.; Thayer, R.; Picciolo, J.J.; Fisher, B.L.; Lanagan, M.T.

    1996-08-01

    Bulk bars for current lead applications were fabricated from (Bi,Pb)- Sr-Ca-Cu-O (Bi-2223) for low thermal conductivity and high critical current. Bars measuring 17.8 cm in length were made by uniaxially pressing Bi-2223 powder of controlled (1.7/0.34)223 and (1.8/0.4)223 phase composition. The bulk bars were densified by subjecting them to a schedule of alternate liquid-phase sintering and cold isostatic pressing. Liquid phase sintering temperatures were optimized from differential thermal analysis and microstructure morphology. Phase purity and microstructure were evaluated by x-ray diffraction and scanning electron microscopy. Low-resistance silver contacts were applied to the bars by hot-pressing at 820{degrees}C and 3 MPa. Critical current densities {approx} 1000 A/cm{sup 3} (critical currents of 750 A at 77 K in self-field conditions) were achieved.

  20. The role of π-bonding on the high temperature structure of the double perovskites Ba2CaUO6 and BaSrCaUO6.

    PubMed

    Reynolds, Emily; Thorogood, Gordon J; Avdeev, Maxim; Brand, Helen E A; Gu, Qinfen; Kennedy, Brendan J

    2015-09-28

    The high temperature structural behaviour of the uranium perovskites Ba2CaUO6 and BaSrCaUO6 has been investigated using a combination of synchrotron X-ray and neutron powder diffraction. Ba2CaUO6 undergoes a complex sequence of structures associated with the progressive loss of cooperative octahedral tilting: P21/n → I2/m → I2/m → I4/m → Fm3[combining macron]m. The observation of the intermediate tetragonal structure, I4/m, in this, contrasts with the previously reported rhombohedral R3[combining macron] intermediate formed by the Ba2SrUO6 oxide. The importance of π-bonding in determining the structural sequence is discussed. PMID:26286063

  1. Sr{sub 2}CaW{sub x}Mo{sub 1−x}O{sub 6}:Eu{sup 3+}, Li{sup +}: An emission tunable phosphor through site symmetry and excitation wavelength

    SciTech Connect

    Xiao, Ning; Shen, Jun; Xiao, Tengjiao; Wu, Bing; Luo, Xiaobing; Li, Li; Wang, Zhongqing; Zhou, Xianju

    2015-10-15

    The emission of Eu{sup 3+} doped Sr{sub 2}CaW{sub x}Mo{sub 1−x}O{sub 6} phosphors could be tunable by the site symmetry of the activators and the excitation wavelengths. - Highlights: • The emission of Eu{sup 3+} depends on site symmetry and excitation wavelengths. • The color of the samples was tunable by structure and excitation wavelength. • The effect of W and Eu content on the properties of the samples was investigated. - Abstract: A series of Eu{sup 3+} substituted double-perovskite Sr{sub 2}CaW{sub x}Mo{sub 1−x}O{sub 6} phosphors were prepared by solid state reactions. The phase, photoluminescence and energy transfer of the phosphors were investigated by X-ray diffraction (XRD), photoluminescence (PL) and luminescence decay respectively. It is found that the emission of the Eu{sup 3+} substituted double perovskites depends on both the site symmetry of the activators and the excitation wavelengths. Based on the decay analysis of Sr{sub 2}CaW{sub x}Mo{sub 1−x}O{sub 6} matrix and Eu{sup 3+} doped samples, the energy transfer efficiencies between the host and activators Eu{sup 3+} were investigated. The results of the emission tunable phosphors indicate their potential applications in LEDs.

  2. Effects of SCN substitution for Cl- on tension, [Ca2+]i, and ionic currents in vascular smooth muscle.

    PubMed

    Standley, P R; Zhang, F; Ravi, J; Ram, J L; Sowers, J R

    1996-01-01

    Substitution of thiocyanate ions (SCN-) for chloride ions (Cl-) in the extracellular medium of aortic rings and strips causes a biphasic contractile response; initial relaxation followed by sustained contraction. Alterations in these responses are sex-specific, and may elucidate fundamental differences in vascular function between males and females. In order to investigate the role of changes in intracellular Ca2+ ([Ca2+]i) in these changes in tension, we investigated effects of SCN- on [Ca2+]i and ionic currents in vascular smooth muscle cells (VSMC). Extracellular substitution of SCN- for Cl- caused a biphasic change in [Ca2+]i. Initially, [Ca2+]i decreased, reaching a minimum within 1-2 min, subsequently returned to original levels within 4-5 min, and then increased to a higher plateau over the next 10 minutes. This pattern of change in [Ca2+]i is identical to the pattern of tension changes in aortic rings, but it occurs somewhat faster. Partial substitution of SCN- for Cl- elicited increased, but no preceding decrease in [Ca2+]i. In the absence of external Ca2+, anion substitution elicited the decrease in [Ca2+]i but not the subsequent increase. Verapamil (1 microM) blocked the increased [Ca2+]i phase but not the decreased [Ca2+]i phase; whereas, R+ verapamil (up to 5 microM for 20 min), an inactive enantiomer, caused no change. Ionic current measurements obtained using whole cell patch and current clamp techniques revealed two responses to anion substitution: (a) a rapid, transient outward shift in holding current, and (b) a sustained increase in peak current and a hyperpolarizing shift in voltage sensitivity of Ca2+ channels. The calcium channel blocker PN200-110 blocked SCN(-)-enhanced current but had no effect on the changes in holding current. S- verapamil, but not R+ verapamil, reduced SCN(-)-enhanced current. In current clamp mode, SCN- caused an initial hyperpolarization followed by a slow depolarization punctuated by spikes. Thus, SCN- causes changes

  3. Effect of local A-site strain on dipole stability in A6GaNb9O30 (A = Ba, Sr, Ca) tetragonal tungsten bronze relaxor dielectrics.

    PubMed

    Miller, Andrew J; Rotaru, Andrei; Arnold, Donna C; Morrison, Finlay D

    2015-06-21

    A series of isovalently A-site substituted relaxor dielectric tetragonal tungsten bronzes of general formula Ba(6-x-y)Sr(x)Ca(y)GaNb(9)O(30) were investigated. The long-range (average) crystal structure as determined by conventional diffraction techniques varies monotonically according to Vegard's law. The dielectric properties, however, do not display a similar, simple "average size" dependence and instead show a dependence on the statistical size variance, i.e. size mismatch, of the A-cation. The difficulties in Vogel-Fulcher analysis of relative permittivity and the complementary approach of using dielectric loss data fitted to Jonscher's empirical universal dielectric relaxation model is discussed. PMID:25687218

  4. Dopant-Induced Nanoscale Electronic Inhomogeneities in Ca2-xSrxRuO4

    SciTech Connect

    Zhang, Jiandi; Ismail, #; Moore, R. G.; Wang, S. -C.; Ding, H.; Jin, Rongying; Mandrus, David; Plummer, E Ward

    2006-01-01

    Ca{sub 2-x}Sr{sub x}RuO{sub 4} single crystals with 0.1 {le} x {le} 2.0 have been studied systematically using scanning tunneling microscopy (STM) and spectroscopy, low-energy electron diffraction, and angle resolved photoelectron spectroscopy (ARPES). In contrast with the well-ordered lattice structure, the local density of states at the surface clearly shows a strong doping dependent nanoscale electronic inhomogeneity, regardless of the fact of isovalent substitution. Remarkably, the surface electronic roughness measured by STM and the inverse spectral weight of quasiparticle states determined by ARPES are found to vary with x in the same manner as the bulk in-plane residual resistivity, following the Nordheim rule. For the first time, the surface measurements - especially those with STM - are shown to be in good agreement with the bulk transport results, all clearly indicating a doping-induced electronic disorder in the system.

  5. High temperature phase equilibria studies in the Bi-Sr-Ca-Cu-O-Ag system

    SciTech Connect

    Margulies, Lawrence

    1999-11-08

    A variety of experimental techniques were utilized to examine the high temperature phase equilibria in the Bi-Sr-Ca-Cu-O-Ag system. Quenching studies were used to determine the liquid solubility of Ag in the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO{sub 2}). A liquid immiscibility region between oxide and Ag liquids in the 8--98 at% range was found above 900 C. Two eutectics were found in the Bi2212-Ag pseudobinary. On the oxide rich side, a eutectic exists at approximately 4 at% Ag. On the Ag rich side, a eutectic exists at approximately 98 at% Ag at a temperature of 15 C below the melting point of pure Ag. Six distinct solid phases were found to be in equilibrium with the partial melt within the Ag content and PO{sub 2} range studied. The stability of these solid phases were found to be highly sensitive to PO{sub 2}, and to a much lesser extent Ag content. High temperature x-ray diffraction (HTXRD) studies of this system are in conflict with these results. It is suggested that these discrepancies are due to experimental artifacts caused by the significant thermal gradients and lack of full bulk sampling which is inherent in conventional HTXRD designs. In part 2, a new furnace design compatible with synchrotron radiation sources is introduced to address these problems. This design allows for full bulk sampling in a low thermal gradient environment using Debye-Scherrer transmission geometry. Sample spinning is also introduced in the design to eliminate preferred orientation and incomplete powder averaging and allow for quantitative phase analysis and structural refinement. Studies on model systems are presented to demonstrate the capabilities for high resolution structural studies (Al{sub 2}O{sub 3}) and time resolved phase transformation studies (SrCO{sub 3}). Finally, the Bi2212 system is examined to confirm the quenching results

  6. Growth of nucleation sites on Pb-doped Bi2Sr2Ca1Cu2O8 + delta

    NASA Astrophysics Data System (ADS)

    Finnemore, D. K.; Xu, Ming; Kouzoudis, D.; Bloomer, T.; Kramer, M. J.; McKernan, Stuart; Balachandran, U.; Haldar, Pradeep

    1996-01-01

    In the growth of Bi2Sr2Ca2Cu3O10+δ from mixed powders of Pb-doped Bi2Sr2Ca1Cu2O8+δ and other oxides, it has been discovered that a dense array of hillocks or mesas grow at the interface between a Ag overlay and Pb-doped Bi2Sr2Ca1Cu2O8+δ grains during the ramp up to the reaction temperature. As viewed in an environmental scanning electron microscope, the Ag coated grains develop a texture that looks like ``chicken pox'' growing on the grains at about 700 °C. These hillocks are about 100 nm across and are spaced at about 500 to 1000 nm. If there is no Ag, this texture does not develop. Preliminary measurements indicate that the hillocks are a recrystallization of (Bi,Pb)2Sr2Ca1Cu2O8+δ, and are definitely not a Pb rich phase.

  7. Chemical removal of contaminants from thin film Bi4Sr3Ca3Cu4O(16 + x) surfaces

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Housley, R. M.

    1990-01-01

    A solution of Br in absolute ethanol, previously shown to be effective in removing nonsuperconducting species from Y-Ba-Cu-O thin film surfaces, is shown also to be effective in treating Bi-Sr-Ca-Cu-O thin film surfaces. X-ray photoelectron spectra obtained after etching are consistent with previously reported results obtained from samples cleaved or scraped in vacuum.

  8. Pb solubility of the high-temperature superconducting phase Bi2Sr2Ca2Cu3O(10+d)

    NASA Technical Reports Server (NTRS)

    Kaesche, Stefanie; Majewski, Peter; Aldinger, Fritz

    1995-01-01

    For the nominal composition of Bi(2.27-x)Pb(x)Sr2 Ca2 Cu3 O(10+d) lead content was varied from x = 0.05 to 0.45. The compositions were examined between 830 and 890 C which is supposed to be the temperature range over which the so-called 2223 phase (Bi2Sr2Ca2Cu3O(10+d)) is stable. Only compositions between x = 0.18 to 0.36 could be synthesized in a single phase state. For x is greater than 0.36 a lead containing phase with a stoichiometry of Pb4(Sr,Ca)5CuO(d) is formed, for x is less than 0.18 mainly Bi2Sr2CaCu2O(10+d) and cuprates are the equilibrium phases. The temperature range for the 2223 phase was found to be 830 to 890 C but the 2223 phase has extremely varying cation ratios over this temperature range. Former single phase 2223 samples turn to multi phase samples when annealed at slightly higher or lower temperatures. A decrease in the Pb solubility with increasing temperature was found for the 2223 phase.

  9. Sea Surface Temperature Records Using Sr/Ca Ratios in a Siderastrea siderea Coral from SE Cuba

    NASA Astrophysics Data System (ADS)

    Fargher, H. A.; Hughen, K. A.; Ossolinski, J. E.; Bretos, F.; Siciliano, D.; Gonzalez, P.

    2015-12-01

    Sea surface temperature (SST) variability from Cuba remains relatively unknown compared to the rest of the Caribbean. Cuba sits near an inflection point in the spatial pattern of SST from the North Atlantic Oscillation (NAO), and long SST records from the region could reveal changes in the influence of this climate system through time. A Siderastrea siderea coral from the Jardínes de la Reina in southern Cuba was drilled to obtain a 220 year long archive of environmental change. The genus Siderastrea has not been extensively studied as an SST archive, yet Sr/Ca ratios in the Cuban core show a clear seasonal signal and strong correlation to instrumental SST data (r2 = 0.86 and 0.36 for monthly and interannual (winter season) timescales, respectively). Annual growth rates (linear extension) of the coral are observed to have a minor influence on Sr/Ca variability, but do not show a direct correlation to SST on timescales from annual to multidecadal. Sr/Ca measurements from the Cuban coral are used to reconstruct monthly and seasonal (winter, summer) SST extending back more than two centuries. Wintertime SST in southern Cuba is compared to other coral Sr/Ca records of winter-season SST from locations sensitive to the NAO in order to investigate the stationarity of the NAO SST 'fingerprint' through time.

  10. Antiferromagnetism in CaAl2Si2-type CaMn2As2 and SrMn2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; Johnston, D. C.

    Magnetic susceptibility versus temperature χ (T) measurements of CaMn2As2 and SrMn2As2 crystals show clear antiferromagnetic (AFM) transitions at TN ~ 65 K and 120 K,1 respectively. The anisotropic behaviors in χ (T <=TN) suggest that both compounds are noncollinear antiferromagnets which may result either from an intrinsic noncollinear structure or from multiple collinear AFM domains that are not aligned collinearly.2 The χ (T) data at T >TN reveal that both compounds exhibit strong short-range AFM ordering, evidently associated with quasi-two-dimensional spin lattices. The electrical resistivities show insulating ground states with activation energies of ~ 63 meV in CaMn2As2 and 44 meV in SrMn2As2 . The experimental results thus reveal that both (Ca , Sr) Mn2As2 materials are AFM insulators at low temperatures and in analogy with the high Tc cuprates, may be potential parent compounds for CaAl2Si2-type superconductors. Work was supported by the USDOE under Contract No. DE-AC02-07CH11358.

  11. Erase-mode recording characteristics of photochromic CaF2, SrTiO3, and CaTiO3 crystals.

    NASA Technical Reports Server (NTRS)

    Duncan, R. C., Jr.

    1972-01-01

    Erase-mode optical recording characteristics of photochromic crystal wafers of CaF2:La,Na; CaF2:Ce,Na; SrTiO3:Ni,Mo,Al; and CaTiO3:Ni,Mo have been measured. An argon laser operating at 5145 A was used for both optical recording and optical readout. Sensitometric curves of optical-density change versus logarithm of exposure are shown for a number of erase-beam intensities between 0.2 mW/sq cm and 2 W/sq cm. In this range, time-intensity reciprocity holds for the CaF2 materials but fails for the titanates, particularly at low intensities. The dependences of sensitivity, gamma, and maximum transmission contrast ratio on wafer thickness and material are discussed. Wafers of SrTiO3, CaTiO3, and CaF2 exhibiting approximately equal maximum contrast ratios have relative sensitivities approximately in the ratio 5:2:1, respectively, at an erase intensity of 1 W/sq cm.

  12. I(f) and SR Ca(2+) release both contribute to pacemaker activity in canine sinoatrial node cells.

    PubMed

    Gao, Zhan; Chen, Biyi; Joiner, Mei-Ling A; Wu, Yuejin; Guan, Xiaoqun; Koval, Olha M; Chaudhary, Ashok K; Cunha, Shane R; Mohler, Peter J; Martins, James B; Song, Long-Sheng; Anderson, Mark E

    2010-07-01

    Increasing evidence suggests that cardiac pacemaking is the result of two sinoatrial node (SAN) cell mechanisms: a 'voltage clock' and a Ca(2+) dependent process, or 'Ca(2+) clock.' The voltage clock initiates action potentials (APs) by SAN cell membrane potential depolarization from inward currents, of which the pacemaker current (I(f)) is thought to be particularly important. A Ca(2+) dependent process triggers APs when sarcoplasmic reticulum (SR) Ca(2+) release activates inward current carried by the forward mode of the electrogenic Na(+)/Ca(2+) exchanger (NCX). However, these mechanisms have mostly been defined in rodents or rabbits, but are unexplored in single SAN cells from larger animals. Here, we used patch-clamp and confocal microscope techniques to explore the roles of the voltage and Ca(2+) clock mechanisms in canine SAN pacemaker cells. We found that ZD7288, a selective I(f) antagonist, significantly reduced basal automaticity and induced irregular, arrhythmia-like activity in canine SAN cells. In addition, ZD7288 impaired but did not eliminate the SAN cell rate acceleration by isoproterenol. In contrast, ryanodine significantly reduced the SAN cell acceleration by isoproterenol, while ryanodine reduction of basal automaticity was modest ( approximately 14%) and did not reach statistical significance. Importantly, pretreatment with ryanodine eliminated SR Ca(2+) release, but did not affect basal or isoproterenol-enhanced I(f). Taken together, these results indicate that voltage and Ca(2+) dependent automaticity mechanisms coexist in canine SAN cells, and suggest that I(f) and SR Ca(2+) release cooperate to determine baseline and catecholamine-dependent automaticity in isolated dog SAN cells. PMID:20380837

  13. Effects of K doping on structural and superconducting properties of Bi{sub 1.5}Pb{sub 0.5}Sr{sub 1.8}CaCu{sub 2}O{sub 8+δ} compounds

    SciTech Connect

    Belala, K; Mosbah, M. F.

    2013-12-16

    Two kinds of potassium doped Bi(Pb)2212 samples are used to investigate the effect of doping the Bi(Pb)2212 ((Bi,Pb){sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}) phase by potassium (K): In the first one K is substituted on the Sr site; In the second one K is added. Using the solid state method reaction samples of Bi{sub 1.5}Pb{sub 0.5}(Sr{sub 1.8−x}K{sub x})CaCu{sub 2}O{sub 8+d} and Bi{sub 1.5}Pb{sub 0.5}Sr{sub 1.8}CaCu{sub 2}O{sub 8+d}K{sub x} (0 ≤ x≤ 0.05) have been prepared from powders of carbonates and primary oxides having purity over 99%. The samples have been characterized by X ray diffraction (XRD), scanning electron microscopy (SEM) and resistivity versus temperature measurements. Results show how the kind and the rate of doping by potassium affects the structural and transport properties of Bi(Pb)2212 phase.

  14. Effect of heterovalent substitution at Mn site on the magnetic and transport properties of La0.67Sr0.33MnO3

    NASA Astrophysics Data System (ADS)

    Priolkar, K. R.; Rawat, R.

    Magnetic and transport properties of Ti substituted La0.67Sr0.33MnO3 are drastically affected with a change in preparation conditions. Low temperature infra-red absorption measurements reveal that this is perhaps due to inhomogeniety in substitution of Ti on Mn sites. It is found that, in the high temperature annealed samples, the substitution of Ti supresses the double exchange interaction due to the formation of Mn-O- Ti chains. While in the low temperature annealed case substitution of Ti causes formation of isolated ferromagnetic clusters linked to each other by a variable range hopping polaron.

  15. Synthesis and luminescence characterization of Sr(0.5)Ca(0.5)TiO3:Sm(3+) phosphor.

    PubMed

    Vidyadharan, Viji; Remya, Mohan P; Gopi, Subhash; Thomas, Sunil; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2015-11-01

    The spectroscopic properties of trivalent samarium doped Sr0.5Ca0.5TiO3 perovskite phosphor material (Sr0.5Ca0.5TiO3:xSm(3+), x=0.05, 0.1, 0.5, 1, 1.5) synthesized by the solid state method have been studied. The X-Ray Diffraction profile confirms the orthorhombic perovskite Sr0.5Ca0.5TiO3 structure of the prepared samples. The SEM study reveals the surface morphology. The Judd-Ofelt intensity parameters were calculated for 0.5 wt% Sm(3+) doped Sr0.5Ca0.5TiO3. Transition probabilities, branching ratios and radiative lifetime were evaluated by using Judd-Ofelt analysis. The emission spectra under 405 nm excitation shows five emission peaks at 564 nm, 599 nm, 645 nm, 707 nm and 776 nm corresponding to the transitions (4)G5/2→(6)Hj (j=5/2, 7/2, 9/2, 11/2 and 13/2) respectively. The higher values of branching ratio and stimulated emission cross-section for (4)G5/2→(6)H7/2 transition of Sr0.5Ca0.5TiO3:0.5 wt% Sm(3+) shows its suitability in the field of visible lasers and optical fiber amplifiers. The experimental lifetimes of Sm(3+) doped samples were estimated using the decay curves corresponding to (4)G5/2→(6)H7/2 transition upon 405 nm excitation. Concentration dependence on emission intensity and experimental lifetime were also studied. From the CIE diagram we can see that as the concentration of Sm(3+) ions increases from 0.05 wt% to 1.5 wt% the CIE color co-ordinates changes from greenish yellow to yellowish orange. PMID:26057096

  16. Synthesis, characterization and biological evaluation of strontium/magnesium-co-substituted hydroxyapatite.

    PubMed

    Geng, Zhen; Wang, Renfeng; Li, Zhaoyang; Cui, Zhenduo; Zhu, Shengli; Liang, Yanqin; Liu, Yunde; Huijing, Bao; Li, Xue; Huo, Qianyu; Liu, Zhili; Yang, Xianjin

    2016-07-01

    The present study aims to investigate the contribution of two biologically important cations, Mg(2+) and Sr(2+), when co-substituted into the structure of hydroxyapatite (Ca10(PO4)6(OH)2, HA). The substituted samples were synthesized by a hydrothermal method that involved the addition of Mg(2+) and Sr(2+) containing precursors to partially replace Ca(2+) in the apatite structure. Four co-substituted HA samples with different concentrations of Mg(2+) and Sr(2+) ((Mg + Sr)/(Mg + Sr + Ca) = 30%) were investigated, and they were compared with pure HA. Experimental results showed that only a limited amount of Mg (Mg/(Mg + Ca + Sr) < 14%) could successfully substitute for Ca in HA. In addition, Mg substitution resulted in reduced crystallinity, thermal stability and lattice parameters of HA. In contrast, Sr could fully substitute for Ca. Furthermore, the addition of Sr increased the lattice parameters of HA. Here, we obtained the cation leach liquor by immersing the prepared samples in a culture medium for cell experiments. The in vitro study showed that 10Mg20Sr promoted better MG63 cell attachment, proliferation and differentiation than HA. Thus, the presence of an appropriate proportion of Mg and Sr could play a significant role in the increased biocompatibility of HA. PMID:26916949

  17. Ion microprobe assessment of the heterogeneity of Mg/Ca, Sr/Ca and Mn/Ca ratios in Pecten maximus and Mytilus edulis (bivalvia) shell calcite precipitated at constant temperature

    NASA Astrophysics Data System (ADS)

    Freitas, P. S.; Clarke, L. J.; Kennedy, H.; Richardson, C. A.

    2009-01-01

    Small-scale heterogeneity of biogenic carbonate elemental composition can be a significant source of error in the accurate use of element/Ca ratios as geochemical proxies. In this study ion microprobe (SIMS) profiles showed significant small-scale variability of Mg/Ca, Sr/Ca and Mn/Ca ratios in new shell calcite of the marine bivalves P. maximus and Mytilus edulis that was precipitated during a constant-temperature culturing experiment. Elevated Mg/Ca, Sr/Ca and Mn/Ca ratios were found to be associated with the deposition of elaborate shell features, i.e. a shell surface stria in P. maximus and surface shell disturbance marks in both species, the latter a common occurrence in bivalve shells. In both species the observed small-scale elemental heterogeneity most likely was not controlled by variable transport of ions to the extra-pallial fluid, but by factors such as shell Mg content influencing Sr and Mn heterogeneity, the influence of shell organic content and/or conditions at the shell crystal-solution interface. Invariant Mg/Ca ratios observed in the mid and innermost regions of the P. maximus shell suggests a potential application as a palaeotemperature proxy.

  18. Diffusion phenomena and crystallization path during the growth of LFZ Bi-Sr-Ca-Cu-O superconducting fibres

    NASA Astrophysics Data System (ADS)

    Costa, F. M.; Silva, R. F.; Vieira, J. M.

    2001-11-01

    The laser floating zone technique is used to grow highly textured fibres in the Bi-Sr-Ca-Cu-O superconducting system. Composition profiles along the fibre axis show a strong segregation of Bi to the molten zone, this region being depleted of Ca. Maximum and minimum values of the effective distribution coefficients (k) of cations are determined, the extreme values of segregation being kCa = 1.64 and kBi = 0.60. The dependence of k on the pulling rate R allowed the calculation of the equilibrium distribution coefficients k0 of the elements and of the average diffusion coefficients DBi = 1.2×10-10 m2 s-1, DSr = 2.7×10-10 m2 s-1 and DCa = 12.8×10-10 m2 s-1 in the Cu-rich melt. The approximate length of the diffusion layer δ is 21 µm. The crystallization path is represented in the composition tetrahedron of Bi2O3-SrO-CaO-CuO. Liquid immiscibility is observed. The non-superconducting (Sr0.3Ca0.7)CuO2 (`1/1') phase, with dendritic morphology, is the first phase to solidify. The superconducting matrix is the result of an early nucleation of `4413' intergrowth on the surface of `1/1' dendrites followed by the side-by-side crystallization of the `4413' and `2212' phases from a peritetic-type reaction.

  19. The Solid Solution Sr(1-x)Ba(x)Ga2: Substitutional Disorder and Chemical Bonding Visited by NMR Spectroscopy and Quantum Mechanical Calculations.

    PubMed

    Pecher, Oliver; Mausolf, Bernhard; Lamberts, Kevin; Oligschläger, Dirk; Niewieszol, Carina; Englert, Ulli; Haarmann, Frank

    2015-09-28

    Complete miscibility of the intermetallic phases (IPs) SrGa2 and BaGa2 forming the solid solution Sr(1-x)Ba(x)Ga2 is shown by means of X-ray diffraction, thermoanalytical and metallographic studies. Regarding the distances of Sr/Ba sites versus substitution degree, a model of isolated substitution centres (ISC) for up to 10% cation substitution is explored to study the influence on the Ga bonding situation. A combined application of NMR spectroscopy and quantum mechanical (QM) calculations proves the electric field gradient (EFG) to be a sensitive measure of different bonding situations. The experimental resolution is boosted by orientation-dependent NMR on magnetically aligned powder samples, revealing in first approximation two different Ga species in the ISC regimes. EFG calculations using superlattice structures within periodic boundary conditions are in fair agreement with the NMR spectroscopy data and are discussed in detail regarding their application on disordered IPs. PMID:26272697

  20. Systematic Study of Compositional and Synthetic Control of Vacancy and Magnetic Ordering in Oxygen-Deficient Perovskites Ca2Fe2 xMnxO5+yand CaSrFe2 xMnxO5+y (x = 1/2, 2/3, and 1; y = 0 1/2)

    SciTech Connect

    Ramezanipour, Farshid; Greedan, John E; Cranswick, Lachlan M.D.; Donaberger, R. L.; Garlea, Vasile O; Siewenie, Joan

    2012-01-01

    Ten compounds belonging to the series of oxygen-deficient perovskite oxides Ca2Fe2 xMnxO5 and CaSrFe2 xMnxO5+y, where x = 1/2, 2/3, and 1 and y 0 0.5, were synthesized and investigated with respect to the ordering of oxygen vacancies on both local and long-range length scales and the effect on crystal structure and magnetic properties. For the set with y 0 the oxygen vacancies always order in the long-range sense to form the brownmillerite structure containing alternating layers of octahedrally and tetrahedrally coordinated cations. However, there is a change in symmetry from Pnma to Icmm upon substitution of Sr for one Ca for all x, indicating local Td chain (vacancy) disorder. In the special case of CaSrFeMnO5 the neutron diffraction peaks broaden, indicating only short-range structural order on a length scale of 160 . This reveals a systematic progression from Ca2FeMnO5 (Pnma, well-ordered tetrahedral chains) to CaSrFeMnO5 (Icmm, disordered tetrahedral chains, overall short-range order) to Sr2FeMnO5 (Pm3m, destruction of tetrahedral chains in a long-range sense). Systematic changes occur in the magnetic properties as well. While long-range antiferromagnetic order is preserved, the magnetic transition temperature, Tc, decreases for the same x when Sr substitutes for one Ca. A review of the changes in Tc for the series Ca2Fe2 xMxO5, taking into account the tetrahedral/octahedral site preferences for the various M3+ ions, leads to a partial understanding of the origin of magnetic order in these materials in terms of a layered antiferromagnetic model. While in all cases the preferred magnetic moment direction is (010) at low temperatures, there is a cross over for x = 0.5 to (100) with increasing temperature for both the Ca2Fe2 xMnxO5 and the CaSrFe2 xMnxO5 series. For the y > 0 phases, while a brownmillerite ordering of oxygen vacancies is preserved for the Ca2 phases, a disordered Pm3m cubic perovskite structure is always found when Sr is substituted for one Ca

  1. Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O{sub 3-y} perovskites - perspective cathode materials for IT-SOFC

    SciTech Connect

    Napolsky, Ph.S.; Drozhzhin, O.A.; Istomin, S.Ya.; Kazakov, S.M.; Antipov, E.V.; Galeeva, A.V.; Gippius, A.A.; Svensson, G.; Abakumov, A.M.; Van Tendeloo, G.

    2012-08-15

    .75}O{sub 3-y}, 0.1{<=}y{<=}0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the {sigma} value from {approx}1 to {approx}50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E{sub p}) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6. - Graphical abstract: The substitution of cobalt in the 314-phase Sr{sub 0.75}Y{sub 0.25}CoO{sub 2.62} by manganese leads to the formation of oxygen deficient compounds Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75, with the cubic and orthorhombic perovskite structures. The conductivity of the x=0.5 sample (110 S/cm) at 1173 K is substantially higher in comparison with x=0.75 (44 S/cm). Together with comparable TEC values for x=0.5 (15.5 ppm K{sup -1}) and 0.75 (15.1 ppm K{sup -1}) samples this makes the former one a promising cathode material for IT-SOFC. Partial replacement of Sr by Ca in Sr{sub 0.75}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} leads to the formation of the solid solution with the orthorhombic perovskite structure, Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}y{<=}0.6. Along with Sr{sub 0.75}Y{sub 0.25}Co{sub 0.5}Mn{sub 0.5}O{sub 3-y}, novel perovskite Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} represent promising cathode material for IT-SOFC due to low TEC value (13.8 ppm K{sup -1}) and high conductivity of 135 S/cm at 1173 K. Highlights: Black-Right-Pointing-Pointer Mn-doped 314-phases Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 were synthesized. Black-Right-Pointing-Pointer Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, x=0.1--0.6, Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} were made. Black-Right-Pointing-Pointer High

  2. Tracing Environmental Variation Over The Past 130 Years In The Barents Sea: Mineral Ratio (Mg/Ca, Sr/Ca, Ba/Ca, And Mn/Ca) Evidence In Shells Of The Circumpolar Greenland Cockle, Serripes groenlandicus

    NASA Astrophysics Data System (ADS)

    Henkes, G. A.; Ambrose, W. G.; Johnson, B. J.; Carroll, M. L.; McMahon, K. W.; Denisenko, S. G.; Thorrold, S. R.

    2007-12-01

    In order to quantify the impacts of human induced climate change on Arctic marine ecosystems it is crucial to establish high-resolution proxies to record regional environmental variability. The Barents Sea region is highly influenced by the annual recession and precession of Arctic sea ice and, as an ecosystem is extremely sensitive to seasonal to decadal climatic changes. Long-lived, sessile, marine bivalves have the potential to provide detailed oceanographic and biological proxy information from the Barents Sea in locations where historic, long- term data logging does not exist. Here, we present preliminary mineral ratio evidence (Mg, Sr, Ba, Mn) for Barents Sea environmental variation from shells of the circumpolar Greenland cockle, Serripes groenlandicus, over the past 130 years from 4 different locations in Norwegian and Russian waters. For all mineral ratios there are clear seasonal trends corresponding with dark winter growth checks on the external surface of each individual. The seasonal patterns of Mg and Sr show progressive change. On average for 9 individuals, Mg/Ca was 10.6 percent greater and Sr/Ca was 5.5 percent lower on the winter checks compared to other values, while Ba/Ca and Mn/Ca ratios show peaks during the middle of the summer growth period. Mineral patterns from the Pechora Sea region are particularly pronounced, which may be related to the influence freshwater from summer river discharge. While the mineral data are initially compelling enough to demonstrate clear seasonal periodicity and inter-annual variation, we believe that a multi-proxy approach to interpreting the information obtained from these bivalves is critical. Therefore, parallel to this study, we are examining external, incremental growth and organic carbon isotopes of shell material from the same collection of bivalves.

  3. Structural studies of the rhombohedral and orthorhombic monouranates: CaUO4, α-SrUO4, β-SrUO4 and BaUO4

    NASA Astrophysics Data System (ADS)

    Murphy, Gabriel; Kennedy, Brendan J.; Johannessen, Bernt; Kimpton, Justin A.; Avdeev, Maxim; Griffith, Christopher S.; Thorogood, Gordon J.; Zhang, Zhaoming

    2016-05-01

    The structures of some AUO4 (A=Ca, Sr, or Ba) oxides have been determined using a combination of neutron and synchrotron X-ray diffraction, supported by X-ray absorption spectroscopic measurements at the U L3-edge. The smaller Ca cation favours a rhombohedral AUO4 structure with 8-coordinate UO8 moieties whilst an orthorhombic structure based on UO6 groups is found for BaUO4. Both the rhombohedral and orthorhombic structures can be stabilised for SrUO4. The structural studies suggest that the bonding requirements of the A site cation play a significant role in determining which structure is favoured. In the rhombohedral structure, Bond Valence Sums demonstrate the A site is invariably overbonded, which, in the case of rhombohedral α-SrUO4, is compensated for by the formation of vacancies in the oxygen sub-lattice. The uranium cation, with its flexible oxidation state, is able to accommodate this by inducing vacancies along its equatorial coordination site as demonstrated by neutron powder diffraction.

  4. Phonons and stability of infinite-layer iron oxides SrFeO2 and CaFeO2

    NASA Astrophysics Data System (ADS)

    Gupta, M. K.; Mittal, R.; Chaplot, S. L.; Tassel, Cédric; Kageyama, Hiroshi; Tomiyasu, K.; Taylor, Jon

    2016-09-01

    We present detailed ab-initio lattice dynamical analysis of the Fe-O infinite-layer compounds CaFeO2 and SrFeO2 in various magnetic configurations. These indicate strong spin-phonon coupling in SrFeO2 in contrast to that in case of CaFeO2. From our ab-initio calculations in SrFeO2 as a function of volume, we suggest that the distortion in SrFeO2 above 300 K is similar to that in CaFeO2 at ambient conditions. The distortion of the planer structure of CaFeO2 involves doubling of the planer unit cell that may be usually expected to be due to a soft phonon mode at the M-point (1/2 1/2 0). However, our ab-initio calculations show quite unusually that all the M-point (1/2 1/2 0) phonons are stable, but two stable M3+ and M2- modes anharmonically couple with an unstable Bu mode at the zone center and lead to the cell doubling and the distorted structure. Magnetic exchange interactions in both the compounds have been computed on the basis of the ideal planar structure (P4/mmm space group) and with increasing amplitude of the Bu phonon mode. These reveal that the magnetic exchange interactions reduce significantly with increasing distortion. We have extended the ab-initio phonon calculation to high pressures, which reveal that, above 20 GPa of pressure, the undistorted planer CaFeO2 becomes dynamically stable. We also report computed phonon spectra in SrFeO3 that has a cubic structure, which is useful to understand the role of the difference in geometry of oxygen atoms around the Fe atom with respect to planer SrFeO2. Finally, powder neutron inelastic scattering experiments on SrFeO2 have also been performed at temperatures from 5 K to 353 K in the antiferromagnetic phase. The 5-K data are compared to the ab-initio calculations.

  5. Optically pumped cerium-doped LiSrAlF{sub 6} and LiCaAlF{sub 6}

    DOEpatents

    Marshall, C.D.; Payne, S.A.; Krupke, W.F.

    1996-05-14

    Ce{sup 3+}-doped LiSrAlF{sub 6} crystals are pumped by ultraviolet light which is polarized along the c axis of the crystals to effectively energize the laser system. In one embodiment, the polarized fourth harmonic light output from a conventional Nd:YAG laser operating at 266 nm is arranged to pump Ce:LiSrAlF{sub 6} with the pump light polarized along the c axis of the crystal. The Ce:LiSrAlF{sub 6} crystal may be placed in a laser cavity for generating tunable coherent ultraviolet radiation in the range of 280-320 nm. Additionally, Ce-doped crystals possessing the LiSrAlF{sub 6} type of chemical formula, e.g. Ce-doped LiCaAlF{sub 6} and LiSrGaF{sub 6}, can be used. Alternative pump sources include an ultraviolet-capable krypton or argon laser, or ultraviolet emitting flashlamps. The polarization of the pump light will impact operation. The laser system will operate efficiently when light in the 280-320 nm gain region is injected or recirculated in the system such that the beam is also polarized along the c axis of the crystal. The Ce:LiSrAlF{sub 6} laser system can be configured to generate ultrashort pulses, and it may be used to pump other devices, such as an optical parametric oscillator. 10 figs.

  6. Optically pumped cerium-doped LiSrAlF.sub.6 and LiCaAlF.sub.6

    DOEpatents

    Marshall, Christopher D.; Payne, Stephen A.; Krupke, William F.

    1996-01-01

    Ce.sup.3+ -doped LiSrAlF.sub.6 crystals are pumped by ultraviolet light which is polarized along the c axis of the crystals to effectively energize the laser system. In one embodiment, the polarized fourth harmonic light output from a conventional Nd:YAG laser operating at 266 nm is arranged to pump Ce:LiSrAlF.sub.6 with the pump light polarized along the c axis of the crystal. The Ce:LiSrAlF.sub.6 crystal may be placed in a laser cavity for generating tunable coherent ultraviolet radiation in the range of 280-320 nm. Additionally, Ce-doped crystals possessing the LiSrAlF.sub.6 type of chemical formula, e.g. Ce-doped LiCaAlF.sub.6 and LiSrGaF.sub.6, can be used. Alternative pump sources include an ultraviolet-capable krypton or argon laser, or ultraviolet emitting flashlamps. The polarization of the pump light will impact operation. The laser system will operate efficiently when light in the 280-320 nm gain region is injected or recirculated in the system such that the beam is also polarized along the c axis of the crystal. The Ce:LiSrAlF.sub.6 laser system can be configured to generate ultrashort pulses, and it may be used to pump other devices, such as an optical parametric oscillator.

  7. Atrial SERCA2a Overexpression Has No Affect on Cardiac Alternans but Promotes Arrhythmogenic SR Ca2+ Triggers

    PubMed Central

    Nassal, Michelle M. J.; Wan, Xiaoping; Laurita, Kenneth R.; Cutler, Michael J.

    2015-01-01

    Background Atrial fibrillation (AF) is the most common arrhythmia in humans, yet; treatment has remained sub-optimal due to poor understanding of the underlying mechanisms. Cardiac alternans precede AF episodes, suggesting an important arrhythmia substrate. Recently, we demonstrated ventricular SERCA2a overexpression suppresses cardiac alternans and arrhythmias. Therefore, we hypothesized that atrial SERCA2a overexpression will decrease cardiac alternans and arrhythmias. Methods Adult rat isolated atrial myocytes where divided into three treatment groups 1) Control, 2) SERCA2a overexpression (Ad.SERCA2a) and 3) SERCA2a inhibition (Thapsigargin, 1μm). Intracellular Ca2+ was measured using Indo-1AM and Ca2+ alternans (Ca-ALT) was induced with a standard ramp pacing protocol. Results As predicted, SR Ca2+ reuptake was enhanced with SERCA2a overexpression (p< 0.05) and reduced with SERCA2a inhibition (p<0.05). Surprisingly, there was no difference in susceptibility to Ca-ALT with either SERCA2a overexpression or inhibition when compared to controls (p = 0.73). In contrast, SERCA2a overexpression resulted in increased premature SR Ca2+ (SCR) release compared to control myocytes (28% and 0%, p < 0.05) and concomitant increase in SR Ca2+ load (p<0.05). Based on these observations we tested in-vivo atrial arrhythmia inducibility in control and Ad.SERCA2a animals using an esophageal atrial burst pacing protocol. There were no inducible atrial arrhythmias in Ad.GFP (n = 4) animals though 20% of Ad.SERCA2a (n = 5) animals had inducible atrial arrhythmias (p = 0.20). Conclusions Our findings suggest that unlike the ventricle, SERCA2a is not a key regulator of cardiac alternans in the atrium. Importantly, SERCA2a overexpression in atrial myocytes can increase SCR, which may be arrhythmogenic. PMID:26352986

  8. In vitro and in vivo studies on biodegradable CaMgZnSrYb high-entropy bulk metallic glass.

    PubMed

    Li, H F; Xie, X H; Zhao, K; Wang, Y B; Zheng, Y F; Wang, W H; Qin, L

    2013-11-01

    In order to enhance the corrosion resistance of the Ca65Mg15Zn20 bulk metallic glass, which has too fast a degradation rate for biomedical applications, we fabricated the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass because of the unique properties of high-entropy alloys. Our results showed that the mechanical properties and corrosion behavior were enhanced. The in vitro tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass could stimulate the proliferation and differentiation of cultured osteoblasts. The in vivo animal tests showed that the Ca20Mg20Zn20Sr20Yb20 high-entropy bulk metallic glass did not show any obvious degradation after 4 weeks of implantation, and they can promote osteogenesis and new bone formation after 2 weeks of implantation. The improved mechanical properties and corrosion behavior can be attributed to the different chemical composition as well as the formation of a unique high-entropy atomic structure with a maximum degree of disorder. PMID:23380208

  9. Ca, Sr, O and D isotope approach to defining the chemical evolution of hydrothermal fluids: example from Long Valley, CA, USA

    USGS Publications Warehouse

    Brown, Shaun T.; Kennedy, B. Mack; DePaolo, Donald J.; Hurwitz, Shaul; Evans, William C.

    2013-01-01

    We present chemical and isotopic data for fluids, minerals and rocks from the Long Valley meteoric-hydrothermal system. The samples encompass the presumed hydrothermal upwelling zone in the west moat of the caldera, the Casa Diablo geothermal field, and a series of wells defining a nearly linear, ∼16 km long, west-to-east trend along the likely fluid flow path. Fluid samples were analyzed for the isotopes of water, Sr, and Ca, the concentrations of major cations and anions, alkalinity, and total CO2. Water isotope data conform to trends documented in earlier studies, interpreted as indicating a single hydrothermal fluid mixing with local groundwater. Sr isotopes show subtle changes along the flow path, which requires rapid fluid flow and minimal reaction between the channelized fluids and the wallrocks. Sr and O isotopes are used to calculate fracture spacing using a dual porosity model. Calculated fracture spacing and temperature data for hydrothermal fluids indicate the system is (approximately) at steady-state. Correlated variations among total CO2, and the concentration and isotopic composition of Ca suggest progressive fluid degassing (loss of CO2), which drives calcite precipitation as the fluid flows west-to-east and cools. The shifts in Ca isotopes require that calcite precipitated at temperatures of 150–180 °C is fractionated by ca. −0.3‰ to −0.5‰ relative to aqueous species. Our data are the first evidence that Ca isotopes undergo kinetic fractionation at high temperatures (>100 °C) and can be used to trace calcite precipitation along hydrothermal fluid flow paths.

  10. High-Resolution Mg/Ca and Sr/Ca Records from Protothaca staminea Mollusc Shells Using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS)

    NASA Astrophysics Data System (ADS)

    Takesue, R. K.; van Geen, A.

