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Sample records for ca sr substitution

  1. Substitution site and effects on magnetism in Sr-for-Ca substituted CaBaCo4O7

    NASA Astrophysics Data System (ADS)

    Aurelio, G.; Curiale, J.; Bardelli, F.; Junqueira Prado, R.; Hennet, L.; Cuello, G.; Campo, J.; Thiaudière, D.

    2015-10-01

    Cationic substitutions in the novel magnetoelectric compound CaBaCo4O7 lead to profound changes in its magnetic and electric behaviors. In this work, we present a structural study of the isovalent substitution Sr-for-Ca in CaBaCo4O7. X-ray diffraction, as well as neutron powder diffraction experiments, are reported for a series of samples Ca1-xSrxBaCo4O7 with 0 ≤ x ≤ 0.10 . Special emphasis is given to the identification of the substitution site, as Sr has also been reported to substitute for Ba in this crystal structure. The solubility limit for Sr at the Ca site is shown to be at x ≃ 0.08 . The variation of lattice constants with Sr-doping firmly supports the Sr-for-Ca substitution. Rietveld refinements of the Sr-substituted samples are presented, and used as starting point to analyse the local structure around Sr by means of X-ray absorption spectroscopy at the Sr K-edge. Both the near-edge absorption and the extended absorption fine-structure confirm the substitution of Sr for Ca, giving definite support to the proposed nominal formula. In addition, macroscopic magnetization measurements are presented which reveal the striking effects of Sr-substitution over the magnetic landscape of this puzzling compound.

  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. On the substitution of bismuth by antimony in the system Bi-Sr-Ca-Cu-O

    NASA Astrophysics Data System (ADS)

    El Metmati, F.; Mansori, M.; Tazi, A.; Badrour, L.; Bendriss, A.

    2005-03-01

    This work concerns the results obtained during attempts of substitution of bismuth by antimony in superconductors Bi-cuprates family. The samples, prepared by dry way, from oxides and carbonates of the corresponding elements, are characterized by IR spectroscopy, X ray diffraction and differential thermal analysis. In every case, two domains appear: - for antimony concentration lower than 50 %, the main phase is isotype with the yellow phase Bi{2}Sr{3}CaO{7}. - for a concentration between 50% and 100%, we systematically obtain a perovskite isotype with Sr{1.45}Sb{0.55}O{3-y}

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

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

    Calcium-for-strontium substituted samples of the misfit-layered cobalt-oxide system, [(Sr 1- xCa x) 2(O,OH) 2] q[CoO 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 1- xCa x) 2(O,OH) 2] q[CoO 2] the properties smoothly evolve towards those previously reported for the x=1.0 end member, [Ca 1.7O 2.1H 2.4] 0.58[CoO 2].

  5. Quaternary system SrO-CaO-BaO-CuO at 950 C. 2: Phase equilibria related to the substitution Sr/Ba in (Sr/Ba){sub 2}Ca{sub 2}Cu{sub 2}Cu{sub 3}O{sub 7} and (Sr/Ba){sub 2}CaCu{sub 2}O{sub 5} samples

    SciTech Connect

    Lebbou, K.; Abraham, R.; Trosset, S.; Cohen-Adad, M.T.

    1997-08-01

    A partial study of the solid-solid equilibria in the quaternary system BaO-SrO-CaO-CuO has been undertaken in order to determine the observed phases and their evolution when Ba is substituted for Sr in mixtures (Sr/Ba){sub 2}CaCu{sub 2}O{sub x} and (Sr/Ba){sub 2}Ca{sub 2}Cu{sub 3}O{sub x}. The temperature was fixed at 950 C and samples were elaborated under 1 bar of flowing oxygen. It has been shown that two four-phased domains exist in this quaternary system, including the following phases: ({und Ba}/Sr/Ca)CuO{sub 2}, ({und Sr/Ca}/Ba){sub 2}CuO{sub 3}, ({und Sr/Ca}/Ba){sub 14}Cu{sub 24}O{sub x}, and Ba{sub 4}CaCu{sub 3}O{sub 8} substituted Sr/Ca for the one and ({und Ba}/Sr/Ca)CuO{sub 2}, ({und Sr/Ca}/Ba){sub 2}CuO{sub 3}, ({und Sr/Ca}/Ba){sub 14}Cu{sub 24}O{sub x}, and ({und Sr/Ca}/Ba/)CuO{sub 2} for the other.

  6. Substitution of Chromium for Univalent Copper in Superconducting Pb 2Sr 2(Ca,Y)Cu 3O 8+δ

    NASA Astrophysics Data System (ADS)

    Seshadri, R.; Maignan, A.; Hervieu, M.; Martin, C.; Raveau, B.; Rao, C. N. R.

    1996-11-01

    Following considerations of geometry and the similarity between chromate and carbonate groups in terms of size and charge, we have investigated the possibility of replacing the two-coordinate Cu Iin superconducting lead cuprates of the general formula Pb 2Sr 2(Ca, Y)Cu 3O 8by 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 Ican be replaced by Cr. While from the present structural study using HRTEM and Rietveld refinement of X-ray powder data we are unable to precisely obtain the oxidation state and oxygen coordination of Cr, we suggest in analogy with Cr substitution in other similar cuprates that in the title phases Cu IO 2rods are partially replaced by tetrahedral CrO 2-4groups. Infrared spectroscopy supports the presence of CrO 2-4groups. The phases Pb 1.75Sr 2Ca 0.2Y 0.8Cu 3O 8+δand Pb 1.75Sr 2Ca 0.2Y 0.8Cu 2.85Cr 0.15O 8+δare superconducting as-prepared, but the substitution of Cr for Cu Iresults in a decrease of the TCas well as the superconducting volume fraction.

  7. Computational insights on crystal structures of the oxygen-evolving complex of photosystem II with either Ca(2+) or Ca(2+) substituted by Sr(2+).

    PubMed

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

    2015-01-27

    The oxygen-evolving complex of photosystem II can function with either Ca(2+) or Sr(2+) as the heterocation, but the reason for different 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 the X-ray crystal structures with either Ca(2+) or Sr(2+) are most consistent with the S-2 state (i.e., Mn4[III,III,III,II] with O4 and O5 protonated). As expected, the QM/MM models show that Ca(2+)/Sr(2+) substitution results in the elongation of the heterocation bonds and the displacement of terminal waters W3 and W4. The optimized structures also show that hydrogen-bonded W5 is displaced in all S states with Sr(2+) as the heterocation, suggesting that this water may play a critical role during water oxidation. PMID:25555204

  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 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 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.

    2016-03-01

    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 - 2x 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. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. Microscopic evidence of dimer breaking up in CuO2 chain for Ca-substituted Sr14Cu24O41 compounds

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Zou, Huamin; Guo, Chao; Wang, Lili; Hu, Ni; Shi, Jing

    2007-05-01

    In this work we measured the temperature dependence of the static magnetic susceptibility for Ca-doped Sr14Cu24O41 compounds, studied the lattice mismatch between a CuO2 chain and a Cu2O3 ladder by using electron diffraction, and found that the magnetic properties and lattice mismatch were sensitive to the Ca content. Applying a modified 'cut and projection' method, it is found that the lattice mismatch induces the dimers in spin chains to be decoupled into free spin Cu2+. Further more, Ca doping makes lattice mismatch larger and more dimers decoupled. The number of dimerized spins and the number of free spins predicted by this method are in good agreement with those obtained by fitting the experimental static susceptibility data. This explanation can be applied not only to the Ca doping cases, but also to the case of oxygen nonstoichiometry.

  19. Effect of Ca2+/Sr2+ substitution on the electronic structure of the oxygen-evolving complex of photosystem II: a combined multifrequency EPR, 55Mn-ENDOR, and DFT study of the S2 state.

    PubMed

    Cox, Nicholas; Rapatskiy, Leonid; Su, Ji-Hu; Pantazis, Dimitrios A; Sugiura, Miwa; Kulik, Leonid; Dorlet, Pierre; Rutherford, A William; Neese, Frank; Boussac, Alain; Lubitz, Wolfgang; Messinger, Johannes

    2011-03-16

    The electronic structures of the native Mn(4)O(x)Ca cluster and the biosynthetically substituted Mn(4)O(x)Sr cluster of the oxygen evolving complex (OEC) of photosystem II (PSII) core complexes isolated from Thermosynechococcus elongatus, poised in the S(2) state, were studied by X- and Q-band CW-EPR and by pulsed Q-band (55)Mn-ENDOR spectroscopy. Both wild type and tyrosine D less mutants grown photoautotrophically in either CaCl(2) or SrCl(2) containing media were measured. The obtained CW-EPR spectra of the S(2) state displayed the characteristic, clearly noticeable differences in the hyperfine pattern of the multiline EPR signal [Boussac et al. J. Biol. Chem.2004, 279, 22809-22819]. In sharp contrast, the manganese ((55)Mn) ENDOR spectra of the Ca and Sr forms of the OEC were remarkably similar. Multifrequency simulations of the X- and Q-band CW-EPR and (55)Mn-pulsed ENDOR spectra using the Spin Hamiltonian formalism were performed to investigate this surprising result. It is shown that (i) all four manganese ions contribute to the (55)Mn-ENDOR spectra; (ii) only small changes are seen in the fitted isotropic hyperfine values for the Ca(2+) and Sr(2+) containing OEC, suggesting that there is no change in the overall spin distribution (electronic coupling scheme) upon Ca(2+)/Sr(2+) substitution; (iii) the changes in the CW-EPR hyperfine pattern can be explained by a small decrease in the anisotropy of at least two hyperfine tensors. It is proposed that modifications at the Ca(2+) site may modulate the fine structure tensor of the Mn(III) ion. DFT calculations support the above conclusions. Our data analysis also provides strong support for the notion that in the S(2) state the coordination of the Mn(III) ion is square-pyramidal (5-coordinate) or octahedral (6-coordinate) with tetragonal elongation. In addition, it is shown that only one of the currently published OEC models, the Siegbahn structure [Siegbahn, P. E. M. Acc. Chem. Res.2009, 42, 1871-1880, Pantazis, D. A. et al. Phys. Chem. Chem. Phys.2009, 11, 6788-6798], is consistent with all data presented here. These results provide important information for the structure of the OEC and the water-splitting mechanism. In particular, the 5-coordinate Mn(III) is a potential site for substrate 'water' (H(2)O, OH(-)) binding. Its location within the cuboidal structural unit, as opposed to the external 'dangler' position, may have important consequences for the mechanism of O-O bond formation. PMID:21341708

  20. Synthesis of BiSrCa(Y)CuO superconductor from the sol-gel method and the effect of Y substitution

    SciTech Connect

    Menassel, S.; Mosbah, M-F.; Altintas, S. P.; Varilci, A.; Bouaicha, F.

    2012-09-06

    Superconducting Bi{sub 2}Sr{sub 2}Ca{sub 1-x}Y{sub x}Cu{sub 2}O{sub 8} ceramics samples have been prepared by Sol-Gel methods using citrate process. The influences of the conditions of preparation of oxide powder compound on structural and superconducting properties have been investigated by X ray diffraction (XRD), Scanning Electron Microscopy (SEM) equipped with EDS. The critical transition temperatures Tc have been determined by resistivity versus temperature measurements. Cell parameters samples were calculated from XRD patterns. The polyacryl amide gel makes the citrate process easier, more rapid and affords the possibility of synthesis of high quality oxide powders.

  1. Cenozoic seawater Sr/Ca evolution

    NASA Astrophysics Data System (ADS)

    Sosdian, Sindia M.; Lear, Caroline H.; Tao, Kai; Grossman, Ethan L.; O'Dea, Aaron; Rosenthal, Yair

    2012-10-01

    Records of seawater chemistry help constrain temporal variations in geochemical processes that impact the global carbon cycle and climate through Earth's history. Here we reconstruct Cenozoic seawater Sr/Ca (Sr/Casw) using fossil Conus and turritellid gastropod Sr/Ca. Combined with an oxygen isotope paleotemperature record from the same samples, the gastropod record suggests that Sr/Caswwas slightly higher in the Eocene (˜11.4 ± 3 mmol/mol) than today (˜8.54 mmol/mol) and remained relatively stable from the mid- to late Cenozoic. We compare our gastropod Cenozoic Sr/Casw record with a published turritellid gastropod Sr/Casw record and other published biogenic (benthic foraminifera, fossil fish teeth) and inorganic precipitate (calcite veins) Sr/Caswrecords. Once the uncertainties with our gastropod-derived Sr/Casw are taken into account the Sr/Casw record agrees reasonably well with biogenic Sr/Caswrecords. Assuming a seawater [Ca] history derived from marine evaporite inclusions, all biogenic-based Sr/Casw reconstructions imply decreasing seawater [Sr] through the Cenozoic, whereas the calcite vein Sr/Casw reconstruction implies increasing [Sr] through the Cenozoic. We apply a simple geochemical model to examine the implications of divergence among these seawater [Sr] reconstructions and suggest that the interpretation and uncertainties associated with the gastropod and calcite vein proxies need to be revisited. Used in conjunction with records of carbonate depositional fluxes, our favored seawater Sr/Ca scenarios point to a significant increase in the proportion of aragonite versus calcite deposition in shelf sediments from the Middle Miocene, coincident with the proliferation of coral reefs. We propose that this occurred at least 10 million years after the seawater Mg/Ca threshold was passed, and was instead aided by declining levels of atmospheric carbon dioxide.

  2. 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.

  3. Phase compatibility and thermoelectric properties of compounds in the Sr-Ca-Co-O system

    NASA Astrophysics Data System (ADS)

    Wong-Ng, W.; Liu, G.; Martin, J.; Thomas, E. L.; Lowhorn, N.; Kaduk, J. A.

    2010-02-01

    Two low-dimensional cobaltite series in the Sr-Ca-Co-O system have been investigated for their solid solution limit, structure, and compatibility phase relationships (850 C in air). Thermoelectric properties have been measured for selected members of these solid solutions. In (Ca,Sr)3Co4O9, which has a misfit layered structure, Sr was found to substitute in the Ca site to a limit of (Ca0.8Sr0.2)3Co4O9. Compounds in the homologous series, An+2ConCo'O3n+3 [where A=Sr, Ca, (Ca,Sr), or (Sr,Ca)], consist of one-dimensional parallel Co2O66- chains that are built from successive alternating face-sharing CoO6 trigonal prisms and "n" units of CoO6 octahedra along the hexagonal c-axis. In the Can+2ConCo'O3n+3 series, only the n=1 phase (Ca3Co2O6) could be prepared under the present synthesis conditions. Sr substitutes in the Ca site of Ca3Co2O6 to a limit of (Ca0.9Sr0.1)3Co2O6. In the Srn+2ConCo'O3n+3 series, Ca substitutes in the Sr site of the n=2, 3, and 4 members to a limit of (Sr0.7Ca0.3)4Co3O9, (Sr0.67Ca0.33)5Co4O12, and (Sr0.725Ca0.275)6Co5O15, respectively. While the members of the Can+2ConCo'O3n+3 and Srn+2ConCo'O3n+3 series have reasonably high Seebeck coefficients and relatively low thermal conductivity, the electrical conductivity needs to be increased in order to achieve high ZT values.

  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. Paraconductivity measurements and comparative studies of fluctuations in BiSrCaCuO, YBaCuO and YBaCuO with Gd substitution

    SciTech Connect

    Patapis, S.K.; Sideridis, L.; Apostolopoulos, G. . Dept. of Physics); Ausloos, M. . Inst. de Physique); Luo, H.L. . Dept. of Electrical and Computer Engineering); Politis, C. . Inst. fuer Nukleare Festkoerperphysik); Puig, T.; Pont, M.; Munoz, J.S. (Univ

    1991-01-01

    Information concerning the dimensionality of the superconductive fluctuations in the new high temperature superconductors can be derived from the excess conductivity (or paraconductivity) near the transition temperature. Here the lowering'' of the sample resistance in the same temperature regions is used for extraction of dimensionality and generally for comparative studies of the critical behaviour of three different samples such as YBa{sub 2}Cu{sub 3}O{sub 7}, Y{sub 0.8}Gd{sub 0.2}Ba{sub 2}Cu{sub 3}O{sub 7} and Bi{sub 0. 85}Pb{sub 0.15}SrCa{sub 1.2}Cu{sub 2}O{sub 6}. The experimental data of the three samples show a similar behaviour with some distinct differences depending rather on the metallurgical'' state of the material than the composition itself. A logarithmic behaviour is present for YBaCuO and Y(Gd)BaCuO samples not close to the critical temperature and, the most important, closer to {Tc} YBaCuO shows a fractal behaviour, observed for the first time, similar to the one of Bi-compound observed many times before.

  6. Paraconductivity measurements and comparative studies of fluctuations in BiSrCaCuO, YBaCuO and YBaCuO with Gd substitution

    SciTech Connect

    Patapis, S.K.; Sideridis, L.; Apostolopoulos, G.; Ausloos, M.; Luo, H.L.; Politis, C.; Puig, T.; Pont, M.; Munoz, J.S.; Balachadran, U.

    1991-12-31

    Information concerning the dimensionality of the superconductive fluctuations in the new high temperature superconductors can be derived from the excess conductivity (or paraconductivity) near the transition temperature. Here the `lowering`` of the sample resistance in the same temperature regions is used for extraction of dimensionality and generally for comparative studies of the critical behaviour of three different samples such as YBa{sub 2}Cu{sub 3}O{sub 7}, Y{sub 0.8}Gd{sub 0.2}Ba{sub 2}Cu{sub 3}O{sub 7} and Bi{sub 0. 85}Pb{sub 0.15}SrCa{sub 1.2}Cu{sub 2}O{sub 6}. The experimental data of the three samples show a similar behaviour with some distinct differences depending rather on the ``metallurgical`` state of the material than the composition itself. A logarithmic behaviour is present for YBaCuO and Y(Gd)BaCuO samples not close to the critical temperature and, the most important, closer to {Tc} YBaCuO shows a fractal behaviour, observed for the first time, similar to the one of Bi-compound observed many times before.

  7. Controls on Sr/Ca in Scleractinian Corals: The Effects of Ca-ATPase and Ca channels on Skeletal Chemistry

    NASA Astrophysics Data System (ADS)

    Allison, N.; Cohen, I.; Finch, A. A.; Erez, J.

    2010-12-01

    Coral skeletal Sr/Ca is a commonly used palaeothermometer and has been used to estimate past sea surface temperatures. However the processes controlling Sr incorporation in coral aragonite are poorly understood. The Sr/Ca chemistry of the massive Porites spp. corals typically used for palaeoenvironmental reconstruction is dominated by short-term (weekly-monthly) oscillations of ~10% which do not reflect seawater temperature. This heterogeneity may reflect variations in the composition of the fluid used for calcification. Coral skeletons precipitate from an extracellular calcifying fluid enclosed in a semi-isolated space between the skeleton and the calicoblastic epithelium (the tissue layer at the base of the coral organism). Seawater diffuses directly to the calcification site and the calcification fluid has a composition derived from that of seawater but modified by other transport processes. In zooxanthellate corals, Ca2+ is transported transcellularly to the calcification site by both calcium channels and by the carrier protein Ca-ATPase. Sr2+ has a similar ionic radius to Ca2+, but it is not clear if Sr2+ can substitute for Ca2+ in these transport mechanisms. Variations in the relative contributions of each of the transport mechanisms to the calcification fluid and the efficiencies with which each process transports Sr2+ and Ca2+ could explain the Sr/Ca heterogeneity observed in coral skeletons. To test the impact of transcellular Ca transport processes on skeletal Sr/Ca and Mg/Ca we cultured Pocillopora damicornis corals in the presence of inhibitors of Ca-ATPase (ruthenium red) and Ca channels (verapamil). The photosynthesis, respiration and calcification rates of the colonies were monitored throughout the experiment. The skeleton subsequently deposited was identified (by 42Ca spike) and analysed by secondary ion mass spectrometry. The Sr/Ca and Mg/Ca of the aragonite deposited in the presence of either of the inhibitors was not significantly different from that of the control, although the coral calcification rate was reduced by up to 66 and 73% in the ruthenium red and verapamil treatments respectively. The typical precision (95% confidence limits) of mean Sr/Ca determinations within any one treatment was ±0.8% and differences in mean Sr/Ca between treatments were correspondingly small. Either Ca-ATPase and Ca channels transport Sr2+ and Ca2+ in virtually the same ratio in which they are present in seawater or any preferential transport of Ca2+ by these processes is so limited as to be insignificant i.e. transcellularly transported Ca contributes little to the total Ca at the calcification site. This suggests that variations in the activities of Ca-ATPase and Ca-channels are not responsible for the short term Sr/Ca heterogeneity observed in coral skeletons or for the differences in mean Sr/Ca which are observed between colonies growing at different rates.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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

  13. Substitution effect of Ba at the Sr sites in Sr(Fe,Re)O3

    NASA Astrophysics Data System (ADS)

    Yamakoshi, T.; Nomura, K.; Kitamori, T.; Shimoyama, J.; Nemeth, Z.; Homonnay, Z.

    2009-06-01

    Substitution effect in double perovskites, Sr(FeRe)O3 (SFRO), was studied by Mssbauer spectroscopy and magnetization measurements. The samples were prepared by a sol-gel method. The fraction of alternately ordered Fe1 for SFRO is 72%, and the magnetization measured is consistent with 3 0.72=2.16{?_B } {f.u.}, but the saturation magnetization drops to about one third of its initial value by substituting 5% Ba for Sr. It was considered to be due to the volume expansion of the lattice and the fine grains formed, as a result of the substitution of Ba ions.

  14. Metabolism controls Sr/Ca ratios in fossil aragonitic mollusks

    NASA Astrophysics Data System (ADS)

    Purton, Louise M. A.; Shields, Graham A.; Brasier, Martin D.; Grime, Geoff W.

    1999-12-01

    Sr/Ca and Mg/Ca ratios in biomineral CaCO3 have recently been regarded as more reliable than δ18O values as proxy for paleotemperature because they are less affected by salinity or polar ice volume. We argue, however, that vital effects can exert a greater control than paleotemperature over fossil Sr/Ca. Seasonal perturbations in isotopic data from the Eocene bivalve Venericardia planicosta reveal a gradually decreasing annual growth rate through ontogeny. High-resolution Sr/Ca ratios, analyzed with a new proton-microbe technique, increase markedly through ontogeny, however, suggesting that more Sr was incorporated as growth rate slowed rather than as a result of changing paleotemperature. Comparative δ18O and Sr/Ca data from the broadly coeval marine gastropod Clavilithes macrospira, which exhibits a linear growth rate through ontogeny, also shows a significant increase in Sr concentration with age as well as seasonal, possibly temperature-related variations. Our observations show that neither growth, calcification rate, nor temperature can be the sole factor controlling Sr incorporation into molluscan aragonite. Metabolic activity, related to factors such as temperature, salinity, age, and growth rate, is likely to exert the primary control over Sr/Ca ratios in aragonitic mollusks.

  15. Interstitial and substitutional Zr in SrTiO3

    NASA Astrophysics Data System (ADS)

    Jaffe, John; van Ginhoven, Renee; Jiang, Weilin

    2011-03-01

    We investigate Zr in SrTi O3 (STO) as an electronic dopant and as a model for nuclear waste forms in which radioactive Sr decays to Y and then to stable Zr through beta emission. Density functional theory (DFT) within the supercell model is used to predict the thermodynamic stability and electronic states of interstitial and Sr- or Ti-substituted Zr atoms in the STO lattice. Native point defects such as vacancies and antisites are also considered. When Zr replaces Sr, its most stable configuration is to simply occupy the Sr site (instead of, for example, replacing a Ti and displacing the Ti to the Sr site.) For Zr added to the lattice, its most stable configuration is to replace a Ti, making a Zr Ti impurity plus a Ti interstitial (as opposed to the Zr just remaining as an interstitial atom.) Zr Sr is predicted to be a double electron donor, Zr Ti is electrically inactive and interstitial Zr and Ti are predicted to be quadruple donors, with all donor levels in the conduction band. Zr Sr and the tetravalent interstitials are all predicted to increase the crystal volume, and the interstitials also are predicted to lead to a tetragonal distortion of the lattice. Experiments with injection of Zr atoms into STO qualitatively confirm these predictions of crystal structural changes. Supported by U.S. Department of Energy Waste Form Campaign.

  16. Interstitial and substitutional zirconium in SrTiO3

    SciTech Connect

    Jaffe, John E.; Van Ginhoven, Renee M.; Jiang, Weilin

    2012-02-22

    We investigate Zr in SrTiO3 (STO) as a model for nuclear waste forms in which the fission product Sr90 eventually decays to stable Zr through beta emission. The transformation of a divalent into a tetravalent constituent is expected to affect the long-term structural and chemical stability of this solid. Computational methods of electronic structure theory, specifically the density functional theory (DFT) within the supercell model, are used to predict the thermodynamic stability and electronic states of interstitial and Sr- or Ti-substituted Zr atoms in the STO lattice. Native defects such as vacancies and antisites are also considered. When Zr replaces Sr, its most stable configuration is to simply occupy the Sr site (instead of, for example, replacing a Ti and displacing the Ti to the Sr site.) For Zr added to the lattice, its most stable configuration is to replace a Ti, making a ZrTi impurity plus a Ti interstitial (as opposed to the Zr just remaining as an interstitial atom.) ZrSr is predicted to be a double electron donor, ZrTi is electrically inactive and interstitial Zr and Ti are predicted to be quadruple donors, with all donor levels in the conduction band. ZrSr and the tetravalent interstitials are all predicted to increase the crystal volume, and the interstitials also are predicted to lead to a tetragonal distortion of the lattice. Experiments with injection of Zr atoms into STO qualitatively confirm these predictions of crystal structural changes.

  17. The role of Sr2+ on the structure and reactivity of SrO-CaO-ZnO-SiO2 ionomer glasses.

    PubMed

    Boyd, Daniel; Towler, Mark R; Watts, Sally; Hill, Robert G; Wren, Anthony W; Clarkin, Owen M

    2008-02-01

    The suitability of Glass Polyalkenoate Cements (GPCs) for use in orthopaedics is retarded by the presence in the glass phase of aluminium, a neurotoxin. Unfortunately, the aluminium ion plays an integral role in the setting process of GPCs and its absence is likely to hinder cement formation. However, the authors have previously shown that aluminium free GPCs may be formulated based on calcium zinc silicate glasses and these novel materials exhibit significant potential as hard tissue biomaterials. To further improve their potential, and given that Strontium (Sr) based drugs have had success in the treatment of osteoporosis, the authors have substituted Calcium (Ca) with Sr in the glass phase of a series of aluminium free GPCs. However to date little data exists on the effect SrO has on the structure and reactivity of SrO-CaO-ZnO-SiO(2) glasses. The objective of this work was to characterise the effect of the Ca/Sr substitution on the structure of such glasses, and evaluate the subsequent reactivity of these glasses with an aqueous solution of Polyacrylic acid (PAA). To this end (29)Si MAS-NMR, differential scanning calorimetry (DSC), X-ray diffraction, and network connectivity calculations, were used to characterize the structure of four strontium calcium zinc silicate glasses. Following glass characterization, GPCs were produced from each glass using a 40 wt% solution of PAA (powder:liquid = 2:1.5). The working times and setting times of the GPCs were recorded as per International standard ISO9917. The results acquired as part of this research indicate that the substitution of Ca for Sr in the glasses examined did not appear to significantly affect the structure of the glasses investigated. However it was noted that increasing the amount of Ca substituted for Sr did result in a concomitant increase in setting times, a feature that may be attributable to the higher basicity of SrO over CaO. PMID:17665132

  18. Late Quaternary Productivity Records from Coccolith Sr/Ca

    NASA Astrophysics Data System (ADS)

    Stoll, H. M.; Burke, A.; Mejia Ramirez, L. M.; Shimizu, N.; Ziveri, P. P. I.

    2014-12-01

    The Sr/Ca of coccoliths has been proposed as an indicator of productivity on the basis of correlation with export production in sediment traps and across upwelling productivity gradients, although the mechanism responsable for this relationship is not clear. For diverse oceanographic settings in the Late Quaternary, we compare coccolith Sr/Ca productivity records with those of other productivity indicators and proxies for mechanisms of productivity forcing. For the Somalia Basin in the Arabian Sea, coccolith Sr/Ca shows a large variation coherent with precessional forcing of wind strength as a mechanism for productivity regulation. During the glacial, the Sr/Ca peak is decoupled from productivity indicators based on organic C accumulation rate. For the Northern Bay of Bengal, coccolith Sr/Ca, Ba/Ti, and relative abundance of G. bulloides, all suggest greater productivity during the interglacial periods, consisted with Nd isotopic evidence for greater riverine nutrient inputs. In the Andaman Sea, coccolith Sr/Ca is highest during precessional maxima in the summer monsoon, consistent with proxies for chemical weathering in the Irawaddy rivershed. In the Eastern Mediterranean, coccolith Sr/Ca is on average low, and peaks during the E. Holocene interval characterized by deposition of sapropel S1. The peak in Sr/Ca however is comparable to the level maintained throughout the Holocene in the Western Mediterranean, where no sapropel occurs, implicating deepwater oxygen levels as a significant contributor to sapropel formation. Finally, on the Agulhas Bank, minima in coccolith Sr/Ca occur during obliquity minima which are periods of anomalous equatorward deposition of IRD in the Southern Ocean. Northward explansion of the westerly wind field during these cold intervals, block upwelling on the Agulhas Bank and result in low productivity.

  19. 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 utilization of Ba/Ca and Sr/Ca in addition to stable isotope ratios (delta13C and delta15N) for the determination of the relative contribution of different food sources to an animal's diet. PMID:14745648

  20. 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

  1. 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.

  2. Controls on Sr/Ca and Mg/Ca in scleractinian corals: The effects of Ca-ATPase and transcellular Ca channels on skeletal chemistry

    NASA Astrophysics Data System (ADS)

    Emif Allison, Nicola; Cohen, Itay; Finch, Adrian A.; Erez, Jonathan

    2011-11-01

    The Sr/Ca of aragonitic coral skeletons is a commonly used palaeothermometer. However skeletal Sr/Ca is typically dominated by weekly-monthly oscillations which do not reflect temperature or seawater composition and the origins of which are currently unknown. To test the impact of transcellular Ca2+ transport processes on skeletal Sr/Ca, colonies of the branching coral, Pocillopora damicornis, were cultured in the presence of inhibitors of Ca-ATPase (ruthenium red) and Ca channels (verapamil hydrochloride). The photosynthesis, respiration and calcification rates of the colonies were monitored throughout the experiment. The skeleton deposited in the presence of the inhibitors was identified (by 42Ca spike) and analysed for Sr/Ca and Mg/Ca by secondary ion mass spectrometry. The Sr/Ca of the aragonite deposited in the presence of either of the inhibitors was not significantly different from that of the solvent (dimethyl sulfoxide) control, although the coral calcification rate was reduced by up to 66% and 73% in the ruthenium red and verapamil treatments, respectively. The typical precision (95% confidence limits) of mean Sr/Ca determinations within any treatment was <±1% and differences in skeletal Sr/Ca between treatments were correspondingly small. Either Ca-ATPase and Ca channels transport Sr2+ and Ca2+ in virtually the same ratio in which they are present in seawater or transcellular processes contribute little Ca2+ to the skeleton and most Ca is derived from seawater transported directly to the calcification site. Variations in the activities of Ca-ATPase and Ca-channels are not responsible for the weekly-monthly Sr/Ca oscillations observed in skeletal chronologies, assuming that the specificities of Ca transcellular transport processes are similar between coral genera.

  3. Controls on Sr/Ca and Mg/Ca in scleractinian corals: The effects of Ca-ATPase and transcellular Ca channels on skeletal chemistry

    NASA Astrophysics Data System (ADS)

    Allison, Nicola; Cohen, Itay; Finch, Adrian A.; Erez, Jonathan; EMIF

    2011-11-01

    The Sr/Ca of aragonitic coral skeletons is a commonly used palaeothermometer. However skeletal Sr/Ca is typically dominated by weekly-monthly oscillations which do not reflect temperature or seawater composition and the origins of which are currently unknown. To test the impact of transcellular Ca 2+ transport processes on skeletal Sr/Ca, colonies of the branching coral, Pocillopora damicornis, were cultured in the presence of inhibitors of Ca-ATPase (ruthenium red) and Ca channels (verapamil hydrochloride). The photosynthesis, respiration and calcification rates of the colonies were monitored throughout the experiment. The skeleton deposited in the presence of the inhibitors was identified (by 42Ca spike) and analysed for Sr/Ca and Mg/Ca by secondary ion mass spectrometry. The Sr/Ca of the aragonite deposited in the presence of either of the inhibitors was not significantly different from that of the solvent (dimethyl sulfoxide) control, although the coral calcification rate was reduced by up to 66% and 73% in the ruthenium red and verapamil treatments, respectively. The typical precision (95% confidence limits) of mean Sr/Ca determinations within any treatment was <±1% and differences in skeletal Sr/Ca between treatments were correspondingly small. Either Ca-ATPase and Ca channels transport Sr 2+ and Ca 2+ in virtually the same ratio in which they are present in seawater or transcellular processes contribute little Ca 2+ to the skeleton and most Ca is derived from seawater transported directly to the calcification site. Variations in the activities of Ca-ATPase and Ca-channels are not responsible for the weekly-monthly Sr/Ca oscillations observed in skeletal chronologies, assuming that the specificities of Ca transcellular transport processes are similar between coral genera.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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 processes with fast biologically driven cycling between soils and biomass.

  9. Assessment of intra-SR free [Ca] and buffering in rat heart.

    PubMed Central

    Shannon, T R; Bers, D M

    1997-01-01

    To measure the free intrasarcoplasmic reticulum [Ca] ([Ca]SR) in isolated rat cardiac microsomes, ventricular tissue was homogenized in the presence of the low-affinity Ca indicator furaptra. Stepwise increases in cuvette [Ca] ([Ca]c) in the presence of ATP caused progressive increases in steady-state intravesicular fluorescence ratio to a maximum (Rmax). Steady-state [Ca]SR/[Ca]c was approximately 7000. Therefore the resting [Ca]SR may approach 700 microM in the rat cardiac myocyte at [Ca]c = 100 nM. The sarcoplasmic reticulum (SR) Ca pump requires a free energy of deltaG approximately 44 kJ x mol(-1) to generate this [Ca] gradient (e.g., approximately 74% of deltaG(ATP)). Total SR 45Ca uptake was also measured in digitonin-permeabilized myocytes as a function of [Ca]c in the absence of precipitating ions. The steady-state SR Ca content at 100 nM [Ca]c was approximately 400 micromol/liter cytosolic volume. Used together, these data allowed evaluation of the in situ SR Ca-buffering properties. The SR Ca-binding site concentration was approximately 14 mM, and Kd(Ca) approximately 0.638 mM [Ca]SR. Images FIGURE 1 PMID:9284319

  10. Mechanochemical synthesis of MgF2 - MF2 composite systems (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Scholz, G.; Breitfeld, S.; Krahl, T.; Düvel, A.; Heitjans, P.; Kemnitz, E.

    2015-12-01

    The capability of mechanochemical synthesis for the formation of MgF2-MF2 (M: Ca, Sr, Ba) composites, solid solutions or well-defined compounds was tested applying a fluorination of different fluorine-free metal sources with NH4F directly at milling. No evidence was found for a substitution of Mg2+ with Ca2+ (Sr2+, Ba2+) ions, or vice versa, in rutile or fluorite structure. However, an equimolar ratio of Mg2+ to the second cation allows the mechanochemical synthesis of tetrafluoromagnesates, MMgF4, which is more and more hampered the smaller the radius of the cation M2+ is. BaMgF4 is formed even phase pure from the acetates, SrMgF4 can only be observed in a mixture accompanied by the binary fluorides. In addition, 19F MAS NMR spectra along with calculations of 19F isotropic chemical shift values according to the superposition model point to the formation of a metastable phase of CaMgF4, which disappears at thermal treatment and decomposes into the binary fluorides CaF2 and MgF2.

  11. Enhancement of magnetic properties in Mn-Zn substituted M-type Sr-hexaferrites

    NASA Astrophysics Data System (ADS)

    Kang, Young-Min; Kwon, Young-Ho; Kim, Min-Ho; Lee, Dong-Young

    2015-05-01

    We report the magnetic properties of Mn-Zn substituted M-type Sr-hexaferrites (SrM), SrFe12-2xMnxZnxO19, and compare them with those of non-substituted SrM and La-Zn substituted SrM. The highest saturation magnetization (MS) of 75.6 emu/g was obtained at a Mn-Zn substitution of x=0.1 (SrFe11.8Mn0.1Zn0.1O19), which is higher than those of the non-substituted SrM and La-Zn substituted SrM by 2.6% and 1.7%, respectively. The enhanced MS can be attributed to the selective substitution of Zn2+ and Mn4+ into the down-spin site of Fe3+ (4f1 or 4f2). Sintered anisotropic magnets fabricated with the optimal Mn-Zn doping level of x=0.1 exhibited a remanent magnetic induction (Br) over 4300 G and maximum energy product (BH)max of ~4.6 MGOe (36.6 kJ/m3).

  12. Magnétisme et supraconductivité par substitution cationique dans les cuprates de bismuth Bi2Sr2Ca{1-x} TRxCu2O{8+δ} : le cérium et le dysprosium

    NASA Astrophysics Data System (ADS)

    Jordan, F.; Peña, O.; Laxmi-Narsaiah, E.

    1994-11-01

    The substitution of divalent calcium in the bismuth cuprates changes the carrier density (variation of T_c) and allows, at the same time, to study the interplay between magnetic phenomena and superconductivity. We report results obtained after substitution by dysprosium (a strongly magnetic element) and by cerium (which may have different behaviours depending on its oxidation state). Solubility domains and texturation phenomena are also reported. La substitution du calcium divalent dans les cuprates de bismuth permet à la fois de changer le nombre de porteurs (variations de T_c) et d'étudier l'existence simultanée de la supraconductivité et du magnétisme (substitution par des lanthanides magnétiques). Dans ce travail, nous reportons nos résultats après substitution du calcium par un élément magnétique (Dy^{3+}) et par un élément à caractère particulier suivant son état d'oxydation (Ce^{3+} ou Ce^{4+}). Les domaines de solubilité ainsi que les phénomènes liés à la texturation dans ces structures feuilletées sont également reportés.

  13. 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.

  14. Tracer diffusion of Mg, Ca, Sr, and Ba in Na-aluminosilicate melts

    NASA Astrophysics Data System (ADS)

    Roselieb, Knut; Jambon, Albert

    2002-01-01

    We employed the thin source technique to investigate tracer diffusion of Mg, Ca, Sr, and Ba in glasses and supercooled melts of albite (NaAlSi 3O 8) and jadeite (NaAlSi 2O 6) compositions. The experiments were conducted at 1 bar and at temperatures between 645 and 1025°C. Typical run durations ranged between 30 min and 35 days. The analysis of the diffusion profiles was performed with the electron microprobe. Diffusivities of Ca, Sr, and Ba were found to be independent of either duration t of the experiment or tracer concentration M, initially introduced into the sample. Mg exhibits a diffusivity depending on run time and concentration and tracer diffusivity is derived by extrapolation to M/√t = 0. Temperature dependence of the diffusivity D can be represented by an Arrhenius equation D = D o exp(-E a/RT), yielding the following least-squares fit parameters (with D in m 2/s and E a in kJ/mol): D Mg = 1.8 · 10 -5 exp(-234 ± 20/RT), D Ca = 3.5 · 10 -6 exp(-159 ± 6/RT), D Sr = 3.6 · 10 -6 exp(-160 ± 6/RT), and D Ba = 6.0 · 10 -6 exp(-188 ± 12/RT) for albite; and D Mg = 8.3 · 10 -6 exp(-207 ± 18/RT), D Ca = 3.8 · 10 -6 exp(-153 ± 4/RT), D Sr = 2.3 · 10 -6 exp(-150 ± 4/RT), and D Ba = 3.7 · 10 -5 exp(-198 ± 4/RT) for jadeite composition. Ca and Sr diffusivities agree within error in both compositions and exhibit the fastest diffusivities, whereas Mg reveals the lowest diffusivity. The relationship between activation energy and radius shows a minimum at Ca and Sr for albite and jadeite compositions extending the relationship already observed elsewhere for alkalies. With increasing substitution of Si by (Na + Al), diffusivities increase, whereas activation energies decrease. Furthermore, a simple model modified from that of Anderson and Stuart (Anderson O. L. and Stuart D. A., "Calculation of activation energy of ionic conductivity in silica glasses by classical methods," J. Am. Ceram. Soc.37, 573-580, 1954) is discussed for calculating the activation energies.

  15. Neutron diffraction study of a (C,Cu)(Sr,Ca) 2(Y,Ca,Sr) Cu 2O 7 superconductor

    NASA Astrophysics Data System (ADS)

    Miyazaki, Y.; Yamane, H.; Kajitani, T.; Morii, Y.; Funahashi, S.; Hirai, T.

    1995-02-01

    The crystal structure of a cuprate containing CO 3 groups, (C 0.58Cu 0.42)(Sr 0.88Ca 0.12) 2(Y 0.50Ca 0.26Sr 0.24)Cu 2O 7, and its high-pressure oxygen-annealed samples were refined by means of the Rietveld method for neutron-powder-diffraction data. The as-prepared sample (non-superconducting) has neither oxygen defect nor carbonate defect in the structure. Noticeable absence of oxygen atoms and carbonate groups are detected for the annealed (superconducting) sample. It is suggested that hole doping is achieved during high-pressure oxygen annealing by the release of some CO 3 groups and by the introduction of oxygen atoms into the vacant ‘apical’ oxygen site, when the CO 3 group is not present.

