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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. Magnetic characterization of Ca substituted Ba and Sr hexaferrites

    NASA Astrophysics Data System (ADS)

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

    1980-04-01

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

  3. 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

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

    PubMed

    Massera, Jonathan; Hupa, Leena

    2014-03-01

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

  5. Electrical conductivity of cobalt-titanium substituted SrCaM hexaferrites

    NASA Astrophysics Data System (ADS)

    Eraky, M. R.

    2012-03-01

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

  6. Substitution of extracellular Ca2+ by Sr2+ prolongs inspiratory burst in pre-Bötzinger complex inspiratory neurons.

    PubMed

    Morgado-Valle, Consuelo; Fernandez-Ruiz, Juan; Lopez-Meraz, Leonor; Beltran-Parrazal, Luis

    2015-02-15

    The pre-Bötzinger complex (preBötC) underlies inspiratory rhythm generation. As a result of network interactions, preBötC neurons burst synchronously to produce rhythmic premotor inspiratory activity. Each inspiratory burst consists of action potentials (APs) on top of a 10- to 20-mV synchronous depolarization lasting 0.3-0.8 s known as inspiratory drive potential. The mechanisms underlying the initiation and termination of the inspiratory burst are unclear, and the role of Ca(2+) is a matter of intense debate. To investigate the role of extracellular Ca(2+) in inspiratory burst initiation and termination, we substituted extracellular Ca(2+) with Sr(2+). We found for the first time an ionic manipulation that significantly interferes with burst termination. In a rhythmically active slice, we current-clamped preBötC neurons (Vm ? -60 mV) while recording integrated hypoglossal nerve (?XIIn) activity as motor output. Substitution of extracellular Ca(2+) with either 1.5 or 2.5 mM Sr(2+) significantly prolonged the duration of inspiratory bursts from 653.4 ± 30.7 ms in control conditions to 981.6 ± 78.5 ms in 1.5 mM Sr(2+) and 2,048.2 ± 448.5 ms in 2.5 mM Sr(2+), with a concomitant increase in decay time and area. Substitution of extracellular Ca(2+) by Sr(2+) is a well-established method to desynchronize neurotransmitter release. Our findings suggest that the increase in inspiratory burst duration is determined by a presynaptic mechanism involving desynchronization of glutamate release within the network. PMID:25429120

  7. 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 (S?) and in a series of reduced states (S?, S??, and S-?). Through comparison with experimental data, we determine that X-ray crystal structures with either Ca²? or Sr²? are most consistent with the S-? state, Mn?[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.

  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 (?-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. Effects of Ca2+ substitution on dielectric properties of (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 ceramics

    NASA Astrophysics Data System (ADS)

    Eoh, Young Jun; Kim, Eung Soo

    2014-08-01

    We investigated the dielectric properties of (Ba0.7Sr0.3-xCax)(Ti0.9Zr0.1)O3 (BSCTZ) and (Ba0.7-yCaySr0.3)(Ti0.9Zr0.1)O3 (BCSTZ) (0 \\leqq x,y \\leqq 0.2) ceramics sintered at 1550 °C for 6 h. With increasing Ca2+ ions substitution for Sr2+ and/or Ba2+ ions, both of the ceramics showed the decreasing unit cell volume due to the smaller ionic size of Ca2+ ion than Ba2+ and/or Sr2+ ion. Also, BSCTZ and BCSTZ ceramics were found to have perovskite structures with tetragonal (P4mm) and cubic (Pm\\bar{3}m) symmetry at room temperature. The dielectric constant (?r) and breakdown voltage of BSCTZ and/or BCSTZ ceramics depended on the average B-site bond valence. The dielectric loss (tan ?) of BSCTZ ceramics significantly increased with Ca2+ ions substitution due to the decrease in grain size, whereas that of BCSTZ ceramics decreased only slightly because of the increase in the cubic phase fraction. Finally, we discuss the dependence of the dielectric properties on the crystal structure characteristics of the BSCTZ and BCSTZ ceramics.

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

    PubMed

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

    2015-10-21

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

  11. 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 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. PMID:26702873

  12. 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.