    2001-12-01

    High resolutions records of past nearshore temperature, salinity, and nutrient enrichments at mid-latitudes would be valuable for reconstructing past changes in climate affecting coastal areas (e.g. changes in precipitation, the nature of wind-driven coastal upwelling or the El Niño-Southern Oscillation (ENSO)). We present here a potential archive of such records in growth-banded mollusc shells. The potential paleo-temperature proxy Mg/Ca, as well as Sr/Ca and stable isotopes (δ 18O, δ 13C) were measured in shells of the clam Protothaca staminea. This bivalve appears favorable for nearshore paleoclimate reconstructions because it occurs over a wide geographic range (Alaska to central America), grows for nearly 10 years, and is present in archeological and geological deposits. P. staminea shells were obtained from a tidal flat in Humboldt Bay, CA (40.8° N; modern), and from the Duncan's Point Cave shell midden (CA Dept. Parks and Recreation site SON-348/H) near Bodega Bay, CA (39.6° N; ~3,000 and ~9,000 cal yr BP). High-resolution (monthly to weekly) Mg/Ca and Sr/Ca measurements were made by (UV Excimer) laser-ablation inductively-coupled plasma (quadrupole) mass spectrometry (LA-ICP-MS) using a spot size of 90 μ m and sample spacing ranging from 100 to 300 μ m. The rapidity of LA-ICP-MS analysis made it possible to analyze a 4 cm-long section of shell within 1 day. Absolute scales for the Mg/Ca and Sr/Ca LA-ICP-MS records were obtained from shell powders drilled with a 0.5 or 0.7 mm burr then dissolved and analyzed by flame atomic absorbtion. Stable isotopes were measured on splits of the shell powders. The Mg/Ca record during the final four years of shell growth in the Humboldt Bay shell shows a regular seasonal pattern with highest values (3.5 mmol/mol) during summer and lowest values (2.5 mmol/mol) during winter corresponding to a nearshore climatological temperature range of 6° C. An abrupt shift in shell Mg/Ca values toward the end of each year

  11. Ion microprobe assessment of the heterogeneity of Mg/Ca, Sr/Ca and Mn/Ca ratios in Pecten maximus and Mytilus edulis (bivalvia) shell calcite precipitated at constant temperature

    NASA Astrophysics Data System (ADS)

    Freitas, P. S.; Clarke, L. J.; Kennedy, H.; Richardson, C. A.

    2009-07-01

    Small-scale heterogeneity of biogenic carbonate elemental composition can be a significant source of error in the accurate use of element/Ca ratios as geochemical proxies. In this study ion microprobe (SIMS) profiles showed significant small-scale variability of Mg/Ca, Sr/Ca and Mn/Ca ratios in new shell calcite of the marine bivalves Pecten maximus and Mytilus edulis that was precipitated during a constant-temperature culturing experiment. Elevated Mg/Ca, Sr/Ca and Mn/Ca ratios were found to be associated with the deposition of elaborate shell features, i.e. a shell surface stria in P. maximus and surface shell disturbance marks in both species, the latter a common occurrence in bivalve shells. In both species the observed small-scale elemental heterogeneity most likely was not controlled by variable transport of ions to the extra-pallial fluid, but by factors such as the influence of shell organic content and/or crystal size and orientation, the latter reflecting conditions at the shell crystal-solution interface. In the mid and innermost regions of the P. maximus shell the lack of significant small-scale variation of Mg/Ca ratios, which is consistent with growth at constant temperature, suggest a potential application as a palaeotemperature proxy. Cross-growth band element/Ca ratio profiles in the interior of bivalve shells may provide more promising palaeo-environmental tools than sampling from the outer region of bivalve shells.

  12. Preparation of 110K (Bi, Pb)-Sr-Ca-Cu-O superconductor from glass precursor

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.

    1989-01-01

    The Bi1.5Pb0.5Sr2Ca2Cu3O(x) glass, prepared by rapid quenching of the melt, showed T(sub g) of 383 C, crystallization temperature of approx. 446 C, melting temperature of approx. 855 C, and bulk density of 5.69 g/cu. cm. in air. The as-quenched glass was oxygen deficient. On heating in O2, it showed a slow, irreversible, and continuous weight gain starting at approx. 530 C. The influence of annealing conditions on the formation of various phases was investigated by XRD and electrical resistivity measurements. The 110K-T(sub c) phase did not form below 840 C. The amount of this phase increased with the sintering time at 840 C. A sample annealed at 840 C for 243 h in air and furnace cooled showed the highest T(sub c)(R=0) of 107.2K and transition width delta T(sub c)(10 to 90 percent) of approx. 2 K.

  13. Sr/Ca proxy sea-surface temperature reconstructions from modern and holocene Montastraea faveolata specimens from the Dry Tortugas National Park

    USGS Publications Warehouse

    Flannery, Jennifer A.; Poore, Richard Z.

    2013-01-01

    Sr/Ca ratios from skeletal samples from two Montastraea faveolata corals (one modern, one Holocene, ~6 Ka) from the Dry Tortugas National Park were measured as a proxy for sea-surface temperature (SST). We sampled coral specimens with a computer-driven triaxial micromilling machine, which yielded an average of 15 homogenous samples per annual growth increment. We regressed Sr/Ca values from resulting powdered samples against a local SST record to obtain a calibration equation of Sr/Ca = -0.0392 SST + 10.205, R = -0.97. The resulting calibration was used to generate a 47-year modern (1961-2008) and a 7-year Holocene (~6 Ka) Sr/Ca subannually resolved proxy record of SST. The modern M. faveolata yields well-defined annual Sr/Ca cycles ranging in amplitude from ~0.3 and 0.5 mmol/mol. The amplitude of ~0.3 to 0.5 mmol/mol equates to a 10-15°C seasonal SST amplitude, which is consistent with available local instrumental records. Summer maxima proxy SSTs calculated from the modern coral Sr/ Ca tend to be fairly stable: most SST maxima from 1961–2008 are 29°C ± 1°C. In contrast, winter minimum SST calculated in the 47-year modern time-series are highly variable, with a cool interval in the early to mid-1970s. The Holocene (~6 Ka) Montastraea faveolata coral also yields distinct annual Sr/Ca cycles with amplitudes ranging from ~0.3 to 0.6 mmol/mol. Absolute Sr/Ca values and thus resulting SST estimates over the ~7-year long record are similar to those from the modern coral. We conclude that Sr/Ca from Montastraea faveolata has high potential for developing subannually resolved Holocene SST records.

  14. Exploring the impact of temperature and fluid chemistry on Ca and Sr isotope composition of Arctica islandica shells via experimental alteration

    NASA Astrophysics Data System (ADS)

    Goos, Manuela; Eisenhauer, Anton; Liebetrau, Volker; Böhm, Florian; Fietzke, Jan; Nehrke, Gernot; Buhl, Dieter; Mavromatis, Vasileios; Dietzel, Martin

    2016-04-01

    Carbonate shells of marine organisms record by their chemical and isotopic composition environmental conditions like temperature, salinity and pH during their formation. However, primary signals can be overprinted by diagenesis, which has to be considered for the interpretation of environmental proxy data and on the other side may provide additional information about distinct reaction pathways throughout diagenesis (e.g. Allison et al, 2007). Aragonitic Arctica islandica shells widely used as proxy archives (e.g. Schöne et al, 2005) were chosen for hydrothermal alteration experiments in order to get a more detailed insight into diagenetic effects. Here we present results of experiments in which Arctica islandica shell fragments were exposed to North Sea seawater at temperatures of 100r{ }C and 175r{ }C at distinct reaction times. Strontium isotope composition of the experimental medium was adjusted from an original composition of δ 88/86SrSRM987= 0.391(1)‰ and 87Sr/86Sr= 0.70921(1) to δ 88/86SrSRM987= 0.179(1)‰ and 87Sr/86Sr= 0.70789(1) by sulfate extraction and Sr replacement procedures. The artificially altered shell material (six sub-samples of six shell fragments) and the corresponding solutions were prepared and analyzed. Results show that at 100r{ }C aragonite is still the predominant phase, but show lower peak intensities with Raman and XRD near the surface of the shell fragments. At 175r{ }C the aragonitic shell material recrystallized almost completely to calcite. In addition a rim of weakly ordered dolomite (10μ m) was found around these samples. Analysis of element concentrations of initial and final solutions show that at 175r{ }C Sr and Ca concentrations increase (Sr: 79 to 183 μ mol/l; Ca: 8 to 30 mmol/l), while Mg concentration decreases (Mg: 42 to 22 mmol/l). A corresponding Sr and Ca depletion along with an increase of Mg occurred in the samples, especially in the dolomite rim. At 100r{ }C only minor increase of Sr, Ca and Mg

  15. Magnetic Superstructure and Metal-Insulator Transition in Mn-Substituted Sr3Ru2O7

    NASA Astrophysics Data System (ADS)

    Hossain, M. A.; Bohnenbuck, B.; Chuang, Y.-D.; Geck, J.; Tokura, Y.; Yoshida, Y.; Hussain, Z.; Keimer, B.; Sawatzky, G. A.; Damascelli, A.

    2010-03-01

    We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr3(Ru1-xMnx)2O7, performed at both Ru and Mn L-edges. Resonant magnetic superstructure reflections, which indicate an incipient instability of the parent compound, are detected below the transition. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x˜0.05 Mn substitution. In collaboration with A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley Lab), I. Zegkinoglou, M.W. Haverkort (MPI, Stuttgart), I.S. Elfimov, D.G. Hawthorn (UBC), R. Mathieu, S. Satow, H. Takagi (Tokyo), H.-H. Wu and C. Sch"ußler-Langeheine (Cologne).

  16. 40K-40Ca and 87Rb-86Sr Dating by SIMS: The Double-Plus Advantage

    NASA Astrophysics Data System (ADS)

    Harrison, T. M.; McKeegan, K. D.; Schmitt, A. K.

    2009-12-01

    retentivity of 40Ca* relative to 40Ar* in white micas. This approach offers the potential to develop a branched-decay thermochronometer (K-Ca-Ar) permitting simultaneous solution of temperature-time history from μm-scale isotopic variations. A further advantage is that even low resolution SIMS instruments (e.g., ims7f) can utilize the double-plus method. Initial investigations using the same double-plus approach for Rb-Sr dating show promise. While resolving 87Rb+ from 87Sr+ requires an MRP of ~290k, unattainable using any current SIMS instrument, 87Rb++ is so strongly suppressed that determination of 87Sr++ is possible with minor peak stripping. 87Rb/86Sr can be determined either from 85Rb+/88Sr+ at MRP≈ 8k or by the use of energy filtering. In addition to micas, these approaches may be applicable to any mineral systems enriched in alkali metals relative to alkaline earths, such as alkali feldspars, feldspathoids, and alkaline halides.

  17. Transition metal substituted SrTiO3 perovskite oxides as promising functional materials for oxygen sensor

    NASA Astrophysics Data System (ADS)

    Misra, Sunasira

    2012-07-01

    Modern industries employ several gases as process fluids. Leakage of these gases in the operating area could lead to undesirable consequences. Even in chemical industries, which use large quantities of inert gases in confined areas, accidental leakage of these process gases would result in the reduction of oxygen partial pressure in atmospheric air. For instance, large amounts of gaseous nitrogen and argon are used in pharmaceutical industries, gas filling/bottling plants, operating area of Fast Breeder reactors, etc. Fall of concentration of oxygen in air below 17% could lead to life risk (Asphyxiation) of the working personnel that has to be checked well in advance. Further, when the leaking gas is of explosive nature, its damage potential would be very high if its concentration level in air increases beyond its lower explosive limit. Surveillance of the ambient within these industries at the critical areas and also in the environment around them for oxygen therefore becomes highly essential. Sensitive and selective gas sensors made of advanced materials are required to meet this demand of monitoring environmental pollution. The perovskite class of oxides (ABO3) is chemically stable even at high temperatures and can tolerate large levels of dopants without phase transformations. The electronic properties of this parent functional material can be tailored by adding appropriate dopants that exhibit different valence states. Aliovalent transition metal substituted SrTiO3 perovskites are good mixed ionic and electronic conductors and potential candidates for sensing oxygen at percentage level exploiting their oxygen pressure dependent electrical conductivity. This paper presents the preparation, study of electrical conductivity and oxygen-sensing characteristics of iron and cobalt substituted SrTiO3.

  18. Persistent Fe moments in the normal-state collapsed-tetragonal phase of the pressure-induced superconductor Ca0.67Sr0.33Fe2As2

    NASA Astrophysics Data System (ADS)

    Jeffries, J. R.; Butch, N. P.; Lipp, M. J.; Bradley, J. A.; Kirshenbaum, K.; Saha, S. R.; Paglione, J.; Kenney-Benson, C.; Xiao, Y.; Chow, P.; Evans, W. J.

    2014-10-01

    Using nonresonant Fe Kβ x-ray emission spectroscopy, we reveal that Sr substitution into CaFe2As2 decouples the Fe moment from the volume collapse transition, yielding a collapsed-tetragonal, paramagnetic normal state out of which superconductivity develops. X-ray diffraction measurements implicate the c-axis lattice parameter as the controlling criterion for the Fe moment, promoting a generic description for the appearance of pressure-induced superconductivity in the alkaline-earth-based 122 ferropnictides (AFe2As2). The evolution of Tc with pressure lends support to theories for superconductivity involving unconventional pairing mediated by magnetic fluctuations.

  19. Evaluation of Sr/Ca-based paleoclimate reconstructions in modern and Medieval Diploria strigosa corals in the northeastern Caribbean

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Pearson, S. P.; Kilbourne, K.

    2013-12-01

    Tropical sea surface temperature (SST) has been implicated as a driver of climate changes during the Medieval Climate Anomaly (MCA, 950-1300 A.D.) but little data exists from the tropical oceans during this time period. We collected three modern and seven sub-fossil Diploria strigosa coral colonies from an overwash deposit on Anegada, British Virgin Islands (18.73 °N, 63.33 °W) in order to reconstruct climate in the northeastern Caribbean and Tropical North Atlantic during the MCA. The first step in our reconstruction was to verify the climate signal from this species at this site. We sub-sampled the modern corals along thecal walls with an average sampling resolution of 11-13 samples per year. Sr/Ca ratios measured in the sub-samples were calibrated to temperature using three different calibration techniques (ordinary least squares, reduced major axis, and weighted least squares (WLS)) on the monthly data that includes the seasonal cycles and on the monthly anomaly data. WLS regression accounts for unequal errors in the x and y terms, so we consider it the most robust technique. The WLS regression slope between gridded SST and coral Sr/Ca is similar to the previous two calibrations of this species. Mean Sr/Ca for each of the three modern corals is 8.993 × 0.004 mmol/mol, 9.127 × 0.003 mmol/mol, and 8.960 × 0.007 mmol/mol. These straddle the mean Diploria strigosa Sr/Ca found by Giry et al., (2010), 9.080 mmol/mol, at a site with nearly the same mean SST as Anegada (27.4 °C vs. 27.5 °C). The climatological seasonal cycles for SST derived from the modern corals are statistically indistinguishable from the seasonal cycles in the instrumental SST data. The coral-based seasonal cycles have ranges of 2.70 × 0.31 °C, 2.65 × 0.08 °C and 2.71 × 0.53 °C. These results indicate that this calibration can be applied to our sub-fossil coral data. We applied the WLS calibration to monthly-resolution Sr/Ca data from multiple sub-fossil corals dating to the medieval

  20. Structure and Properties of Egyptian Blue Monolayer Family: XCuSi4O10 (X = Ca, Sr, and Ba).

    PubMed

    Chen, Yu; Kan, Min; Sun, Qiang; Jena, Puru

    2016-02-01

    Motivated by the recent experimental advances in exfoliating Egyptian blue monolayers, we have carried out extensive calculations using density functional theory to understand their geometry, stability, mechanical properties, electronic structures, and magnetism. Upon exfoliation from the bulk, XCuSi4O10 (X = Ca, Sr, and Ba) monolayers are found to change symmetry from tetragonal to orthorhombic. They all satisfy Born criteria and are mechanically stable. Each Cu site carries a magnetic moment of 1.0 μB but with degenerate ferromagnetic and antiferromagnetic coupling states. From Ca to Sr and Ba, as the atomic number increases, the thickness, elastic constants, Young's moduli, and Poisson's ratios of the monolayers increase, while the band gaps decrease. Applying strain can tune the magnitude of energy band gaps, but the direct gap feature remains. Complementing the widely studied graphene, MXenes, black phosphorus, and dichalcogenide sheets, the Egyptian blue monolayers add additional features to the family of two-dimensional materials. PMID:26763651

  1. Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae=Ca,Sr,Ba, as thermoelectric materials

    SciTech Connect

    Parker, David S; Singh, David J

    2013-01-01

    We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2 Sn, Sr2 Sn and Ba2 Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli - roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.

  2. Magnetic flux oscillations in partially irradiated Bi2Sr2CaCu2O8+δ crystals

    NASA Astrophysics Data System (ADS)

    Barness, D.; Sinvani, M.; Shaulov, A.; Trautmann, C.; Tamegai, T.; Yeshurun, Y.

    2009-04-01

    We report on generation of spatiotemporal oscillations of magnetic flux in a Bi2Sr2CaCu2O8+δ crystal irradiated in part with 2.2 GeV Au ions. Flux oscillations are spontaneously excited after exposing the sample to a steady magnetic field near the order-disorder vortex phase transition line. The oscillations originate at the border between the irradiated and nonirradiated parts of the sample and propagate into the nonirradiated region toward the sample edge. Previously reported flux oscillations were observed in the vicinity of undefined defects in as grown Bi2Sr2CaCu2O8+δ crystals. Observation of spontaneous oscillations in partially irradiated samples present the first attempt to generate such oscillations in a controlled manner.

  3. Fabrication of Bi-(Pb)-Sr-Ca-Cu-O mono- and multifilamentary superconductors and improvement in critical current density

    NASA Astrophysics Data System (ADS)

    Sekine, H.; Inoue, K.; Maeda, H.; Numata, K.

    1989-09-01

    This paper describes procedures for the fabrication of the Bi-(Pb)-Sr-Ca-Cu-O superconducting material as tapes without sheathing and as multifilamentary wires and tapes with Ag sheathing, together with results from metallurgical studies and measurements of superconducting properties. Tape specimens of 0.5-1.0-mm thickness, prepared by combination and repetition of cold work and sintering, showed critical current density Jc as high as 5000 A/sq cm at 77 K, with good reproducibility and reliability. A 1330-filament Bi-Pb-Sr-Ca-Cu-O wire with an Ag sheath showed critical temperature of about 105 K, and a multifilamentary tape specimen showed Jc of 1050 A/sq cm at 77 K. The process of repetition of cold work and sintering had the effect of Jc enhancement on multifilamentary tapes.

  4. Strain-induced topological transition in SrRu2O6 and CaOs2O6

    DOE PAGESBeta

    Ochi, Masayuki; Arita, Ryotaro; Trivedi, Nandini; Okamoto, Satoshi

    2016-05-24

    The topological property of SrRu$_2$O$_6$ and isostructural CaOs$_2$O$_6$ under various strain conditions is investigated using density functional theory. Based on an analysis of parity eigenvalues, we anticipate that a three-dimensional strong topological insulating state should be realized when band inversion is induced at the A point in the hexagonal Brillouin zone. For SrRu$_2$O$_6$, such a transition requires rather unrealistic tuning, where only the $c$ axis is reduced while other structural parameters are unchanged. However, given the larger spin-orbit coupling and smaller lattice constants in CaOs$_2$O$_6$, the desired topological transition does occur under uniform compressive strain. Our study paves a waymore » to realize a topological insulating state in a complex oxide, which has not been experimentally demonstrated so far.« less

  5. Electron-phonon superconductivity in APt3P (A=Sr, Ca, La) compounds: From weak to strong coupling

    NASA Astrophysics Data System (ADS)

    Subedi, Alaska; Ortenzi, Luciano; Boeri, Lilia

    2013-04-01

    We study the newly discovered Pt phosphides APt3P (A=Sr, Ca, La) [T. Takayama , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.237001 108, 237001 (2012)] using first-principles calculations and Migdal-Eliashberg theory. Given the remarkable agreement with the experiment, we exclude the charge-density wave scenario proposed by previous first-principles calculations, and give conclusive answers concerning the superconducting state in these materials. The pairing increases from La to Ca and Sr due to changes in the electron-phonon matrix elements and low-frequency phonons. Although we find that all three compounds are well described by conventional s-wave superconductivity and spin-orbit coupling of Pt plays a marginal role, we show that it could be possible to tune the structure from centrosymmetric to noncentrosymmetric opening new perspectives towards the understanding of unconventional superconductivity.

  6. Triadin/Junctin Double Null Mouse Reveals a Differential Role for Triadin and Junctin in Anchoring CASQ to the jSR and Regulating Ca2+ Homeostasis

    PubMed Central

    Boncompagni, Simona; Thomas, Monique; Lopez, Jose R.; Allen, Paul D.; Yuan, Qunying; Kranias, Evangelia G.; Franzini-Armstrong, Clara; Perez, Claudio F.

    2012-01-01

    Triadin (Tdn) and Junctin (Jct) are structurally related transmembrane proteins thought to be key mediators of structural and functional interactions between calsequestrin (CASQ) and ryanodine receptor (RyRs) at the junctional sarcoplasmic reticulum (jSR). However, the specific contribution of each protein to the jSR architecture and to excitation-contraction (e-c) coupling has not been fully established. Here, using mouse models lacking either Tdn (Tdn-null), Jct (Jct-null) or both (Tdn/Jct-null), we identify Tdn as the main component of periodically located anchors connecting CASQ to the RyR-bearing jSR membrane. Both proteins proved to be important for the structural organization of jSR cisternae and retention of CASQ within them, but with different degrees of impact. Our results also suggest that the presence of CASQ is responsible for the wide lumen of the jSR cisternae. Using Ca2+ imaging and Ca2+ selective microelectrodes we found that changes in e-c coupling, SR Ca2+content and resting [Ca2+] in Jct, Tdn and Tdn/Jct-null muscles are directly correlated to the effect of each deletion on CASQ content and its organization within the jSR. These data suggest that in skeletal muscle the disruption of Tdn/CASQ link has a more profound effect on jSR architecture and myoplasmic Ca2+ regulation than Jct/CASQ association. PMID:22768324

  7. Triadin/Junctin double null mouse reveals a differential role for Triadin and Junctin in anchoring CASQ to the jSR and regulating Ca(2+) homeostasis.

    PubMed

    Boncompagni, Simona; Thomas, Monique; Lopez, Jose R; Allen, Paul D; Yuan, Qunying; Kranias, Evangelia G; Franzini-Armstrong, Clara; Perez, Claudio F

    2012-01-01

    Triadin (Tdn) and Junctin (Jct) are structurally related transmembrane proteins thought to be key mediators of structural and functional interactions between calsequestrin (CASQ) and ryanodine receptor (RyRs) at the junctional sarcoplasmic reticulum (jSR). However, the specific contribution of each protein to the jSR architecture and to excitation-contraction (e-c) coupling has not been fully established. Here, using mouse models lacking either Tdn (Tdn-null), Jct (Jct-null) or both (Tdn/Jct-null), we identify Tdn as the main component of periodically located anchors connecting CASQ to the RyR-bearing jSR membrane. Both proteins proved to be important for the structural organization of jSR cisternae and retention of CASQ within them, but with different degrees of impact. Our results also suggest that the presence of CASQ is responsible for the wide lumen of the jSR cisternae. Using Ca(2+) imaging and Ca(2+) selective microelectrodes we found that changes in e-c coupling, SR Ca(2+)content and resting [Ca(2+)] in Jct, Tdn and Tdn/Jct-null muscles are directly correlated to the effect of each deletion on CASQ content and its organization within the jSR. These data suggest that in skeletal muscle the disruption of Tdn/CASQ link has a more profound effect on jSR architecture and myoplasmic Ca(2+) regulation than Jct/CASQ association. PMID:22768324

  8. Epitaxial thin films of ATiO(3-x)H(x) (A = Ba, Sr, Ca) with metallic conductivity.

    PubMed

    Yajima, Takeshi; Kitada, Atsushi; Kobayashi, Yoji; Sakaguchi, Tatsunori; Bouilly, Guillaume; Kasahara, Shigeru; Terashima, Takahito; Takano, Mikio; Kageyama, Hiroshi

    2012-05-30

    Epitaxial thin films of titanium perovskite oxyhydride ATiO(3-x)H(x) (A = Ba, Sr, Ca) were prepared by CaH(2) reduction of epitaxial ATiO(3) thin films deposited on a (LaAlO(3))(0.3)(SrAl(0.5)Ta(0.5)O(3))(0.7) substrate. Secondary ion mass spectroscopy detected a substantial amount and uniform distribution of hydride within the film. SrTiO(3)/LSAT thin film hydridized at 530 °C for 1 day had hydride concentration of 4.0 × 10(21) atoms/cm(3) (i.e., SrTiO(2.75)H(0.25)). The electric resistivity of all the ATiO(3-x)H(x) films exhibited metallic (positive) temperature dependence, as opposed to negative as in BaTiO(3-x)H(x) powder, revealing that ATiO(3-x)H(x) are intrinsically metallic, with high conductivity of 10(2)-10(4) S/cm. Treatment with D(2) gas results in hydride/deuteride exchange of the films; these films should be valuable in further studies on hydride diffusion kinetics. Combined with the materials' inherent high electronic conductivity, new mixed electron/hydride ion conductors may also be possible. PMID:22563869

  9. Strain analysis and structural characterization of SrCuO 2/CaCuO 2 infinite layer superlattices

    NASA Astrophysics Data System (ADS)

    Del Vecchio, A.; Mirenghi, L.; Tapfer, L.; Aruta, C.; Petrocelli, G.; Balestrino, G.

    1997-02-01

    A detailed structural characterization of SrCuO 2/CaCuO 2 infinite layer superlattices is presented. The analyses are performed by using high-resolution X-ray diffraction, reciprocal space mapping and X-ray specular reflectivity. In addition, preliminary results of X-ray photoelectron spectroscopy are reported. The X-ray analyses confirm the high structural quality of infinite layer superlattices deposited by pulsed laser technique on slightly misoriented SrTiO 3 substrates. The strain analyses indicate that (i) a macroscopic tilt of the superlattice with respect to the substrate lattice occurs, and (ii) the SrCuO 2 layers are in a relaxed state, while the CaCuO 2 unit cells are tetragonally distorted with respect the SrCuO 2 lattice. The low-angle X-ray measurements reveal good interfacial properties and indicate a partial correlation of the interface roughness across the layers. A computer simulation of the experimental X-ray specular reflectivity patterns yields an average interface roughness of about 4 Å. Finally, the X-ray photoelectron spectroscopy investigations confirm the good quality of the infinite layer superlattices with a correct stoichiometric contents and, particularly, a chemical state of CuO 2 planes similar to that of typical high quality superconducting YBCO thin films.

  10. Magnetic Superstructure and Metal-Insulator Transition in Mn-Substituted Sr3 Ru 2 O 7

    NASA Astrophysics Data System (ADS)

    Hossain, M. A.; Zhu, Z. H.; Bohnenbuck, B.; Chuang, Y.-D.; Yoshida, Y.; Hussain, Z.; Keimer, B.; Elfimov, I. S.; Sawatzky, G. A.; Damascelli, A.

    2011-03-01

    We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr 3 (Ru 1-x Mn x)2 O7 , performed at both Ru and Mn L -edges. Resonant magnetic superstructure reflections together with ab-initio density functional theory calculations identify the ground state as a spin checkerboard with blocks of 4 spins up and 4 spins down. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x ~ 0.05 Mn substitution. Perhaps more important, our results suggest that the same checkerboard instability might be present already in the parent compound Sr 3 Ru 2 O7 . In collaboration with: A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley) I. Zegkinoglou, M.W. Haverkort (MPI) J. Geck, D.G. Hawthorn (UBC) R. Mathieu, Y. Tokura, S. Satow, H. Takagi (Tokyo) H.-H. Wu and C. Schussler-Langeheine (Cologne).

  11. Cluster Chemistry in Electron-Poor Ae-Pt-Cd Systems (Ae=Ca, Sr, Ba): (Sr,Ba)Pt2Cd4, Ca6Pt8Cd16, and Its Known Antitype Er6Pd16Sb8

    SciTech Connect

    Samal, Saroj L.; Gulo, Fakhili; Corbett, John D.

    2013-02-18

    Three new ternary polar intermetallic compounds, cubic Ca6Pt8Cd16, and tetragonal (Sr, Ba)Pt2Cd4 have been discovered during explorations of the Ae–Pt–Cd systems. Cubic Ca6Pt8Cd16 (Fm-3m, Z = 4, a = 13.513(1) Å) contains a 3D array of separate Cd8 tetrahedral stars (TS) that are both face capped along the axes and diagonally bridged by Pt atoms to generate the 3D anionic network Cd8[Pt(1)]6/2[Pt(2)]4/8. The complementary cationic surface of the cell consists of a face-centered cube of Pt(3)@Ca6 octahedra. This structure is an ordered ternary variant of Sc11Ir4 (Sc6Ir8Sc16), a stuffed version of the close relative Na6Au7Cd16, and a network inverse of the recent Er6Sb8Pd16 (compare Ca6Pt8Cd16). The three groups of elements each occur in only one structural version. The new AePt2Cd4, Ae = Sr, Ba, are tetragonal (P42/mnm,Z = 2, a ≈ 8.30 Å, c ≈ 4.47 Å) and contain chains of edge-sharing Cd4 tetrahedra along c that are bridged by four-bonded Ba/Sr. LMTO-ASA and ICOHP calculation results and comparisons show that the major bonding (Hamilton) populations in Ca6Pt8Cd16 and Er6Sb8Pd16 come from polar Pt–Cd and Pd–Sb interactions, that Pt exhibits larger relativistic contributions than Pd, that characteristic size and orbital differences are most evident for Sb 5s, Pt8, and Pd16, and that some terms remain incomparable, Ca–Cd versus Er–Pd.

  12. High-density Bi-Pb-Sr-Ca-Cu-O superconductor prepared by rapid thermal melt processing

    SciTech Connect

    Moon, B.M.; Lalevic, B. ); Kear, B.H.; McCandlish, L.E.; Safari, A.; Meskoob, M.

    1989-10-02

    A high quality, dense Bi-Pb-Sr-Ca-Cu-O superconductor has been successfully synthesized by rapid thermal melt processing. Conventionally sintered pellets were melted at 1200 {degree}C, cooled rapidly, and then annealed. As-melted samples exhibited semiconductor behavior, which upon annealing became superconducting at 115 K ({ital T}{sub {ital c}}(zero)=105 K). A detailed study of various processing techniques has been carried out.

  13. Magnetic behaviour of the MTbF6 fluoroterbates (M=Cd, Ca, Sr, (α/β)-Ba)

    NASA Astrophysics Data System (ADS)

    Josse, M.; El-Ghozzi, M.; Avignant, D.; André, G.; Bourée, F.; Isnard, O.

    2012-01-01

    Neutron powder diffraction has been performed on the MTbF6 fluorides (M=Cd, Ca, Sr, (α/β)-Ba). Four of these fluorides (Cd, Ca, Sr, β-Ba) are built of a (pseudo-) tetragonal packing of [TbF6]2- chains and only differs by the chains relative orientations. Thus this series represents a valuable opportunity to evaluate the Tb4+-Tb4+ magnetic interactions. All the compounds displayed antiferromagnetic order (TN=2.70 K (Cd), 2.15 K (Ca), 2.60 K (Sr), 2.10 K (β-Ba)), except for the α form of BaTbF6. The crystal structure of this latter fluoroterbate has also been investigated by means of high-resolution neutron powder diffraction. From Neutron Powder Diffraction data, CdTbF6 and β-BaTbF6 magnetic structures were determined, together with the metamagnetic behaviour of β-BaTbF6 as a function of an external magnetic field. A tentative phase diagram is then given for β-BaTbF6. Advantage was taken of the polymorphism of the BaTbF6 fluoroterbate to analyse, on the basis of topological parameters such as bond distances and angles, the magnetic behaviour of its α and β forms. It was shown that superexchange interactions are present in β-BaTbF6, and that these interactions may also rule the magnetic behaviour of the other MTbF6 (M=Ca, Sr, Cd) tetravalent terbium fluorides.

  14. Photoemission resonance study of sintered and single-crystal Bi4Ca3Sr3Cu4O16+x

    NASA Astrophysics Data System (ADS)

    Tang, Ming; Chang, Y.; Zanoni, R.; Onellion, M.; Joynt, Robert; Huber, D. L.; Margaritondo, G.; Morris, P. A.; Bonner, W. A.; Tarascon, J. M.; Stoffel, N. G.

    1989-02-01

    We present soft x-ray photoemission spectra that probe the valence and core electronic structure of the high-Tc superconductor Bi4Ca3Sr3Cu4O16+x. The identification of spectral features was helped by the observation of the resonant behavior of a Cu-related satellite feature. The resonance occurs at photon energies near the Cu3p optical absorption edge, and affects a peak 12.5 eV below the Fermi edge. We identified this feature as a correlation satellite characteristic of Cu in the 2+ valence state. Other features observed in the spectra more than 7 eV below the Fermi edge are due to several different core levels. In particular, we observed a strong Bi5d doublet. Other core level peaks are due to the Sr4p and Ca3p orbitals, and to Bi, Sr and Ca s-orbitals. Within 7 eV of the Fermi edge, the spectra are dominated by valence states. The most important feature is the Bi4Ca3Sr3Cu4O16+x Fermi edge itself, which we observed for the first time on this, and whose existence was subsequently confirmed by several other groups. On the contrary, no edge was observed in the photoemission spectra of materials in the YBa2Cu3O7-x family. The observation of the Fermi edge has important implications for the theoretical interpretation of high-Tc superconductivity. Furthermore, it enabled us to see near-edge changes associated with the superconducting transition.

  15. Effects of calcination on microscopic and mesoscopic structures in Ca- and Sr-doped nano-crystalline lanthanum chromites

    SciTech Connect

    Bhatt, Himal; Bahadur, J.; Deo, M.N.; Ramanathan, S.; Pandey, K.K.; Sen, D.; Mazumder, S.; Sharma, Surinder M.

    2011-01-15

    Calcination behavior of nano-crystalline lanthanum chromites doped with calcium and strontium has been probed by Fourier transform infrared spectroscopy, X-ray diffraction and small-angle neutron scattering as a function of temperature. Infrared spectroscopic results imply that over a range of temperatures, some intermediate phase of dopant chromates evolve and then dissolve back, which has also been confirmed by the XRD. Neutron scattering data reveal a fractal type correlation of building blocks in virgin powders. Increase in fractal dimension and reduction in upper cutoff vis-a-vis the densification of agglomerates were found with increasing calcination temperature. Calcination, beyond 900 {sup o}C, results in breaking down of the fractal morphology almost completely. Such shrinkage event also results in a modification of the microscopic structure. These changes have been attributed to the compaction of agglomerates of both Ca- and Sr-doped lanthanum chromites, assisted via liquid state sintering by the melting of the intermediate phases at intermediate calcination stages. -- Graphical Abstract: Dopant chromates evolve as intermediate phases during calcination of Ca- and Sr-doped nano-crystalline lanthanum chromites at intermediate temperatures, around 900 {sup o}C, evident from infrared spectroscopy. Such an event results in a modification of the microscopic and mesoscopic structures. Display Omitted Research highlights: {yields} Meso/microscopic structures of La{sub 0.7}Ca{sub 0.3}CrO{sub 3} and La{sub 0.8}Sr{sub 0.2}CrO{sub 3} modify during calcination. {yields} Transient phases CaCrO{sub 4} and SrCrO{sub 4} appear at intermediate temperatures. {yields} Bond length, unit cell volume, etc. modify as intermediate phases evolve and extinct. {yields} Compaction of the agglomerates takes place due to liquid state assisted sintering.

  16. In-plane quasi-particle tunneling into Bi 2Sr 2CaCu 2O 8

    NASA Astrophysics Data System (ADS)

    Aubin, H.; Pugel, D. E.; Badica, E.; Greene, L. H.; Jain, Sha; Hinks, D. G.

    2000-11-01

    Planar tunneling spectroscopy is performed into the a-b plane of the high-temperature superconductor Bi 2Sr 2CaCu 2O 8. The tunneling spectra exhibit a zero-bias conductance peak (ZBCP). Preliminary studies as a function of temperature, crystallographic orientation, magnetic field magnitude and direction confirm the ZBCP is an Andreev bound state (ABS) at zero energy. Below 5K, a depletion in the density of states at zero energy is observed

  17. Magnetic relaxation in the 110 K superconducting phase in Bi-Sr-Ca-Cu-O thin films

    NASA Technical Reports Server (NTRS)

    Tanaka, Atsushi; Crain, Jason; Kamehara, Nobuo; Niwa, Koichi

    1991-01-01

    We have investigated the time dependence of remnant moment decay in a highly oriented, nearly single high T(sub c) phase Bi-Sr-Ca-Cu-O thin film. A strictly logarithmic time dependence was observed over a 20 K temperature range for observation intervals of 2000 seconds. The normalized decay rate exhibits a peak around 14 K and has a relatively weak magnetic field dependence. These data are then compared with existing data on the YBCO and Eu-based superconductors.

  18. Combined effects of annealing/quenching and transition metal substitution on physical properties of CaFe2As2

    NASA Astrophysics Data System (ADS)

    Ran, Sheng; Bud'Ko, Sergey; Canfield, Paul

    2013-03-01

    Our previous work on CaFe2As2 single crystals grown out of FeAs flux has shown that a process of annealing and quenching can be used as an additional control parameter which can tune the ground state of CaFe2As2 systematically, in a manner similar to applied pressure. With combined effect of annealing/quenching and transition metal substitution, CaFe2As2 system offers ready access to the salient low-temperature states associated with Fe-based superconductors: antiferromagnetic/orthorhombic, superconducting, and nonmagnetic/collapsed tetragonal. In this talk we will present systematic studies of the combined effects of annealing/quenching and chemical substitution with various transition metals (Co, Ni, Rh) on the physical properties of CaFe2As2 and construct phase diagrams for different substitution levels and different annealing/quenching temperatures. Supported by the U.S. Department of Energy Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

  19. Mg/Ca, Sr/Ca, and stable isotopes in modern and Holocene Protothaca staminea shells from a northern California coastal upwelling region

    USGS Publications Warehouse

    Takesue, R.K.; VanGeen, A.

    2004-01-01

    This study explores the potential of intertidal Protothaca staminea shells as high-resolution geochemical archives of environmental change in a coastal upwelling region. Mg/Ca and Sr/Ca ratios were analyzed by excimer laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) at sub-weekly temporal resolution in shells growing ???1 mm per month. Growth patterns of a modern P. staminea shell from Humboldt Bay, California, collected in December 1999 made it possible to infer a lifespan from 1993 to 1998. Growth hiatuses in the shell may have excluded records of extreme events. Mg/Ca ratios appeared to be partly controlled by water temperature; the correlation coefficient between temperature and Mg/Ca was r = 0.71 in one of four growth increments. Significant year-to-year differences in the sensitivity of Mg/Ca to temperature in P. staminea could not be explained, however. Sr/Ca ratios appeared to be more closely related to shell growth rate. Oxygen isotopes, measured at 2-week temporal resolution in the same shell, did not show a clear relation to local temperature in summer, possibly because temperatures were higher and less variable at the King Salmon mudflat, where the shell was collected, than in the main channel of Humboldt Bay, where water properties were monitored. Negative shell ??13C values (<-0.5???) marked spring and summer coastal upwelling events. The Mg contents of P. staminea midden shells dated to ???3 ka and ???9 ka were significantly lower than in the modern shell. This may have resulted from degradation of a Mg-rich shell organic matrix and precluded quantitative interpretation of the older high-resolution records. Elevated ??13C values in the ???3 ka shell suggested that the individual grew in highly productive or stratified environment, such as a shallow coastal embayment or lagoon. Copyright ?? 2004 Elsevier Ltd.

  20. Ultracold magnetically tunable interactions without radiative-charge-transfer losses between Ca+, Sr+, Ba+, and Yb+ ions and Cr atoms

    NASA Astrophysics Data System (ADS)

    Tomza, Michał

    2015-12-01

    The Ca+, Sr+, Ba+, and Yb+ ions immersed in an ultracold gas of the Cr atoms are proposed as experimentally feasible heteronuclear systems in which ion-atom interactions at ultralow temperatures can be controlled with magnetically tunable Feshbach resonances without charge transfer and radiative losses. Ab initio techniques are applied to investigate electronic-ground-state properties of the (CaCr)+, (SrCr)+, (BaCr)+, and (YbCr)+ molecular ions. The potential energy curves, permanent electric dipole moments, and static electric dipole polarizabilities are computed. The spin-restricted open-shell coupled-cluster method restricted to single, double, and noniterative triple excitations and the multireference configuration-interaction method restricted to single and double excitations are employed. The scalar relativistic effects are included within the small-core energy-consistent pseudopotentials. The leading long-range induction and dispersion interaction coefficients are also reported. Finally, magnetic Feshbach resonances between the Ca+, Sr+, Ba+, and Yb+ ions interacting with the Cr atoms are analyzed. The present proposal opens the way towards robust quantum simulations and computations with ultracold ion-atom systems free of radiative charge-transfer losses.

  1. Magnetic exchange interactions and antiferromagnetism of ATcO3 (A= Ca, Sr, Ba) studied from first principles

    NASA Astrophysics Data System (ADS)

    Borisov, V. S.; Maznichenko, I. V.; Böttcher, D.; Ostanin, S.; Ernst, A.; Henk, J.; Mertig, I.

    2012-04-01

    The magnetic properties of ATcO3 (A = Ca, Sr, Ba) perovskites were studied from first principles using multiple-scattering theory. For each system, the most preferable magnetic order is antiferromagnetic where the magnetic moments of the nearest Tc atoms are aligned antiparallel to each other. In the case of CaTcO3 and SrTcO3, their recently observed antiferromagnetism is supported by our calculation of the Tc-Tc exchange coupling parameters. The Néel temperatures TN estimated for CaTcO3 and SrTcO3 are in a good agreement with experiment. For BaTcO3, which is not synthesized so far, we predict a fundamental band gap of 0.3 eV and TN below 900 K. In general, TN increases with volume expansion, whereas the presence of vacancies on both the oxygen and cation sites of ATcO3 should significantly suppress the critical temperature as well as the magnetic moment of Tc. Electronic correlations play a minor role in the formation of the magnetic state, although they may improve the calculated value of TN.

  2. Chronology of lunar granite 12033,576: Resetting of Rb-Sr and K-Ca isochrons

    NASA Technical Reports Server (NTRS)

    Shih, C.-Y.; Wiesmann, H.; Garrison, D. H.; Nyquist, L. E.; Bogard, D. D.

    1993-01-01

    Lunar granite 12033,576 is a subsample of the 'large' (approximately 1 g) felsite 12033,507 which was identified from a collection of 4-10 mm particles from the 12033 soil sampled from the north rim of Head Crater in the eastern part of Oceanus Procellarum. Discordant ages of approximately 3.6, approximately 0.8, approximately 3.9, and approximately 2.2 Ga for this lunar granite were obtained, respectively, by the K-Ca, Ar-39/Ar-40, and U-Pb zircon methods in previous studies and by the Rb-Sr method is this study. Assuming the granite crystallized approximately 3.9 Ga ago (zircon age) and was shocked by meteoritic impacts at 0.8 Ga ago (Ar-39-Ar-40 age), the intermediate apparent ages by the Rb-Sr and K-Ca methods can be interpreted as reset by diffusion of the parent and daughter nuclides. The Rb-Sr age is less resistant to resetting than the K-Ca age, but more resistant that the Ar-39/Ar-40 age.

  3. Electronic band structures and photovoltaic properties of MWO{sub 4} (M=Zn, Mg, Ca, Sr) compounds

    SciTech Connect

    Kim, Dong Wook; Cho, In-Sun; Shin, Seong Sik; Lee, Sangwook; Noh, Tae Hoon; Kim, Dong Hoe; Jung, Hyun Suk; Hong, Kug Sun

    2011-08-15

    Divalent metal tungstates, MWO{sub 4}, with wolframite (M=Zn and Mg) and scheelite (M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO{sub 4} and MgWO{sub 4}) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO{sub 4} and SrWO{sub 4}), which was attributed to their enhanced electron transfer resulting from their appropriate band positions. - Graphical abstract: The electronic band structures of divalent metal tungstates are described from the combination of experimental results and theoretical calculations, and their electronic structure-dependent photovoltaic performances are also studied. Highlights: > MWO{sub 4} compounds with wolframite (M=Zn and Mg) and scheelite structure (M=Ca and Sr) were prepared. > Their electronic band structures were investigated by the calculations and the measurements. > Their photovoltaic properties were determined by the crystal and electronic structures.