  16. 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

  17. 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; Lazareth et al., 2003, Est. Coast. Shelf Sci. 17, 1461-1470).

  18. The influence of Sr and H3PO4 concentration on the hydration of SrCaHA bone cement.

    PubMed

    Guo, Dagang; Mao, Mengmeng; Qi, Wenli; Li, Hongyuan; Ni, Pengfei; Gao, Guohan; Xu, Kewei

    2011-12-01

    Sr-contained calcium hydroxyapatite (SrCaHA) cement is a potential biomaterial for in vivo bone repair and surgery fixation due to its excellent biodegradability, bioactivity, biocompatibility, easily shaping and self-hardening. We had ever reported the in vitro physiochemical properties, biocompatibility and in vivo degradability of the SrCaHA cement obtained by mixing a cement powder of Ca(4)(PO(4))(2)O/CaHPO(4)/SrHPO(4) and a cement liquid of diluted H(3)PO(4) aqueous solution. In the present study, we intensively studied the influences of both Sr content and H(3)PO(4) concentration in diluted phosphoric acid aqueous solution on the setting time, hydration heat-liberation behaviours, and real-time microstructure and phase evolutions of the SrCaHA cement. The results show that both PO(4)(3-) and H(+) ions in PA solution attended the hydration reaction as reactants, and thus the increase of the PA concentration not only promoted the dissolution of Ca(4)(PO(4))(2)O but also pushed the hydration progress of SrCaHA bone cement. Sr content exhibits a remarkable retardation role on the apatite transformation of the SrCaHA cement pastes which probably attributed to its higher degree of supersaturation for yielding apatite crystals and lower transformation rate when exposed to the Sr(2+)-containing hydration system. This present results contribute to a better understanding on the hydration mechanism of the new SrCaHA cement and help to the more precisely controlling of its hydration process. PMID:21979165

  19. 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.

  20. Ca2+ Alternans in a Cardiac Myocyte Model that Uses Moment Equations to Represent Heterogeneous Junctional SR Ca2+

    PubMed Central

    Huertas, Marco A.; Smith, Gregory D.; Györke, Sándor

    2010-01-01

    Abstract Multiscale whole-cell models that accurately represent local control of Ca2+-induced Ca2+ release in cardiac myocytes can reproduce high-gain Ca2+ release that is graded with changes in membrane potential. Using a recently introduced formalism that represents heterogeneous local Ca2+ using moment equations, we present a model of cardiac myocyte Ca2+ cycling that exhibits alternating sarcoplasmic reticulum (SR) Ca2+ release when periodically stimulated by depolarizing voltage pulses. The model predicts that the distribution of junctional SR [Ca2+] across a large population of Ca2+ release units is distinct on alternating cycles. Load-release and release-uptake functions computed from this model give insight into how Ca2+ fluxes and stimulation frequency combine to determine the presence or absence of Ca2+ alternans. Our results show that the conditions for the onset of Ca2+ alternans cannot be explained solely by the steepness of the load-release function, but that changes in the release-uptake process also play an important role. We analyze the effect of the junctional SR refilling time constant on Ca2+ alternans and conclude that physiologically realistic models of defective Ca2+ cycling must represent the dynamics of heterogeneous junctional SR [Ca2+] without assuming rapid equilibration of junctional and network SR [Ca2+]. PMID:20643055

  1. 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.

  2. 87Sr/ 86Sr and Sr/Ca in speleothems for paleoclimate reconstruction in Central China between 70 and 280 kyr ago

    NASA Astrophysics Data System (ADS)

    Li, Hong-Chun; Ku, Teh-Lung; You, Chen-Feng; Cheng, Hai; Edwards, R. Lawrence; Ma, Zhi-Bang; Tsai, Wang-sheng; Li, Mung-Dar

    2005-08-01

    Limestone cave deposits (speleothems) provide archives for past changes in regional climates over a range of timescales. While δ 18O and δ 13C in speleothem calcite have been commonly used for reconstruction of paleoclimates, we report here further efforts in the use of 87Sr/ 86Sr and Sr/Ca signals in speleothem calcite to deduce paleomonsoon variability near the Loess Plateau of central China. A two end-member mass-balance model of concentration and isotopic composition of strontium in a cave system is used to estimate variation of the 87Sr/ 86Sr ratio in sediments overlying a limestone cave. We show that this ratio reflects climate-driven variations in the provenance and the extent of chemical weathering of the epikarstic sediments. The measurements of 87Sr/ 86Sr made on a well-dated stalagmite, SFL, from Buddha Cave (33 o40N' 109 o05'E) show ratios of 0.71092 to 0.71133 (±0.00001 as 2σ) during relatively cold periods (e.g., Marine Isotope Stage (MIS) 5b, 5d, and 8), lower than ratios of 0.71133 to 0.71194 during relatively warm periods (e.g., MIS 5a, 5c, 5e, and 7). As changes in the Sr/Ca ratio may affect speleothem 87Sr/ 86Sr, we show that the direct use of speleothem 87Sr/ 86Sr is less ideal than our modeled 87Sr/ 86Sr for the exogenic Sr source above the cave as a paleomonsoon proxy. Using the δ 18O, δ 13C, Sr/Ca, and 87Sr/ 86Sr records of the stalagmite, we reconstruct the variability of the East Asian monsoon for the time period between 70 and 280 kyr ago. The results show that summer monsoons were more intense during interglacial periods than during glacial periods.

  3. 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 INa inhibition. PMID:25990311

  4. Structure of Sr-substituted photosystem II at 2.1 A resolution and its implications in the mechanism of water oxidation.

    PubMed

    Koua, Faisal Hammad Mekky; Umena, Yasufumi; Kawakami, Keisuke; Shen, Jian-Ren

    2013-03-01

    Oxygen-evolving complex of photosystem II (PSII) is a tetra-manganese calcium penta-oxygenic cluster (Mn4CaO5) catalyzing light-induced water oxidation through several intermediate states (S-states) by a mechanism that is not fully understood. To elucidate the roles of Ca(2+) in this cluster and the possible location of water substrates in this process, we crystallized Sr(2+)-substituted PSII from Thermosynechococcus vulcanus, analyzed its crystal structure at a resolution of 2.1 Å, and compared it with the 1.9 Å structure of native PSII. Our analysis showed that the position of Sr was moved toward the outside of the cubane structure of the Mn4CaO5-cluster relative to that of Ca(2+), resulting in a general elongation of the bond distances between Sr and its surrounding atoms compared with the corresponding distances in the Ca-containing cluster. In particular, we identified an apparent elongation in the bond distance between Sr and one of the two terminal water ligands of Ca(2+), W3, whereas that of the Sr-W4 distance was not much changed. This result may contribute to the decrease of oxygen evolution upon Sr(2+)-substitution, and suggests a weak binding and rather mobile nature of this particular water molecule (W3), which in turn implies the possible involvement of this water molecule as a substrate in the O-O bond formation. In addition, the PsbY subunit, which was absent in the 1.9 Å structure of native PSII, was found in the Sr-PSII structure. PMID:23426624

  5. 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.

  6. SR33805, a Ca2+ antagonist with length-dependent Ca2+-sensitizing properties in cardiac myocytes

    PubMed Central

    Cazorla, Olivier; Lacampagne, Alain; Fauconnier, Jeremy; Vassort, Guy

    2003-01-01

    This study examined the effects of SR33805, a fantofarone derivative with reported strong Ca2+ -antagonistic properties, on the contractile properties of intact and skinned rat ventricular myocytes. On intact cells loaded with the Ca2+-fluorescent indicator Indo-1, the application of low concentrations of SR33805 enhanced the amplitude of unloaded cell shortening and decreased the duration of cell shortening. Amplitude of the Ca2+ transient was also decreased. These effects were accompanied with a shortening of the action potential and a dose-dependent blockade of L-type calcium current (IC50=2.4 10?8 M). On skinned cardiac cells, the application of a low SR33805 concentration (10?8 M) induced a significant increase in maximal Ca2+-activated force at the two-tested sarcomere lengths (SLs), 1.9 and 2.3 ?m. The application of a larger dose of SR33805 (10?610?5 M) induced a significant leftward shift of the tensionpCa relation that accounts for Ca2+-sensitization of the myofilaments, particularly at 2.3 ?m SL. In conclusion, despite its strong Ca2+-antagonistic properties SR33805 increases cardiac cell contractile activity as a consequence of its Ca2+-sensitizing effects. These effects are attributable to both an increase in the maximal Ca2+-activated force and a length-dependent Ca2+-sensitization. PMID:12746228

  7. 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 when the DSr greatly deviates from one, as this indicates the dominance of biological controls on Sr/Ca ratios.

  8. 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

  9. Migration and Rearing Histories of Chinook Salmon (Oncorhynchus tshawytscha) Determined by Ion Microprobe Sr Isotope and Sr/Ca Transects of Otoliths

    NASA Astrophysics Data System (ADS)

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

    2004-05-01

    With the goal of monitoring fish habitat during the first year of life, we used the Stanford-USGS SHRIMP RG ion microprobe to determine 87Sr/86Sr and Sr/Ca ratios in 25 × 35 μ m areas along radial transects of otoliths from juvenile Chinook salmon (Oncorhynchus tshawytscha) native to four watersheds of markedly different geology. Otoliths from ocean-type Chinook salmon from the Skagit River estuary, Washington, have pre-hatch regions with 87Sr/86Sr ratios (~0.709) suggesting a marine signature inherited maternally, extensive freshwater growth zones with 87Sr/86Sr ratios similar that of the Skagit River (~0.705), and marine-like 87Sr/86Sr ratios near edges. Otoliths from stream-type Chinook salmon from three watersheds in central Idaho have pre-hatch 87Sr/86Sr ratios >0.711, indicating that a maternal marine Sr isotopic signature is not preserved after the ~1000-1400 km migration from the Pacific Ocean. The 87Sr/86Sr ratios in the outer portions of these otoliths are similar to those of their respective streams (~0.708-0.722). For the Skagit juveniles, freshwater growth is marked by a small decrease in otolith Sr/Ca ratio, with an increase in Sr/Ca corresponding to the observed increase in 87Sr/86Sr with migration into salt water. Otoliths from the Idaho fish have similar Sr/Ca radial variation patterns that appear to record seasonal fluctuation in ambient water Sr/Ca ratio documented by our water analyses and USGS NASQAN time series data. The ability of the ion microprobe to measure both 87Sr/86Sr and Sr/Ca ratios of otolith aragonite at high spatial resolution in situ provides a new dimension in studies of fish rearing and migration.

  10. Crystallization of metal-oxide glasses in Bi-Sr-Ca-Cu-O systems

    NASA Astrophysics Data System (ADS)

    Shi, Donglu; Tang, Ming; Boley, M. S.; Hash, Mark; Vandervoort, K.; Claus, H.; Lwin, Y. N.

    1989-08-01

    A crystallization study has been carried out for rapidly solidified Bi-Sr-Ca-Cu-O glasses with nominal compositions Bi2Sr2Ca2Cu3Ox, Bi2Sr2Ca3Cu4Ox, and Bi2Sr2Ca4Cu5Ox. A temperature-time-transformation diagram for the glass with nominal composition Bi2Sr2Ca2Cu3Ox has been constructed, within which crystalline superconducting and nonsuperconducting phase regions are identified. Eutectic and primary crystallization have been found to occur during the annealing process in these metal oxides. Glass transition temperature Tg values, superconducting transition temperature values of crystallized products, and microstructural changes are measured and analyzed by differential thermal analysis, electrical resistivity, and magnetization shielding, x-ray diffraction, and scanning electron microscopy experiments. Also discussed are thermodynamics and kinetics of crystallization processes and the formation of the 110-K superconducting phase.

  11. Substitution Effects in the Itinerant Electron Metamagnetic Compound SrCo2P2

    NASA Astrophysics Data System (ADS)

    Imai, Masaki; Michioka, Chishiro; Ueda, Hiroaki; Matsuo, Akira; Kindo, Koichi; Yoshimura, Kazuyoshi

    The ThCr2Si2-type layered compound SrCo2P2 shows an itinerant-electron metamagnetic transition at high magnetic field. To investigate substitution effects on the itinerant metamagnetic transition, we synthesized Sr1-xLaxCo2P2 and SrCo2(P1-xGex)2 and measured their magnetic properties, including magnetizations under pulsed high magnetic fields. We have revealed a strong x dependence of the metamagnetic transition which is consistent with the band theory describing the physical properties in metals.

  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. 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.

  14. Structural disorder in AMoO4 (A = Ca, Sr, Ba) scheelite nanocrystals.

    PubMed

    Rabuffetti, Federico A; Culver, Sean P; Suescun, Leopoldo; Brutchey, Richard L

    2014-01-21

    The crystal structure of sub-15 nm AMoO4 (A = Ca, Sr, Ba) scheelite nanocrystals has been investigated using a dual-space approach that combines Rietveld and pair distribution function (PDF) analysis of synchrotron X-ray diffraction data. Rietveld analysis yields an average crystal structure in which the Mo-O bond distance exhibits an anomalously large contraction (2.8%) upon chemical substitution of Ba(2+) for Ca(2+). Such a dependence on chemical composition contradicts the well-known rigid character of Mo(VI)-O bonds and the resulting rigidity of MoO4 tetrahedra in scheelites. Unlike Rietveld, PDF analysis yields a local crystal structure in which the Mo-O bond distance shows a negligible contraction (0.4%) upon going from Ba(2+) to Ca(2+) and, therefore, appears independent of the chemical composition. Analysis of the anisotropic displacement parameters of the oxygen atom reveals that the disagreement between the average and local structural models arises from the presence of static orientational disorder of the MoO4 tetrahedra. Rietveld analysis averages the random rotations of the MoO4 tetrahedra across the scheelite lattice yielding an apparent Mo-O bond distance that is shorter than the true bond distance. In contrast, PDF analysis demonstrates that the structural integrity of the MoO4 tetrahedra remains unchanged upon chemical substitution of the alkaline-earth cation, and that their orientational disorder is accommodated through geometric distortions of the AO8 dodecahedra. PMID:24266706

  15. 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] Tripati, A., Sampson, D., and Allmon, W. (2009) Earth and Planetary Science Letters, 282, doi:10.1016/j.epsl.2009.03.020; [3] Kobashi, T., Grossman, E.L., Yancey, T.E., and Dockery, D.T. (2001) Geology, 29, 983-986.

  16. Transport Properties and Cationic Substitutions in Sr2IrO4

    NASA Astrophysics Data System (ADS)

    Klein, Y.; Terasaki, I.

    2009-07-01

    We realized cationic substitutions in Sr2IrO4 and measured resistivity, thermoelectric power, and the Hall coefficient. A two-carrier model, reflecting the presence of thermally activated carriers at high temperature, qualitatively explains the behavior of the Hall coefficient of Sr1.95La0.05IrO4 in comparison with Sr2IrO4. Concerning the substitution of Ir by different transition metals, Pt with 5 d orbitals does not affect the transport properties, contrary to Ti and Rh with 3 d and 4 d orbitals, respectively. This may be explained by strong spin-orbit coupling involved in Ir and Pt, in comparison with 3 d or 4 d transition metals.

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

    NASA Astrophysics Data System (ADS)

    Moreau, M.; Corrge, T.; Dassi, 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.

  18. (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.

  19. 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

  20. Variation of the Ru moment in the Ca0.3Sr0.7Ru1 - xMnxO3 system

    NASA Astrophysics Data System (ADS)

    Mizusaki, S.; Naito, M.; Taniguchi, T.; Nagata, Y.; Itou, M.; Sakurai, Y.; Noro, Y.; Ozawa, T. C.; Samata, H.

    2010-04-01

    The variation of the magnetic moment on Ru and Mn atoms in the Ca0.3Sr0.7Ru1 - xMnxO3 system was investigated by the magnetic Compton scattering technique using synchrotron radiation. The Ca0.3Sr0.7Ru1 - xMnxO3 system has ferrimagnetism with an antiferromagnetic coupling between Ru and Mn, and the dominant magnetic component changes from ferromagnetic Ru to ferromagnetic Mn at x ~ 0.25 as the Mn substitution proceeds. The mechanism for the change in the magnetism of Ca0.3Sr0.7Ru1 - xMnxO3 is discussed.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  3. 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

  4. Yellow-to-orange emission from B2+-doped RF2 (R = Ca and Sr) phosphors.

    PubMed

    Cao, Renping; Zhang, Fangteng; Liao, Chenxing; Qiu, Jianrong

    2013-07-01

    RF2:Bi (R = Ca and Sr) phosphors were synthesized by solid state reaction method in air and their luminescence properties were investigated. Broad yellow-to-orange emissions peaking at ~550 nm (CaF2:Bi) and ~600 nm (SrF2:Bi) were observed under ~260 nm excitation. The emission centers inRF2:Bi (R = Ca and Sr) phosphors are Bi2+ ions, and the excitation and emission bands of RF2:Bi (R = Ca and Sr) phosphors can be attributed to 2P 1/2 → 2S 1/2 and 2P 3/2(1) → 2P 1/2 transitions of Bi2+ ions, respectively. The phosphors are promising for application in lighting due to broad yellow-to-orange emission. PMID:23842359

  5. Thin films of the Bi2Sr2Ca2Cu3O(x) superconductor

    NASA Technical Reports Server (NTRS)

    Mei, YU; Luo, H. L.; Hu, Roger

    1990-01-01

    Using RF sputtering technique, thin films of near single phase Bi2Sr2Ca2Cu3O(x) were successfully prepared on SrTiO3(100), MgO(100), and LaAlO3(012) substrates. Zero resistance of these films occurred in the range of 90-105 K.

  6. 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.

  7. Bamboo coral skeletal Sr/Ca: An indicator of growth rate or other vital effects?

    NASA Astrophysics Data System (ADS)

    Hill, T. M.; Lavigne, M.; Spero, H. J.; Guilderson, T. P.

    2009-12-01

    Research has demonstrated that intermediate waters (300-2000m) may play an important role in forcing and responding to perturbations to the climate system, via circulation (ventilation), temperature, carbon cycling, and nutrients. Here we investigate the geochemistry of deep-sea bamboo corals, collected on a transect across intermediate water depths (250-2500m) on the California margin. Radiocarbon dating of the calcite skeleton of coral specimens indicates that bamboo corals live for centuries, with growth rates of ~50-100 microns/year, consistent with previous bamboo coral investigations (Roark et al., 2005). Although skeletal Sr/Ca is typically interpreted as a temperature proxy in aragonitic surface corals, it is less clear what factors influence the incorporation of Sr/Ca in calcitic deep sea corals. Recent results indicate that while a strong vital effect is present in bamboo coral stable isotopes (d18O, d13C), Sr/Ca ratios do not covary with isotopic values, indicating different biological or growth factors must control these tracers. Laser ablation ICPMS results from California margin bamboo corals show reproducible Sr/Ca variations in agreement with the timing of PDO shifts for corals collected from different California margin locations. Synchronous coral Sr/Ca and PDO index variability suggest that bamboo coral Sr/Ca trends are related to PDO phase, and may be dictated by surface-driven processes such as food source, quality, or quantity. These results suggest that intermediate waters are impacted by surface water environmental shifts such as changes in productivity and carbon export. Additional work is required to determine whether such shifts in Sr/Ca are apparent through multiple PDO cycles, and to understand the origin of Sr/Ca shifts.

  8. Interlaboratory comparison study of Mg/Ca and Sr/Ca measurements in planktonic foraminifera for paleoceanographic research

    NASA Astrophysics Data System (ADS)

    Rosenthal, Yair; Perron-Cashman, Suzanne; Lear, Caroline H.; Bard, Edouard; Barker, Stephen; Billups, Katharina; Bryan, Martha; Delaney, Margaret L.; Demenocal, Peter B.; Dwyer, Gary S.; Elderfield, Henry; German, Chris R.; Greaves, Mervyn; Lea, David W.; Marchitto, Thomas M.; Pak, Dorothy K.; Paradis, Georges L.; Russell, Ann D.; Schneider, Ralph R.; Scheiderich, Kathleen; Stott, Lowell; Tachikawa, Kazuyo; Tappa, Eric; Thunell, Robert; Wara, Michael; Weldeab, Syee; Wilson, Paul A.

    2004-04-01

    Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg/Ca and Sr/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg/Ca and Sr/Ca ratios showed that the intralaboratory instrumental precision is better than 0.5% for both Mg/Ca and Sr/Ca measurements, regardless whether ICP-OES or ICP-MS is used. The interlaboratory precision on the analysis of standard solutions was about 1.5% and 0.9% for Mg/Ca and Sr/Ca measurements, respectively. These are equivalent to Mg/Ca-based temperature repeatability and reproducibility on the analysis of solutions of ±0.2°C and ±0.5°C, respectively. The analysis of foraminifera suggests an interlaboratory variance of about ±8% (%RSD) for Mg/Ca measurements, which translates to reproducibility of about ±2-3°C. The relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability (about ±1-2°C) and a bias (about 1°C) due to the application of different cleaning methods by different laboratories. Improving the consistency of cleaning methods among laboratories will, therefore, likely lead to better reproducibility. Even more importantly, the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility.

  9. Constraints on Ca/Sr as a Proxy for Calcium in Forest Ecosystems

    NASA Astrophysics Data System (ADS)

    Hoff, C. J.; Hobbie, E. A.; Hallett, R.; Colpaert, J.; Bryce, J. G.

    2004-05-01

    Calcium is a key plant nutrient and important base cation in ecosystems. Our current efforts to quantify Ca cycling in ecosystems rely on indirect proxies, e.g., Ca/Sr or Sr isotopic systems (1). An important assumption in these applications is that the elemental ratio of calcium to strontium faithfully represents calcium cycling and that little fractionation occurs through biogeochemical and physiological processes. However, several researchers have reported variations in Ca/Sr, e.g. among different tree tissues (2) and during weathering processes (3), raising doubts about the suitability of the proxy. To address the question of reliability, we measured Ca/Sr values in a culture study in which Scots pines were grown at low or high nutrient supply rates (3% per day or 5% per day). Because mycorrhizal fungi are intimately involved in plant nutrient supply, plants were also grown either uncolonized or colonized with one of two different species of mycorrhizal fungi (Suillus luteus and Thelephora terrestris). Our preliminary results indicate that Ca/Sr values differ between high and low nutrient treatments, root and foliage, and mycorrhizal treatments. In individual seedlings, roots have lower Ca/Sr than foliage by absolute factors of 2-5. The magnitude of the effect is apparently determined by a combination of environmental factors including both the nutrient and mycorrhizal treatments. These results indicate that Ca and Sr are partitioned differently between nutrient and mycorrhizal treatments and between plant fractions despite the common nutrient broth and substrate. Thus, Ca/Sr values alone are not reliable tracers of Ca within an ecosystem because of partitioning of Ca and Sr during nutrient transport within the plant-mycorrhizal system. We are presently refining analytical techniques and conducting leachate experiments to improve the quantification of this Ca/Sr fractionation. We are also exploring the use of isotopic tracers to study calcium biogeochemical cycling in forest ecosystems. (1) Blum, J.D., et al. 2002. Nature 417: 729-731. (2) Bailey, S.W., et al. 1996. Water Resources Research 32: 707-719. (3) Vitousek, P.M., et al. 1999. Oecologia 121: 255- 259.

  10. High precision measurement of Mg/Ca and Sr/Ca ratios in carbonates by cool plasma quadrupole inductively coupled plasma mass spectrometry

    NASA Astrophysics Data System (ADS)

    Shen, C.; Chui, H.; Chu, M.; Chen, M.; Wei, K.; Steinke, S.

    2004-12-01

    We have developed a high-precision analytical technique using an quadrupole inductively coupled plasma mass spectrometer Agilent 7500s, for simultaneously measuring Mg/Ca and Sr/Ca ratios in carbonates, which are broadly used as environmental and climatic proxies in the Earth Sciences. Cool plasma technique with 650-W RF power was employed to diminish spectral interference. A desolvation introduction system was used to enhance sensitivity, improve detection limit and reduce sample size. Intensities of isotopes, including 24Mg, 43Ca and 86Sr, were all detected in pulse-counting mode. Mg/Ca and Sr/Ca ratios were calculated directly from intensity ratios, 24Mg/43Ca and 86Sr/43Ca, using external matrix-matched standards to correct for instrumental mass discrimination and low-frequency ratio drift. For Mg/Ca analysis, matrix effect of Ca level is 0.018 Mg/Ca (mmol/mol) / [Ca] (ppm). This problem can be overcome by holding [Ca] from 6-8 ppm in sample solution or correcting measured ratio with an empirical formula. Different Sr/Ca also slightly affects Mg/Ca determination with a slope of 0.017 Mg/Ca (mmol/mol) / Sr/Ca (mmol/mol). It is mainly caused by the formation of doubly-charge ion of 86Sr, which biases intensity measurement of 43Ca+ ion beam. This effect brings about only a trivial offset less than 0.1% on Mg/Ca determination for Quaternary foraminiferal and coral samples. Internal precision given by our method ranges 0.1-0.2% (2sd). Replicate measurements made on standards and samples show that external uncertainties of 0.5% and 0.4% (2sd) can be achieved for Mg/Ca and Sr/Ca, respectively. Requirement of a small sample size of only 3.5 microgram carbonate even allows investigating characteristics of single foraminiferal chamber.

  11. Thermoelectric properties of n-type double substituted SrTiO3 bulk materials.

    PubMed

    Cui, Yanjie; He, Jian; Amow, Gisele; Kleinke, Holger

    2010-01-28

    A series of La, Ta double substituted Sr(1-x)La(x)Ti(1-x)Ta(x)O(3), with x = 0.01, 0.05 and 0.10, and La, Nb double substituted Sr(0.90)La(0.10)Ti(0.90)Nb(0.10)O(3) for comparison were investigated in this project. Rietveld refinements were performed to check for purity and symmetry reduction. Electronic structure calculations indicate n-type conduction with steep and flat bands in the vicinity of the Fermi level for x = 0.125. Seebeck coefficient, electrical conductivity, and thermal conductivity measurements on hot-pressed and spark-plasma-sintered samples were performed over a wide range of temperatures. Best results were obtained by spark-plasma-sintering of double substituted Sr(0.99)La(0.01)Ti(0.99)Ta(0.01)O(3) with a thermoelectric figure-of-merit of 0.13 at 660 K. PMID:20066188

  12. Characterization of the Sr(2+)- and Cd(2+)-Substituted Oxygen-Evolving Complex of Photosystem II by Quantum Mechanics/Molecular Mechanics Calculations.

    PubMed

    Pitari, Fabio; Bovi, Daniele; Narzi, Daniele; Guidoni, Leonardo

    2015-09-29

    The Mn4CaO5 cluster in the oxygen-evolving complex is the catalytic core of the Photosystem II (PSII) enzyme, responsible for the water splitting reaction in oxygenic photosynthesis. The role of the redox-inactive ion in the cluster has not yet been fully clarified, although several experimental data are available on Ca2+-depleted and Ca2+-substituted PSII complexes, indicating Sr2+-substituted PSII as the only modification that preserves oxygen evolution. In this work, we investigated the structural and electronic properties of the PSII catalytic core with Ca2+ replaced with Sr2+ and Cd2+ in the S2 state of the Kok−Joliot cycle by means of density functional theory and ab initio molecular dynamics based on a quantum mechanics/ molecular mechanics approach. Our calculations do not reveal significant differences between the substituted and wild-type systems in terms of geometries, thermodynamics, and kinetics of two previously identified intermediate states along the S2 to S3 transition, namely, the open cubane S2 A and closed cubane S2 B conformers. Conversely, our calculations show different pKa values for the water molecule bound to the three investigated heterocations. Specifically, for Cd-substituted PSII, the pKa value is 5.3 units smaller than the respective value in wild type Ca-PSII. On the basis of our results, we conclude that, assuming all the cations sharing the same binding site, the induced difference in the acidity of the binding pocket might influence the hydrogen bonding network and the redox levels to prevent the further evolution of the cycle toward the S3 state. PMID:26346422

  13. 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.

  14. 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.

  15. Study on the site preference of Ca in superconducting oxides Bi{sub 2}Sr{sub 2−x}Ca{sub x}CuO{sub 6+δ} (0.1 ≤ x ≤ 1.0)

    SciTech Connect

    Sun, B.Z.; Zhou, S.L.; Wang, H.; Fei, Z.Y.; Lu, X.M.; Wang, T.L.; Qi, Y.

    2014-01-15

    A series of compound with the nominal composition of Bi{sub 2}Sr{sub 2−x}Ca{sub x}CuO{sub 6+δ} (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were synthesized by the sol–gel method. Constituent phases and crystal structure of samples were analyzed by X-ray diffraction. It can be found that the Ca-doped Bi-2201 system was composed of Bi-2201 phase containing Ca and a small quantity of Bi{sub 16}(Sr,Ca){sub 14}O{sub 38}. For Bi-2201 unit cell containing Ca, chemical component and site preference of Ca atoms were characterized systematically by transmission electron microscopy. With the introduction of Ca atoms, Sr-sites have been occupied partially by Ca{sup 2+} in Bi-2201 unit cell, which leads to a decrease in the lattice parameters c and b of the Bi-2201 phase when the Ca-content x is below 0.6. Two types of new orthorhombic lattices are formed in the substitution. One is a lattice with space group Pma2 as the two nearest neighbor Sr-sites in the same Sr–O layer are occupied by Ca{sup 2+}. Its lattice parameters can be characterized as a = 5.402 Å, b = 5.313 Å and c = 24.272 Å, respectively. When two nearest Sr ions of the second neighboring Sr–O layers are replaced by Ca{sup 2+} ions, the lattice with the space group Pmn2{sub 1} can be formed. Its lattice parameters are close to that of the previous. The modulation vector is lying in the a*–c* plane in the two new orthorhombic lattices (Pma2 and Pmn2{sub 1}). Bi/Ca-2201 lattice (with Ca) and Bi-2201 lattice (without Ca) coexist in the same Bi{sub 2}Sr{sub 2−x}Ca{sub x}CuO{sub 6}+{sub δ} grain, which can be described as an intergrowth structure.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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. CaB6, SrB6, BaB6 and the ternary hexaborides CaxSr1-xB6, CaxBa1-xB6, SrxBa1-xB6 (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 CaB6 (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process.

  18. 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.

  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, and PO4 solutions show greater Sr and Sr-90 incorporation during initial precipitation and less initial mobilization with solutions with low Ca2+ concentration. While all solutions showed nearly the same Sr uptake into apatite (14 to 17% by 2 weeks, 21% to 30% by 5 weeks), the incorporation efficiency (i.e., mM Sr incorporated per mM PO4 injected) was higher for solutions containing citrate. The Sr incorporation rate into apatite during initial precipitation (by 1 month) averaged 4.64 ± 1.9 x 10-4 h-1 (half-life 1500 ± 430 h, 8.85 x 10-7 mg Sr/day/mg apatite). The injection solution used in field injections #3 to #18 (10 mM PO4, 1 mM Ca, 2.5 mM citrate), which is deficient in Ca (a total of 16.7 mM needed to form apatite with 10 mM of PO4), resulted in the initial Sr and Ca peak (24 h) at 4.7x groundwater. By 30 days, the aqueous Sr concentration was 0.28x groundwater and Ca 0.43x groundwater, as both Sr and Ca are used to form initial apatite precipitates. Reactive transport simulation of the complex ion exchange, biodegradation, and precipitation processes showed that the initial Sr groundwater increase mobilized only 1.5% of the Sr mass in sediments. Citrate biodegradation, a necessary step in Ca-citrate-PO4 solutions forming apatite, had an average half-life of 50 h (at aquifer sediment/water ratio and temperature), and decreased an order of magnitude with sediment depth as the microbial biomass decreased five orders of magnitude. The rate of citrate biodegradation was relatively invariant with biomass and water saturation (50% to 100%, for vadose zone infiltration) possibly due to significant microbial injection using river water and subsurface microbial mobilization.

  20. Large magnetothermopower effect in Dirac materials (Sr/Ca)MnBi2

    NASA Astrophysics Data System (ADS)

    Wang, Kefeng; Wang, Limin; Petrovic, C.

    2012-03-01

    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.

  1. 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

  2. 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 values cluster between -0.2 and -0.3; we have few Mg data for these rocks so far, but they appear to be in a similar range. Hence the mantle-derived granitoids have relatively homogeneous Ca and Mg that is slightly enriched in light isotopes relative to mantle rocks. For samples with strong crustal Nd and Sr isotope signatures, there is a wide range of both Ca and Mg isotope ratios, from heavier to lighter than BSE. The δ44Ca values suggest that Ca from ancient marine limestones is a major component of the magma source regions, whereas the δ26Mg values require that pelites provide a substantial amount of the Mg. Considering that both Ca and Mg are minor components of granitic magmas, this result can be understood in terms of the involvement of carbonate-bearing pelitic rock as a major component of the crustal granitic source regions.

  3. 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.

  4. 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.

  5. Investigation of the phase equilibria and phase transformations associated with the Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] superconductor

    SciTech Connect

    Holesinger, T.G.

    1993-01-01

    Compositional measurements of the Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] (2212) solid solution region were performed in the TEM to separate intergrowth and solid solubility effects. Most of the solid solubility is accounted for by changes in the Sr and Ca concentrations. Changes in the Bi concentration account for the rest. Two substitution schemes were determined: the interchange between Sr and Ca and the substitution of Bi for Sr or Ca. It appears to be unfavorable for Sr or Ca to substitute for Bi. The Cu content of the 2212 phases was nearly constant. The 2212 phase was found with 12 other phases, most of which were also solid solutions. Variations in the overall cation stoichiometry and oxygen partial pressure are accommodated by changes in (1) the amount, types, and composition of the secondary phases, (2) the number of intergrowths within the 2212 phase, and/or (3) the solid solution composition of the 2212 phase. Crystallization of nominal 2212 glasses proceeded in two steps with the formation of Bi[sub 2]Sr[sub 2[minus]x]Ca[sub x]CuO[sub y] (2201) and Cu[sub 2]O followed by Bi[sub 2]Sr[sub 3[minus]x]Ca[sub x]O[sub y], CaO, and SrO. The 2212 phase converts from the 2201 phase with increasing temperatures and was kinetically limited by diffusion below 800[degrees]C. At 800[degrees]C and above, a nearly full conversion to the 2212 phase was achieved after only one minute although considerably longer anneal times were necessary for the system to reach equilibrium. An eutectic was determined to separate the 2212/2201 phases that are stable at high oxygen partial pressures from the Bi[sub 2]Sr[sub 3[minus]x]Ca[sub x]O[sub y] (23x) and Bi[sub 2]Sr[sub 2[minus]x]Ca[sub x]O[sub y] (22x) phases present at low oxygen partial pressures. At high oxygen partial pressures, it was found that the separation of CaO in the melt and the initial crystallization of alkaline-earth cuprates resulted in a Bi-rich liquid from which it was impossible to form single-phase 2212.

  6. 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.

  7. 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.

  8. Reduced pressure MOCVD of C-axis oriented BiSrCaCuO thin films

    NASA Technical Reports Server (NTRS)

    Hamaguchi, Norihito; Vigil, J.; Gardiner, R.; Kirlin, P. S.

    1990-01-01

    BiSrCaCuO thin films were deposited on MgO (100) single-crystal substrates by metalorganic chemical vapor deposition at 500 C and 2 torr using fluorinated beta-diketonate complexes of Sr, Ca, and Cu and triphenylbismuth. An inverted vertical reaction chamber allowed uniform film growth over large areas (7.7 cm diameter). The as-deposited films were amorphous mixtures of oxides and fluorides; a two-step annealing protocol (750 C + 850-870 C) was developed which gives c-axis oriented films of Bi2Sr2Ca1Cu2O(x). The postannealed films showed onsets in the resistive transition of 110 K, and zero resistivity was achieved by 83 K. Critical current densities as high as 11,000 A/sq cm were obtained at 25 K.

  9. 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.

  10. Processing Bi-Pb-Sr-Ca-Cu-O superconductors from amorphous state

    NASA Technical Reports Server (NTRS)

    Chiang, C. K.; Freiman, S. W.; Wong-Ng, W.; Hwang, N. M.; Shapiro, A. J.; Hill, M. D.; Cook, L. P.; Shull, R. D.; Swartzendruber, L. J.; Bennett, L. H.

    1990-01-01

    Researchers produced superconducting ceramics of the Bi-Pb-Sr-Ca-Cu-O system started from a glass. To form the glass, the mixed oxide powder was melted at 1200 C in air. The liquid was quenched rapidly by pouring it onto an aluminum plate and rapidly pressing with another plate. The quenched compound was in the form of black amorphous solid, whose x-ray powder pattern has no crystalline peaks. After heat treatment at high temperatures, the glass crystallized into a superconductor. The crystalline phases in the superconductor identified using x-ray diffraction patterns. These phases were that associated with the superconducting phases of T(sub c) = 80 K (Bi2Ca1Sr2Cu2Ox) and of T(sub c) = 110 K (Bi2Ca2Sr2Cu3Ox). The dc resistivity and the ac susceptibility of these superconductors were studied.

  11. 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.

  12. 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.

  13. 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.

  14. Postcontractile force depression in humans is associated with an impairment in SR Ca(2+) pump function.

    PubMed

    Tupling, R; Green, H; Grant, S; Burnett, M; Ranney, D

    2000-01-01

    To investigate the hypothesis that intrinsic changes in sarcoplasmic reticulum (SR) Ca(2+)-sequestration function can be implicated in postcontractile depression (PCD) of force in humans, muscle tissue was obtained from the vastus lateralis and determinations of maximal Ca(2+) uptake and maximal Ca(2+)-ATPase activity were made on homogenates obtained before and after the induction of PCD. Eight untrained females, age 20.6+/-0.75 yr (mean +/- SE), performed a protocol consisting of 30 min of isometric exercise at 60% maximal voluntary contraction and at 50% duty cycle (5-s contraction and 5-s relaxation) to induce PCD. Muscle mechanical performance determined by evoked activation was measured before (0 min), during (15 and 30 min), and after (60 min) exercise. The fatiguing protocol resulted in a progressive reduction (P<0.05) in evoked force, which by 30 min amounted to 52% for low frequency (10 Hz) and 20% for high frequency (100 Hz). No force restoration occurred at either 10 or 100 Hz during a 60-min recovery period. Maximal SR Ca(2+)-ATPase activity (nmol x mg protein(-1) x min(-1)) and maximal SR Ca(2+) uptake (nmol. mg protein(-1) x min(-1)) were depressed (P<0.05) by 15 min of exercise [192+/-45 vs. 114+/-8.7 and 310+/-59 vs. 205+/-47, respectively; mean +/- SE] and remained depressed at 30 min of exercise. No recovery in either measure was observed during the 60-min recovery period. The coupling ratio between Ca(2+)-ATPase and Ca(2+) uptake was preserved throughout exercise and during recovery. These results illustrate that during PCD, Ca(2+) uptake is depressed and that the reduction in Ca(2+) uptake is due to intrinsic alterations in the Ca(2+) pump. The role of altered Ca(2+) sequestration in Ca(2) release, cytosolic-free calcium, and PCD remains to be determined. PMID:10644625

  15. Preferential occupancy and composition-driven c-axis variation in (Pb0.5Cd0.5)(Sr,Y,Ca)3Cu2O7-δ

    NASA Astrophysics Data System (ADS)

    Min, Jinrong; Liang, Jingkui; Chen, Xiaolong; Wang, Cong; Rao, Guanghui; Wu, Fei; Dong, Cheng

    1995-04-01

    The effects of chemical substitution on the crystal structure and superconducting properties of (Pb0.5Cd0.5)(Sr,Y,Ca)3Cu2O7-δ have been studied in (Pb0.5Cd0.5)Sr2(Y1-xCax)Cu2O7-δ, (Pb0.5Cd0.5) Sr2-xY1-u+xCauCu2O7-δ (u=0.0,0.3,0.5), and (Pb0.5Cd0.5) Sr2-xCav+xY1-vCu2O7-δ (v=0.0,0.1,0.3). The single-phase region of (Pb0.5Cd0.5)Sr3-x-yCaxYyCu2O7-δ is 0<=x<=0.5 and 0.8<=y<=1.0. In (Pb0.5Cd0.5)Sr2(Y1-xCax)Cu2O7-δ, the lattice parameter c anomalously decreases while a remains nearly unchanged with the substitution of Ca for Y (0<=x<=0.2). This phenomenon is related to the decrease of the oxygen content. The investigations of (Pb0.5Cd0.5) Sr2-xY1-u+xCauCu2O7-δ (u=0.0,0.3,0.5) reveal that it is difficult for Y to enter the Si site (2h) and Ca can enter the Sr site (2h). The chemical formula of (Pb0.5Cd0.5) Sr2-xY1-u+xCauCu2O7-δ (u=0.3,0.5) for the x>0 sides can be written as (Pb0.5Cd0.5)(Sr2-xCax) (Y1-u+xCau-x) Cu2O7-δ (u=0.3,0.5). Besides, we have also studied the relationships between the lattice parameters and chemical substitution, and found that the substitution of Ca for Sr in the Y site (1d) and Ca for Sr in the Sr site (2h) has different influence on the lattice parameters. The variations of lattice parameters with composition are linear for x<0 or x>0. The Δc/Δx values are -0.12 Å and -0.32 Å for x<=0 and x>=0, respectively.

  16. 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.

  17. 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.

  18. 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.