  13. 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 (S?) and in a series of reduced states (S?, S??, and S-?). Through comparison with experimental data, we determine that X-ray crystal structures with either Ca²? or Sr²? are most consistent with the S-? state, Mn?[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

  14. Effect of Y-substitution on the electrical properties of epitaxial Bi 2Sr 2Ca 1-xY xCu 2O 8+? thin films

    NASA Astrophysics Data System (ADS)

    Baca, E.; Holguin, V.; Lopera, W.; Prieto, P.

    We have performed a study on the preparation conditions and electrical transport properties of epitaxial Bi 2Sr 2Ca 1-xY xCu 2O 8+? thin films. The deposition of the films was carried out “ in situ” by a high oxygen pressure dc-sputtering technique on (100) SrTiO 3 substrates. The structural properties were determined by x-ray diffraction. By increasing the yttrium content the temperature dependence of resistivity change from a metallic to an insulating behavior. For x<0.50, the samples showed a metalic behavior in the normal state and the transition temperature decrease with increasing yttrium concentration. Superconductor transition Width ?TC and d?n/ dT as function of the x value has been analized. For x?0.50, the samples showed a semiconductor behavior what correspond to a variable-range-hopping conduction between localized states in according to a two-dimensional system given by ? = ? 0 exp (- {T 0}/{T}) {1}/{3}. Ultra-thin Bi 2Sr 2Ca 1-xY xCu 2O 8+? films (for x=1) have been used as artificial barriers in tunneling heterostructures with Bi 2Sr 2CaCu 2O 8+? superconducting electrodes.

  15. 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.

  16. Normal state thermoelectric power of vanadium-substituted (Bi 0.8Pb 0.2-yV y) 2Sr 2Ca 2Cu 3O x superconducting pellets

    NASA Astrophysics Data System (ADS)

    Chanda, Bitasta; Ghatak, S. K.; Dey, T. K.

    1994-10-01

    The temperature dependence of vanadium-substituted (Bi 0.8Pb 0.2- yV y) 2Sr 2Ca 2Cu 3O x samples with 0< y<0.075 is reported between Tco and 300 K. Thermoelectric power of all the samples was found to be positive and to increase approximately linearly with decrease of temperature up to about 120 K, before falling to zero at Tco. The measured data have been analysed on the basis of three relevant theoretical models and from which we conclude that the temperature variation of TEP of pure and vanadium-substituted (Bi-Pb) cuprates could be explained extremely well (within 1%) according to the expression proposed by Forro et al. using a modified two-band model.

  17. 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.

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

    E-print Network

    Mora, Miguel A.

    Regional and interspecific variation in Sr, Ca, and Sr/Ca ratios in avian eggshells from the USA in strontium (Sr), which at high concentrations may reduce eggshell quality, increase egg breakage and reproductive failure, we analyzed Sr, and calcium (Ca) concentrations and Sr/Ca ratios in eggshells from 20

  19. Effect of substitution of Fe for Mn on the structural, magnetic properties and magnetocaloric effect of LaNdSrCaMnO3

    NASA Astrophysics Data System (ADS)

    Dhahri, Ja.; Dhahri, A.; Oummezzine, M.; Hlil, E. K.

    2015-03-01

    We have studied the structural, magnetic and magnetocaloric properties of La0.6Nd0.1Sr0.15Ca0.15Mn1-xFexO3 (LNSCMFex) perovskite samples. The samples were synthesized using the solid-state reaction at high temperature and were analyzed by XRD data based on the Rietveld refinement technique. LNSCMFex samples crystallized in orthorhombic symmetry with Pnma space group. Besides, the curves of magnetization reveals that all samples exhibit a magnetic transition from the paramagnetic to ferromagnetic phase at the Curie temperature TC, which decreases from 327 K to 296 K with the increase of the Fe doping level from x=0 to x=0.1. The thermal evolution of magnetization in the ferromagnetic phase at low temperature varies as T3/2 in accordance with Bloch's law. The magnitude of the isothermal magnetic entropy, (- ?SMmax), at the FM Curie temperature increases from 3.79 J/kg K for x=0 composition to 5.8 J/kg K for x=0.1, under a magnetic field of 5 T. For an applied magnetic field of 5 T, the relative cooling power (RCP) values are found to vary between 173.66 and 231.76 J/kg. These results suggest that these materials could be used as an active magnetic refrigerant around room temperature.