  4. XPS and ARPES study of the metal-insulator transition in Mn-substituted Sr3Ru2O7

    NASA Astrophysics Data System (ADS)

    Zhu, Zhihuai; Levy de Castro, G.; Hossain, M. A.; Manju, U.; McCheyney, J. L.; Bostwick, A.; Rotenberg, E.; Yoshida, Y.; Elfimov, I. S.; Panaccione, G.; Damascelli, A.

    2010-03-01

    We have studied the metal-insulator transition in Mn-substituted Sr3Ru2O7 by core-level x-ray photoemission (XPS) and angle-resolved photoemission spectroscopy (ARPES). In XPS, both the surface- and bulk-sensitive spectra show a two-peak structure, corresponding to the well screened and the unscreened excitations. The intensity of the well-screened peak is suppressed upon increasing the concentration of Mn, reflecting a metal-to-insulator transition induced by Mn impurities. In ARPES, changes in Fermi surface topology and band dispersions are observed as the system crosses over from a metal to a - possibly Mott - insulator. We observed a variation and enhancement of the Fermi-surface nesting upon Mn substitution, which might be connected to the emergence of the magnetic superstructure revealed by our resonant elastic soft x-ray scattering results [1].[4pt] [1] M.A. Hossain et al., arXiv:0906.0035 (2009).

  5. Photoluminescence performance of thulium doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} under irradiation of ultraviolet and vacuum ultraviolet lights

    SciTech Connect

    Wang, Zhaofeng; Li, Yezhou; Liu, Xiong; Wei, Xingmin; Chen, Yueling; Zhou, Fei; Wang, Yuhua

    2014-11-15

    Highlights: • A novel blue-emitting phosphor Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} was reported. • Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} exhibited excellent thermal and irradiation stability. • Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} was found to possess high color purity. - Abstract: In this work, we synthesized Tm{sup 3+} doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors and investigated their photoluminescence properties under the excitation of ultraviolet and vacuum ultraviolet lights. The crystal structure analysis and variation of cell parameters confirm that Tm{sup 3+} ions have been successfully doped in the structure of Li{sub 4}SrCa(SiO{sub 4}){sub 2} host by occupying the sites of Ca{sup 2+} with the coordination number of 6. The luminescence results suggest that Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} is a good blue-emitting phosphor when excited by ultraviolet and vacuum ultraviolet irradiations. In addition, it is observed that there is nearly no degradation for Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} after undergoing thermal and irradiation treatments. Possible mechanisms for the luminescence processes are proposed on the basis of the discussion of excitation and emission spectra. In particular, the emission color of Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tm{sup 3+} by excitation of 147 and 172 nm irradiations is very close to the standard blue color, suggesting that it could be potentially applied in plasma display panels and mercury-free fluorescence lamps.

  6. Calcilytic Ameliorates Abnormalities of Mutant Calcium-Sensing Receptor (CaSR) Knock-In Mice Mimicking Autosomal Dominant Hypocalcemia (ADH).

    PubMed

    Dong, Bingzi; Endo, Itsuro; Ohnishi, Yukiyo; Kondo, Takeshi; Hasegawa, Tomoka; Amizuka, Norio; Kiyonari, Hiroshi; Shioi, Go; Abe, Masahiro; Fukumoto, Seiji; Matsumoto, Toshio

    2015-11-01

    Activating mutations of calcium-sensing receptor (CaSR) cause autosomal dominant hypocalcemia (ADH). ADH patients develop hypocalcemia, hyperphosphatemia, and hypercalciuria, similar to the clinical features of hypoparathyroidism. The current treatment of ADH is similar to the other forms of hypoparathyroidism, using active vitamin D3 or parathyroid hormone (PTH). However, these treatments aggravate hypercalciuria and renal calcification. Thus, new therapeutic strategies for ADH are needed. Calcilytics are allosteric antagonists of CaSR, and may be effective for the treatment of ADH caused by activating mutations of CaSR. In order to examine the effect of calcilytic JTT-305/MK-5442 on CaSR harboring activating mutations in the extracellular and transmembrane domains in vitro, we first transfected a mutated CaSR gene into HEK cells. JTT-305/MK-5442 suppressed the hypersensitivity to extracellular Ca(2+) of HEK cells transfected with the CaSR gene with activating mutations in the extracellular and transmembrane domains. We then selected two activating mutations locating in the extracellular (C129S) and transmembrane (A843E) domains, and generated two strains of CaSR knock-in mice to build an ADH mouse model. Both mutant mice mimicked almost all the clinical features of human ADH. JTT-305/MK-5442 treatment in vivo increased urinary cAMP excretion, improved serum and urinary calcium and phosphate levels by stimulating endogenous PTH secretion, and prevented renal calcification. In contrast, PTH(1-34) treatment normalized serum calcium and phosphate but could not reduce hypercalciuria or renal calcification. CaSR knock-in mice exhibited low bone turnover due to the deficiency of PTH, and JTT-305/MK-5442 as well as PTH(1-34) increased bone turnover and bone mineral density (BMD) in these mice. These results demonstrate that calcilytics can reverse almost all the phenotypes of ADH including hypercalciuria and renal calcification, and suggest that calcilytics can become a

  7. X-ray absorption investigation of the valence state and electronic structure of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} in comparison with La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}

    SciTech Connect

    Haas, O.; Ludwig, Chr.; Bergmann, U.; Singh, R.N.; Braun, A.; Graule, T.

    2011-12-15

    3d metal K-shell X-ray absorption spectra of perovskites with the composition La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8) are compared on the basis of pre-edges, white line features and extended fine structures. The measurements were performed at 300 K and for La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} also at temperatures as low as 10-20 K. Going to low-temperature the measurements indicate an increase in t{sub 2g}{sup Low-Asterisk} and a decrease in e{sub g}{sup Low-Asterisk} orbital occupancy, which is most accentuated in the LaCoO{sub 3} sample. Virtually no Co K-edge shift was observed for the La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} compounds and the Co-O distances are also not significantly reduced when La{sup 3+} is partially substituted by Ca{sup 2+} or Sr{sup 2+}. From the pre-edge features of these perovskites we are tended to conclude that the t{sub 2g}{sup Low-Asterisk} orbitals are less, and the e{sub g}{sup Low-Asterisk} orbitals are more occupied with increasing x in the Ca and Sr substituted compounds, whereas the total d-electron density is not changing. These results indicate that cobalt prefers a valence state of 3{sup +} in these Co perovskites. This could also be confirmed with iodometric titrations. The Fe perovskites behave differently. In contrast to the Co perovskites, for La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites the Fe K-edge is shifted, the pre-edge features intensity is increasing and the Fe-O bond length is decreasing with increasing x. The valence states of the iron in the La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites in fact increase as much as x increases. - Graphical abstract: Co K and Fe K pre-edge of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites one of the

  8. Luminescence and energy transfer in Eu2+, Mn2+ co-doped Ca2SrNaLa(PO4)3F

    NASA Astrophysics Data System (ADS)

    Shanshan, Hu; Wanjun, Tang

    2013-12-01

    A new compound Ca2SrNaLa(PO4)3F, isotypic with hexagonal Ca(Sr,Na,Ca)(Ca,Sr,Ce)3(PO4)3F, is reported. Its cell parameters have been determined from X-ray powder diffraction data. Crystallization occurs in the hexagonal space group P63 (No. 173) with a = 9.515(1) Å, c = 7.028(1) Å, and Z = 2. Eu2+ and Mn2+ activated Ca2SrNaLa(PO4)3F phosphors have been prepared. The energy transfer of Eu2+ → Mn2+ has been investigated. The resonant type energy transfer from Eu2+ to Mn2+ has been demonstrated, and the energy transfer efficiency has also been calculated according to their PL decay curves. A color-tunable emission in Ca2SrNaLa(PO4)3F phosphors can be realized by Eu2+ → Mn2+ energy transfer. White light can be achieved in a single-phased Ca2SrNaLa(PO4)3F host by co-doping Eu2+ and Mn2+ with CIE (0.32, 0.31). Our results demonstrate that the potential application of these phosphors in solid-state lighting and (or) other areas.

  9. Structure-magnetism correlation induced by Mn substitution in bilayered perovskite Sr3(Ru1-xMnx)2O7

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Ye, Feng; Chi, Songxue; Mesa, Dalgis; Tian, Wei; Jin, Rongying; Plummer, Ward; Zhang, Jiandi

    Elastic neutron scattering technique was employed to investigate the effect of Mn substitution on the structure, magnetism and their correlation in Sr3(Ru1-xMnx)2 O7(x =6%, 12% and 16%) crystals. While parent compound Sr3Ru2O7is paramagnetic, a small amount of Mn substitution induces an E-type antiferromagnetic order. With the increase of Mn substitution from 6 % to 16%, the ordered moment at Ru/Mn site increases significantly with an enhanced TN from 20 K for x =6 % to 80 K for x = 16%, and the in-plane magnetic correlation lengths increase to achieve the maximum for x = 16% as indicated by the resolution-limited linewidth of the Hscans through QAFM = (0.5, 0, 0). Accompanied by the enhancement of TN, the (Ru/Mn)O6 octahedron rotation is found to be suppressed simultaneously, suggesting a correlation between (Ru/Mn)O6 octahedron rotation and magnetism due to Mn substitution. Our findings indicate that Mn substitution on Ru in Sr3Ru2O7 has a significant effect on the microscopic structure and magnetism as well as the correlations between them. This work is supported by the U.S. Department of Energy under EPSCoR Grant No. DE-SC0012432 with additional support from the Louisiana Board of Regents.

  10. Oxygen reduction at a YSZ interface with cathode materials La{sub 1-x}(Ca or Sr){sub x}MnO{sub 3} or Y{sub 1-x}CaMnO{sub 3}

    SciTech Connect

    Youngblood, G.E.; Windisch, C.F. Jr.; Bates, J.L.

    1993-09-01

    Impedance spectroscopy combined with an unbonded interface cell (UIC) design, was used to assess oxygen reduction at an yttria-stabilized zirconia electrolyte interface with several substituted yttrium and lanthanum manganite cathode compositions. By analyzing impedance spectra taken using the UIC, effective length of reaction zone at the solid-gas triple phase boundary can be estimated and used to normalize the oxygen reduction reaction rate for each cell, thus effectively removing effect of interface morphology. Intrinsic reaction rates (specific oxygen activities) were determined from spectra as function of temperature and oxygen partial pressure for cathodes La{sub 1-x}(Ca or Sr){sub x}MnO{sub 3} and Y{sub 1-x}Ca{sub x}MnO{sub 3} (LCM, LSM and YCM, respectively) and for Pt. Specific activities in the temperature and P(O{sub 2}) ranges of an operating solid oxide fuel cell (SOFC) cathode, 1173--1273K and 10{sup 5}-10{sup 3} Pa, were highest for LCM intermediate for YCM and lowest for LSM. For LCM and YCM, compositions with x=0.5 gave highest specific activities. Specific activities for all of the tested manganite compositions exceeded the platinum specific activities by at least an order of magnitude. Shapes of impedance spectra for all the manganite systems were similar. Examination of spectra shapes revealed that the overall cathodic polarization process was rather complex and made up of at least two or more fundamental steps.

  11. Eu2+-Activated CaSrSiO4: a New Red-Emitting Oxide Phosphor for White-Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Tezuka, Satoko; Sato, Yasushi; Komukai, Tetsufumi; Takatsuka, Yuji; Kato, Hideki; Kakihana, Masato

    2013-07-01

    Ca1-xSr1-xEu2xSiO4 (CaSrSiO4:Eu2+) phosphors were prepared by a novel aqueous solution technique using propylene glycol-modified silane (PGMS), combined with a freeze-drying process. The precursors were heat-treated under a reducing atmosphere with BaCl2 flux. X-ray diffraction indicated that the obtained phosphors exhibited an α'-CaSrSiO4 structure. The wavelength at the phosphors' maximum emission was systematically shifted beyond 600 nm as the Eu2+ concentration was increased. The corresponding excitation spectra were extended to the visible light region (400-500 nm) with increasing Eu2+ concentration. These results implied that CaSrSiO4:Eu2+ is a red-emitting phosphor excited by near-UV and blue-light-emitting diodes.

  12. Thermodynamic properties of Sr-doped LaMnO{sub 3} perovskite in the La-Sr-Mn-O system

    SciTech Connect

    Zheng, F.; Pederson, L.R.

    1999-08-01

    Thermodynamic properties of Sr-doped perovskite-type lanthanum manganites (LSM) were generated by measuring the electromotive force (EMF) of test materials, using the solid galvanic cell technique. The cell consisted of an anode (SrO/SrF{sub 2}), an electrolyte (CaF{sub 2} or SrF{sub 2}) and a cathode (LSM/SrF{sub 2}). Two types of cells were tested in which type 1 used a CaF{sub 2} electrolyte and type 2 used a SrF{sub 2} electrolyte. The activity of SrO substituting into various LSM compositions was calculated using the measured EMF. The Sr content was varied from 0.16 to 0.6 mol, and the temperature of interest varied from 700 to 1000 C. It was found that the SrO activity decreased with increasing temperature (at fixed composition) and increased with increasing Sr content (at fixed temperature).

  13. An apparent “vital effect” of calcification rate on the Sr/Ca temperature proxy in the reef coral Montipora capitata

    NASA Astrophysics Data System (ADS)

    Kuffner, Ilsa B.; Jokiel, Paul L.; Rodgers, Ku'ulei S.; Andersson, Andreas J.; MacKenzie, Fred T.

    2012-08-01

    Measuring the strontium to calcium ratio in coral skeletons reveals information on seawater temperatures during skeletal deposition, but studies have shown additional variables may affect the ratio. Here we measured Sr/Ca in the reef coral Montipora capitata grown in six mesocosms continuously supplied with seawater from the adjacent reef flat. Three mesocosms were ambient controls, and three had seawater chemistry simulating "ocean acidification" (OA). We found that Sr/Ca was not affected by the OA treatment and neither was coral calcification for these small colonies (larger colonies did show an OA effect). The lack of OA effects allowed us to test the hypothesis that coral growth rate can affect Sr/Ca using the natural range in calcification rates of the corals grown at the same temperature. We found that Sr/Ca was inversely related to calcification rate (Sr/Ca = 9.385 - 0.0040 (calcification rate)). Using a previously published calibration curve for this species, a 22 mg d-1 colony-1increase in calcification rate introduced a 1°C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9°C, with mean 26.6 ± 0.9°C standard deviation. Our results lend support to hypotheses invoking kinetic processes and growth rate to explain vital effects on Sr/Ca. However, uncertainty in the slope of the regression of Sr/Ca on calcification and a low R-squared value lead us to conclude that Sr/Ca could still be a useful proxy in this species given sufficient replication or by including growth rate in the calibration.

  14. Magnetic and dielectric properties of Bi3+ substituted SrFe12O19 hexaferrite

    NASA Astrophysics Data System (ADS)

    Auwal, I. A.; Erdemi, H.; Sözeri, H.; Güngüneş, H.; Baykal, A.

    2016-08-01

    In the present study, SrBixFe12-xO19 (0.0≤x≤1.0) nanomaterials were successfully synthesized by using chemical co-precipitation method. Products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Vibrating sample magnetometer (VSM), Mössbauer spectroscopy, AC conductivity and dielectric measurements. The crystal structural information studied by X-ray diffraction (XRD) indicated the formation of single phase pure hexagonal structure, while electron-dispersive X-ray spectroscopy (EDX) revealed the stoichiometric ratio among Bi, Sr, Fe elements. The crystallite sizes of the products were in the range of 65-82 nm. VSM analysis showed a tendency in saturation magnetization as Bi2O3 concentration raises, which can be ascribed to preferential site occupied by Bi3+ ions. The frequency-dependent ac conductivity plots exhibited similar trends for all samples. A significant temperature-dependent behavior was only observed at low and medium frequencies. The replacement of non-magnetic Bi3+ ions by Fe3+ ones having magnetic moment of 5 μB decrease the magnetic moment of 4f1 site. The AC conductivity increases with frequency as hopping of the charge carriers increases between Fe2+and Fe3+. The DC conductivity exhibited an improvement with increasing temperature and Bi content, and the highest conductivity was measured as 2.84×10-9 S cm-1 for x=0.8 at 120 °C. The variation of dielectric constant, dielectric loss and tangent loss was observed with the frequency and temperature due to change of electrical conductivity as x changes.

  15. Determining Solute Sources and Water Flowpaths in a Forested Headwater Catchment: Advances With the Ca-Sr-Ba Multi-tracer

    NASA Astrophysics Data System (ADS)

    Bullen, T. D.; Bailey, S. W.; McGuire, K. J.; Zimmer, M. A.; Ross, D. S.

    2011-12-01

    Determining solute sources and water flowpaths in catchments is of critical importance to development of models that effectively describe catchment function. For solutes in soil water and stream water, simple mass balance models that compare precipitation input to catchment outlet compositions can predict average mineral weathering contributions for the catchment as a whole, but fail to provide information about either variability of contributions from different portions of the catchment and different soil depths or processes such as ion exchange and biological cycling. In order to better understand how forested headwater catchments function, we are interpreting concentration and isotope ratios of the alkaline earth elements Ca, Sr and Ba in streamwater, groundwater, the soil ion exchange pool and plants in a hydropedologic context at the 41 hectare hydrologic reference catchment (Watershed 3) at the Hubbard Brook Experimental Forest, New Hampshire, USA. This forested headwater catchment consists of a beech-birch-maple-spruce forest growing on vertically- and laterally-developed Spodosols and Inceptisols formed on granitoid glacial till that mantles Paleozoic metamorphic bedrock. Across the watershed in terms of the soil ion exchange pool, the forest floor has high Sr/Ba and Ca/Sr ratios, mineral soils have intermediate Sr/Ba and low Ca/Sr, and relatively unweathered till in the C horizon has low Sr/Ba and high Ca/Sr. Waters moving through these various compartments will obtain Sr/Ba and Ca/Sr ratios reflecting these characteristics, and thus variations of Sr/Ba and Ca/Sr of streamwater provide evidence of the depth of water flowpaths feeding the streams. 87Sr/86Sr of exchangeable Sr spans a broad range from 0.715 to 0.725, with highest values along the mid-to upper flanks of the catchment and lowest values in a broad zone along the central axis of the catchment associated with numerous groundwater seeps. Thus, variations of 87Sr/86Sr in streamwater provide

  16. Understanding cold bias: Variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals.

    PubMed

    Cole, Catherine; Finch, Adrian; Hintz, Christopher; Hintz, Kenneth; Allison, Nicola

    2016-01-01

    Coral skeletal Sr/Ca is a palaeothermometer commonly used to produce high resolution seasonal sea surface temperature (SST) records and to investigate the amplitude and frequency of ENSO and interdecadal climate events. The proxy relationship is typically calibrated by matching seasonal SST and skeletal Sr/Ca maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal Sr/Ca is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present Sr/Ca analyses of 3 genotypes of massive Porites spp. corals (the genus most commonly used for palaeoclimate reconstruction), cultured under seawater pCO2 reflecting modern, future (year 2100) and last glacial maximum (LGM) conditions. Skeletal Sr/Ca is indistinguishable between duplicate colonies of the same genotype cultured under the same conditions, but varies significantly in response to seawater pCO2 in two genotypes of Porites lutea, whilst Porites murrayensis is unaffected. Within P. lutea, the response is not systematic: skeletal Sr/Ca increases significantly (by 2-4%) at high seawater pCO2 relative to modern in both genotypes, and also increases significantly (by 4%) at low seawater pCO2 in one genotype. This magnitude of variation equates to errors in reconstructed SST of up to -5 °C. PMID:27241795

  17. Understanding cold bias: Variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals

    PubMed Central

    Cole, Catherine; Finch, Adrian; Hintz, Christopher; Hintz, Kenneth; Allison, Nicola

    2016-01-01

    Coral skeletal Sr/Ca is a palaeothermometer commonly used to produce high resolution seasonal sea surface temperature (SST) records and to investigate the amplitude and frequency of ENSO and interdecadal climate events. The proxy relationship is typically calibrated by matching seasonal SST and skeletal Sr/Ca maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal Sr/Ca is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present Sr/Ca analyses of 3 genotypes of massive Porites spp. corals (the genus most commonly used for palaeoclimate reconstruction), cultured under seawater pCO2 reflecting modern, future (year 2100) and last glacial maximum (LGM) conditions. Skeletal Sr/Ca is indistinguishable between duplicate colonies of the same genotype cultured under the same conditions, but varies significantly in response to seawater pCO2 in two genotypes of Porites lutea, whilst Porites murrayensis is unaffected. Within P. lutea, the response is not systematic: skeletal Sr/Ca increases significantly (by 2–4%) at high seawater pCO2 relative to modern in both genotypes, and also increases significantly (by 4%) at low seawater pCO2 in one genotype. This magnitude of variation equates to errors in reconstructed SST of up to −5 °C. PMID:27241795

  18. Understanding cold bias: Variable response of skeletal Sr/Ca to seawater pCO2 in acclimated massive Porites corals

    NASA Astrophysics Data System (ADS)

    Cole, Catherine; Finch, Adrian; Hintz, Christopher; Hintz, Kenneth; Allison, Nicola

    2016-05-01

    Coral skeletal Sr/Ca is a palaeothermometer commonly used to produce high resolution seasonal sea surface temperature (SST) records and to investigate the amplitude and frequency of ENSO and interdecadal climate events. The proxy relationship is typically calibrated by matching seasonal SST and skeletal Sr/Ca maxima and minima in modern corals. Applying these calibrations to fossil corals assumes that the temperature sensitivity of skeletal Sr/Ca is conserved, despite substantial changes in seawater carbonate chemistry between the modern and glacial ocean. We present Sr/Ca analyses of 3 genotypes of massive Porites spp. corals (the genus most commonly used for palaeoclimate reconstruction), cultured under seawater pCO2 reflecting modern, future (year 2100) and last glacial maximum (LGM) conditions. Skeletal Sr/Ca is indistinguishable between duplicate colonies of the same genotype cultured under the same conditions, but varies significantly in response to seawater pCO2 in two genotypes of Porites lutea, whilst Porites murrayensis is unaffected. Within P. lutea, the response is not systematic: skeletal Sr/Ca increases significantly (by 2–4%) at high seawater pCO2 relative to modern in both genotypes, and also increases significantly (by 4%) at low seawater pCO2 in one genotype. This magnitude of variation equates to errors in reconstructed SST of up to ‑5 °C.

  19. Observation of the flux line lattice and crystal defects in Bi-Sr-Ca-Cu-O single crystals

    NASA Astrophysics Data System (ADS)

    Furusawa, K.; Zhao, Y.; Chikumoto, N.; Kishio, K.; Nagatomo, T.; Murakami, M.

    2003-10-01

    We have observed flux line lattice (FLL) structure in two different types of Bi 2Sr 2CaCu 2O 8+ δ (Bi-2212) single crystals with different pinning by using a Bitter decoration technique. We have also observed the microstructure and analyzed local chemical composition with wave dispersive spectroscopic analyses. In a low Jc sample, we found two types of line defects, one with Ca-rich and the other with Ca-deficient. These defects extended almost parallel to the growth direction, which caused a distortion in the FLL structure. In contrast, no such defects were observed in the matrix in a high- Jc sample, and a relatively ordered FLL was observed.

  20. The Effect of the CO32- to Ca2+ Ion activity ratio on calcite precipitation kinetics and Sr2+ partitioning

    SciTech Connect

    Tsigabu Gebrehiwet; Mikala S. Beig; George Redden; Yoshiko Fujita; Robert W. Smith

    2012-01-01

    Engineering the precipitation of calcium carbonate, which can co-precipitate trace metal contaminants, is a proposed strategy for remediating toxic or radioactive metals in subsurface environments. Engineering precipitation of multi-component minerals will involve injection of chemical amendments that must be mixed at a molecular level to supersaturated conditions that are sufficient to promote rapid mineral precipitation relative to natural systems. In subsurface systems this often means reactant mixing zones will be formed that are characterized by gradients in solute concentrations, saturation state, and solute activity ratios. To better understand the effect of ion activity ratios on CaCO{sub 3} precipitation kinetics and Sr{sup 2+} co-precipitation we experiments were conducted under constant composition conditions where the supersaturation state ({Omega}) with respect to calcite was held constant at 9.4, but the ion activity ratio (r = a{sub co{sub 3}{sup 2-}}/a{sub Ca{sup 2+}}) ranged from 0.003 to 4.15. Results: Under the chosen experimental conditions the CaCO{sub 3} phase formed was calcite and initial precipitation rates varied from a maximum rate of 84.7 {mu}mol/ m{sup 2}/min for a carbonate to calcium activity ratio of (0.21). However, precipitation rates were found to vary with time which could be indicative of variations in precipitation mechanisms that are related to the ion activity ratio. The observed trends in the distribution coefficients for co-precipitated Sr2+ (D{sup P}{sub Sr}{sup 2+}) relative to the calcite precipitation rate (i.e. a positive correlation) indicate that increasing calcite precipitation rates increase the incorporation of Sr{sup 2+}. Conclusion: The observed variation between the rate maxima and minima based on the ion activity ratio could have great deal of implication for sequestering radionuclides (e.g. {sup 90}Sr) and other toxic metals in engineered systems at contaminated sites. Extending our data plot range allowed us

  1. Influence of chemical substitution on the photoluminescence of Sr{sub (1−x)}Pb{sub x}WO{sub 4} solid solution

    SciTech Connect

    Hallaoui, A.; Taoufyq, A.; Arab, M.; Bakiz, B.; Benlhachemi, A.; Bazzi, L.; Villain, S.; Valmalette, J-C.; Guinneton, F.; Gavarri, J-R.

    2015-07-15

    The solid solution Sr{sub 1−x}Pb{sub x}WO{sub 4} based on luminescent tungstates SrWO{sub 4} and PbWO{sub 4} has been synthesized by solid-state reaction for all compositions 0≤x≤1. Using Rietveld method, the structural data of all polycrystalline samples have been refined and crystal cell parameters exhibited a linear behavior as a function of x. All substituted structures are of scheelite type. Scanning electron microscopy showed that a high level of crystallization characterized the samples, with modifications in sizes and shapes depending on composition x. Infrared and Raman spectroscopy have been performed to characterize the evolution of vibrational modes with substitution rate. Finally, a systematic study of luminescence under X-ray excitation has been performed: in the composition range x=0.2 to 0.4, intensities of emission exhibited increased values. The luminescence profiles have been interpreted in terms of four Gaussian components, two of them depending on substitution rate. - Graphical abstract: Photoluminescence under X-ray excitation of Sr{sub 1−x}Pb{sub x}WO{sub 4} solid solution: (left) decomposition of emission large band into four components for composition x=0.3; (right) variation of total emission intensity with composition x. - Highlights: • Structural study of solid solution Sr{sub 1−x}Pb{sub x} WO{sub 4} using Rietveld analyses. • Variation of Debye–Waller factor with composition x, disorder parameter. • Existence of four components of luminescence under X-ray excitation. • Effect of substitution of Sr by Pb on two components, due to Pb–O–W interactions. • Enhancement of luminescence intensity in a specific composition range.

  2. Enhancement of redox- and phase-stability of thermoelectric CaMnO{sub 3−δ} by substitution

    SciTech Connect

    Thiel, Philipp; Populoh, Sascha; Yoon, Songhak; Weidenkaff, Anke

    2015-09-15

    Redox Reactivity and structural phase transitions have a major impact on transport and me-chemical properties of thermoelectric CaMnO{sub 3−δ}. In this study series of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} (0≤x,y≤0.8) compounds, each with A-site (Dy{sup 3+}, Yb{sup 3+}) or B-site (Nb{sup 5+}, Ta{sup 5+} and Mo{sup 6+}, W{sup 6+}) substitution, were synthesized and crystallographically analyzed. It was found that the high-temperature oxygen content is widely independent from the substituent. Subsequently, with increasing temperature the differences in the Seebeck coefficient vanish above 1200 K. With increasing substitution the orthorhombic distortion of the perovskite-like phase increases. The orthorhombic distortion and the upper temperature limit of the stability of the orthorhombic crystal structure show an almost linear dependency. Accordingly, the mechanical stability of all-oxides thermoelectric converters at temperatures exceeding 1000 K will be increased employing materials with high substitution level and substituents inducing a high orthorhombic distortion. - Graphical abstract: Thermoelectric n-type CaMn{sub 0.98}W{sub 0.02}O{sub 3−δ}—Transport properties and expansion coefficient of: Oxygen loss (green region) and upper stability limit of the orthorhombic phase (yellow region) strongly affect the transport properties. Both features also cause lattice expansion, which leads to cracking of thermoelectric all-oxide converters. We report how the upper limit for application can be shifted to even higher temperatures. - Highlights: • Level of Mn{sup 3+} at RT determines reduction behavior of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} at HT. • Differences in Seebeck coefficient vanish at T>1200 K independent from substitution. • Substitution increases orthorhombicity of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ}. • Linear dependence of orthorhombicity and phase stability. • Design guidelines for

  3. High-Tc superconductivity at the interface between the CaCuO2 and SrTiO3 insulating oxides

    DOE PAGESBeta

    Di Castro, D.; Cantoni, C.; Ridolfi, F.; Aruta, C.; Tebano, A.; Yang, N.; Balestrino, G.

    2015-09-28

    At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low Tc. We report the occurrence of high Tc superconductivity in the bilayer CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case can oxygen ions be incorporated in themore » interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 planes. In addition, a detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1–2 CaCuO2 unit cells close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3 interface can be extended to multilayered high Tc cuprates, contributing to explaining the dependence of Tc on the number of CuO2 planes in these systems.« less

  4. Store-operated Ca²⁺ entry and depolarization explain the anomalous behaviour of myometrial SR: effects of SERCA inhibition on electrical activity, Ca²⁺ and force.

    PubMed

    Noble, Debbie; Borysova, Lyudmyla; Wray, Susan; Burdyga, Theodor

    2014-09-01

    In the myometrium SR Ca(2+) depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca(2+) sparks-STOCs coupling mechanism to explain this. Given the importance of the control of contractility for successful parturition, we have examined, in pregnant rat myometrium, the effects of SR Ca(2+)-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca(2+) transients and force. Simultaneous recording of electrical activity, calcium and force showed that SERCA inhibition, by cyclopiazonic acid (CPA 20 μM), caused time-dependent changes in excitability, most noticeably depolarization and elevations of baseline [Ca(2+)]i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca(2+) spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca(2+) and depolarization continued a point was reached when electrical and Ca(2+) spikes and phasic contractions ceased, and a maintained, tonic force and Ca(2+) was produced. Lanthanum, a non-selective blocker of store-operated Ca(2+) entry, but not the L-type Ca(2+) channel blocker nifedipine (1-10 μM), could abolish the maintained force and calcium. Application of the agonist, carbachol, produced similar effects to CPA, i.e. depolarization, elevation of force and calcium. A brief, high concentration of carbachol, to cause SR Ca(2+) depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca(2+) release is coupled to marked Ca(2+) entry, via store operated Ca(2+) channels, leading to depolarization and enhanced electrical and mechanical activity. PMID:25084623

  5. The deposition of strontium-substituted hydroxyapatite coatings.

    PubMed

    Boyd, Adrian R; Rutledge, L; Randolph, L D; Mutreja, I; Meenan, B J

    2015-02-01

    Strontium substituted hydroxyapatite (SrHA) coatings have received a lot of interest recently as strontium (Sr) has been shown to have the dual benefit of promoting bone formation and reducing bone resorption, in vivo. In this work, SrHA coatings were deposited onto polycrystalline titanium surfaces using radio frequency (RF) magnetron co-sputtering and compared to those deposited from HA alone. In particular, the influence of different levels of Sr-substitution of the sputtering targets (5 and 13% Sr-substituted HA targets) on the properties of the deposited coatings produced at a low discharge power level (150 W) were investigated using FTIR, XPS, XRD, ToFSIMS and AFM techniques (both before and after annealing at 500 °C). The results show that Sr could be successfully incorporated into the HA lattice to form SrHA coatings and that they contained no other impurities. However, the coating produced from the 13% Sr-substituted target had a higher Ca+Sr/P ratio (1.95±0.14) and Sr content when compared to the coating produced from the 5% Sr-substituted target (1.58±0.20). The deposition rate also decreased with increasing Sr content of the sputtering targets. Furthermore, as the Sr content of the coatings increased, so did the preferred 002 orientation of the coating along with increased surface roughness and heterogeneity of the surface features. Therefore, this study has shown that RF magnetron sputtering offers a means to control attendant properties of Sr-substituted HA, such as the crystallinity, stoichiometry, phase purity and surface topography. PMID:25631262

  6. M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion

    SciTech Connect

    Popa, Karin; Wallez, Gilles; Bregiroux, Damien; Loiseau, Pascal

    2011-10-15

    Three earth alkali-germanium monophosphates M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO{sub 4}){sub 2} and high-temperature {beta}-SrGe(PO{sub 4}){sub 2} (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO{sub 4}){sub 2} and low-temperature {alpha}-SrGe(PO{sub 4}){sub 2} (C2/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The thermal expansion, resulting from several structural mechanisms, is very anisotropic. - Graphical abstract: The superstructure of SrGe(PO{sub 4}){sub 2} at room temperature ({alpha}) results from the off-centering of cation Sr{sup II}. Highlights: > Crystal structures of yavapaiite-type M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) have been solved. > Distortion and superstructure result from Ca and Sr off-centering. > A global scheme for the polymorphism of yavapaiites is proposed.

  7. Characterization of hot isostatically pressed Bi-Sr-Ca-Cu-O as a function of consolidation variables

    SciTech Connect

    Goretta, K.C.; Miller, D.J.; Poeppel, R.B. ); Nash, A.S. )

    1991-11-01

    Fully dense, bulk Bi{sub 2}Sr{sub 1.7}CaCu{sub 2}O{sub x} (2212) superconductor pellets were made by hot isostatic pressing in an inert atmosphere. Electron microscopy revealed that rotation and bending of the platelike 2212 grains were responsible for much of the densification. Under processing conditions of 825{degrees}C and 105 MPa, dense pellets were obtained in 15 min. Many dislocations, planar faults, and, perhaps, intergrowths of the Bi{sub 2}Sr{sub 2}CuO{sub x} phase were produced during pressing. The dislocations were largely present in subgrain boundaries when the pressing times were increased to 45--120 min.

  8. Structural and Magnetic Phase Coexistence in Oxygen Deficient Perovskites (Sr,Ca)FeO 2 . 5 + δ

    NASA Astrophysics Data System (ADS)

    Carlo, J. P.; Evans, M. E.; Anczarski, J. A.; Ock, J.; Boyd, K.; Pollichemi, J. R.; Leahy, I. A.; Vogel, W.; Viescas, A. J.; Papaefthymiou, G. C.

    A variety of compounds crystallize into perovskite and similar structures, making them versatile laboratories for many phenomena and applications, including multiferroicity, superconductivity, and photovoltaics. Oxygen-deficient perovskites ABOx have attracted interest for use in fuel cells and related applications due to high oxygen mobility and the possibility of charge disproportionation. Vast chemical flexibility is obtained through reductions in lattice symmetry and rotation/distortion of the BO6 octahedra, as well as ordering of oxygen vacancies. We have synthesized and studied the structural and magnetic properties of oxygen-deficient perovskites (Sr,Ca)FeO2 . 5 + δ using x-ray diffraction and Mossbauer spectroscopy. While the ideal perovskite has δ = 0.5, this requires Fe4+, and hence strongly oxidizing environments. When grown in air, Fe3+ is favored, yielding δ ~ 0. SrFeO2 . 5 + δ exhibits cubic symmetry and paramagnetism at 300K, but CaFeO2 . 5 + δ crystallizes into the orthorhombic brownmillerite structure, and is magnetically ordered at 300K. In the doped intermediaries we find coexistence of cubic/paramagnetic and orthorhombic/magnetic phases over a wide range of Ca content. Financial support from the Villanova Undergraduate Research Fellowship program and the Research Corporation for Science Advancement.

  9. Interaction of overlayers of Al and Rb with single-crystalline surfaces of Bi2Sr2CaCu2O8

    NASA Astrophysics Data System (ADS)

    Lindberg, P. A. P.; Wells, B. O.; Shen, Z.-X.; Dessau, D. S.; Lindau, I.; Spicer, W. E.; Mitzi, D. B.; Kapitulnik, A.

    1990-03-01

    Photoemission results from Al and Rb interfaces with single crystals of Bi2Sr2CaCu2O8 high-temperature superconductors are reported. The Al and Rb adsorbates are found to react quite differently with the Bi2Sr2CaCu2O8 substrate. While adatoms of Rb significantly affect only the Bi and O atoms in the top atomic layer, the Al adsorbate profoundly disrupts the bonding character of the whole Bi2Sr2CaCu2O8 material. For Al, the Bi and Cu states are strongly reduced, and the Sr and O states show evidence of oxidized components. In addition, Al causes a strong out-diffusion of oxygen from the bulk. The differences in the reactivity of Al and Rb are discussed in terms of the different mobility of the two atoms.

  10. Microstructure and magnetic properties of electrospun one-dimensional Al{sup 3+}-substituted SrFe{sub 12}O{sub 19} nanofibers

    SciTech Connect

    Liu, Mingquan; Shen, Xiangqian; Song, Fuzhan; Xiang, Jun; Meng, Xianfeng

    2011-04-15

    SrAl{sub x}Fe{sub 12-x}O{sub 19} (x=0-3.0) nanofibers with diameters about 100 nm have been prepared by electrospinning and subsequent heat treatment. With Al{sup 3+} ion content ranging from 0 to 3.0, the lattice parameters decrease due to Fe{sup 3+} ions substituted by smaller Al{sup 3+} ions and the average grain size calculated by the Scherrer's equation reduces from 65 to 37 nm. The magnetization shows a continuous reduction with the Al content and its value measured at 77 K is higher than at room temperature, which can be explained by Bloch's law. For the coercivity, its value initially increases, reaching a maximum value of 617 (298 K) and 547 kA m{sup -1} (77 K) at x=2.0, and then reduces with the Al content further increase largely arising from the substituted Al{sup 3+} ion arrangement in different interstitial sites of the strontium ferrite unit cell. -- Graphical abstract: Al{sup 3+} ions substituted strontium ferrite nanofibers have been prepared by the electrospinning with a diameter of about 100 nm and the Al{sup 3+} ion substitution has a great effect on the microstructure and magnetic property of SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers. Display Omitted Research highlights: {yields} SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers have been fabricated by the electrospinning. {yields} There is a relation between the Al{sup 3+} ions substitution and microstructure. {yields} The magnetic property can be tuned effectively by Al{sup 3+} ion substitution. {yields} The magnetic property is influenced by measurement temperature.

  11. Thermal expansion behaviour in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Competing effects of water and oxygen ordering

    SciTech Connect

    Zhou Qingdi; Kennedy, Brendan J.; Avdeev, Maxim

    2011-09-15

    Neutron diffractions studies reveal the presence of oxygen disorder in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Synchrotron X-ray studies demonstrate that these oxides have a double perovskite-type structure with the cell size increasing as the size of the B cation increases from 8.2114(2) A for B=Ca to 8.4408(1) A for B=Ba. It is postulated that a combination of local clustering of the anions and vacancies together with water-water and water-host hydrogen bonds plays a role in defining the volume of the encapsulated water clusters and that changes in the local structure upon heating result in anomalous thermal expansion observed in variable temperature diffraction measurements. - Graphical abstract: The oxides Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba) have unusual anion disorder. There is a lag in the contraction in the cell size of Sr{sub 2}CaSbO{sub 5.5}nH{sub 2}O established from X-ray diffraction measurements following the loss of water suggesting changes on the local structure are important. Highlights: > The average structures of the defect perovskites Sr{sub 2}MSbO{sub 5.5} established. > Anion and cation disorder quantified by neutron and synchrotron X-ray diffraction. > Anomalous thermal expansion due to local clustering of anions and vacancies observed.

  12. Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy2Ti2O7

    NASA Astrophysics Data System (ADS)

    Anand, V. K.; Tennant, D. A.; Lake, B.

    2015-11-01

    Physical properties of partially Ca substituted hole-doped Dy2Ti2O7 have been investigated by ac magnetic susceptibility {χ\\text{ac}}(T) , dc magnetic susceptibility χ (T) , isothermal magnetization M(H) and heat capacity {{C}\\text{p}}(T) measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a spin-glass type freezing behavior near 16 K. Our frequency dependent {χ\\text{ac}}(T) data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly influenced by Ca substitution. The effect of partial nonmagnetic Ca2+ substitution for magnetic Dy3+ is similar to the previous study on nonmagnetic isovalent Y3+ substituted Dy2-x Y x Ti2O7 (for low levels of dilution), however the suppression of spin-freezing behavior is substantially stronger for Ca than Y. The Cole-Cole plot analysis reveals semicircular character and a single relaxation mode in Dy1.8Ca0.2Ti2O7 as for Dy2Ti2O7. No noticeable change in the insulating behavior of Dy2Ti2O7 results from the holes produced by 10% Ca2+ substitution for Dy3+ ions.

  13. Manganite based hetero-junction structure of La0.7Sr(0.7-x)CaxMnO3 and CaMnO(3-δ) for cross-point arrays.

    PubMed

    Lee, Hong-Sub; Park, Hyung-Ho

    2015-07-10

    Resistive random access memory and the corresponding cross-point array (CPA) structure have received a great deal of attention for high-density next generation non-volatile memory. However, the cross-talk issue of CPA structure by sneak current should be overcome to realize the highest density integration. To accomplish this, the sneak current can be minimized by high, nonlinear characteristic behaviors of resistive switching (RS). Therefore this study fabricated pnp bipolar hetero-junction structure using the perovskite manganite family, such as La0.7Sr(0.3-x)CaxMnO3 (LSCMO) and CaMnO(3-δ) (CMO), to obtain nonlinear RS behavior. The pnp structure not only shows nonlinear characteristics, but also a tunable characteristic with Ca substitution. PMID:26086277

  14. Detection of a Cooper-pair density wave in Bi2Sr2CaCu2O8+x.

    PubMed

    Hamidian, M H; Edkins, S D; Joo, Sang Hyun; Kostin, A; Eisaki, H; Uchida, S; Lawler, M J; Kim, E-A; Mackenzie, A P; Fujita, K; Lee, Jinho; Davis, J C Séamus

    2016-04-21

    The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state with a spatially modulated Cooper-pair density. Such a state has been created in ultracold (6)Li gas but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase of the copper oxide superconductors contains such a 'pair density wave' state. Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy to image Cooper pair tunnelling from a d-wave superconducting microscope tip to the condensate of the superconductor Bi2Sr2CaCu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms and at the Bi2Sr2CaCu2O8+x crystal supermodulation. Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors QP ≈ (0.25, 0)2π/a0 and (0, 0.25)2π/a0 in Bi2Sr2CaCu2O8+x. The amplitude of these modulations is about five per cent of the background condensate density and their form factor exhibits primarily s or s' symmetry. This phenomenology is consistent with Ginzburg-Landau theory when a charge density wave with d-symmetry form factor and wavevector QC = QP coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase. PMID:27074504

  15. Detection of a Cooper-pair density wave in Bi2Sr2CaCu2O8+x

    NASA Astrophysics Data System (ADS)

    Hamidian, M. H.; Edkins, S. D.; Joo, Sang Hyun; Kostin, A.; Eisaki, H.; Uchida, S.; Lawler, M. J.; Kim, E.-A.; MacKenzie, A. P.; Fujita, K.; Lee, Jinho; Davis, J. C. Séamus

    2016-04-01

    The quantum condensate of Cooper pairs forming a superconductor was originally conceived as being translationally invariant. In theory, however, pairs can exist with finite momentum Q, thus generating a state with a spatially modulated Cooper-pair density. Such a state has been created in ultracold 6Li gas but never observed directly in any superconductor. It is now widely hypothesized that the pseudogap phase of the copper oxide superconductors contains such a ‘pair density wave’ state. Here we report the use of nanometre-resolution scanned Josephson tunnelling microscopy to image Cooper pair tunnelling from a d-wave superconducting microscope tip to the condensate of the superconductor Bi2Sr2CaCu2O8+x. We demonstrate condensate visualization capabilities directly by using the Cooper-pair density variations surrounding zinc impurity atoms and at the Bi2Sr2CaCu2O8+x crystal supermodulation. Then, by using Fourier analysis of scanned Josephson tunnelling images, we discover the direct signature of a Cooper-pair density modulation at wavevectors QP ≈ (0.25, 0)2π/a0 and (0, 0.25)2π/a0 in Bi2Sr2CaCu2O8+x. The amplitude of these modulations is about five per cent of the background condensate density and their form factor exhibits primarily s or s‧ symmetry. This phenomenology is consistent with Ginzburg–Landau theory when a charge density wave with d-symmetry form factor and wavevector QC = QP coexists with a d-symmetry superconductor; it is also predicted by several contemporary microscopic theories for the pseudogap phase.