  19. Claudin-14 regulates renal Ca++ transport in response to CaSR signalling via a novel microRNA pathway

    PubMed Central

    Gong, Yongfeng; Renigunta, Vijayaram; Himmerkus, Nina; Zhang, Jiaqi; Renigunta, Aparna; Bleich, Markus; Hou, Jianghui

    2012-01-01

    The paracellular claudin channel of the thick ascending limb (TAL) of Henle is critical for Ca++ reabsorption in the kidney. Genome-wide association studies (GWASs) have identified claudin-14 associated with hypercalciuric nephrolithiasis. Here, we show that claudin-14 promoter activity and transcript are exclusively localized in the TAL. Under normal dietary condition, claudin-14 proteins are suppressed by two microRNA molecules (miR-9 and miR-374). Both microRNAs directly target the 3′-UTR of claudin-14 mRNA; induce its mRNA decay and translational repression in a synergistic manner. Through physical interaction, claudin-14 blocks the paracellular cation channel made of claudin-16 and -19, critical for Ca++ reabsorption in the TAL. The transcript and protein levels of claudin-14 are upregulated by high Ca++ diet, while downregulated by low Ca++ diet. Claudin-14 knockout animals develop hypermagnesaemia, hypomagnesiuria, and hypocalciuria under high Ca++ dietary condition. MiR-9 and miR-374 transcript levels are regulated by extracellular Ca++ in a reciprocal manner as claudin-14. The Ca++ sensing receptor (CaSR) acts upstream of the microRNA-claudin-14 axis. Together, these data have established a key regulatory role for claudin-14 in renal Ca++ homeostasis. PMID:22373575

  20. 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.

  1. Hole distribution in (Sr,Ca,Y,La){sub 14}Cu{sub 24}O{sub 41} ladder compounds studied by x-ray absorption spectroscopy

    SciTech Connect

    Nu''cker, N.; Merz, M.; Kuntscher, C. A.; Gerhold, S.; Schuppler, S.; Neudert, R.; Golden, M. S.; Fink, J.; Schild, D.; Stadler, S.

    2000-12-01

    The unoccupied electronic structure for the Sr{sub 14}Cu{sub 24}O{sub 41} family of two-leg ladder compounds was investigated for different partial substitutions of Sr{sup 2+} by Ca{sup 2+}, leaving the nominal hole count constant, and by Y{sup 3+} or La{sup 3+}, reducing the nominal hole count from its full value of 6 per formula unit. Using polarization-dependent x-ray absorption spectroscopy on single crystals, hole states on both the chain and ladder sites could be studied. While for intermediate hole counts all holes reside on O sites of the chains, a partial hole occupation on the ladder sites in orbitals oriented along the legs is observed for the fully doped compound Sr{sub 14}Cu{sub 24}O{sub 41}. On substitution of Ca for Sr orbitals within the ladder planes but perpendicular to the legs receive some hole occupation as well.

  2. 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.

  3. 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.

  4. An intensity ratio calibration method for the accurate determination of Mg/Ca and Sr/Ca of marine carbonates by ICP-AES

    NASA Astrophysics Data System (ADS)

    de Villiers, Stephanie; Greaves, Mervyn; Elderfield, Henry

    2002-01-01

    An inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method for the accurate and precise simultaneous measurement of the Mg/Ca and Sr/Ca content of carbonates was established. While a precision of <0.3% (1σ standard deviation (SD)) is easily obtainable for both Mg/Ca and Sr/Ca analysis, a Ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures. An alternative ratio calibration procedure is proposed which overcomes the Ca matrix effects and ensures the accuracy of the Mg/Ca and Sr/Ca analysis of marine carbonates to <0.3%, almost an order of magnitude better than conventional calibration methods. The longer-term precision is <0.1% if the batch run average values are corrected for longer-term drift. The method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples.

  5. Environmental and biological controls on elemental (Mg/Ca, Sr/Ca and Mn/Ca) ratios in shells of the king scallop Pecten maximus

    NASA Astrophysics Data System (ADS)

    Freitas, Pedro S.; Clarke, Leon J.; Kennedy, Hilary; Richardson, Christopher A.; Abrantes, Fátima

    2006-10-01

    The relationship between potential elemental proxies (Mg/Ca, Sr/Ca and Mn/Ca ratios) and environmental factors was investigated for the bivalve Pecten maximus in a detailed field study undertaken in the Menai Strait, Wales, U.K. An age model constructed for each shell by comparison of measured and predicted oxygen-isotope ratios allowed comparison on a calendar time scale of shell elemental data with environmental variables, as well as estimation of shell growth rates. The seasonal variation of shell Mn/Ca ratios followed a similar pattern to one previously described for dissolved Mn 2+ in the Menai Strait, although further calibration work is needed to validate such a relationship. Shell Sr/Ca ratios unexpectedly were found to co-vary most significantly with calcification temperature, whilst shell Mg/Ca ratios were the next most significant control. The temporal variation in the factors that control shell Sr/Ca ratios strongly suggest the former observation most likely to be the result of a secondary influence on shell Sr/Ca ratios by kinetic effects, the latter driven by seasonal variation in shell growth rate that is in turn influenced in part by seawater temperature. P. maximus shell Mg/Ca ratio to calcification temperature relationships exhibit an inverse correlation during autumn to early spring (October to March-April) and a positive correlation from late spring through summer (May-June to September). No clear explanation is evident for the former trend, but the similarity of the records from the three shells analysed indicate that it is a real signal and not a spurious observation. These observations confirm that application of the Mg/Ca proxy in P. maximus shells remains problematic, even for seasonal or absolute temperature reconstructions. For the range of calcification temperatures of 5-19 °C, our shell Mg/Ca ratios in P. maximus are approximately one-fourth those in inorganic calcite, half those in the bivalve Pinna nobilis, twice those in the bivalve Mytilus trossulus, and four to five times higher than Mg/Ca ratios in planktonic and benthonic foraminifera. Our findings further support observations that Mg/Ca ratios in bivalve shell calcite are an unreliable temperature proxy, as well as substantial taxon- and species-specific variation in Mg incorporation into bivalves and other calcifying organisms, with profound implications for the application of this geochemical proxy to the bivalve fossil record.

  6. Rapid analysis of high-precision Sr/Ca ratios in corals and other marine carbonates

    NASA Astrophysics Data System (ADS)

    Schrag, Daniel P.

    1999-04-01

    A method for rapid determination of high-precision Sr/Ca ratios in scleractinian corals is presented. Using an inductively coupled plasma atomic emission spectrophotometer, samples are corrected for instrument drift using a reference solution, similar to the approach used for analysis of stable isotopes using gas-source mass spectrometry. Further correction for variation of the Sr/Ca ratio with Ca concentration is accomplished using internal standards. The precision, once all corrections have been made, is better than 0.1% (relative standard deviation, 1?) for samples of similar Ca concentration and better than 0.2% for samples with variable Ca concentrations. This method increases the sample throughput by approximately a factor of 20 relative to thermal ionization mass spectrometry and significantly reduces instrument and per sample costs. Comparison of Sr/Ca data for a coral from the Galapagos Islands with an instrumental temperature record shows excellent agreement and demonstrates the potential for application of this technique to samples of modern and fossil scleractinian corals and other marine carbonates, including foraminifera.

  7. Effect of Zn substitution for Cu on Ca2-xNaxCuO2Cl2 near the hole concentration of {1}/{8} per Cu

    NASA Astrophysics Data System (ADS)

    Satoh, Kohki H.; Hiraishi, Masatoshi; Miyazaki, Masanori; Takeshita, Soshi; Koda, Akihiro; Kadono, Ryosuke; Yamada, Ikuya; Oka, Kengo; Azuma, Masaki; Shimakawa, Yuichi; Takano, Mikio

    2009-04-01

    A weakening of superconductivity upon substitution of Cu by Zn (0.5-1%) is observed in a high- Tc cuprate, Ca2-xNaxCuO2Cl2, near the hole concentration of {1}/{8} per Cu. The superconducting transition temperature and its volume fraction, estimated by magnetic susceptibility, exhibit a sizable anomaly for x=0.12-0.14, where the slowing down of Cu spin fluctuations below 5 K is demonstrated by muon spin relaxation experiments. These observations are in close resemblance to other typical cuprates including YBa2Cu3O, and Bi2Sr2Ca1-xYxCu2O, providing further evidence that Zn-induced “stripe” correlation is a universal feature of high- Tc cuprate superconductors common to that of La2-xAxCuO4 ( A=Ba, Sr).

  8. 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

  9. 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.

  10. Annealing effects on the properties of BFe2As2 (B = Ca, Sr, Ba) superconducting parents.

    PubMed

    Saparov, Bayrammurad; Sefat, Athena S

    2014-10-28

    The effects of thermal-annealing on the antiferromagnetic (TN) and structural (Ts) transition temperatures of ThCr2Si2-type BaFe2As2 and SrFe2As2 ('122') crystals are reported and compared to that of CaFe2As2. Although the shift in transition temperature for CaFe2As2 can be as high as 75 K, we find modest changes of ∼6 K for BaFe2As2 and SrFe2As2. Such findings are based on the measurements of temperature dependence of electrical resistivity, magnetization, and heat capacity. Residual resistivity ratios show an improvement of crystal quality upon annealing for both BaFe2As2 and SrFe2As2. We confirm the pressure-like influence of annealing on the 122 crystals. PMID:24901039

  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. Nonequilibrium THz Conductivity of Bi2Sr2CaCu2O8+d

    SciTech Connect

    Carnahan, M.A.; Kaindl, R.A.; Orenstein, J.; Chemla, D.S.; Oh,S.; Eckstein, J.N.

    2003-05-27

    Using high sensitivity visible-pump/THz-probe spectroscopywe investigate the dynamics of the complex optical conductivity inoptimally-doped Bi2Sr2CaCu2O8+d films directly after photoexcitation. Thephotoinduced change in the imaginary part, indicative of a reduction inthe superconducting condensate density, saturates at higherlaser-fluences and shows a complete destruction of thecondensate.

  13. Cooper pair formation dynamics in Bi2Sr2CaCu2O8+delta

    SciTech Connect

    Kaindl, R.A.; Carnahan, M.A.; Orenstein, J.; Chemla, D.S.; Oh,S.; Eckstein, J.N.

    2003-11-25

    We utilize ultrafast terahertz pulses to monitor the carrierdynamics in the high-TC superconductor Bi2Sr2CaCu2O8+delta. Thetemperature, density and timedependence distinctly exposes a bimolecularrecombination process of quasiparticles which underlies formation ofCooper pairs.

  14. Modulated structures of the main phase in Bi-Sr-Ca-Cu-O superconductor

    SciTech Connect

    Zhu, J.; Lin, X.W.; Ye, H.Q.; He, A.Q.; Feng, S.Q.; Zhu, X.; Gan, Z.Z.

    1989-02-01

    An important structure characteristic of the main phase in Bi-Sr-Ca-Cu-O superconductor is the modulated structure. In this paper, two types of one dimensional modulation, one type of two-dimensional modulation as well as other modulations have been observed by using TEM and discussed.

  15. 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

  16. 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.

  17. 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

  18. The calibration of D[Sr/Ca]versus sea surface temperature relationship for Porites corals

    NASA Astrophysics Data System (ADS)

    Shen, Chuan-Chou; Lee, Typhoon; Chen, Chi-Yun; Wang, Chung-Ho; Dai, Chang-Feng; Li, Lung-An

    1996-10-01

    Taking advantage of the availability of a continuous sea surface temperature (SST) record at Kenting, southern Taiwan, we have carried out a calibration of D[Sr/Ca]-SST ( D: distribution coefficient) relationships for Porites lobata and P. lutea. Between 22°C ˜ 28°C, the best fitting linear relationships for the two species agree within their respective errors with a maximum deviation less than 0.3°C. Our calibration overlaps with the only published calibration for Porites ( deVilliers et al., 1994) but is somewhat less temperature sensitive. The maximum temperature differences for the two calibrations between 21°C and 27°C are ± 1.2°C. The D-SST relationship calculated using the data of Beck et al. (1992, 1994) and their unpublished seawater data lies between these two calibrations. Our calibration removes some discrepancies previously described in the studies of McCulloch et al. (1994a) on the Great Barrier Reef and of Min et al. (1995) on New Caledonia. We found little growth rate effect on the calibration for P. lutea between 18 mm/yr and 23 mm/yr. We have also monitored the seawater [Sr/Ca] for the entire 1993. The observed variation of 0.033 mmol/mol can cause a temperature artifact of 0.7°C and is thus a dominant error in using this new paleo-thermometer. To carry out this experiment, we have developed a microsurgical technique that can be used to sample corals at better than 0.15 mm resolution. The analytical precision should ultimately allow SST reconstruction of better than 0.2°C. Furthermore, the insensitivity of the calibration against growth rate variation and species differences suggests a promising future for this new thermometer, in contrast to the pessimism of deVilliers et al. (1995). However, inter-laboratory differences and the question of seawater [Sr/Ca] variation need to be addressed first. We recommend a single SST calibration for the Sr/Ca thermometer on coral Porites: Sr/Ca N = 10.286-0.0514 × SST (N: normalized to Hawaii seawater [Sr/Ca] = 8.510 mmol/mol) or D[Sr/Ca] = 1.2077 - 0.006011 × SST.

  19. 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 AS springs (Aq. 2) have parallel profile with total REE concentration from 9 to 98 μg/l. The highest REE concentration (207 μg/l) is observed in slightly acid shallow cold Ca-SO 4 ground waters draining fresh and old pyroclastic deposits rich in magmatic anhydrite. It is suggested that the main mechanism controlling the concentration of REE in waters of El Chichón is the acidity. As low pH results from the shallow oxidation of H 2S contained in hydrothermal vapors, REE distribution in thermal waters reflects the dissolution of volcanic rocks close to the surface or lake sediments as is the case for the crater lake.

  20. Structural phase transition in early growth of Bi2Sr2CaCu2O8+x films on SrTiO3 substrates

    NASA Astrophysics Data System (ADS)

    Abrecht, M.; Ariosa, D.; Onellion, M.; Margaritondo, G.; Pavuna, D.

    2002-02-01

    We used pulsed laser deposition, with a Bi2Sr2CaCu2O8+x target, to grow films ranging from (1/4) to 10 unit cells thick. We studied these films, and reference Bi2Sr2CaCu2O8+x single crystal samples, using angle-integrated photoemission, core level photoemission, and x-ray diffraction. The data indicate that all films exhibit a metallic-like Fermi edge in the photoemission data. More strikingly, a structural phase transition occurs at a nominal Bi2Sr2CaCu2O8+x thickness of approximately one unit cell, converting the precursor Bi2O2.33 highly coherent thin film into a Bi2Sr2CaCu2O8+x structure.

  1. Direct comparison of a Ca+ single-ion clock against a Sr lattice clock to verify the absolute frequency measurement.

    PubMed

    Matsubara, Kensuke; Hachisu, Hidekazu; Li, Ying; Nagano, Shigeo; Locke, Clayton; Nogami, Asahiko; Kajita, Masatoshi; Hayasaka, Kazuhiro; Ido, Tetsuya; Hosokawa, Mizuhiko

    2012-09-24

    Optical frequency comparison of the (40)Ca(+) clock transition ?(Ca)((2)S(1/2-)(2D(5/2), 729 nm) against the (87)Sr optical lattice clock transition ?(Sr) ((1)S(0)-(3)P(0), 698 nm) has resulted in a frequency ratio ?(Ca) / ?(Sr) = 0.957 631 202 358 049 9(2 3). The rapid nature of optical comparison allowed the statistical uncertainty of frequency ratio ?(Ca) / ?(Sr) to reach 1 10(-15) in 1000s and yielded a value consistent with that calculated from separate absolute frequency measurements of ?(Ca) using the International Atomic Time (TAI) link. The total uncertainty of the frequency ratio using optical comparison (free from microwave link uncertainties) is smaller than that obtained using absolute frequency measurement, demonstrating the advantage of optical frequency evaluation. We note that the absolute frequency of (40)Ca(+) we measure deviates from other published values by more than three times our measurement uncertainty. PMID:23037353

  2. 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.

  3. 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}.

  4. Growth of congruently melting Ca0.59Sr0.41F2 crystals and study of their properties

    NASA Astrophysics Data System (ADS)

    Karimov, D. N.; Komar'kova, O. N.; Sorokin, N. I.; Bezhanov, V. A.; Chernov, S. P.; Popov, P. A.; Sobolev, B. P.

    2010-05-01

    Homogeneous crystals of Ca0.59Sr0.41F2 alloy (sp. gr., Fm bar 3 m, a = 0.56057 nm), corresponding to the point of minimum in the melting curve in the CaF2-SrF2 phase diagram, have been grown by the vertical Bridgman method. The optical, mechanical, electrical, and thermophysical properties of Ca0.59Sr0.41F2 and MF2 crystals ( M = Ca, Sr) have been studied and comparatively analyzed. Ca0.59Sr0.41F2 crystals are transparent in the range of 0.133-11.5 μm, have refractive index n D = 1.436, microhardness H μ = 2.63 ± 0.10 GPa, ion conductivity σ = 5 × 10-5 S/cm at 825 K, and thermal conductivity k = 4.0 W m-1 K-1 at 300 K. It is shown that the optical properties of Ca0.59Sr0.41F2 crystals are intermediate between those of CaF2 and SrF2, whereas their mechanical and electrical characteristics are better than the latter compounds.

  5. Variations in Mg/Ca and Sr/Ca ratios of planktonic foraminifera caused by postdepositional dissolution: Evidence of shallow Mg-dependent dissolution

    NASA Astrophysics Data System (ADS)

    Brown, Sarah J.; Elderfield, Henry

    1996-10-01

    A comparative study has been made of two species of planktonic foraminifera, G. tumida and G. sacculifer, in a depth transect on the Ontong Java Plateau, western equatorial Pacific. G. tumida tests from core-top sediments showed decreasing Mg/Ca (2.65-1.25 mmol/mol) and Sr/Ca (1.50-1.16 mmol/mol) ratios with increasing water depth (1600-4400 m), while no such variation was found in G. sacculifer tests in excess of 355 µm (average Mg/Ca, 3.6 mmol/mol, Sr/Ca, 1.4 mmol/mol). Artificial dissolution of G. tumida tests led to a decrease in both Mg/Ca and Sr/Ca, but in G. sacculifer, there was no significant change in the ratios. Analyses by electron microprobe revealed that Mg/Ca of the inner (chamber) calcite in G. tumida tests was much higher than that of the calcite crust (keel), whereas Sr/Ca was only slightly elevated. There were no consistent spatial differences in either Mg/Ca or Sr/Ca for G. sacculifer tests. Dissolution in the oceans gives rise to the removal of the chamber calcite in G. tumida (about 30% of the total calcite), leaving the keel calcite. Although G. tumida is thought of as a dissolution-resistant form, the majority of Mg/Ca and Sr/Ca depletion (and chamber loss) occurs above the lysocline. It is also possible that much of the Mg-enriched gametogenic calcite has been lost by dissolution from G. sacculifer above 1600 m. Mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera. Calculations show that the saturation horizon for Mg-rich parts of tests may be elevated by several hundred meters compared with normal calcite.

  6. Effect of the ionic radius of A-cations on the magnetic and magnetocaloric properties of charge-ordered manganite La0.5Ca0.5- x Sr x MnO3 (0 < x < 0.5)

    NASA Astrophysics Data System (ADS)

    Gamzatov, A. G.; Batdalov, A. B.; Aliev, A. M.; Amirzadeh, P.; Kameli, P.; Ahmadvand, H.; Salamati, H.

    2015-12-01

    The effect of substitution of Sr2+ ions for Ca2+ ions on the magnetic and magnetocaloric properties of a charge-ordered La0.5Ca0.5MnO3 manganite has been studied. The direct and inverse magnetocaloric effects corresponding to the paramagnetic-ferromagnetic and ferromagnetic-antiferromagnetic transitions have been detected. It has been shown that the substitution Ca2+ → Sr2+ leads to the suppression of the charge-ordered phase and to an increase in the Curie temperature T C. The evolution of the destruction of the charge-ordered phase is nonmonotonic, which is associated with the change in the type of antiferromagnetic ordering.

  7. High frequency electromagnetic reflection loss performance of substituted Sr-hexaferrite nanoparticles/SWCNTs/epoxy nanocomposite

    NASA Astrophysics Data System (ADS)

    Gordani, Gholam Reza; Ghasemi, Ali; saidi, Ali

    2015-10-01

    In this study, the electromagnetic properties of a novel nanocomposite material made of substituted Sr-hexaferrite nanoparticles and different percentage of single walled carbon nanotube have been studied. The structural, magnetic and electromagnetic properties of samples were studied as a function of volume percentage of SWCNTs by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometer and vector network analysis. Well suitable crystallinity of hexaferrite nanoparticles was confirmed by XRD patterns. TEM and FESEM micrographs were shown the good homogenity and high level of dispersivity of SWCNTs and Sr-hexaferrite nanoparticles in nanocomposite samples. The VSM results shown that with increasing in amount of CNTs (0-6 vol%), the saturation of magnetization decreased up to 11 emu/g for nanocomposite sample contains of 6 vol% of SWCNTs. The vector network analysis results show that the maximum value of reflection loss was -36.4 dB at the frequency of 11 GHz with an absorption bandwidth of more than 4 GHz (<-20 dB). The results indicate that, this nanocomposite material with appropriate amount of SWCNTs hold great promise for microwave device applications.

  8. Charge localization and magnetocrystalline anisotropy in La, Pr, and Nd substituted Sr hexaferrites

    NASA Astrophysics Data System (ADS)

    Chlan, Vojtěch; Kouřil, Karel; Uličná, Kateřina; Štěpánková, Helena; Töpfer, Jörg; Seifert, Daniela

    2015-09-01

    Charge compensation in strontium M-type hexaferrites Ax3 +Sr1 -xFe12O19(A =La,Nd ,orPr ) is studied by means of calculations of electronic structure and 57Fe nuclear magnetic resonance (NMR) experiments. Two different states are realized in the calculations: a localized scenario as a ground state with the extra valence charge preferentially in the octahedral 2a sites and a delocalized scenario with the charge delocalized over multiple sites. From the calculations and NMR experiments, it is deduced that the localized state Fe2 +(2a) occurs at low temperatures regardless of the type of used substitution and that the distribution of ferric and ferrous ions within the 2a sublattice is static at low temperatures. The magnetocrystalline anisotropy energy of Sr and La hexaferrites is calculated and the contributions of individual Fe sublattices are evaluated. The temperature dependence of the anisotropy for La hexaferrite is explained as a transition between localized and delocalized states causing changes in the single ion contributions of Fe in 2a and also 12k sites.

  9. Structural consideration on the emission properties of Eu²⁺-doped Ba(Sr, Ca)₂MgSi₂O₈

    SciTech Connect

    Yonesaki, Yoshinori

    2013-05-01

    Emission properties of Eu²⁺-doped Ba(Sr, Ca)₂MgSi₂O₈ are discussed in terms of the crystal structure refined by Rietveld method. Ba(Sr, Ca)₂MgSi₂O₈ has glaserite-type layered structure. In response to Sr/(Sr+Ca) ratio, the layer-framework build up by corner-sharing of MgO₆ octahedra and SiO₄ tetrahedra twists around C₃ axes to match the size of B-site cation (Sr²⁺/Ca²⁺). This twist significantly affects the unit cell size and the coordination environment around B-site. Eu²⁺-doped Ba(Sr, Ca)₂MgSi₂O₈ exhibited blue emission under ultraviolet irradiation. The emission spectra have been characterized by two emission components derived from Eu²⁺ ions occupying A- and B-site. Both components showed similar wavelength shift for different Sr/(Sr+Ca), in response to Si–O₁ polarization and to the structural change. - Graphical abstract: Emission properties of Eu²⁺-doped Ba(Sr, Ca)₂MgSi₂O₈ are discussed in terms of the crystal structure refined by Rietveld method. Highlights: • Glaserite-type Ba(Sr, Ca)₂MgS₂O₈ has been prepared by a solid state reaction. • Ba(Sr, Ca)₂MgSi₂O₈ changes the crystal structure, depending on Sr/(Sr+Ca) ratio. • Eu²⁺-doped Ba(Sr, Ca)₂MgSi₂O₈ exhibits blue emission under ultraviolet irradiation. • Emission from Ba(Sr, Ca)₂MgSi₂O₈ is characterized by two Eu²⁺ emission components. • The two emissions show wavelength shift in a similar manner against Sr/(Sr+Ca)

  10. Suppression of superconductivity in orthorhombic La{sub 2-x}M{sub x}CuO{sub 4} (M = Ca,Sr)

    SciTech Connect

    Dabrowski, B.; Wang, Z.; Jorgensen, J.D.; Hitterman, R.L.; Wagner, J.L.; Hunter, B.A.; Radaelli, P.G.; Hinks, D.G.

    1994-05-01

    We have extended the calcium solid-solubility limit in La{sub 2{minus}x} Ca{sub x}CuO{sub 4} to x = 0.2 using synthesis at high oxygen pressure. The superconducting transition temperature increases with doping to 34 K at x = 0.15 and is suppressed for x > 0.15, similar to the Sr-substituted material. At a fixed doping level, the optimum superconducting properties (the highest {Tc}) are found for flat and square CuO{sub 2}planes.

  11. Lazulite and Ba, Sr, Ca, K-rich phosphates-sulphates in quartz veins from metaquartzites of Tribeč Mountains, Western Carpathians, Slovakia: Compositional variations and evolution

    NASA Astrophysics Data System (ADS)

    Uher, Pavel; Mikuš, Tomáš; Milovský, Rastislav; Biroň, Adrian; Spišiak, Ján; Lipka, Jozef; Jahn, Ján

    2009-10-01

    The phosphate-sulphate mineralization occurs in quartz veins in Lower Triassic metaquartzites of the Tribeč Mts., Central Western Carpathians, Slovakia. The mineralization comprises of lazulite, Ba, Sr, Ca, K-rich phosphates-sulphates and barite in an association with muscovite, hematite, locally rutile, zircon, chlorite and tourmaline. The most widespread lazulite forms up to 10 cm large pale to deep blue aggregates in massive quartz. Electron-microprobe analyses show a relatively uniform composition with Mg/(Mg + Fe) =0.85 to 0.93. The Mössbauer spectroscopy reveals 11-30% Fe 3+/Fe total. Possible primary goedkenite-bearthite binary s.s. shows the highest known Sr contents worldwide: Sr/(Sr + Ca) = 0.67-0.71; Mg, Ba and REE contents are negligible. The lazulite is replaced by a secondary association of Ba, Sr, Ca, K-rich phosphates-sulphates: gorceixite, rarely goyazite, crandallite, svanbergite, jarosite and a rare phase, close to (Ba,K,Sr)(Fe 3+,Al) 3[(OH,H 2O) 6(PO 4)(SO 4)] composition (Ba,Fe,S,P-phase). Gorceixite exhibits more restricted compositional variations between gorceixite-goyazite and gorceixite-crandallite s.s.: Ba/(Ba + Sr) = 0.73-0.99, Ba/(Ba + Ca) = 0.78-0.99 and (P - 1)/[(P - 1) + S] = 0.84-0.99. On the contrary, the secondary Sr, Ca-dominant phosphates-sulphates of the crandallite and beudantite groups show wide compositional variations and complex quarternary solid-solution series between goyazite-crandallite and svanbergite-woodhouseite with Sr/(Sr + Ca) = 0.16 to 0.99 and (P - 1)/[(P - 1) + S] = 0.07 to 0.97. The K, Ba-dominant phosphates-sulphates of the alunite and beudantite groups occur along jarosite-Ba,Fe,S,P-phase s.s. line with Ba/(Ba + K) = 0.07 to 0.56, Fe/(Fe + Al) = 0.55 to 0.99, P/(P + S) = 0.14 to 0.57 and elevated Sr and Ca (up to 0.24 and 0.12 apfu, respectively). The compositions indicate a close relationship and mutual substitutions between the crandallite, beudantite and alunite groups. Unlike to analogous phosphate-bearing assemblages in the Alps, investigated phosphate-sulphate association doesn't contains REE, Y and Sc minerals but it is rich in Ba-phases (barite, gorceixite). The peak metamorphic conditions of the host rocks estimated using the Kübler index of phyllosilicates point to anchizone/epizone boundary, i.e. ca. 270-350 °C. Fluid inclusions study constrained the minimum formation temperatures of the lazulite to 144-257 °C and of the superimposed sulphate-phosphate mineralization to 175-289 °C. Lazulite crystallized from brines of the system H 2O-Na-Mg-Cl-CO 2 with a salinity of 17.2 to 19.8 wt.% NaCl eq. We propose, that the studied mineralization originated from fluids enriched in elements from breakdown of feldspars, biotite, apatite and other phosphates in underlying Hercynian granites. The fluids passed upwards into the metaquartzites and precipitated discrete minerals, due to absence of any suitable sink for the elements among rock-forming minerals.

  12. Diagenesis and its impact on Sr/Ca ratio in Holocene Acropora corals

    NASA Astrophysics Data System (ADS)

    Ribaud-Laurenti, A.; Hamelin, B.; Montaggioni, L.; Cardinal, D.

    2001-06-01

    The effect of early diagenesis on Sr/Ca ratios encapsulated in coral skeletons was evaluated by comparing mineralogical, structural and geochemical characteristics of modern and Holocene, branching Acropora colonies. The modern specimens ( Acropora danai, Acropora formosa) come from Réunion island (Western Indian Ocean) and the Great Barrier Reef of Australia respectively. The Sr/Ca ratios of modern specimens range from 9.08 to 9.37 mmol/mol. The fossil acroporids ( Acropora group danai-robusta) were collected from a 50-m core drilled through a barrier reef in Tahiti island; their C-14 ages range from 3,200 to 10,200 calendar years B.P. Fossil skeletons are 100% aragonite. Earlier diagenesis has occurred in the marine environment; it is expressed by growth of secondary inorganic aragonite over primary skeletal aragonite needles, development of syntaxial aragonite cements within intraskeletal cavities and decrease in size of original 1-1,050-µm-wide pores (residual porosity ranges from 25 to 28%), which results in a volume reduction by 34 to 49%. Cementation increases with increasing age of the corals. Later diagenesis has occurred in a mixed marine-freshwater environment. It includes partial dissolution of skeletal and growth of cement aragonite fibres in the form of spherolites, irregular meshes of large squarely terminated laths; this results in an increase in porosity from 30 to 59%. By reference to modern well-preserved acroporids, this diagenetic alteration has led to an increase of Sr/Ca values (from 9.08-9.37 to 8.89-10.55 mmol/mol). This variation in Sr/Ca ratio can be linked to the increase in the amount of Sr-enriched cements relative to the volume of the skeletal aragonite and to a more homogeneous distribution of these cements throughout the skeleton. The uncritical use of Sr/Ca ratios as paleothermometers from diagenetically altered skeletons may cause serious misinterpretations. Accordingly, estimate of the degree of diagenetic alteration in skeletons is a prerequisite to any paleoclimatic reconstruction based on coral records.

  13. A-site substitution effect on physical properties of Sr3Fe2-xCoxO7-δ

    NASA Astrophysics Data System (ADS)

    Tozawa, J.; Akaki, M.; Akahoshi, D.; Kuwahara, H.; Itatani, K.

    2010-01-01

    We have investigated the Ln3+ -substitution (Ln = lanthanoid) effect of a quasi two-dimensional ferromagnet Sr3Fe2-xCoxO7-δ (x = 0.5). With increasing Ln3+-concentration, the ferromagnetism is gradually suppressed and the resistivity is increasing, which are ascribed to an increase in antiferromagnetic (AFM) clusters created by Ln3+-substitution. In Sr2.7Gd0.3Fe1.5Co0.5O7-δ, the magnetoresistance (MR) is enhanced by about 20 % compared with that of Sr3Fe1.5Co0.5O7-δ. Coexistence of ferromagnetic (FM) and AFM phases is essential for the enhancement of the MR. Applied magnetic fields align the FM clusters in the same direction, resulting in a reduction in the resistivity. A metamagnetic transition observed in the Ln3+-doped samples also contributes to the enhancement of the MR.

  14. 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.

  15. Processing Bi-Pb-Sr-Ca-Cu-O superconductors from amorphous state

    NASA Technical Reports Server (NTRS)

    Chiang, C. K.; Wong-Ng, W.; Cook, L. P.; Freiman, S. W.; Hwang, N. M.; Vaudin, M.; Hill, M. D.; Shull, R. D.; Shapiro, A. J.; Swartzendruber, L. J.

    1991-01-01

    The bismuth based high T sub c superconductors can be processed via an amorphous Bi-Pb-Sr-Ca-Cu oxide. The amorphous oxides were prepared by melting the constituent powders in an alumina crucible at 1200 C in air followed by pouring the liquid onto an aluminum plate, and rapidly pressing with a second plate. In the amorphous state, no crystalline phase was identified in the powder x ray diffraction pattern of the quenched materials. After heat treatment at high temperature the amorphous materials crystallized into a glass ceramic containing a large fraction of the Bi2Sr2Ca2Cu3O(x) phase T sub c = 110 K. The processing method, crystallization, and results of dc electrical resistivity and ac magnetic susceptibility measurements are discussed.

  16. 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.

  17. 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

  18. The structural and magnetic properties of Sr-doped multiferroic CaMn7O12

    NASA Astrophysics Data System (ADS)

    Zhang, Hong-Guang; Ma, Xiao-Chen; Xie, Liang

    2015-10-01

    The structural and magnetic properties of Sr-doped multiferroic CaMn7O12 were investigated by X-ray diffraction (XRD), Raman spectra, X-ray absorption spectroscopy and temperature dependence of magnetization. The XRD indicates that the samples are rhombohedral lattice (space group R3¯) with small additional phase Mn3O4. The refined lattice parameters of the main phase increases by the Sr doping. The Raman spectra demonstrate the phonon vibration direction is affected, which is probably due to the rotation of MnO6 octahedral. However, as the valence state of Sr and Ca is same at +2, the samples with doping show nonvariation of peak position at Mn 2p X-ray absorption spectra, indicating that the ratio of Mn3+ and Mn4+ ions is unchanged. And the magnetic transition temperature both at T1 = 90K and T2 = 42K is also not tunable because the amount of magnetic interaction between Mn3+ and Mn4+ is not influenced by doping Sr ion. Only the enhancement of the magnetization at low temperature is observed, which is the same as the effect caused by external magnetic fields. An unsaturated wasp-waist type hysteresis loop is observed, indicating the competition between ferromagnetic-like and antiferromagnetic order.

  19. 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.

  20. 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.

  1. 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 +}.

  2. Investigation into the effect of Si doping on the performance of Sr(1-y)Ca(y)MnO(3-δ) SOFC cathode materials.

    PubMed

    Porras-Vazquez, Jose M; Losilla, Enrique R; Keenan, Philip J; Hancock, Cathryn A; Kemp, Thomas F; Hanna, John V; Slater, Peter R

    2013-04-21

    In this paper we report the successful incorporation of silicon into Sr1-yCayMnO3-δ perovskite materials for potential applications in cathodes for solid oxide fuel cells. The Si substitution onto the B site of a (29)Si enriched Sr1-yCayMn1-xSixO3-δ perovskite system is confirmed by (29)Si MAS NMR measurements at low B0 field. The very large paramagnetic shift (~3000-3500 ppm) and anisotropy (span ~4000 ppm) suggests that the Si(4+) species experiences both Fermi contact and electron-nuclear dipolar contributions to the paramagnetic interaction with the Mn(3+/4+) centres. An improvement in the conductivity is observed for low level Si doping, which can be attributed to two factors. The first of these is attributed to the tetrahedral coordination preference of Si leading to the introduction of oxide ion vacancies, and hence a partial reduction of Mn(4+) to give mixed valence Mn. Secondly, for samples with high Sr levels, the undoped systems adopt a hexagonal perovskite structure containing face sharing of MnO6 octahedra, while Si doping is shown to help to stabilise the more highly conducting cubic perovskite containing corner linked octahedra. The level of Si, x, required to stabilise the cubic Sr1-yCayMn1-xSixO3-δ perovskite in these cases is shown to decrease with increasing Ca content; thus cubic symmetry is achieved at x = 0.05 for the Sr0.5Ca0.5Mn1-xSixO3-δ series; x = 0.075 for Sr0.7Ca0.3Mn1-xSixO3-δ; x = 0.10 for Sr0.8Ca0.2Mn1-xSixO3-δ; and x = 0.15 for SrMn1-xSixO3-δ. Composites with 50% Ce0.9Gd0.1O1.95 were examined on dense Ce0.9Gd0.1O1.95 pellets. For all series an improvement in the area specific resistances (ASR) values is observed for the Si-doped samples. Thus these preliminary results show that silicon can be incorporated into perovskite cathode materials and can have a beneficial effect on the performance. PMID:23420186

  3. 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 litterfall. This observation implicates an uptake flux from an additional source which we attribute to biolifting. We view the heavy exchangeable Ba relative to soil parent values in deeper soils at sites where P is enriched in surface soils, and indeed at all but the wettest site across the climosequence, to represent the complement of an isotopically light Ba fraction removed from these soils by plant roots consistent with the biolifting hypothesis. We further suggest that decreasing heaviness of depth-integrated exchangeable Ba in deeper soils with increasing median annual precipitation across the climosequence reflects greater reliance on shallow nutrient sources as site water balance increases. While the Ca, Sr and Ba isotopes considered together were useful in confirming an important role for nutrient biolifting across the climosequence, the Ba isotopes provided the most robust tracer of biolifting and have the greatest potential to find application as an isotopic proxy for P dynamics in soils.

  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 Central

    Noble, Debbie; Borysova, Lyudmyla; Wray, Susan; Burdyga, Theodor

    2014-01-01

    In the myometrium SR Ca2+ depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca2+ 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 Ca2+-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca2+ 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 [Ca2+]i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca2+ spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca2+ and depolarization continued a point was reached when electrical and Ca2+ spikes and phasic contractions ceased, and a maintained, tonic force and Ca2+ was produced. Lanthanum, a non-selective blocker of store-operated Ca2+ entry, but not the L-type Ca2+ 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 Ca2+ depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca2+ release is coupled to marked Ca2+ entry, via store operated Ca2+ channels, leading to depolarization and enhanced electrical and mechanical activity. PMID:25084623

  5. Chemical interactions between Bi2Sr3CaO7(Bi-2310) and Bi2Sr2Ca0.8Dy0.2Cu2O8 (Bi-2212(Dy))

    NASA Astrophysics Data System (ADS)

    Rahier, S.; Lafort, A.; Henrist, C.; Ausloos, M.; Cloots, R.; Vertruyen, B.

    2006-01-01

    The chemical interactions between Bi2Sr3CaO7 (Bi-2310) and Bi2Sr2Ca0.8Dy0.2Cu2O8 (Bi-2212(Dy)) at 965 °C were investigated by means of: (i) an interdiffusion couple and (ii) layers deposited by dip coating on oxidized nickel substrates. The samples were characterized by optical and electron microscopies, energy-dispersive x-ray (EDX) analysis and x-ray diffraction. It turns out that at the peritectic temperature of Bi-2212(Dy), the Bi-2310 phase reacts with the liquid phase resulting from the peritectic decomposition of the Bi-2212(Dy) phase. Dissolution of Bi-2310 leads to an enrichment in Sr and an impoverishment in Cu of the liquid phase, resulting in a shift of the composition of the insoluble phase towards the Ca-rich end of the (Ca, Sr)O solid solution.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. Crystallization of Bi--Sr--Ca--Cu--O glasses in oxygen

    SciTech Connect

    Holesinger, T.G. Department of Materials Science and Engineering, Ames Laboratory and Iowa State University, 214 Wilhelm, Ames, Iowa 50011 ); Miller, D.J. ); Chumbley, L.S. )

    1992-07-01

    A detailed study of the crystallization process for compositions near Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub {ital y}} was undertaken using differential thermal analysis (DTA), transmission and scanning electron microscopy (TEM and SEM), and x-ray diffraction (XRD). Glasses prepared by a splat-quench technique were free of secondary phases in most cases. A two-step crystallization process in oxygen was observed in which partial crystallization of the glass occurs initially with the nucleation of 2201'' and Cu{sub 2}O, and is completed with the formation of SrO, CaO, and Bi{sub 2}Sr{sub 3{minus}}{sub {ital x}}Ca{sub {ital x}}O{sub {ital y}}. No specific thermal event could be associated with the formation of the 2212'' phase. Rather, formation occurs via conversion of 2201 into 2212. This was a kinetically limited process at temperatures below 800 {degree}C as other phases were found to evolve in addition to the 2212 phase during extended anneals. In contrast, a nearly full conversion to the 2212 phase occurred after only 1 minute of annealing at 800 {degree}C and above. However, changes in resistivity data, secondary phases, and the measured 2212 composition upon extended anneals at 865 {degree}C showed that considerably longer heat treatments were necessary for the sample to reach its equilibrium state.

  12. 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.

  13. 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

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

    USGS Publications Warehouse

    Wong, C.I.; Banner, J.L.; Musgrove, M.

    2011-01-01

    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 4-6weeks. 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 CO2 concentrations. These results are consistent with lower cave-air CO2, 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 caves is likely: (1) speleothem trace-element records may provide seasonal signals, and (2) such records may be biased toward recording climate conditions during the season when calcite is depositing. Additionally, we use our results to construct a forward model that illustrates the types of speleothem Mg/Ca and Sr/Ca variations that would result from varying controls on dripwater compositions. The model provides a basis for interpreting paleo-dripwater controls from high frequency Mg/Ca and Sr/Ca variations for speleothems from caves at which long term monitoring studies are not feasible. ?? 2011 Elsevier Ltd.