  20. 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.

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

    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.

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

    PubMed

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

    2015-08-17

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

  3. 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

  4. ERK signaling mediates CaSR-promoted axon growth

    PubMed Central

    Vizard, Thomas N.; Newton, Michael; Howard, Laura; Wyatt, Sean; Davies, Alun M.

    2015-01-01

    The extracellular calcium-sensing receptor (CaSR) is a G-protein coupled receptor that monitors the systemic extracellular free ionized calcium level ([Ca2+]o) in organs involved in systemic [Ca2+]o homeostasis. CaSR is widely expressed in the nervous system and its activation promotes axon and dendrite growth during development, but the mechanism by which it does this is not known. Here we show that enhanced axon growth and branching from cultured embryonic sympathetic neurons by activation of the endogenous CaSR depends on the presence of nerve growth factor (NGF). Our observation that activation of overexpressed CaSR promotes axon growth in NGF-free medium has enabled us to investigate CaSR downstream signaling contributing to axon growth in the absence of NGF signaling. We show that activation of overexpressed CaSR leads to activation of ERK1 and ERK2, and pharmacological inhibition of CaSR-dependent ERK1/ERK2 activation prevents CaSR-dependent axon growth. Analysis of axon growth from cultured neurons expressing deletion mutants of the CaSR cytoplasmic tail revealed that the region between alanine 877 and glycine 907 is required for promoting axon growth that is distinct from the high-affinity filamin-A binding site that has previously been implicated in ERK1/ERK2 activation. PMID:26200251

  5. Are seawater Sr/Ca variations preserved in Quaternary foraminifera?

    SciTech Connect

    Stoll, H.M.; Schrag, D.P.; Clemens, S.C.

    1999-11-01

    High precision measurements of Sr/Ca in planktonic foraminifera for the last 150 ka reveal Sr/Ca variations of up to 12% on glacial/interglacial time scales. Although records showing the largest variations appear to be strongly influenced by selective dissolution, other records show Sr/Ca variations of 3--5% that do not covary with indicators of dissolution intensity and that are reproduced in sites of contrasting Quaternary dissolution histories. These systematic variations are characterized by high Sr/Ca ratios during glacial maxima, followed by steep decreases during deglaciation and gradual increases through interstadial periods, closely following {delta}{sup 18}O curves. Foraminiferal Sr/Ca variations may reflect changes in the Sr/Ca ratio of seawater, or they may be due to kinetically or biologically induced changes in Sr partitioning. Coupled numerical models of the Sr and Ca budgets of the ocean reveal that sea level changes, together with large changes in river fluxes and carbonate accumulation rates, can produce seawater Sr/Ca variations that approximate both the shape and amplitude of foraminiferal Sr/Ca variations. However, such extreme changes in river and carbonate fluxes conflict with existing data on carbonate accumulation rates and Sr isotopic constraints on the magnitude of variations in the river flux. Smaller variations (1--3%) in the Sr/Ca ratio of seawater likely characterize Quaternary glacial cycles. Changes in Sr partitioning due to glacial-interglacial changes in the carbonate ion concentration and other environmental factors likely produce additional variation in the Sr/Ca record of planktonic foraminifera.

  6. Sr 2+/Ca 2+ and 44Ca/ 40Ca fractionation during inorganic calcite formation: II. Ca isotopes

    NASA Astrophysics Data System (ADS)

    Tang, Jianwu; Dietzel, Martin; Böhm, Florian; Köhler, Stephan J.; Eisenhauer, Anton