  16. Gas-phase particle size distributions and lead loss during spray pyrolysis of (Bi,Pb)--Sr--Ca--Cu--O

    SciTech Connect

    Gurav, A.S.; Kodas, T.T.; Joutsensaari, J.; Kauppinen, E.I.; Zilliacus, R.

    1995-07-01

    Gas-phase particle size distributions and lead loss were measured during formation of (Bi,Pb)--Sr--Ca--Cu--O and pure PbO particles by spray pyrolysis at different temperatures. A differential mobility analyzer (DMA) in conjunction with a condensation particle counter (CPC) was used to monitor the gas-phase particle size distributions, and a Berner-type low-pressure impactor was used to obtain mass size distributions and a Berner-type low-pressure impactor was used to obtain mass size distributions and size-classified samples for chemical analysis. For (Bi,Pb)--Sr--Ca--Cu--O, as the processing temperature was raised from 200 to 700 {degree}C, the number average particle size decreased due to metal nitrate decomposition, intraparticle reactions forming mixed-metal oxides and particle densification. The geometric number mean particle diameter was 0.12 {mu}m at 200 {degree}C and reduced to 0.08 and 0.07 {mu}m, respectively, at 700 and 900 {degree}C. When the reactor temperature was raised from 700 and 800 {degree}C to 900 {degree}C, a large number ({similar_to}10{sup 7} no./cm{sup 3}) of new ultrafine particles were formed from PbO vapor released from the particles and the reactor walls. Particles made at temperatures up to 700 {degree}C maintained their initial stoichiometry over the whole range of particle size monitored, however; those made at 800 {degree}C and above were heavily depleted in lead in the size range 0.5--5.0 {mu}m. The evaporative losses of lead oxide from (Bi,Pb)--Sr--Ca--Cu--O particles were compared with the losses from PbO particles to gain insight into the pathways involved in lead loss and the role of intraparticle processes in controlling it.

  17. Structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Cinthia, A. Jemmy; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Iyakutti, K.

    2015-04-01

    The structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba) in the cubic (B1, B2 and B3) phases and in the wurtzite (B4) phase are investigated using density functional theory calculations as implemented in VASP code. The lattice constants, cohesive energy, bulk modulus, band structures and the density of states are computed. The calculated lattice parameters are in good agreement with the experimental and the other available theoretical results. Electronic structure reveals that all the five alkaline earth metal oxides exhibit semiconducting behavior at zero pressure. The estimated band gaps for the stable wurtzite phase of BeO is 7.2 eV and for the stable cubic NaCl phases of MgO, CaO, SrO and BaO are 4.436 eV, 4.166 eV, 4.013 eV, and 2.274 eV respectively. A pressure induced structural phase transition occurs from wurtzite (B4) to NaCl (B1) phase in BeO at 112.1 GPa and from NaCl (B1) to CsCl (B2) phase in MgO at 514.9 GPa, in CaO at 61.3 GPa, in SrO at 42 GPa and in BaO at 14.5 GPa. The elastic constants are computed at zero and elevated pressures for the B4 and B1 phases for BeO and for the B1 and B2 phases in the case of the other oxides in order to investigate their mechanical stability, anisotropy and hardness. The sound velocities and the Debye temperatures are calculated for all the oxides using the computed elastic constants.

  18. Thermodynamic investigation of the magnetic phase transitions of CaMnO3 and SrRuO3

    NASA Astrophysics Data System (ADS)

    Neumeier, J. J.; Cornelius, A. L.; Andres, K.

    2001-11-01

    Measurements of the linear thermal expansion Δl/l and molar heat capacity CP at constant pressure are presented on antiferromagnetic CaMnO3 and ferromagnetic SrRuO3 in the neighborhood of their magnetic phase transitions. The jumps in the linear thermal-expansion coefficient α and CP are used to calculate the influence of pressure on the magnetic ordering temperatures Tc through the Ehrenfest relation. Good agreement is obtained with measured values of dTc/dP.

  19. Magnetic behaviour of the MTbF{sub 6} fluoroterbates (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba)

    SciTech Connect

    Josse, M.; El-Ghozzi, M.; Avignant, D.; Andre, G.; Bouree, F.; Isnard, O.

    2012-01-15

    Neutron powder diffraction has been performed on the MTbF{sub 6} fluorides (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba). Four of these fluorides (Cd, Ca, Sr, {beta}-Ba) are built of a (pseudo-) tetragonal packing of [TbF{sub 6}]{sup 2-} chains and only differs by the chains relative orientations. Thus this series represents a valuable opportunity to evaluate the Tb{sup 4+}-Tb{sup 4+} magnetic interactions. All the compounds displayed antiferromagnetic order (T{sub N}=2.70 K (Cd), 2.15 K (Ca), 2.60 K (Sr), 2.10 K ({beta}-Ba)), except for the {alpha} form of BaTbF{sub 6}. The crystal structure of this latter fluoroterbate has also been investigated by means of high-resolution neutron powder diffraction. From Neutron Powder Diffraction data, CdTbF{sub 6} and {beta}-BaTbF{sub 6} magnetic structures were determined, together with the metamagnetic behaviour of {beta}-BaTbF{sub 6} as a function of an external magnetic field. A tentative phase diagram is then given for {beta}-BaTbF{sub 6}. Advantage was taken of the polymorphism of the BaTbF{sub 6} fluoroterbate to analyse, on the basis of topological parameters such as bond distances and angles, the magnetic behaviour of its {alpha} and {beta} forms. It was shown that superexchange interactions are present in {beta}-BaTbF{sub 6}, and that these interactions may also rule the magnetic behaviour of the other MTbF{sub 6} (M=Ca, Sr, Cd) tetravalent terbium fluorides. - Graphical abstract: Powder neutron diffraction revealed magnetic order in four of the five investigated fluoroterbates, while crystal chemical analyses of {alpha} and {beta} forms of BaTbF{sub 6} evidenced the existence of superexchange interactions. Highlights: Black-Right-Pointing-Pointer Five fluoroterbates are investigated by Powder Neutron Diffraction (PND). Black-Right-Pointing-Pointer Four of them are antiferromagnetically ordered at 1.4 K. Black-Right-Pointing-Pointer Magnetic structures of {beta}-BaTbF{sub 6} and CdTbF{sub 6} are determined. Black

  20. The GW electronic structure of cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Syrotyuk, Stepan V.; Shved, Vira M.

    2015-09-01

    The electronic energy band spectra of cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba) have been evaluated within the projector augmented waves (PAW) approach by means of the ABINIT code. The Kohn-Sham single-particle states have been found in the LDA framework. Our parameters of the electron energy bands obtained in the LDA are in good agreement with the published results of other authors. The calculated GW band gaps and dielectric constants are well compared with the available experimental data. The quasiparticle energies and density of states of electrons as well as the dielectric constants were obtained in the approximation GW for the first time.

  1. Stitching of fluxoids parallel to the superconducting sheet in Bi 2Sr 2CaCu 2O 8+ δ

    NASA Astrophysics Data System (ADS)

    Nakaharai, S.; Ishiguro, T.; Watauchi, S.; Shimoyama, J.; Kishio, K.

    2001-09-01

    In the two-dimensional superconductor Bi 2Sr 2CaCu 2O 8+ δ, the fluxoids parallel to the superconducting plane can move freely along the plane, but when on an incline in relation to the plane their movement is impeded by pinned pancake vortices. This behavior was studied in detail in the present study based on rf susceptibility measurements. The relaxation time for depinning was evaluated as a function of temperature and field by swinging crystals in a magnetic field in the proximity of the plane. The contribution of vortex-antivortex annihilation to the liberation of fluxoids is also discussed.

  2. Superconducting properties of doped and off-stoichiometric Bi 2Sr 2CaCu 2O 8 single crystals

    NASA Astrophysics Data System (ADS)

    Balakrishnan, G.; Paul, D. M. c.K.; Lees, M. R.

    1994-02-01

    High quality single crystals and grain aligned rods of off-stoichiometric Bi-2212 superconductor have been grown by the ‘floating zone’ method using an infra-red image furnace. Growths starting from off-stoichiometric compositions have been performed to optimize the size of the crystals and their superconducting properties. Aligned rods and single crystals of the Y doped compound, Bi 2.2Sr 1.64Ca 0.96Y 0.2Cu 2O 8, have also been grown successfully and characterized. The effects of annealing and oxygen stoichiometry on the superconducting properties of these crystals are presented.

  3. Crystallography, chemistry and structural disorder in the new high-Tc Bi-Ca-Sr-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Veblen, D. R.; Heaney, P. J.; Angel, R. J.; Finger, L. W.; Hazen, R. M.

    1988-01-01

    Diffraction experiments are reported which indicate that the new Bi-Ca-Sr-Cu-O layer-structure superconductor possesses a primitive orthorhombic unit cell with probable space group Pnnn. The material exhibits severe structural disorder which is primarily related to stacking within the layers. The apparent orthorhombic structure is an average resulting from orthorhombic material mixed with monoclinic domains in two twinned orientations. Two distinct types of structural disorder that are common in materials synthesized to date are also described. This disorder complicates the crystallographic analysis and suggests that X-ray and neutron diffraction methods may yield only an average structure.

  4. Properties of Bi(Pb)-Sr-Ca-Cu-O superconducting tapes prepared by the doctor-blade process

    SciTech Connect

    Yanagisawa, E.; Morimoto, T.; Dietderich, D. R.; Kumakura, H.; Togano, K.; Maeda, H.

    1989-06-19

    Improved superconducting and mechanical properties were obtained forBi(Pb)-Sr-Ca-Cu-O tapes, prepared by the combined process of doctor-bladecasting, cold rolling, and sintering. The tape has an oriented microstructurewith the high /ital T//sub /ital c// plate-like grains having their /ital c/ axesperpendicular to the rolling surface. The tape is flexible and can be bentwithout any degradation of /ital J//sub /ital c// to just before fracture (strainlarger than /similar to/0.12%).

  5. Photoluminescence property of A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] phosphors.

    PubMed

    Singh, Roshani; Dhoble, S J

    2013-01-01

    A new efficient phosphor, A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] has been synthesized by the solid-state method at high temperature. X-ray diffraction analysis confirmed the formation of the compound. Photoluminescence excitation measurements show that the phosphor can be efficiently excited by near-ultraviolet light from 300 nm to 400 nm to realize emission covering the 397-647 nm region of visible spectrum. Therefore, newly synthesized novel phosphor may be useful as green-emitting phosphor in solid-state lighting. PMID:22961920

  6. Resonant phase escape in Bi2Sr2CaCu2O8+δ surface intrinsic Josephson junctions

    NASA Astrophysics Data System (ADS)

    Yu, H. F.; Zhu, X. B.; Ren, J. K.; Peng, Z. H.; Cui, D. J.; Deng, H.; Cao, W. H.; Tian, Ye; Chen, G. H.; Zheng, D. N.; Jing, X. N.; Lu, Li; Zhao, S. P.

    2013-09-01

    We present a study of phase escape in surface Bi2Sr2CaCu2O8+δ intrinsic Josephson junctions in the presence of microwave radiation. The measured switching current distributions display clear double-peak structures in the microwave field, which result from the single- and two-photon resonant escape processes accompanied by microwave-induced potential barrier suppression. We show that these results can be well explained by a quantum-mechanical model proposed by Fistul et al (2003 Phys. Rev. B 68 060504), from which the power and frequency dependences of the switching current distributions can be reproduced.

  7. Replicating and calibrating Haitian microatoll coral Sr/Ca variations to build confidence in sea surface temperature reconstructions

    NASA Astrophysics Data System (ADS)

    Ouellette, G., Jr.; DeLong, K. L.; Kilbourne, K. H.; Taylor, F. W.; Mann, P.; Jean, P.

    2014-12-01

    Paleoclimatologists reconstruct sea surface temperature (SST) from corals by sampling boulder-shaped massive corals along the vertical growth direction or the assumed maximum growth axis to avoid kinetic effects related to variations in growth rate. Microatolls are a morphological variation of long-lived massive coral colonies that grow laterally just beneath the ocean surface. Cross-sections from five Siderastrea siderea microatolls, 35 km west of Port-au-Prince Haiti (18.479070°N, 72.668659°W), were recovered following the 2010 earthquake. Two colonies (10BELOC4 and 10LEO1), ~5.5 km apart, were sampled along paths oriented at 25° and 91° from the vertical growth direction; respectively, to determine differences in path orientation and between colonies. We find mean linear extension rates are similar (4.2 ±1.2 mm/year-1, 1σ for 10LEO1; and 4.3 ±1.3 mm/year-1, 1σ for 10BELOC4) with no significant correlation between intercolony linear extension rates (r=0.52, p=0.18, n=8) or between linear extension rates and SST (r=-0.20, p=0.31, n=29 for 10LEO1). We find similar intercolony seasonal variability in coral Sr/Ca (1.35 ±0.04 mmol/mol, 1σ for 10LEO1; and 1.41 ±0.05 mmol/mol, 1σ for 10BELOC4) and no significant difference (p<0.001) in mean coral Sr/Ca (8.90 ±0.05 mmol/mol, 1σ for 10LEO1; and 8.83 ±0.06 mmol/mol, 1σ for 10BELOC4; n=100). Calibration of coral Sr/Ca to OISST for the 1º grid including our study site results in a slope similar to previous studies using boulder-shaped S. siderea colonies (Sr/Ca=7.91-0.04(SST), r2=0.96, n=57). These results suggest that reliable SST reconstructions that span many centuries can be derived from large S. siderea microatolls.

  8. Multi-species Coral Sr/Ca-Based Sea-Surface Temperature Reconstruction Using Orbicella faveolata and Siderastrea siderea from Dry Tortugas National Park, FL

    NASA Astrophysics Data System (ADS)

    Flannery, J. A.; Richey, J. N.; Thirumalai, K.; Poore, R. Z.

    2015-12-01

    Massive coral skeletons provide an important geologic archive of climate information over the past several centuries, due to their annual banding patterns and longevity. The ratio of strontium to calcium (Sr/Ca) in coral skeletons is dependent on the temperature of the seawater at the time of growth and, therefore, provides a powerful proxy of historic sea-surface temperature (SST). This study used cores from two modern coral colonies—Orbicella faveolata (formerly Montastraea faveolata) and Siderastrea siderea—collected from the Dry Tortugas National Park, Florida (DRTO), located in the southern Gulf of Mexico. The corals were subsampled at monthly resolution and Sr/Ca determinations were made using ICP-OES. Sr/Ca was calibrated to SST using previously-published calibration equations specific to each species. Both the O. faveolata (1893-2008) and S. siderea (1837-2012) records have well-defined annual cycles of Sr/Ca, which suggest a seasonal SST range of ~10-15°C: a range consistent with in situ instrumental SST records from DRTO. Our reconstructions of mean annual Sr/Ca-based SST and Sr/Ca variability from the two coral species show similar multi-decadal trends and strong coherency through overlapping time intervals. We investigated the intervals of divergence among the three independent DRTO records (two different species), and found that sudden drops in linear extension in S. siderea likely skewed the mean annual temperature record. This result underscores the importance of using multiple-coral geochemical records when reconstructing regional climate. A stacked record of SST derived from the three different coral colonies growing at DRTO from 1837-2008 showed a distinct trend toward cooler mean annual Sr/Ca-based SST from the late 1950s to the late 1960s, which coincides with a cooling trend found in several other Northern Hemisphere temperature reconstructions, and is likely linked to variability of the Atlantic Multi-decadal Oscillation.

  9. Effects of antimony substitution on bismuth based superconductors

    NASA Technical Reports Server (NTRS)

    Barrientos, Alfonso

    1990-01-01

    The effect of Sb substitution and simultaneous substitution of Pb and Sb on the superconducting transition temperatures in the BiSrCaCuO system is investigated. The 2:2:2:3 phase is of particular interest since any small increase in the transition temperature could be of great interest. More that 90 different samples were prepared based on 2:2:2:3 stoichiometry in the BiSrCaCuO system. After this preliminary attempt, four different families of samples were investigated. In the first family of samples, Bi was substituted by Sb to form Bi(1.9)Sb(0.1)Sr2Ca2Cu3O(y). The second group of samples were prepared by simultaneous addition of Pb and Sb with nominal composition Bi(1.8)Pb(0.1)Sb(0.1)Sr2Ca2Cu3O(y). The third and fourth groups were prepared to determine the effect created when the Pb concentration is increased with the nominal compositions being Bi(1.7)Pb(0.1)Sr2Ca2Cu3O(y) and Bi(1.6)Sb(0.1)Sr2Ca2Cu3O(y). The results of these investigations are presented with a discussion.

  10. Molecular beam epitaxy fabrication of SrTiO3 and Bi2Sr2CaCu2O8 heterostructures using a novel reflection high-energy electron diffraction monitoring technique

    NASA Astrophysics Data System (ADS)

    Bodin, Peter; Sakai, Shigeki; Kasai, Yuji

    1992-07-01

    SrTiO3 and Bi2Sr2CaCu2O8 layered structures were continuously grown by the molecular beam epitaxy technique with in situ reflection high-energy electron diffraction (RHEED). By using a new RHEED picture subtraction technique, intensity changes due to only the topmost layer could be displayed. This method allows us to sensitively detect roughness on the atomic scale and excess phase formation. The SrTiO3 layer could be grown by sequential shuttering as well as coevaporation. A heterostructure with a 60 a Bi2Sr2CaCu2O8 film had a superconducting transition temperature of 53 K.

  11. The series Bi2Sr2Ca(n-1) Cu(n)O(2n+4) (1 less than or equal to n less than or equal to 5): Phase stability and superconducting properties

    NASA Technical Reports Server (NTRS)

    Deguire, Mark R.; Bansal, Narottam P.; Farrell, David E.; Finan, Valerie; Kim, Cheol J.; Hills, Bethanie J.; Allen, Christopher J.

    1989-01-01

    Phase relations at 850 and 870 C, melting transitions in air, oxygen, and helium were studied for Bi(2.1)Sr(1.9) CuO6 and for the Bi2Sr2Ca(n-1) Cu(n)O(2n+4) for n = 1, 2, 3, 4, 5, and infinity (CaCuO2). Up to 870 C, the n = 2 composition resides in the compatibility tetrahedron bounded by Bi(2+x)(Sr,Ca)(3-y) Cu2O8, (Sr,Ca)14 Cu24O41, Ca2CuO3, and a Bi-Sr-Ca-O phase. The n is greater than or equal to 3 compositions reside in the compatibility tetrahedron Bi(2+x)(Sr,Ca)(3-y) Cu2O8 - (Sr,Ca)14 Cu24O41 - Ca2CuO3 - CuO up to 850 C. However, Bi(2+x)Sr(4-y) Cu3O10 forms for n is greater than or equal to 3 after extended heating at 870 C. Bi(2+x)Sr(2-y) CuO6 and Bi(2+x)(Sr,Ca)(3-y) Cu2O8 melt in air at 914 C and 895 C respectively. During melting, all of the compositions studied lose 1 to 2 percent by weight of oxygen from the reduction of copper. Bi(2+x)Sr(2-y) CuO6, Bi(2+n)(Sr,Ca)(3-y) Cu2O8, and Bi(2+x)(Sr,Ca)(4-y) Cu3O10 exhibit crystallographic alignment in a magnetic field, with the c-axes orienting parallel to the field.

  12. Endohedral metallofullerenes, M@C60 (M = Ca, Na, Sr): selective adsorption and sensing of open-shell NOx gases.

    PubMed

    Tawfik, Sherif Abdulkader; Cui, X Y; Ringer, S P; Stampfl, C

    2016-08-21

    Based on density-functional theory and non-equilibrium Green's function calculations, we demonstrate that endohedral metallofullerenes (EMFs) are reactive to open-shell gases, and therefore have the potential application as selective open-shell gas sensors. The adsorption of eight gas species (CO, H2O, H2S, NO2, NO, SO2, O2 and NH3) on three EMFs (M@C60, M = Ca, Na and Sr) shows that the adsorption energies of the EMFs towards NO2 and NO are significantly higher than the closed-shell species. Moreover, the high selectivity appears relatively insensitive to the inserted metal atoms. The calculated current-voltage characteristics of gold-M@C60-gold structures (M = Ca, Na) show that the adsorption of NO2 leads to significant change in conductivity, suggesting a potential application as an EMF gas resistive sensing device. PMID:27426253

  13. Oxygen partial pressure dependence of magnetic, optical and magneto-optical properties of epitaxial cobalt-substituted SrTiO₃ films.

    PubMed

    Onbaşlı, Mehmet C; Goto, Taichi; Tang, Astera; Pan, Annia; Battal, Enes; Okyay, Ali K; Dionne, Gerald F; Ross, C A

    2015-05-18

    Cobalt-substituted SrTiO3 films (SrTi0.70Co0.30O(3-δ)) were grown on SrTiO3 substrates using pulsed laser deposition under oxygen pressures ranging from 1 μTorr to 20 mTorr. The effect of oxygen pressure on structural, magnetic, optical, and magneto-optical properties of the films was investigated. The film grown at 3 μTorr has the highest Faraday rotation (FR) and magnetic saturation moment (M(s)). Increasing oxygen pressure during growth reduced M(s), FR and optical absorption in the near-infrared. This trend is attributed to decreasing Co2+ ion concentration and oxygen vacancy concentration with higher oxygen partial pressure during growth. PMID:26074589

  14. Tropical Atlantic SSTS at the Last Glacial Maximum derived from Sr/Ca ratios of fossil coral

    NASA Astrophysics Data System (ADS)

    Cohen, A. L.; Saenger, C. P.

    2006-12-01

    The sensitivity of the tropics to climate change is a particularly controversial issue in paleoclimatology. At the heart of this controversy are disagreements amongst different proxy datasets regarding the amplitude of glacial-interglacial changes in temperature, particularly at the sea surface. Data obtained from the aragonitic skeletons of massive reef corals have contributed in no small measure to the debate, yielding LGM and deglacial SSTs 5-6°C cooler than today (Guilderson et al., 1994; McCulloch et al., 1999; Correge et al., 2004), that imply a high sensitivity of Earth's climate to changes in boundary conditions (Crowley, 2000). We used SIMS ion microprobe to analyze Sr/Ca ratios of small pieces of Montastrea coral retrieved from a Barbados drillcore (Guilderson et al., 2001). U/Th dates place the samples between 22 and 24 kyr BP. Localized areas of dissolution and re-growth of secondary (diagenetic) aragonite crystals were identified at centers of septa. Sr/Ca ratios of these crystals were higher than Sr/Ca ratios of original coral crystals preserved in adjacent fasciculi and yielded relatively cooler derived SSTs. The original coral crystals, recognized by their size and orientation, were selectively targeted for analysis using a 20 micron-diameter sample spot. Our calibration study using modern corals from Bermuda, St Croix (USVI) and Barbados indicates that Montastrea Sr/Ca is strongly correlated with SST and with annual extension (growth) rate (Saenger et al., 2006). Growth rate of the fossil corals was determined from measurement of daily growth bands identified in petrographic thin-sections. Application of a growth-dependent Sr/Ca-T calibration yielded Barbados SSTs that were, on average, 2.5°C cooler than today during the LGM and ~1°C cooler than today during Heinrich Event 2. Our LGM SSTs are consistent with the original CLIMAP estimates (CLIMAP, 1976) and with more recent Mg/Ca-based SSTs derived from calcitic foraminifera in the Caribbean

  15. Mg/Ca, Sr/Ca, δ18O and δ13C chemistry of Quaternary lacustrine ostracode shells from the North American continental interior

    NASA Astrophysics Data System (ADS)

    Ito, Emi

    The application of fossil ostracode shell chemistry to the reconstruction of past continental climate must take into consideration both short-term and long-term changes in the hydrologic budget of the lakes. This is particularly true when working in areas of strong seasonality in temperature and precipitation and negative effective moisture where many lakes owe their existence to inflow from groundwater. Moreover the chemistry (especially Mg/Ca and Sr/Ca) and δ18O of lake water may respond differently to hydrologic changes depending on whether they are caused by climate or other factors. These complications make clear how important it is to have information on ostracode ecology, to conduct a time-series monitoring study of the modern system, and to employ other proxy records. Examples of such studies are available from many semi-arid and arid regions of the world. Here I use Rice and Coldwater Lakes, North Dakota, as examples from the northern Great Plains of North America to illustrate these points. Decadally resolved Mg/Ca ratio variations for Rice Lake for the last 2000 years show excellent correlation with the GISP2 ice core δ18O record sampled at the same temporal resolution. Mg/Ca data for Rice and Coldwater Lakes also show good agreement with each other and with diatom-inferred salinity records for Coldwater as well as for Moon Lake located 100 km NNE of Coldwater Lake. However, δ18O records for neither lake are correlated with Mg/Ca records and highlight the importance of knowing the hydrology of each system.

  16. Assessing the impact of diagenesis on δ11B, δ13C, δ18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite

    NASA Astrophysics Data System (ADS)

    Edgar, Kirsty M.; Anagnostou, Eleni; Pearson, Paul N.; Foster, Gavin L.

    2015-10-01

    The geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo-climatic, -oceanographic and -ecological changes. However, dissolution of biogenic calcite and precipitation of inorganic calcite (overgrowth and recrystallization) at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test, biasing any resulting paleoenvironmental reconstruction. The δ11B of planktic foraminiferal calcite is a promising ocean pH-proxy but the effect of diagenesis is still poorly known. Here we present new δ11B, δ13C, δ18O, Sr/Ca and B/Ca data from multiple species of planktic foraminifera from time-equivalent samples for two low latitude sites: clay-rich Tanzanian Drilling Project (TDP) Site 18 from the Indian Ocean containing well-preserved ('glassy') foraminifera and carbonate-rich Ocean Drilling Program (ODP) Site 865 from the central Pacific Ocean hosting recrystallized ('frosty') foraminifera. Our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis. Planktic foraminiferal δ18O and δ13C records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration. Sr/Ca and B/Ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa. In contrast, δ11B values indicate no large differences between well-preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the δ11B of biogenic calcite appears robust, potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing CaCO3. Our finding may remove one potential source of uncertainty in δ11B based p

  17. Processing, microstructure, and critical current density of Silver-sheathed Bi2Sr2CaCu2Ox multifilamentary round wire

    NASA Astrophysics Data System (ADS)

    Shen, Tengming

    Ag-sheathed multifilamentary Bi2Sr2CaCu2Ox round wire is one of the leading hightemperature superconductors that can generate a magnetic field exceeding the maximum of ~23 T available in present Nb-based low-temperature superconducting magnet technology. However, the magnet fabrication of power-in-tube (PIT) Ag-Bi2Sr2CaCu 2Ox multifilamentary round wire to develop critical current density Jc > 105 A/cm2 in magnetic fields up to 45 T is difficult, due to complicated material processing, as-yet incompletely understood microstructure, and the problem that Jc is sensitive to high-temperature reactions. This thesis analyzed the critical steps of melt processing PIT Bi2Sr2CaCu2Ox multifilamentary wires, systematically investigating the relationships between processing, microstructure, and conductor & magnet performance. The phase transformation and microstructure development during the melt processing of Bi2Sr2CaCu2Ox wires were thoroughly examined using a brine-quench technique that preserves the high-temperature microstructures. On heating to the maximum temperature (~890 °C), Bi2Sr2CaCu2Ox powder melts incongruently, producing a mixture of liquid and secondary solid phases. On subsequent cooling, the liquid reacts with the solid phases and Bi 2Sr2CaCu2Ox reforms. The phase reaction to Bi2Sr2CaCu2Ox is often incomplete, leaving remnant nonsuperconducting phases from the melt and the Bi2Sr 2CaCu2Ox phase and intergrowth in the superconducting matrix, all of which become current limiting mechanisms (CLMs) and block current flow. Moreover, the gas between precursor powder grains accumulates into large pores upon melting, which divide the filament into segments. The consequence of having large pores in the melt is that the pore regions may become bottlenecks for current flow in fully reacted wires. The high population of CLMs strongly indicates that the fraction of oxide filament area that is effectively used for carrying current is low and increasing the connectivity is

  18. Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped CaF{sub 2} and SrF{sub 2} crystals

    SciTech Connect

    Barandiarán, Zoila Seijo, Luis

    2015-10-14

    Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF{sub 2} and Yb/Sr pairs in SrF{sub 2} crystals to investigate the mechanism of photoconductivity. The results show that, in these crystals, dopant-to-host electron transfer is a two-photon process mediated by the 4f{sup N−1}5d excited states of Y b{sup 2+}: these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b{sup 2+} + Ca{sup 2+} (Sr{sup 2+}) → Y b{sup 3+} + Ca{sup +} (Sr{sup +}) electron phototransfer. This mechanism applies to all the observed Y b{sup 2+} 4f–5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF{sub 2}:Y b{sup 2+} because the Y b{sup 3+}–Ca{sup +} states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF{sub 2}:Y b{sup 2+} at the wavelengths of the first 4f–5d absorption band, but the mechanism is different from that described above: first, the two-photon excitation process occurs within the Y b{sup 2+} active center, then, non-radiative Yb-to-Sr electron transfer can occur. All of these features allow to interpret consistently available photoconductivity experiments in these materials, including the modulation of the photoconductivity by the absorption spectrum, the differences in photoconductivity thresholds observed in both hosts, and the peculiar photosensitivity observed in the SrF{sub 2} host, associated with the lowest 4f–5d band.

  19. High-pressure modifications of CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2}: Implications for Laves phase structural trends

    SciTech Connect

    Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Haeussermann, Ulrich

    2008-11-15

    High-pressure forms of intermetallic compounds with the composition CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2} were synthesized from CeCu{sub 2}-type precursors (CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}) and Ba{sub 21}Al{sub 40} by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl{sub 2} and BaAl{sub 2}), X-ray single-crystal diffraction (CaZn{sub 2}), and electron microscopy (SrZn{sub 2}). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu{sub 2} (C15) structure, the dizincides adopt the hexagonal MgZn{sub 2} (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. - Graphical abstract: CeCu{sub 2}-type polar intermetallics can be transformed to Laves phases upon simultaneous application of pressure and temperature. The observed structures are controlled by the valence electron concentration.

  20. Preparation of Bi2Sr2CaCu2Oy films on alumina substrates with a CuAl2O4 buffer layer

    NASA Astrophysics Data System (ADS)

    Lee, Kiejin; Song, Insang; Park, Gwangseo

    1993-07-01

    High-Tc Bi2Sr2CaCu2Oy films have been prepared using the surface diffusion process, with the screen printing of Bi2O3, SrCO3, and CaCO3 (Bi:Sr:Ca=2:2:2) mixed powders on Cu-deposited alumina substrates. Through the heating at temperatures above 400 °C, CuAl2O4 buffer layers were formed via an interaction between the Cu layer and alumina. The Bi2Sr2CaCu2Oy films, heat treated at 860 °C for 30 min in air, have a zero resistance at 72 K. The x-ray diffraction, scanning electron microscope, and energy dispersive x-ray analysis studies show that the Bi2Sr2Ca1Cu2Oy films are strongly c-axis oriented along the direction normal to the alumina substrate, and the CuAl2O4 buffer layer acted as a barrier to suppress the interdiffusion of Al ions into the superconducting films.

  1. The effect of chemical pressure on the structure and properties of A2CrOsO6 (A=Sr, Ca) ferrimagnetic double perovskite

    NASA Astrophysics Data System (ADS)

    Morrow, Ryan; Soliz, Jennifer R.; Hauser, Adam J.; Gallagher, James C.; Susner, Michael A.; Sumption, Michael D.; Aczel, Adam A.; Yan, Jiaqiang; Yang, Fengyuan; Woodward, Patrick M.

    2016-06-01

    The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized and characterized with neutron powder diffraction, electrical transport measurements, and high field magnetization experiments. As reported previously Sr2CrOsO6 crystallizes with R 3 bar symmetry due to a-a-a- octahedral tilting. A decrease in the tolerance factor leads to a-a-b+ octahedral tilting and P21/n space group symmetry for Ca2CrOsO6. Both materials are found to be ferrimagnetic insulators with saturation magnetizations near 0.2 μB. Sr2CrOsO6 orders at 660 K while Ca2CrOsO6 orders at 490 K. Variable temperature magnetization measurements suggest that the magnetization of the Cr3+ and Os3+ sublattices have different temperature dependences in Sr2CrOsO6. This leads to a non-monotonic temperature evolution of the magnetic moment. Similar behavior is not seen in Ca2CrOsO6. Both compounds have similar levels of Os/Cr antisite disorder, with order parameters of η=80.2(4)% for Sr2CrOsO6 and η=76.2(5)% for Ca2CrOsO6, where η=2θ-1 and θ is the occupancy of the osmium ion on the osmium-rich Wyckoff site.

  2. SrZn2Sn2 and Ca2Zn3Sn6 — two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    NASA Astrophysics Data System (ADS)

    Stegmaier, Saskia; Fässler, Thomas F.

    2012-08-01

    SrZn2Sn2 and Ca2Zn3Sn6, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn2Sn2 comprises (anti-)PbO-like {ZnSn4/4} and {SnZn4/4} layers. Ca2Zn3Sn6 shows similar {ZnSn4/4} layers and {Sn4Zn} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn2Sn2 adopts the SrPd2Bi2 structure type, and Ca2Zn3Sn6 is isotypic to the R2Zn3Ge6 compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn2Sn2 and Ca2Zn3Sn6 are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {Sn4Zn} layers of Ca2Zn3Sn6.

  3. Evidence for Local Moment Magnetism in Superconducting Bi2Sr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Tranquada, John; Xu, G. Y.; Gu, G. D.; Huecker, M.; Fauque, B.; Perring, T. G.; Stock, C.; Regnault, L.-P.

    2009-03-01

    We have used inelastic neutron scattering to measure the dynamic spin susceptibility in optimally-doped Bi2Sr2CaCu2O8+δ (Tc = 91 K). Four crystals with a total mass of 19 g were measured on the MAPS spectrometer at ISIS for temperatures of 10 K and 100 K. We have been able to identify the magnetic excitations in the energy range 20-90 meV. The magnetic nature of the scattering has been confirmed with spin-polarization analysis on IN22 at the ILL. While we see temperature-dependent changes for energies around 40 meV that are consistent with earlier studies, we find that the Q-integrated signal shows a much weaker variation with temperature. The absolute magnetic cross section is quite comparable to that of spin fluctuations in stripe ordered La1.875Ba0.125CuO4. As the magnetism in the latter system has been shown to have a dominant contribution from local moments [1], we argue that the same must be true for Bi2Sr2CaCu2O8+δ. [1] M. Huecker et al., Phys. Rev. B (accepted); cond-mat/0503417v3.

  4. Nonlinear-optical susceptibility of hilgardite-like borates MBOX(M=Pb,Ca,Sr,Ba; X=Cl,Br)

    NASA Astrophysics Data System (ADS)

    Plachinda, Paul A.; Dolgikh, Valery A.; Stefanovich, Sergey Yu.; Berdonosov, Petr S.

    2005-10-01

    Usage of non-centrosymmetric boron oxide derivative crystals as nonlinear elements may be a key solution of pressing problem of obtaining powerful radiation at shorter wavelengths via frequency multiplication of solid state laser radiations. It is shown that Pb 2B 5O 9Br and some other members of hilgardite-like borohalogenides demonstrate in powder form, high non-linear optical activity in the SHG experiments. An attempt is made using the Philips-Van Vechten-Levine-Xue bond theory to calculate second-order nonlinear coefficients for isostructural to mineral hilhardite noncentrosymmetric crystals MBOX with M=Pb, Sr, Ba, Eu, Ca and X=Cl, Br. Theoretically obtained values of nonlinear optical coefficients d only partly correlate with the results of SHG measurements. In particular, the experiments distinctively show sharp increase of nonlinear activity along the series Ca < Sr < Ba < Pb and Cl < Br of metal boro-halogenides, while theoretical estimations give substantially more slack composition dependences. Analysis of contribution of different boron-oxygen bonds to optical nonlinearities of the compounds reveals important role of planar BO 3 triangles, though this factor is yet unable to explain enormously high SHG output from Pb 2B 5O 9Br.

  5. Encapsulating MAl 2O 4:Eu 2+, Dy 3+ (M = Sr, Ca, Ba) phosphors with triethanolamine to enhance water resistance

    NASA Astrophysics Data System (ADS)

    Ji, Ping Ting; Chen, Xiang Ying; Wu, Ye Qin

    2011-12-01

    Traditional aluminates phosphors with persistent luminescence are chemically unstable to water or moisture. Thus, how to improve the water-resistance of these phosphors is becoming a key issue in their practical applications. In this work, a series of alkaline earth aluminate phosphors including MAl 2O 4:Eu 2+, Dy 3+ (M = Sr, Ca, Ba) have been prepared by a co-precipitation synthesis and postannealing approach, using 8-hydroxyquinoline and sodium oxalate as precipitants. The samples before and after encapsulation were well characterized by means of XRPD, FESEM, FT-IR, TGA-DTG and PL techniques as well as water resistance measurements. The precipitants involved can react with Al 3+ and Sr 2+ (or Ca 2+, Ba 2+) to form complex compounds in aqueous solution, which further convert into porous phosphors by postannealing method under reducing atmosphere. Next, triethanolamine encapsulation at room temperature was conducted onto their surfaces to improve the water resistance. The results reveal that the encapsulation of aluminate phosphors with triethanolamine can effectively enhance the water resistance, and minimally affect on persistent phosphorescence.

  6. Laser performance of diode-pumped Nd, Y-codoped CaF 2-SrF 2 mixed crystal

    NASA Astrophysics Data System (ADS)

    Liu, J.; Fan, M. W.; Su, L. B.; Jiang, D. P.; Ma, F. K.; Zhang, Q.; Xu, J.

    2014-03-01

    A disordered Nd, Y-codoped CaF2-SrF2 mixed crystal was obtained by the temperature gradient technique (TGT). The absorption and fluorescence spectra of the crystal were measured at room temperature. Diode-pumped continuous-wave (CW) and Q-switched laser operations were demonstrated at 1056 nm with a 0.65 at.% Nd, 10 at.% Y-codoped crystal, for the first time to our knowledge. The CW output power of 724 mW was obtained in a compact linear cavity. Also the Q-switched pulse characteristics of Nd, Y:CaF2-SrF2 laser crystal were reported based on Cr4+:YAG saturable absorbers in a folded cavity. The shortest pulse width of 110 ns and the highest peak power of 383 W were obtained when the initial transmission of the Cr4+:YAG crystals was 90%. The dependence of the operational parameters on the pump power was also investigated experimentally.

  7. A Robust and Fully-Automated Chromatographic Method for the Quantitative Purification of Ca and Sr for Isotopic Analysis

    NASA Astrophysics Data System (ADS)

    Smith, H. B.; Kim, H.; Romaniello, S. J.; Field, P.; Anbar, A. D.

    2014-12-01

    High throughput methods for sample purification are required to effectively exploit new opportunities in the study of non-traditional stable isotopes. Many geochemical isotopic studies would benefit from larger data sets, but these are often impractical with manual drip chromatography techniques, which can be time-consuming and demand the attention of skilled laboratory staff. Here we present a new, fully-automated single-column method suitable for the purification of both Ca and Sr for stable and radiogenic isotopic analysis. The method can accommodate a wide variety of sample types, including carbonates, bones, and teeth; silicate rocks and sediments; fresh and marine waters; and biological samples such as blood and urine. Protocols for these isotopic analyses are being developed for use on the new prepFAST-MCTM system from Elemental Scientific (ESI). The system is highly adaptable and processes up to 24-60 samples per day by reusing a single chromatographic column. Efficient column cleaning between samples and an all Teflon flow path ensures that sample carryover is maintained at the level of background laboratory blanks typical for manual drip chromatography. This method is part of a family of new fully-automated chromatographic methods being developed to address many different isotopic systems including B, Ca, Fe, Cu, Zn, Sr, Cd, Pb, and U. These methods are designed to be rugged and transferrable, and to allow the preparation of large, diverse sample sets via a highly repeatable process with minimal effort.

  8. Trapping control of phase development in zone melting of Bi-Sr-Ca-Cu-O superconducting fibres

    NASA Astrophysics Data System (ADS)

    Costa, F. M.; Carrasco, M. F.; Silva, R. F.; Vieira, J. M.

    2003-03-01

    Highly-texturized polycrystalline fibres of the Bi-Sr-Ca-Cu-O system have been grown by the laser floating zone technique at seven different pulling rates: (1.1, 2.2, 4.17, 8.3, 16.7, 33.3, 60.5) × 10-6 m s-1. The assessment of the cation segregation at the solid/liquid interface allowed us to calculate their equilibrium and effective distribution coefficients. The equilibrium distribution coefficients (k0,Bi = 0.55, k0,Sr = 0.97, k0,Ca = 1.67, k0,Cu = 1.10) were estimated using the Burton, Primm and Slichter (BPS) theory by taking into account the determined effective values. The effective distribution coefficients tend to unity as long as the pulling rate increases. The composition profiles along the initial transient region of the solidified fibres show a fast approach to the nominal composition as the pulling rate increases. The outstanding effect of the growth speed on superconducting phase type development is explained based on the solute trapping phenomena. The sequence of crystallization for superconducting phases ('2212' rightarrow '4413' rightarrow '2201') with pulling rate is a spontaneous effect of the system thermodynamics in order to balance the Bi trapping. This phase sequence corresponds to the smallest change of Bi chemical potential from the liquid phase to the solid phase. A diagram of free energy curves of the interdendritic superconducting phases illustrates the partitionless solidification phenomena at the highest growth speed.

  9. Disorder promotes ferromagnetism: rounding of the quantum phase transition in Sr(1-x)Ca(x)RuO3.

    PubMed

    Demkó, L; Bordács, S; Vojta, T; Nozadze, D; Hrahsheh, F; Svoboda, C; Dóra, B; Yamada, H; Kawasaki, M; Tokura, Y; Kézsmárki, I

    2012-05-01

    The subtle interplay of randomness and quantum fluctuations at low temperatures gives rise to a plethora of unconventional phenomena in systems ranging from quantum magnets and correlated electron materials to ultracold atomic gases. Particularly strong disorder effects have been predicted to occur at zero-temperature quantum phase transitions. Here, we demonstrate that the composition-driven ferromagnetic-to-paramagnetic quantum phase transition in Sr(1-x)Ca(x)RuO3 is completely destroyed by the disorder introduced via the different ionic radii of the randomly distributed Sr and Ca ions. Using a magneto-optical technique, we map the magnetic phase diagram in the composition-temperature space. We find that the ferromagnetic phase is significantly extended by the disorder and develops a pronounced tail over a broad range of the composition x. These findings are explained by a microscopic model of smeared quantum phase transitions in itinerant magnets. Moreover, our theoretical study implies that correlated disorder is even more powerful in promoting ferromagnetism than random disorder. PMID:22681090

  10. Effect of high Xe-concentration in a plasma display panel with a SrCaO cold cathode

    SciTech Connect

    Uchida, Giichiro; Kajiyama, Hiroshi; Shinoda, Tsutae; Uchida, Satoshi; Akiyama, Toshiyuki

    2010-05-15

    We present here measurements of high Xe-contents plasma display panel (PDP) with SrCaO cold cathode. Luminous efficacy ({eta}) shows a two-step increase with Xe-concentration in Ne/Xe gas mixture: {eta} drastically increases up to Xe-concentration of 30% (Xe: 30%), and then attains 5 lm/W at the highest Xe-concentration of Xe: 100%. The high performance PDP with Xe: 100% can be operated at low applied voltage between 230 and 377 V due to the high secondary electron emission from the SrCaO cathode. Emission measurements clearly show the change in discharge characteristics at Xe: 30%, where the discharge changes from a Ne/Xe mixture discharge to an almost pure Xe discharge, and the vacuum ultraviolet (VUV) radiation from the combination of resonance and excimer radiations to only excimer radiation. Theoretical analysis solving Boltzmann equation for electron demonstrates that increasing Xe-concentration enhances the collision frequency for electron impact excitation directly from ground state to lower levels concerned with the VUV radiation, resulting in a drastic increase in luminous efficacy up to Xe: 30%. Also, one-dimensional fluid simulation of a Ne/Xe dielectric barrier discharge clearly shows that a combination of high secondary electron emission cathode and high Xe-concentration is quite effective for high VUV radiation efficiency because it induces a drastic increase in electron-heating efficiency.