  15. 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 caves is likely: (1) speleothem trace-element records may provide seasonal signals, and (2) such records may be biased toward recording climate conditions during the season when calcite is depositing. Additionally, we use our results to construct a forward model that illustrates the types of speleothem Mg/Ca and Sr/Ca variations that would result from varying controls on dripwater compositions. The model provides a basis for interpreting paleo-dripwater controls from high frequency Mg/Ca and Sr/Ca variations for speleothems from caves at which long term monitoring studies are not feasible.

  16. 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 during these intervals, benthic foraminiferal Sr/Ca was affected by similar large-scale variables. One of these variables may be the average marine Sr/Ca ratio; however, comparison with model predictions [H.M. Stoll and D.P. Schrag, Geochim. Cosmochim. Acta 62 (1998) 1107-1118] suggests other factors must also be considered. The discrepancies between the two sites may be related to the different water mass histories for the Caribbean and eastern Atlantic. Our results suggest that variation of the seawater Sr budget only partially contributed to C. wuellerstorfi Sr/Ca records, while other significant factors still need to be quantified. At present we cannot confidently determine past seawater Sr/Ca variation from our foraminiferal records.

  17. An assessment of the Sr/Ca ratio in shallow water hermatypic corals as a proxy for sea surface temperature

    NASA Astrophysics Data System (ADS)

    Marshall, John F.; McCulloch, Malcolm T.

    2002-09-01

    The high precision measurement of the Sr/Ca ratio in corals has the potential for measuring past sea surface temperatures at very high accuracy. However, the veracity of the technique has been questioned on the basis that there is both a spatial and temporal variation in the Sr/Ca ratio of seawater, and that kinetic effects, such as the calcification rate, can affect the Sr/Ca ratio of corals, and produce inaccuracies of the order of 2-4 °C. In the present study, a number of cores of the massive hermatypic scleractinian coral Porites, from the central Great Barrier Reef, have been analyzed for Sr/Ca at weekly to monthly resolution. Results from a 24 year record from Myrmidon Reef show an overall variation from 22.7 °C to 30.4 °C. The record shows a warming/cooling trend with maximum warming centred on the 1986-1987 summer. While some bleaching was reported to have occurred at Myrmidon Reef in 1982, the Sr/Ca record indicates that subsequent summer temperatures were much higher. The 4.5 year record from Stanley Reef shows a maximum SST of 30 °C during the 1997-1998 El Niño event. The calibrations from Myrmidon and Stanley Reefs are in excellent agreement with previously published calibrations from nearby reefs. While corals do not calcify in equilibrium with seawater due to physiological control on the uptake of Sr and Ca into the lattice of coralline aragonite, it can be argued that, provided only a single genus such as Porites sp. is used, and that the coral is sampled along a major vertical growth axis, then the Sr/Ca ratio should vary uniformly with temperature. Similarly, objections based on the spatial and temporal variability of the Sr/Ca activity ratio of seawater can be countered on the basis that in most areas where coral reefs grow there is a uniformity in the Sr/Ca activity ratio, and there does not appear to be a change in this ratio over the growth period of the coral. Evidence from several corals in this study suggest that stress can be a major cause of the breakdown in the Sr/Ca-SST relationship. Thermal stress, resulting from either extremely warm or cool temperatures, can produce anomalously low Sr/Ca derived SSTs as a result of the breakdown of the biological control on Sr/Ca fractionation. It is considered that other stresses, such as increased nutrients and changes in light intensity, can also lead to a breakdown in the Sr/Ca-SST relationship. Two of the main issues affecting the reliability of the Sr/Ca method are the calibration of the Sr/Ca ratio with measured SST and the estimation of tropical last glacial maximum (LGM) palaeotemperatures. Instead of producing a constant calibration, just about every one published so far is different from the others. What is obvious is that for most calibrations while the slope of the calibration equation is similar, the intercepts are not. While the cause for this variation is still unknown, it would appear that corals from different localities around the world are responding to their own particular environment or that certain types of environments exert a control on the corals' physiology. Sr/Ca derived SST estimates for the LGM and deglaciation of 5 °C-6 °C cooler than present are at odds with estimates of 2 °C-3 °C cooling by other climate proxies. The apparent lack of reef growth during the LGM suggests that SSTs were too cold in many parts of the tropics for reefs to develop. This would lend support to the idea that tropical SSTs were much cooler than what the CLIMAP data suggests.

  18. 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

  19. Enhanced dielectric and ferroelectric properties of Ca2+ substituted sodium bismuth titanate

    NASA Astrophysics Data System (ADS)

    Bharti, Chandrahas; Sen, A.; Sinha, T. P.

    2013-02-01

    In order to find the environmental friendly materials for various possible applications in near future, We have synthesized a series of new complex perovskite oxides CaxNa1-x(Bi1/2Ti1/2)O3 (CNBT) (where x = 0.00, 0.25, 0.50 and 0.75) by solid state reaction technique and studied the effect of Ca substitution in Na(Bi1/2Ti1/2)O3 through the microstructure, dielectric and ferroelectric properties. The frequency dependence of the dielectric constant at room temperature shows that the value of dielectric constant increases with Ca2+ substitution at room temperature. The analysis of real part of the dielectric permittivity shows Debye like relaxation with frequency at room temperature. The polarization hysteresis loops plotted at room temperature reveal the ferroelectric property for all compositions of the CNBT samples.

  20. A comprehensive review of the XRD data of the primary and secondary phases present in the BSCCO superconductor system: Part 1, Ca-Sr-Cu oxides

    SciTech Connect

    Reardon, B.J.; Hubbard, C.R.

    1992-01-01

    X-ray powder patterns for the phases in the CaO-SrO-CuO ternary system, along with the corresponding crystal structures, were obtained from the literature and from the Powder Diffraction File (PDF). Available X-ray diffraction (XRD) patterns were compared with each other and, when possible, with a simulated pattern for each phase, yielding a recommended reference pattern. The simulated powder patterns presented here deal with the phases found within the (Ca, Sr)O, (Ca,Sr){sub 2}CuO{sub 3}, (Ca,Sr){sub 14}Cu{sub 24}O{sub 41}, (Ca,Sr)CuO{sub 2}, (Ca,Sr)Cu{sub 2}O{sub 3}, and (Ca,Sr)Cu{sub 2}O{sub 2} solid solution series and are recommended for the PDF.

  1. Multiproxy deglacial record of climate change in central Florida from fresh water ostracodes using paired Mg/Ca, Sr/Ca, and O-18.

    NASA Astrophysics Data System (ADS)

    Hastings, D. W.; Hollweg, T.; Flower, B. P.; Cronin, T. M.; Edgar, N. T.; Quinn, T. M.

    2004-12-01

    An 11.28 m core collected in Tampa Bay, FL reveals lacustrine sediments during the deglacial warming. Mg/Ca, Sr/Ca and O-18 were measured on two species of brackish water ostracodes. Our interpretation is that variations in Sr/Ca reflect changes in water chemistry and Mg/Ca variations reflect changes in both water temperature and chemistry. Applying Sr distribution coefficients results in virtually identical records of (Sr/Ca)_ {water} for both species. (Sr/Ca)water is relatively constant from 20 to 14.1 ka, increases by a factor of two from 14.1 to 12.5 ka. High Sr/Ca values imply increased salinity due to higher evaporation during drier climates and vice-versa. The major trend in Mg/Ca for both species is a doubling of Mg/Ca starting at 13.8 ka with a relative maximum at 12.5 ka. Reliable Mg distribution coefficients as a function of temperature do not exist for these species so we can only infer relative temperature changes. There is a 2.0\\permil decrease in O-18 from 13.7 to 11.5 ka. The overall scenario depicted by these three proxies is a relatively cool and wet climate during the Bolling/Allerod from 14.3 to 13.8 ka, changing to a warmer and drier climate during the Younger Dryas, with the driest and warmest period centered at 12.6 ka. These results will be compared with pollen data from the same core. This contrasts with high latitude pollen and ice core data indicating a cold Younger Dryas. These results support the observation that western tropical Atlantic SST was out-of phase with Greenland climate during the deglaciation.

  2. 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.

  3. 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 with low export efficiency. These data confirm a relationship between coccolith Sr/Ca ratios and productivity. Sr/Ca ratios of the smaller and more slowly sinking Emiliania huxleyi at Bermuda show very small (<4%) seasonal Sr/Ca variations. In contrast, nutrient-limited culture experiments for this species reveal significant (>35%) increases in Sr/Ca with nitrate-stimulated growth rates. The high dominance of E. huxleyi production during bloom events, coupled with suspension of small E. huxleyi coccoliths below the photic zone with very long transport times, appears to attenuate significantly the amplitude of Sr/Ca variations in trap material. Coccoliths from these traps possess low Mg/Ca ratios characteristic of low-Mg calcite, so that higher Mg ratios obtained in some extant coccoliths in cultures are not representative of typical open-ocean coccoliths recovered in sediment trap samples. A significant correlation of Mg/Ca with sea-surface temperature is observed only for H. carteri coccoliths in the Arabian Sea, and not in C. leptoporus in either site.

  4. Modulation of the ferromagnetic insulating phase in Pr0.8Ca0.2MnO3 by Co substitution

    NASA Astrophysics Data System (ADS)

    Harada, T.; Ohkubo, I.; Lippmaa, M.; Matsumoto, Y.; Sumiya, M.; Koinuma, H.; Oshima, M.

    2011-01-01

    Ferromagnetic insulator Pr0.8Ca0.2Mn1-yCoyO3 (0 <= y <= 0.7) thin films were epitaxially grown on (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (100) substrates by pulsed laser deposition. To probe the ferromagnetic insulator state of hole-doped manganites, the Co content dependences of the structural, magnetic, and transport properties were studied. Variation of lattice constant by the substitution of Co ions is well reproduced considering that divalent and trivalent Co ions substitute for Mn ions at the perovskite B-sites. For 0 <= y <= 0.3, the Curie temperature, saturation magnetization, and magnetoresistance increase with increasing Co content, retaining the insulating properties. Detailed analyses of transport and magnetic properties indicate the contribution of both double exchange and superexchange interactions to the appearance of the ferromagnetic insulating phase.

  5. 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.

  6. Excited state absorption measurements of Sm sup 2+ in CaF sub 2 , SrF sub 2 , and SrCl sub 2

    SciTech Connect

    Lawson, J.K.; Lee, H.W.H.; Payne, S.A. ); Boatner, L.A. )

    1991-04-01

    We measured the pump-probe spectrum of the Sm{sup 2+} ion in three materials: CaF{sub 2}, SrF{sub 2}, and SrCl{sub 2}. The onset of the observed prominent excited-state absorption band is consistent with an electrostatic model for impurity levels in a solid-state material. 15 refs., 4 figs., 1 tab.

  7. Nanometer level etching and deposition of Bi-Sr-Ca-Cu-O superconducting thin films

    SciTech Connect

    Sakai, S.; Oohira, T.; Kasai, Y.; Migita, S.; Suzuki, A.

    1996-12-31

    In situ accurate flux monitoring technique utilizing atomic absorption spectroscopy (AAS) for the molecular beam epitaxy (MBE) growth is described. The AAS signal data are calibrated using the inductively coupled plasma spectroscopic technology. The calibration curves are not influenced by variations of both the substrate temperature and ozone flux rate within the range of MBE growth conditions. SrO and CaO are epitaxially grown on SrTiO{sub 3} substrates with RHEED intensity oscillations. This fact becomes another convenient and practically important method for calibrating the AAS data. A method for estimating the ozone flux is also discussed. A gas-laser-etching of Bi-Sr-Ca-Cu-O thin films is carried out by digitally counting an etch process loop. Laser irradiation and NF{sub 3} gas-supply are separately made. At a laser fluence range the etch depth is independent of the laser fluence, suggesting that the etching is limited by the amounts of adsorption gas molecules. The way how the etch depth depends on the etching loop count is intensively investigated. The depth is saturated after etching of a few loops. The surfaces of the etched area are flattened and smoothed. Possible models about the etch depth saturation and surface flattening are discussed.

  8. 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.

  9. Low-temperature synthesis of Bi sbnd Sr sbnd Ca sbnd Cu sbnd O films by photo CVD method

    NASA Astrophysics Data System (ADS)

    Nakabayashi, Masaaki; Shiraishi, Tadashi; Hashimoto, Takuya; Chaudhary, Khaliq A.; Koinuma, Hideomi

    Using purified β-diketonate complexes of copper and alkaline earth metals as well as triphenyl bismuth as source gases, Ca 2CuO 3, SrCuO 2 and c-axis oriented Bi 2Sr 2CuO x and Bi 2Sr 2CaCu 2O x films have been prepared under UV irradiation at temperatures of 500°C and below. UV irradiation has been proved to be effective for the preferential formation of complex oxides rather than carbonates as well as for the improvement of film crystallinity. The temperature dependence of resistivity and morphology of the obtained films are also investigated.

  10. 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. Using a tracer mass balance model, we computed the fraction of K from the mineral source in the total biomass, which decreased with longer growth time and more K supply from the solution source. For Ca, the model results suggested that the mineral was the major source of Ca in the plants throughout the experiment. Comparison of results for above- and below-ground biomass showed significantly higher Ca/Sr and K/Rb ratios above ground, indicating strong fractionation of Ca and K during transport within the tree. Our results highlight the potential importance of species-specific and temporal variations in cation uptake that may require consideration as we work to understand water and nutrient cycles in aggrading forest ecosystems.

  11. Composition, structure, and electrical properties of Bi sub 2 Sr sub 2 Ca sub 1 minus y Y sub y Cu sub 2 O sub 8 : A single-crystal study

    SciTech Connect

    Kendziora, C.; Forro, L.; Mandrus, D.; Hartge, J.; Stephens, P.; Mihaly, L. ); Reeder, R.; Moecher, D. ); Rivers, M.; Sutton, S. )

    1992-06-01

    A systematic study of yttrium substitution for calcium in the high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} has been performed. Single crystals were grown, cleaved, and characterized with use of x-ray fluorescence, electron microprobe, and electron- and x-ray-diffraction techniques. The dc resistivity, diamagnetic shielding, and Hall coefficient of the samples were also measured as functions of the temperature from 4 to 300 K for different dopant concentrations. We conclude that our systematic substitution in the family Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}{ital y}}Y{sub {ital y}}Cu{sub 2}O{sub 8} gives an insight into this high-temperature superconducting material as well as into weak localization and metal-insulator transitions.

  12. Bi2Sr2Ca2Cu3O10+δ based Josephson junctions and SQUIDs

    NASA Astrophysics Data System (ADS)

    Frey, U.; Meffert, H.; Haibach, P.; Üstüner, K.; Jakob, G.; Adrian, H.

    1996-03-01

    Josephson junctions and SQUIDs on SrTiO3 bicrystal substrates were prepared from epitaxial Bi2Sr2Ca2Cu3O10+δ thin films with critical temperatures around 95K. The current-voltage characteristics are well described by the resistively and capacitively shunted junction model. I c R n products of 50μV at 77K and 0.7m V at 4.2K have been reached. The I c (B) dependence is symmetric to B=0 with an I c suppression of 90% in the first minimum. Nevertheless it turns out, that the junctions are inhomogeneous on a μm scale. The flux-voltage transfer function of a SQUID reached 2.7 μV/Ф0 at 78K.

  13. 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

  14. Green-emitting (La,M,Tb)OCl (M = Mg, Ca, and Sr) phosphors

    NASA Astrophysics Data System (ADS)

    Kim, Sun Woog; Jyoko, Kazuya; Masui, Toshiyuki; Imanaka, Nobuhito

    2012-12-01

    Green-emitting (La1-x-yMxTby)OCl (0 ⩽ x ⩽ 0.13, 0.03 ⩽ y ⩽ 0.15, M = Mg, Ca, and Sr) single phase phosphors were synthesized using a liquid-phase method and their photoluminescence properties were characterized. The excitation spectrum consisted of a strong broad band from 220 to 290 nm, which corresponds to the 4f-5d transition of Tb3+. The oxychloride phosphors exhibit typical emission peaks assigned to the transition from 5D4 to 7FJ (J = 6, 5, 4, and 3) of Tb3+, and the luminescence emission intensity was successfully enhanced by doping divalent alkaline earth metal ions (M = Mg2+, Ca2+, and Sr2+) into La3+ sites of the host LaOCl lattice. The highest green emission intensity was obtained for (La0.88Ca0.05Tb0.07)OCl, of which the relative emission intensity was 75% of that for a commercial green-emitting (La0.52Ce0.31Tb0.17)PO4 phosphor.

  15. 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.

  16. 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).

  17. 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.

  18. In vitro performance assessment of new brushite-forming Zn- and ZnSr-substituted beta-TCP bone cements.

    PubMed

    Pina, S; Vieira, S I; Torres, P M C; Goetz-Neunhoeffer, F; Neubauer, J; da Cruz E Silva, O A B; da Cruz E Silva, E F; Ferreira, J M F

    2010-08-01

    The present study investigated the in vitro performance of brushite-forming Zn- and ZnSr-substituted beta-TCP bone cements in terms of wet mechanical strength and biological response. Quantitative phase analysis and structural refinement of the powdered samples were performed by X-ray powder diffraction and Rietveld refinement technique. Initial and final setting times of the cement pastes, measured using Gilmore needles technique, showed that ZnSrCPC sets faster than ZnCPC. The measured values of the wet strength after 48 h of immersion in PBS solution at 37 degrees C showed that ZnSrCPC cements are stronger than ZnCPC cements. Human osteosarcoma-derived MG63 cell line proved the nontoxicity of the cement powders, using the resazurin metabolic assay. PMID:20574977

  19. 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.

  20. 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.

  1. New method for fabrication of superconducting pipes in the Bi-Sr-Ca-Cu-O system

    NASA Astrophysics Data System (ADS)

    Abe, Yoshihiro; Hosono, Hideo; Lee, Won-Hyuk; Hosoe, Masahiro; Nakamura, Koichi; Inukai, Eikichi

    1993-01-01

    Pipes or hollow cylinders in the Bi-Sr-Ca-Cu-O system were found to be fabricated easily by inspiring or sucking the low viscosity melt into a cold silica glass tube. The outer part of the cast rod-like melt solidified, and the inner hot low-viscosity part of the rod melt was expired. The precursor pipes were reheated at 800 C for 50 h in air, resulting in the formation of superconducting (Tc = 87 K) pipes which were of smooth surface without machining and high bending strength (100-150 MPa).

  2. 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.

  3. 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.).

  4. Spectroscopy of LiCa and RbSr Molecules on Helium Nanodroplets

    NASA Astrophysics Data System (ADS)

    Lackner, Florian; Krois, Gunter; Ernst, Wolfgang E.

    2013-06-01

    We report on the investigation of mixed alkali metal (Ak) - alkaline earth metal (Ake) molecules on the surface of helium nanodroplets (He_{N}). These molecules have recently attracted considerable attention as candidates for the formation of ultracold molecules with a magnetic and an electronic dipole moment. In our experiments, LiCa and RbSr molecules are formed in a sequential pick-up process in their X^{2}Σ^{+} ground state and cool down rapidly to the droplet temperature of 0.38 K. Excitation spectra of LiCa and RbSr were recorded by using resonance enhanced multi-photon ionization time-of-flight (REMPI-TOF) spectroscopy and laser induced fluorescence (LIF) spectroscopy. On the helium droplet, vibronic transitions in Ak-Ake molecules are broadened and show a characteristic asymmetric peak form, which is caused by the interaction between the molecule and the superfluid He_{N} environment. For the lower electronic transitions in LiCa and RbSr progressions of vibrational bands excited from the X^{2}Σ^{+} (ν'' = 0) state are observed. The LiCa spectra can be compared to molecular beam experiments, which enables the assignment of three band systems near 15260 cm^{-1}, 19300 cm^{-1} and 22120 cm^{-1} as ^{2}Σ^{+}, ^{2}Π_{Ω} and ^{2}Π band, respectively. In the RbSr excitation spectrum we observe a vibrationally resolved band system near 14020 cm^{-1}. Upon electronic excitation, a fraction of the molecules desorb from the droplet surface and dispersed fluorescence spectra allow to study the X^{2}Σ^{+} ground state and excited states of free Ak-Ake molecules. H. Hara, Y. Takasu, Y. Yamaoka, J.M. Doyle, Y. Takahashi, Phys. Rev. Lett. 106, 205304 (2011) C. Callegari and W. E. Ernst, Helium Droplets as Nanocryostats for Molecular Spectroscopy - from the Vacuum Ultraviolet to the Microwave Regime, in: Handbook of High-Resolution Spectroscopy, eds. M. Quack and F. Merkt, John Wiley & Sons, Chichester, (2011) L. M. Russon, G. K. Rothschopf, M. D. Morse, A. I. Boldyrev, J. Simons, J. Chem. Phys. 109, 6655-6665 (1998)

  5. 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.

  6. 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}.

  7. 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.

  8. Energetics of La{sub 1-x}A{sub x}CrO{sub 3-{delta}} perovskites (A=Ca or Sr)

    SciTech Connect

    Cheng Jihong; Navrotsky, Alexandra . E-mail: anavrotsky@ucdavis.edu

    2005-01-15

    A series of perovskites with the general formula La{sub 1-x}A{sub x}CrO{sub 3-{delta}} (A=Ca or Sr) have been synthesized in the solid solution range 0.0Ca-doped samples, and from -440+/-150 to -290+/-50kJ/mol O{sub 2} for Sr-doped ones. This dependence of enthalpy of oxidation on composition suggests oxygen vacancies are increasingly short-range ordered in reduced samples. The higher oxidation state of chromium is stabilized by the substitution of alkaline earth ions, but with increasing doping, the enthalpy of formation of the fully oxidized sample in both Ca and Sr-doped systems becomes more endothermic. This destabilization effect is attributed to the large endothermic enthalpy of oxygen vacancy formation (395+/-30kJ/mol of V{sub O}{sup ..}) for the reaction A{sub A}{sup x}+O{sub O}{sup x}=A{sub La}{sup '}+0.5V{sub O}{sup ..}+0.5O{sub 2}(A=Ca or Sr) that over-rides the exothermic enthalpies of oxidation. At a given composition, Sr-doped LaCrO{sub 3} is more stable than its Ca-doped counterpart, which is consistent with basicity arguments.

  9. 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 by the calcification rate of the organism. However, the Sr/Ca-temperature relation of our L. pertusa specimens suggest, that mean values are more reliable for temperature reconstruction along a larger temperature range than local high-resolution investigations. Additionally, our results plot on same line of Sr/Ca-temperature relationship like tropical corals indicating a similar behaviour of element incorporation during calcification. References: Adkins JF, Boyle EA (1997) Changing atmospheric ∆14C and the record of deep water paleoventilation ages. Paleoceanography 12:337-344 Blamart D, Rollion-Bard C, Cuif J-P, Juillet-Leclerc A, Lutringer A, Weering Tv, Henriet J-P (2005) C and O isotopes in a deep-sea coral (Lophelia pertusa) related to skeletal microstructure. In: Freiwald A, Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Berlin Heidelberg, p 1005-1020 Cohen AL, Gaetani GA, Lundälv T, Corliss BH, George RY (2006) Compositional variability in a cold-water scleractinian, Lophelia pertusa: New insights into vital effects. Geochemistry, Geophysics, Geosystems 7:Q12004, doi:12010.11029/12006GC001354 López Correa M, Montagna P, Rüggeberg A, McCulloch M, Taviani M, Freiwald A (2008) Trace elements and stable isotopes in recent North Atlantic Lophelia pertusa along a latitudal gradient and from fossil Mediterranean sites. ASLO 2008 Summer Meeting, St. John's, Newfoundland & Labrador, Canada, 08.06.-13.06.2008, p. 47 Lutringer A, Blamart D, Frank N, Labeyrie L (2005) Paleotemperatures from deep-sea corals: scale effects. In: Freiwald A, Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Berlin, Heidelberg, p 1081-1096 Montagna P, López-Correa M, Rüggeberg A, McCulloch M, Rodolfo-Metalpa R, Dullo W-C, Ferrier-Pagès C, Freiwald A, Henderson G, Mazzoli C, Russo S, Silenzi S, Taviani M (2008) Coral Li/Ca in micro-structural domains as a temperature proxy. Goldschmidt Conference, Vancouver, British Columbia, Canada Rüggeberg A, Fietzke J, Liebetrau V, Eisenhauer A, Dullo W-C, Freiwald A (2008) Stable strontium isotopes (delta88/86Sr) in cold-water corals — A new proxy for reconstruction of intermediate ocean water temperatures. Earth and Planetary Science Letters 269:569-574 Shirai K, Kusakabe M, Nakai S, Ishii T, Watanabe T, Hiyagon H, Sano Y (2005) Deep-sea coral geochemistry: Implication for the vital effect. Chemical Geology 224:212-222 Smith JE, Schwarcz HP, Risk MJ (2002) Patterns of isotopic disequilibria in azooxanhtellate coral skeletons. Hydrobiologia 471:111-115 Smith JE, Schwarcz HP, Risk MJ, McConnaughey TA, Keller N (2000) Paleotemperatures from deep-sea corals: Overcoming 'vital effects'. Palaios 15:25-32

  10. Sr-90 Immobilization by Infiltration of a Ca-Citrate-PO4 Solution into the Hanford 100-N Area Vadose Zone

    SciTech Connect

    Szecsody, Jim E.; Fruchter, Jonathan S.; Burns, Carolyn A.; Rockhold, Mark L.; Oostrom, Mart; Williams, Mark D.; Vermeul, Vince R.

    2008-01-11

    This project was initiated to develop a strategy for infiltration of a Ca-citrate-PO4 solution in order to precipitate apatite [Ca6(PO4)10(OH)2] in desired locations in the vadose zone for Sr-90 remediation. Laboratory experiments have demonstrated that infiltration of a Ca-citrate-PO4 solution into sediments at low and high water saturation results in citrate biodegradation and formation of apatite. The citrate biodegradation rate was relatively uniform, in spite of the spatial variability of sediment microbial biomass, likely because of microbial transport processes that occur during solution infiltration. The precipitate was characterized as hydroxyapatite, and the Sr-90 substitution into apatite was shown to have a half-life of 5.5 to 16 months. 1-D and 2-D laboratory infiltration experiments quantified the spatial distribution of apatite that formed during solution infiltration. Slow infiltration in 2-D experiments at low water saturation show the apatite precipitate concentrated in the upper third of the infiltration zone. More rapid 1-D infiltration studies show the apatite precipitate concentrated at greater depth.

  11. Sr-90 Immobilization by Infiltration of a Ca-Citrate-PO{sub 4} Solution into the Hanford 100-N Area Vadose Zone

    SciTech Connect

    Szecsody, J.E.; Fruchter, J.S.; Burns, C.A.; Rockhold, M.L.; Oostrom, M.; Williams, M.D.; Vermeul, V.R.

    2008-07-01

    This project was initiated to develop a strategy for infiltration of a Ca-citrate-PO{sub 4} solution in order to precipitate apatite [Ca{sub 6}(PO{sub 4}){sub 10}(OH){sub 2}] in desired locations in the vadose zone for Sr-90 remediation. Laboratory experiments have demonstrated that infiltration of a Ca-citrate-PO{sub 4} solution into sediments at low and high water saturation results in citrate biodegradation and formation of apatite. The citrate biodegradation rate was relatively uniform, in spite of the spatial variability of sediment microbial biomass, likely because of microbial transport processes that occur during solution infiltration. The precipitate was characterized as hydroxyapatite, and the Sr-90 substitution into apatite was shown to have an incorporation half-life of 5.5 to 16 months. One and two dimensional (1-D and 2-D) laboratory infiltration experiments quantified the spatial distribution of apatite that formed during solution infiltration. Slow infiltration in 2-D experiments at low water saturation show the apatite precipitate concentrated in the upper third of the infiltration zone. More rapid 1-D infiltration studies show the apatite precipitate concentrated at greater depth. (authors)

  12. 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.

  13. 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.

  14. Calculation of the hyperfine structure constants in 43 Ca+ and 87 Sr+

    NASA Astrophysics Data System (ADS)

    Yu, Kai-Zhi; Wu, Li-Jin; Gou, Bing-Cong; Shi, Ting-Yun

    2004-07-01

    A relativistic many-body calculation is performed for the low-lying states of the alkaline earth ions Ca+43 and Sr+87 . The zeroth-order hyperfine structure constants are evaluated with Dirac-Fock wave functions, and the finite basis sets of the Dirac-Fock equation are constructed by B splines. With the finite basis sets, the core polarization and the correlation effect are calculated. The final results for Ca+43 are a(4S1/2)=-805.3MHz , a(4P1/2)=-143.1MHz , a(4P3/2)=-30.5MHz , b(4P3/2)/Q=151.8MHzb-1 , a(3D3/2)=-47.8MHz , b(3D3/2)/Q=68.1MHzb-1 , a(3D5/2)=-3.6MHz , and b(3D5/2)/Q=100.2MHzb-1 . The results for Sr+87 are a(5S1/2)=-1003.2MHz , a(5P1/2)=-178.4MHz , a(5P3/2)=-35.1MHz , b(5P3/2)/Q=274.3MHzb-1 , a(4D3/2)=-47.4MHz , b(4D3/2)/Q=118.2MHzb-1 , a(4D5/2)=2.5MHz , and b(4D5/2)/Q=169.5MHzb-1 .

  15. Structure and refinement of the composition of Bi-Sr-Ca-Cu oxide crystals

    SciTech Connect

    Naumov, D. Yu.; Kozeeva, L. P.; Kameneva, M. Yu.; Kuratieva, N. V.; Podberezskaya, N. V.

    2008-03-15

    The composite structure of the red phase, which accompanies the 2212 and 2201 superconducting phases prepared upon cooling of a melt in the Bi-Sr-Ca-Cu-O system, is revealed by scanning electron microscopy and X-ray diffraction analysis. The matrix component in two crystals I and II under investigation has a monoclinic structure with space group C2/m and the unit cell parameters a = 21.832(2) and 21.8142(9) Angstrom-Sign , b = 4.3809(4) and 4.3771(2) Angstrom-Sign , c = 12.9430(12) and 12.9378(6) Angstrom-Sign , {beta} = 102.832(2) Degree-Sign and 102.839(1) Degree-Sign , and V = 1207.0(2) and 1204.45(9) Angstrom-Sign {sup 3}, respectively. The composition is described by the general formula Bi{sub 4}(Ca{sub 2-x}Sr{sub 1.5+x})O{sub 9.5} with x = 0.13(2) for crystal I and x = 0.19(2) for crystal II. The matrix contains intergrowing clusters of the composition Cu{sub 2}O. It is demonstrated that the presence of the second component is structurally justified by the commensurability of the systems of body-centered subcells of cations in the host matrix and anion sublattices in the structure of the Cu{sub 2}O oxide.

  16. Structure and refinement of the composition of Bi-Sr-Ca-Cu oxide crystals

    SciTech Connect

    Naumov, D. Yu.; Kozeeva, L. P.; Kameneva, M. Yu.; Kuratieva, N. V.; Podberezskaya, N. V.

    2008-03-15

    The composite structure of the red phase, which accompanies the 2212 and 2201 superconducting phases prepared upon cooling of a melt in the Bi-Sr-Ca-Cu-O system, is revealed by scanning electron microscopy and X-ray diffraction analysis. The matrix component in two crystals I and II under investigation has a monoclinic structure with space group C2/m and the unit cell parameters a = 21.832(2) and 21.8142(9) A, b = 4.3809(4) and 4.3771(2) A, c = 12.9430(12) and 12.9378(6) A, {beta} = 102.832(2) deg. and 102.839(1) deg., and V = 1207.0(2) and 1204.45(9) A{sup 3}, respectively. The composition is described by the general formula Bi{sub 4}(Ca{sub 2-x}Sr{sub 1.5+x})O{sub 9.5} with x = 0.13(2) for crystal I and x = 0.19(2) for crystal II. The matrix contains intergrowing clusters of the composition Cu{sub 2}O. It is demonstrated that the presence of the second component is structurally justified by the commensurability of the systems of body-centered subcells of cations in the host matrix and anion sublattices in the structure of the Cu{sub 2}O oxide.

  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. 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-? and Bi1,6Pb0,4Sr2CaCu2O8-?) 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.

  19. Effects of Gd substitution on microstructures and low temperature dielectric relaxation behaviors of SrTiO{sub 3} ceramics

    SciTech Connect

    Fang Liang; Dong Wen; Zheng Fengang; Shen Mingrong

    2012-08-01

    In this paper, Sr{sub 1-3x/2}Gd{sub x}TiO{sub 3} ceramics (0.00 {<=} x {<=} 0.05) were prepared from powders obtained by a sol-gel method. X-ray diffraction results showed that the Gd ion substituted Sr site, and the unit cell volume of doped samples decreased with increasing Gd doping concentrations, which was due to the difference between Sr/Gd ionic radii. Moreover, the structural change also led to an increase in the antiferrodistortive transition temperature. Dielectric properties of all samples were investigated over broad temperature and frequency ranges, and four dielectric relaxation behaviors were identified in different samples. It was found that two intrinsic dielectric relaxation behaviors for the pure SrTiO{sub 3} ceramics could be gradually disappeared with increasing Gd doping concentrations, which was ascribed to the change of domain state induced by Sr vacancies. On the other hand, the other two dielectric relaxation behaviors were induced by Gd doping. The relaxation behavior with activation energy in the range of 100-130 meV was originated from oxygen vacancies, while another relaxation behavior with activation energy in the range of 200-230 meV corresponded to the thermal motions of Ti{sup 4+} ions.

  20. Thermoelectric Properties of Sintered and Textured Nd-Substituted Ca3Co4O9 Ceramics

    NASA Astrophysics Data System (ADS)

    Prevel, Marlène; Reddy, Eddula Sudhakar; Perez, Olivier; Kobayashi, Wataru; Terasaki, Ichiro; Goupil, Christophe; Noudem, Jacques Guillaume

    2007-10-01

    We present the results of low- and high-temperature measurements, from 5 to 800 K, of the electrical resistivity and thermoelectric power of polycrystalline and c-axis-oriented textured samples of Ca3-zNdzCo4O9 (0≤ z≤ 0.9). Crystallographic structure, microstructure and texture analyses of the samples have also been carried out. The substitution of the lighter rare-earth large ionic Nd for Ca results in an increase in the Seebeck coefficient. However, the resistivity of the samples also increases accordingly. In addition, the Hall effect of the polycrystalline Ca3-zNdzCo4O9 sample was studied in the 50-300 K interval. This measurement showed that the variation of Seebeck coefficient and resistivity are caused by a decrease in carrier concentration with Nd content. The decomposition temperatures of the samples with Nd content were observed to increase to values beyond the melting point of Ag, the technically important contact material for the fabrication of thermoelectric modules. The studies on the thermoforged samples indicate that the electrical resistivity of the textured samples decreased by 2.5-fold as compared with that of the conventional sintered samples. The increase in the decomposition temperature and the high Seebeck coefficient with low resistivity in thermoforged samples make the Nd-doped Ca3Co4O9 oxide as one of the candidate materials for high-temperature thermoelectric modules.

  1. 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

  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. Experimental Determination of Sr partitioning and Ca Isotope Fractionation in the CaSO4-NaCl-H2O system

    NASA Astrophysics Data System (ADS)

    Brown, S. T.; DePaolo, D. J.

    2012-12-01

    Anhydrite and gypsum are important, retrograde soluble minerals in geologic environments including mid ocean ridge hydrothermal systems and saline aquifers. Precipitation and/or dissolution of Ca-sulfate phases may control the distribution of stable Ca isotopes and Sr concentrations between fluids and minerals. Considerable research in the CaCO3-H2O system suggests that stable isotope fractionation of Ca between the dissolve pool and precipitating mineral are primarily controlled by the mineral growth rates. The partitioning of Sr appears to be growth rate dependent as well. We designed a series of hydrothermal precipitation experiments to test the idea that similar rate dependent isotope and trace metal fractionation occurs in the CaSO4-H2O system. Experiments were conducted between 110-160C using a titanium Parr mini bench top reactor. Mixtures of CaCl2, SrCl2 and Na2SO4 were dissolved in water and loaded into a Teflon lined vessel. Sealed experiments were purged with nitrogen gas for approximately 20 minutes to create a CO2-free environment. Experiments were rapidly charged to approximately 250 psi and heated to the desired run temperature. Experiment duration was between 36 and 360 hours. Completed experiments were depressurized and solid run products were recovered by filtration. Fluid samples from the beginning and end of each experiment were preserved for elemental and isotopic measurements. Preliminary results for experiments with CaSO4 supersaturation ~10 have thin needle-like crystals of mixed gypsum-bassanite-anhydrite based on SEM and XRD analysis. Sr distribution coefficients range between 0.48-0.74, greater than published equilibrium values, while D44Ca = 0.7-1.1 per mil, similar to low temperature carbonates.

  4. I-STAL, a model for interpretation of Mg/Ca, Sr/Ca and Ba/Ca variations in speleothems and its forward and inverse application on seasonal to millennial scales

    NASA Astrophysics Data System (ADS)

    Stoll, Heather M.; Müller, Wolfgang; Prieto, Manolo

    2012-09-01

    Trace element ratios Mg/Ca, Sr/Ca, and Ba/Ca are readily measured in speleothems and may be closely related to hydrological balance, enhancing paleoclimate information inferred from stable isotope measurements. We develop a model which simulates the variation in dripwater chemistry resulting from variable degree of water-rock interaction and prior calcite precipitation (PCP), with the latter process depending both on drip interval and drip oversaturation with respect to CaCO3. Partition coefficients between speleothem and dripwater are dependent on temperature for Mg and on speleothem growth rate for Sr and Ba, as observed in laboratory experiments. The drip oversaturation state, regulated both by cave pCO2 and the dilution and soil karst dissolution processes, strongly affects stalagmite trace element concentrations by modulating the extent of PCP and speleothem growth rates. Application of an inverse model confirms that seasonal CO2 cycles can explain the uncorrelated seasonal cycles in Mg/Ca and Sr/Ca observed in our speleothem records from NW Spain for which high CO2 coincides with dry season. In absence of seasonal variations in drip interval, cycles in cave pCO2 can produce seasonal covariation in Sr/Ca, Mg/Ca and Ba/Ca. In long time series (104 yr) where seasonal sampling resolution is not obtained in stalagmites, a change from dominance of summer to winter rainfall can shift the season of strongest stalagmite deposition to one of lower mean CO2 and hence greater PCP and higher Mg/Ca, Sr/Ca and Ba/Ca ratios. Caves best suited to record a dominantly water balance signal, such as mean drip intervals, are those with minimal seasonal variation in cave pCO2.

  5. 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

  6. Average and local structure of the Pb-free ferroelectric perovskites (Sr,Sn )TiO 3 and (Ba ,Ca ,Sn )TiO3

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The characteristic structural off-centering of Pb2 + in oxides, associated with its 6 s2 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 different 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. We find that even at these small 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.

  7. 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.

  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 tunneling conductance inside the unit cell of Bi 2Sr 2CaCu 2O 8

    NASA Astrophysics Data System (ADS)

    Guo, J.; Jiang, J. F.; Cai, Q. Y.

    2000-11-01

    We model the unit cell of Bi 2Sr 2CaCu 2O 8 as six equally spacing layers based on the layered nature of the material and solve the Hamiltonian matrix of the system in Nambu representation. The tunneling current through the junction between Cu sbnd O planes in the unit cell is calculated and then differentiated to obtain the tunneling conductance. Our calculation results indicate that the conductance has peak values near double energy gap and characteristic fine structures. The results may be applied for accurate calculation of behaviors of single-electron devices made by unit cells of Bi 2Sr 2CaCu 2O 8.

  10. 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.

  11. Thermoelectric Properties of p-type La2-xMxCuO4 (M = Ca, Sr, Ba) Thin Films Prepared by Pulsed Laser Deposition Method

    NASA Astrophysics Data System (ADS)

    Yoshida, Yutaka; Yoshikawa, Tomoki; Ichino, Yusuke; Takai, Yoshiaki

    La2-xMxCuO4 (LMCO:M=Ba, Sr, Ca) thin films were deposited on SrTiO3 (100) substrates by pulsed laser deposition method. From the X-ray diffraction (XRD) patterns, the SCCO (Sm2-xCexCuO4) thin films on the SrTiO3(STO) substrate were confirmed that c-axis was parallel to the substrate normal and in-plane alignment was cube-on-cube for the substrate. The Seebeck coefficient and the resistivity decreased with the increasing an amount of M-element substitution. We calculated the power factor from these values and found that the highest value of 1.2 mW/mK2 at 330 K was achieved by the La2-xSrxCO thin film with x = 0.02. This value was almost equal to the reported value in Bi2Te3 film at room temperature. High power factor values in low temperature demonstrate the potential of RE2CuO4 system for the thermoelectric device.

  12. Inducing structural collapse and superconductivity in CaFe2As2 by systematic substitutions of rare earths

    NASA Astrophysics Data System (ADS)

    Saha, Shanta; Drye, Tyler; Butch, Nicholas; Hu, Rongwei; Kirshenbaum, Kevin; Ziemak, Steven; Paglione, Johnpierre; Zavalij, Peter; Lynn, Jeffrey

    2012-02-01

    Recently, we have reported structural collapse and 47 K superconductivity in CaFe2As2 by aliovalent rare earth substitutions for Ca atoms [1]. We will present the evolution of structural and superconducting properties in single crystals of CaFe2As2 by systematic substitutions of R (=La, Ce, Pr, and Nd) for Ca, causing electron doping that is indirect to FeAs layer. Effect of annealing, growth method, etching, and pressure on Ca1-xRxFe2As2, indicating the intrinsic nature of this high Tc superconductivity, the highest in 122 Fe-based materials, will be discussed. Ref. [1] S. R. Saha et al. arXiv:1105.4798.