  11. The North Atlantic Oscillation Reconstructed at Bermuda for 220 Years Using Sr/Ca Ratios in Diploria labyrinthiformis (brain coral)

    NASA Astrophysics Data System (ADS)

    Goodkin, N. F.; Hughen, K. A.; Cohen, A. L.; Curry, W. B.; Doney, S. C.

    2006-12-01

    The North Atlantic Oscillation (NAO) is a meridional oscillation in atmospheric mass measured by pressure anomalies between Iceland (65°N, 23°W) and the Azores (38°N, 26°W) (Hurrell, 1995). Changes between the positive and negative phase of the NAO strongly influence weather patterns across the US, Europe and the Middle East. A shift in recent decades toward a sustained positive NAO has raised questions about the influence of greenhouse gas emissions on this system. Unfortunately, instrumental records are too short to identify the natural baseline variability of the NAO, and NAO reconstructions generally encompass only land-based proxies, excluding ocean processes. Winter-time sea surface temperatures (SST) in the Sargasso Sea have previously been shown to correlate to the NAO (Visbeck et al., 2001), and thus a long winter SST record based on proxy data could be used to reconstruct NAO variability back in time. Here we present an annually resolved winter-time strontium to calcium ratio (Sr/Ca) record from a 220-year old brain coral (Diploria labyrinthiformis) collected from the south shore of Bermuda. Brain coral is prevalent in Bermuda and shows distinct annual banding in its skeleton providing precise age models. Winter-time coral Sr/Ca has previously been shown to accurately record winter SST free from growth rate influences (Goodkin et al., 2005), and that relationship is confirmed here. Cross-spectral analysis between winter-time coral Sr/Ca and four instrumental and proxy records of the NAO (Hurrell, 1995, Jones et al., 1997, Luterbacher et al., 2001, Cook et al., 2002) show two frequencies of coherence with >95% confidence. At periods greater than 20 years and between 3 and 5 years, the coral Sr/Ca effectively captures the NAO variability. Filtering the coral record to these frequencies and comparing to the instrumental and proxy records, including another marine-based NAO reconstruction from the North and Norwegian Seas (Schoene et al., 2003), show

  12. Synthesis, structure and chemical bonding of CaFe{sub 2−x}Rh{sub x}Si{sub 2} (x=0, 1.32, and 2) and SrCo{sub 2}Si{sub 2}

    SciTech Connect

    Hlukhyy, Viktor Hoffmann, Andrea V.; Fässler, Thomas F.

    2013-07-15

    The finding of superconductivity in Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2} put the attention on the investigation of compounds that crystallize with ThCr{sub 2}Si{sub 2} structure type such as AT{sub 2}X{sub 2} (A=alkali/alkaline earth/rare earth element; T=transition metal and X=element of the 13–15th group). In this context the silicides CaFe{sub 2}Si{sub 2}, CaFe{sub 0.68(6)}Rh{sub 1.32(6)}Si{sub 2}, CaRh{sub 2}Si{sub 2} and SrCo{sub 2}Si{sub 2} have been synthesized by reaction of the elements under an argon atmosphere. Single crystals were obtained by special heat treatment in welded niobium/tantalum ampoules. The compounds were investigated by means of powder and single crystal X-ray diffraction. All compounds crystallize in the ThCr{sub 2}Si{sub 2}-type structure with space group I4/mmm (No. 139): a=3.939(1) Å, c=10.185(1) Å, R{sub 1}=0.045, 85 F{sup 2} values, 8 variable parameters for CaFe{sub 2}Si{sub 2}; a=4.0590(2) Å, c=9.9390(8) Å, R{sub 1}=0.030, 90 F{sup 2} values, 10 variable parameters for CaFe{sub 0.68(6)}Rh{sub 1.32(6)}Si{sub 2}; a=4.0695(1) Å, c=9.9841(3) Å, R{sub 1}=0.031, 114 F{sup 2} values, 9 variable parameters for CaRh{sub 2}Si{sub 2}; and a=3.974(1) Å, c=10.395(1) Å, R{sub 1}=0.036, 95 F{sup 2} values, 8 variable parameters for SrCo{sub 2}Si{sub 2}. The structure of SrCo{sub 2}Si{sub 2} contains isolated [Co{sub 2}Si{sub 2}]{sup 2−} 2D-layers in the ab-plane whereas in CaFe{sub 2−x}Rh{sub x}Si{sub 2} the [T{sub 2}Si{sub 2}] layers (T=Fe and Rh) are interconnected along the c-axis via Si3Si bonds resulting in a three-dimentional (3D) [T{sub 2}Si{sub 2}]{sup 2−} polyanions and therefore belong to the so-called collapsed form of the ThCr{sub 2}Si{sub 2}-type structure. The SrCo{sub 2}Si{sub 2} and CaRh{sub 2}Si{sub 2} are isoelectronic to the parent 122 iron–pnictide superconductors AeFe{sub 2}As{sub 2} (Ae=alkaline earth elements), whereas CaFe{sub 2}Si{sub 2} is a full substituted variant (As/Si) of CaFe{sub 2}As{sub 2

  13. Ca, Sr, Mo and U isotopes evidence ocean acidification and deoxygenation during the Late Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Silva-Tamayo, Juan Carlos; Payne, Jon; Wignall, Paul; Newton, Rob; Eisenhauer, Anton; Weyer, Stenfan; Neubert, Nadja; Lau, Kim; Maher, Kate; Paytan, Adina; Lehrmann, Dan; Altiner, Demir; Yu, Meiyi

    2014-05-01

    The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, ca. 252 Mya. Ocean acidification and global oceanic euxinia have each been proposed as causes of this biotic crisis, but the magnitude and timing of change in global ocean chemistry remains poorly constrained. Here we use multiple isotope systems - Ca, Sr, Mo and U - measured from well dated Upper Permian- Lower Triassic sedimentary sections to better constrain the magnitude and timing of change in ocean chemistry and the effects of ocean acidification and de-oxygenation through this interval. All the investigated carbonate successions (Turkey, Italy and China) exhibit decreasing δ44/40Ca compositions, from ~-1.4‰ to -2.0‰ in the interval preceding the main extinction. These values remain low during most of the Griesbachian, to finally return to -1.4‰ in the middle Dienerian. The limestone succession from southern Turkey also displays a major decrease in the δ88/86Sr values from 0.45‰ to 0.3‰ before the extinction. These values remain low during the Griesbachian and finally increase to 0.55‰ by the middle Dienerian. The paired negative anomalies on the carbonate δ44/40Ca and δ88/86Sr suggest a decrease in the carbonate precipitation and thus an episode of ocean acidification coincident with the major biotic crisis. The Mo and U isotope records also exhibit significant rapid negative anomalies at the onset of the main extinction interval, suggesting rapid expansion of anoxic and euxinic marine bottom waters during the extinction interval. The rapidity of the isotope excursions in Mo and U suggests substantially reduced residence times of these elements in seawater relative to the modern, consistent with expectations for a time of widespread anoxia. The large C-isotope variability within Lower Triassic rocks, which is similar to that of the Lower-Middle Cambrian, may reflect biologically controlled perturbations of the oceanic carbon cycle

  14. Variations in the Sr/Ca, δ44Ca and δ18O composition of calcite as a function of solution chemistry and crystal growth rate

    NASA Astrophysics Data System (ADS)

    Watkins, J. M.; DePaolo, D. J.; Ryerson, F. J.

    2012-12-01

    The trace element and isotopic composition of calcite can be used to probe the temperatures and rates of mineral formation as well as the degree of post-mineralization alteration. The accuracy with which these effects can be interpreted is limited by our ability to distinguish signatures arising from equilibrium partitioning versus kinetic or mass transport effects. Our focus in this work is on mass transport effects in aqueous environments, and specifically, the growth rate-dependence of trace element and isotopic incorporation into calcite. This requires experiments in which the degree of supersaturation, or the solution chemistry, is held constant and the rate of crystal growth can be determined. In our experiments, N2+CO2 gas mixture is bubbled through a beaker containing 1300 mL of solution (30 mM CaCl2 + 5 mM NH4Cl + 0.1 mM SrCl2). The degree of supersaturation with respect to calcite is controlled by the pCO2 of the gas mixture, which is constantly replenished from a gas source. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls and the pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. During an experiment we control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate. At the same time we monitor the total alkalinity, the pCO2 of the gas outflow, the gas outflow rate, and the amount of NaOH added. The rate of calcite precipitation can be determined in three ways: (1) the change in total alkalinity due to Ca2+ removal, mass balance of C in the system, and (3) post-run measurement of [Ca2+] in aliquots of solution taken during an experiment. We present results from experiments where growth rates are estimated to range from 0.5 to 16 mmol/m2/hr. Our experiments thus far have yielded calcite crystals that are out of calcium and oxygen isotopic equilibrium with the parent solution. Crystals are enriched in the light isotope of Ca by 0.4 to 1.8‰. The light isotope

  15. Microwave property improvement of Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ perovskite by A-site substitution

    NASA Astrophysics Data System (ADS)

    Hu, Mingzhe; Xiong, Gang; Ding, Zhao

    2016-04-01

    The crystal structure and microwave dielectric properties of Ca[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramic (CLNZ) are tuned by A-site substitution of Sr2+ and Ba2+ ions in the present paper. The tuning effect on the crystal structure is investigated by the X-ray diffraction (XRD) pattern and it illustrates that single phase of orthorhombic perovskite structure is formed, however, minor amount of BaNb2O6-type second phase is also detected in (Ca1‑xBax)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramics (CBLNZ) in the range of x ≥ 0.025, while pure perovskite phase is obtained in (Ca1‑xSrx)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ ceramics (CSLNZ) in the whole investigation range of 0 ≤ x ≤ 0.2. With the increase of x value, the unit cell volumes of both CBLNZ and CSLNZ perovskites gradually expand, which results in the degradation of the vibration bond strength between the B-site ions and oxygen in the perovskites. The microscopic structure related thermal parameters in CSLNZ and CBLNZ perovskites are analyzed in terms of Clausius-Mossotti equation to reveal the original contributors in the temperature coefficients. The results show that both Sr2+ and Ba2+ substitution can effectively improve the permittivity and Qf value, especially, improve the temperature coefficient of CLNZ ceramic in a certain range.

  16. Seasonal Variability of Riverine Geochemistry (87Sr/86Sr, δ13CDIC, δ44/40Ca, and major ions) in Permafrost Watersheds on the North Slope of Alaska

    NASA Astrophysics Data System (ADS)

    Lehn, G. O.; Jacobson, A. D.; Douglas, T. A.; McClelland, J. W.; Khosh, M. S.; Barker, A. J.

    2014-12-01

    Global climate models predict amplified warming at high latitudes, where permafrost soils have historically acted as a carbon sink. As warming occurs, the seasonally thawed active layer will propagate downward into previously frozen mineral-rich soil, releasing carbon and introducing unique chemical weathering signatures into rivers. We use variations in the 87Sr/86Sr, δ13CDIC, δ44/40Ca, and major ion geochemistry of rivers to track seasonal active layer dynamics. We collected water from six streams on the North Slope of Alaska between May and October, 2009 and 2010. All rivers drain continuous permafrost but three drain tussock tundra-dominated watersheds and three drain steeper bedrock catchments with minor tundra coverage. In tundra streams, elevated 87Sr/86Sr ratios, low δ13CDIC values and major ions ([Na+]+[K+]/ [Ca+2]+[Mg+2]) in spring melt runoff suggest flushing of shallow soils with relatively low carbonate content. By July, 87Sr/86Sr ratios stabilize at relatively low values and δ13CDIC at relatively higher values, indicating the active layer thawed into deeper carbonate-rich soils. In bedrock streams, elevated 87Sr/86Sr ratios correlate with high discharge. By late fall, bedrock stream 87Sr/86Sr ratios decrease steadily, consistent with increased carbonate weathering. Nearly constant δ13CDIC values and high [SO4-2] for most of the melt season imply significant sulfuric acid-carbonate weathering in bedrock streams. δ13CDIC values suggest a shift to carbonic acid-carbonate weathering in late 2010, possibly due to limited oxygen for pyrite oxidation during freezing of the active layer. δ44/40Ca values in both tundra and bedrock streams increase during the seasons, suggesting increased uptake of 40Ca by plants. δ44/40Ca values of rivers are at least 0.1-0.2‰ higher than their watershed soils, rocks and sediments, suggesting significant plant uptake. Our findings show how seasonal changes in mineral weathering have potential for tracking active

  17. Thermal exposure effects on the in vitro degradation and mechanical properties of Mg-Sr and Mg-Ca-Sr biodegradable implant alloys and the role of the microstructure.

    PubMed

    Bornapour, M; Celikin, M; Pekguleryuz, M

    2015-01-01

    Magnesium is an attractive biodegradable material for medical applications due to its non-toxicity, low density and good mechanical properties. The fast degradation rate of magnesium can be tailored using alloy design. The combined addition of Sr and Ca results in a good combination of mechanical and corrosion properties; the alloy compositions with the best performance are Mg-0.5Sr and Mg-0.3Sr-0.3Ca. In this study, we investigated an important effect, namely thermal treatment (at 400 °C), on alloy properties. The bio-corrosion of the alloys was analyzed via in vitro corrosion tests in simulated body fluid (SBF); the mechanical properties were studied through tensile, compression and three-point bending tests in two alloy conditions, as-cast and heat-treated. We showed that 8h of heat treatment increases the corrosion rate of Mg-0.5Sr very rapidly and decreases its mechanical strength. The same treatment does not significantly change the properties of Mg-0.3Sr-0.3Ca. An in-depth microstructural investigation via transmission electron microscopy, scanning electron microscopy, electron probe micro-analysis and X-ray diffraction elucidated the effects of the thermal exposure. Microstructural characterization revealed that Mg-0.3Sr-0.3Ca has a new intermetallic phase that is stable after 8h of thermal treatment. Longer thermal exposure (24h) leads to the dissolution of this phase and to its gradual transformation to the equilibrium phase Mg17Sr2, as well as to a loss of mechanical and corrosion properties. The ternary alloy shows better thermal stability than the binary alloy, but the manufacturing processes should aim to not exceed exposure to high temperatures (400 °C) for prolonged periods (over 24 h). PMID:25491955

  18. Surface modification of MAl2O4:Eu2+,Dy3+ (M = Sr, Ca, Ba) phosphors to enhance water resistance by combustion method

    NASA Astrophysics Data System (ADS)

    Deng, Suqing; Xue, Zhiping; Yang, Qu; Liu, Yingliang; Lei, Bingfu; Xiao, Yong; Zheng, Mingtao

    2013-10-01

    A facile combustion method was introduced into surface modification of MAl2O4:Eu2+,Dy3+ (M = Sr, Ca, Ba) phosphors to improve their water resistance. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), pH measurements and photoluminescence (PL) spectrophotometry were used to characterize the phosphors before and after modification, respectively. Experimental results showed that compact layer of MAl2B2O7 (M = Sr, Ca, Ba) substance was formed on the surface of aluminate phosphors by direct chemical reaction between aluminate and boracic acid. MAl2B2O7 (M = Sr, Ca, Ba) substance is chemically stable in water and could improve water resistance of aluminate phosphors effectively with little influence of luminescence property. It was considered that the versatility of combustion method for surface modification of aluminate phosphors has been confirmed.

  19. Synthesis, Structure, and Magnetic Properties of Sr2NiOsO6 and Ca2NiOsO6: Two New Osmium-Containing Double Perovskites

    SciTech Connect

    Macquart,R.; Kim, S.; Gemmill, W.; Stalick, J.; Lee, Y.; Vogt, Tzur Loye, H.

    2005-01-01

    Two new double perovskite oxides, Ca{sub 2}NiOsO{sub 6}and Sr{sub 2}NiOsO{sub 6}, have been prepared as polycrystalline powders by solid state synthesis. The two oxides were structurally characterized by variable-temperature powder neutron diffraction. Ca{sub 2}NiOsO{sub 6} was found to adopt a monoclinic structure (P2{sub 1}/n), while Sr{sub 2}NiOsO{sub 6} was found to be tetragonal (I4/m). Magnetic susceptibility measurements indicate that Ca2NiOsO6 orders in a canted antiferromagnetic state at about 175 K while Sr{sub 2}NiOsO{sub 6} orders antiferromagnetically at about 50 K.

  20. Evidence of Sr/Ca and Mg/Ca Temperature Invariance in Live Aragonitic Hoeglundina elegans Tests from the Little Bahama Bank

    NASA Astrophysics Data System (ADS)

    Blanks, J. K.; Hintz, C. J.; Chandler, G. T.; Shaw, T. J.; McCorkle, D. C.; Bernhard, J. M.

    2007-12-01

    Mg/Ca and Sr/Ca were analyzed from core-top individual Hoeglundina elegans aragonitic tests collected from three continental slope depths within the South Carolina and Little Bahama Bank continental slope environs (220 m to 1084 m). Our study utilized only individuals that labeled with the vital probe CellTracker Green - unlike bulk core-top material often stained with Rose Bengal, which has known inconsistencies in distinguishing live from dead foraminifera. DSr x 10 values were consistently 1.74 $ pm 0.23 across all sampling depths. The analytical error in DSr values (0.7%) determined by ICP-MS between repeated measurements on individual H. elegans tests across all depths was less than analytical error on repeated measurements from standards. Variation in DSr values was not directly explained by a linear temperature relationship (p=0.0003, R2=0.44) over the temperature range of 4.9-11.4°C with a sensitivity of 59.8 μmol/mol/1°C. The standard error by regressing DSr across temperature yields + 3.4°C, which is nearly 3x greater that reported in previous studies. Sr/Ca was more sensitive for calibrating temperature than Mg/Ca in H. elegans. Observed scatter in DSr was too great across individuals of the same size and of different sizes to resolve ontogenetic effects. However, higher DSr values were associated with smaller individuals and warmer/shallower sampling depths. The highest DSr values were observed at the intermediate sampling depth (~600 m). No significant ontogenetic relationship was found across DSr values in different sized individuals due to tighter overall constrained variance; however lower DSr values were observed from several smaller individuals. Several dead tests of H. elegans showed no significant differences in DSr values compared to live specimens cleaned by standard cleaning methods, unlike higher dead than live DMg values observed for the same individuals. There were no significant deviations in DSr across batches cleaned on separate

  1. Hydrothermal preparation and characterization of ultralong strontium-substituted hydroxyapatite whiskers using acetamide as homogeneous precipitation reagent.

    PubMed

    Xu, Jianqiang; Yang, Yaoqi; Wan, Rong; Shen, Yuhui; Zhang, Weibin

    2014-01-01

    The ultralong strontium- (Sr-) substituted hydroxyapatite (SrHAp) whiskers were successfully prepared using acetamide as homogeneous precipitation reagent. The effect of the Sr substitution amount on the lattice constants and proliferation of human osteoblast cells (MG-63) was further investigated. The results showed that the SrHAp whiskers with diameter of 0.2-12 μm and ultralong length up to 200 μm were obtained and the Sr substitution level could be facilely tailored by regulating the initial molar ratio of Sr/(Sr + Ca) in raw materials. The Sr(2+) replaced part of Ca(2+) and the lattice constants increased apparently with the increase of the Sr substitution amount. Compared with the pure HAp whiskers, the Sr substitution apparently stimulated the proliferation of MG-63 at certain extracted concentrations. Our study suggested that the obtained SrHAp whiskers might be used as bioactive and mechanical reinforcement materials for hard tissue regeneration applications. PMID:24592192

  2. Hydrothermal Preparation and Characterization of Ultralong Strontium-Substituted Hydroxyapatite Whiskers Using Acetamide as Homogeneous Precipitation Reagent

    PubMed Central

    Xu, Jianqiang; Yang, Yaoqi; Wan, Rong; Zhang, Weibin

    2014-01-01

    The ultralong strontium- (Sr-) substituted hydroxyapatite (SrHAp) whiskers were successfully prepared using acetamide as homogeneous precipitation reagent. The effect of the Sr substitution amount on the lattice constants and proliferation of human osteoblast cells (MG-63) was further investigated. The results showed that the SrHAp whiskers with diameter of 0.2–12 μm and ultralong length up to 200 μm were obtained and the Sr substitution level could be facilely tailored by regulating the initial molar ratio of Sr/(Sr + Ca) in raw materials. The Sr2+ replaced part of Ca2+ and the lattice constants increased apparently with the increase of the Sr substitution amount. Compared with the pure HAp whiskers, the Sr substitution apparently stimulated the proliferation of MG-63 at certain extracted concentrations. Our study suggested that the obtained SrHAp whiskers might be used as bioactive and mechanical reinforcement materials for hard tissue regeneration applications. PMID:24592192

  3. Influence of tungsten substitution and oxygen deficiency on the thermoelectric properties of CaMnO3-δ

    NASA Astrophysics Data System (ADS)

    Thiel, Philipp; Eilertsen, James; Populoh, Sascha; Saucke, Gesine; Döbeli, Max; Shkabko, Andrey; Sagarna, Leyre; Karvonen, Lassi; Weidenkaff, Anke

    2013-12-01

    Polycrystalline tungsten-substituted CaMn1-xWxO3-δ (0.00 ≤ x ≤ 0.05) powders were synthesized from a polymeric precursor, pressed and sintered to high density. The impact of tungsten substitution on the crystal structure, thermal stability, phase transition, electronic and thermal transport properties is assessed. Tungsten acts as an electron donator and strongly affects high-temperature oxygen stoichiometry. Oxygen vacancies form in the high figure-of-merit (ZT)-region starting from about T = 1000 K and dominate the carrier concentration and electronic transport far more than the tungsten substitution. The analysis of the transport properties yields that in the investigated regime the band filling is sufficiently high to overcome barriers of polaron transport. Therefore, the Cutler-Mott approach describes the electrical transport more accurately than the Mott approach for small polaron transport. The lattice thermal conductivity near room temperature is strongly suppressed with increasing tungsten concentration due to mass-difference impurity scattering. A ZT of 0.25 was found for x = 0.04 at 1225 K.

  4. Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO{sub 3}

    SciTech Connect

    Tsekouras, George Boudoire, Florent; Braun, Artur; Pal, Banabir; Sarma, D. D.; Vondráček, Martin; Prince, Kevin C.

    2015-09-21

    The electronic structure of the (La{sub 0.8}Sr{sub 0.2}){sub 0.98}Mn{sub 1−x}Cr{sub x}O{sub 3} model series (x = 0, 0.05, or 0.1) was measured using soft X-ray synchrotron radiation at room and elevated temperature. O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra showed that low-level chromium substitution of (La,Sr)MnO{sub 3} resulted in lowered hybridisation between O 2p orbitals and M 3d and M 4sp valance orbitals. Mn L{sub 3}-edge resonant photoemission spectroscopy measurements indicated lowered Mn 3d–O 2p hybridisation with chromium substitution. Deconvolution of O K-edge NEXAFS spectra took into account the effects of exchange and crystal field splitting and included a novel approach whereby the pre-peak region was described using the nominally filled t{sub 2g}↑ state. 10% chromium substitution resulted in a 0.17 eV lowering in the energy of the t{sub 2g}↑ state, which appears to provide an explanation for the 0.15 eV rise in activation energy for the oxygen reduction reaction, while decreased overlap between hybrid O 2p–Mn 3d states was in qualitative agreement with lowered electronic conductivity. An orbital-level understanding of the thermodynamically predicted solid oxide fuel cell cathode poisoning mechanism involving low-level chromium substitution on the B-site of (La,Sr)MnO{sub 3} is presented.

  5. Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO3

    NASA Astrophysics Data System (ADS)

    Tsekouras, George; Boudoire, Florent; Pal, Banabir; Vondráček, Martin; Prince, Kevin C.; Sarma, D. D.; Braun, Artur

    2015-09-01

    The electronic structure of the (La0.8Sr0.2)0.98Mn1-xCrxO3 model series (x = 0, 0.05, or 0.1) was measured using soft X-ray synchrotron radiation at room and elevated temperature. O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra showed that low-level chromium substitution of (La,Sr)MnO3 resulted in lowered hybridisation between O 2p orbitals and M 3d and M 4sp valance orbitals. Mn L3-edge resonant photoemission spectroscopy measurements indicated lowered Mn 3d-O 2p hybridisation with chromium substitution. Deconvolution of O K-edge NEXAFS spectra took into account the effects of exchange and crystal field splitting and included a novel approach whereby the pre-peak region was described using the nominally filled t2g↑ state. 10% chromium substitution resulted in a 0.17 eV lowering in the energy of the t2g↑ state, which appears to provide an explanation for the 0.15 eV rise in activation energy for the oxygen reduction reaction, while decreased overlap between hybrid O 2p-Mn 3d states was in qualitative agreement with lowered electronic conductivity. An orbital-level understanding of the thermodynamically predicted solid oxide fuel cell cathode poisoning mechanism involving low-level chromium substitution on the B-site of (La,Sr)MnO3 is presented.

  6. DFT+ U study of electronic structure and Curie temperature of A2 B ReO6 (A=Sr, Ca and B=Cr, Fe)

    NASA Astrophysics Data System (ADS)

    Lee, Alex; Marianetti, Chris

    Re-based double perovskites (DPs) have attracted much attention due to their high Curie temperature (TC) and colossal magneto resistance with large potential for spintronic applications. Here we investigate the electronic and magnetic properties of the Re-based DPs A2 B ReO6 (A=Sr, Ca and B=Cr, Fe) using density functional theory + U (DFT+ U) calculations. While monoclinic Ca2CrReO6 and Ca2FeReO6 (monoclinic) are insulating within GGA+ U, tetragonal Sr2CrReO6 (a0a0c0) and Sr2FeReO6 (a0a0c-) remain metallic. We show that both on-site interaction U and octahedral tilting are critical to obtain the insulating phases. The a0a0c- -phase of Sr2CrReO6 is most stable and insulating with nonzero U, suggesting that the high quality Sr2CrReO6 film on STO substrate can be a semiconductor as reported in recent experiments. We explain that the insulator-to-metal transition (MIT) of Ca2FeReO6 at 140K is predominantly due to a structural phase transition which drives the insulating state. Curie temperatures of Re-based DPs are calculated using the classical Monte Carlo simulations based on the Heisenberg model.

  7. Significantly enhanced ferroelectricity and magnetic properties in (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3}-modified BiFeO{sub 3} ceramics

    SciTech Connect

    Liu, Juan; Liu, Xiao Qiang E-mail: xmchen59@zju.edu.cn; Chen, Xiang Ming E-mail: xmchen59@zju.edu.cn

    2015-05-07

    BiFeO{sub 3} multiferroic ceramics were modified by introducing (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} to form solid solutions. The single phase structure was easy to be obtained in Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the present solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with M{sub r} = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe{sup 3+} by Ti{sup 4+}, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.

  8. Synthesis and luminescence properties of red-emitting M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) phosphors by a simple nitrate reduction

    NASA Astrophysics Data System (ADS)

    Chen, ChangCheng; Xie, ErQing

    2014-03-01

    M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) red-emitting phosphors are fabricated at relatively low temperature (1200°C) and atmospheric pressure using a simple solid-state reaction process. Several processing parameters are systematically investigated to optimize the phosphors structural characterization and photoluminescence performance, including the amount of europium and the properties of the precursor materials. The as-prepared M2Si5N8:Eu2+-based (M=Ca, Sr, Ba) phosphors are orange in color and are intensively emitted in the red region of 580-670 nm under 465 nm excitation.

  9. Dy3+-activated NaM4(VO4)3 (M = Ca, Ba, Sr) phosphor for near-UV solid-state lighting.

    PubMed

    Singh, Roshani; Dhoble, S J

    2011-01-01

    We report the photoluminescence characterization of Dy(3+)-activated NaM(4)(VO(4))(3) (M = Ca, Ba, Sr) phosphors prepared by a solid-state method. The synthesis was confirmed by X-ray diffraction (XRD) characterization and photoluminescence (PL) emission results showed sharp blue and yellow bands for NaM(4)(VO(4))(3) (M = Ca, Ba, Sr):Dy(3+) phosphors at the excitation wavelength of 323 nm, which is near-UV excitation. Thus, these phosphors could be applicable for near-UV excited solid-state lighting devices. PMID:21618681

  10. A high-resolution Sr/Ca and [delta][sup 18]O coral record from the Great Barrier Reef, Australia, and the 1982-1983 El Nino

    SciTech Connect

    McCulloch, M.T.; Gagan, M.K.; Mortimer, G.E.; Chivas, A.R. ); Isdale, P.J. )

    1994-06-01

    A high-resolution (near weekly) Sr/Ca and oxygen isotopic record is presented for a coral from the Pandora Reef in the Great Barrier Reef (GBR) of Australia during the period of 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has significantly modified the [delta][sup 18]O value of seawater. Using the Sr/Ca temperature calibration of De Villiers et al., the Sr/Ca records exhibit seasonally controlled cyclical SST (sea surface temperature) variations of from [approximately] 21 to [approximately] 28[degrees]C. During the very strong El Nino of 1982-1983, the Sr/CA systematics indicate a sharp drop in the winter SST to [approximately] 18.5[degrees]C. This represents a temperature anomaly of -3[degrees]C which is approximately twice that given by the [delta][sup 18]O variations, suggesting an [approximately] x2 amplification of the anomaly by the Sr/Ca system, possibly due to the increasing dominance of inorganically controlled aragonite-seawater fractionation. The oxygen isotope systematics show the combined effects of both temperature and changing seawater [delta][sup 18]O values, the latter reflecting the influx of [sup 18]O-depleted runoff during periods of high rainfall. Due to the extremely low ([approximately] 10[sup [minus]3]) Sr and Ca contents of river runoff relative to seawater, it is possible to use the Sr/Ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the [delta][sup 18]O value of seawater. Using this approach it is possible to quantitatively reproduce the volume of runoff from the Burdekin River during the periods of major flooding that occurred in early 1979 and 1981. The results of this study demonstrate that the combined use of high-resolution Sr/Ca and [delta][sup 18]O systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate.

  11. Protective effect of antioxidants against sarcoplasmic reticulum (SR) oxidation by Fenton reaction, however without prevention of Ca-pump activity.

    PubMed

    Voss, Peter; Engels, Martina; Strosova, Miriam; Grune, Tilman; Horakova, Lubica

    2008-10-01

    The Ca(2+)-ATPase of the sarcoplasmic reticulum (SERCA) of rabbit skeletal muscle was oxidized by Fe2+/H2O2/ascorbic acid (AA), a system which generates HO(.) radicals according to the Fenton reaction: (Fe2(+)+H2O2-->HO(.)+OH(-)+Fe(3+)) under conditions similar to the pathological state of inflammation. Under these conditions, when hydroxyl-radicals and/or ferryl-radicals are generated, a 50% decrease of the SERCA activity was observed, a significant decrease of SH groups and an increase of protein carbonyl groups and lipid peroxidation were identified. Two new bands, time dependent in density, appeared in the SERCA protein electrophoresis after incubation with the Fenton system (at approximately 50 and 75kDa), probably due to structural changes as supported also by trypsin digestion. Immunoblotting of DNPH derivatized protein bound carbonyls detected a time dependent increase after incubation of SERCA with the Fenton system. Trolox and the pyridoindole stobadine (50microM) protected SR against oxidation induced via the Fenton system by preventing SH group oxidation and lipid peroxidation. Pycnogenol((R)) and EGb761 (40microg/ml) protected SERCA in addition against protein bound carbonyl formation. In spite of the antioxidant effects, trolox and stobadine were not able to prevent a decrease in the SERCA Ca(2+)-ATPase activity. Pycnogenol and EGb761 even enhanced the decrease of the Ca(2+)-ATPase activity induced by the Fenton system, probably by secondary oxidative reactions. PMID:18692562

  12. 4f and 5d energy levels of the divalent and trivalent lanthanide ions in M{sub 2}Si{sub 5}N{sub 8} (M=Ca, Sr, Ba)

    SciTech Connect

    Kate, O.M. ten; Zhang, Z.; Dorenbos, P.; Hintzen, H.T.; Kolk, E. van der

    2013-01-15

    Optical data of Sm, Tb and Yb doped Ca{sub 2}Si{sub 5}N{sub 8} and Sr{sub 2}Si{sub 5}N{sub 8} phosphors that have been prepared by solid-state synthesis, are presented. Together with luminescence data from literature on Ce{sup 3+} and Eu{sup 2+} doping in the M{sub 2}Si{sub 5}N{sub 8} (M=Ca, Sr, Ba) hosts, energy level schemes were constructed showing the energy of the 4f and 5d levels of all divalent and trivalent lanthanide ions relative to the valence and conduction band. The schemes were of great help in interpreting the optical data of the lanthanide doped phosphors and allow commenting on the valence stability of the ions, as well as the stability against thermal quenching of the Eu{sup 2+}d-f emission. Tb{sup 3+} substitutes on both a high energy and a low energy site in Ca{sub 2}Si{sub 5}N{sub 8}, due to which excitation at 4.77 eV led to emission from both the {sup 5}D{sub 3} and {sup 5}D{sub 4} levels, while excitation at 4.34 eV gave rise to mainly {sup 5}D{sub 4} emission. Doping with Sm resulted in typical Sm{sup 3+}f-f line absorption, as well as an absorption band around 4.1 eV in Ca{sub 2}Si{sub 5}N{sub 8} and 3.6 eV in Sr{sub 2}Si{sub 5}N{sub 8} that could be identified as the Sm{sup 3+} charge transfer band. Yb on the other hand was incorporated in both the divalent and the trivalent state in Ca{sub 2}Si{sub 5}N{sub 8}. - Graphical abstract: Energy level schemes showing the 4f ground states of the trivalent ( Black-Down-Pointing-Small-Triangle ) and divalent ( Black-Up-Pointing-Small-Triangle ) lanthanide ions and lowest energy 5d states of the trivalent ({nabla}) and divalent ({Delta}) ions with respect to the valence and conduction bands of Ca{sub 2}Si{sub 5}N{sub 8} (left) and Sr{sub 2}Si{sub 5}N{sub 8} (right). Highlights: Black-Right-Pointing-Pointer Construction of energy level schemes of all lanthanides within the M{sub 2}Si{sub 5}N{sub 8} hosts. Black-Right-Pointing-Pointer Construction was done by analyzing existing as well as new

  13. Theoretical survey on M@C80 (M = Ca, Sr, and Ba): Behavior of different alkaline earth metal impacting the chemical stability and electronic properties

    NASA Astrophysics Data System (ADS)

    Cui, Jin-Bo; Guo, Yi-Jun; Li, Qiao-Zhi; Zhao, Pei; Zhao, Xiang

    2016-08-01

    Structures of mono-metallofullerenes M@C80 (M = Ca, Sr, and Ba) that separated in early experiment are determined owning the C2v(31920)-C80 cage. The change rule of properties for M@C80 (M = Ca, Sr, and Ba) influenced by different inner metal are discussed. As the trapped metal changes from calcium to barium, performance of thermodynamic stabilities for M@C2v(31920)-C80, M@C2v(31922)-C80, and M@D5h(31923)-C80 are significantly different. Orbital analysis suggests that the lowest unoccupied molecular orbitals (LUMOs) of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 are mostly located on the trapped metal, whereas reduction reactions of Ca@C2v(31920)-C80 and Ca@D5h(31923)-C80 occur on the fullerene cage. Natural electron configuration analyses demonstrates that the decentralized electron back-donation of Ba@C2v(31920)-C80 would take responsible for the instability of itself. Electronic properties such as electron affinities and ionization potentials are significantly affected by encapsulated metal are also found. Computational UV-visible-NIR spectra for M@C2v(31920)-C80 (M = Ca, Sr, Ba) are in perfect accord with the spectra obtained experimentally.

  14. Overcoming phase instability of RBaCo2O5+ (R = Y and Ho) by Sr substitution for application as cathodes in solid oxide fuel cells

    SciTech Connect

    Kim, Jung-Hyun; Young Nam, Kim; Bi, Zhonghe; Manthiram, Arumugam; Paranthaman, Mariappan Parans; Huq, Ashfia

    2013-01-01

    Phase instabilities of the RBaCo2O5+ (R = Y and Ho) layered-perovskites and their decompositions into RCoO3 and BaCoO3-z at 800 oC in air were investigated. This will restrict their high temperature applications such as cathodes in solid oxide fuel cell (SOFC). However, appropriate amount of Sr substitution ( 60 % for R = Y and 70 % for R = Ho) for Ba successfully stabilized the R(Ba1-xSrx)Co2O5+ phase at elevated temperatures. This can be explained by decreasing oxygen vacancies at R-O layer, decreasing R-O bonding length, and consequent improvement of structural integrity. In addition, the Sr substitution (x = 0.6 - 1.0) for Ba provided added benefit with respect to the chemical stability against Ce0.8Gd0.2O1.9 (GDC) electrolyte, which is a critical requirement for the cathodes in SOFC. Among the various compositions investigated, the Y(Ba0.3Sr0.7)Co2O5+ + GDC composite cathode delivered the optimum electrochemical performances with a stable phase demonstrating the potential as a cathode in SOFC.

  15. Structural, electrical, dielectric and magnetic properties of Gd-Sn substituted Sr-hexaferrite synthesized by sol-gel combustion method

    NASA Astrophysics Data System (ADS)

    Ashiq, Muhammad Naeem; Shakoor, Sajeela; Najam-ul-Haq, Muhammad; Warsi, Muhammad Farooq; Ali, Irshad; Shakir, Imran

    2015-01-01

    The effect of Gd-Sn substitution on the structural, electrical and magnetic properties of Sr1-xGdx Fe12-ySny O19 (where x=0.00, 0.025, 0.05, 0.075, 0.1) and (y=0.00, 0.25, 0.5, 0.75, 1) prepared by the sol-gel combustion method has been investigated. The XRD analysis shows the presence of Fe2O3 phase at higher substitution. The average crystallite size obtained lies between 19-42 nm which is beneficial in obtaining suitable signal-to-noise ratio in high density recording media. The FTIR spectra of annealed samples of SrFe12O19, Sr0.95Gd0.05 Fe11.5Sn0.5O19 show that strontium hexaferrite nanoparticles have been synthesized successfully. DC electrical resistivity shows metal-to-semiconductor transition with temperature. The value of transition temperature increases with dopant content. Room temperature dc resistivity and energy of activation decreases while drift mobility increases on increasing the dopant concentration. The magnetic properties such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) decreases with increasing the dopant concentration.

  16. CaMKIIδ mediates β-adrenergic effects on RyR2 phosphorylation and SR Ca2+ leak and the pathophysiological response to chronic β-adrenergic stimulation

    PubMed Central

    Grimm, Michael; Ling, Haiyun; Pereira, Laetitia; Willeford, Andrew; Gray, Charles B. B.; Erickson, Jeffrey R.; Sarma, Satyam; Respress, Jonathan L.; Wehrens, Xander H.T.; Bers, Donald M.; Brown, Joan Heller

    2015-01-01

    Chronic activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) has been implicated in the deleterious effects of β-adrenergic receptor (β-AR) signaling on the heart, in part by enhancing RyR2-mediated sarcoplasmic reticulum (SR) Ca2+ leak. We used CaMKIIδ knockout (CaMKIIδ-KO) mice, and knock-in mice with an inactivated CaMKII site S2814 on the ryanodine receptor type-2 (S2814A), to interrogate the involvement of these processes in β-AR signaling and cardiac remodeling. Langendorff-perfused hearts from CaMKIIδ-KO mice showed inotropic and chronotropic responses to isoproterenol (ISO) that were similar to those of wild type (WT) mice, however in CaMKIIδ-KO mice CaMKII phosphorylation of phospholamban and RyR2 was decreased and isolated myocytes from CaMKIIδ-KO mice had reduced SR Ca2+ leak in response to isoproterenol (ISO). Chronic catecholamine stress with ISO induced comparable increases in relative heart weight and other measures of hypertrophy from day 9 through week 4 in WT and CaMKIIδ-KO mice, but development of cardiac fibrosis was prevented in CaMKIIδ-KO animals. A 4-week challenge with ISO resulted in reduced cardiac function and pulmonary congestion in WT, but not in CaMKIIδ-KO or S2814A mice, implicating CaMKIIδ-dependent phosphorylation of RyR2-S2814 in the cardiomyopathy, independent of hypertrophy, induced by prolonged β-AR stimulation. PMID:26080362

  17. Effect of Cd substitution on the optical and transport properties of CaCu_3Ti_4O_12 boldmath

    NASA Astrophysics Data System (ADS)

    Homes, C. C.; Vogt, T.; Subramanian, M. A.; Ramirez, A. P.

    2003-03-01

    The effect of Cd doping on the transport and optical properties of CaCu_3Ti_4O_12 has been studied. At room temperature, CaCu_3Ti_4O_12 has a very high dielectric constant, \\varepsilon_0 ˜ 10^4. However, substituting Cd for Ca reduces \\varepsilon0 by nearly two orders of magnitude. Cd has a strong effect on the low frequency infrared active modes, and in addition a new mode is activated. A normal coordinate analysis has been performed to determine the nature of the vibrational modes, in particular the activated mode as well as the low frequency vibration, where an anomalous increase in the oscillator strength has been observed.(C.C. Homes et al.), Science 293, 673 (2001). It has been suggested that the large values of \\varepsilon0 may be due to a internal barrier layer capacitance effect due to twinning. The lower value for \\varepsilon0 in the Cd material may have implications for the degree of twinning and the associated changes in vibrational structure. This work was supported by the Department of Energy under contract number DE-AC02-98CH10886.

  18. Effects of electron correlation, electron-phonon coupling, and spin-orbit coupling on the isovalent Pd-substituted superconductor SrPt3P

    NASA Astrophysics Data System (ADS)

    Hu, Kangkang; Gao, Bo; Ji, Qiucheng; Ma, Yonghui; Li, Wei; Xu, Xuguang; Zhang, Hui; Mu, Gang; Huang, Fuqiang; Cai, Chuanbing; Xie, Xiaoming; Jiang, Mianheng

    2016-06-01

    We present a systematical study on the roles of interactions among electron correlation, electron-phonon coupling, and spin-orbit coupling in the isovalent Pd-substituted superconductor SrPt3P . By using the solid state reaction method, the Pd element with the 4 d orbital was successfully substituted in the strong spin-orbit coupling superconductors Sr (Pt1-xPdx) 3P . As increasing the isovalent Pd concentrations without introducing any extra electron/hole carriers, the superconducting transition temperature Tc decreases monotonously. In addition, combining the data of resistivity and specific heat, as well as electronic band structure calculations, we found that the electron correlation is enhanced while the electron-phonon coupling and the spin-orbit coupling are suppressed by Pd substitution. Our results may provide significant insights in the natures of the interplay among the electron correlation, electron-phonon coupling, and spin-orbit coupling in superconductivity, and may also pave a route for understanding the mechanism of superconductivity in heavily 5 d -based superconductors.

  19. Effect of sintering temperature on structural and dielectric properties of Bi and Li co-substituted SrTiO3

    NASA Astrophysics Data System (ADS)

    Alkathy, Mahmoud S.; Goud, J. Pundareekam; Raju, K. C. James

    2016-05-01

    Sintering is an important factor that affects the microstructure development in ceramics. In this work, Bi and Li co-substituted Strontium Titanate (ST) ceramics samples sintered at different temperatures are prepared and analyzed by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD was used to detect phase structure of the sintered samples and SEM was used for microstructure analysis. Dielectric properties of Bi and Li co-substituted SrTiO3 samples were measured using Agilent 4294A Impedance analyzer in the frequency range 40 Hz to 5 MHz at room temperature. The result reveals that the dielectric constant of Bi and Li co-substituted SrTiO3 ceramics increases with increasing sintering temperature up to 1250°C and then decreases beyond that. The highest value of dielectric constant obtained is 860 at 1KHz frequency and lowest dielectric loss observed is 0.04 at the same frequency for samples sintered at 1250°C. Also the grain size increases with increase of sintering temperature.

  20. Structural and Optoelectronic Properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) Anti-Perovskite Compounds

    NASA Astrophysics Data System (ADS)

    Ullah, Imran; Murtaza, G.; Khenata, R.; Mahmood, Asif; Muzzamil, M.; Amin, N.; Saleh, M.

    2016-01-01

    We employed first-principles calculations to predict the structural and optoelectronic properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) anti-perovskite compounds using an all-electron full-potential linearized augmented plane-wave method. Optimized structural parameters are found to be in good agreement with the available experimental measurements. The electronic band structure is calculated using different exchange-correlation potentials which reveal that the investigated compounds are narrow direct band gap semiconductors. A direct narrow band gap at the center of the Brillouin zone emphasises the optical activity of these compounds. Prediction of the optical properties, such as the real and imaginary parts of the dielectric function and refractive index along with reflectivity and optical conductivity, reveals the importance of these compounds in the visible and near UV optoelectronic devices industry.

  1. Superconductivity on a Crossover Phenomenon of Spin-Ladder System SrCa13Cu24O41 Single Crystals

    NASA Astrophysics Data System (ADS)

    Hisada, Akihiko; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Fujiwara, Naoki; Deng, Guochu; Pomjakushina, Ekaterina; Conder, Kazimierz; Mohan Radheep, Dinadhayalane; Thiyagarajan, Raman; Esakkimuthu, Sankaran; Arumugam, Sonachalam

    2014-07-01

    Electrical resistivity and alternating current susceptibility measurements were performed for the spin-ladder compound SrCa13Cu24O41 under hydrostatic pressure up to 8 GPa. The superconducting transition was observed below TC = 14.7 K at pressures above 2 GPa. By using high-quality single crystals, the bulk superconductivity with a volume fraction of 50% and temperature quadratic behavior of the normal state resistivity were observed above 3.7 GPa. They suggest that a strong interladder interaction induces the bulk superconductivity and transforms the system into a Fermi-liquid-like state. The optimal pressure was in a crossover region and the highest TC was observed without going through the bulk superconducting state. Our results suggest that the superconducting state on the crossover phenomenon presents the feature of the doped two-leg spin-ladder system because the spin gap was observed in this compound.

  2. Ultraviolet to near-infrared downconversion in Yb3+-Na+ codoped Sr2CaWO6

    NASA Astrophysics Data System (ADS)

    Li, Yong; Li, XuZhi; Wei, XianTao; Li, ZhongYuan; Chen, Hongmei; Wang, WenMing; Zhao, Wei; Ji, Yuexia

    2016-07-01

    This study investigated photoluminescent properties of Sr2CaWO6:Yb3+, Na+ phosphor. The samples were successfully synthesized via a solid-state reaction method with various doping concentrations. The phosphor can efficiently absorb ultraviolet photons of 250-350 nm and transfer its absorbed photon energy to Yb3+ ions. Then subsequent quantum cutting between WO6 groups and Yb3+ ions takes place, down-converting an absorbed ultraviolet photon into two photons of 1007 nm radiations. Analyses of decay curves of different samples reveal an efficient energy transfer from WO6 groups to Yb3+ ions. Cooperative energy transfer from host to Yb3+ ions is responsible for downconversion via lifetime analysis. Quantum efficiencies were calculated, and estimated maximum efficiency reached 190%. These phosphors combine wide wavelength absorption in the ultraviolet range with high quantum efficiency, enabling potential application of efficiency enhancement of Si solar cell.

  3. Investigation of noble metal substrates and buffer layers for BiSrCaCuO thin films

    NASA Astrophysics Data System (ADS)

    Matthiesen, M. M.; Rubin, L. M.; Williams, K. E.; Rudman, D. A.

    Noble metal buffer layers and substrates for Bi2Sr2CaCu2O8 (BSCCO) films were investigated using bulk ceramic processing and thin-film techniques. Highly oriented, superconducting BSCCO films were fabricated on polycrystalline Ag substrates and on Ag/MgO and Ag/YSZ structures. Such films could not be produced on Au or Pt substrates under any annealing conditions. In addition, superconducting BSCCO films could not be produced on Ag/Al2O3, Ag/SiO2/Si, or Ag/(Haynes 230 alloy) structures using high annealing temperatures (870 C). However, oriented although poorly connected, superconducting BSCCO films were fabricated on Ag/Al2O3 structures by using lower annealing temperatures (820 C). Once lower processing temperatures are optimized, Ag may be usable as a buffer layer for BSCCO films.

  4. Experimental search for the chiral glass transition in a ceramic Bi2 Sr2 Ca Cu2 O8 sample

    NASA Astrophysics Data System (ADS)

    Papadopoulou, E. L.; Nordblad, P.; Svedlindh, P.

    2004-08-01

    The nonlinear susceptibility of a melt-cast Bi2Sr2CaCu2O8 sample, displaying both the paramagnetic Meissner effect and magnetic aging, has been studied experimentally. The presence of magnetic aging in this sample proves that the spontaneous orbital magnetic moments exhibit correlated and frustrated dynamics at low temperatures. The possible existence of a chiral-glass phase transition was investigated by extracting a quantity corresponding to the order parameter susceptibility of the glass phase. It is shown that the expected divergent behavior of this quantity is hampered by relaxation effects and that the sample is out-of-equilibrium already at temperatures slightly below the superconducting transition temperature (Tc) . Time dependent magnetization experiments indicate that the magnetic relaxation at temperatures close to but below Tc is due to isolated orbital magnetic moments, not yet being part of the collective orbital moment state that develops at slightly lower temperatures.

  5. Fabrication and microwave properties of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films

    NASA Astrophysics Data System (ADS)

    Sobolewski, Roman; Konopka, Janusz; Kula, Witold; Gierlowski, Piotr; Konopka, Anna

    1989-03-01

    Studies are reported of the interaction of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films with microwaves. The films were prepared on cubic zirconia and magnesium oxide substrates using a modified spray deposition technique. The tested films were about 1-3 microns thick and exhibited good superconducting properties. Several test structures have been designed by spraying a mixture of nitrate precursors on heated substrates through very thin stencil marks. The supercurrent dependence on millimeter wavelength microwave illumination was measured, and microwave detection and mixing experiments were performed. The films of both materials exhibited properties characteristic of granular superconductors, with Josephson-type coupling at the intergrain connections. The results also indicate that these materials can be successfully used as very sensitive millimeter radiation detectors operational at liquid-nitrogen temperatures.

  6. Structural and Optoelectronic Properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) Anti-Perovskite Compounds

    NASA Astrophysics Data System (ADS)

    Ullah, Imran; Murtaza, G.; Khenata, R.; Mahmood, Asif; Muzzamil, M.; Amin, N.; Saleh, M.

    2016-06-01

    We employed first-principles calculations to predict the structural and optoelectronic properties of X3ZN (X = Ca, Sr, Ba; Z = As, Sb, Bi) anti-perovskite compounds using an all-electron full-potential linearized augmented plane-wave method. Optimized structural parameters are found to be in good agreement with the available experimental measurements. The electronic band structure is calculated using different exchange-correlation potentials which reveal that the investigated compounds are narrow direct band gap semiconductors. A direct narrow band gap at the center of the Brillouin zone emphasises the optical activity of these compounds. Prediction of the optical properties, such as the real and imaginary parts of the dielectric function and refractive index along with reflectivity and optical conductivity, reveals the importance of these compounds in the visible and near UV optoelectronic devices industry.

  7. Exfoliated Bi2Sr2CaCu2O8+x thin flakes for electronic transport experiments

    NASA Astrophysics Data System (ADS)

    Lee, Menyoung; Neumann, Michael; Goldhaber-Gordon, David; Sandilands, Luke; Burch, Kenneth; Xu, Zhijun; Yang, Alina; Gu, Genda

    2013-03-01

    Bismuth-based cuprates are the model high-temperature superconductor of choice for experimental probes that are spectroscopic and sensitive to the surface (STM, ARPES), while studies of transport properties have typically focused on rare-earth element-based compounds. We will first discuss preparation methods for and characterization of tape-exfoliated single crystal thin (few to tens nm) flakes of the Bi2Sr2CaCu2O8+x compound, in particular focusing on protocols designed to produce exposed conducting surfaces that are atomically smooth over several microns, and addressing the factors that influence the surface morphology and Raman scattering properties of BSCCO thin flakes. In addition, data from electronic transport measurements, aimed at observing a modulation of critical temperature and an insulator to superconductor transition as a function of hole density in the compound, will be presented.

  8. The photo-catalytic activities of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) microparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Shi, Yuanji; Zhao, Zongshan; Song, Weijie; Cheng, Yang

    2014-02-01

    For the good performance of apatite-based materials in the removal of dyes and their environment-friendly advantage, five kinds of apatite microparticles of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) were synthesized by a simple precipitation method and their photo-catalytic properties were invested. Better performance in the decolorization of methyl orange (MO) under the assistance of H2O2 than that of TiO2 were obtained for all the MPs. The photo-catalytic activity was mainly affected by surface area, energy band, impurity, crystallinity and crystal structure. The DFT calculation results demonstrated that the 2p of O and 3p of P in PO43- played the main role in the photo-catalytic process. This work would be helpful to design and synthesize low cost apatite materials with good photo-catalytic performance.

  9. Terahertz electromagnetic radiation from Bi2Sr2CaCu2Oy intrinsic Josephson junction stack

    NASA Astrophysics Data System (ADS)

    Oikawa, Dai; Irie, Akinobu; Yamaki, Kazuhiro; Oya, Gin-ichiro

    We have observed terahertz (THz) electromagnetic wave radiation from Bi2Sr2CaCu2Oy intrinsic Josephson junction (IJJ) stacks using high sensitive detector made of a small IJJ mesa. In this study, we focused on the THz radiation from a few hundred IJJs. We fabricated the IJJ oscillator and detector. The oscillators consist of 55 ∼ 300 IJJs with the lateral dimensions of 290 ¥ 50 μm2. The current-voltage characteristics of the IJJ oscillators showed a negative resistance accompanied with large hysteresis. The THz radiation was observed for several samples when the oscillator was biased at some current in the negative resistance region. We attribute the observed radiation to synchronized emission from many IJJs in the stack and find the emission frequency corresponds to the in-phase cavity resonance frequency.

  10. Fabrication of Ultrasmall High-Quality Bi2Sr2CaCu2O8+δ Intrinsic Josephson Junctions

    NASA Astrophysics Data System (ADS)

    Matsumoto, Tetsuro; Kashiwaya, Hiromi; Shibata, Hajime; Eisaki, Hiroshi; Yoshida, Yoshiyuki; Kashiwaya, Satoshi

    2008-10-01

    The fabrication of ultrasmall high-quality intrinsic Josephson junctions (IJJs) using a cuprate superconductor is critical for the realization of a qubit. We investigated the mechanism of damage induced by a Ga+ beam in a Bi2Sr2CaCu2O8+δ IJJ during focused ion beam (FIB) processing. On the basis of the results, we developed a process that allowed the successful fabrication of an ultrasmall and high-quality IJJ. The damage induced by the FIB is reduced by restricting the direction of the Ga+ beam so that the junction area is not directly irradiated by the ion beam. The fabricated ultrasmall IJJ device has a junction area of 0.3 µm2 and shows excellent current-voltage characteristics.

  11. Macroscopic Quantum Tunneling in a Bi2Sr2CaCu2O8+δ Single Crystalline Whisker

    NASA Astrophysics Data System (ADS)

    Kubo, Yuimaru; Takahide, Yamaguchi; Ueda, Shinya; Takano, Yoshihiko; Ootuka, Youiti

    2010-06-01

    Macroscopic quantum tunneling (MQT) has been observed in an intrinsic Josephson junction (IJJ) stack of a Bi2Sr2CaCu2O8+δ (BSCCO) single crystalline whisker with high precision using a home made setup. The cross-over temperature between thermal activation and MQT was about 260 mK, and the Josephson plasma frequency was estimated to be 86 GHz. Both the thermal escape theory and the MQT theory are consistent with the experiments. These facts strongly suggest that single crystalline BSCCO whiskers are high enough quality to be used as intrinsic Josephson quantum devices such as intrinsic Josephson phase qubits. This is the first demonstration of MQT in BSCCO single crystalline whiskers.

  12. Crystal structure and magnetic properties of Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy

    SciTech Connect

    Rangi, Manisha; Agarwal, Ashish Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.

    2014-08-15

    Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A{sup 2+} results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe{sup 4+} ruled out by Mössbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi{sub 0.8}Ba{sub 0.2}FeO{sub 3} sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

  13. The Effect of the CO32- to Ca2+ Ion activity ratio on calcite precipitation kinetics and Sr2+ partitioning

    PubMed Central

    2012-01-01

    Background A proposed strategy for immobilizing trace metals in the subsurface is to stimulate calcium carbonate precipitation and incorporate contaminants by co-precipitation. Such an approach will require injecting chemical amendments into the subsurface to generate supersaturated conditions that promote mineral precipitation. However, the formation of reactant mixing zones will create gradients in both the saturation state and ion activity ratios (i.e., aCO32-/aCa2+). To better understand the effect of ion activity ratios on CaCO3 precipitation kinetics and Sr2+ co-precipitation, experiments were conducted under constant composition conditions where the supersaturation state (Ω) for calcite was held constant at 9.4, but the ion activity ratio (r=aCO32-/aCa2+) was varied between 0.0032 and 4.15. Results Calcite was the only phase observed, by XRD, at the end of the experiments. Precipitation rates increased from 41.3 ± 3.4 μmol m-2 min-1 at r = 0.0315 to a maximum rate of 74.5 ± 4.8 μmol m-2 min-1 at r = 0.306 followed by a decrease to 46.3 ± 9.6 μmol m-2 min-1 at r = 1.822. The trend was simulated using a simple mass transfer model for solute uptake at the calcite surface. However, precipitation rates at fixed saturation states also evolved with time. Precipitation rates accelerated for low r values but slowed for high r values. These trends may be related to changes in effective reactive surface area. The aCO32-/aCa2+ ratios did not affect the distribution coefficient for Sr in calcite (DPSr2+), apart from the indirect effect associated with the established positive correlation between DPSr2+ and calcite precipitation rate. Conclusion At a constant supersaturation state (Ω = 9.4), varying the ion activity ratio affects the calcite precipitation rate. This behavior is not predicted by affinity-based rate models. Furthermore, at the highest ion ratio tested, no precipitation was observed, while at the lowest ion ratio precipitation occurred immediately

  14. San Francisco Estuary Striped Bass Migration History Determined by Electron-microprobe Analysis of Otolith Sr/Ca Ratio

    SciTech Connect

    Ostrach, D J; Phillis, C C; Weber, P K; Ingram, B L; Zinkl, J G

    2004-09-17

    Habitat use has been shown to be an important factor in the bioaccumulation of contaminants in striped bass. This study examines migration in striped bass as part of a larger study investigating bioaccumulation and maternal transfer of xenobiotics to progeny in the San Francisco Estuary system. Habitat use, residence time and spawning migration over the life of females (n = 23) was studied. Female striped bass were collected between Knights Landing and Colusa on the Sacramento River during the spawning runs of 1999 and 2001. Otoliths were removed, processed and aged via otolith microstructure. Subsequently, otoliths were analyzed for strontium/calcium (Sr/Ca) ratio using an electron-microprobe to measure salinity exposure and to distinguish freshwater, estuary, and marine habitat use. Salinity exposure during the last year before capture was examined more closely for comparison of habitat use by the maternal parent to contaminant burden transferred to progeny. Results were selectively confirmed by ion microprobe analyses for habitat use. The Sr/Ca data demonstrate a wide range of migratory patterns. Age of initial ocean entry differs among individuals before returning to freshwater, presumably to spawn. Some fish reside in freshwater year-round, while others return to more saline habitats and make periodic migrations to freshwater. Frequency of habitat shifts and residence times differs among fish, as well as over the lifetime of individual fish. While at least one fish spent its final year in freshwater, the majority of spawning fish spent their final year in elevated salinity. However, not all fish migrated to freshwater to spawn in the previous year. Results from this investigation concerning migration history in striped bass can be combined with contaminant and histological developmental analyses to better understand the bioaccumulation of contaminants and the subsequent effects they and habitat use have on fish populations in the San Francisco Estuary system.

  15. Electronic structure of the ingredient planes of the cuprate superconductor Bi2Sr2CuO6 +δ : A comparison study with Bi2Sr2CaCu2O8 +δ

    NASA Astrophysics Data System (ADS)

    Lv, Yan-Feng; Wang, Wen-Lin; Ding, Hao; Wang, Yang; Ding, Ying; Zhong, Ruidan; Schneeloch, John; Gu, G. D.; Wang, Lili; He, Ke; Ji, Shuai-Hua; Zhao, Lin; Zhou, Xing-Jiang; Song, Can-Li; Ma, Xu-Cun; Xue, Qi-Kun

    2016-04-01

    By means of low-temperature scanning tunneling microscopy, we report on the electronic structures of the BiO and SrO planes of the Bi2Sr2CuO6 +δ (Bi-2201) superconductor prepared by argon-ion bombardment and annealing. Depending on post annealing conditions, the BiO planes exhibit either a pseudogap (PG) with sharp coherence peaks and an anomalously large gap magnitude of 49 meV or van Hove singularity (vHS) near the Fermi level, while the SrO is always characteristic of a PG-like feature. This contrasts with the Bi2Sr2CaCu2O8 +δ (Bi-2212) superconductor where vHS occurs solely on the SrO plane. We disclose the interstitial oxygen dopants (δ in the formulas) as a primary cause for the occurrence of vHS, which are located dominantly around the BiO and SrO planes, respectively, in Bi-2201 and Bi-2212. This is supported by the contrasting structural buckling amplitude of the BiO and SrO planes in the two superconductors. Our findings provide solid evidence for the irrelevance of PG to the superconductivity in the two superconductors, as well as insights into why Bi-2212 can achieve a higher superconducting transition temperature than Bi-2201, and by implication, the mechanism of cuprate superconductivity.

  16. Electronic structure of the ingredient planes of the cuprate superconductor Bi2Sr2CuO6+δ: A comparison study with Bi2Sr2CaCu2O8+δ

    DOE PAGESBeta

    Yan -Feng Lv; Gu, G. D.; Wang, Wen -Lin; Ding, Hao; Wang, Yang; Ding, Ying; Zhong, Ruidan; Schneeloch, John; Wang, Lili; He, Ke; et al

    2016-04-15

    By means of low-temperature scanning tunneling microscopy, we report on the electronic structures of the BiO and SrO planes of the Bi2Sr2CuO6+δ (Bi-2201) superconductor prepared by argon-ion bombardment and annealing. Depending on post annealing conditions, the BiO planes exhibit either a pseudogap (PG) with sharp coherence peaks and an anomalously large gap magnitude of 49 meV or van Hove singularity (vHS) near the Fermi level, while the SrO is always characteristic of a PG-like feature. This contrasts with the Bi2Sr2CaCu2O8+δ (Bi-2212) superconductor where vHS occurs solely on the SrO plane. We disclose the interstitial oxygen dopants (δ in the formulas)more » as a primary cause for the occurrence of vHS, which are located dominantly around the BiO and SrO planes, respectively, in Bi-2201 and Bi-2212. This is supported by the contrasting structural buckling amplitude of the BiO and SrO planes in the two superconductors. Furthermore, our findings provide solid evidence for the irrelevance of PG to the superconductivity in the two superconductors, as well as insights into why Bi-2212 can achieve a higher superconducting transition temperature than Bi-2201, and by implication, the mechanism of cuprate superconductivity.« less

  17. Concentrations and ratios of Sr, Ba and Ca along an estuarine river to the Gulf of Mexico - implication for sea level rise effects on trace metal distribution

    NASA Astrophysics Data System (ADS)

    He, S.; Xu, Y. J.

    2015-11-01

    Strontium and barium to calcium ratios are often used as proxies for tracking animal movement across salinity gradients. As sea level rise continues, many estuarine rivers in the world face saltwater intrusion, which may cause changes in mobility and distribution of these metals upstream. Despite intensive research on metal adsorption and desorption in marine systems, knowledge of the spatiotemporal distribution of these elements along estuarine rivers is still limited. In this study, we conducted an intensive monitoring of Sr and Ba dynamics along an 88 km long estuary, the Calcasieu River in South Louisiana, USA, which has been strongly affected by saltwater intrusion. Over the period from May 2013 to August 2015, we collected monthly water samples and performed in-situ water quality measurements at six sites from the upstream to the river mouth, with a salinity range from 0.02 to 29.50 ppt. Water samples were analyzed for Sr, Ba, and Ca concentrations. In-situ measurements were made on salinity, pH, water temperature, dissolved oxygen concentration, and specific conductance. We found that the Sr and Ca concentrations and the Sr / Ca ratio all increased significantly with increasing salinity. The average Sr concentration at the site closest to the Gulf of Mexico (site 6) was 46.21 μmol L-1, which was about 130 times higher than that of the site furthest upstream (site 1, 0.35 μmol L-1). The average Ca concentration at site 6 was 8.19 mmol L-1, which was about 60 times higher than that of site 1 (0.13 mmol L-1). The average Sr / Ca ratio at site 6 (8.41 mmol mol-1) was about 3 times the average Sr / Ca ratio at site 1 (2.89 mmol mol-1). However, the spatial variation in Ba concentration was marginal, varying from 0.36 μmol L-1 at site 6 to 0.47 at site 5. The average Ba / Ca ratio at site 1 (4.82 mmol mol-1) was about 54 times the average Ba / Ca ratio at site 6 (0.09 mmol mol-1), showing a clear negative relation between the Ba / Ca ratio and increasing

  18. Experimental demonstration of hybrid improper ferroelectricity and the presence of abundant charged walls in (Ca,Sr)3Ti2O7 crystals.

    PubMed

    Oh, Yoon Seok; Luo, Xuan; Huang, Fei-Ting; Wang, Yazhong; Cheong, Sang-Wook

    2015-04-01

    On the basis of successful first-principles predictions of new functional ferroelectric materials, a number of new ferroelectrics have been experimentally discovered. Using trilinear coupling of two types of octahedron rotation, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the Ruddlesden-Popper compounds (Ca3Ti2O7, Ca3Mn2O7 and (Ca/Sr/Ba)3(Sn/Zr/Ge)2O7). However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. Here we provide the first experimental demonstration of room-temperature switchable polarization in bulk crystals of Ca3Ti2O7, as well as Sr-doped Ca3Ti2O7. Furthermore, (Ca, Sr)3Ti2O7 is found to exhibit an intriguing ferroelectric domain structure resulting from orthorhombic twins and (switchable) planar polarization. The planar domain structure accompanies abundant charged domain walls with conducting head-to-head and insulating tail-to-tail configurations, which exhibit a conduction difference of two orders of magnitude. These discoveries provide new research opportunities, not only for new stable ferroelectrics of Ruddlesden-Popper compounds, but also for meandering conducting domain walls formed by planar polarization. PMID:25581628

  19. High-temperature phase equilibria studies in the Bi-Sr- Ca-Cu-O-Ag system

    NASA Astrophysics Data System (ADS)

    Margulies, Lawrence

    A variety of experimental techniques were utilized to examine the high temperature phase equilibria in the Bi- Sr-Ca-Cu-O-Ag system. Quenching studies were used to determine the liquid solubility of Ag in the Bi2Sr 2CaCu2O8 (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO2). A liquid immiscibility region between oxide and Ag liquids in the 8-98 at% range was found above 900°C. Two eutectics were found in the Bi2212-Ag pseudo-binary. On the oxide rich side, a eutectic exists at approximately 4 at% Ag. On the Ag rich side, a eutectic exists at approximately 98 at% Ag at a temperature of 15°C below the melting point of pure Ag. Six distinct solid phases were found to be in equilibrium with the partial melt within the Ag content and PO2 range studied. The stability of these solid phases were found to be highly sensitive to PO2, and to a much lesser extent Ag content. High temperature x-ray diffraction (HTXRD) studies of this system are in conflict with these results. It is suggested that these discrepancies are due to experimental artifacts caused by the significant thermal gradients and lack of full bulk sampling which is inherent in conventional HTXRD designs. In part II, a new furnace design compatible with synchrotron radiation sources is introduced to address these problems. This design allows for full bulk sampling in a low thermal gradient environment using Debye- Scherrer transmission geometry. Sample spinning is also introduced in the design to eliminate preferred orientation and incomplete powder averaging and allow for quantitative phase analysis and structural refinement. Studies on model systems are presented to demonstrate the capabilities for high resolution structural studies (Al 2O3) and time resolved phase transformation studies (SrCO 3). Finally, the Bi2212 system is examined to confirm the quenching results of part I, and to demonstrate the degree to which

  20. Structural, electronic and magnetic properties of the series of double perovskites (Ca,Sr){sub 2−x}La{sub x}FeIrO{sub 6}

    SciTech Connect

    Bufaiçal, L.; Adriano, C.; Lora-Serrano, R.; Duque, J.G.S.; Mendonça-Ferreira, L.; Rojas-Ayala, C.; Baggio-Saitovitch, E.; Bittar, E.M.; Pagliuso, P.G.

    2014-04-01

    Polycrystalline samples of the series of double perovskites Sr{sub 2−x}La{sub x}FeIrO{sub 6} were synthesized. Their structural, electronic and magnetic properties were investigated by X-ray powder diffraction, Mössbauer spectroscopy, magnetic susceptibility, heat capacity and electrical resistivity experiments. The compounds crystallize in a monoclinic structure and were fitted in space group P2{sub 1}/n, with a significant degree of Fe/Ir cationic disorder. As in Ca{sub 2−x}La{sub x}FeIrO{sub 6} the Sr-based system seems to evolve from an antiferromagnetic ground state for the end members (x=0.0 and x=2.0) to a ferrimagnetic order in the intermediate regions (x∼1). Since Mössbauer spectra indicate that Fe valence remains 3+ with doping, this tendency of change in the nature of the microscopic interaction could be attributed to Ir valence changes, induced by La{sup 3+} electrical doping. Upon comparing both Ca and Sr series, Sr{sub 2−x}La{sub x}FeIrO{sub 6} is more structurally homogenous and presents higher magnetization and transition temperatures. Magnetic susceptibility measurements at high temperatures on Sr{sub 1.2}La{sub 0.8}FeIrO{sub 6} indicate a very high ferrimagnetic Curie temperature T{sub C}∼700K. For the Sr{sub 2}FeIrO{sub 6} compound, electrical resistivity experiments under applied pressure suggest that this material might be a Mott insulator. - Graphical abstract: The Weiss constant as a function of La doping for the (Ca,Sr){sub 2−x}La{sub x}FeIrO{sub 6} series, indicating changes in Fe–Ir magnetic coupling on both families. - Highlights: • The double perovskite series (Ca,Sr){sub 2−x}La{sub x}FeIrO{sub 6} were synthesized. • Changes in the Fe-Ir magnetic coupling due to La doping on both series. • Evidence of high T{sub C} on Sr{sub 1.2}La{sub 0.8}FeIrO{sub 6}. • Indication of Mott insulator behavior on Sr{sub 2}FeIrO{sub 6}.

  1. Nanostructured silicate substituted calcium phosphate (NanoSiCaPs) nanoparticles - Efficient calcium phosphate based non-viral gene delivery systems.

    PubMed

    Shekhar, Sudhanshu; Roy, Abhijit; Hong, Daeho; Kumta, Prashant N

    2016-12-01

    Nanostructured ceramic particles, particularly, nanoparticles of calcium phosphate (CaP) remain an attractive option among the various types of non-viral gene delivery vectors studied because of their safety, biocompatibility, biodegradability, and ease of handling as well as their adsorptive capacity for DNA. We have accordingly developed an enhanced version of nanostructured calcium phosphates (NanoCaPs), by substituting known amounts of silicate for phosphate in the hydroxyapatite (HA) lattice (NanoSiCaPs). Results indicate that in addition to the excellent transfection levels exhibited by un-substituted NanoCaPs alone in vitro, an additional 20-50% increase in transfection is observed for NanoCaPs containing 8.3-50mol% silicate aptly called NanoSiCaPs, owing to its rapid dissolution properties enabling nanoparticles escaping the lysosomal degradation. However, high silicate substitution (>50mol%) resulted in a drastic decline in transfection as the synthesized NanoCaPs deviated far from the characteristic hydroxyapatite phase formed as evidenced by the materials characterization results. PMID:27612739

  2. c-Axis oriented thin Bi 2Sr 2CaCu 2O 8+δ-films prepared by flash- evaporation

    NASA Astrophysics Data System (ADS)

    Stölzel, C.; Huth, M.; Adrian, H.

    1992-12-01

    Superconducting thin films of Bi 2Sr 2CaCu 2O 8+δ were prepared by flash-evaporation. Fine grained powder of the stoichiometry Bi 2Sr 2.5Ca 2Cu 2O y was periodically dropped onto and flash-evaporated by a 1900°C hot tantalum boat and deposited on an unheated <100>-SrTiO 3-substrate. Post-annealing yielded highly c-axis oriented, single phase films, which showed superconductivity up to 81 K. Resistive transitions and critical current densities were measured in magnetic fields up to 6 T with the field direction parallel and perpendicular to the c-axis.

  3. Creep of polycrystalline (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x}

    SciTech Connect

    Martinez-Fernandez, J.; Dominguez-Rodriguez, A.; Routbort, J.L.; Goretta, K.C.

    2000-04-14

    Plastic deformation has proved to be essential to the manufacture of bulk (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) superconductors. Compressive creep of dense, forged Bi-2223, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi-2212), and Bi{sub 2}Sr{sub 2}CuO{sub x} (Bi-2201) superconductors has been studied. These previous studies left unanswered questions about the large variation in Q among the Bi-superconductors and the rate-controlling deformation mechanism. The goals of this work were to test high-quality bulk Bi-2223 to determine whether steady state can be established, and if so, to determine the dominant creep mechanism and the values of n and Q.

  4. In vitro synthesis of amorphous Mg-, Ca-, Sr- and Ba-carbonates: What do we learn about intracellular calcification by cyanobacteria?

    NASA Astrophysics Data System (ADS)

    Cam, N.; Georgelin, T.; Jaber, M.; Lambert, J.-F.; Benzerara, K.

    2015-07-01

    Some cyanobacteria, including Candidatus Gloeomargarita lithophora, which was isolated from Lake Alchichica (Mexico), can form intracellular carbonates. This contradicts the common paradigm that cyanobacterial calcification is always extracellular and suggests that calcification might be controlled by these cyanobacterial species. Intracellular carbonates have several peculiar characteristics: they are relatively small (between 60 and 500 nm), they are poorly crystalline, and they have Sr/Ca and Ba/Ca ratios much higher than the solution in which the cells grow. It is therefore crucial to understand whether these unique features may indicate the involvement of specific biological processes. Here, in vitro abiotic syntheses were performed to synthesize Mg-, Ca-, Sr- and Ba-containing carbonates with compositions, crystallinities and sizes close to those observed in intracellularly calcifying cyanobacteria. Precipitates were characterized by scanning and transmission electron microscopies coupled with energy dispersive X-ray spectroscopy, thermogravimetric analysis and X-ray diffraction. The size and the poor crystallinity of cyanobacterial intracellular carbonates could be mimicked under these abiotic conditions. It was shown that similarly to Mg, elements such as Sr and Ba can favor stabilization of poorly crystalline carbonates. In contrast, the differential partitioning of Sr, Ba and Ca between the solution and the solids as observed in cyanobacteria could not be mimicked in vitro. This provides keys to a better understanding of biological processes involved in the formation of intracellular carbonates by some cyanobacteria, including the involvement of membrane transporters.

  5. Evaluation of the effects of microscale chemical and isotopic heterogeneity of coral skeleton on conventional Sr/Ca and O paleothermometers

    NASA Astrophysics Data System (ADS)

    Mitsuguchi, Takehiro

    2013-10-01

    Recent studies using secondary ion mass spectrometry revealed microscale heterogeneity of Sr/Ca and O in shallow-water coral skeletons, i.e., Sr/Ca and O differ significantly between two basic microfeatures of the skeleton: the center of calcification (COC) and surrounding fibrous skeleton (SFS). The COC, in contrast with the SFS, consists of highly irregular crystals intermingled with significant amount of organic matter; therefore, analyzing the SFS only would probably be favourable for paleotemperature reconstruction. Conventional Sr/Ca and O paleothermometers are, however, based on the analysis of the mixture of the COC and SFS, and thus may be significantly affected by the above-mentioned heterogeneity. In this study, I have evaluated the heterogeneity-induced effects on the conventional paleothermometers of Porites skeletons using published Sr/Ca, O and volume-fraction data of the COC and SFS and published observations of seasonal variability of bulk skeletal density. Results indicate that the effects may yield significant or serious errors in paleotemperature reconstruction.

  6. Comment on ``Electrical and dielectric propertiesof the Bi4Sr3Ca3Cu4Ox (4:3:3:4) glassy semiconductor''

    NASA Astrophysics Data System (ADS)

    Ghosh, A.

    1997-01-01

    A recent paper from Som and Chaudhuri [Phys. Rev. B 41, 1581 (1990)], regarding the electrical and dielectric properties of Bi4Sr3Ca3Cu4Ox glass is reanalyzed. It is shown that the theoretical analysis for the ac conductivity and its frequency exponent performed by the authors is incorrect.

  7. Aurivillius-Popper mixed superconductors in BiO--CuO--(Sr/sub 0. 5/, Ca/sub 0. 5/)O system

    SciTech Connect

    Fukuhara, M.; Bhalla, A.S.; Mulay, L.N.; Newnham, R.E.

    1989-03-01

    We report the effect of inhomogeneities on the electric resistivity and ac magnetic susceptibility in Aurivillius-like bismuth mixed phase oxides of the BiO--Cuo--(Sr/sub 0.5/, Ca/sub 0.5/)O system and propose a crystal structure of the major phase having highest T/sub c/. Nominal Aurivillius compositions with molar ratios of BiO/(Sr/sub 0.5/, Ca/sub 0.5/)O = 1/2 are superconductors with T/sub c/ ranging from 83 to 107 K, and are accompanied by a large expansion during sintering due to the formation of Kirkendall voids. T/sub c/ increases with decreasing of the c lattice parameter. An oxide BiSrCaCu/sub 2/O/sub x/ (n = 2) shows a maximum T/sub c/ value of 107 K and an onset of superconductivity at a much higher temperature. It seems that the structure of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ consists of an Aurivillius-like phase having two perovskite layers and a Popper mixed phase. The ac magnetic susceptibility showed an overall decrease in susceptibility with time up to 220 days. This appears to be related to the relief of intralattice strain.

  8. Coral Sr/Ca-based sea surface temperature and air temperature variability from the inshore and offshore corals in the Seribu Islands, Indonesia.

    PubMed

    Cahyarini, Sri Yudawati; Zinke, Jens; Troelstra, Simon; Suharsono; Aldrian, Edvin; Hoeksema, B W

    2016-09-30

    The ability of massive Porites corals to faithfully record temperature is assessed. Porites corals from Kepulauan Seribu were sampled from one inshore and one offshore site and analyzed for their Sr/Ca variation. The results show that Sr/Ca of the offshore coral tracked SST, while Sr/Ca variation of the inshore coral tracked ambient air temperature. In particular, the inshore SST variation is related to air temperature anomalies of the urban center of Jakarta. The latter we relate to air-sea interactions modifying inshore SST associated with the land-sea breeze mechanism and/or monsoonal circulation. The correlation pattern of monthly coral Sr/Ca with the Niño3.4 index and SEIO-SST reveals that corals in the Seribu islands region respond differently to remote forcing. An opposite response is observed for inshore and offshore corals in response to El Niño onset, yet similar to El Niño mature phase (December to February). SEIO SSTs co-vary strongly with SST and air temperature variability across the Seribu island reef complex. The results of this study clearly indicate that locations of coral proxy record in Indonesia need to be chosen carefully in order to identify the seasonal climate response to local and remote climate and anthropogenic forcing. PMID:27181035

  9. Ag-clad Bi-Sr-Ca-Cu-O wires I. Phase study of fully processed 2:2:1:2 wires

    NASA Astrophysics Data System (ADS)

    Ray, R. D.; Hellstrom, E. E.

    1991-01-01

    We have studied the composition of phases in fully processed Ag-clad wires containing Bi-Sr-Ca-Cu-O with a starting cation ratio of 2:2:1:2 using electron probe microanalysis. Wires that were processed at temperatures not exceeding 850°C contained two phases: the two-CuO 2 layer superconductor (“2212”) and Bi 0.06Sr 8.87Ca 4.87Cu 24O x, which is a member of the “ {14}/{24}” solid solution that is in equilibrium with “2212” at 850°C. Phases identified in wires melt processed at temperatures up to 920°C then annealed at 830-840°C were “2212”, (Sr 1- xCa x)CuO 2, and Ag particles. This appears to be a nonequilibrium phase assemblage as the superconductor is not reported to be in equilibrium with (Sr 1- xCa x)CuO 2 at 800-850°C.

  10. Spectroscopic and photoluminescence characterization of Dy(3+) in Sr0.5Ca0.5TiO3 phosphor.

    PubMed

    Vidyadharan, Viji; Sreeja, E; Jose, Saritha K; Joseph, Cyriac; Unnikrishnan, N V; Biju, P R

    2016-02-01

    The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy(3+))-doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid-state reaction method were studied. The X-ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd-Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy(3+). The photoluminescence spectrum of Dy(3+)-doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to (4)F9/2 →(6)H15/2, (4)F9/2 →(6)H13/2 and (4)F9/2 →(6)H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy(3+) concentrations is discussed. The decay profiles of (4)F9/2 excited levels of Dy(3+) ions show bi-exponential behaviour and also a decrease in average lifetime with increase in Dy(3+) concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co-ordinates and correlated color temperature were also calculated for different concentrations of Dy(3+)-doped Sr0.5Ca0.5TiO3 phosphor at different λex. PMID:26032295

  11. Electronic, Dielectric, and Plasmonic Properties of Two-Dimensional Electride Materials X2N (X=Ca, Sr): A First-Principles Study.

    PubMed

    Guan, Shan; Yang, Shengyuan A; Zhu, Liyan; Hu, Junping; Yao, Yugui

    2015-01-01

    Based on first-principles calculations, we systematically study the electronic, dielectric, and plasmonic properties of two-dimensional (2D) electride materials X2N (X=Ca, Sr). We show that both Ca2N and Sr2N are stable down to monolayer thickness. For thicknesses larger than 1-monolayer (1-ML), there are 2D anionic electron layers confined in the regions between the [X2N](+) layers. These electron layers are strongly trapped and have weak coupling between each other. As a result, for the thickness dependence of many properties such as the surface energy, work function, and dielectric function, the most dramatic change occurs when going from 1-ML to 2-ML. For both bulk and few-layer Ca2N and Sr2N, the in-plane and out-of-plane real components of their dielectric functions have different signs in an extended frequency range covering the near infrared, indicating their potential applications as indefinite media. We find that bulk Ca2N and Sr2N could support surface plasmon modes in the near infrared range. Moreover, tightly-bounded plasmon modes could exist in their few-layer structures. These modes have significantly shorter wavelengths (few tens of nanometers) compared with that of conventional noble metal materials, suggesting their great potential for plasmonic devices with much smaller dimensions. PMID:26192245

  12. Dipole polarizability of alkali-metal (Na, K, Rb)–alkaline-earth-metal (Ca, Sr) polar molecules: Prospects for alignment

    SciTech Connect

    Gopakumar, Geetha Abe, Minori; Hada, Masahiko; Kajita, Masatoshi

    2014-06-14

    Electronic open-shell ground-state properties of selected alkali-metal–alkaline-earth-metal polar molecules are investigated. We determine potential energy curves of the {sup 2}Σ{sup +} ground state at the coupled-cluster singles and doubles with partial triples (CCSD(T)) level of electron correlation. Calculated spectroscopic constants for the isotopes ({sup 23}Na, {sup 39}K, {sup 85}Rb)–({sup 40}Ca, {sup 88}Sr) are compared with available theoretical and experimental results. The variation of the permanent dipole moment (PDM), average dipole polarizability, and polarizability anisotropy with internuclear distance is determined using finite-field perturbation theory at the CCSD(T) level. Owing to moderate PDM (KCa: 1.67 D, RbCa: 1.75 D, KSr: 1.27 D, RbSr: 1.41 D) and large polarizability anisotropy (KCa: 566 a.u., RbCa: 604 a.u., KSr: 574 a.u., RbSr: 615 a.u.), KCa, RbCa, KSr, and RbSr are potential candidates for alignment and orientation in combined intense laser and external static electric fields.

  13. Effects of Cl(-) substitution on electrophysiological properties, Ca(2+) influx and prolactin secretion of rat lactotropes in vitro.

    PubMed

    Garcia, L; Couderc, B; Odessa, M F; Dufy-Barbe, L; Sartor, P

    1999-11-01

    In this study, we compared the effects of different chloride (Cl(-)) substitutes - methane sulfonate (CH(3)SO(-)(3)), bromide (Br(-)), nitrate (NO(-)(3)), thiocyanate (SCN(-)) and perchlorate (ClO(-)(4)) - on the secretory activity and calcium current activation of rat lactotropes in primary culture. We observed that CH(3)SO(-)(3) decreased basal prolactin (PRL) secretion. Br(-) had no effect, whereas the more lyotropic anions, such as NO(-3), SCN(-) and C1O(-4), increased basal PRL secretion. The latter three substitutes induced a significant shift in the voltage dependence of T-type calcium channel activation towards hyperpolarized values. However, this shift alone cannot explain the increase in secretion. Anion permeability studies also demonstrated that the organic anion CH(3)SO(-3) was less permeant than Cl(-), whereas monovalent inorganic anions were more permeant, with the following anion permeability sequence: SCN(-) > ClO(-4) > NO(-3) > Br(-). In conclusion, deprivation of Cl(-) ions has converse consequences on basal and induced secretion; permeating anions result in a transient increase in intracellular Ca(2+) ions. This process involves voltage-dependent Ca(2+) channels. We propose that an alteration in intracellular anion concentrations may influence the activation of internal effectors such as G proteins or channel proteins and, therefore, interfere with exocytosis. These effects are correlated with an external action of lyotropic anions, particularly NO(-3), ClO(-4) and SCN(-), on the gating properties of T-type calcium channels, probably through changes in cell surface charges. The results demonstrate the modulatory effect of anions on the secretory activity of rat lactotropes and underline the specific role played by chloride in stimulus-secretion coupling. PMID:10567859

  14. Dissolution of aragonite-strontianite solid solutions in nonstoichiometric Sr (HCO3)2-Ca (HCO3)2-CO2-H2O solutions

    USGS Publications Warehouse

    Plummer, L.N.; Busenberg, E.; Glynn, P.D.; Blum, A.E.

    1992-01-01

    Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO2-saturated non-stoichiometric solutions of Sr(HCO3)2 and Ca(HCO3)2 at 25??C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca(HCO3)2 solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr(HCO3)2 solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HCO3)2 solutions and 0-4 layers thick in Ca(HCO3)2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation of a more stable Sr-rich solid. The compositions of secondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HCO3)2 and Ca(HCO3)2 solutions, respectively. In Sr(HCO3)2 solutions, the XPS signal from the outer ~ 60 A?? on aragonite indicates a composition of 16 mol% SrCO3 after only 2 min of contact, and 14-18 mol% SrCO3 after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO3 after 2 min of contact with Ca(HCO3)2 solution, and is 34-39 mol% CaCO3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer ~25

  15. Synthesis, structure, and properties of four ternary compounds: CaSrTt, Tt=Si, Ge, Sn, Pb

    SciTech Connect

    Liu Shengfeng; Corbett, John D. . E-mail: jcorbett@iastate.edu

    2006-03-15

    The title compounds were synthesized and characterized by structural measurements and electronic structure calculations. Single-crystal X-ray diffraction analyses established that they all have the orthorhombic inverse-PbCl{sub 2}-type structure (Pnma, Z=4, a=8.108(2), 8.124(2), 8.421(2), 8.509(2)A; b=4.944(1), 4.949(1), 5.168(1), 5.189(1)A; c=9.170(2), 9.184(2), 9.685(2), 9.740(2)A, respectively). The tetrel (Tt) atoms are situated in tricapped trigonal prisms of ordered Sr and Ca atoms in which the smaller Ca atoms play a distinctive role. The structure is distinguishable from the Co{sub 2}Si type by its more nearly ideal 6+3 (TCTP) environment about Tt rather than a higher coordination by cations. Other representations of the two structural types are also considered. Electronic band structure calculations suggest that the compounds are semiconductors, in agreement with literature data on their Ae{sub 2}Tt analogues.

  16. Synthesis, structure and chemical bonding of CaFe2-xRhxSi2 (x=0, 1.32, and 2) and SrCo2Si2

    NASA Astrophysics Data System (ADS)

    Hlukhyy, Viktor; Hoffmann, Andrea V.; Fässler, Thomas F.