  13. Impurity Substitution Effect on Magnetoelectric Properties of CaBaCo4O7 Crystals

    NASA Astrophysics Data System (ADS)

    Oda, Ryosuke; Kajihara, Ryo; Nishina, Kosuke; Akaki, Mitsuru; Kuroe, Haruhiko; Kuwahara, Hideki

    We have investigated effects of impurity substitution of Fe for Co sites on magnetic and dielectric properties in CaBa(Co1-xFex)4O7 crystals in magnetic fields. The non-doped compound, CaBaCo4O7 with the polar space group Pbn21, shows a large change of electric polarization ΔP along the c axis below a ferrimagnetic transition temperature. With increasing x, the transition temperatures for the ferrimagnetic and ferroelectric-like phases are shifted towards lower and these phases are completely collapsed above x=1.56%. We have also investigated the magnetic field effects for CaBa(Co1-xFex)4O7 crystal with a doping level x=0.5% where the ferrimagnetic and ferroelectric-like phases sustain. Then a relatively large magnetocapacitance, Δɛ(H)/ɛ(0) tbnd6 [ɛ(H) - ɛ(0)]/ɛ(0), of 45% at 58 K was observed, which is not significantly reduced from the parent compound.

  14. FT-Raman and infrared spectroscopic study of aragonite-strontianite (Ca xSr 1 - xCO 3) solid solution

    NASA Astrophysics Data System (ADS)

    Alía, J. M.; de Mera, Y. Díaz; Edwards, H. G. M.; Martín, P. González; Andres, S. López

    1997-11-01

    Synthetic aragonite-strontianite solid-solution samples have been studied using dispersive IR and FT-Raman spectroscopy. In addition to the end-members, nine samples over a range of composition from Ca 0.9Sr 0.1CO 3 to Ca 0.1Sr 0.9CO 3 were analysed. Carbonate anion internal modes are examined in detail by means of band-shape analysis and component fitting procedures. Positional disorder induced by the random cationic substitution results in strong increase of the halfwidth in several vibrational bands. Results obtained for the doubly degenerate modes (antisymmetric stretching and bending, ν3 and ν4) reveal the presence of three components both in the IR antisymmetric stretching band as well as in the Raman antisymmetric bending band. These observations are interpreted in terms of an overtone 2 ν4 in possible Fermi resonance with the corresponding ν3 fundamental in the IR spectra, and the presence of Davidov (factor group) splitting in the FT-Raman ν4 band. Lattice modes in the FT-Raman spectra demonstrate weaker cohesion between the cation/carbonate/cation layers in aragonite ( synth) than in strontianite ( synth).

  15. Two-dimensional Dirac fermions and quantum transport in (Sr/Ca)MnBi2

    NASA Astrophysics Data System (ADS)

    Wang, Kefeng; Graf, D.; Wang, Limin; Lei, Hechang; Tozer, S. W.; Petrovic, Cedomir

    2012-02-01

    We report two dimensional Dirac fermions and quantum transport behavior in single crystals of SrMnBi2 and CaMnBi2. The non-zero Berry's phase, small cyclotron resonant mass and first-principle band structure suggest the existence of the Dirac fermions in the Bi square nets. Angular dependent magnetoresistance and quantum oscillations suggest dominant two-dimensional (2D) Fermi surfaces. The in-plane transverse magnetoresistance exhibits a crossover at a critical field B^* from semiclassical weak-field B^2 dependence to the high-field unsaturated linear magnetoresistance (˜120% in 9 T at 2 K) due to the quantum limit of the Dirac fermions. The temperature dependence of B^* satisfies quadratic behavior, which is attributed to the splitting of linear energy dispersion in high field. Our results demonstrate the universal existence of two dimensional Dirac fermions in different materials with Bi square nets.

  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. Bipolar resistive switchings in Bi2Sr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Tulina, N. A.; Borisenko, I. Yu; Sirotkin, V. V.

    2013-09-01

    Investigations of bipolar resistive switchings in Bi2Sr2CaCu2O8+δ single crystal heterostructures are reported. The current-voltage characteristics of heterocontacts with switching effects exhibit a diode nature with Schottky-like barriers on high doped semiconductors. In this case the carrier tunneling processes are responsible for the current transfer in the structure. The voltage of switching into the metastable state is determined by barrier-controlled carrier tunneling. Spatial carrier inhomogeneity produces a field influence on the potential barrier in the interface of heterostructures with the BRS effect, redistribution of carriers and first order phase transition in the phase separation system. The numerical simulation method was used to consider the influence of inhomogeneous electrical field distribution in the heterocontact interface on the BRS effect in the oxide compounds.

  18. 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.

  19. Preparation of high density superconducting ceramics in the Bi-Sr-Ca-Cu-O system. IV

    NASA Astrophysics Data System (ADS)

    Sato, H.; Zhu, W.; Miller, M. M.; Ishiguro, T.; Shindo, D.

    Preparation of high-Tc superconductors in the Bi-Sr-Ca-Cu-O system from amorphous precursors obtained by quenching from melts offers special advantages over the conventional sintering technique in that high-density materials can easily be obtained, the control of phases by heat treatment is easier, etc. Growth of high-Tc phase occurs in elongated platelets in a direction parallel to the basal plane of the structure. The n = 2 and the n = 3 structures intergrow in a microsyntactic fashion. For specimens with high Cu contents, all structural variants known to exist in this system (the n = 1, the n = 2, and the n = 3 structures) can be prepared at the same composition by different heat treatments. Also, Tc does not seem to have any specific relation with the structure, but it still is sensitive to the atmosphere of heat treatment. Relations of Tc to Cu content and the hole content are suggested.

  20. Vortex matter in Bi2Sr2CaCu2O8 with pointlike disorder

    NASA Astrophysics Data System (ADS)

    Konczykowski, M.; van der Beek, C. J.; Koshelev, A. E.; Mosser, V.; Li, M.; Kes, P. H.

    2009-03-01

    We investigate the effect of point-like disorder, introduced by irradiation with 2.3 MeV electrons, on the mixed state phase diagram of Bi2Sr2CaCu2O8 single crystals. We focus on the higher irradiation doses that produce a significant depression of the critical temperature Tc, to as low as 2/3 of the initial value. Surprisingly, the first order phase transition (FOT) of the vortex ensemble, from a crystal to the pancake vortex liquid, persists in those highly disordered samples. The second peak in the irreversible magnetization, observed at low temperatures, is equally observed after high irradiation doses, but at much lower magnetic fields. A simple scaling of the phase diagram for samples with various degrees of disorder is not possible, indicating that several fundamental parameters of the superconductor are affected. From the analysis of the angular dependence of the FOT, we deduce that the effective anisotropy factor increases after irradiation.

  1. LFZ growth of (Bi,Pb)--Sr--Ca--Cu--O superconducting fibers

    SciTech Connect

    de la Fuente, G.F.; Navarro, R.; Lera, F.; Rillo, C.; Bartolome, J.; Badia, A. ); Beltran, D.; Ibanez, R.; Beltran, A. ); Sinn, E. )

    1991-04-01

    Powder x-ray diffraction, d.c. and a.c. susceptibilities, and SEM have been used to study (Bi{sub 1{minus}{ital x}}Pb{sub {ital x}}){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+{delta}} fibers grown by the Laser Floating Zone method. The well-oriented, long-grained superconductor fiber properties are shown to be highly dependent on the partial pressure of oxygen in the growth atmosphere, as well as on fiber pulling rate. Slowly grown fibers contain initially the 2212 (80 K) phase; the 2223 (110 K) phase also appears upon annealing in air. Faster growth rates result in fibers that contain a mixture of the 2212 and 2201 phases and, in this case, long annealing procedures are necessary to observe the 2223 phase.

  2. 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.

  3. Quaternary system SrO-CaO-BaO-CuO at 950 C. 1: Phase relationships in the limiting ternary system SrO-CaO-CuO

    SciTech Connect

    Lebbou, K.; Abraham, R.; Trosset, S.; Cohen-Adad, M.T.; Jorda, J.L.

    1997-08-01

    Knowledge of the succession of phases in dependence on composition and temperature is essential in order to control the formation of pure superconducting thallium-based cuprates (Tl/Pb){sub m}Sr{sub 2}Ca{sub n{minus}1}Cu{sub n}O{sub x}. Mixtures (Sr/Ba)O-CaO-CuO are used as precursors in their elaboration. In the first stage of their investigation, the ternary system SrO-CaO-CuO has been reinvestigated at 950 C, in order to determine precisely the phase relationships in the ternary subsystem. In the second stage, the study will be extended to the quaternary BaO-SrO-CaO-CuO system. The present paper reports the results concerning the polyphased fields in the ternary system under isothermal conditions at 950 C under 1 bar of oxygen. A comparison with literature data shows that new domains are observed. Solid phases mentioned in the literature are confirmed, but the observed three phases equilibria are not the same.

  4. 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 in vascular smooth muscle [Ca2+]i that could underlie both phases of its effects on tension in isolated aortas and may be explained by the following model: an initial outward shift in current causes hyperpolarization with a consequent decrease in cell excitability, and the somewhat slower increase in Ca2+ channel excitability eventually leads to enhanced calcium influx and tension. These data shed light on possible mechanisms underlying gender-related differences in VSMC physiology. PMID:8761027

  5. DHPR activation underlies SR Ca2+ release induced by osmotic stress in isolated rat skeletal muscle fibers

    PubMed Central

    Pickering, James D.; White, Ed; Duke, Adrian M.

    2009-01-01

    Changes in skeletal muscle volume induce localized sarcoplasmic reticulum (SR) Ca2+ release (LCR) events, which are sustained for many minutes, suggesting a possible signaling role in plasticity or pathology. However, the mechanism by which cell volume influences SR Ca2+ release is uncertain. In the present study, rat flexor digitorum brevis fibers were superfused with isoosmotic Tyrode's solution before exposure to either hyperosmotic (404 mOsm) or hypoosmotic (254 mOsm) solutions, and the effects on cell volume, membrane potential (Em), and intracellular Ca2+ ([Ca2+]i) were determined. To allow comparison with previous studies, solutions were made hyperosmotic by the addition of sugars or divalent cations, or they were made hypoosmotic by reducing [NaCl]o. All hyperosmotic solutions induced a sustained decrease in cell volume, which was accompanied by membrane depolarization (by 14–18 mV; n = 40) and SR Ca2+ release. However, sugar solutions caused a global increase in [Ca2+]i, whereas solutions made hyperosmotic by the addition of divalent cations only induced LCR. Decreasing osmolarity induced an increase in cell volume and a negative shift in Em (by 15.04 ± 1.85 mV; n = 8), whereas [Ca2+]i was unaffected. However, on return to the isoosmotic solution, restoration of cell volume and Em was associated with LCR. Both global and localized SR Ca2+ release were abolished by the dihydropyridine receptor inhibitor nifedipine by sustained depolarization of the sarcolemmal or by the addition of the ryanodine receptor 1 inhibitor tetracaine. Inhibitors of the Na-K-2Cl (NKCC) cotransporter markedly inhibited the depolarization associated with hyperosmotic shrinkage and the associated SR Ca2+ release. These findings suggest (1) that the depolarization that accompanies a decrease in cell volume is the primary event leading to SR Ca2+ release, and (2) that volume-dependent regulation of the NKCC cotransporter contributes to the observed changes in Em. The differing effects of the osmotic agents can be explained by the screening of fixed charges by divalent ions. PMID:19398777

  6. Scanning tunneling spectroscopy of 3d transition metal oxides and superconductivity of Bi-Sr-Ca-Cu-O artificial lattices

    SciTech Connect

    Kanai, Masaki; Kawai, Tomoji

    1996-12-31

    The density of states (DOS) near the Fermi level (E{sub F}) has been observed by scanning tunneling spectroscopy (STS) of La{sub 2{minus}x}Sr{sub x}CuO{sub 4} and La{sub 2{minus}x}Sr{sub x}NiO{sub 4} thin films. In La{sub 2{minus}x}Sr{sub x}CuO{sub 4}, the DOS around E{sub F} gradually appears with tailing both from the conduction band and the valence band edges accompanied with the increase of carrier concentration. Compared with cuprate thin films, the DOS variation of la{sub 2{minus}x}Sr{sub x}NiO{sub 4} with carrier increase is slow and no clear differences in the STS are observed in the region with 0.15 < x < 0.5 in the nickelate. However, the DOS of heavily doped La{sub 2{minus}x}Sr{sub x}NiO{sub 4} with x > 1.0 is quite similar to that of doped cuprates. Systematic investigation of superconducting transition temperatures ({Tc}) has been performed on the Bi{sub 2}O{sub 2}/SrO-inserted infinite-layer lattices, Bi{sub 2}O{sub 2}/SrO + (Ca{sub 1{minus}x}Sr{sub x}CuO{sub 2}){sub n}, with n = 2 to 10. The n dependence of {Tc} varies depending upon the Sr/Ca ratio at alkaline earth metal sites. The observed results are explained by the prediction based on inter-layer effect between two-dimensional resonating valence bond sheets.

  7. Thermoelectric properties of Al substituted misfit cobaltite Ca3(Co1- x Al x )4O9 at low temperature

    NASA Astrophysics Data System (ADS)

    Liu, Yi; Chen, Hong-mei; Hu, Jin-lian; Tang, Xu-bing; Li, Hai-jin; Wang, Wei

    2014-07-01

    Thermoelectric properties of Al substituted compounds Ca3(Co1- x Al x )4O9 ( x = 0, 0.03, 0.05), prepared by a sol-gel process, have been investigated in the temperature range 305-20 K. The results indicate that after Al substitution for Co in Ca3(Co1- x Al x )4O9, the direct current electrical resistivity and thermopower increase due to the reduction of carrier concentration. Experiments show that Al substitution results in decreased lattice thermal conductivity. The figure of merit of temperature behavior suggests that Ca3(Co0.97Al0.03)4O9 would be a promising candidate thermoelectric material for high-temperature thermoelectric application.

  8. 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

  9. Microdistribution of Mg/Ca, Sr/Ca, and Ba/Ca ratios in Pulleniatina obliquiloculata test by using a NanoSIMS: Implication for the vital effect mechanism

    NASA Astrophysics Data System (ADS)

    Kunioka, Daisuke; Shirai, Kotaro; Takahata, Naoto; Sano, Yuji; Toyofuku, Takashi; Ujiie, Yurika

    2006-12-01

    The Mg/Ca ratio within foraminiferal calcareous tests (shells) is widely used to reconstruct past seawater temperature. However, recent studies reported that the organic components within a test affect the Mg/Ca distribution. In this study, we have measured the Mg/Ca, Sr/Ca, and Ba/Ca ratios within the planktonic foraminifera Pulleniatina obliquiloculata by using a NanoSIMS (secondary ion mass spectrometer (SIMS)), which has excellent spatial resolution (˜1 μm) and allows us to compare the distribution of chemical compositions with that of the organic components. Element compositions show banding distributions composed of alternately higher and lower values of those elemental ratios. The Mg/Ca ratios, previously considered to be mainly controlled by calcification temperature, show larger variations than the values expected from the seawater temperature at the habitat depth of P. obliquiloculata. Comparison of the elemental distribution with the test microstructure reveals that the bands of high Mg/Ca and Sr/Ca ratios correspond with layers of the organic components. Such coincidence suggests that the organic components strongly affect the Mg/Ca and Sr/Ca ratios within a test. In spite of the heterogeneous distribution, temperature estimated from the averaged Mg/Ca ratio within a test is consistent with seawater temperature at the habitat depth of P. obliquiloculata, indicating that whole Mg/Ca ratio of foraminiferal test may be useful as paleotemperature proxy. In contrast to the Mg/Ca ratio the heterogenity in Ba/Ca ratio, which previously has been considered to be mainly controlled by the ambient seawater composition, is not fully matched with the layers of the organic compositions. Although the organic components concentrate Ba, other unknown factors appear to also cause heterogenity in Ba incorporation.

  10. 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.

  11. 1H NMR, 31P NMR and Raman Study of CaHPO4 and SrHPO4

    NASA Astrophysics Data System (ADS)

    Louati, B.; Guidara, K.; Gargouri, M.; Fourati, M.

    2005-02-01

    CaHPO4 and SrHPO4 were investigated using Raman, 1H NMR and 31P NMR techniques to study the environment of their PO3-4 tetrahedra and the percentage of mobile protons. 1H NMR spectra at room temperature suggest the presence of three types of protons, in agreement with RX investigation. The percentage of mobile protons in SrHPO4 is greater than in CaHPO4 because Sr2+ is bigger than Ca2+. 31P NMR spectra at room temperature show two lines in the spectrum of SrHPO4, revealing an equal environment of two sets of pairs of PO3- 4 . The 31P NMR spectrum of CaHPO4, however, exhibits three lines. This result was confirmed using a cross polarization (CP) sequence program. The first peak is attributed to the first set of pairs of P(1)O4 units and the two other ones to P(2)O4 and P(2)O4 units.

  12. New observations on the pressure dependence of luminescence from Eu2+-doped MF2 (M = Ca, Sr, Ba) fluorides.

    PubMed

    Su, Fu Hai; Chen, Wei; Ding, Kun; Li, Guo Hua

    2008-05-29

    The luminescence from Eu(2+) ions in MF2 (M = Ca, Sr, Ba) fluorides has been investigated under the pressure range of 0-8 GPa. The emission band originating from the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) ions in CaF2 and SrF2 shows the red-shift as increasing pressure with pressure coefficients of -17 meV/GPa for CaF2 and -18 meV/GPa for SrF2. At atmospheric pressure, the emission spectrum of BaF2:Eu(2+) comprises two peaks at 2.20 and 2.75 eV from the impurity trapped exciton (ITE) and the self-trapped exciton (STE), respectively. As the pressure is increased, both emission peaks shift to higher energies, and the shifting rate is slowed by the phase transition from the cubic to orthorhombic phase at 4 GPa. Due to the phase transition at 4-5 GPa pressure, the ITE emission disappears gradually, and the STE emission is gradually replaced by the 4f(6)5d(1) --> 4f(7) transition of Eu(2+). Above 5 GPa, the pressure behavior of the 4f(6)5d(1) --> 4f(7) transition of Eu(2+) in BaF2:Eu(2+) is the same as the normal emission of Eu(2+) in CaF2 and SrF2 phosphors. PMID:18444634

  13. Dipole polarizability of alkali-metal (Na, K, Rb)-alkaline-earth-metal (Ca, Sr) polar molecules: prospects for alignment.

    PubMed

    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 (2)?(+) ground state at the coupled-cluster singles and doubles with partial triples (CCSD(T)) level of electron correlation. Calculated spectroscopic constants for the isotopes ((23)Na, (39)K, (85)Rb)-((40)Ca, (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. PMID:24929384

  14. 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.

  15. Multiferroicity in Mn-deficient Ca3CoMnO6: The consequence of Fe substitution

    NASA Astrophysics Data System (ADS)

    Lin, L.; Xie, Y. L.; Liu, M. F.; Guo, Y. J.; Yan, Z. B.; Liu, J.-M.

    2013-07-01

    We present careful experiments on the multiferroicity in Ca3CoMn0.92O6 by Fe substitution of Mn. It is revealed that a proper Fe substitution modulates the Co/Mn spin order, favoring the ferroelectricity. The multifold interactions between the intra-chain spins and inter-chain spins are analyzed. It is suggested that the Mn deficiency and Fe substitution can break the inter-chain interactions to some extent, resulting in the delicate competition between these mutual interactions. The modulation of the ionic (charge) disorder and spin frustration order is the core physics for improving the ferroelectric performance.

  16. Temperature-dependent phonon Raman scattering and spectroscopic ellipsometry of pure and Ca-doped Sr x Ba1-x Nb2O6 ferroelectric ceramics across the phase transition region

    NASA Astrophysics Data System (ADS)

    Peng, Liang; Jiang, Kai; Zhang, Jinzhong; Hu, Zhigao; Wang, Genshui; Dong, Xianlin; Chu, Junhao

    2016-01-01

    Optical phonons and the phase transition of relaxor ferroelectric ceramics Sr x Ba1-x Nb2O6 (SBN) and Ca y (Sr0.5Ba0.5)1-y Nb2O6 (CSBN) with different composition (0.3≤slant x≤slant 0.5 , 0.1≤slant y≤slant 0.2 ) have been investigated by variable-temperature Raman scattering and spectroscopic ellipsometry. The anomalous temperature dependence of Tauc gap energy (E t ) is used to fit the phonon energy dependence of the permittivity, and the Raman intensity of some interesting optical phonons can be ascribed to the phase transition from a ferroelectric to a paraelectric structure. The Curie temperature of SBN decreases from 556 to 359 K with increasing Sr composition, which can be attributed to the substitution of smaller Sr2+ for Ba2+. On increasing the Ca composition, however, the phase transition temperature of CSBN remains nearly unchanged at about 350 K. This could be due to the fact that most doped Ca2+ ions move into the oxygen ion site and exhibit no obvious effect on the vibrational properties. Therefore, the general disorder which results from Sr2+ substituting Ba2+ , dominates the phase transition process for SBN-based ferroelectric oxides. Meanwhile, the dielectric functions from 200 to 600 K have been evaluated with the aid of the Tauc-Lorentz model. The electronic transition is located at about 5 eV and decreases with increasing temperature for all the samples. Moreover, the phase transition temperature range derived from the spectroscopic ellipsometry agrees well with that from the Raman scattering. It reveals that the variation of the fundamental energy gap may be associated with the phase transition of SBN ceramics. Both Raman scattering and spectroscopic ellipsometry are proven to be a effective method of exploring the phase transition of ferroelectric oxides.

  17. Effect of Ca2+, Ba2+, and Sr2+ on alginate microbeads.

    PubMed

    Mrch, Yrr A; Donati, Ivan; Strand, Berit L; Skjk-Braek, Gudmund

    2006-05-01

    Microcapsules of alginate cross-linked with divalent ions are the most common system for cell immobilization. In this study, we wanted to characterize the effect of different alginates and cross-linking ions on important microcapsule properties. The dimensional stability and gel strength increased for high-G alginate gels when exchanging the traditional Ca2+ ions with Ba2+. The use of Ba2+ decreased the size of alginate beads and reduced the permeability to immunoglobulin G. Strontium gave gels with characteristics lying between calcium and barium. Interestingly, high-M alginate showed an opposite behavior in combination with barium and strontium as these beads were larger than beads of calcium-alginate and tended to swell more, also resulting in increased permeability. Binding studies revealed that different block structures in the alginate bind the ions to a different extent. More specifically, Ca2+ was found to bind to G- and MG-blocks, Ba2+ to G- and M-blocks, and Sr2+ to G-blocks solely. PMID:16677028

  18. 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.

  19. 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.

  20. High-pressure synthesis of the “zero-charge-reservoir” 0223 superconductor in the Sr-Ca-Cu-O system

    NASA Astrophysics Data System (ADS)

    Ushiki, Masako; Motohashi, Teruki; Yamauchi, Hisao; Karppinen, Maarit

    2002-10-01

    We have refined the high-pressure synthesis of the “zero-charge-reservoir” 0223 phase of the Sr-Ca-Cu-O system. Samples were prepared from three different starting cation compositions of Sr 2CaCu 2O 6+ y, Sr 2Ca 2Cu 3O 8+ y and Sr 2Ca 3Cu 4O 10+ y. The amount of oxygen, y, was controlled by using different amounts of SrO 2 in the starting material mixture. With SrO 2 of commercial grade, two types of HRTEM images were observed for the a- b plane: one with a double periodicity and another with no periodicity. TEM-EELS analysis revealed that the former was due to carbonate inclusions. Using freshly synthesized SrO 2, crystalline samples with Tc≈110 K were obtained. The samples showed body-centered symmetry in ED patterns, being thus of the 0 (Sr)2 (Ca)23 phase. The actual amount of oxygen in the obtained samples as determined by wet-chemical analysis was found considerably lower than the nominal value. However, the wet-chemical analysis revealed a much higher oxidation state for the 0 (Sr)2 (Ca)23 phase than generally expected for a high- Tc superconductor.

  1. 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

  2. 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.

  3. Growth, structural and electrical characterization of [(Ca,Sr)CuO 2] m/[BaCuO 2] n superlattices

    NASA Astrophysics Data System (ADS)

    Balestrino, G.; Martellucci, S.; Medaglia, P. G.; Paoletti, A.; Petrocelli, G.

    1998-06-01

    In this paper we show that (CaCuO 2) m/(BaCuO 2) n and (SrCuO 2) m/(BaCuO 2) n superlattices with good crystallographic quality can be engineered by Pulsed Laser Deposition (PLD) in a wide range of composition, namely for n=2 and m=1-6. However, Sr- and Ca-based superlattices result to have qualitatively different electrical transport properties. Superconductivity is observed in Ca-containing superlattices only. This effect is explained by the large Ba⇔Sr interdiffusion. The resistivity behaviour of the Ca-containing superlattices grown at high oxygen pressure (>0.2 mbar) is metallic with a full transition to a superconductive state at temperatures as high as 70 K (zero resistance temperature). Such value of Tc, the highest till now reported for an artificial structure, is still lower than those of the related CuBa 2Ca n-1Cu nO x compounds ( Tc=116 K) obtained by high pressure synthesis. Such difference can be due either to a still unoptimized growth procedure or to the intrinsically higher disorder typical of these artificial structures.

  4. 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. Long-range magnetic order is also lost, giving way to spin glass or cluster-glass-like behavior below 50 K. For the x = 0.5 phase, neutron pair distribution function (NPDF) studies show a local structure related to brownmillerite ordering of oxygen vacancies. Neutron diffraction data at 3.8 K show a broad magnetic feature, incommensurate with any multiple of the chemical lattice, and with a correlation length (magnetic domain) of 6.7(4) .

  5. 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

  6. Effect of Ba substitution in CsSrI3:Eu2+

    NASA Astrophysics Data System (ADS)

    Wei, H.; Zhuravleva, M.; Yang, K.; Blalock, B.; Melcher, C. L.

    2013-12-01

    CsSrI3:Eu2+ was previously reported by our group as a highly efficient scintillator, and we now report the advantages of partial replacement of Sr by Ba. Scintillation and physical properties of CsSr1-xBaxI3:Eu2+ crystals are presented for 0≤x≤0.24. We found that the hygroscopicity decreased with increasing Ba concentration while density and effective atomic number increased, thus enhancing the X-ray and gamma ray detection efficiency. The scintillation light yield ranged from 22,000 to 28,000 photons per MeV for Ba concentrations between 3% and 24%. The principle scintillation decay time ranged from 1.8 to 2.1 μs.

  7. 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

    Oxygen deficient perovskites 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, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a={radical}(2) Multiplication-Sign a{sub per}, b=2 Multiplication-Sign a{sub per}, c={radical}(2) Multiplication-Sign a{sub per} (a{sup 0}b{sup -}b{sup -} tilt system, space group Imma) was revealed by electron diffraction. The solid solution 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{<=}x{<=}0.6 and compound Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92} were prepared in air at 1573 K for 48 h. The crystal structure of Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92} was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) A, R{sub p}=0.057, R{sub wp}=0.056, {chi}{sup 2}=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 and Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92(1)} are 15.5, 15.1, and 13.8 ppm K{sup -1}, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr{sub 0.15}Ca{sub 0.6}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} and Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92}. Conductivity of 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 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of 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 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-temperature conductivity properties and crystal structure were studied. Black-Right-Pointing-Pointer High-temperature thermal expansion behavior was investigated.

  8. Accurate climate reconstruction from coral aragonite: The impact of seawater pH on skeletal Sr/Ca

    NASA Astrophysics Data System (ADS)

    Cole, C. S.; Allison, N.; Hintz, C.; Finch, A.

    2014-12-01

    The geochemistry of skeletal aragonite deposited by massive tropical corals preserves a valuable record of past climate. In particular, coral skeletal Sr/Ca records sea surface temperature (SST) at the time of deposition and is a widely used palaeothermometer. However, SSTs estimated from many fossil corals are significantly cooler than those predicted from other proxies and climate models. Accurately interpreting the SST records encoded in coral aragonite requires a greater understanding of the controls on skeletal Sr/Ca, including the effect of variations in seawater pH. We have developed an aquarium system to culture corals over a range of pCO2 scenarios that range from the last glacial maximum (180 ppm) to levels projected by the end of this century (750 ppm). We acclimated heads of massive Porites corals, the coral genus most commonly used in palaeoenvironmental studies, to four pCO2 scenarios over a period of > 6 months. Using SIMS we are measuring the Sr/Ca of the aragonite deposited over a five-week experimental period, following this long acclimation, at a 1-2 day resolution. We explore the relationship between seawater pH and skeletal Sr/Ca, and we investigate how skeletal Sr/Ca varies between fast- and slow-growing axes within the same coral, and between different genotypes within the same treatment. We have quantified net photosynthesis, respiration and calcification rates in each coral head throughout the experimental period, and we observe that calcification in the light is significantly reduced at a pCO2 of 750 ppm compared to 180 ppm (0.94 ± 0.17 and 0.45 ± 0.23 μmol CaCO3 cm-2 hr-1, respectively; p < 0.01). We investigate whether these differences influence skeletal geochemistry within our controlled culture conditions. Understanding the effect of changes in seawater pH, metabolic and calcification rates on the Sr/Ca of coral skeletons will significantly advance the application of this proxy in past climate reconstruction.

  9. Pharmacological evidence that potentiation of plasmalemmal Ca(2+)-extrusion is functionally coupled to inhibition of SR Ca(2+)-ATPases in vascular smooth muscle cells.

    PubMed

    Zhang, Wen-Bo; Kwan, Chiu-Yin

    2016-04-01

    Cyclopiazonic acid (CPA), a specific inhibitor of sarcoplasmic reticulum (SR) Ca(2+)-ATPases, causes slowly developing and subsequently diminishing characteristic contractions in vascular smooth muscle, and the second application of CPA has incompletely repeatable effects, depending on the vessel type. The objective of the present study was to examine the mechanisms underlying the significant decrease of CPA-induced contractions upon the second application. A pharmacological intervention of Ca(2+) extrusion process as a strategy was performed to modulate vasoconstrictor effects of CPA in rat aortic ring preparations. CPA-induced contractions, expressed as percentages of the contractions induced by KCl (80 mM), were significantly decreased from 44.1 ± 5.7 to 7.6 ± 1.8 % (P < 0.001) upon the second application. The contractions, however, were completely repeatable in the presence of vanadate, an inhibitor of ATPases, but not of ouabain, an inhibitor of Na(+)-pumps. Strikingly, CPA-induced contractions were sustained and completely repeatable in Na(+)-free and low Na(+) medium. Furthermore, we found that the contractions were completely repeatable in the presence of 2',4'-dichlorobenzamil, an inhibitor of the forward mode of Na(+)/Ca(2+) exchangers, but not of KBR7943, an inhibitor of the reverse mode of Na(+)/Ca(2+) exchangers. Our findings indicate that CPA by inducing a transient rise in cytosolic Ca(2+) level causes a long-lasting upregulation of plasma membrane (PM) Ca(2+) extruders and thus leads to a diminished contraction upon its second application in blood vessels. This suggests that there is a functional coupling between PM Ca(2+) extruders and SR Ca(2+)-ATPases in rat aortic smooth muscle cells. PMID:26842648

  10. X-ray absorption investigation of the valence state and electronic structure of La 1- xCa xCoO 3- δ in comparison with La 1- xSr xCoO 3- δ and La 1- xSr xFeO 3- δ

    NASA Astrophysics Data System (ADS)

    Haas, O.; Ludwig, Chr.; Bergmann, U.; Singh, R. N.; Braun, A.; Graule, T.

    2011-12-01

    3 d metal K-shell X-ray absorption spectra of perovskites with the composition La 1- xCa xCoO 3- δ ( x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La 1- xSr xCoO 3- δ ( x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La 1- xSr xFeO 3- δ ( 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 1- xCa xCoO 3- δ also at temperatures as low as 10-20 K. Going to low-temperature the measurements indicate an increase in t2g* and a decrease in eg* orbital occupancy, which is most accentuated in the LaCoO 3 sample. Virtually no Co K-edge shift was observed for the La 1- xCa xCoO 3- δ and La 1- xSr xCoO 3- δ compounds and the Co-O distances are also not significantly reduced when La 3+ is partially substituted by Ca 2+ or Sr 2+. From the pre-edge features of these perovskites we are tended to conclude that the t2g* orbitals are less, and the eg* 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 + 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 1- xSr xFeO 3- δ 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 1- xSr xFeO 3- δ perovskites in fact increase as much as x increases.

  11. Crystal structure and magnetic properties and Zn substitution effects on the spin-chain compound Sr{sub 3}Co{sub 2}O{sub 6}

    SciTech Connect

    Wang, Xia; Guo, Yanfeng; Sun, Ying; Tsujimoto, Yoshihiro; Matsushita, Yoshitaka; Yamaura, Kazunari

    2013-08-15

    The effects of substituting Co on the spin-chain compound Sr{sub 3}Co{sub 2}O{sub 6} with Zn were investigated by synchrotron X-ray diffraction, magnetic susceptibility, isothermal magnetization, and specific heat measurements. To the best of our knowledge, this is the first report to describe the successful substitution of Co in Sr{sub 3}Co{sub 2}O{sub 6} with Zn. The substitution was carried out by a method involving high pressures and temperatures to obtain Sr{sub 3}CoZnO{sub 6}, which crystalized into a K{sub 4}CdCl{sub 6}-derived rhombohedral structure with a space group of R-3c, similar to the host compound. With the Zn substitution, the Ising-type magnetic anisotropy of the host compound remarkably reduced; the newly formed Sr{sub 3}CoZnO{sub 6} became magnetically isotropic with Heisenberg-type characteristics. This could probably be ascribed to the establishment of a different interaction pathway, –Co{sup 4+}(S=1/2)–O–Zn{sup 2+}(S=0)–O–Co{sup 4+}(S=1/2)–. Details of the magnetic properties of Zn substituted Sr{sub 3}Co{sub 2}O{sub 6} were reported. - Graphical abstract: Crystal structure of the spin-chain compound Sr{sub 3}CoZnO{sub 6} synthesized at 6 GPa. Zn atoms preferably occupy the trigonal prism sites rather than the octahedral sites. As a result, the compound is much magnetically isotropic. Highlights: • Effects of substituting Co with Zn on spin-chain magnetism of Sr{sub 3}Co{sub 2}O{sub 6} were studied. • High-pressure synthesis resulted in a solid solution of Sr{sub 3}CoZnO{sub 6}. • Sr{sub 3}CoZnO{sub 6} showed more isotropic magnetism than the host Sr{sub 3}Co{sub 2}O{sub 6}.

  12. 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.

  13. Diamagnetism to ferromagnetism in Sr-substituted epitaxial BaTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Singamaneni, Srinivasa Rao; Punugupati, Sandhyarani; Prater, John T.; Narayan, Jagdish

    2016-04-01

    We report on the ferromagnetic-like behavior in otherwise diamagnetic BaTiO3 (BTO) thin films upon doping with non-magnetic element Sr having the composition Ba0.4Sr0.6TiO3 (BST). The epitaxial integration of BST (˜800 nm) thick films on Si (100) substrate was achieved using MgO (40 nm) and TiN (20 nm) as buffer layers to prepare BST/MgO/TiN/Si (100) heterostructure by pulsed laser deposition. The c-axis oriented and cube-on-cube epitaxial BST is formed on Si (100) as evidenced by the in-plane and out-of-plane X-ray diffraction. All the deposited films are relaxed through domain matching epitaxy paradigm as observed from X-ray diffraction pattern and A1TO3 mode (at 521.27 cm-1) of Raman spectra. As-deposited BST thin films reveal ferromagnetic-like properties, which persist up to 400 K. The magnetization decreases two-fold upon oxygen annealing. In contrast, as-deposited un-doped BTO films show diamagnetism. Electron spin resonance measurements reveal no evidence of external magnetic impurities. XRD and X-ray photoelectron spectroscopy spectra show significant changes influenced by Sr doping in BTO. The ferromagnetic-like behavior in BST could be due to the trapped electron donors from oxygen vacancies resulting from Sr-doping.

  14. 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.

  15. 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.

  16. 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

  17. The formation and stability of 80 K phase in the BiPbSrCaCuO system

    SciTech Connect

    Zhu, W.; Kuo, C.K.; Nicholson, P.S.

    1996-08-01

    The formation of Pb-doped 80 K phase from nitrate precursors was studied in the Bi{sub 1.84}Pb{sub 0.34}Sr{sub 1.91}Ca{sub 2.00}Cu{sub 3.04}O{sub 10.05} system. Sr(Pb,Bi)O{sub 3}, Ca{sub 5}Bi{sub 14}O{sub 26}, CuO and CaO were found to be the intermediate compounds reacting to produce 80 K phase between 60 and 820{degree}C. Synthesis was complete at 800{degree}C for 24 h. 110 K phase formed at the expense of 80 K phase at temperatures above 820{degree}C. Partial melting was detected and 80 K and 110 K phases were unstable in the presence of liquid phase. They decomposed to 2201, Cu{sub 2}O, and (Ca, Sr, Cu) complex oxides. The melting and decomposition were accompanied by oxygen loss. {copyright} {ital 1996 Materials Research Society.}

  18. 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.

  19. 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 suggests that the mean value (3.0 mmol/mol) may be biased toward warm temperatures due to a cessation in shell growth during the winter, however. In comparison, at ~3,000 and ~9,000 cal yr BP shell Mg/Ca ratios averaged 1.5 and 1.0 mmol/mol, respectively, consistent with colder nearshore temperatures relative to today. Shell Mg/Ca time series will be compared with shell δ 18O, coastal temperature, and Humboldt Bay salinity measurements. Shell Sr/Ca ratios appear to be primarily determined by temperature but show an overprint from low salinity run-off events.

  20. 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.

  1. Sr/Ca and Mg/Ca Heterogeneity Across Individual Foram Tests as Revealed by Ion Microprobe Analysis

    NASA Astrophysics Data System (ADS)

    Austin, W. E.; Allison, N.

    2002-12-01

    Many benthic foraminifera live for >= 1 year and the chemistry of individual tests may preserve information on seawater temperature changes over this time. Microanalysis of individual tests is complicated by the combination of thin test walls and the presence of surface contaminants, not held within the carbonate structure. We optimised conditions for the analysis of Mg and Sr in the benthic foraminifera Ammonia batavus, by ion microprobe. The use of field and contrast apertures restricted the size of the analysed area to ~10 μm and reduced the effects of sample contamination. Sr concentrations were unaffected by any contamination encountered and Mg could be determined provided checks were made for silicate contamination using Al, Si and K intensities. Measured Mg and Sr concentrations were in reasonable agreement with previously reported values. Mn was present at a level too low to permit clean analysis, even at very low levels of contamination. Significant variations in Sr concentrations occurred within individual test chambers and may reflect the juxtapositioning of calcite of different ages as the test is deposited. Significant variations in Mg and Sr concentrations occurred between test chambers. Sr increased in concentration in the outermost (most recently deposited) parts of the test. This may reflect an increase in test calcification rate coincident with increases in bottom water temperature or food availability. The development of this method provides a valuable tool for investigating geochemical variations across individual foraminifera tests.

  2. Electro-optic effect in SrTiO3 and Sr1- x Ca x TiO3 ( x = 0.014)

    NASA Astrophysics Data System (ADS)

    Markovin, P. A.; Guzhva, M. E.

    2016-01-01

    The results of the investigation of the quadratic electro-optic effect in Sr1- x Ca x TiO3 with x = 0.014 (SCT) and in nominally pure SrTiO3 (STO) at room temperature in applied direct-current (dc) and alternating-current (ac) electric fields have been presented. It has been shown that the quadratic (in polarization) electro-optic coefficients of STO and SCT crystals coincide within the accuracy of the determination (±5%). It has been found that, in nominally pure STO measured in a dc electric field, there is a relaxation of the electro-optic effect with a relaxation time τ ≈ 30 s due to the formation of a space charge in the sample. No similar effect in SCT has been observed. A possible mechanism for the formation of a space charge in STO and SCT has been discussed.

  3. 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.

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

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.

    1990-01-01

    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 107.2 K and transition width delta T(sub c) (10 to 90 percent) of approx. 2 K.

  5. Superconducting properties of melt-cast Bi-Sr-Ca-Cu-O (abstract)

    NASA Astrophysics Data System (ADS)

    Goldfarb, R. B.; Ciszek, T. F.; Evans, C. D.

    1988-11-01

    Sintered solid copper-oxide superconductors generally have an intergranular coupling component that is evident in curves of ac susceptibility versus temperature: a broad peak in the imaginary (loss) part, χ`, and a corresponding inflection in the real part, χ'.1 Polycrystalline Bi-Sr-Ca-Cu-O samples have been prepared from the melt. They are very different from typical sintered materials. Some have a single superconducting phase, while others have two superconducting phases. Most of the superconducting platelets are partially surrounded by nonsuperconducting material.2 An unusual feature of the susceptibility curves is that they show almost no coupling losses. This might be explained if the superconducting grains were isolated from each other, as is the case in susceptibility measurements of powdered superconductors.3 However, the characteristics of the melt-cast samples differ from those of powdered samples in three ways. (1) The resistivity goes to zero at low temperatures, which indicates some connectivity between crystallites. (2) χ' approaches -1 at low temperature, indicating substantial bulk shielding. (3) χ' decreases in magnitude with increasing field at low temperature, an effect not seen in powdered samples. We therefore believe that there is substantial superconductor grain-to-grain coupling, even though the susceptibility curves show little evidence of the usual intergranular coupling losses. We conclude that the coupling component in these melt-cast samples is virtually lossless.

  6. 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.

  7. 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

    The decay of 40K to 40Ar forms the basis of the potassium-argon dating method, although only one out of every 10 parent atoms decays to daughter 40Ar. The other 90% decay to 40Ca giving, in principle, the 40K-40Ca decay system great potential for dating samples with high K/Ca. This method, however, has not been utilized as an ion-microprobe-based geochronometer, largely because these isotopes require a very high mass resolving power (MRP) of ~25k for full separation. We found that limiting secondary ion transmission in our ims1270 ion microprobe to ~20% permits sufficient separation of 40K from 40Ca (MRP≈ 20k) to permit isotope ratio analysis, albeit with 40Ca+ on the shoulder of the more intense 40K+ peak. A pegmatitic muscovite from Jack Hills (K-Ca age = 2.54 Ga; Fletcher et al., Chem. Geol. 138, 289) yields ~104 cps of both 40K+ and 40Ca+ with a 15 μm primary spot size and O- beam current of 10 nA. The 40Ca+ signal is >90% radiogenic and reflects a “common” Ca content of ≤ 100 ppm. However, application of the relative sensitivity factor (RSF) calculated from the Jack Hills muscovite to unknowns yields relatively high age dispersion, perhaps related to the incompletely separated mass interferences. Theorizing that the noble gas electronic structure of K+ would likely resist further electron loss, we investigated an alternative approach involving analysis of Ca++/K++. The double-plus method provides an important advantage in that K++ species are suppressed by a factor of ~103 relative to K+, thereby effectively removing 40K++ from the spectrum at m/e≈ 20 and leaving 40Ca++ free from any significant interferences at an MRP≈ 4k. Measurement of the much more abundant 39K++ then permits 40Ca++/40K++ to be calculated from the known 39K/40K ratio. We applied this approach to Precambrian muscovite samples obtaining ages similar to, but generally younger than, their associated 40Ar/39Ar ages. This could reflect a minor matrix effect or a lower intrinsic 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.

  8. 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.

  9. 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

  10. Optical and Electromagnetic Properties of LaCoO3:Li+;M2+ (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Fesich, I. V.; Trachevsky, V. V.; Dziazko, A. G.; Nedilko, S. A.; Melnik, A. K.

    2014-09-01

    Lanthanum cobaltates modified by alkaline-earth-metal (0.10 mol%) and lithium (0.05 mol%) ions were synthesized. The samples had an orthorhombic distorted perovskite-like structure according to x-ray diffraction phase analysis. Addition of Li+ and M2+ (M = Ca, Sr, Ba) to the LaCoO3 matrix was shown to increase the unit-cell parameters, the optical band width (Eg), and the average Co oxidation state (Con+). Pure and doped LaCoO3 were characterized by the presence of paramagnetic centers as isolated structural and surface Co2+ ions and adsorption complexes [Co3 + ⋯ O{2/-}]· on the surface of the oxide matrix at a concentration that increased in the order Ba > Sr > Ca. The cobaltates were found to possess Mott hopping conduction in the temperature range 77-298 K.

  11. 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.

  12. 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

  13. 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.

  14. Hyperfine splittings and Zeeman infrared absorption of Tb3+ -doped CaF2 and SrF2

    NASA Astrophysics Data System (ADS)

    Wells, Jon-Paul R.; Jones, Glynn D.

    2009-09-01

    We report on the observation of pseudoquadrupole splittings of sharp infrared-absorption lines of CaF2:Tb3+ . These splittings are large enough to be directly observed because the Tb3+ electronic ground levels consists of two singlets separated by only 0.18cm-1 for the F- C4v center. Both the hyperfine splittings and measured Zeeman splittings for F- C4v centers in CaF2:Tb3+ and SrF2:Tb3+ can be accounted for using wave functions derived from a previously published crystal-field analysis of experimental energy levels.

  15. 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.

  16. 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.

  17. Investigating the potential preservation of seasonal dripwater Mg/Ca and Sr/Ca variations in a speleothem from central Texas

    NASA Astrophysics Data System (ADS)

    Cunningham, M. T.; Wong, C. I.; Banner, J. L.; Miller, N. R.

    2011-12-01

    High resolution paleoclimate records are critical for improving understanding of past climate. Speleothems have the potential to record climate variations on a seasonal time scale. Fast growing (≥0.5 mm/year) speleothems have been shown to preserve annual chemical laminae recorded as cyclical variations in trace elements. This study investigates the potential preservation of seasonal Mg/Ca and Sr/Ca variations in a slow growing (< ~0.05 mm/year) speleothem in central Texas. The speleothem was collected from a site that underlies a drip with observed seasonal variation in Mg/Ca and Sr/Ca, making it ideal for evaluating preservation of seasonal chemical laminae. The speleothem was cored, slabbed, dated (using U-series methods) and analyzed for high resolution variations in Mg and Sr concentrations using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Three sets of parallel transects were ablated (using a 6 x 50 μm slit aperture) parallel to the stalagmite growth axis. The laser scanned at 1 μm/second and made three measurements per second, resulting in sub-micron sampling. Parallel transects were ablated along different growth intervals to determine signal reproducibility of high frequency Mg and Sr variations. Wavelet analysis was conducted using detrended time series to determine presence and length of statistically significant cyclicity. Preliminary U-series ages (n=2) indicate the interval of interest (1.6 cm) grew from around 10 ka to 8 ka, but the chronology is not well constrained. The median growth rate estimated from U-series dating is 15 μm /year with a range from approximately 4 μm/year to >1.6 cm/year. Line scans of several standard materials (NIST 612, BHVO-2G, MACS-3) and scans perpendicular to the stalagmite growth axis were measured with the same analytical parameters used for scans parallel to the stalagmite growth axis in order to eliminate the possibility that cyclicity could be an instrumental artifact. Wavelet analysis of these scans demonstrates that cyclicity greater than 2 μm/sec cannot be attributed to the instrument. There is good correspondence between Mg and Sr variations in three sets of paired, parallel transects. Detrended data show that Mg and Sr varied concordantly on smaller length scales despite differences in Mg and Sr variations over larger length scales. Wavelet analysis results indicate statistically significant cyclicity of Mg and Sr concentrations between 30 and 60 μm in 5 of 6 transects, suggesting that this speleothem may be recording chemical laminae of annual growth. Growth rate estimates (30-60 μm/year) derived from cyclical Mg and Sr variations are consistent with growth rate estimates from the preliminary U-series chronology. In addition, growth rates are comparable in magnitude to some regional speleothems from the same time interval. These results suggest that it may be possible to observe seasonal geochemical banding in a slow growing stalagmite from central Texas.

  18. Temperature and wavevector dependence of overdoped Bi_2Sr_2CaCu_2O_8+x single crystal samples

    NASA Astrophysics Data System (ADS)

    Rast, S.; Klohs, A.; Frazer, B. H.; Hirai, Y.; Schmauder, T.; Gatt, R.; Abrecht, M.; Pavuna, D.; Margaritondo, G.; Onellion, M.

    2000-03-01

    We report on measuring the temperature and wavevector change of angle-resolved photoemission spectra for overdoped Bi_2Sr_2CaCu_2O_8+x single crystal samples. Spectra taken from close to <0, π > to close to <π , π > were analyzed. The changes of spectral lineshape with temperature and wave vector indicate qualitatively different behavior in different parts of the Brillouin zone and will be analyzed and presented.

  19. Temperature-dependent photoemission features for overdoped Bi2Sr2CaCu2O8 + x cuprates

    NASA Astrophysics Data System (ADS)

    Rast, S.; Frazer, B. H.; Onellion, M.; Schmauder, T.; Abrecht, M.; Touzelet, O.; Berger, H.; Margaritondo, G.; Pavuna, D.

    2000-07-01

    We report temperature-dependent angle-resolved photoemission spectra for overdoped Bi2Sr2CaCu2O8 + x single-crystal samples. The data indicate that there is a special temperature (T+) where the spectral function changes intensity, and where the energy difference between the peak and dip features changes. The data also demonstrate that immediately above the superconducting transition temperature, the system exhibits a non-Lorentzian lineshape. We discuss implications of the data.

  20. 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.

  1. CaF2, BaF2 and SrF2 crystals’ optical anisotropy parameters

    NASA Astrophysics Data System (ADS)

    Snetkov, I. L.; Yakovlev, A. I.; Palashov, O. V.

    2015-09-01

    Using the original method, based on measurements of thermally induced depolarization, the optical anisotropy parameters of CaF2, BaF2 and SrF2 cubic crystals were measured and compared with what is known from the literature. Euler angles of crystallographic axis orientation [C], in which the thermally induced depolarization is minimal, were determined using experimental results for studied fluorides.

  2. 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.

  3. 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.

  4. Effect of Sn substitution on structural and transport properties of (La0.67Sr0.33)MnO3

    NASA Astrophysics Data System (ADS)

    Tank, Tejas M.; Sridharan, V.; Samatham, S. Shanmukharao; Ganesan, V.; Sanyal, S. P.

    2013-06-01

    We investigate the effects of Sn substitution on structural and electrical transport mechanism of polycrystalline samples La0.67Sr0.33Mn1-xSnxO3 (x = 0, 0.05, 0.10, 0.15). Resistivity data have been fitted with the variable range hopping model to estimate the density of state at Fermi level. It was observed that the substitution of Sn in the series leads to a decrease in conductivity of the doped manganites samples, with conduction being controlled by the disorder induced localization of charge carriers. The value of M-I transition temperature (TP) decreases while resistivity increases with Sn substitution.

  5. Determination of Mg/Ca and Sr/Ca ratios in microgram-quantity coral and foraminiferal samples with permil-level precision by cold plasma inductively coupled plasma sector field mass spectrometry

    NASA Astrophysics Data System (ADS)

    Shen, C.; Lu, C.; Lo, L.; Qu, D.; Wei, K.; Gagan, M. K.

    2006-12-01

    A permil-level analytical technique for determination of coral and foraminiferal Mg/Ca and Sr/Ca ratios using inductively coupled plasma sector-field mass spectrometry (ICP-SF-MS, Thermo Electron ELEMENT2) has been established. Cold plasma technique with an 800-W RF power was employed to diminish spectral interference. A wet introduction system with Scott-type double-pass spray chamber and an ESI micro- nebulizer with a sample uptake rate of 50 microliter per minute were used, which can offer low blank and high stability. Intensities of ion beams, ^{24}Mg, ^{43}Ca and 86Sr, were detected in pulse-counting mode. Mg/Ca and Sr/Ca ratios were determined directly from intensity ratios using external, matrix-matched standard to correct for mass discrimination and low-frequency ratio drift. Other elemental ratios, such as Al/Ca, Mn/Ca, Fe/Ca, Cd/Ca, and Ba/Ca were also determined. Three different matrix effects were observed in this system. (1) Acid effect: Elemental intensities and ratios vary with increasing HNO3 from 1-6%. 5% HNO3 was determined to be ideal for routine measurement. (2) Ca effect: Mg/Ca ratio decreases 2.5% with [Ca] from 0.5-2.5 ppm and less than 0.5% with [Ca] from 3-5 ppm. (3) Sr/Ca effect on Mg/Ca: Sr/Ca slightly affects Mg/Ca determination with a slope of 0.18% per mmol/mol. This effect causes only 0.1 s or less for Mg/Ca ratio in both foraminiferal and coral samples. Replicate measurements made on standards and samples show that our method can give an internal precision of 1-2 (2RSD) and reproducibility of 4.5% for Mg/Ca and 3.5 for Sr/Ca. Corresponding errors are 0.05 C for foraminiferal Mg thermometer and 0.5 C for coral Sr thermometer. Advantages of this new method include (1) short measurement time of 3 minutes and (2) only 2-mircogram carbonate consumed for each sample, and (3) throughput of 10 samples per hour.

  6. Influence of the mercury source on the synthesis of Hg 0.8Re 0.2Ba 2- ySr yCa 2Cu 3O 8+ δ at normal pressures

    NASA Astrophysics Data System (ADS)

    Bastidas, D. M.; Piñol, S.; Plain, J.; Puig, T.; Obradors, X.

    2004-04-01

    The influence of the mercury source on the synthesis of the superconducting phases Hg 0.8Re 0.2Ba 2- ySr yCa 2Cu 3O 8+ δ with 0⩽ y⩽0.4 has been investigated using the vacuum sealed quartz tube technique with HgO or HgCaO 2 as internal or external source, respectively. The superconductors were prepared from stoichiometric precursor powders of elemental oxides and carbonates. The synthesis was carried out in different steps: Firstly, the multiphase precursor was homogenized, pressed and annealed in oxygen atmosphere. Then, the precursor powders were mixed and pressed with stoichiometric additions of HgO for the internal source method or were pressed and placed separately with a pellet of HgCaO 2 inside the quartz tube for the external source method. In both methods, the samples were encapsulated in an evacuated quartz tube and annealed at different heating rates and temperatures in order to optimize the purity of the phase. Different Sr compositions were studied but only a small concentration ( y⩽0.3) was found to be appropriate to obtain pure superconducting phase. The substitution of Sr by Ba increases the grain size of the superconducting phase and the density of the pellets, however the intergranular connectivity is only slightly improved.

  7. Al{sub 2}O{sub 3} additions for isothermal melt processing of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub {ital y}}

    SciTech Connect

    Holesinger, T.G.

    1996-09-01

    It is shown that additions of Al{sub 2}O{sub 3} (1.0 wt.{percent}) can significantly aid in the isothermal melt processing of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub {ital y}} (Bi{endash}2212). Al{sub 2}O{sub 3} additions provide a means for grain refinement of phases present in the partial melt. By limiting grain growth in the partial melt, solidification to form Bi{endash}2212 proceeds more efficiently, resulting in fewer secondary phases and improved transport properties. Aluminum does not substitute into the superconducting phase to any appreciable extent and is present in fully processed material as small, secondary grains of approximate composition Sr{sub 2{minus}{ital x}}Ca{sub {ital x}}AlO{sub {ital y}} or Bi{sub 2}Sr{sub 4{minus}{ital x}}Ca{sub {ital x}}Al{sub 3}O{sub {ital y}}Al{sub 2}O{sub 3} additions were applied to the isothermal melt processing of Bi{endash}2212 thick films and current leads. {copyright} {ital 1996 Materials Research Society.}

  8. Extracellular Calcium-Sensing Receptor Inhibition of Intestinal EpithelialTNF Signaling Requires CaSR-Mediated Wnt5a/Ror2 Interaction

    PubMed Central

    Kelly, Jacqueline C.; Lungchukiet, P.; MacLeod, R. John

    2010-01-01

    Tumor necrosis factor alpha (TNFα) and its receptor TNFR1 play a central role in the development of colitis-associated colon cancer. To understand a role for the extracellular calcium-sensing receptor (CaSR) and its non-canonical Wnt mediators, Wnt5a/Ror2, we used reductionistic systems. We added lipopolysaccharide (LPS) to mouse peritoneal macrophages, RAW264.7 cells, a murine macrophage cell line, and 18Co colonic myofibroblasts, to stimulate TNFα secretion and then activated endogenous CaSR. CaSR activation inhibited TNFα secretion, which in RAW264.7 cells knockdown of CaSR by short-interfering RNA (siRNA) duplex reversed. LPS-stimulated NFκB promoter activity in RAW264.7 cells was inhibited by CaSR activation with Ca2+ or other polyvalent CaSR agonists. Reducing CaSR expression with siRNA duplex prevented this inhibition. Following LPS addition to CaSR–HEK cells or RAW264.7 macrophages, CaSR stimulation deneddylated Cullin1. Wnt5a added to HT-29 cells which overexpressed Ror2 or T84 monolayers treated with 3 mM Ca2+ reduced TNFR1 protein expression ∼70%. TNFα/INFγ addition to high resistance T84 monolayers reduced transepithelial resistance 50% within 4 h. CaSR activation (3 mM Ca2+) together with rhWnt5a (200 ng/ml) prevented this reduction while Wnt3a addition had no effect. LPS-stimulated TNFα secretion from RAW264.7 cells was not effected by rhWnt5a but increased 10-fold by Wnt3a. Together our results suggest that following LPS challenge, CaSR activation will inhibit NFκB activity and reduce TNFα secretion from macrophages and stroma while Wnt5a/Ror2 engagement on intestinal epithelia reduces TNFR1 expression, allowing TNFα signaling to be titrated. Our results also suggest that canonical Wnt signaling may enhance TLR4 stimulation of TNFα secretion from murine macrophages. PMID:21603229

  9. Interaction between endoplasmic/sarcoplasmic reticulum stress (ER/SR stress), mitochondrial signaling and Ca2+ regulation in airway smooth muscle (ASM)1

    PubMed Central

    Delmotte, Philippe; Sieck, Gary C.

    2015-01-01

    Airway inflammation is a key aspect of diseases such as asthma. Several inflammatory cytokines (e.g., TNFα and IL-13) increase cytosolic Ca2+ ([Ca2+]cyt) responses to agonist stimulation and Ca2+ sensitivity of force generation, thereby enhancing airway smooth muscle (ASM) contractility (hyper-reactive state). Inflammation also induces ASM proliferation and remodeling (synthetic state). In normal ASM, the transient elevation of [Ca2+]cyt induced by agonists leads to a transient increase in mitochondrial Ca2+ ([Ca2+]mito) that may be important in matching ATP production with ATP consumption. In human ASM (hASM) exposed to TNFα and IL-13, the transient increase in [Ca2+]mito is blunted despite enhanced [Ca2+]cyt responses. We also found that TNFα and IL-13 induce reactive oxidant species (ROS) formation and endoplasmic/sarcoplasmic reticulum (ER/SR) stress (unfolded protein response) in hASM. ER/SR stress in hASM is associated with disruption of mitochondrial coupling with the ER/SR membrane, which relates to reduced mitofusin 2 (Mfn2) expression. Thus, in hASM it appears that TNFα and IL-13 result in ROS formation leading to ER/SR stress, reduced Mfn2 expression, disruption of mitochondrion–ER/SR coupling, decreased mitochondrial Ca2+ buffering, mitochondrial fragmentation, and increased cell proliferation. PMID:25506723

  10. Interaction between endoplasmic/sarcoplasmic reticulum stress (ER/SR stress), mitochondrial signaling and Ca(2+) regulation in airway smooth muscle (ASM).

    PubMed

    Delmotte, Philippe; Sieck, Gary C

    2015-02-01

    Airway inflammation is a key aspect of diseases such as asthma. Several inflammatory cytokines (e.g., TNFα and IL-13) increase cytosolic Ca(2+) ([Ca(2+)]cyt) responses to agonist stimulation and Ca(2+) sensitivity of force generation, thereby enhancing airway smooth muscle (ASM) contractility (hyper-reactive state). Inflammation also induces ASM proliferation and remodeling (synthetic state). In normal ASM, the transient elevation of [Ca(2+)]cyt induced by agonists leads to a transient increase in mitochondrial Ca(2+) ([Ca(2+)]mito) that may be important in matching ATP production with ATP consumption. In human ASM (hASM) exposed to TNFα and IL-13, the transient increase in [Ca(2+)]mito is blunted despite enhanced [Ca(2+)]cyt responses. We also found that TNFα and IL-13 induce reactive oxidant species (ROS) formation and endoplasmic/sarcoplasmic reticulum (ER/SR) stress (unfolded protein response) in hASM. ER/SR stress in hASM is associated with disruption of mitochondrial coupling with the ER/SR membrane, which relates to reduced mitofusin 2 (Mfn2) expression. Thus, in hASM it appears that TNFα and IL-13 result in ROS formation leading to ER/SR stress, reduced Mfn2 expression, disruption of mitochondrion-ER/SR coupling, decreased mitochondrial Ca(2+) buffering, mitochondrial fragmentation, and increased cell proliferation. PMID:25506723

  11. 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.

  12. 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.

  13. 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.

  14. Kinetics of the Ca(2+), H(+), and Mg(2+) interaction with the ion-binding sites of the SR Ca-ATPase.

    PubMed Central

    Peinelt, Christine; Apell, Hans-Jrgen

    2002-01-01

    Electrochromic styryl dyes were used to investigate mutually antagonistic effects of Ca(2+) and H(+) on binding of the other ion in the E(1) and P-E(2) states of the SR Ca-ATPase. On the cytoplasmic side of the protein in the absence of Mg(2+) a strictly competitive binding sequence, H(2)E(1) <==> HE(1) <==> E(1) <==> CaE(1) <==> Ca(2)E(1), was found with two Ca(2+) ions bound cooperatively. The apparent equilibrium dissociation constants were in the order of K(1/2)(2 Ca) = 34 nM, K(1/2)(H) = 1 nM and K(1/2)(H(2)) = 1.32 microM. Up to 2 Mg(2+) ions were also able to enter the binding sites electrogenically and to compete with the transported substrate ions (K(1/2)(Mg) = 165 microM, K(1/2)(Mg(2)) = 7.4 mM). In the P-E(2) state, with binding sites facing the lumen of the sarcoplasmatic reticulum, the measured concentration dependence of Ca(2+) and H(+) binding could be described satisfactorily only with a branched reaction scheme in which a mixed state, P-E(2)CaH, exists. From numerical simulations, equilibrium dissociation constants could be determined for Ca(2+) (0.4 mM and 25 mM) and H(+) (2 microM and 10 microM). These simulations reproduced all observed antagonistic concentration dependences. The comparison of the dielectric ion binding in the E(1) and P-E(2) conformations indicates that the transition between both conformations is accompanied by a shift of their (dielectric) position. PMID:11751306

  15. 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.

  16. 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 evidences in favor of {delta}=x/2 for the Co-perovskites and {delta}=0 for the Fe-perovskites. Highlights: Black-Right-Pointing-Pointer XAS a valuable tool to evaluate the valence states of Co and Fe perovskites. Black-Right-Pointing-Pointer For La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} perovskites {delta} is close to x/2. Black-Right-Pointing-Pointer For La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} series {delta} is close to 0. Black-Right-Pointing-Pointer Discussion of the x dependency of the pre-edge bands.

  17. Modulated structures and intergrowth in Pb-doped Bi-Sr-Ca-Cu-O superconducting oxides

    SciTech Connect

    Wen, J.G.; Yang, C.Y.; Yan, Y.F.; Fung, K.K. Beijing Laboratory of Electron Microscopy, Chinese Academy of Sciences, P.O. Box 2724, Beijing 100080 )

    1990-09-01

    Modulated structures and intergrowths in superconducting phases of nominal (Bi{sub 1{minus}{ital x}}Pb{sub {ital x}}){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} (2:2:2:3) compounds have been studied by transmission electron microscopy. Three kinds of modulations have been observed, one is a two-dimensional modulation and the other two are one-dimensional modulations with superspace groups {ital N} 1{bar 1}1{sup {ital B}{ital b}{ital m}{ital b}} (no. 66a), {ital P}{sup {ital Bbml}}{sub 1{bar 1}1} (no. 66a). The space group of the average structure of the two-dimensional modulated structure is {ital Bbmb}, and its Bravais class is {ital C}{sup {ital Cmmm}}{sub 1{ital p}112} in a two-line symbol or {ital C}{sub {ital m}{ital m}{ital m}}(1,0,{gamma};0,0,{nu}) (no. 2-24) in a one-line symbol. It is found that phases with the same point group and similar structure (forming intergrowths) have the same modulation. Intergrowths with each of the three modulations have been observed. The next highest member of the structural series, the 2:2:3:4 phase, has been found as having intergrowths. On the basis of the modulations of the intergrowths being the same, the modulations in the 2:2:3:4 phase have been determined.

  18. 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.

  19. Effects of Mn substitution on the thermoelectric properties of the electron-doped perovskite Sr1-xLaxTiO3

    NASA Astrophysics Data System (ADS)

    Okuda, T.; Hata, H.; Eto, T.; Nishina, K.; Kuwahara, H.; Nakamura, M.; Kajimoto, R.

    2014-12-01

    We have tried to improve the n-type thermoelectric properties of the electron- doped Perovskite Sr1-xLaxTiO3 by a Mn substitution. The 1 ~ 2 % Mn substitution enhances the Seebeck coefficient (S) and reduces the thermal conductivity (κ) by about 50 % at room temperature (RT) without largely increasing the resistivity for the 5 % electron-doped SrTiO3. Consequently, the power factor at RT keeps a large value comparable to that of Bi2Te3 and the dimensionless figure-of-merits at RT increases twofold by the slight Mn substitution. Such a large reduction of κ at RT is perhaps due to the effect of Jahn-Teller active Mn3+ ions, around which dynamical local lattice distortion may occur.

  20. 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).

  1. Probing the electronic properties of ternary AnM3n-1B2n (n = 1: A = Ca, Sr; M = Rh, Ir and n = 3: A = Ca, Sr; M = Rh) phases: observation of superconductivity

    NASA Astrophysics Data System (ADS)

    Takeya, Hiroyuki; ElMassalami, Mohammed; Terrazos, Luis A.; Rapp, Raul E.; Capaz, Rodrigo B.; Fujii, Hiroki; Takano, Yoshihiko; Doerr, Mathias; Granovsky, Sergey A.

    2013-06-01

    We follow the evolution of the electronic properties of the titled homologous series when n as well as the atomic type of A and M are varied where for n = 1, A = Ca, Sr and M = Rh, Ir while for n = 3, A = Ca, Sr and M = Rh. The crystal structure of n = 1 members is known to be CaRh2B2-type (Fddd), while that of n = 3 is Ca3Rh8B6-type (Fmmm); the latter can be visualized as a stacking of structural fragments from AM3B2 (P6/mmm) and AM2B2. The metallic properties of the n = 1 and 3 members are distinctly different: on the one hand, the n = 1 members are characterized by a linear coefficient of the electronic specific heat γ ≈ 3 mJ mol-1 K-2, a Debye temperature θD ≈ 300 K, a normal conductivity down to 2 K and a relatively strong linear magnetoresistivity for fields up to 150 kOe. The n = 3 family, on the other hand, exhibits γ ≈ 18 mJ mol-1 K-2, θD ≈ 330 K, a weak linear magnetoresistivity and an onset of superconductivity (for Ca3Rh8B6, Tc = 4.0 K and Hc2 = 14.5 kOe, while for Sr3Rh8 B6, Tc = 3.4 K and Hc2 ≈ 4.0 kOe). These remarkable differences are consistent with the findings of the electronic band structures and density of state (DOS) calculations. In particular, satisfactory agreement between the measured and calculated γ was obtained. Furthermore, the Fermi level, EF, of Ca3Rh8B6 lies at almost the top of a pronounced local DOS peak, while that of CaRh2B2 lies at a local valley: this is the main reason behind the differences between the, e.g., superconducting properties. Finally, although all atoms contribute to the DOS at EF, the contribution of the Rh atoms is the strongest.

  2. 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 to have clues about the differences in mechanism calcite precipitation, which would have significance in our understanding of mineral precipitation modes in subsurface remediation strategies. The positive correlation between D{sup P}{sub Sr}{sup 2+} and calcite precipitation rate could be indicative of the impact calcite precipitation would have on sequestering toxic metals in subsurface environment.

  3. M2PO3N (M = Ca, Sr): ortho-Oxonitridophosphates with β-K2SO4 Structure Type.

    PubMed

    Marchuk, Alexey; Schultz, Peter; Hoch, Constantin; Oeckler, Oliver; Schnick, Wolfgang

    2016-01-19

    Two novel oxonitridophosphates M2PO3N with M = Ca and Sr were synthesized under high-pressure high-temperature (7 GPa and 1100 °C) using the multianvil technique or by solid-state reaction in the silica ampules (1100 °C) from amorphous phosphorus oxonitride (PON) and the respective alkaline earth oxides MO (M = Ca, Sr). The products represent the first examples of alkaline earth ortho-oxonitridophosphates containing noncondensed [PO3N](4-) ions. The crystal structures were elucidated by single-crystal X-ray diffraction. Sr2PO3N [space group Pnma (No. 62), Z = 4, a = 7.1519(5) Å, b = 5.5778(3) Å, c = 9.8132(7) Å, R1 = 0.020, wR2 = 0.047] crystallizes in the β-K2SO4 structure type. The structure of Ca2PO3N was solved and refined in the (3 + 1)D superspace group Pnma(α00)0ss [Z = 4, a = 6.7942(7) Å, b = 5.4392(6) Å, c = 9.4158(11) Å, R1 = 0.041, wR2 = 0.067]. It exhibits an incommensurate modulation along [100] with a modulation vector q = [0.287(5), 0, 0]. Rietveld refinements support the structural models as well as the phase purity of the products. Upon doping with Eu(2+), Ca2PO3N exhibits luminescence in the green range (λem = 525 nm) of the visible spectrum if excited by near-UV light (λexc = 400 nm). PMID:26702816

  4. Spin-on Bi4Sr3Ca3Cu4O(16+x) superconducting thin films from citrate precursors

    NASA Astrophysics Data System (ADS)

    Furcone, S. L.; Chiang, Y.-M.

    1988-06-01

    Thin films in the Bi-Sr-Ca-Cu-O system have been synthesized from homogeneous liquid citrate precursors by a spin-coating and pyrolysis method. Films prepared on SrTiO3 substrates of 100-line orientation show strongly textured orientations with the c axis of the predominant Bi4Sr3Ca3Cu(4)O(16+x) phase normal to the film plane. In a single coating and firing, crack-free films of 0.2-0.5 thickness are obtained. For films fired to peak temperatures of 850-875 C, linearly decreasing resistance with temperature is observed. Clear onsets of superconductivity are observed at 90-100 K, with occasional films showing smaller resistant drops at 110-120 K. For all films, T(c) (R = 0) occurs in the range 70-75 K. High critical current densities at 4.2 K of 500,000-800,000 A/sq cm are measured by direct transport.

  5. 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

  6. Influence of W/Ta substitution at the Mo site on the Fe valence and magnetoresistive properties of Sr 2FeMoO 6

    NASA Astrophysics Data System (ADS)

    Lindén, J.; Yamamoto, T.; Yamauchi, H.; Karppinen, M.

    2002-03-01

    High-purity Sr2Fe(Mo1-xTx)O6 samples with T=W, Ta and 0⩽x⩽1 were synthesized using a solid-state reaction scheme. During synthesis a strongly reducing atmosphere was maintained by confining the precursors and an Fe/FeO oxygen getter to fused-silica tubes. Sample quality and homogeneity were confirmed by X-ray diffraction and energy-dispersive X-ray analysis. For the non-substituted samples, 57Fe Mössbauer spectra indicate that the Fe ions occupy a mixed-valence state of +2.5. W6+ forces increasing amounts of Fe to enter the +2 state, whereas Ta5+ substitution yields increasing amounts of Fe3+. Non-substituted samples exhibit a characteristic tunneling-type magnetoresistance below TC. Both W and Ta substitution were found to enhance the low-temperature magnetoresistance around the Néel temperature of the pure Sr2FeWO6 and Sr2FeTaO6 phases, respectively. The enhancement is related to the colossal magnetoresistance effect at the paramagnetic to antiferromagnetic transitions of areas rich in W or Ta.

  7. 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

  8. High-pressure synthesis of the cubic perovskite BaRuO3 and evolution of ferromagnetism in ARuO3 (A = Ca, Sr, Ba) ruthenates

    PubMed Central

    Jin, C.-Q.; Zhou, J.-S.; Goodenough, J. B.; Liu, Q. Q.; Zhao, J. G.; Yang, L. X.; Yu, Y.; Yu, R. C.; Katsura, T.; Shatskiy, A.; Ito, E.

    2008-01-01

    The cubic perovskite BaRuO3 has been synthesized under 18 GPa at 1,000°C. Rietveld refinement indicates that the new compound has a stretched Ru–O bond. The cubic perovskite BaRuO3 remains metallic to 4 K and exhibits a ferromagnetic transition at Tc = 60 K, which is significantly lower than the Tc ≈ 160 K for SrRuO3. The availability of cubic perovskite BaRuO3 not only makes it possible to map out the evolution of magnetism in the whole series of ARuO3 (A = Ca, Sr, Ba) as a function of the ionic size of the A-site rA, but also completes the polytypes of BaRuO3. Extension of the plot of Tc versus rA in perovskites ARuO3 (A = Ca, Sr, Ba) shows that Tc does not increase as the cubic structure is approached, but has a maximum for orthorhombic SrRuO3. Suppressing Tc by Ca and Ba doping in SrRuO3 is distinguished by sharply different magnetic susceptibilities χ(T) of the paramagnetic phase. This distinction has been interpreted in the context of a Griffiths' phase on the (Ca Sr)RuO3 side and bandwidth broadening on the (Sr,Ba)RuO3 side. PMID:18480262

  9. 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.

  10. 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.

  11. 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.

  12. Manganite based hetero-junction structure of La0.7Sr0.7-xCaxMnO3 and CaMnO3-δ for cross-point arrays

    NASA Astrophysics Data System (ADS)

    Lee, Hong-Sub; Park, Hyung-Ho

    2015-07-01

    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 La0.7Sr0.3-xCaxMnO3 (LSCMO) and CaMnO3-δ (CMO), to obtain nonlinear RS behavior. The pnp structure not only shows nonlinear characteristics, but also a tunable characteristic with Ca substitution.

  13. 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.

  14. White-light emitting thin film electroluminescent devices with stacked SrS:Ce/CaS:Eu active layers

    NASA Astrophysics Data System (ADS)

    Ono, Yoshimasa A.; Fuyama, Moriaki; Onisawa, Ken-ichi; Tamura, Katsumi; Ando, Masahiko

    1989-12-01

    By stacking blue-green emitting SrS:Ce and red-emitting CaS:Eu active layers, white-light emitting electroluminescent (EL) devices were fabricated. Luminance improvement and EL characteristics of SrS:Ce and CaS:Eu EL devices were discussed. The electrooptical characteristics of white-light emitting EL devices with stacked SrS:Ce/CaS:Eu active layers were presented. Color changed from blue-green to white by changing the voltage or frequency. Finally, feasibility of multicolor EL devices by using the fabricated white-light emitting EL devices with color filters were discussed. UFpg5523,5527 UFid992922JAP UFttIn situ ac magnetic susceptibility of gadolinium thin films UFauF. H. SalasSUPa),b) and M. Mirabal-GarciaaSUPc) UFloInstitut fuur Atom- und Festkourperphysik, Freie Universitaut Berlin, D-1000 Berlin 33, ufquadFederal Republic of Germany UFsd(Received 27 April 1989; accepted for publication 3 August 1989) UFabWe report measurements of the ac magnetic susceptibility on Gd(0001)/W(110) thin films grown in ultrahigh vacuum. The measurements were made by using a pickup coil, in which the geometry and the number of turns were optimized. We applied an alternating magnetic field of about 2 Grms at frequencies of 180 and 340 Hz. The growth mode and the deposition rate of the Gd films were determined by performing conventional Auger electron spectroscopy during film growth. In films with thickness larger than 10 nm our technique is sensitive up to 1016 atoms/Grms , which allowed us to study the critical behavior of the magnetic susceptibility as the Curie temperature is approached from above, TT+C . A sharp maximum, which may be related to the Hopkinson effect, is observed at a temperature TH 289 K.

  15. 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

  16. Iodide and bromide inhibit Ca(2+) uptake by cardiac sarcoplasmic reticulum.

    PubMed

    Kargacin, G J; Ali, Z; Zhang, S J; Pollock, N S; Kargacin, M E

    2001-04-01

    Recent studies indicate that the Ca(2+) permeability of the sarcoplasmic reticulum (SR) can be affected by its anionic environment. Additionally, anions could directly modulate the SR Ca(2+) pump or the movement of compensatory charge across the SR membrane during Ca(2+) uptake or release. To examine the effect of anion substitution on cardiac SR Ca(2+) uptake, fluorometric Ca(2+) measurements and spectrophotometric ATPase assays were used. Ca(2+) uptake into SR vesicles was inhibited in a concentration-dependent manner when Br(-) or I(-) replaced extravesicular Cl(-) (when Br(-) completely replaced Cl(-), uptake velocity was approximately 70% of control; when I(-) completely replaced Cl(-), uptake velocity was approximately 39% of control). Replacement of Cl(-) with SO(2)(-4) had no effect on SR uptake. Although both I(-) and Br(-) inhibited net Ca(2+) uptake, neither anion directly inhibited the SR Ca(2+) pump nor did they increase the permeability of the SR membrane to Ca(2+). Our results support the hypothesis that an anionic current that occurs during SR Ca(2+) uptake is reduced by the substitution of Br(-) or I(-) for Cl(-). PMID:11247773

  17. Sr/Ca profile of long-lived Tridacna gigas bivalves from South China Sea: A new high-resolution SST proxy

    NASA Astrophysics Data System (ADS)

    Yan, Hong; Shao, Da; Wang, Yuhong; Sun, Liguang

    2013-07-01

    High-resolution δ18O and Sr/Ca ratio profiles of a modern (live-caught) and a fossil (dead-collected) giant bivalve shell (Tridacna gigas) from northern South China Sea were analyzed. The high-resolution δ18O profiles, as documented in most of previous studies, showed pronounced seasonal cycles and recorded the combined influence of seawater δ18O and sea surface temperature. The Sr/Ca ratio profiles derived from ICP-OES had well-defined annual cycles and significant and negative correlation with sea surface temperature, while the Sr/Ca profiles derived from LA-ICP-MS did not reveal clear annual cycles. This difference was likely caused by the organics contents in T. gigas shells, which had a chemical composition different than CaCO3 crystals and a heterogeneous distribution across the shell, the sampling methods, and the experimental errors. Two calibration equations between Sr/Ca ratios, determined by ICP-OES, of modern T. gigas shell and instrumental SST were calculated based on all monthly and extremum SST data, and the equation from extremum data produced better SST predictions. These results suggested that the high-resolution ICP-OES derived Sr/Ca ratios of T. gigas in the South China Sea had the potential of providing a good proxy of historical SST.

  18. Magnetic and magnetoelectric properties of M-type substitution hexaferrites TSc x Fe12 - x O19 ( T = Ba, Sr)

    NASA Astrophysics Data System (ADS)

    Balbashov, A. M.; Ivanov, V. Yu.; Mukhin, A. A.; Iskhakova, L. D.; Popov, Yu. F.; Vorob'ev, G. P.; Voronchikhina, M. E.

    2015-04-01

    Single crystals of M-type substitution hexaferrites BaSc x Fe12 - x O19 and SrSc x Fe12 - x O19 ( x = 1.3-1.7) have been grown. Their anisotropic magnetic and magnetoelectric properties have been studied at temperatures of 2-360 K in magnetic fields up to 200 kOe. In all compounds under study, a spontaneous transition from the collinear ferrimagnetic uniaxial phase to a conical structure has been detected with a decrease in the temperature at a temperature increasing with the concentration of Sc up to room temperature. In magnetic fields both parallel and perpendicular to the c axis, the conical phase is suppressed and the transition to the collinear ferrimagnetic structure occurs. Phase diagrams have been plotted in H- T coordinates. In conical magnetic structures, a magnetic-field-induced electric polarization (higher than 40 μC/m2 at 4 K) has been detected in the geometry corresponding to the inverse Dzyaloshinskii-Moriya interaction mechanism (spin current). A higher stability of the polar state with respect to magnetic fields (higher than 50 kOe) and temperatures (up to 100 K) has been revealed as compared to previous studies of the Ba system. Various possibilities of controlling the chirality of the conical structure determining the sign of the polarization, which is important for applications, have been demonstrated.

  19. Characterization of Sr-substituted W-type hexagonal ferrites synthesized by sol-gel autocombustion method

    NASA Astrophysics Data System (ADS)

    Ahmad, Mukhtar; Grössinger, R.; Kriegisch, M.; Kubel, F.; Rana, M. U.

    2013-04-01

    The magnetic and microwave characterization of single phase hexaferrites of entirely new composition Ba1-xSrxCo2AlFe15O27 (x=0.2-1.0) for application in a microwave absorber, have been reported. The samples synthesized by sol-gel method were investigated by differential thermal analyzer, Fourier transform infrared spectroscope, X-ray diffractometer, field emission gun scanning electron microscope, vibrating sample magnetometer and vector network analyzer. Platelet grains exhibit well defined hexagonal shape which is a better shape for microwave absorption. M-H loops for a selected sample were measured for a temperature range of 4.2-400 K. Moreover M-H loops for all Sr-substituted samples were also measured at room temperature up to a maximum applied field of 9 T. Saturation magnetization values were calculated by the law of approach to saturation. The room temperature coercivity for all the samples is found to be a few hundred oersteds which is necessary for electromagnetic materials and makes these ferrites ideal for microwave devices, security, switching and sensing applications. The complex permittivity, permeability and reflection losses of a selected ferrite-epoxy composite were also investigated over a frequency range of 0.5-13 GHz.

  20. Improved Thermoelectric Properties of Bi-M-Co-O (M = Sr, Ca) Misfit Compounds by Laser Directional Solidification

    NASA Astrophysics Data System (ADS)

    Diez, J. C.; Rasekh, Sh.; Madre, M. A.; Guilmeau, E.; Marinel, S.; Sotelo, A.