    2013-07-01

    The finding of superconductivity in Ba0.6K0.4Fe2As2 put the attention on the investigation of compounds that crystallize with ThCr2Si2 structure type such as AT2X2 (A=alkali/alkaline earth/rare earth element; T=transition metal and X=element of the 13-15th group). In this context the silicides CaFe2Si2, CaFe0.68(6)Rh1.32(6)Si2, CaRh2Si2 and SrCo2Si2 have been synthesized by reaction of the elements under an argon atmosphere. Single crystals were obtained by special heat treatment in welded niobium/tantalum ampoules. The compounds were investigated by means of powder and single crystal X-ray diffraction. All compounds crystallize in the ThCr2Si2-type structure with space group I4/mmm (No. 139): a=3.939(1) Å, c=10.185(1) Å, R1=0.045, 85 F2 values, 8 variable parameters for CaFe2Si2; a=4.0590(2) Å, c=9.9390(8) Å, R1=0.030, 90 F2 values, 10 variable parameters for CaFe0.68(6)Rh1.32(6)Si2; a=4.0695(1) Å, c=9.9841(3) Å, R1=0.031, 114 F2 values, 9 variable parameters for CaRh2Si2; and a=3.974(1) Å, c=10.395(1) Å, R1=0.036, 95 F2 values, 8 variable parameters for SrCo2Si2. The structure of SrCo2Si2 contains isolated [Co2Si2]2- 2D-layers in the ab-plane whereas in CaFe2-xRhxSi2 the [T2Si2] layers (T=Fe and Rh) are interconnected along the c-axis via Si3Si bonds resulting in a three-dimentional (3D) [T2Si2]2- polyanions and therefore belong to the so-called collapsed form of the ThCr2Si2-type structure. The SrCo2Si2 and CaRh2Si2 are isoelectronic to the parent 122 iron-pnictide superconductors AeFe2As2 (Ae=alkaline earth elements), whereas CaFe2Si2 is a full substituted variant (As/Si) of CaFe2As2. The crystal chemistry and chemical bonding in the title compounds are discussed in terms of LMTO band structure calculations and a topological analysis using the Electron Localization Function (ELF).

  17. Methods for estimating a critical value for determining the freshwater/estuarine habitat residence of American eels from otolith Sr:Ca data

    NASA Astrophysics Data System (ADS)

    Jessop, B. M.; Shiao, J. C.; Iizuka, Y.

    2013-11-01

    Linear discriminant analysis (LDA) and habitat discrimination critical value (HDCV) methods are alternatives for evaluating the migratory history, such as the proportion of residence in freshwater (%fwr) and estuarine/marine habitats, of individual American eels (Anguilla rostrata) via the analysis of otolith Sr:Ca data. The LDA process requires Sr:Ca data from both freshwater and estuarine/marine groups while the mean + cSD method requires only a freshwater standard. For the two group (freshwater, estuarine/marine), single predictor variable (Sr:Ca) case, the LDA process defaults to Fisher's linear discriminant where the HDCV equals the average of the group mean Sr:Ca values. The difference between freshwater and estuarine resident eel mean otolith Sr:Ca values, based on 13 published studies and the current study (n = 14), decreased with increasing freshwater group otolith mean (r = 0.80, p < 0.001), reflecting a relatively constant estuarine group mean (r = 0.38, p = 0.17). A process is proposed for estimating a HDCV from freshwater group otolith Sr:Ca mean and SD values based on empirical linear relations between the LDA, HDCV and freshwater mean (n = 14, r = 0.90, p < 0.0001) and c and SD (n = 14, r = -0.89, p < 0.0001) from the equation HDCV = mean + cSD. Variation in the sample sizes of otolith Sr:Ca values used in the discriminant process of estimating a HDCV, while statistically significant, had trivial effect sizes that were likely of little biological consequence. However, larger sample sizes are preferred over smaller sample sizes. Estimates of %fwr increased with increases in the HDCV. Differences in %fwr estimates over a range of HDCVs were highly statistically significant and effect sizes increased with increased HDCV difference. As HDCV levels increased, growth rate estimates increased for a given %fwr value. A HDCV difference of ≤0.5 × 10-3 produced a small effect size. Accurate estimation of a HDCV is fundamental to the assessment of the habitat

  18. A Modern Sr/Ca-δ18O-Sea Surface Temperature Calibration for Isopora Corals in the Great Barrier Reef

    NASA Astrophysics Data System (ADS)

    Brenner, L. D.; Linsley, B. K.; Potts, D. C.

    2014-12-01

    Most coral-based paleoceanographic studies have used massive colonies of Porites or Faviidae, due to their long, continuously accreted skeletal records and sub-annual resolution, but other sub-massive corals provide an untapped resource. The genus Isopora is a dominant reef builder in some high-energy environments in the tropical western Pacific, and was a major component of cores recovered on IODP Leg 325 off the Great Barrier Reef (GBR). Despite its abundance, Isopora remains largely unexplored and hence underutilized in paleoceanographic studies. We present a modern Sr/Ca-δ18O-Sea Surface Temperature (SST) calibration of modern Isopora corals (n=3) collected from inner and outer reef locations ranging from 1-13m depth by Heron Island in the southern GBR in 2012. Pairing the Isopora Sr/Ca record with monthly SST yielded an average relationship of SST=-11.48×(Sr/Ca)+131.1 (r2 = 0.42-0.78). The Sr/Ca sensitivity of -0.087 mmol/mol/°C is similar to the sensitivity for Porites that was corrected for tissue layer smoothing effects determined by Gagan et al. (2012). The similarity between our Sr/Ca-SST sensitivity and the corrected sensitivity for Porites suggests tissue layer effects are minimal in Isopora. The mean annual SST amplitude recorded by the corals from 2008-2011 (full annual cycles) was 5.3°C and the average δ18O annual cycle of 1.1‰ approximates that expected if salinity had little effect on coral δ18O, assuming a previously established conversion of -0.23‰ (δ18O)/°C for biogenic aragonite. The average annual salinity amplitude of 0.3 in gridded data from around Heron Island supports our conclusion that δ18O variability is forced almost completely by SST. This modern Sr/Ca-SST calibration will expand the paleoceanographic utility of Isopora and, by assisting interpretation of Sr/Ca data from fossil corals collected during IODP 325, will better constrain the timing and magnitude of sea level changes and surface conditions since the Last

  19. Effect of cryogenic temperature on spectroscopic and laser properties of Er,La:SrF2-CaF2 crystal

    NASA Astrophysics Data System (ADS)

    Švejkar, Richard; Šulc, Jan; Němec, Michal; Jelínková, Helena; Doroshenko, Maxim E.; Nakladov, Andrei N.; Osiko, Vjatcheslav V.

    2016-03-01

    The laser and spectroscopic properties of crystal Er,La:SrF2-CaF2 at temperature range 80 - 300 K, which is appropriate for generation of radiation around 2.7 um is presented. The sample of Er,La:SrF2-CaF2 (concentration Er(0.04), La(0.12):Ca(0.77)Sr(0.07)) had plan-parallel face-polished faces without anti-reflection coatings (thickness 8.2 mm). During spectroscopy and laser experiments the Er,La:SrF2-CaF2 was attached to temperature controlled copper holder and it was placed in vacuum chamber. The transmission and emission spectra of Er,La:SrF2-CaF2 together with the fluorescence decay time were measured in dependence on temperature. The excitation of Er,La:SrF2-CaF2 was carried out by a laser diode radiation (pulse duration 5 ms, repetition rate 20 Hz, pump wavelength 973 nm). Laser resonator was hemispherical, 140 mm in length with at pumping mirror (HR @ 2.7 µm) and spherical output coupler (r = 150 mm, R = 95 % @ 2.5 - 2.8 µm). Tunability of laser at 80 K in range 2690 - 2765 nm was obtained using MgF2 birefringent filter. With decreasing temperature of sample the fluorescence lifetime of manifold 4I11/2 (upper laser level) became shorter and intensity of up-conversion radiation was increasing. The highest slope efficiency with respect to absorbed power was 2.3 % at 80 K. The maximum output of peak amplitude power was 0.3 W at 80 K, i.e. 1.5 times higher than measured this value at 300 K. The wavelength generated by Er,La:SrF2-CaF2 laser (2.7 µm) is relatively close to absorption peak of water (3 µm) and so, one of the possible usage should be in medicine and spectroscopy.

  20. A new calibration for the Sr/Ca-temperature relationship in sclerosponges reveals synchronous changes in Caribbean specimens indicative of warming and multi-decadal climate variability

    NASA Astrophysics Data System (ADS)

    Waite, A. J.; Swart, P. K.; Rosenheim, B. E.

    2009-12-01

    Previous work defined the calibration between the skeletal Sr/Ca ratio of the sclerosponge Ceratoporella nicholsoni and the ambient seawater temperature. However, application of this calibration to records throughout the Caribbean reveals a nearly 4°C warming over the last 150 years, in excess of what one might expect from global climate averages. As the original C. nicholsoni Sr/Ca-temperature relationship was calibrated between 26 and 30°C, it is possible that the relationship differed outside of the examined temperature window. This suspicion is confirmed by the measurement of Sr/Ca ratios from additional specimens of the same species. These show a significantly different slope between Sr/Ca and temperature at lower temperatures (21 to 26°C). Using this information, the calibration equation has been refined and the subsequent reconstructions of temperature are much more realistic, indicating a warming of approximately 1°C over the last 150 years. Applying this new calibration to additional published sclerosponge records of Sr/Ca reveals remarkable agreements between records from the Bahamas and Jamaica, both in amplitude of warming and smaller scale variability. In addition, the depth versus temperature relationship associated with these specimens is preserved. The refined temperature reconstruction of a 600 year record from Exuma Sound, Bahamas, demonstrates the cyclic nature of its variability (~15 and 28 year periodicities). Further use of these data and stable oxygen isotopes to calculate salinity reveals variability on multi-decadal timescales. This includes an approximately 20 year periodicity between 1400 and 1790. From 1790 to 2000, the dominant mode appears to switch to a roughly 60 year periodicity, consistent with that of the Atlantic Multi-decadal Oscillation (AMO).

  1. Effect of Mn and Ti substitution on the reflection loss characteristic of Ba0.6Sr0.4Fe11-zMnTizO19 (z = 0, 1, 2 and 3)

    NASA Astrophysics Data System (ADS)

    Gunanto, Y. E.; Cahyadi, L.; Adi, W. Ari

    2016-04-01

    The synthesis and characterization of composition Ba0.6Sr0.4Fe11-zMnTizO19 (z = 0; 1; 2 and 3) compound by solid state reaction using mechanical milling have been performed. The raw materials were BaCO3, SrCO3, Fe2O3, MnCO3, and TiO2. The mixed powder was compacted and sintered at 1000°C for 5 hours. X-ray diffraction studies indicate expansion of hexagonal unit cell and compression of atomic density with substitution of Mn2+ and Ti4+ ions. Effect of substitution upon magnetic properties revealed that total magnetization, remanence, and coercivity changed with substitution due to preferential site occupancy of substituted Mn2+ and Ti4+ ions. Since the coercivity and total magnetization may be controlled by substitution while maintaining resistive properties, this material is useful for microwave absorber.

  2. Combined effects of transition metal (Ni and Rh) substitution and annealing/quenching on the physical properties of CaFe2As2

    SciTech Connect

    Ran, S; Bud'ko, S L; Straszheim, W E; Canfield, P C

    2014-08-01

    We performed systematic studies of the combined effects of annealing/quenching temperature (TA/Q) and T=Ni, Rh substitution (x) on the physical properties of Ca(Fe1-xTx)2As2. We constructed two-dimensional, TA/Q-x phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co substitution. Ni substitution, which brings one more extra electron per substituted atom and suppresses the c-lattice parameter at roughly the same rate as Co substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic phase space in the TA/Q-x space as that found for Co substitution, but the parameter range for superconductivity has been shrunk (roughly by a factor of 2). This result is similar to what is found when Co- and Ni-substituted BaFe2As2 are compared. On the other hand, Rh substitution, which brings the same amount of extra electrons as does Co substitution, but suppresses the c-lattice parameter more rapidly, has a different phase diagram. The collapsed tetragonal phase exists much more pervasively, to the exclusion of the normal, paramagnetic, tetragonal phase. The range of antiferromagnetic/orthorhombic phase space is noticeably reduced, and the superconducting region is substantially suppressed, essentially truncated by the collapsed tetragonal phase. In addition, we found that whereas for Co substitution there was no difference between phase diagrams for samples annealed for 1 or 7 days, for Ni and Rh substitutions a second, reversible effect of annealing was revealed by 7-day anneals.

  3. Effect of Ca substitution on some physical properties of nano-structured and bulk Ni-ferrite samples

    NASA Astrophysics Data System (ADS)

    Assar, S. T.; Abosheiasha, H. F.

    2015-01-01

    Nanoparticles of Ni1-xCaxFe2O4 (x=0.0, 0.02, 0.04, 0.06 and 0.10) were prepared by citrate precursor method. A part of these samples was sintered at 600 °C for 2 h in order to keep the particles within the nano-size while the other part was sintered at 1000 °C to let the particles to grow to the bulk size. The effect of Ca2+ ion substitution in nickel ferrite on some structural, magnetic, electrical and thermal properties was investigated. All samples were characterized by using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). A two probe method was used to measure the dc electrical conductivity whereas the photoacoustic (PA) technique was used to determine the thermal diffusivity of the samples. To interpret different experimental results for nano and bulk samples some cation distributions were assumed based on the VSM and XRD data. These suggested cation distributions give logical explanations for other experimental results such as the observed values of the absorption bands in FTIR spectra and the dc conductivity results. Finally, in the thermal measurements it was found that increasing the Ca2+ ion content causes a decrease in the thermal diffusivity of both nano and bulk samples. The explanation of this behavior is ascribed to the phonon-phonon scattering.

  4. Sr-containing hydroxyapatite: morphologies of HA crystals and bioactivity on osteoblast cells.

    PubMed

    Aina, Valentina; Bergandi, Loredana; Lusvardi, Gigliola; Malavasi, Gianluca; Imrie, Flora E; Gibson, Iain R; Cerrato, Giuseppina; Ghigo, Dario

    2013-04-01

    A series of Sr-substituted hydroxyapatites (HA), of general formula Ca(10-x)Srx(PO4)6(OH)2, where x=2 and 4, were synthesized by solid state methods and characterized extensively. The reactivity of these materials in cell culture medium was evaluated, and the behavior towards MG-63 osteoblast cells (in terms of cytotoxicity and proliferation assays) was studied. Future in vivo studies will give further insights into the behavior of the materials. A paper by Lagergren et al. (1975), concerning Sr-substituted HA prepared by a solid state method, reports that the presence of Sr in the apatite composition strongly influences the apatite diffraction patterns. Zeglinsky et al. (2012) investigated Sr-substituted HA by ab initio methods and Rietveld analyses and reported changes in the HA unit cell volume and shape due to the Sr addition. To further clarify the role played by the addition of Sr on the physico-chemical properties of these materials we prepared Sr-substituted HA compositions by a solid state method, using different reagents, thermal treatments and a multi-technique approach. Our results indicated that the introduction of Sr at the levels considered here does influence the structure of HA. There is also evidence of a decrease in the crystallinity degree of the materials upon Sr addition. The introduction of increasing amounts of Sr into the HA composition causes a decrease in the specific surface area and an enrichment of Sr-apatite phase at the surface of the samples. Bioactivity tests show that the presence of Sr causes changes in particle size and/or morphology during soaking in MEM solution; on the contrary the morphology of pure HA does not change after 14 days of reaction. The presence of Sr, as Sr-substituted HA and SrCl2, in cultures of human MG-63 osteoblasts did not produce any cytotoxic effect. In fact, Sr-substituted HA increased the proliferation of osteoblast cells and enhanced cell differentiation: Sr in HA has a positive effect on MG-63 cells

  5. The suitability of annual tree growth rings as environmental archives: Evidence from Sr, Nd, Pb and Ca isotopes in spruce growth rings from the Strengbach watershed

    NASA Astrophysics Data System (ADS)

    Stille, Peter; Schmitt, Anne-Désirée; Labolle, François; Pierret, Marie-Claire; Gangloff, Sophie; Cobert, Florian; Lucot, Eric; Guéguen, Florence; Brioschi, Laure; Steinmann, Marc; Chabaux, François

    2012-05-01

    The combination of the Sr, Nd and Pb isotope systems, recognized as tracers of sources, with the Ca isotope system, known to reveal biology-related fractionations, allowed us to test the reliability of spruce (Picea abies) growth rings as environmental archives through time (from 1916 to 1983) in a forest ecosystem affected by acid atmospheric deposition. Sr and Pb isotopes have already been applied in former tree-ring studies, whereas the suitability of Nd and Ca isotope systems is checked in the present article. Our Sr and Nd isotope data indicate an evolution in the cation origin with a geogenic origin for the oldest rings and an atmospheric origin for the youngest rings. Ca isotopes show, for their part, an isotopic homogeneity which could be linked to the very low weathering flux of Ca. Since this flux is weak the spruces' root systems have pumped the Ca mainly from the organic matter-rich top-soil over the past century. In contrast, the annual growth rings studied are not reliable and suitable archives of past Pb pollution.

  6. Canted ferrimagnetism in Ca2+Sc3+ substituted yttrium-iron-garnet

    NASA Astrophysics Data System (ADS)

    Pardavi-Horváth, M.; Thavendrarajah, A.; Wigen, P. E.; DeGasperis, P.

    1988-11-01

    The temperature dependence of the magnetization of Y3-y-zCayLuzFe5-xScxO12 (0.6≤x≤1.2, 0≤y≤0.3, 0≤z≤0.9) epitaxial garnet films was measured from 4.2 K up to the Curie temperature. For x=0.7 and T≥50 K, 4πMs is enhanced by about 10% compared to the magnetization of Sc0.7 YIG. At T<50 K, a reduction of the magnetization, increasing with increasing substitution, was observed for all the measured samples. Agreement between the experimental results and molecular field models was obtained by taking into account the canting of the unsubstituted sublattice, the presence of charge compensating Fe4+ ions, a low-temperature ordering of Fe3+ ions with less than two magnetic nearest neighbors, and assuming a lattice parameter-dependent exchange interaction ratio with d(Jdd/Jad)/da =28 nm.-1 For x=1.2 and T<10 K the magnetization can be influenced by cooling through the Curie point in a magnetic field.

  7. Aberration Corrected Scanning Transmission Electron Microscopy of (Ca , Sr)Fe2O5 Brownmillerite superlattices

    NASA Astrophysics Data System (ADS)

    Mukherjee, Debangshu; Stone, Greg; Moon, Eun Ju; Young, Joshua; Gopalan, Venkatraman; Rondinelli, James; May, Steven; Alem, Nasim

    The brownmillerite phase A2B2O5 consists of ordered oxygen vacancies in alternate perovskite layers forming chiral tetrahedral chains. The handedness of these tetrahedral chains control the polarization of the structure. The current study focuses on 1-1 brownmillerite superlattices grown on a SrTiO3 substrates using molecular beam epitaxy. The B-site in this structure is iron throughout the superlattice film, while the A-site alternates between calcium and strontium in the superlattice layers. In this study, we use atomic resolution aberration corrected scanning transmission electron microscopy (STEM) to investigate the structure and chemistry of the film-substrate interface as well as the chemical structure of the superlattice. Atom positions are determined to measure displacement vectors of A-site cations in the superlattice structure. D.M., G.A.S., V.G. and N.A. were supported by the National Science Foundation under Grant No. DMR-1420620. E.J.M. and S.J.M. were supported by the National Science Foundation under Grant No. DMR-1151649.

  8. Preparation of Superconducting Bi-Sr-Ca-Cu-O Coating Films by the Sol-Gel Method Using an Aqueous Solution of Metal Acetates

    NASA Astrophysics Data System (ADS)

    Zhuang, Haoren; Kozuka, Hiromitsu; Yoko, Toshinobu; Sakka, Sumio

    1990-07-01

    Superconducting Bi-Sr-Ca-Cu-O coating films have been prepared on YSZ (yttria-stabilized zirconia) and Al2O3 substrates by the sol-gel method using an aqueous solution of metal acetates containing tartaric acid. A film of 20 μm thickness on the YSZ substrate showed Tc(onset) at 115 K and Tc(end) at 79 K, consisting of Bi2Sr2CaCu2Ox crystals with the c-axis perpendicular to the substrate. The reaction between the film and the YSZ and Al2O3 substrates produced CaZrO3 and CuAl2O4, respectively, during heat treatment, which suppresses the formation of superconducting phases and causes the degradation of the superconducting properties of the films.

  9. [Effect of N+ (N = Li, Na, K) on the spectra of M3 (M = Ca, Sr, Ba) Y2 (BO3)4 : Eu3+ luminescent phosphor].

    PubMed

    Li, Pan-Lai; Wang, Zhi-Jun; Gao, Hui-Ying; Yang, Zhi-Ping

    2008-11-01

    The M3 (M = Ca, Sr, Ba) Y2 (BO3)4 : Eu3+ red phosphor was synthesized by firing twice at 800 and 1 050 degrees C each for 4 h and 4 h in air, respectively. Y2O3 (99.9%), Eu2O3 (99.9%), H3BO3 (99.9%), CaCO3 (99.9%), SrCO3 (99.9%), BaCO3 (99.9%), Li2CO3 (99.9%), Na2CO3 (99.9%) and K2CO3 (99.9%) were used as starting materials, and the doping Eu3+ concentration was 3 mol%. The excitation spectrum was measured by a SHIMADZU RF-540 ultraviolet spectrophotometer. The emission spectrum was measured by a SPEX1404 spectrophotometer. All the luminescence characteristics of the phosphors were investigated at room temperature. The emission spectrum of M3 (M = Ca, Sr, Ba) Y2 (BO3)4 : Eu3+ phosphor exhibited a 613 nm red emission corresponding to the electric dipole 55D0 - 7F2 transition of Eu3+ under 365 nm excitation. The excitation spectrum for 613 nm indicates that the phosphor can be effectively excited by ultraviolet (UV) (254, 365 and 400 nm) and blue (470 nm) light. The effect of Li+ , Na+ and K+ on the excitation and emission spectra of M3 (M = Ca, Sr, Ba)Y2 (BO3)4 : Eu3+ phosphor was studied. The results show that the location of the excitation and emission spectrum of M3 (M = Ca, Sr, Ba) Y2 (BO3)4 : Eu3+ phosphor was not influenced by Li+, Na+ and K+. However, the excitation and emission spectrum intensities were greatly influenced by Li+, Na+ and K+, and the emission peak intensities were all enhanced. Under the condition of the same Li+, Na+ and K+ concentration, the emission peak intensities of M3 (M = Ca, Sr, Ba)Y2 (BO3)4 : Eu3+ phosphor were compared, and the result shows that the accretion effect of doping Li+ is the best. The effect of Li+ concentration on the emission peak intensity of Sr3 Y2 (BO3)4 : Eu3+ phosphor was studied. The results show that the emission peak intensity firstly increased with the increasing Li+ concentration, then decreased, and reached the maximum value at 5 mol% Li+, and the maximum value is about twice as much as the Li-undoped one

  10. Effect of hydrophobic residue substitutions with glutamine on Ca(2+) binding and exchange with the N-domain of troponin C.

    PubMed

    Tikunova, Svetlana B; Rall, Jack A; Davis, Jonathan P

    2002-05-28

    Troponin C (TnC) is an EF-hand Ca(2+) binding protein that regulates skeletal muscle contraction. The mechanisms that control the Ca(2+) binding properties of TnC and other EF-hand proteins are not completely understood. We individually substituted 27 Phe, Ile, Leu, Val, and Met residues with polar Gln to examine the role of hydrophobic residues in Ca(2+) binding and exchange with the N-domain of a fluorescent TnC(F29W). The global N-terminal Ca(2+) affinities of the TnC(F29W) mutants varied approximately 2340-fold, while Ca(2+) association and dissociation rates varied less than 70-fold and more than 45-fold, respectively. Greater than 2-fold increases in Ca(2+) affinities were obtained primarily by slowing of Ca(2+) dissociation rates, while greater than 2-fold decreases in Ca(2+) affinities were obtained by slowing of Ca(2+) association rates and speeding of Ca(2+) dissociation rates. No correlation was found between the Ca(2+) binding properties of the TnC(F29W) mutants and the solvent accessibility of the hydrophobic amino acids in the apo state, Ca(2+) bound state, or the difference between the two states. However, the effects of these hydrophobic mutations on Ca(2+) binding were contextual possibly because of side chain interactions within the apo and Ca(2+) bound states of the N-domain. These results demonstrate that a single hydrophobic residue, which does not directly ligate Ca(2+), can play a crucial role in controlling Ca(2+) binding and exchange within a coupled and functional EF-hand system. PMID:12022873

  11. Development of anode material based on La-substituted SrTiO 3 perovskites doped with manganese and/or gallium for SOFC

    NASA Astrophysics Data System (ADS)

    Escudero, M. J.; Irvine, J. T. S.; Daza, L.

    Materials based on La-substituted SrTiO 3 perovskites doped with manganese and/or gallium for SOFC have been studied as novel anodes for solid oxide fuel cell. La 4Sr 8Ti 11Mn 1- xGa xO 38- δ (0 ≤ x ≤ 1) oxides were synthesized by solid state reaction and the influences of the manganese and/or gallium content on the structure, morphology, thermal properties and electrical conductivity of these materials has been investigated. All compounds show cubic structure with a space group Pm-3m. These compounds presented high electrical conductivity values under reducing atmosphere between 7.9 and 6.8 S cm -1 at 900 °C. For the composition x ≥ 0.5, the thermal expansion coefficient in both reducing and oxidizing atmosphere are close to that of SOFC electrolytes (8YSZ, CGD). In general, the substitution of Ga by Mn causes a slight reduction in each of the following, lattice parameter, degree of oxygen loss on reduction, thermal expansion coefficient, and electrical conductivity.

  12. Towards a high thermoelectric performance in rare-earth substituted SrTiO3: effects provided by strongly-reducing sintering conditions.

    PubMed

    Kovalevsky, A V; Yaremchenko, A A; Populoh, S; Thiel, P; Fagg, D P; Weidenkaff, A; Frade, J R

    2014-12-28

    Donor-substituted strontium titanate ceramics demonstrate one of the most promising performances among n-type oxide thermoelectrics. Here we report a marked improvement of the thermoelectric properties in rare-earth substituted titanates Sr0.9R0.1TiO3±δ (R = La, Ce, Pr, Nd, Sm, Gd, Dy, Y) to achieve maximal ZT values of as high as 0.42 at 1190 K < T < 1225 K, prepared via a conventional solid state route followed by sintering under strongly reducing conditions (10%H2-90%N2, 1773 K). As a result of complex defect chemistry, both electrical and thermal properties were found to be dependent on the nature of the rare-earth cation and exhibit an apparent correlation with the unit cell size. High power factors of 1350-1550 μW m(-1) K(-2) at 400-550 K were observed for R = Nd, Sm, Pr and Y, being among the largest reported so far for n-type conducting bulk-ceramic SrTiO3-based materials. Attractive ZT values at high temperatures arise primarily from low thermal conductivity, which, in turn, stem from effective phonon scattering in oxygen-deficient perovskite layers formed upon reduction. The results suggest that highly-reducing conditions are essential and should be employed, whenever possible, in other related micro/nanostructural engineering approaches to suppress the thermal conductivity in target titanate-based ceramics. PMID:25377924

  13. Effect of hypergravity on the Ca/Sr composition of developing otoliths of larval cichlid fish (Oreochromis mossambicus).

    PubMed

    Anken, R H; Ibsch, M; Breuer, J; Rahmann, H

    2001-02-01

    The amounts of calcium and strontium were measured by inductively coupled plasma mass spectrometry (ICP-MS) in saccular and utricular inner ear otoliths (sagittae and lapilli, respectively) of developing cichlid fish. These fish had been maintained for 22 days at 3-g hypergravity conditions within a centrifuge. During this time-span, the animals completed their ontogenetic development from hatch to the free-swimming stage. Neither the morphogenetic development nor the timely onset and gain of performance of the swimming behaviour was impaired by the experimental conditions. Experimental and control animals also did not differ concerning their size (total length). ICP-MS revealed that the otoliths contained significantly less calcium (in microg/otolith) after hyper-g exposure compared to parallelly raised 1-g control specimens (lapilli: 0.74+/-0.21 vs. 1.16+/-0.41; sagittae: 2.09+/-0.49 vs. 2.76+/-0.47). The content of strontium (in microg/otolith: lapilli: 0.0044+/-0.0023 vs. 0.0022+/-0.0013; sagittae: 0.0094+/-0.0026 vs. 0.0081+/-0.0016) and, consequently, the Sr/Ca ratio (Sr/Cax100) was increased (lapilli: 0.607+/-0.267 vs. 0.201+/-0.12; sagittae: 0.439+/-0.093 vs. 0.301+/-0.086). Since the calcium content can be taken as a proxy for otolith weight, and because parallelly undertaken morphometric investigations revealed smaller otoliths (maximum radius and surface area) due to hyper-g exposure, the results suggest that the growth of otoliths at hyper-g is slowed down. Since the concentration of trace elements incorporated into otoliths is likely based on the composition of the respective protein matrix, our findings suggest that the protein metabolism is affected by hypergravity. PMID:11223398

  14. Rolled-up tubes and cantilevers by releasing SrRuO3-Pr0.7Ca0.3MnO3 nanomembranes

    PubMed Central

    2011-01-01

    Three-dimensional micro-objects are fabricated by the controlled release of inherently strained SrRuO3/Pr0.7Ca0.3MnO3/SrRuO3 nanometer-sized trilayers from SrTiO3(001) substrates. Freestanding cantilevers and rolled-up microtubes with a diameter of 6 to 8 μm are demonstrated. The etching behavior of the SrRuO3 film is investigated, and a selectivity of 1:9,100 with respect to the SrTiO3 substrate is found. The initial and final strain states of the rolled-up oxide layers are studied by X-ray diffraction on an ensemble of tubes. Relaxation of the sandwiched Pr0.7Ca0.3MnO3 layer towards its bulk lattice parameter is observed as the major driving force for the roll-up of the trilayers. Finally, μ-diffraction experiments reveal that a single object can represent the ensemble proving a good homogeneity of the rolled-up tubes. PACS: 81.07.-b; 68.60.-p; 68.37.Lp; 81.16.Dn. PMID:22151894

  15. Spectroscopy of laser properties of Nd(3+)-doped CaF2, SrF2, and BaF2

    NASA Astrophysics Data System (ADS)

    Payne, Stephen A.; Caird, John A.; Chase, L. L.; Smith, L. K.; Nielsen, N. D.; Krupke, William F.

    1990-03-01

    The optical properties of Nd(3+) in CaF2, SrF2, and BaF2 were investigated in order to determine if these materials are useful as laser-pumped amplifier media. The CaF2:Nd crystal was found to not be useful because the impurities tend to cluster at very low concentration, leading to the formation of nonluminescent centers. On the other hand, the Nd(3+) centers in BaF2 exhibit unacceptably low transition strengths. SrF2:Nd appears to have adequate absorption strength, and, in addition, to have a remarkably long emission lifetime of 1280 microns. A maximum doping of 0.20 atomic percent Nd(3+) can be tolerated in SrF2 without the occurrence of detrimental clustering. The peak emission cross section of SrF2:Nd is 1.7 x 10(exp -20) sq cm at 1036.5 nm. Direct measurement of the gain spectrum of SrF2:Nd(3+) reveals the presence of the F-4(sub 3/2) yields G-2(sub 9/2) excited state absorption lines, although the impact on the emission cross section is minor.

  16. Superconducting ceramics in the Bi1.5SrCaCu2O sub x system by melt quenching technique

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Deguire, Mark R.

    1989-01-01

    Bi sub 1.5 SrCaCu sub 2 O sub x has been prepared in the glassy state by rapid quenching of the melt. The kinetics of crystallization of various phases in the glass have been evaluated by a variable heating rate differential scanning calorimetry method. The formation various phases on thermal treatments of the glass has been investigated by powder X-ray diffraction and electrical resistivity measurements. Heating at 450 C formed Bi sub 2 Sr sub 2 CuO sub 6, which disappeared on further heating at 765 C, where Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 formed. Prolonged heating at 845 C resulted in the formation of a small amount of a phase with T sub c onset of approx. 108 K, believed to be Bi sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub 10. This specimen showed zero resistivity at 54 K. The glass ceramic approach could offer several advantages in the fabrication of the high-T sub c superconductors in desired practical shapes such as continuous fibers, wires, tapes, etc.

  17. Upconversion-luminescent/magnetic dual-functional sub-20 nm core-shell SrF2:Yb,Tm@CaF2:Gd heteronanoparticles.

    PubMed

    Li, Ai-Hua; Lü, Mengyun; Yang, Jun; Chen, Lin; Cui, Xiaohong; Sun, Zhijun

    2016-04-01

    Sub-20 nm core-shell and water-soluble SrF2:Yb,Tm@CaF2:Gd heteronanoparticles with both upconversion luminescence (UCL) and magnetic resonance imaging (MRI) capabilities were designed and synthesized via a two-step hydrothermal method. In the design of the heteronanoparticles, SrF2:Yb,Tm nanoparticles with high UCL efficiency are chosen as the core material for strong UCL output; and by epitaxially coating the SrF2:Yb,Tm core particles with inert and biocompatible shells of CaF2:Gd, the core-shell heteronanoparticles are endowed with a magnetic capability (longitudinal relaxivity of 2.4 mM(-1) s(-1)) for MRI, as well as an enhancement of the near infrared (NIR) UCL by 9.2 times. The aqueous dispersion of SrF2:Yb,Tm@CaF2:Gd heteronanoparticles with a concentration of 2.6 wt% can emit NIR UCL so as to be easily detected with a fiber optical spectrometer under illumination of a 975 nm laser diode with a power density of 8.8 W cm(-2). Such a dispersion with a Gd(3+) concentration of 0.0143 mM in the shell region of the heteronanoparticles can also generate the detectable quickening of longitudinal relaxation. The results promise the strong potential of this nanomaterial for applications in bioimaging as a dual-functional probe. PMID:26934836

  18. Combined effects of post-growth thermal treatment and chemical substitution on physical properties of CaFe2As2

    SciTech Connect

    Ran, Sheng

    2014-12-01

    This thesis summarizes experimental work using process of postgrowth thermal treatment and chemical substitution as tuning parameters in the study of physical properties of CaFe2As2. Details of sample preparation and characterization are given as well as various phase diagrams.

  19. Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices—A designed playground for honeycomb physics

    NASA Astrophysics Data System (ADS)

    Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori

    2015-04-01

    We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.

  20. Fabrication of (111)-oriented Ca{sub 0.5}Sr{sub 0.5}IrO{sub 3}/SrTiO{sub 3} superlattices—A designed playground for honeycomb physics

    SciTech Connect

    Hirai, Daigorou; Matsuno, Jobu; Takagi, Hidenori

    2015-04-01

    We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca{sub 0.5}Sr{sub 0.5}IrO{sub 3} perovskite and two layers of SrTiO{sub 3} perovskite on SrTiO{sub 3}(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.

  1. In situ-preparation of Bi 2Sr 2CaCu 2O y-thin films by DC-sputtering

    NASA Astrophysics Data System (ADS)

    Wagner, P.; Adrian, H.; Tomé-Rosa, C.

    1992-06-01

    We report the preparation of Bi 2Sr 2CaCu 2O 8+δ thin films on (100)-SrTiO 3 substrates by a sample DC-sputtering method in high pressure oxygen atmosphere. The inductively measured Tc onset reaches values up to 86K. Films were characteized by X-ray diffraction in Bragg-Brentano-and-Seeman-Bohlin-configuration;transport measurements were performed. In detail, we studied resistive transitions for B‖v c and B‖u c in magnetic fields up to 6 T, the angular dependence of Π ab near Tc and the critical current density Jc at 77 K.

  2. Melt processing of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} superconductor in oxygen and argon atmospheres

    SciTech Connect

    Holesinger, T.G.; Miller, D.J.; Chumbley, L.S.

    1992-08-01

    Solidification and subsequent annealing of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O{sub 2} and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutetic structure of Bi{sub 2}Sr{sub 3-x}Ca{sub x}O{sub y} and Cu{sub 2}O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi{sub 2.15}Sr{sub 2}Ca{sub 0.85}Cu{sub 2}O{sub y}.

  3. Melt processing of the Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] superconductor in oxygen and argon atmospheres

    SciTech Connect

    Holesinger, T.G.; Miller, D.J. ); Chumbley, L.S. )

    1992-08-01

    Solidification and subsequent annealing of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O[sub 2] and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutetic structure of Bi[sub 2]Sr[sub 3-x]Ca[sub x]O[sub y] and Cu[sub 2]O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi[sub 2.15]Sr[sub 2]Ca[sub 0.85]Cu[sub 2]O[sub y].

  4. Effect of electron correlation in Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3}: Density functional calculation

    SciTech Connect

    Hadipour, H.; Akhavan, M.

    2010-07-15

    We have investigated the electronic structure of Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3} using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr{sup 4+}-Ru{sup 4+} hybridization is responsible for the high Curie temperature T{sub C} in SrRu{sub 1-x}Cr{sub x}O{sub 3}, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu{sub 1-x}Cr{sub x}O{sub 3} clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr-Ru hybridization. The antiferromagnetic coupling of Cr{sup 3+} with Ru{sup 4+,5+} lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted Ca-based compounds as compared to the Sr-based systems shows that the hybridization mechanism is not relevant for these compounds. The bigger exchange splitting of Ru 4d and Cr 3d at the Fermi level with Ru{sup 4+,5+} and Cr{sup 3+,4+} orbital occupancies of CaRu{sub 0.75}Cr{sub 0.25}O{sub 3} in the LSDA+U calculation, compared with that of the LSDA calculation, shows that repulsion between electrons tend to keep the localized spins from overlapping. The low screening of the Ru t{sub 2g} electrons increases T{sub C} in the Ca-based systems, which is consistent with the both high Ru exchange splitting and magnetic moment. The insulating behavior of the high Cr-doped systems can be explained by considering the Ru{sup 4+}+Cr{sup 4+{yields}}Ru{sup 5+}+Cr{sup 3+} charge transfer. - Graphical Abstract: We have investigated the electronic structure of Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3} using different ab-initio calculation such as LSDA and LSDA+U approximation. The antiferromagnetic hybridization of Cr{sup 3+} with Ru{sup 4+,5+} lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The LSDA+U calculation for the more distorted Cr impurity doped Ca

  5. Monoclinic distortion and magnetic coupling in the double perovskite Sr{sub 2−x}Ca{sub x}YRuO{sub 6}

    SciTech Connect

    Bernardo, P.L.; Ghivelder, L.; Eslava, G.G.; Amorim, H.S.; Felner, I.; Garcia, S.

    2014-12-15

    Abstracts: This work investigates in the insulating double perovskites Sr{sub 2−x}Ca{sub x}YRuO{sub 6}. We address the angular dependence of the strength of the magnetic coupling due to the deviation from planarity of the basal layers of the monoclinic structure, characterized by the in-plane angle α<180°, in order to probe the impact of the structural distortions in the magnetic properties of the compounds. High resolution x-ray powder diffraction, susceptibility, and specific heat measurements were performed. The deviation from planarity significantly increases (α=144° for x=1) while the bond distances vary in a complex way as a consequence of the strong monoclinic distortion. We found that the magnetic transition temperature, T{sub M}, shows a linear dependence on cos [(π−α)/2]. This result is discussed in terms of t{sub 2g}(π)–e{sub g}(σ) mixing of the magnetic orbitals of the Ru{sup 5+} ions and unbalanced competitive super-exchange interactions. The deleterious effect of Ca doping for the magnetic coupling is confirmed by the reduction in the short-range antiferromagnetic correlations characteristic of the parent compound at T>>T{sub M} and the enhancement of magnetic frustration for TSr{sub 2−x}Ca{sub x}YRuO{sub 6} due to strong monoclinic distortions. - Highlights: • Neel temperatures in SrCaYRuO were correlated quantitatively with lattice distortions. • Bending of Ru–O–Y planes plays a major role in the magnetic properties of SrCaYRuO. • The structural–magnetic correlation is due to π–σ mixing of the magnetic orbitals.

  6. Effects of Pb doping on structural and electronic properties of Bi2Sr2Ca2Cu3O10

    NASA Astrophysics Data System (ADS)

    Camargo-Martínez, J. A.; Baquero, R.

    2016-02-01

    Pb doping effect in the Bi2Sr2Ca2Cu3O10 compound (Bi2223) on the structural and electronic properties were investigated, using the Local Density (LDA) and Virtual Crystal (VCA) approximations within the framework of the Density Functional Theory (DFT), taking as reference the procedure implemented by Lin et al. (2006) in the Bi2212 compound. Results show that, the incorporation of Pb-dopant in Bi2223 lead a rigid displacement of the Bi/Pb-O bands toward higher energies, with a null contribution at the Fermi level, around the high symmetry point M bar in the irreducible Brillouin zone, for Pb doping concentration equal to or more than 26%, avoiding the presence of the so-called Bi-O pockets in the Fermi surface, in good agreement with angle-resolved photoemission spectroscopy (ARPES) and nuclear magnetic resonance (NMR) experiments, although a slight metallic character of the Bi-O bonds is still observed which would disagree with some experimental reports. The calculations show that the changes on the structural properties are associated to the presence or absence of the Bi-O pockets in the Fermi surface.

  7. Thermal contact conductance of metallic coated BiCaSrCuO superconductor/copper interfaces at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Ochterbeck, J. M.; Peterson, G. P.; Fletcher, L. S.

    1992-02-01

    The effects of vapor deposited coatings on the thermal contact conductance of cold pressed, normal state BiCaSrCuO superconductor/oxygen-free copper interfaces were experimentally investigated over a pressure range of 200 to 2000 kPa. Using traditional vapor deposition processes, thin coatings of indium or lead were applied to the superconductor material to determine the effect on the heat transfer occurring at the interface. The test data indicate that the contact conductance can be enhanced using these coatings, with indium providing the greater enhancement. The experimental program revealed the need for a better understanding and control of the vapor deposition process when using soft metallic coatings. Also, the temperature-dependent microhardness of copper was experimentally determined and found to increase by approximately 35 percent as the temperature decreased from 300 to 85 K. An empirical model was developed to predict the effect of soft coatings on the thermal contact conductance of the superconductor/copper interfaces. When applied, the model agreed well with the data obtained in this investigation at low coating thicknesses but overpredicted the data as the thickness increased. In addition, the model agreed very well with data obtained in a previous investigation for silver-coated nickel substrates at all coating thicknesses.

  8. Thermal contact conductance of metallic coated BiCaSrCuO superconductor/copper interfaces at cryogenic temperatures

    SciTech Connect

    Ochterbeck, J.M.; Peterson, G.P.; Fletcher, L.S. )

    1992-02-01

    The effects of vapor deposited coatings on the thermal contact conductance of cold pressed, normal state BiCaSrCuO superconductor/oxygen-free copper interfaces were experimentally investigated over a pressure range of 200 to 2,000 kPa. Using traditional vapor deposition processes, thin coatings of indium or lead were applied to the superconductor material to determine the effect on the heat transfer occurring at the interface. The test data indicate that the contact conductance can be enhanced using these coatings, with indium providing the greater enhancement. The experimental program revealed the need for a better understanding and control of the vapor deposition process when using soft metallic coatings. Also, the temperature-dependent microhardness of copper was experimentally determined and found to increase by approximately 35 percent as the temperature decreased from 300 to 85 K. An empirical model was developed to predict the effect of soft coatings on the thermal contact conductance of the superconductor/copper interfaces. When applied, the model agreed well with the data obtained in this investigation at low coating thicknesses but overpredicted the data as the thickness increased. In addition, the model agreed very well with data obtained in a previous investigation for silvercoated nickel substrates at all coating thicknesses.

  9. Composite superconducting wires obtained by high-rate tinning in molten Bi-Pb-Sr-Ca-Cu-O system

    NASA Technical Reports Server (NTRS)

    Grosav, A. D.; Konopko, L. A.; Leporda, N. I.

    1991-01-01

    Long lengths of metal superconductor composites were prepared by passing a copper wire through the bismuth based molten oxide system at a constant speed. The key to successful composite preparation is the high pulling speed involved, which permits minimization of the severe interaction between the unbuffered metal surface and the oxide melt. Depending on the temperature of the melt and the pulling speed, a coating with different thickness and microstructure appeared. The nonannealed thick coatings contained a Bi2(Sr,Ca)2Cu1O6 phase as a major component. After relatively short time annealing at 800 C, both resistivity and initial magnetization versus temperature measurements show superconducting transitions beginning in the 110 to 115 K region. The effects of annealing and composition on obtained results are discussed. This method of manufacture led to the fabrication of wire with a copper core in a dense covering with uniform thickness of about h approximately equal to 5 to 50 microns. Composite wires with h approximately equal to 10 microns (h/d approximately equal to 0.1) sustained bending on a 15 mm radius frame without cracking during flexing.