    2010-09-01

    In this work, improvement of the thermoelectric properties of bulk samples due to texture developed by a directional laser-assisted solidification process (laser floating zone melting method) is reported for cobaltite materials with compositions Bi2Sr2Co1.8O y and Bi2Ca2Co1.7O y . Sample composition and microstructure have been studied using x-ray diffraction and scanning electron microscopy. Thermoelectric properties have been measured between 4 K and 300 K by simultaneous determination of electrical resistivity and thermopower. All textured samples showed remarkable increase of power factor values as compared with conventional sintered ceramics.

  1. 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-Right-Pointing-Pointer PND under magnetic field emphasises the metamagnetic behaviour of {beta}-BaTbF{sub 6}. Black-Right-Pointing-Pointer Comparison of {alpha} and {beta}-BaTbF{sub 6} evidences superexchange interactions in fluoroterbates.

  2. Spectroscopic Signatures of Defect-Induced Pair Breaking in Bi2Sr2CaCu2O8+x

    NASA Astrophysics Data System (ADS)

    Vobornik, I.; Berger, H.; Pavuna, D.; Onellion, M.; Margaritondo, G.; Rullier-Albenque, F.; Forró, L.; Grioni, M.

    1999-04-01

    We investigated the effect of disorder on the spectral properties of the high temperature superconductor Bi2Sr2CaCu2O8+x. We find that small defect densities, in the low 10-3 range, already suppress the characteristic spectral signature of the superconducting state, while new excitations appear within the gap. We conclude that, due to defect-induced pair breaking, superconducting pairs and normal carriers coexist below Tc. At higher levels of disorder the normal state is also strongly affected, and the quasiparticle features progressively smeared out.

  3. 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.

  4. 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.

  5. Loss of interplane correlation in Bi2Sr2CaCu2O8 single crystals

    NASA Astrophysics Data System (ADS)

    Arribére, A.; Pastoriza, H.; Goffman, M. F.; de La Cruz, F.; Mitzi, D. B.; Kapitulnik, A.

    1993-09-01

    By means of dc magnetization and the ac response of Bi2Sr2CaCu2O6 single crystals it is shown that at the dc irreversibility line the vortex system has no long-range order in the c direction. We find an energy dissipation peak at 7 Hz for interplane current that takes place at a temperature well below the irreversibility line. In this sense, the irreversibility line marks the temperature where quasi-two-dimensional vortices are depinned. The experimental data clearly show the different nature of two dissipation peaks in the susceptibility: one related to the interplane currents and the other associated with the intraplane ones.

  6. First order phase transition at the irreversibility line of Bi2Sr2CaCu2O8

    NASA Astrophysics Data System (ADS)

    Pastoriza, H.; Goffman, M. F.; Arribére, A.; de La Cruz, F.

    1994-05-01

    Magnetization and susceptibility measurements show a first order phase transition in the magnetic flux structure at the irreversibility line of Bi2Sr2CaCu2O8+δ single crystals, in the field range 0

  7. Critical state of the weakly coupled two-dimensional superconductor Bi2Sr2CaCu2O8

    NASA Astrophysics Data System (ADS)

    Rodríguez, E.; Goffman, M. F.; Arribére, A.; de La Cruz, F.; Schneemeyer, L. F.

    1993-11-01

    Transport measurements show that the critical current in the c direction, Jcc of Bi2Sr2CaCu2O8 single crystals increases with temperature for low temperature zero field cooled (ZFC) measurements. As a consequence, the c direction electrical resistance of the ZFC critical state, at a given dc current, is finite, goes to zero with increasing temperature, and becomes finite again at higher temperatures. The results are consistent with a loss of the c axis long range correlation induced by the critical current flowing in the ab planes, Jabc, and an increase of that correlation with temperature, as a consequence of the corresponding decrease of Jabc.

  8. 280-year Long Sr/Ca and δ 18O Records From Flinders Reef, Western Coral Sea

    NASA Astrophysics Data System (ADS)

    Calvo, E.; Marshall, J. F.; Pelejero, C.; McCulloch, M. T.; Lough, J.; Gagan, M. K.

    2003-12-01

    The combination of parallel Sr/Ca and δ 18O records in corals allows reconstruction of past changes in sea surface temperature (SST) and seawater δ 18O composition (McCulloch et al., 1994). The latter provides climatic information related to changes in the hydrologic cycle and can be interpreted as a salinity proxy. Since the δ 18O signal is affected by both SST and seawater isotopic composition, a salinity record can be obtained by removing the temperature signal using a parallel Sr/Ca record, a proxy for SST, obtained from the same coral. Low resolution (5-year intervals) Sr/Ca and δ 18O analyses, going back to 1710 AD, have been performed on a Porites coral core collected from Flinders Reef, an offshore reef on the Queensland Plateau (17° S, 149° E), 250 km from the north-east coast of Australia. For the last 280 years, the preliminary Sr/Ca-SST record shows an increasing long-term trend towards the warm temperatures recorded during 1990, when the coral was collected. An increasing trend towards more negative δ 18O values (warmer and/or less saline conditions) is also observed in the isotopic record, which also reflects the 20th century warming. Despite this general common trend, interdecadal variability differences between both records suggest that temperature alone cannot explain the δ 18O changes observed in this site of the Coral Sea. A freshening of surface waters after 1870 has recently been reported from coral cores collected from the inshore region in the Great Barrier Reef and interpreted as indicating a weakening in trade winds and ocean circulation (Hendy, 2002). In the Flinders coral, however, an apparent freshening occurs in the early 1800s, followed by a subsequent transition to more saline conditions during the first half of the 20th century. Our data will be compared to that from the GBR and elsewhere in the SW Pacific (Quinn, 1998). Hendy, E. J. et al. Science 295, 1511-1514 (2002) McCulloch, M.T. et al. Geochimica at Cosmochimica Acta, 58, 2747-2754 (1994) Quinn, T.M. et al. Paleoceanography 13, 412-426 (1998)

  9. 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.

  10. Juxtaglomerular cell CaSR stimulation decreases renin release via activation of the PLC/IP(3) pathway and the ryanodine receptor.

    PubMed

    Ortiz-Capisano, M Cecilia; Reddy, Mahendranath; Mendez, Mariela; Garvin, Jeffrey L; Beierwaltes, William H

    2013-02-01

    The calcium-sensing receptor (CaSR) is a G-coupled protein expressed in renal juxtaglomerular (JG) cells. Its activation stimulates calcium-mediated decreases in cAMP content and inhibits renin release. The postreceptor pathway for the CaSR in JG cells is unknown. In parathyroids, CaSR acts through G(q) and/or G(i). Activation of G(q) stimulates phospholipase C (PLC), and inositol 1,4,5-trisphosphate (IP(3)), releasing calcium from intracellular stores. G(i) stimulation inhibits cAMP formation. In afferent arterioles, the ryanodine receptor (RyR) enhances release of stored calcium. We hypothesized JG cell CaSR activation inhibits renin via the PLC/IP(3) and also RyR activation, increasing intracellular calcium, suppressing cAMP formation, and inhibiting renin release. Renin release from primary cultures of isolated mouse JG cells (n = 10) was measured. The CaSR agonist cinacalcet decreased renin release 56 ± 7% of control (P < 0.001), while the PLC inhibitor U73122 reversed cinacalcet inhibition of renin (104 ± 11% of control). The IP(3) inhibitor 2-APB also reversed inhibition of renin from 56 ± 6 to 104 ± 11% of control (P < 0.001). JG cells were positively labeled for RyR, and blocking RyR reversed CaSR-mediated inhibition of renin from 61 ± 8 to 118 ± 22% of control (P < 0.01). Combining inhibition of IP(3) and RyR was not additive. G(i) inhibition with pertussis toxin plus cinacalcet did not reverse renin inhibition (65 ± 12 to 41 ± 8% of control, P < 0.001). We conclude stimulating JG cell CaSR activates G(q), initiating the PLC/IP(3) pathway, activating RyR, increasing intracellular calcium, and resulting in calcium-mediated renin inhibition. PMID:23220722

  11. Juxtaglomerular cell CaSR stimulation decreases renin release via activation of the PLC/IP3 pathway and the ryanodine receptor

    PubMed Central

    Ortiz-Capisano, M. Cecilia; Reddy, Mahendranath; Mendez, Mariela; Garvin, Jeffrey L.

    2013-01-01

    The calcium-sensing receptor (CaSR) is a G-coupled protein expressed in renal juxtaglomerular (JG) cells. Its activation stimulates calcium-mediated decreases in cAMP content and inhibits renin release. The postreceptor pathway for the CaSR in JG cells is unknown. In parathyroids, CaSR acts through Gq and/or Gi. Activation of Gq stimulates phospholipase C (PLC), and inositol 1,4,5-trisphosphate (IP3), releasing calcium from intracellular stores. Gi stimulation inhibits cAMP formation. In afferent arterioles, the ryanodine receptor (RyR) enhances release of stored calcium. We hypothesized JG cell CaSR activation inhibits renin via the PLC/IP3 and also RyR activation, increasing intracellular calcium, suppressing cAMP formation, and inhibiting renin release. Renin release from primary cultures of isolated mouse JG cells (n = 10) was measured. The CaSR agonist cinacalcet decreased renin release 56 ± 7% of control (P < 0.001), while the PLC inhibitor U73122 reversed cinacalcet inhibition of renin (104 ± 11% of control). The IP3 inhibitor 2-APB also reversed inhibition of renin from 56 ± 6 to 104 ± 11% of control (P < 0.001). JG cells were positively labeled for RyR, and blocking RyR reversed CaSR-mediated inhibition of renin from 61 ± 8 to 118 ± 22% of control (P < 0.01). Combining inhibition of IP3 and RyR was not additive. Gi inhibition with pertussis toxin plus cinacalcet did not reverse renin inhibition (65 ± 12 to 41 ± 8% of control, P < 0.001). We conclude stimulating JG cell CaSR activates Gq, initiating the PLC/IP3 pathway, activating RyR, increasing intracellular calcium, and resulting in calcium-mediated renin inhibition. PMID:23220722

  12. 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.

  13. Spectroscopic properties of UV active medium Ce3+:LiSr0.8Ca0.2AlF6

    NASA Astrophysics Data System (ADS)

    Nizamutdinov, A. S.; Shavelev, A. A.; Marisov, M. A.; Semashko, V. V.

    2016-02-01

    The aim of this work is phase composition and near UV spectroscopic studies of UV active media in fluoride crystals with colquiriite structure, such as Ce3+:LiSr0.8Ca0.2AlF6. Colquiriite structure mixed crystals show higher segregation coefficient of Ce3+ activator ions than common LiCaAlF6 hosts. An important result is based on the fact that this enhancement was achieved for two types of Ce3+ centers in a multisite Ce:LiSr0.8Ca0.2AlF6 system. Thus, it provides a higher gain coefficient for the 5d-4f transitions of Ce3+ ions and it spans a wider continuous wavelength tuning range between 280 and 320 nm for tunable Ce:LiSr0.8Ca0.2AlF6 laser systems.

  14. Improved conductivity of NdFeO₃ through partial substitution of Nd by Ca: a theoretical study.

    PubMed

    Wang, You; Wang, Yun; Ren, Wei; Liu, Porun; Zhao, Huijun; Chen, Jun; Deng, Jinxia; Xing, Xianran

    2015-11-21

    NdFeO3 is an important candidate material for gas sensors and intermediate-temperature solid oxide fuel cells (IT-SOFC). However, its low conductivity prohibits its applications. In this study, we report that the doping of Ca by partially replacing Nd can effectively increase its conductivity. Through the electronic structure analysis of Nd(1-x)Ca(x)FeO3 (x = 0.00, 0.25, 0.50, 0.75 or 1.00) based on the first-principles density functional theory calculations, it is found that the hole states introduced by Ca substitution appear just above the Fermi level, which implies a high mobility of electrons/holes along the Fe-O-Fe bonding network. Specifically, it becomes easier to form O vacancies after Ca doping. Since the diffusion of O anions occurs through a vacancy hopping mechanism, the ion conductivity is also improved. These findings help us to gain an in-depth understanding of the colossally increased conductivity of Ca doped NdFeO3 and turn the electronic conduction for its practical application in gas sensors and IT-SOFC. PMID:26460605

  15. 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.

  16. 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.

  17. 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 (Schmidt et al., 2004). References: CLIMAP Project members (1976) The surface of the ice-age Earth, Science, 191(4232), 1131-1137. Correge T, Gagan MK, Beck JW, Burr GS, Cabioch G, Le Cornec F (2004) Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dryas event, Nature, (6986) 927-928 Crowley TJ (2000) CLIMAP SSTs re-revisited, Climate Dynamics, 16, 241-255 Guilderson TP, Fairbanks RG, Rubenstone JL (1994) Tropical temperature variations since 20,000 years ago: modulating interhemspheric climate change, Science, 263:663-665. Guilderson TP, Fairbanks RG, Rubenstone JL (2001) Tropical Atoantic coral oxygen isotopes: glacial- interglacial sea surface temperatures and climate change, Marine Geology, 172, 75-89 McCulloch MT, Tudhope AW, Esat TM, Mortimer GE, Chappell J, Pillans B, Chivas, AR, Omura A (1999) Coral record of equatorial sea-surface temperatures during the pen-ultimate deglaciation at Huon Peninsula, Science, 283, 202-204 Saenger CP, Cohen AL, Oppo D, Hubbard D (2006) Tropical North Atlantic Coral-Based Sea Surface Temperature and Salinity Reconstructions From the Little Ice Age and Early Holocene. Abstract, Fall AGU.

  18. 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 pH reconstructions and provide us with greater confidence in our ability to reconstruct pH in the ancient oceans from at least some recrystallized foraminiferal calcite. However, further investigations should extend this approach to test the robustness of our findings across a range of taphonomies, ages and burial settings.

  19. Effect of anionic substitution on the structural and magneto-electrical properties of La-Ca-Mn-O perovskite manganites

    NASA Astrophysics Data System (ADS)

    Altintas, S. P.; Mahamdioua, N.; Amira, A.; Terzioglu, C.

    2014-11-01

    The role of anion substitution of oxygen by fluorine in La0.7Ca0.3MnO3-δFx (x=0.0 and 0.6) system has been investigated by means of X-ray powder diffraction, electrical resistivity and magnetization measurements. The oxygen content of the samples, estimated by a redox back titration method, decreases with doping while the lattice parameters and unit cell volume increase slightly. The Curie temperature and the metal-insulator transition temperatures of the samples are also found to increase with doping. The deduced magnetoresistance is slightly higher for the doped sample.

  20. Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped CaF2 and SrF2 crystals

    NASA Astrophysics Data System (ADS)

    Barandiarán, Zoila; Seijo, Luis

    2015-10-01

    Dopant-to-host electron transfer is calculated using ab initio wavefunction-based embedded cluster methods for Yb/Ca pairs in CaF2 and Yb/Sr pairs in SrF2 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 4fN-15d excited states of Y b2+: these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b2+ + Ca2+ (Sr2+) → Y b3+ + Ca+ (Sr+) electron phototransfer. This mechanism applies to all the observed Y b2+ 4f-5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF2:Y b2+ because the Y b3+-Ca+ states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF2:Y b2+ 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 b2+ 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 SrF2 host, associated with the lowest 4f-5d band.

  1. Metal-to-metal charge transfer between dopant and host ions: Photoconductivity of Yb-doped CaF2 and SrF2 crystals.

    PubMed

    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 CaF2 and Yb/Sr pairs in SrF2 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(N-1)5d excited states of Y b(2+): these are reached by the first photon excitation; then, they absorb the second photon, which provokes the Y b(2+) + Ca(2+) (Sr(2+)) → Y b(3+) + Ca(+) (Sr(+)) electron phototransfer. This mechanism applies to all the observed Y b(2+) 4f-5d absorption bands with the exception of the first one: Electron transfer cannot occur at the first band wavelengths in CaF2:Y b(2+) because the Y b(3+)-Ca(+) states are not reached by the two-photon absorption. In contrast, Yb-to-host electron transfer is possible in SrF2:Y b(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(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 SrF2 host, associated with the lowest 4f-5d band. PMID:26472390

  2. 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.

  3. Measurement of RyR permeability reveals a role of calsequestrin in termination of SR Ca2+ release in skeletal muscle

    PubMed Central

    Sztretye, Monika; Yi, Jianxun; Figueroa, Lourdes; Zhou, Jingsong; Royer, Leandro; Allen, Paul; Brum, Gustavo; Ríos, Eduardo

    2011-01-01

    The mechanisms that terminate Ca2+ release from the sarcoplasmic reticulum are not fully understood. D4cpv-Casq1 (Sztretye et al. 2011. J. Gen. Physiol. doi:10.1085/jgp.201010591) was used in mouse skeletal muscle cells under voltage clamp to measure free Ca2+ concentration inside the sarcoplasmic reticulum (SR), [Ca2+]SR, simultaneously with that in the cytosol, [Ca2+]c, during the response to long-lasting depolarization of the plasma membrane. The ratio of Ca2+ release flux (derived from [Ca2+]c(t)) over the gradient that drives it (essentially equal to [Ca2+]SR) provided directly, for the first time, a dynamic measure of the permeability to Ca2+ of the releasing SR membrane. During maximal depolarization, flux rapidly rises to a peak and then decays. Before 0.5 s, [Ca2+]SR stabilized at ∼35% of its resting level; depletion was therefore incomplete. By 0.4 s of depolarization, the measured permeability decayed to ∼10% of maximum, indicating ryanodine receptor channel closure. Inactivation of the t tubule voltage sensor was immeasurably small by this time and thus not a significant factor in channel closure. In cells of mice null for Casq1, permeability did not decrease in the same way, indicating that calsequestrin (Casq) is essential in the mechanism of channel closure and termination of Ca2+ release. The absence of this mechanism explains why the total amount of calcium releasable by depolarization is not greatly reduced in Casq-null muscle (Royer et al. 2010. J. Gen. Physiol. doi:10.1085/jgp.201010454). When the fast buffer BAPTA was introduced in the cytosol, release flux became more intense, and the SR emptied earlier. The consequent reduction in permeability accelerated as well, reaching comparable decay at earlier times but comparable levels of depletion. This observation indicates that [Ca2+]SR, sensed by Casq and transmitted to the channels presumably via connecting proteins, is determinant to cause the closure that terminates Ca2+ release. PMID:21788611

  4. 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.

  5. Mechanical relaxation in thermoelectric oxide Ca{sub 3−x}Sr{sub x}Co{sub 4}O{sub 9+δ} (x=0, 0.25, 0.5, 1.0) associated with oxygen vacancies

    SciTech Connect

    Liu, H.; Lin, G.C.; Ding, X.D.; Zhang, J.X.

    2013-04-15

    Ca{sub 3}Co{sub 4}O{sub 9+δ} has a unique structure that leads to exceptionally good thermoelectric (TE) properties. To change the concentration of oxygen vacancies (OVs) of the sample, the same sintered Ca{sub 3}Co{sub 4}O{sub 9+δ} polycrystalline ceramic suffered treating in 30 wt% oxydol (H{sub 2}O{sub 2}) solution and then annealing at 600 °C in pure N{sub 2}-gas atmosphere. Before and after each treatment, we performed dynamic mechanical analysis (DMA) with different frequencies, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) on the sample. A relaxation peak was observed at the temperature range from 90 °C to 150 °C, and the relaxation process is most likely caused by the migration of single OVs. The consistency in the results from TGA and XPS could well support the conclusion that the OVs of Ca{sub 3}Co{sub 4}O{sub 9+δ} are located on the O site of CoO layer in Ca{sub 2}CoO{sub 3} subsystem. Further DMA investigations on the Ca{sub 3−x}Sr{sub x}Co{sub 4}O{sub 9+δ} (x=0, 0.25, 0.5, 1.0) ceramic indicated that Sr substitution of Ca could suppress the relaxation peak, suggesting the migration of single OVs mainly processes between CoO and CaO layers of Ca{sub 2}CoO{sub 3} subsystem. - Graphical abstract: A relaxation peak and a transition peak could be observed in the internal friction spectra of Ca{sub 3}Co{sub 4}O{sub 9+δ}. The calculated activation energy indicates the relaxation process is associated with migration of oxygen vacancies. Highlights: ► We performed dynamic mechanical analysis on the thermoelectric oxide Ca{sub 3}Co{sub 4}O{sub 9+δ}. ► We observed a relaxation peak and a transition peak. ► The oxygen vacancies are located in CoO layer of Ca{sub 2}CoO{sub 3} subsystem. ► The relaxation peak originates from migration of single oxygen vacancies.

  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. Electrochemical insertion of lithium into the Bi2Sr2CaCu2O8+ y high- Tc superconductor

    NASA Astrophysics Data System (ADS)

    Fleischer, Niles A.; Manassen, Joost; Coppens, Philip; Lee, Peter; Gao, Yan; Greenbaum, Steven G.

    1992-01-01

    The insertion compound LixBi2Sr2CaCu2O8+ y (for lithium contents up to the studied level of x=2) was prepared by electro-chemical insertion of lithium into Bi2Sr2CaCu2O8+ y pellets at room temperature in galvanic cells using 1.4 M LiAsF 6 in 2Me-THF as electrolyte. The reaction proceeds with retention of the host crystal structure and without the appearance of any new phases. Bulk superconductivity persists but the superconducting fraction appears to be lower in the reacted samples. XRD data show that insertion of Li ions is accompanied by interlayer expansion between BiO planes and a small increase in the a and b cell lattice parameters. 7Li NMR measurements indicate a substantial donation of electrons to the 2212 host lattice. The changes in the a and b lattice parameters and the effect on superconductivity is consistent with some of the donated electrons entering the CuO planes and reducing holes in these layers.

  8. 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.

  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. 110 K Bi 2Sr 2Ca 2Cu 3O y superconductors by Pb and Sb doping

    NASA Astrophysics Data System (ADS)

    Padmanaban, V. P. N.; Shahi, K.

    1992-07-01

    110 K superconductors with nominal compositions Bi 1.9Pb 0.3Sr 2Ca 2Cu 3O y and Bi 1.6Pb 0.3Sb 0.1Sr 2Ca 2Cu 3O y have been prepared by a liquid-phase-aided process involving a matrix method. The carbonate calcination and (Bi, Pb, Sb)SrCaO matrix formation at 820°C is followed by a short-time heating of the matrix-CuO mixture at 900°C and subsequent sintering at 850-860°C and furnace cooling to 400°C. The short-time heating and optimal sintering temperature are vital to achieve superconductivity at temperatures higher than 100 K. The samples are characterized by XRD, DTA, resistivity and TEP measurements. TEP data show that these are hole-type superconductors. Pb and Sb combined doping has an advantage over Pb-doping in that it brings down the sintering temperature and duration by making the kinetics of the reaction faster.

  11. Microstructure and electrical properties of pure 110K phase in the BiPbSrCaCuO system

    NASA Astrophysics Data System (ADS)

    Holguin, E.; Berger, H.; Lévy, F.; Dwir, B.; Pavuna, D.; Burri, G.

    1991-01-01

    The temperature dependence of the d.c. resistivity and a.c. magnetic susceptibility was investigated in bulk ceramics of the BiPbSrCaCuO system with 2212 - free (2223) phase. The temperature domain needed to synthesize this phase was small and, according to the actual temperature used, the superconducting properties of the samples were strongly modified. The corresponding X-ray diffraction lines of the 110K phase can be indexed in the pseudo-orthorhombic unit cell with parameters 5.40x5.41x37Å 3. SEM microprobe study revealed the presence of several non-superconducting phases and a composition 2.1:0.1:2:2:3 for the cation ratio Bi:Pb:Sr:Ca:Cu of the 110K phase. Electrical measurements (d.c. resistivity and a.c. susceptibility) confirmed the existence of a 2212 - free (2223) phase. A low temperature "tail" in the d.c. electrical resistivity marks the low value of critical current in the samples.

  12. 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.

  13. 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.

  14. Electron beam flash evaporation for YBaCuO and BiCaSrCuO thin films

    NASA Technical Reports Server (NTRS)

    Davis, Matthew F.; Wosik, Jaroslaw L.; Wolfe, J. C.

    1989-01-01

    An electron beam flash evaporation technique is described which reproduces the stoichiometry of superconducting YBa(2)Cu(3)O(x) (123), Bi(2)CaSr(2)Cu(2)O(y) (2122), and Bi(2)Ca(2)Sr(2)Cu(3)O(z) (2223) source powders. Films of each material deposited with this technique exhibit zero resistance temperatures of 78 K or above when furnace annealed; 75 K zero temperatures are obtained for 123 films in situ annealed with atomic oxygen at 775 C. Transport critical current densities are 10,000 A/sq cm in 25-micron stripes patterned from 123 films, and 60,000 A/sq cm in 1-mm stripes of 2122 and 2223 films using a 1-microV/mm measurement criteria. Typical normal state resistivities are 700 micro-ohm cm for 2122 and 2223 films and 5 micro-ohm cm for 123 films. The 2122 films are highly textured with the c axis normal to the substrate. All results are for films deposited on MgO.

  15. Spin-density-wave-induced anomalies in the optical conductivity of AFe2 As2 , (A=Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Charnukha, Aliaksei; Proepper, Daniel; Larkin, Timofei; Sun, Dunlu; Li, Z. W.; Lin, Chengtian; Wolf, Thomas; Keimer, Bernhard; Boris, Alexander

    2014-03-01

    We report the complex dielectric function of high-quality AFe2As2, (A=Ca,Sr,Ba) single crystals with TN=150K, 200K, and 138K, respectively, determined by broadband spectroscopic ellipsometry. In CaFe2As2 we identify the optical spin-density-wave gap 2ΔSDW ~ 1250cm-1 . The 2ΔSDW /(kBTN) ratio amounts to 12 in CFA, significantly larger than the corresponding values for the SFA and BFA compounds: 8.7 and 5.3, respectively. We further show that, similarly to the Ba-based compound, two characteristic SDW energy gaps can be identified in the infrared-conductivity spectra of both SFA and CFA and investigate their detailed temperature dependence in all three materials. This analysis reveals the existence of an anomaly in CFA at a temperature T*=80K, well below the Néel temperature of this compound, which implies weak coupling between the two SDW subsystems. The coupling between the two subsystems evolves to intermediate in the Sr-based and strong in the Ba-based material. Our results single out CFA in the class of 122 iron-based materials by demonstrating the existence of two weakly coupled and extremely metallic electronic subsystems. This project was supported by the German Science Foundation under grant BO 3537/1-1 within SPP 1458.

  16. Energy transfer dynamics and luminescence properties of Eu(3+) in CaMoO4 and SrMoO4.

    PubMed

    Gupta, Santosh K; Sahu, M; Ghosh, P S; Tyagi, Deepak; Saxena, M K; Kadam, R M

    2015-11-21

    Undoped and europium doped CaMoO4 and SrMoO4 scheelites are synthesized using a complex polymerization method. The phase purity of the sample is confirmed using powder X-ray diffraction (PXRD). X-ray photoelectron spectroscopy (XPS) was carried out to confirm the oxidation states of various constituents and dopant elements and also the presence of oxygen vacancies. Interestingly both CaMoO4 and SrMoO4 on irradiation with UV light give blue and green emission respectively. On europium doping, it was found that molybdate to Eu(3+) ion energy transfer is more efficient in SrMoO4:Eu compared to CaMoO4:Eu. It is also justified using a luminescence lifetime study which shows biexponential decay in the case of CaMoO4:Eu corresponding to both the host and europium ion; whereas a single lifetime is observed in the case of SrMoO4:Eu. Anomalies in host-dopant energy transfer are suitably explained using density functional theory (DFT) calculations and XPS. The actual site symmetry for the europium ion in CaMoO4 and SrMoO4 was also evaluated based on a Stark splitting pattern which turns out to be D2 and C2v respectively although it is S4 for Ca/Ba(2+) in AMoO4. This is also reflected in higher Ω2 values for SrMoO4:Eu than CaMoO4:Eu. PMID:26468623

  17. 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}. 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). - Graphical abstract: The SrCo{sub 2}Si{sub 2} and CaFe{sub 2−x}Rh{sub x}Si{sub 2} (x==0, 1.32, and 2) crystallize in the ThCr{sub 2}Si{sub 2}-type. The structure of SrCo{sub 2}Si{sub 2} contains isolated [Co{sub 2}Si{sub 2}]{sup 2−} layers in the ab-plane, whereas the [T{sub 2}Si{sub 2}] layers in CaFe{sub 2−x}Rh{sub x}Si{sub 2} are interconnected along the c-axis via Si3Si bonds resulting in a [T{sub 2}Si{sub 2}]{sup 2−} network. - Highlights: • Synthesis and structure of ternary silicides SrCo{sub 2}Si{sub 2} and CaFe{sub 2−x}Rh{sub x}Si{sub 2} (x=0, 1.32, and 2). • 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}. • CaFe{sub 2}Si{sub 2} is a full substituted variant (As/Si) of superconductor CaFe{sub 2}As{sub 2}. • The title compounds demonstrate the tunable Si3Si distances.

  18. Sol-gel preparation of high-T/sub c/ Bi-Ca-Sr-Cu-O and Y-Ba-Ca-O superconductors

    SciTech Connect

    Fransaer, J.; Roos, J.R.; Delaey, L.; Van Der Biest, O.; Arkens, O.; Celis, J.P.

    1989-04-15

    High-T/sub c/ superconducting oxides have been prepared by a liquid-mix technique using etylene-diamine-tetra-acetic acid (EDTA) as a complexing agent. Bi-Sr-Ca-Cu oxides and Y-Ba-Cu oxides were made using this technique giving a better compositional homogeneity, a more precise control of the cation stoichiometry and a decreased firing temperature as compared to conventional material produced by a solid-state reaction. This technique extends the amorphous citrate process to those systems where no citrate complex exists. EDTA binds with most metallic elements of the periodic table, making this technique a versatile tool in the production and study of these new ceramic materials. Therefore, the method is easily adapted to the preparation of new superconducting oxides.

  19. 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. These findings strengthen the evidence for a global ocean acidification event coupled with rapid expansion of anoxic zones as drivers of end-Permian extinction in the oceans.

  20. 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 enrichment increases with growth rate and is correlated with Sr/Ca in calcite. These results are in excellent agreement with the results of Tang et al. (2008) for crystals grown at 25°C and suggest that mass discrimination is controlled by mass transport kinetics at the mineral-solution interface. Oxygen isotopes are more complicated because of the addition of CO2 to the bulk solution. For crystals grown from our stock solution, the O composition is highly variable and not correlated with growth rate. We attribute this to relatively slow kinetics of O isotope exchange between gaseous or dissolved CO2 and water. For crystals grown in the presence of 0.01 grams of bovine carbonic anhydrase (CA), an enzyme which catalyzes the interconversion of CO2 and H2O to bicarbonate and protons, the O isotope composition of calcite appears to be independent of growth rate. Hence addition of CA to solution might offer a means of determining the equilibrium fractionation factor for oxygen isotopes in carbonate minerals. We will present results from additional experiments that test how CA and other organic molecules in solution affect the growth rate and mass discrimination during mineral precipitation.

  1. 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.

  2. Preparation of nearly single phase 2223 in Bi 1.6Pb 0.4Sr 2Ca 2Cu 3O y composition by a semi-wet route using Pb 0.2SrCa(CO 3) 2.2 precursor

    NASA Astrophysics Data System (ADS)

    Pandey, Dhananjai; Mahesh, R.; Singh, A. K.; Tiwari, V. S.; Kak, S. K.

    1991-12-01

    A new method for the synthesis of nearly single phase 2223 in Bi 1.6Pb 0.4Sr 2Ca 2Cu 3O y composition within 72 h of total heat treatment, using coprecipitates of (1) 0.2 Pb, Ca, Sr as carbonates and (2) 1.6 Bi, 3 Cu as oxalate, is reported. Samples prepared have been characterized by their crystal structure using XRD, microstructure using SEM and electrical resistivity.

  3. Alterations in the force-frequency relationship by tert-butylbenzohydroquinone, a putative SR Ca2+ pump inhibitor, in rabbit and rat ventricular muscle.

    PubMed Central

    Baudet, S.; Do, E.; Noireaud, J.; Le Marec, H.

    1996-01-01

    1. The effects of 2,5 di-(tert-butyl)-1,4-benzohydroquinone (TBQ), a putative inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, on twitch tension, time course and SR Ca2+ content have been studied at different stimulation frequencies (0.5-3 Hz) in isolated preparations from the rabbit and rat right ventricle, at 37 degrees C. 2. At 0.5Hz, 30 microM TBQ induced a marked negative inotropic effect in both species (-57% in the rabbit and -68% in the rat) and decreased the rate of rise and fall of twitch tension. In parallel, SR Ca2+ content (assessed by rapid cooling contractures) was depressed in the rabbit by 42%. The force-frequency relationship (positive for the rabbit and negative for the rat) was significantly attenuated. In the rabbit, this alteration was shown to rely on insufficient SR Ca2+ reloading with increasing frequencies. 3. Exposure of TBQ-treated preparations to 8 mM extracellular Ca2+ or 5 microM isoprenaline were effective in reloading the SR with Ca2+ whereas 20 mM caffeine emptied this compartment. 4. In the rabbit ventricle, increase in stimulation frequency shortened control twitch time course by decreasing both the time to peak tension (TTP) and the time to half relaxation (t1/2). TBQ did not differentially affect the pattern for t1/2 but significantly attenuated the frequency-induced decrease of TTP. 5. In rabbit ventricular muscle, the action potential duration increased between 0.5 and 3 Hz whether or not TBQ was present. However, TBQ induced a small but significant additional action potential shortening. 6. TBQ decreased twitch tension in the rat ventricle between 0.5 and 3 Hz but the negative staircase was not differentially affected by the SR Ca2+ pump inhibitor. In control conditions and in the presence of 30 microM TBQ, t1/2 was frequency-independent but TBQ consistently increased this parameter (by approximately 29%). 7. These data argue in favour of a specific and partial inhibition of the SR Ca2+ pump by 30 microM TBQ in the rabbit and rat ventricle and emphasise the importance of SR Ca2+ uptake in the force-frequency phenomenon. PMID:8789377

  4. 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

  5. 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 layer dynamics.

  6. Spin Gap in the Zigzag Spin-1/2 Chain Cuprate Sr0.9Ca0.1CuO2

    NASA Astrophysics Data System (ADS)

    Hammerath, F.; Nishimoto, S.; Grafe, H.-J.; Wolter, A. U. B.; Kataev, V.; Ribeiro, P.; Hess, C.; Drechsler, S.-L.; Büchner, B.

    2011-07-01

    We report a comparative study of Cu63 nuclear magnetic resonance spin lattice relaxation rates T1-1 on undoped SrCuO2 and Ca-doped Sr0.9Ca0.1CuO2 spin chain compounds. A temperature independent T1-1 is observed for SrCuO2 as expected for an S=1/2 Heisenberg chain. Surprisingly, we observe an exponential decrease of T1-1 for T<90K in the Ca-doped sample evidencing the opening of a spin gap. The data analysis within the J1-J2 Heisenberg model employing density-matrix renormalization group calculations suggests an impurity driven small alternation of the J2-exchange coupling as a possible cause of the spin gap.

  7. 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.

  8. In-plane thermoelectric properties of heavily underdoped high-temperature superconductor Bi2Sr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Horiuchi, Y.; Tamura, W.; Fujii, T.; Terasaki, I.

    2010-06-01

    We have measured and analyzed the in-plane thermoelectric parameters from 25 to 210 K in single-crystal samples of Bi2(Sr, La)2CaCu2O8+δ and Bi2(Sr, Ca, La)3Cu2O8+δ, which are known as heavily underdoped high-temperature superconductor Bi2Sr2CaCu2O8+δ. Although the resistivity and thermopower are nearly the same as those of the thermoelectric layered cobalt oxides in this temperature range, the thermal conductivity is twice as large, and the dimensionless figure of merit ZT retains a small value of 0.025 at 210 K. A possible value upper limit for ZT in the layered copper oxides is discussed based on the present results.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Giant magneto-caloric effect around room temperature at moderate low field variation in La 0.7(Ca 1-xSr x) 0.3MnO 3 perovskites

    NASA Astrophysics Data System (ADS)

    Islam, M. S.; Hanh, D. T.; Khan, F. A.; Hakim, M. A.; Minh, D. L.; Hoang, N. N.; Hai, N. H.; Chau, N.

    2009-08-01

    Among the perovskite manganites, a series of La 1-xCa xMnO 3 has the largest magneto-caloric effect (MCE) (|Δ Sm| max=3.2-6.7 J/kg K at Δ H=13.5 kOe), but the Curie temperatures, TC, are quite low (165-270 K). The system of LaSrMnO 3 has quite high TC but its MCE is not so large. The manganites La 0.7(Ca 1-xSr x) 0.3MnO 3 ( x=0, 0.05, 0.10, 0.15, 0.20, 0.25) have been prepared by solid state reaction technique with an expectation of large MCE at room temperature region. The samples are of single phase with orthorhombic structure. The lattice parameters as well as the volume of unit cell are continuously increased with the increase of x due to large Sr 2+ ions substituted for smaller Ca 2+ ions. The field-cooled (FC) and zero-field-cooled (ZFC) thermomagnetic measurements at low field and low temperatures indicate that there is a spin-glass like (or cluster glass) state occurred. The Curie temperature TC increases continuously from 258 K (for x=0) to 293 K (for x=0.25). A large MCE of 5 J/kg K has been observed around 293 K at the magnetic field change Δ H=13.5 kOe for the sample x=0.25. The studied samples can be considered as giant magneto-caloric materials, which is an excellent candidate for magnetic refrigeration at room temperature region.

  15. Characteristics of a diode-pumped Yb:CaF2-SrF2 mode-locked laser using a carbon nanotube absorber

    NASA Astrophysics Data System (ADS)

    Liu, J.; Feng, C.; Su, L. B.; Jiang, D. P.; Zheng, L. H.; Qian, X. B.; Wang, J. Y.; Xu, J.; Wang, Y. G.

    2013-10-01

    Yb:CaF2-SrF2 disordered crystals are successfully grown by the TGT method. By using a double-walled carbon nanotube saturable absorber (DWCNT-SA), the continuous-wave mode-locked (CWML) laser properties of Yb:CaF2-SrF2 crystals are demonstrated under diode pumping for the first time. The mode-locked laser delivers pulses as short as 5 ps at a center wavelength of 1045.5 nm without any dispersion compensation. The oscillator operating at a repetition rate of ˜87 MHz delivers 292 mW average output power.

  16. 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.

  17. A comprehensive review of the XRD data of the primary and secondary phases present in the BSCCO superconductor system. Part 2, Ca-Sr-Pb oxides

    SciTech Connect

    Reardon, B.J.; Hubbard, C.R.

    1992-02-01

    X-ray powder patterns for the phases in the CaO-SrO-PbO ternary system, along with the corresponding crystal structures, were obtained from the literature and from the Powder Diffraction File (PDF). Available X-ray diffraction (XRD) patterns were compared with each other and, when possible, with a calculated pattern for each phase, yielding a recommended reference pattern. The simulated powder patterns presented here deal with the phases found within the (Ca,Sr){sub 2}PbO{sub 4} solid solution series and are recommended for the PDF.

  18. Effect of doping by low content of yttrium at Ca and Sr sites of Bi(Pb)-2212 superconducting ceramics

    NASA Astrophysics Data System (ADS)

    Amira, Abderrezak; Boudjadja, Y.; Saoudel, A.; Varilci, A.; Akdogan, M.; Terzioglu, C.; Mosbah, M. F.

    2011-02-01

    In this work, a comparative study of the effect of doping by low content of Y 3+ between (Ca site) and out of (Sr site) the CuO 2 planes of Bi(Pb)-2212 phase is presented. Ceramics of Bi 1.6Pb 0.4Sr 2Ca 1- xY xCu 2O 8+d (called CY series) and Bi 1.6Pb 0.4Sr 2- xY xCaCu 2O 8+d (called SY series) with x=0, 0.025, 0.05, 0.075 and 0.1 are elaborated in air by conventional solid state reaction. They are characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy (SEM), density, Vickers microhardness and resistivity measurements. The refinement of cell parameters is done by considering the structural modulation. In comparison with the undoped sample ( x=0), the cell parameters a, b and c are reduced by the doping for both series while the b component of the modulation vector increases. A good correlation between the variations of the bulk density and the Vickers microhardness with x is obtained. For both series, the SEM analysis shows that the doped samples exhibit a reduced grain size than that of the undoped one. The variation of resistivity with temperature shows that all samples exhibit a metallic-like character in the normal state. For all doping levels, the CY series presents higher onset critical transition temperature than that of the undoped sample, which is equal to 85.43 K. The opposite is obtained for SY series. The highest value of this temperature is obtained for x=0.075 in the doped samples and is about 92.15 and 79.96 K for CY and SY series, respectively. These values may correspond to a near optimally doped state since the slope ( dρ/dT) of resistivity shows a maximum at the same value of x=0.075. For both series, when Y 3+ is introduced into the samples, the residual resistivity decreases first for x=0.025 and increases gradually after this value until x=0.1.

  19. Periodic c-axis modulation and crystallographic Fourier analysis of Bi 2Sr 2Ca nCu n+1O 6+2n+x ( n=0,1) single crystals with excess Bi

    NASA Astrophysics Data System (ADS)

    Ariosa, D.; Berger, H.; Schmauder, T.; Pavuna, D.; Margaritondo, G.; Christensen, S.; Kelley, R. J.; Onellion, M.

    2001-04-01

    We report on a distortion of Bi 2Sr 2Ca nCu n+1O 6+2n+x ( n=0,1) single crystals, perpendicular to the CuO 2 planes (the c-axis), for non-stoichiometric samples containing an excess of Bi. The distortion involves two parts: (a) symmetric displacements in the SrO and CuO 2 planes along the c-axis, and (b) an antisymmetric longitudinal compressive wave. The latter is revealed by observing odd harmonics in the X-ray diffraction (XRD) data. Such odd harmonics are typically extinguished for the I4/mmm space group of the exact stoichiometric phase. The antisymmetric compressive wave is reported for both BSCCO-2201 and BSCCO-2212 Bi excess samples, as well as for La-doped BSCCO-2201 samples. We have performed XRD model calculations for all samples studied, combined with Fourier analysis of the periodic c-axis modulation. The antisymmetric compressive wave was proven by reconstructing the atomic position profile from the intensity of odd XRD peaks caused by this commensurate modulation. Our results indicate preferential ordered substitution of Bi ions on nominally Sr ion positions. We also discuss implications for oxygen mobility, reversible sample doping, and electronic properties.

  20. High-T(c) Superconductivity at the Interface between the CaCuO2 and SrTiO3 Insulating Oxides.

    PubMed

    Di Castro, D; Cantoni, C; Ridolfi, F; Aruta, C; Tebano, A; Yang, N; Balestrino, G

    2015-10-01

    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 T(c). We report the occurrence of high T(c) superconductivity in the bilayer CaCuO(2)/SrTiO(3), where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO(2)/SrTiO(3) interface must be realized between the Ca plane of CaCuO(2) and the TiO(2) plane of SrTiO(3). Only in this case can oxygen ions be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO(2) planes. 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 CaCuO(2) unit cells close to the interface with SrTiO(3). The results obtained for the CaCuO(2)/SrTiO(3) interface can be extended to multilayered high T(c) cuprates, contributing to explaining the dependence of T(c) on the number of CuO(2) planes in these systems. PMID:26551817

  1. Structural, vibrational, electronic, and luminescence properties of the cyclotetravanadates A2M(VO3)4 ( A=Na,Ag ; M=Ca,Sr )

    NASA Astrophysics Data System (ADS)

    Zubkov, V. G.; Surat, L. L.; Tyutyunnik, A. P.; Berger, I. F.; Tarakina, N. V.; Slobodin, B. V.; Kuznetsov, M. V.; Denisova, T. A.; Zhuravlev, N. A.; Perelyaeva, L. A.; Baklanova, I. V.; Shein, I. R.; Ivanovskii, A. L.; Shulgin, B. V.; Ishchenko, A. V.; Tcherepanov, A. N.; Svensson, G.; Forslund, B.; Skripkin, M. Yu.

    2008-05-01

    The physical properties of the family of cyclotetravanadates A2M(VO3)4 , where A=Na,Ag and M=Ca,Sr , have been studied by means of x-ray powder diffraction, neutron diffraction, electron diffraction, infrared, Raman, NMR, photoexcitation and pulse cathode beam excitation, and x-ray photoelectron spectroscopies, and band structure calculations. The differences between the structural, vibrational, luminescence, and electronic properties of the alkali metal-containing [ Na2Ca(VO3)4 and Na2Sr(VO3)4 ] and the d metal-containing cyclotetravanadates [ Ag2Ca(VO3)4 and Ag2Sr(VO3)4 ] are analyzed. Na2Ca(VO3)4 , Ag2Ca(VO3)4 , Na2Sr(VO3)4 , and Ag2Sr(VO3)4 have tetragonal structures, P4/nbm , with a=10.43849(6) , 10.44524(5) , 10.63449(4) , and 10.62574(6) , and c=4.93873(5) , 4.96845(5) , 4.96205(4) , and 4.97930(4)Å , respectively. The main structural feature of A2M(VO3)4 is the tetracyclic [V4O12] units. The hybridized O2p-V3d states of the tetracyclic [V4O12] units have a dominant influence on the electronic structure of these compounds. The compounds are semiconducting with a local density approximation band gap increasing from 1.85 eV for Ag2Ca(VO3)4 to 3.02 eV for Na2Ca(VO3)4 . The prospects of these compounds as advanced materials for detectors of photon and corpuscular radiation as well as for color correction of light emission sources such as lamp and light emitting diode sources are discussed.

  2. 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.

  3. Structure and ferroelectric properties of BaBi 3.8M 0.2(Ti 3.8Nb 0.2)O 15 (M=Mg, Ca, Sr and Ba) ceramics

    NASA Astrophysics Data System (ADS)

    Chakrabarti, A.; Bera, J.

    2011-07-01

    Bismuth layer structured compounds BaBi 3.8M 0.2(Ti 3.8Nb 0.2)O 15, with M=Mg, Ca, Sr and Ba, were synthesized through a modified chemical route. Phase and structure of the compounds were analyzed by X-ray diffraction. The structure of Mg 2+ based compound was orthorhombic, while it was tetragonal for the other three compositions. Experimental results indicate that Mg 2+ prefers to substitute in the Bi 2O 2 layer. The room temperature permittivity was maximum for Ba 2+ based compound (∼432). The piezoelectric coefficient was significantly enhanced in Mg 2+ based compound. The Curie temperature was found to decrease gradually in the order Mg>Ca>Sr>Ba based compound. There was a marked improvement in the relaxor behavior and remnant polarization for Ba 2+ based compound. The structural changes and dielectric, ferroelectric and piezoelectric properties of all the compounds was discussed and co-related.

  4. 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.

  5. First principles investigation of Sr and P doping of CaFe2As2

    NASA Astrophysics Data System (ADS)

    Jeschke, Harald O.; Tomic, Milan; Valenti, Roser

    2013-03-01

    The doping-temperature-pressure phase diagrams of the 122 family of superconductors have been discussed intensively due to electronic nematicity above the structural and superconducting transition and the complex coupling between electronic and lattice degrees of freedom. We employ density functional theory to determine the structure of supercells of Ca1-xSrxFe2As2 and CaFe2(As1-xPx)2. We then predict structural transitions of the doped compounds under pressure and compare to the parent compound. We carefully analyze the changes in the electronic structure caused by doping and stress.

  6. Isovalent-substitution effect on the Verwey-type transition in the A-site-ordered double perovskite (Ba,Sr)RFe{sub 2}O{sub 5}

    SciTech Connect

    Nakamura, J.; Karppinen, M.; Yamauchi, H.; Karen, P.; Linden, J.

    2004-10-01

    Two types of chemical-pressure effects on the Verwey-type transition in BaSmFe{sub 2}O{sub 5} are studied, viz., ionic-size contractions at the Ba and Sm sites. Whereas the replacement of Sm by the smaller Eu and Gd atoms increases the transition temperature T{sub V} from 232 K to 264 K, the Sr-for-Ba substitution decreases it from 232 K to 180 K for x=0.15 in (Ba{sub 1-x}Sr{sub x})SmFe{sub 2}O{sub 5}. Of various structural parameters determined by synchrotron x-ray diffraction above T{sub V}, the magnitude of the orthorhombic distortion (=b-a) is found to correlate with T{sub V} in a manner that unifies both substitution schemes. It is suggested that when an increase in b-a above T{sub V} is achieved by means of the structural substitution, it makes it easier for the d{sub xz} Fe{sup 2+} orbital ordering to occur below T{sub V}.

  7. NMR studies of pseudogap and electronic inhomogeneity in Bi2Sr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Crocker, J.; Dioguardi, A. P.; Aproberts-Warren, N.; Shockley, A. C.; Grafe, H.-J.; Xu, Z.; Wen, J.; Gu, G.; Curro, N. J.

    2011-12-01

    We report 17O NMR measurements in single crystals of overdoped Bi2Sr2CaCu2O8+δ with Tc=82 K. We measure the full anisotropy of the planar oxygen Knight shift, electric field gradient, and spin-lattice-relaxation rate tensors, and show that the entire temperature dependence is determined by the suppression of the density of states in the pseudogap below T*˜94 K. The linewidth can be explained by a combination of magnetic and quadrupolar broadening as a result of an inhomogeneous distribution of local hole concentrations that is consistent with scanning tunneling microscopy measurements. This distribution is temperature independent, does not break C4 symmetry, and exhibits no change below T* or Tc.

  8. 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.

  9. 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.

  10. Numerical Investigation of the Quench Behavior of Bi2Sr2CaCu2Ox Wire

    SciTech Connect

    Arbelaez, D.; Prestemon, S. O.; Dietderich, D. R.; Godeke, A.; Ye, L.; Hunte, F.; Schwartz, J.

    2010-08-01

    The quench behavior of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi2212) wire is investigated through numerical simulations. This work is part of the U.S. Very High Field Superconducting Magnet Collaboration (VHFSMC). Numerical simulations are carried out using a one-dimensional computational model of thermal transport in Bi2212 composite wires. A quench is simulated by introducing heat in a section of the wire, and the voltage and temperature are monitored as function of time and position. The quench energy, normal zone propagation velocity, and spatial distribution of temperature are calculated for varying transport current and applied magnetic field. The relevance of these simulations in defining criteria for experimental measurements is discussed.

  11. Giant Enhancement in the Physical Properties of LaFeO3 by Substitution of Divalent Ions

    NASA Astrophysics Data System (ADS)

    Ahmed, M. A.; Dek, S. I.; Arman, M. M.

    2013-03-01

    Perovskites with the general formula La1-xMxFeO3, x = 0.0 and x = 0.3, M = Ca2+, Sr2+ and Ba2+ were prepared by the double sintering ceramic technique. The X-ray powder diffraction, IR and TEM were carried out to characterize the samples. The molar magnetic susceptibility (χM) was enhanced by substitution the divalent metal ion (M2+ = Ca2+, Sr2+ and Ba2+) instead of La+3. The saturation magnetization for both Ca2+ and Sr2+ substituted samples is increased up to 10 times its values for the parent which allow to use these samples in many applications. The Ca substitution improves the conductivity by more than 18 times while the Sr enhances it by 25 times.

  12. 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 and valid rate measurements could not be made. The maximum measured precipitation rate was 2-fold greater than the minima, and occurred at a carbonate to calcium ion activity ratio of 0.306. These findings have implications for predicting the progress and cost of remediation operations involving enhanced calcite precipitation where mineral precipitation rates, and the spatial/temporal distribution of those rates, can have significant impacts on the mobility of contaminants. PMID:22280318

  13. 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 salinity. All the elemental concentrations and ratios had considerable seasonal variations, with significant differences among sampling months for the Sr, Ba concentrations and the Ba / Ca ratio (p < 0.01). The results from this study suggest that concentrations of Sr and Ca in the world's estuaries will very likely increase in the future as sea level rise continues. For low-gradient estuarine rivers such as the Calcasieu River in South Louisiana, USA, water chemistry upstream would experience substantial Sr and Ca enrichment, which could affect aquatic environments and biological communities.

  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. Composite superconducting wires obtained by high-rate tinning in molten Bi-Pb-Sr-Ca-Cu-O system

    NASA Technical Reports Server (NTRS)

    Grozav, A. D.; Konopko, L. A.; Leporda, N. I.

    1990-01-01

    The preparation of high-T(sub c) superconducting long composite wires by short-time tinning of the metal wires in a molten Bi-Pb-Sr-Ca-Cu-O compound is discussed. The application of this method to the high-T(sub c) materials is tested, possibly for the first time. The initial materials used for this experiment were ceramic samples with nominal composition Bi(1.5)Pb(0.5)Sr2Ca2Cu3O(x) and T(sub c) = 80 K prepared by the ordinary solid-state reaction, and industrial copper wires from 100 to 400 microns in diameter and from 0.5 to 1 m long. The continuously moving wires were let through a small molten zone (approximately 100 cubic mm). The Bi-based high-T(sub c) ceramics in a molten state is a viscous liquid and it has a strongly pronounced ability to spread on metal wire surfaces. The maximum draw rate of the Cu-wire, at which a dense covering is still possible, corresponds to the time of direct contact of wire surfaces and liquid ceramics for less than 0.1 s. A high-rate draw of the wire permits a decrease in the reaction of the oxide melt and Cu-wire. 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.

  16. 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.

  17. Observation of the flux line lattice in high T c-superconductor Bi 2.2Sr 2CaCu 2O X and Ti 2Ba 2CaCu 2O X single crystals

    NASA Astrophysics Data System (ADS)

    Vinnikov, L. Ya.; Gurevich, L. A.; Emelchenko, G. A.; Kazaryan, G. A.; Kolesnikov, N. N.; Kulakov, M. P.; Lenchinenko, D. Ya.; Ossipyan, Yu. A.

    1989-06-01

    The flux-line lattice (FLL) has been observed on the (001) face of high T c Bi 2.2Sr 2CaCu 2O X and Ti 2Ba 2CaCu 2O X single cristals using the technique of decorating the sample with small ferromagnetic particles. Strong pinning of the Abrikosov vortices by plane defects along (100) and (010) planes has been found out on Bi 2.2Sr 2CaCu 2O X. The triangular FLL with a long-range order has been observed on the perfect Ti 2Ba 2CaCu 2O X single crystal. The penetration depth for a magnetic field parallel to (001) axis has been evaluated as ≤0.2μm at 4.2K for both materials.

  18. Experimental demonstration of hybrid improper ferroelectricity and the presence of abundant charged walls in (Ca,Sr)3Ti2O7 crystals

    NASA Astrophysics Data System (ADS)

    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.

  19. 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

  20. Sr substitution for Ba in Y(Ba{sub 1{minus}x}Sr{sub x}){sub 2}Cu{sub 3}O{sub 7{minus}d} at varying d

    SciTech Connect

    Licci, F.; Gauzzi, A.; Marezio, M.; Radaelli, G.P.; Masini, R.; Chaillout-Bougerol, C.

    1999-04-20

    In order to understand the difference between the effects induced by chemical substitutions and those induced by applying mechanical pressure, the authors synthesized and characterized samples of Y(Ba{sub 1{minus}x}Sr{sub x}){sub 2}Cu{sub 3}O{sub 7{minus}d}. The structural refinements based on powder neutron diffraction data were carried out as a function of x and, for x = 0.5, as a function of d. The electric and magnetic properties have also been measured and correlated with the structural parameters and oxygen content. It seems that the Ba cations play an important role in the high {Tc} of YBCO. Its substitution with a smaller cation corresponds to the application of a chemical pressure, but the release of the associated strain seems to play a negative role on {Tc}.

  1. 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

  2. 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.

  3. Oxidized Hastelloy Cloth Insulation for a Wind-and-React Processed Ag/Bi2Sr2CaCu2O8 Superconducting Magnet

    NASA Astrophysics Data System (ADS)

    Watanabe, K.; Nishijima, G.; Awaji, S.; Hikichi, Y.; Hasegawa, T.

    2006-03-01

    Practical multifilamentary Ag/Bi2Sr2CaCu2O8 round wires 1 mm in diameter exhibit critical current properties without anisotropy in fields up to 30 T and 4.2 K. We concentrate on the development of a Ag/Bi2Sr2CaCu2O8 insert coil by a wind-and-react method for a high field NMR superconducting magnet. Hastelloy cloth was used for the insulation for the wind-and-react process. A ?0.05 mm Hastelloy X (Hx) filament was knitted into a braid tube, and has a high mechanical strength and a good tolerance to oxidization at high temperature. We fabricated multifilamentary Ag/Bi2Sr2CaCu2O8 wires with Hx cloth, and heat-treated them at around 890 C in an oxygen atmosphere. It was found that the surface of Hx cloth is oxidized enough for a good electric insulation. Multifilamentary Ag/Bi2Sr2CaCu2O8 wires with oxidized Hx cloth insulation have the critical current of 720 A at 4.2 K in a self field.

  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. 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

  6. 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.

  7. Effects of Ca and Sr chemical doping on the average superconducting kinetic energy of YBa2Cu3O7-δ

    NASA Astrophysics Data System (ADS)

    Vieira, V. N.; Mendonça, A. P. A.; Dias, F. T.; Hneda, M. L.; Pureur, P.; Schaf, J.; Mesquita, F.

    2015-03-01

    In this brief communication we applied the MZFC(T) and MFCC(T) reversible dc magnetizations to get the average superconducting kinetic energy density, kS(T,B) of YBa2Cu3O7-δ, Y0.95Ca0.05Ba2Cu3O7-δ and YBa1.75Sr0.25Cu3O7-δ ceramic samples with the aim of study the effects of Ca and Sr doping on the kS(T,B). The MZFC(T) and MFCC(T) measurements were performed with a SQUID magnetometer from quantum design to dc magnetic fields up to 50kOe. The determination of the kS(T,B) from reversible dc magnetization is supported by virial theorem of superconductivity [kS(T,B) = - MB]. The kS(T,B) results show an common temperature profile for all the samples which is smoothly affected by the magnetic field. On the other hand the kS(T,B) results to T > Tc could not be associated to the pseudogap phenomenon. The Ca doping affects more effectively the kS(T,B) behaviour then Sr doping. A possible explanation to this feature could be associated to the fact that the hole doping promoted by Ca doping depress more considerably the superconducting state and enhances the granular character of the YBa2Cu3O7-δ superconductor than the chemical pressure effect promoted by Sr doping.

  8. Impurity-trapped excitons and electron traps in CaF2:Yb2+ and SrF2:Yb2+ probed by transient photoluminescence enhancement

    NASA Astrophysics Data System (ADS)

    Senanayake, P. S.; Wells, J. P. R.; Reid, M. F.; Berden, G.; Meijerink, A.; Reeves, R. J.

    2013-01-01

    CaF$_2$:Yb$^{2+}$ and SrF$_2$:Yb$^{2+}$ crystals have been investigated by a two-color UV + IR transient photoluminescence enhancement technique. The enhancement gives information about both changes in internal energy levels of the excitons and liberation of electrons from traps in the crystals.

  9. 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.

  10. Compton-profile measurements on (Bi 1.6Pb 0.4)Sr 2Ca 2Cu 3O 10+ x superconductor

    NASA Astrophysics Data System (ADS)

    Priftis, G. D.; Anastassopoulos, D. L.; Vradis, A. A.; Suryanarayanan, R.

    1994-04-01

    In this paper the measured Compton profiles (CP's) of the ceramic superconductor (Bi 1.6Pb 0.4)Sr 2Ca 2Cu 3O 10+ x above and below Tc are presented. The observed difference in the CP's between the normal and superconducting state suggests a redistribution of the electron momentum during the superconducting transition.

  11. 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

  12. Assessing the accuracy of oxygen isotopes and Sr/Ca as proxies of sea surface temperature at the extreme latitudinal limits of Porites corals

    NASA Astrophysics Data System (ADS)

    Hirabayashi, S.; Yokoyama, Y.; Suzuki, A.; Kawakubo, Y.; Miyairi, Y.; Okai, T.; Nojima, S.

    2014-12-01

    Oxygen isotope and Sr/Ca ratios in harmatypic coral skeletons are widely employed as proxies of sea-surface temperature (SST) in paleoclimatology, yet they are considered to be influenced from growth rate of corals. Corals in temperate regions have lower skeletal growth rate because of relatively stressful environment, in particular lower SST than those in the tropics or subtropics. Dependency on SST proxies from those effects are required to be validated to better understand paleo-environment using temperate corals. This study reports Sr/Ca-based SST reconstructions for three temperate Porites coral colonies (USB93, USB12-01, USB12-03) collected from Kyushu, Japan, near the northern latitudinal limits of Porites. Results clearly indicated that Sr/Ca reliably reproduced SST variation, independent from growth rate variations, in contrast to δ18O-based reconstruction (Hirabayashi et al., 2013, Geochemical Journal). The inter-colony variation of skeletal Sr/Ca of two Porites corals (USB12-01, USB12-03) were observed. This is attributed to the difference in calcification processes between so called "smooth type" and "sharp type" proposed by Gagan et al. (2012) as is defined by the ratio of tissue thickness/extension rate. According to these observations, summer SST reconstruction can be achieved by a limited number of coral specimens in a temperate region with comparable accuracy to tropical and subtropical corals.

  13. 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 A?? (as much as 26 mol% SrCO3 on aragonite and 44 mol% CaCO3 on strontianite). The results indicate rapid formation of a solid-solution surface phase from subsaturated aqueous solutions. The surface phase continually adjusts in composition in response to changes in composition of the bulk fluid as net dissolution proceeds. Dissolution rates of the endmembers are greatly reduced in nonstoichiometric solutions relative to dissolution rates observed in stoichiometric solutions. All solids dissolve more slowly in solutions spiked with the least soluble component ((Sr(HCO3)2)) than in solutions spiked with the more soluble component (Ca(HCO3)2), an effect that becomes increasingly significant as stoichiometric saturation is approached. It is proposed that the formation of a non-stoichiometric surface reactive zone significantly decreases dissolution rates. ?? 1992.

  14. 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).

  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. 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 Glacial Maximum.

  17. 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.

  18. Oceanographic variability in the South Pacific Convergence Zone region over the last 210 years from multi-site coral Sr/Ca records

    NASA Astrophysics Data System (ADS)

    Wu, Henry C.; Linsley, Braddock K.; Dassié, Emilie P.; Schiraldi, Benedetto; Demenocal, Peter B.

    2013-05-01

    the South Pacific Convergence Zone (SPCZ), the variability in a sub-seasonally resolved microatoll Porites colony Sr/Ca record from Tonga and a previously published high-resolution record from Fiji are strongly influenced by sea surface temperature (SST) over the calibration period from 1981 to 2004 (R2 = 0.67-0.68). However, the Sr/Ca-derived SST correlation to instrumental SST decreases back in time. The lower frequency secular trend (~1°C) and decadal-scale (~2-3°C) modes in Sr/Ca-derived SST are almost two times larger than that observed in instrumental SST. The coral Sr/Ca records suggest that local effects on SST generate larger amplitude variability than gridded SST products indicate. Reconstructed δ18O of seawater (δ18Osw) at these sites correlate with instrumental sea surface salinity (SSS; r = 0.64-0.67) but not local precipitation (r = -0.10 to -0.22) demonstrating that the advection and mixing of different salinity water masses may be the predominant control on δ18Osw in this region. The Sr/Ca records indicate SST warming over the last 100 years and appears to be related to the expansion of the western Pacific warm pool (WPWP) including an increasing rate of expansion in the last ~20 years. The reconstructed δ18Osw over the last 100 years also shows surface water freshening across the SPCZ. The warming and freshening of the surface ocean in our study area suggests that the SPCZ has been shifting (expanding) southeast, possibly related to the southward shift and intensification of the South Pacific gyre over the last 50 years in response to strengthened westerly winds.

  19. 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).

  20. 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.

  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. Thin CaSO4:Dy thermoluminescent dosimeters for calibration of 90Sr+90Y applicators.

    PubMed

    Antonio, Patrícia L; Oliveira, Mércia L; Caldas, Linda V E

    2012-04-01

    Clinical applicators are used in brachytherapy to treat superficial lesions of skin and eye. They should be periodically calibrated according to quality control programs and international recommendations. Thin CaSO(4):Dy thermoluminescent dosimeters were used to calibrate various applicators with a dermatological applicator as a reference. The obtained absorbed dose rates were compared with those quoted in their calibration certificates. Depth-dose curves were constructed for all the applicators. A mail dosimetry system was developed for calibration of clinical applicators. PMID:22304964

  3. Strontium in coral aragonite: 3. Sr coordination and geochemistry in relation to skeletal architecture

    NASA Astrophysics Data System (ADS)

    Allison, Nicola; Finch, Adrian A.; Newville, Matthew; Sutton, Stephen R.

    2005-08-01

    Use of the coral Sr palaeothermometer assumes that the Sr in coral skeletons is substituted randomly for Ca in the aragonite structure. The presence of Sr in additional phases e.g., strontianite, or the non random distribution of Sr across metal sites in aragonite, would complicate the Sr/Ca-sea surface temperature relationship. We have used Sr K-edge microEXAFS (extended X-ray absorption fine structure) to determine the structural state of Sr across selected microvolumes of four coral skeletons ( Porites lobata, Acropora palmata, Pavona clavus, and Montastrea annularis). We used a 5 × 3 μm beam to analyse specific areas of the coral skeletal architecture, i.e., centres of calcification, fasciculi, and dissepiments. All EXAFS analyses refine, within error, to an ideally substituted Sr in aragonite, and we found no evidence of strontianite or partly ordered structural states. Anisotropy in the first shell responses results from the fact that the analysed microvolumes are not necessarily averaged for the responses of all crystal orientations in the aragonite. Although secondary ion mass spectrometry confirmed that Sr/Ca composition can vary substantially between skeletal components, we find no evidence for any contrast in Sr structural state. Sr heterogeneity may result from kinetic effects, reflecting complex disequilibrium processes during crystal precipitation, or biological effects, resulting from variations in the composition of the calcifying fluid which are biologically mediated.

  4. 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.

  5. 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

  6. 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

  7. Synthesis and structure of new bismuth containing oxychlorides: BiSr 3O 3Cl 3 and BiCa 3O 3Cl 3

    NASA Astrophysics Data System (ADS)

    Huang, Jinfan; Sleight, Arthur W.

    1992-01-01

    A new bismuth strontium oxychloride BiSr 3O 3Cl 3 has been synthesized and structurally characterized from single crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma (#62) with a=6.687(2) , b=11.4618(8) , c=11.565(2) , V=886,4(3) 3, and Z=4. From the formula weight of 626.20, the density is calculated to be 4.693 g/cm 3. The structure of BiSr 3O 3Cl 3 can be described as a layered structure arranged in sequence Cl/Sr-O/Bi-Sr-O-Cl/Sr-O/Cl along the b axis. The Bi-Sr-O-Cl layer is unique among all the known bismuth oxyhalides in that oxygen and halide are mixed in one layer. Two types of Sr atom and one type of Bi atom are found. Strontium of the Sr-O layer is coordinated by three O atoms with Sr-O distances ranging from 2.404(7) to 2.557(6) and by five Cl atoms with Sr-Cl distances from 3.010(2) to 3.394(3) . Strontium of the Bi-Sr-O-Cl layer is coordinated to three oxygen atoms with Sr-O distances in the range of 2.419(8) to 2.505(6) and to six chlorine atoms with Sr-Cl distances in the range 2.922(3) to 3.796(4) . The Bi atom is coordinated by three O atoms and two Cl atoms with Bi-O bond lengths ranging from 2.062(8) to 2.071(6) and Bi-Cl bond lengths of 3.472(3) . The isostructural compound BiCa 3O 3Cl 3 was also synthesized; the cell dimensions from single crystal data are a=6.383(3) , b=10.803(3) , and c=11.422(3) .

  8. 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

  9. 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.

  10. 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

  11. 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.

  12. SUBSTITUTING SOY PROTEIN FOR MEAT PROTEIN DID NOT AFFECT CALCIUM (CA) RETENTION OR BIOMARKERS OF BONE AND CARDIOVASCULAR HEALTH IN A CONTROLLED FEEDING STUDY OF HEALTHY POSTMENOPAUSAL WOMEN

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effects of substituting soy protein for meat protein on bone and cardiovascular health are not known. The primary aim of this controlled feeding study was to measure Ca retention from a diet with meat (CONTROL) to a diet in which 25 g/day of soy protein (SOY; 3.72 mg isoflavones/g protein) was s...

  13. High-mobility group box 1 (HMGB1) impaired cardiac excitation-contraction coupling by enhancing the sarcoplasmic reticulum (SR) Ca(2+) leak through TLR4-ROS signaling in cardiomyocytes.

    PubMed

    Zhang, Cuicui; Mo, Miaohua; Ding, Wenwen; Liu, Wenjuan; Yan, Dewen; Deng, Jianxin; Luo, Xinping; Liu, Jie

    2014-09-01

    High-mobility group box 1 (HMGB1) is a proinflammatory mediator playing an important role in the pathogenesis of cardiac dysfunction in many diseases. In this study, we explored the effects of HMGB1 on Ca(2+) handling and cellular contractility in cardiomyocytes to seek for the mechanisms underlying HMGB1-induced cardiac dysfunction. Our results show that HMGB1 increased the frequency of Ca(2+) sparks, reduced the sarcoplasmic reticulum (SR) Ca(2+) content, and decreased the amplitude of systolic Ca(2+) transient and myocyte contractility in dose-dependent manners in adult rat ventricular myocytes. Inhibiting high-frequent Ca(2+) sparks with tetracaine largely inhibited the alterations of SR load and Ca(2+) transient. Blocking Toll-like receptor 4 (TLR4) with TAK-242 or knockdown of TLR4 by RNA interference remarkably inhibited HMGB1 induced high-frequent Ca(2+) sparks and restored the SR Ca(2+) content. Concomitantly, the amplitude of systolic Ca(2+) transient and myocyte contractility had significantly increased. Furthermore, HMGB1 increased the level of intracellular reactive oxygen species (ROS) and consequently enhanced oxidative stress and CaMKII-activated phosphorylation (pSer2814) in ryanodine receptor 2 (RyR2). TAK-242 pretreatment significantly decreased intracellular ROS levels and oxidative stress and hyperphosphorylation in RyR2, similar to the effects of antioxidant MnTBAP. Consistently, MnTBAP normalized HMGB1-impaired Ca(2+) handling and myocyte contractility. Taken together, our findings suggest that HMGB1 enhances Ca(2+) spark-mediated SR Ca(2+) leak through TLR4-ROS signaling pathway, which causes partial depletion of SR Ca(2+) content and hence decreases systolic Ca(2+) transient and myocyte contractility. Prevention of SR Ca(2+) leak may be an effective therapeutic strategy for the treatment of cardiac dysfunction related to HMGB1 overproduction. PMID:24937603

  14. 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.

  15. 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.

  16. 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.

  17. The CASR gene: alternative splicing and transcriptional control, and calcium-sensing receptor (CaSR) protein: structure and ligand binding sites.

    PubMed

    Hendy, Geoffrey N; Canaff, Lucie; Cole, David E C

    2013-06-01

    The calcium-sensing receptor (CaSR) is a G protein-coupled receptor encoded by a single copy gene. The human CASR gene spans ~103-kb and has eight exons. Promoters P1 and P2 drive transcription of exons 1A and 1B, respectively, encoding alternative 5'-UTRs that splice to exon 2 encoding the common part of the 5'-UTR. Exons 2-7 encode the CaSR protein of 1078 amino acids. Functional elements responsive to 1,25-dihydroxyvitamin D, proinflammatory cytokines, and glial cells missing-2 are present in the CASR promoters. Evolutionarily, the exon structure, first seen in aquatic vertebrates, is well-conserved with a single linkage disequilibrium haplotype block for protein coding exons 2-7. Structural features of the human CaSR protein are: an N-terminal signal peptide (19 amino acids (aa)); an extracellular domain (~600 aa) having a bi-lobed Venus Flytrap (VFT) domain with several Ca(2+)-binding sites; and a nine-cysteines domain that transduces the activation signal to the 7-transmembrane domain (250 aa) and the C-terminal tail (216 aa). PMID:23856260

  18. 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}.

  19. 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].

  20. Electron-spectroscopy investigation of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{ital y}} single-crystal cleaved surfaces

    SciTech Connect

    Ori, D.M.; Goldoni, A.; del Pennino, U.

    1995-08-01

    This paper presents spectroscopic investigations of the normal-state properties of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{ital y}} single crystals. Ultraviolet photoemission and electron energy loss data are consistent with the filling in of the charge transfer gap upon doping due to spectral weight transfer mechanisms. The modifications occurring in the surface electronic properties after exposure to pure O{sub 2} and after the deposition of one monolayer of bismuth are studied and discussed.

  1. 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.

  2. Regional variation in otolith Sr:Ca ratios of African longfinned eel Anguilla mossambica and mottled eel Anguilla marmorata: a challenge to the classic tool for reconstructing migratory histories of fishes.

    PubMed

    Lin, Y-J; Jessop, B M; Weyl, O L F; Iizuka, Y; Lin, S-H; Tzeng, W-N; Sun, C-L

    2012-07-01

    Otolith Sr:Ca ratios of the African longfinned eel Anguilla mossambica and giant mottled eel Anguilla marmorata from nine freshwater sites in four rivers of South Africa were analysed to reconstruct their migratory life histories between freshwater and saltwater habitats. For A. mossambica, the Sr:Ca ratios in the otolith edge differed significantly among rivers and had large effect sizes, but did not differ among sites within a river. Otolith Sr:Ca ratios did not differ among rivers for A. marmorata. When rivers were pooled, the edge Sr:Ca ratios of A. mossambica were not significantly different from those of A. marmorata. According to the river-specific critical Sr:Ca ratio distinguishing freshwater from saltwater residence, most A. mossambica and A. marmorata had saltwater habitat experience after settlement in fresh water. This was primarily during their elver stage or early in the yellow eel stage. During the middle and late yellow eel stage, freshwater residency was preferred and only sporadic visits were made to saltwater habitats. The data also suggest that regional variations in otolith Sr:Ca ratios affect the critical Sr:Ca value and are a challenge for the reconstruction of migratory life histories that should be explicitly considered to avoid bias and uncertainty. PMID:22803718

  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. X-ray Structural Studies of Bi2Sr2CaCu2O8 + δ Exfoliated Nanocrystals

    NASA Astrophysics Data System (ADS)

    Lupascu, Andreea; Feng, Renfei; Sandilands, Luke J.; Nie, Zixin; Baydina, Viktoriya; Gu, Genda; Ono, Shimpei; Ando, Yoichi; Burch, Kenneth S.; Kim, Young-June

    2013-03-01

    Structural studies of nanocrystals produced via mechanical exfoliation are not only essential for examining structure quality or structural changes at reduced-dimensionality, but also for understanding the role of substrates in the exfoliation process. Highly focused, tunable synchrotron X-ray beams enable the use of non-destructive characterization tools to study exfoliated samples on a variety of substrates. We demonstrate that structural and spectroscopic information can be obtained on nanocrystals as thin as 6 nm, by using a combination of micro X-ray fluorescence (μ XRF), micro X-ray absorption near-edge spectroscopy (μ XANES), and X-ray microdiffraction (μ XRD) techniques. μ XRF is used to locate the sample of desired thickness; μ XANES and μ XRD are used to obtain electronic and structural information, respectively. We report a substantial substrate effect for Bi2Sr2CaCu2O8 + δ nanocrystals exfoliated on Si/SiO2 and mica substrates. The ``4.7 b'' structural modulation, characteristic of bulk crystals, vanishes below a thickness of 60 nm on mica, and is drastically suppressed below 60 nm for the Si/SiO2 substrate.

  5. Geometry dependent resistivity behavior in mesoscopic Bi 2Sr 2CaCu 2O 8+δ single crystals

    NASA Astrophysics Data System (ADS)

    Mirkovic, J.; Kashiwagi, T.; Saito, T.; Yamamoto, T.; Kadowaki, K.

    2011-11-01

    In order to investigate the interaction between Josephson vortices and pancake vortices in a layered Bi 2Sr 2CaCu 2O 8+δ superconductor, c-axis resistivity measurements were carried out on fabricated mesoscopic single crystals for two experimental geometries, when an applied high magnetic field of 14 T is perpendicular ( Bex⊥ L) and parallel ( Bex∥ L) to the width of sample. In the first case, the angular dependence of the resistance obtained near the ab-plane at T = 30 K exhibited hysteretic non-monotonic behavior with local maxima at θ = 0.6° away from the ab-plane and dips and spikes at θ = 0.2° marking a vortex lock-in transition. In the second geometry ( Bex∥ L), instead of a local maximum, peculiar resistance shoulders were observed. At higher temperatures, hysteresis is reduced, while the vortex lock-in transition becomes considerably broader indicating the interaction of pancake and Josephson vortices.

  6. Magnetic field effects on THz radiation from Bi2Sr2CaCu2O8+? 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+? 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.

  7. 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.

  8. 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.

  9. Imaging of Current Sharing in (BiPb)_2Sr_2Ca_2Cu_3Ox Composite Conductors.

    NASA Astrophysics Data System (ADS)

    Peterson, Ted B.; Welp, U.; Crabtree, G. W.; Vasanthamohan, N.; Singh, J. P.; Lanagan, M. T.; Vlasko-Vlasov, V. K.; Nikitenko, V. I.

    1997-03-01

    Using a high-resolution magneto-optical imaging technique, we study the flow of transport currents around cracks in mono-filament (BiPb)_2Sr_2Ca_2Cu_3Ox composite conductors. Shunting through the Ag clad is directly observed. The current in the silver decays exponentially with distance from the crack (as expected in a one dimentional resistor model). At 77K, the decay length, λ, is approximately 0.04 cm, implying an interface resistivity of 1.5 10-7Ωcm^2. This decay length is found to increase with increasing temperature. For crack densities higher than 26/cm, a portion of the current resides in the clad. ^This work is supported by the U.S. DOE, BES-Materials Science (TBP,UW,GWC) and EERE (NV,JPS,MTL) under contract #W-31-109-ENG-38, and the Russian foundation of Fundamental Studies Grant Potok(VKV,VIN) ^Permanent Address: Institute for Solid State Physics, 142432 Chernogolovka, Moscow district, Russia

  10. Vortex imaging with varying temperature revealed by SHPM on Bi 2Sr 2CaCu 2O 8+ y

    NASA Astrophysics Data System (ADS)

    Mihalache, V.; Dede, M.; Oral, A.; Sandu, V.

    2008-04-01

    Scanning Hall probe microscopy with an effective spatial resolution of ∼1 μm has been used to investigate the vortex structures in superconducting Bi2Sr2CaCu2O8+δ single crystals in the temperature range 77.3-81.3 K and zero applied field (in the presence of the earth field). The vortex images were obtained in real time mode as the temperature increased slowly for 3.36 h. At 77.3 K, the vortices were arranged in a chain structure. With the increase of the temperature, two jumps in the vortex array occur at 77.3 K, immediately when the temperature starts to rise, and at 79.2 K with a good stability between jumps. The second jump is accompanied by the jump in the average magnetic induction when bundles of 4-5 additional vortices enter the scanning area and the vortex array get disordered. These directly visualized transitions in the vortex lattice are consistent with a vortex creep over the surface barriers at high temperatures. A short movie is presented.

  11. 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.

  12. Mechanisms controlling the in-situ formation and superconducting properties of Bi-Sr-Ca-Cu-O films

    SciTech Connect

    Kampwirth, R.T.; Grace, J.M.; Miller, D.J.; McDonald, D.B.; Gray, K.E.; Reiten, M.; Ascolese, M.; Latvakoski, H.

    1990-01-01

    We have previously shown that sputtered films of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (BSCCO) deposited onto single crystal MgO substrates held at substrate temperatures, T{sub s}, near 700{degree}C and slowly cooled in oxygen, from High Temperature Superconducting (HTS) films with T{sub czero} between 50 and 70 K. The conditions necessary to achieve superconductivity include having close to stoichiometric composition at the T{sub s} required to form the superconductor. Both T{sub czero} and c-axis orientation increase with T{sub s} while the relative bismuth content decreases. Bismuth film content is affected by the type and amount of oxidant, total system pressure, target-to-substrate spacing, and substrate bias. We suggest oxygen resputtering of the film may play a role similar to the reported for YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO). Oxygen partial pressure during and cooldown rate from T{sub s} to {approx}350{degree}C also affects the superconducting properties. 8 refs., 8 figs.

  13. Josephson Plasma Resonance in Partially Irradiated Bi_2Sr_2CaCu_2O_8+y

    NASA Astrophysics Data System (ADS)

    Tamegai, Tsuyoshi; Kameda, Naoto; Tokunaga, Masashi; Konczykowski, Marcin

    2002-03-01

    We study the Josephson plasma resonance in Bi_2Sr_2CaCu_2O_8+y which is partially irradiated by heavy-ions. The plasma resonance in such inhomogeneous samples is not a superposition of two resonances of constituent parts, but occurs at fields intermediate to pristine and irradiated parts. By changing the spatial extent of the inhomogeneities, the phase coherence length L_Φ, where the phase coherence is averaged, is found to be over 100 μ m. In half irradiated sample, the resonance changes its character below and above the crossover frequency, ω_cr. At frequencies lower than ω_cr, the resonance shows the behavior characteristic of the irradiated part. The resonance in three microwave configurations are compared, i.e., (a) E_acallel c-axis, (b) H_acallel ab-plane allel boundary, and (c) H_acallel ab-plane⊥boundary. A clear resonance is observed only in configurations (a) and (b). These behavior are compared with recent theoretical calculation by Koyama.

  14. Tilted vortex lattice in irradiate Bi2Sr2CaCu2O8+δ single crystals

    NASA Astrophysics Data System (ADS)

    Mirkovic, J.; Kakeya, I.; Savel'ev, S.; Kashiwagi, T.; Markovic, B.; Kadowaki, K.

    2016-01-01

    In order to enlighten the structure of vortex matter in irradiated layered Bi2Sr2CaCu2O8+δ single crystals, the interaction of Josephson vortices and pancake vortices in was investigated by means of the local ac-magnetic permeability measurements by using the miniature local coils, while vortex matter in pristine crystals was studied by in-plane resistivity measurements. The transition anomaly, separating the strong pinning phase and the weak pinning vortex phase was found by both techniques deep in the vortex solid phase solid near ab-plane, indicating crossover from the vortex chains + lattice phase to tilted vortex chains phase. While the columnar defects affect strongly the first-order vortex-lattice melting transition, the magnetic permeability anomaly, associated with the crossover from vortex chains + lattice phase to tilted lattice, is surprisingly still clear, deep in the vortex solid phase. However, the stronger columnar defects eventually affect the crossover anomaly that it disappears too.

  15. 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.

  16. 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.

  17. 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.

  18. 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 electro