  10. Artificially induced hotspots in Bi2Sr2CaCu2O8 mesa terahertz sources

    NASA Astrophysics Data System (ADS)

    Hao, Yang; Welp, Ulrich; Koshelev, Alexei; Vlasko-Vlasov, Vitalii; Kwok, Wai-Kwong; Kadowaki, Kazuo; Benseman, Timothy

    Mesa-shaped devices comprising stacked Intrinsic Josephson Junctions (IJJs) in the high-temperature superconductor Bi2Sr2CaCu2O8 can be used as compact sources of coherent terahertz radiation. Achieving high emission levels of THz emission power from these devices depends on efficient synchronization of the approximately 600 IJJs in the stack. Theoretical simulations of stacked IJJs, as well as some empirical results, suggest that thermal inhomogeneity of the stack may enhance THz emission power. There are a number of possible mechanisms by which this might occur, including a hotspot acting as a local resistive shunt for the IJJs (thus altering the spread of bias voltages in the stack and the junction damping dynamics) or by local self-heating reducing the phase-stiffness of the superconducting condensate in critical locations. Here we report results of artificially inducing local heating in these devices with thin film micro-heaters patterned on their surfaces, in order to determine which mechanism(s) could be responsible for self-heating-induced THz emission enhancement. Sample patterning was performed at the Center for Nanoscale Materials, an Office of Science user facility, supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  11. Bipartite electronic superstructures in the vortex core of Bi2Sr2CaCu2O8+δ

    PubMed Central

    Machida, T.; Kohsaka, Y.; Matsuoka, K.; Iwaya, K.; Hanaguri, T.; Tamegai, T.

    2016-01-01

    The central issue in the physics of cuprate superconductivity is the mutual relationship among superconductivity, pseudogap and broken-spatial-symmetry states. A magnetic field B suppresses superconductivity, providing an opportunity to investigate the competition among these states. Although various B-induced electronic superstructures have been reported, their energy, spatial and momentum-space structures are unclear. Here, we show using spectroscopic-imaging scanning tunnelling microscopy on Bi2Sr2CaCu2O8+δ that there are two distinct B-induced electronic superstructures, both being localized in the vortex core but appearing at different energies. In the low-energy range where the nodal Bogoliubov quasiparticles are well-defined, we observe the so-called vortex checkerboard that we identify as the B-enhanced quasiparticle interference pattern. By contrast, in the high-energy region where the pseudogap develops, the broken-spatial-symmetry patterns that pre-exist at B=0 T is locally enhanced in the vortex core. This evidences the competition between superconductivity and the broken-spatial-symmetry state that is associated with the pseudogap. PMID:27230420

  12. Bipartite electronic superstructures in the vortex core of Bi2Sr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Machida, T.; Kohsaka, Y.; Matsuoka, K.; Iwaya, K.; Hanaguri, T.; Tamegai, T.

    2016-05-01

    The central issue in the physics of cuprate superconductivity is the mutual relationship among superconductivity, pseudogap and broken-spatial-symmetry states. A magnetic field B suppresses superconductivity, providing an opportunity to investigate the competition among these states. Although various B-induced electronic superstructures have been reported, their energy, spatial and momentum-space structures are unclear. Here, we show using spectroscopic-imaging scanning tunnelling microscopy on Bi2Sr2CaCu2O8+δ that there are two distinct B-induced electronic superstructures, both being localized in the vortex core but appearing at different energies. In the low-energy range where the nodal Bogoliubov quasiparticles are well-defined, we observe the so-called vortex checkerboard that we identify as the B-enhanced quasiparticle interference pattern. By contrast, in the high-energy region where the pseudogap develops, the broken-spatial-symmetry patterns that pre-exist at B=0 T is locally enhanced in the vortex core. This evidences the competition between superconductivity and the broken-spatial-symmetry state that is associated with the pseudogap.

  13. Preparation of Bi2Sr2CaCu2O8- x tracks and thick films by jet printing

    NASA Astrophysics Data System (ADS)

    Glowacki, B. A.

    2000-05-01

    The formation of the 2212 phase material on both silver and magnesium oxide (100) substrates was successfully achieved by the dropwise deposition of solutions of 2212 dissolved in nitric acid or organic acids such as acetic acid or propionic acid using commercial ink-jet printing head using so-called technique `droplet-on-request'. Precursor solutions were prepared by dissolving either a mixture of metal nitrates (Bi(NO3)3.5H2O, Sr(NO3)2, Ca(NO3)2.4H2O and Cu(NO3)2.3H2O) or 2212 superconducting powder in acid solutions. From this initial study using simple solutions on conventional substrates such as polycrystalline silver and large MgO single crystals, the preparation of the textured thick 2212 film for superconducting circuits and interconnections by the ink-jet printing process appears quite promising. The critical temperatures of the selected superconducting coatings were in range of 82-92 K.

  14. Vanishing of phase coherence in underdopedBi_2Sr_2CaCu_2O_8+d

    SciTech Connect

    Corson, John; Mallozzi, R.; Orenstein, J.; Eckstein, N.; Bozovic,I.

    1998-10-21

    Although the binding of electrons into Cooper pairs is essential in forming the superconducting state, its remarkable properties--zero resistance and perfect diamagnetism--require phase coherence among the pairs as well. When coherence is lost at the transition temperature Tc, pairing remains, together with phase correlations which are finite in space and time. In conventional metals, Cooper pairs with short-range phase coherence survive no more than 1 K above Tc. In underdoped high-Tc copper oxides, spectroscopic evidence for some form of pairing is found up to a temperature T*, which is roughly 100 K above Tc (refs 1,2,3). How this pairing and Cooper-pair formation are related is a central problem in high-Tc superconductivity. The nature of this relationship hinges on the extent to which phase correlations accompany pairing in the normal state4. Here we report measurements of high-frequency conductivity that track the phase-correlation time tau in the normal state of the Bi2Sr2CaCu2O8+delta family of underdoped copper oxide superconductors. Just above Tc, we find that tau reflects the motion of thermally generated topological defects in the phase, or vortices5,6. However, vortex proliferation reduces tau to a value indistinguishable from the lifetime of normal-state electrons at 100 K, well below T*.

  15. Characterization of the macrocyclic carbon suboxide factors as potent Na,K-ATPase and SR Ca-ATPase inhibitors.

    PubMed

    Kerek, Franz; Stimac, Robert; Apell, Hans-Jürgen; Freudenmann, Frank; Moroder, Luis

    2002-12-23

    Recently discovered macrocyclic carbon suboxide (MCS) factors with the general formula (C(3)O(2))(n) were found to strongly inhibit rabbit and rat Na,K-ATPase as well as SR Ca-ATPase. Highly active MCS factors were obtained by a base/acid treatment of their lipophilic precursor isolated from plants. In the ESI-MS spectra, the dominant molar mass ion of 431 Da corresponds to a 1:1 complex of the carbon suboxide hexamer (n=6; M(r)=408 Da) with a Na(+) ion. Additional mass ions identified in positive and negative ion mode were assigned as complexes of the MCS hexamer (n=6) and octamer (n=8) with Na(+) or with TFA(-) in various ratios. The dominant mass ion values of these active MCS factors from plants are also found in mass spectra of previously described endogenous digitalis-like factors (EDLF) from animals. This would suggest that ubiquitously distributed MCS factors may function as putative endogenous regulatory substances of Na,K-ATPase and possibly of other ATPases. With the symmetric display of several equivalent carbonyl or hydroxy groups, the structure of MCS factors is particularly suited for interactions with proteins and other bio-molecules. This could explain the high biological activity and the unusual properties of the MCS factors. PMID:12488055

  16. Bipartite electronic superstructures in the vortex core of Bi2Sr2CaCu2O8+δ.

    PubMed

    Machida, T; Kohsaka, Y; Matsuoka, K; Iwaya, K; Hanaguri, T; Tamegai, T

    2016-01-01

    The central issue in the physics of cuprate superconductivity is the mutual relationship among superconductivity, pseudogap and broken-spatial-symmetry states. A magnetic field B suppresses superconductivity, providing an opportunity to investigate the competition among these states. Although various B-induced electronic superstructures have been reported, their energy, spatial and momentum-space structures are unclear. Here, we show using spectroscopic-imaging scanning tunnelling microscopy on Bi2Sr2CaCu2O8+δ that there are two distinct B-induced electronic superstructures, both being localized in the vortex core but appearing at different energies. In the low-energy range where the nodal Bogoliubov quasiparticles are well-defined, we observe the so-called vortex checkerboard that we identify as the B-enhanced quasiparticle interference pattern. By contrast, in the high-energy region where the pseudogap develops, the broken-spatial-symmetry patterns that pre-exist at B=0 T is locally enhanced in the vortex core. This evidences the competition between superconductivity and the broken-spatial-symmetry state that is associated with the pseudogap. PMID:27230420

  17. Magnetic field effects on THz radiation from Bi2Sr2CaCu2O8+δ mesa structures

    NASA Astrophysics Data System (ADS)

    Kitamura, Takeo; Kashiwagi, Takanari; Tsujimoto, Manabu; Delfanazari, Kaveh; Sawamura, Masashi; Ishida, Kazuya; Sekimoto, Shunsuke; Watanabe, Chiharu; Yamamoto, Takashi; Minami, Hidetoshi; Tachiki, Masashi; Kadowaki, Kazuo

    2013-03-01

    In a previous our study, coherent and continuous electromagnetic radiation phenomena in mesa structures of Bi2Sr2CaCu2O8+δ single crystal have been investigated precisely in magnetic fields up to only 150 Oe. This experimental result showed that the emission intensity decreases sharply for the field parallel to the c-axis, while it decreases gradually as increasing magnetic field for the in-plane field. In order to improve the measurement, we developed a new system with a better angular resolution and much wider magnetic field range up to 6 T, and a mesa having much stronger THz emission power. The mesa structure is also changed to the stand-alone type of mesa, which produces higher power THz radiation with ideal distribution of radiation. In this presentation, the recent detailed results will be shown in magnetic fields both parallel and perpendicular to the ab-plane of Bi2212, where the Josephson and pancake vortices are playing an important role for THz radiation. This work was supported in part by CREST-JST, WPI-MANA project (NIMS) and Strategic Initiative category (A) at the University of Tsukuba.

  18. Direct imaging of hot spot in Bi2Sr2CaCu2O8+δ mesa terahertz sources

    NASA Astrophysics Data System (ADS)

    Benseman, Timothy; Gray, Ken; Koshelev, Alexei; Kwok, Wai-Kwong; Welp, Ulrich; Vlasko-Vlasov, Vitalii; Kadowaki, Kazuo; Minami, Hidetoshi

    2013-03-01

    Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi2Sr2CaCu2O8+δ (Bi-2212) are a promising source of coherent continuous-wave terahertz radiation. When electrical power is applied to these devices, it is thought that hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power from Bi-2212 stacks. In order to better understand these hot spots, we have performed a thermal imaging study of BSCCO stacks which generate approximately 50 microwatts of radiation power at 0.59 THz. Utilizing the temperature-dependent 612nm fluorescence line of Eu3+, we are able to directly measure the temperature distribution at the top surface of these stacks with a resolution of +/- 1K. The images reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission. This research was funded by the Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  19. A momentum-dependent perspective on quasiparticleinterference in Bi2Sr2CaCu2O_8+delta

    SciTech Connect

    Vishik, I. M.

    2010-04-29

    Angle Resolved Photoemission Spectroscopy (ARPES) probes the momentum-space electronic structure of materials, and provides invaluable information about the high-temperature superconducting cuprates. Likewise, cuprates real-space, inhomogeneous electronic structure is elucidated by Scanning Tunneling Spectroscopy (STS). Recently, STS has exploited quasiparticle interference (QPI) - wave-like electrons scattering off impurities to produce periodic interference patterns - to infer properties of the QP in momentum-space. Surprisingly, some interference peaks in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212) are absent beyond the antiferromagnetic (AF) zone boundary, implying the dominance of particular scattering process. Here, we show that ARPES sees no evidence of quasiparticle (QP) extinction: QP-like peaks are measured everywhere on the Fermi surface, evolving smoothly across the AF zone boundary. This apparent contradiction stems from different natures of single-particle (ARPES) and two-particle (STS) processes underlying these probes. Using a simple model, we demonstrate extinction of QPI without implying the loss of QP beyond the AF zone boundary.

  20. Geometry-dependent penetration fields in superconducting Bi2Sr2CaCu2O8+δ platelets

    SciTech Connect

    By: Curran, P. J.; Clem, J. R.; Bending, S. J.; Tsuchiya, Y.; Tamegai, T.

    2010-10-01

    Magneto-optical imaging has been used to study vortex penetration into regular polygon-shaped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} platelets with various geometries (disks, pentagons, squares, and triangles) but known fixed areas. In all cases we observe an exponential dependence of the field of first penetration, H{sub p}, on temperature, consistent with a dominant Bean-Livingston barrier for pancake vortices at our measurement temperatures (45-80 K). However, the penetration field consistently decreases with decreasing degree of sample symmetry, in stark contrast to conventional estimates of demagnetization factors using equivalent ellipsoids based on inscribed circles, which predict the reverse trend. Surprisingly, this observation does not appear to have been reported in the literature before. We demonstrate empirically that estimates using equivalent ellipsoids based on circumscribed circles predict the correct qualitative experimental trend in H{sub p}. Our work has important implications for the estimation of appropriate effective demagnetization factors for flux penetration into arbitrarily shaped superconducting bodies.

  1. Geometry-dependent penetration fields of superconducting Bi2Sr2CaCu2O8+δ platelets

    SciTech Connect

    Curran, P. J.; Clem, J. R.; Bending, S. J.; Tsuchiya, Y.; Tamegai, T.

    2010-10-01

    Magneto-optical imaging has been used to study vortex penetration into regular polygon-shaped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} platelets with various geometries (disks, pentagons, squares, and triangles) but known fixed areas. In all cases we observe an exponential dependence of the field of first penetration, H{sub p}, on temperature, consistent with a dominant Bean-Livingston barrier for pancake vortices at our measurement temperatures (45-80 K). However, the penetration field consistently decreases with decreasing degree of sample symmetry, in stark contrast to conventional estimates of demagnetization factors using equivalent ellipsoids based on inscribed circles, which predict the reverse trend. Surprisingly, this observation does not appear to have been reported in the literature before. We demonstrate empirically that estimates using equivalent ellipsoids based on circumscribed circles predict the correct qualitative experimental trend in Hp. Our work has important implications for the estimation of appropriate effective demagnetization factors for flux penetration into arbitrarily shaped superconducting bodies.

  2. Quench Behavior and Degradation Limit of Ag-sheathed Bi 2Sr2CaCu2Ox Round Wires

    NASA Astrophysics Data System (ADS)

    Ye, Liyang

    High field superconducting magnets are important for scientific research in a variety of disciplines. With nearly field-independent critical current density over a wide range of magnetic field at 4.2 K up to 50 T, Ag-sheathed Bi2Sr2CaCu2Ox (Bi-2212) round wires offer the possibility to generate magnetic fields of 30 T and above. One of the key issues in high field Bi-2212 magnet development is the quench detection and protection. A quench occurs when a part of a superconducting winding, after receiving a small disturbance, enters into the normal (resistive) state, and the event follows with significant temperature rise due to joule heating. An unprotected quench may degrade or even destruct an entire superconducting magnet system. This thesis focuses on experimentally investigating the quench behavior and degradation limit of the state-of-the-art multifilamentary Ag/Bi-2212 round wires to guide the development of Bi-2212 high field magnet, especially the quench detection and protection system. (Abstract shortened by ProQuest.).

  3. Flux creep in Bi2Sr2CaCu2O8(sub +x) single crystals

    NASA Technical Reports Server (NTRS)

    Agostinelli, E.; Balestrino, G.; Fiorani, D.; Muzi, R.; Paroli, P.; Tejada, J.; Testa, A. M.

    1990-01-01

    The results of a magnetic study on a Bi2Sr2CaCu2O(8+x) single crystal are reported. Low field susceptibility (dc and ac), magnetization cycles and time dependent measurements were performed. With increasing the temperature the irreversible regime of the magnetization cycles is rapidly restricted to low fields, showing that the critical current J(sub c) becomes strongly field dependent well below T(sub c). At 2.4 K the critical current in zero field, determined from the remanent magnetization by using the Bean formula for the critical state, is J(sub c) = 2 10(exp 5) A/sq cm. The temperature dependence of J(sub c) is satisfactorily described by the phenomenological law J(sub c) = J(sub c) (0) (1 - T/T(sub c) (sup n), with n = 8. The time decay of the zero field cooled magnetization and of the remanent magnetization was studied at different temperatures for different magnetic fields. The time decay was found to be logarithmic in both cases, at least at low temperatures. At T = 4.2 K for a field of 10 kOe applied parallel to the c axis, the average pinning energy, determined by using the flux creep model, is U(sub o) = 0.010 eV.

  4. Suppression of structural phase transition by Sr substitution in the improper ferroelectric BaAl2O4

    NASA Astrophysics Data System (ADS)

    Mori, Shigeo; Ishii, Yui; Tanaka, Eri; Tsukasaki, Hirofumi; Kawaguchi, Shogo

    2015-10-01

    To clarify lattice fluctuations and precursor phenomena accompanied by structural phase transition in stuffed tridymite compounds, changes in diffuse scattering as a function of temperature in Ba0.6Sr0.4Al2O4 have been carefully investigated by powder X-ray diffraction using synchrotron radiation, electron diffraction and transmission electron microscopy (TEM) experiments. In situ electron diffraction experiments revealed that Ba0.6Sr0.4Al2O4 exhibits lattice fluctuation manifested as a unique honeycomb-shaped diffuse scattering in the wide temperature range between 298 and 100 K. Unlike in the case of BaAl2O4, Ba0.6Sr0.4Al2O4 shows no structural phase transition to the ferroelectric structure with the hexagonal P63 space group in the temperature range. In contrast, it is revealed that the electron beam irradiation to the Ba0.6Sr0.4Al2O4 sample inside the transmission electron microscope induced structural change from the hexagonal P6322 structure to the modulated structure with double periodicity in the three equivalent <110> directions in the low-temperature region. This implies that the total energy difference between these two structures is small. The hexagonal P6322 structure transforms into the modulated one with short correlation length owing to some small external perturbations.

  5. Effect of La{sup 3+} substitution with Gd{sup 3+} on the resistive switching properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films

    SciTech Connect

    Lee, Hong-Sub; Park, Chang-Sun; Park, Hyung-Ho

    2014-05-12

    This study demonstrated that the resistive switching voltage of perovskite manganite material could be controlled by A-site cation substitution in “A” MnO{sub 3} perovskite manganite structure. A partial substitution of La{sup 3+} in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} with smaller cation Gd{sup 3+} induced A-site vacancy of the largest Sr{sup 2+} cation with surface segregation of SrO{sub y} due to ionic size mismatch, and the induced vacancies reduced migration energy barrier. The operating voltage decreased from 3.5 V to 2.5 V due to a favorable condition for electrochemical migration and redox of oxygen ions. Moreover, surface-segregated SrO{sub y} was enhanced with Gd-substitution and the SrO{sub y} reduced Schottky-like barrier height and resistive switching ratio from the potential drop and screening effect. The relationship between A-site vacancy generation resulting in surface segregation of SrO{sub y} and resistive switching behavior was also investigated by energy resolved x-ray photoelectron spectroscopy, O 1s near edge x-ray absorption spectroscopy, and current voltage measurement.

  6. Investigation of Ca substitution on the gas sensing potential of LaFeO3 nanoparticles towards low concentration SO2 gas.

    PubMed

    Palimar, Sowmya; Kaushik, S D; Siruguri, V; Swain, Diptikanta; Viegas, Alison E; Narayana, Chandrabhas; Sundaram, Nalini G

    2016-09-14

    The present work investigates the superior ability of LaFeO3 (LaFeO) and La0.8Ca0.2FeO2.95 (LaCaFeO) nanoparticles to detect 3 ppm SO2 gas. The influence of calcium substitution on the sensing behaviour of LaFeO has been studied. High resolution TEM images show that the particle sizes of LaFeO and LaCaFeO are less than 100 nm and SEM images show the agglomeration of interconnected nanoparticles. Both LaFeO and LaCaFeO crystallize in the orthorhombic crystal system with the space group Pbnm. Rietveld analysis of neutron diffraction data showed that LaCaFeO has lattice oxygen vacancies. In addition, magnetic refinements on both the samples have been carried out. The presence of lattice oxygen vacancies in LaCaFeO is qualitatively supported by Raman and XPS measurements. Electrical characterization showed increased conductivity for the LaCaFeO sample, influencing their sensing performance significantly. The LaCaFeO nanoparticles exhibit higher sensitivity, faster response time, rapid recovery time and good recyclability for sensing 3 ppm SO2 gas. This enhanced sensing behaviour is attributed to the increased oxygen vacancies in the lattice as well as the surface. As a consequence, increased active sites are created in LaCaFeO, promoting redox reaction between the analyte and the sensing material. The results demonstrated that while LaFeO is a good gas sensor, p-type substitution by Ca(2+) renders this material an improved resistivity based gas sensor to detect low concentration SO2. PMID:27507535

  7. Shrinking of anionic polyacrylate coils induced by Ca2+, Sr2+ and Ba2+: A combined light scattering and ASAXS study

    NASA Astrophysics Data System (ADS)

    Schweins, R.; Goerigk, G.; Huber, K.

    2006-10-01

    Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly, precipitation thresholds were established for three different alkaline earth cations Ca2+, Sr2+ and Ba2+. Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl2]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations Ca2+, Sr2+ and Ba2+. Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr counterions around the polyacrylate chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful separation of the pure-resonant terms, which solely stem from the counterions. The Sr2+ scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of [SrCl2]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains. Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly smaller than the respective overall size of the NaPA particles.

  8. Ternary CaCu{sub 4}P{sub 2}-type pnictides AAg{sub 4}Pn{sub 2} (A=Sr, Eu; Pn=As, Sb)

    SciTech Connect

    Stoyko, Stanislav S.; Khatun, Mansura; Scott Mullen, C.; Mar, Arthur

    2012-08-15

    Four ternary pnictides AAg{sub 4}Pn{sub 2} (A=Sr, Eu; Pn=As, Sb) were prepared by reactions of the elements at 850 Degree-Sign C and their crystal structures were determined from single-crystal X-ray diffraction studies. These silver-containing pnictides AAg{sub 4}Pn{sub 2} adopt the trigonal CaCu{sub 4}P{sub 2}-type structure (Pearson symbol hR21, space group R3-bar m, Z=3; a=4.5555(6) A, c=24.041(3) A for SrAg{sub 4}As{sub 2}; a=4.5352(2) A, c=23.7221(11) A for EuAg{sub 4}As{sub 2}; a=4.7404(4) A, c=25.029(2) A for SrAg{sub 4}Sb{sub 2}; a=4.7239(3) A, c=24.689(2) A for EuAg{sub 4}Sb{sub 2}), which can be derived from the trigonal CaAl{sub 2}Si{sub 2}-type structure of the isoelectronic zinc-containing pnictides AZn{sub 2}Pn{sub 2} by insertion of additional Ag atoms into trigonal planar sites within [M{sub 2}Pn{sub 2}]{sup 2-} slabs built up of edge-sharing tetrahedra. Band structure calculations on SrAg{sub 4}As{sub 2} and SrAg{sub 4}Sb{sub 2} revealed that these charge-balanced Zintl phases actually exhibit no gap at the Fermi level and are predicted to be semimetals. - Graphical abstract: SrAg{sub 4}As{sub 2} and related pnictides adopt a CaCu{sub 4}P{sub 2}-type structure in which additional Ag atoms enter trigonal planar sites within slabs built from edge-sharing tetrahedra. Highlights: Black-Right-Pointing-Pointer AAg{sub 4}Pn{sub 2} are the first Ag-containing members of the CaCu{sub 4}P{sub 2}-type structure. Black-Right-Pointing-Pointer Ag atoms are stuffed in trigonal planar sites within CaAl{sub 2}Si{sub 2}-type slabs. Black-Right-Pointing-Pointer Ag-Ag bonding develops through attractive d{sup 10}-d{sup 10} interactions.

  9. Synthesis and characterisation of chloro-vanadato-apatites M5(VO4)3ClM5(VO4)3Cl (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Beck, Horst P.; Douiheche, Maoiheb; Haberkorn, Robert; Kohlmann, Holger

    2006-01-01

    The synthesis of chloro-vanadato-apatites M5(VO 4) 3Cl ( M = Ca, Sr, Ba) in a two step solid state procedure is reported. IR spectra show a considerable shift of the frequencies attributed to the tetrahedral group to lower energies compared with the phosphato-apatites. The structure of these compounds is determined by powder diffraction data and refined using Rietveld methods. An elaborate analysis of the data shows that the chloride anions are to be found at different positions along a channel along [001] with varying probability. They are fairly well localised in the case of the Sr and the Ba compound. In the Ca compound they are spread over a larger region along c. A refinement according to a new concept of "metric distortion" gives a good fit of the data and indicates that the delocalisation of electron density seen in a Difference-Fourier plot is best described by a static picture of disorder.

  10. Improving γ-ray energy resolution, non-proportionality, and decay time of NaI:Tl+ with Sr2+ and Ca2+ co-doping

    NASA Astrophysics Data System (ADS)

    Yang, K.; Menge, P. R.

    2015-12-01

    Commercially available thallium activated sodium iodide scintillators are typically characterized by a γ-ray energy resolution of 6.5% at 662 keV and a scintillation decay time constant of 230 ns. Energy resolution, non-proportionality, and scintillation decay time are improved when the crystal is co-doped with alkaline earth metals (Sr2+ and Ca2+). The energy resolution of NaI:Tl+ is improved to 5.3%, and the decay time is simultaneously reduced to 170 ns with Sr2+ and Ca2+ co-doping. The improvement in energy resolution, non-proportionality, and decay time are likely due to the suppression of the slow scintillation processes in NaI:Tl+.

  11. Orbital orderings and optical conductivity of SrRuO(3) and CaRuO(3): first-principles studies.

    PubMed

    Wang, Guang-Tao; Zhang, Min-Ping; Yang, Zong-Xian; Fang, Zhong

    2009-07-01

    The Jahn-Teller (JT) distortion induced orbital order and optical conductivity in SrRuO(3) and CaRuO(3) are investigated by first-principles calculations. The total energy and optical conductivity of all the spin ordering states of SrRuO(3) and CaRuO(3) are calculated in the LDA+U scheme with U(eff) = 2.5 eV. The down-spin t(2g) of Ru show antiferromagnetic-like orbital order in the a-b plane. We observe a d-d transition peak at an energy of about 1.0 eV in the calculated optical conductivity and analyze the reason for it not being observed in previous experiments. PMID:21828475

  12. Crossover from crossing to tilted vortex phase in Bi2Sr2CaCu2O8+δ single crystals near ab-plane

    NASA Astrophysics Data System (ADS)

    Mirkovic, Jovan; Buzdin, Alexandre; Kashiwagi, Takanari; Yamamoto, Takashi; Kadowaki, Kazuo

    2013-01-01

    In extremely anisotropic layered superconductors of Bi2Sr2CaCu2O8+δ the stacks of vortex pancakes (PV) and the Josephson vortex (JV) interpenetrate, and due to PV-JV mutual pinning energy, weakly interact and form various tilted and crossing lattice structures including vortex chains, stripes, mixed chain + lattice phases, etc. In order to study these phenomena, it is decisive to have excellent quality of samples and the ideal experimental techniques. The vortex phases in high-quality Bi2Sr2CaCu2O8+δ single crystals were studied by in-plane resistivity measurement and local ac magnetic permeability. The sharp crossover was shown by both techniques, deep in the vortex solid state separating the Abrikosov dominant ‘strong pinning’ phase from the Josephson dominant ‘weak pinning’ phase. Those two vortex states were recognized as the mixed chain + lattice vortex phase and chains (tilted) vortex phase, respectively.

  13. Terahertz emission from a stack of intrinsic Josephson junctions in Bi2Sr2Ca2Cu3O10+δ

    NASA Astrophysics Data System (ADS)

    Tsujimoto, Manabu; Kakeya, Itsuhiro; Adachi, Shintaro; Watanabe, Takao; Kashiwagi, Takanari; Minami, Hidetoshi; Kadowaki, Kazuo

    Terahertz radiation in the 0.3-10 THz frequency range is a technologically attractive form of electromagnetic radiation, because it has applications in numerous fields. Terahertz generation from stacks of intrinsic Josephson junctions fabricated from Bi2Sr2CaCu2O8+δ (Bi-2212) has become a major focus of both experimental and theoretical research [U. Welp et al., Nat. Photonics 7, 702 (2013)]. Here, we observe continuous terahertz emission from a stack of intrinsic Josephson junctions made of Bi2Sr2Ca2Cu3O10+δ (Bi-2223). We investigate how triple CuO2 planes affect the c-axis current-voltage and emission characteristics. The terahertz emission spectra are measured by Fourier-transform infrared spectroscopy.

  14. Luminescence Properties of Self-Activated Mm(VO4)2 (M = Mg, Ca, Sr, and Ba) Phosphors Synthesized by Solid-State Reaction Method.

    PubMed

    Min, Xin; Huang, Zhaohui; Fang, Minghao; Liu, Yan'gai; Tang, Chao; Wu, Xiaowen

    2016-04-01

    In this paper, M3(VO4)2 (M = Mg, Ca, Sr, and Ba) self-activated phosphors were prepared by a solid-state reaction method at 1,000 °C for 5 h. The phase formation and micrographs were analyzed by X-ray diffraction and scanning electron microscopy. The Ca3(VO4)2 phosphor does not show any emission peaks under excitation with ultraviolet (UV) light. However, the M3(VO4)2 (M = Mg, Sr, and Ba) samples are effectively excited by UV light chips ranging from 200 nm to 400 nm and exhibit broad emission bands due to the charge transfer from the oxygen 2p orbital to the vacant 3d orbital of the vanadium in the VO4. The color of these phosphors changes from yellow to light blue via blue-green with increasing ionic radius from Mg to Sr to Ba. The luminescence lifetimes and quantum yield decrease with the increasing unit cell volume and V-V distance, in the order of Mg3(VO4)2 to Sr3(VO4)2 to Ba3(VO4)2. The emission intensity decreases with the increase of temperatures, but presents no color shift. This confirms that these self-activated M3(VO4)2 phosphors can be suggested as candidates of the single-phase phosphors for light using UV light emitting diodes (LEDs). PMID:27451689

  15. Formation of superconducting Bi sub 2-y Pb sub y Sr sub 2 Ca sub 2 Cu sub 3 O sub x from coprecipitated oxalates

    SciTech Connect

    Bernhard, K.; Gritzner, G.; Wang, Xianzhong; Baeuerle, D. )

    1990-06-01

    The conditions for the coprecipitation of Bi{sup 3+}, Pb{sup 2+}, Ca{sup 2+} as oxalates are reported. These oxalates were used as precursors for the formation of Bi{sub 2-y}Pb{sub y}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconducting ceramics. The behavior of the oxalates upon heat treatment was studied by thermogravimetry. Both the oxalates and the superconducting oxides were analyzed and characterized by atomic absorption spectroscopy and by X-ray diffraction.

  16. Superconductivity up to 114 K in the Bi-Al-Ca-Sr-Cu-O compound system without rare-earth elements

    NASA Technical Reports Server (NTRS)

    Chu, C. W.; Bechtold, J.; Gao, L.; Hor, P. H.; Huang, Z. J.

    1988-01-01

    Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-Ca-Sr-Cu-O multiphase systems without any rare-earth elements. Pressure has only a slight positive effect on T(c). These observations provide an extra material base for the study of the mechanism of high-temperature superconductivity and also the prospect of reduced material cost for future applications of superconductivity.

  17. Ab initio prediction of the structural, electronic, elastic and thermodynamic properties of the tetragonal ternary intermetallics XCu2Si2 (X = Ca, Sr)

    NASA Astrophysics Data System (ADS)

    Reffas, Mounir; Bouhemadou, Abdelmadjid; Haddadi, Khelifa; Bin-Omran, Saad; Louail, Layachi

    2014-12-01

    Structural parameters, electronic structure, elastic constants and thermodynamic properties of the tetragonal ternary intermetallics CaCu2Si2 and SrCu2Si2 are investigated theoretically for the first time using the plane-wave ultra-soft pseudopotential method based on the density functional theory. The calculated equilibrium structural parameters agree well with the existing experimental data. Pressure dependence of the structural parameters is also explored. Analysis of the band structure, total and site-projected l-decomposed densities of states and valence charge distributions reveals the conducting character of both considered materials with a mixture of ionic-covalent chemical bonding character. Pressure dependences of the single-crystal elastic constants C ij for CaCu2Si2 and SrCu2Si2 are explored. The elastic wave velocities propagating along the principal crystallographic directions are numerically estimated. The elastic anisotropy is estimated and further illustrated by 3D-direction-dependent of the Young's modulus. A set of some macroscopic elastic moduli, including the bulk, Young's and shear moduli, Poisson's coefficient, average elastic wave velocities and Debye temperature, were calculated for polycrystalline CaCu2Si2 and SrCu2Si2 from the C ij via the Voigt-Reuss-Hill approximations. Through the quasiharmonic Debye model, which takes into account the phonon effects, the temperature and pressure dependencies of the bulk modulus, unit cell volume, volume thermal expansion coefficient, Debye temperature and volume constant and pressure constant heat capacities of CaCu2Si2 and SrCu2Si2 are explored systematically in the ranges of 0-40 GPa and 0-1400 K.

  18. Metal-semiconductor-transition observed in Bi{sub 2}Ca(Sr, Ba){sub 2}Co{sub 2}O{sub 8+δ} single crystals

    SciTech Connect

    Dong, Song-Tao; Zhang, Bin-Bin; Zhang, Lun-Yong; Yao, Shu-Hua E-mail: shyao@nju.edu.cn; Zhou, Jian; Zhang, Shan-Tao; Gu, Zheng-Bin; Chen, Yan-Feng; Chen, Y. B. E-mail: shyao@nju.edu.cn

    2014-07-28

    Electrical property evolution of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} single crystals (AE = Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+δ} and Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} demonstrates semiconductor-like properties. But Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} to semiconductor-like Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} can be attributed to Anderson localization. However the semiconductor behaviour of Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} and Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+δ} is related to electronic correlations effect that is inferred by large negative magnetoresistance (∼70%). The theoretical electronic structures and valence X-ray photoemission spectroscopy substantiate that there is a relative large density of state around Fermi level in Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} compared with other two compounds. It suggests that Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} is more apt to be metal in this material system.

  19. Preparation of Bi-Pb-Sr-Ca-Cu-O oxide superconductors by coprecipitation of nanosize oxalate precursor powders in the aqueous core of water-in-oil microemulsions

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Pillai, V.; Shah, D. O.

    1993-02-01

    We describe a new technique for the synthesis of ultrahomogeneous nanoparticles of precursor oxalate powder by coprecipitation in the aqueous core of a water-in-oil microemulsion for the preparation of Bi-Pb-Sr-Ca-Cu-O (2223) oxide superconductor. This process ensures a uniform mixing of metal cations down to a scale of at least 10 nm. This finely dispersed precursor powder results in phase pure (2223) oxide superconductor after proper heat treatment.

  20. Infrared spectra, Raman spectra, microwave dielectric properties and simulation for effective permittivity of temperature stable ceramics AMoO4-TiO2 (A = Ca, Sr).

    PubMed

    Guo, Jing; Zhou, Di; Wang, Lu; Wang, Hong; Shao, Tao; Qi, Ze M; Yao, Xi

    2013-02-01

    In this work, temperature stable microwave dielectric materials (1 - x)AMoO(4)-xTiO(2) (A = Ca, Sr) were prepared by a solid state reaction method. The phase composition, sintering behaviors, microstructures, microwave dielectric properties, effective permittivity and vibrational phonon modes were investigated. The X-ray diffraction pattern and scanning electron microscope analysis indicated that the AMoO(4) (A = Ca, Sr) phase could coexist with the TiO(2) phase. The effective dielectric constants of the AMoO(4)-TiO(2) composites were calculated by the finite element method (FEM), compared with the measured values and the numerical results obtained by the classical mixing rules. The correlation between the dielectric properties and the crystal structures were studied using IR and Raman spectroscopy. The infrared spectra were analyzed using the classical harmonic oscillator model, and revealed that the external vibration modes of AMoO(4) (A = Ca, Sr) had the most significant influence on the dielectric constant. The Raman spectra showed that there were strong interactions in the [MoO(4)] tetrahedron due to the sharp and intense Raman modes. Finally, the low-firing (900 °C) microwave dielectric ceramics were obtained with 3 wt% H(3)BO(3)-CuO addition (BCu), and they possess good microwave dielectric properties with ε(r) = 10.6-13, high Q×f values (40 700-72 050 GHz), and near-zero temperature coefficients of resonant frequency (TCF or τ(f) values). These results also show that (1 - x)AMoO(4)-xTiO(2)-BCu (A = Ca, Sr) ceramics are good candidates for microwave electronic device applications. PMID:23124534

  1. Inter-Colony Fidelity of Sr/Ca Variability in the Massive Caribbean Coral Siderastrea siderea: a Sub-Fossil Example

    NASA Astrophysics Data System (ADS)

    Maupin, C. R.; Quinn, T. M.; Poore, R. Z.; Lin, K.; Shen, C.

    2008-12-01

    Coral-based reconstructions of climate variability in the Atlantic Warm Pool (AWP) in the pre-instrumental period are sparse. Multi-century Sr/Ca records generated from the skeleton of the widely distributed, massive, slow growing (~0.5 cm yr-1) coral Siderastrea siderea have the potential to address this data gap by providing robust proxies of interannual- to centennial-scale sea surface temperature (SST) variability in the AWP. However, before modern and fossil geochemical time series from S. siderea can be interpreted in terms of climate variability, reproducibility tests must be performed on individual coral colonies from the same location. Here we provide one such assessment of inter-colony reproducibility in the geochemistry of S. siderea using cores from the Dry Tortugas National Park (~24°33'N, 82°53'W). Time series of Sr/Ca from a large colony cored live in the summer of 1993 and a second, sub-fossil colony core, with a high-precision mass spectrometric U/Th date of 110 ± 1.7 (2σ) yrs, are compared. The 25-year overlap exhibits excellent reproducibility in both monthly and monthly anomaly space, and the average absolute difference between monthly data from the two time series is within instrumental precision. The results of this work suggest that individual monthly Sr/Ca records from S. siderea can be deemed representative of local SST variability, and that continuous local Sr/Ca records can be successfully spliced together from living and sub-fossil corals using high precision U/Th dating.

  2. Vortex line pinning in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals with columnar defects

    SciTech Connect

    van der Beek, C.J.; Vinokur, V.M.; Crabtree, G.W.; Schmidt, B.; Konczykowski, M.

    1994-05-01

    The ac transmittivity of heavy-ion irradiated Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals shows a sharp cusp as function of the dc field orientation with respect to the columnar defects. This unambiguously demonstrates the connected nature of vortices in these samples. In contrast, the irreversibility line does not reveal a cusp.

  3. Structural and photoluminescence properties of Dy3+ co-doped and Eu2+ activated MAl2O4 (M = Ba, Ca, Sr) nanophosphors

    NASA Astrophysics Data System (ADS)

    Dejene, F. B.; Kebede, M. A.; Redi-Abshiro, M.; Kgarebe, B. V.

    2013-09-01

    Long afterglow alkaline earth aluminates MAl2O4:Eu, Dy (M: Ca, Sr, Ba) phosphors are generally synthesized by the solid-state process which is more feasible than other conventional processes in terms of operation and large-scale production. However, the constituents of phosphors synthesized using this process are usually not mixed well, the particles agglomerates and very high temperature requirement to synthesize the final powder make it undesirable. In order to circumvent these problems, MAl2O4:Eu, Dy (Ca, Ba, Sr) phosphors were prepared at low temperatures (500 °C) by the solution-combustion of corresponding metal nitrate-urea solution mixtures, over a time of 5-10 min. In order to elucidate the relationship between the constituent, structure and PL properties product's particle size, morphological and structural properties were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), while the characteristic luminescence properties were investigated using emission spectra. The low temperature monoclinic structure for both CaAl2O4 and SrAl2O4 and the hexagonal structure of BaAl2O4 were observed. The emission spectra of these phosphors indicated that all of them are broad band, and the only emission peaks around 448, 490 and 515 nm of CaAl2O4:Eu, Dy, BaAl2O4:Eu, Dy and SrAl2O4:Eu, Dy, respectively, are due to 5d → 4f transition of Eu2+. The decay curves implied that these phosphors contain fast, medium and slow-decay process. The Dy3+ trap levels may be considered to be responsible for the long afterglow phosphorescence at room temperature.

  4. Impact of warming events on reef-scale temperature variability as captured in two Little Cayman coral Sr/Ca records

    NASA Astrophysics Data System (ADS)

    von Reumont, J.; Hetzinger, S.; Garbe-Schönberg, D.; Manfrino, C.; Dullo, W.-Chr.

    2016-03-01

    The rising temperature of the world's oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970-2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (>33°C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6 year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs.

  5. Luminescent nitridophosphates CaP2 N4 :Eu(2+) , SrP2 N4 :Eu(2+) , BaP2 N4 :Eu(2+) , and BaSr2 P6 N12 :Eu(2.).

    PubMed

    Pucher, Florian J; Marchuk, Alexey; Schmidt, Peter J; Wiechert, Detlef; Schnick, Wolfgang

    2015-04-20

    Nitridophosphates MP2 N4 :Eu(2+) (M=Ca, Sr, Ba) and BaSr2 P6 N12 :Eu(2+) have been synthesized at elevated pressures and 1100-1300 °C starting from the corresponding azides and P3 N5 with EuCl2 as dopant. Addition of NH4 Cl as mineralizer allowed for the growth of single crystals. This led to the successful structure elucidation of a highly condensed nitridophosphate from single-crystal X-ray diffraction data (CaP2 N4 :Eu(2+) (P63 , no. 173), a=16.847(2), c=7.8592(16) Å, V=1931.7(6) Å(3) , Z=24, 2033 observed reflections, 176 refined parameters, wR2 =0.096). Upon excitation by UV light, luminescence due to parity-allowed 4f(6) ((7) F)5d(1) →4f(7) ((8) S7/2 ) transition was observed in the orange (CaP2 N4 :Eu(2+) , λmax =575 nm), green (SrP2 N4 :Eu(2+) , λmax =529 nm), and blue regions of the visible spectrum (BaSr2 P6 N12 :Eu(2+) and BaP2 N4 :Eu(2+) , λmax =450 and 460 nm, respectively). Thus, the emission wavelength decreases with increasing ionic radius of the alkaline-earth ions. The corresponding full width at half maximum values (2240-2460 cm(-1) ) are comparable to those of other known Eu(2+) -doped (oxo)nitrides emitting in the same region of the visible spectrum. Following recently described quaternary Ba3 P5 N10 Br:Eu(2+) , this investigation represents the first report on the luminescence of Eu(2+) -doped ternary nitridophosphates. Similarly to nitridosilicates and related oxonitrides, Eu(2+) -doped nitridophosphates may have the potential to be further developed into efficient light-emitting diode phosphors. PMID:25765825

  6. Micro-oxidation treatment to improve bonding strength of Sr and Na co-substituted hydroxyapatite coatings for carbon/carbon composites

    NASA Astrophysics Data System (ADS)

    Zhang, Leilei; Li, Hejun; Li, Kezhi; Zhang, Yulei; Liu, Shoujie; Guo, Qian; Li, Shaoxian

    2016-08-01

    To improve the bonding strength of Sr and Na co-substituted hydroxyapatite (SNH) coatings for carbon/carbon composites, carbon/carbon composites are surface modified by micro-oxidation treatment. The micro-oxidation treatment could generate large number of pores containing oxygenic functional groups on the surface of carbon/carbon composites. SNH is nucleated on the inwall of the pores and form a flaky shape coating with 10-50 nm in thickness and 200-900 nm in width. The bonding strength between SNH coating and carbon/carbon composites increases from 4.27 ± 0.26 MPa to 10.57 ± 0.38 MPa after the micro-oxidation treatment. The promotion of bonding strength is mainly attributed to the pinning effect caused by the pores and chemical bonding generated by the oxygenic functional groups.

  7. Metallic Nonsuperconducting Phase and D -Wave Superconductivity in Zn-Substituted La{sub 1.85}Sr{sub 0.15}CuO{sub 4}

    SciTech Connect

    Karpinska, K.; Cieplak, Marta Z.; Guha, S.; Malinowski, A.; Skoskiewicz, T.; Plesiewicz, W.; Berkowski, M.; Boyce, B.; Lemberger, Thomas R.; Lindenfeld, P.

    2000-01-03

    Measurements of the resistivity, magnetoresistance, and penetration depth were made on films of La{sub 1.85} Sr{sub 0.15} CuO{sub 4} , with up to 12 at. % of Zn substit