    2008-08-01

    Ca isotope fractionation during inorganic calcite formation was experimentally studied by spontaneous precipitation at various precipitation rates (1.8 < log R < 4.4 ?mol/m 2/h) and temperatures (5, 25, and 40 °C) with traces of Sr using the CO 2 diffusion technique. Results show that in analogy to Sr/Ca [see Tang J., Köhler S. J. and Dietzel M. (2008) Sr 2+/Ca 2+ and 44Ca/ 40Ca fractionation during inorganic calcite formation: I. Sr incorporation. Geochim. Cosmochim. Acta] the 44Ca/ 40Ca fractionation during calcite formation can be followed by the Surface Entrapment Model (SEMO). According to the SEMO calculations at isotopic equilibrium no fractionation occurs (i.e., the fractionation coefficient ?calcite-aq = ( 44Ca/ 40Ca) s/( 44Ca/ 40Ca) aq = 1 and ? 44/40Ca calcite-aq = 0‰), whereas at disequilibrium 44Ca is fractionated in a primary surface layer (i.e., the surface entrapment factor of 44Ca, F44Ca < 1). As a crystal grows at disequilibrium, the surface-depleted 44Ca is entrapped into the newly formed crystal lattice. 44Ca depletion in calcite can be counteracted by ion diffusion within the surface region. Our experimental results show elevated 44Ca fractionation in calcite grown at high precipitation rates due to limited time for Ca isotope re-equilibration by ion diffusion. Elevated temperature results in an increase of 44Ca ion diffusion and less 44Ca fractionation in the surface region. Thus, it is predicted from the SEMO that an increase in temperature results in less 44Ca fractionation and the impact of precipitation rate on 44Ca fractionation is reduced. A highly significant positive linear relationship between absolute 44Ca/ 40Ca fractionation and the apparent Sr distribution coefficient during calcite formation according to the equation ?Ca=(-1.90±0.26)·logD-2.83±0.28 is obtained from the experimental results at 5, 25, and 40 °C. Thus, Sr partitioning during calcite formation directly reflects Ca isotopic fractionation, independent of temperature, precipitation rate, and molar (Sr/Ca) aq ratio of the aqueous solution. If the (Sr/Ca) aq ratio is constant, ? 44/40Ca calcite-aq values can be directly followed by the Sr content of the precipitated calcite. A (Sr/Ca) aq ratio close to that of modern seawater yields the equation ?Ca=(-0.000940±0.000108)·Sr(mg/kgCaCO)-0.07±0.09. Our experimental results indicate that neither precipitation rate nor temperature dominantly controls Ca isotope fractionation. However, Ca isotopes and Sr content of inorganic calcite comprise an excellent environmental multi-proxy in natural and applied systems.

  7. The (Tl,Pb)(Sr2-xBax)Ca2Cu3Oz superconducting system

    NASA Astrophysics Data System (ADS)

    Jorda, J. L.; Lebbou, K.; Couach, M.; Galez, Ph.; Trosset, S.; Cohen-Adad, M. T.

    1996-03-01

    High quality ceramic samples with a purity more than 90% have been prepared in the (Tl,Pb)(Sr2-xBax)Ca2Cu3Oz system using results from phase equilibrium studies. For the equimolar Tl-Pb composition, a solid solution is observed as Ba substitutes Sr up to Sr=0.5. A multiphase system with the perovskite (Tl,Pb)BaO3 as major impurity is formed for higher Ba contents. In the single phase field, the formation of (Tl,Pb)(Ba,Sr)-1223 by solid state reaction is a two-step process implying the corresponding (Tl,Pb)(Ba,Sr)-1212 phase. Conversion from 1212 to 1223 was found to be maximum for x=0.4. The decrease of the liquidus temperature with increasing x is of great interest for grain growth improvement, in relation with the superconducting properties.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Control of the superconducting properties of Sr2-xCaxVO3FeAs through isovalent substitution

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    The effect of the isovalent substitution of Sr2+ by Ca2+ on the structure and superconducting properties of Sr2-xCaxVO3FeAs is described in the compositional range 0?x?0.5. SQUID magnetometry measurements reveal that after an initial increase in Tc, which is maximised at 29.5 K in Sr1.95Ca0.05VO3FeAs, a rapid suppression of superconductivity is observed with increasing x. XANES spectra of Sr2-xCaxVO3FeAs 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 Tc 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 Tc maximised in samples with regular FeAs4-tetrahedra.

  14. 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 ?mo/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.

  15. 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.

  16. Synthesis of BiPbSrCaCuO superconductor

    DOEpatents

    Hults, William L. (Los Alamos, NM); Kubat-Martin, Kimberly A. (Espanola, NM); Salazar, Kenneth V. (Espanola, NM); Phillips, David S. (Los Alamos, NM); Peterson, Dean E. (Los Alamos, NM)

    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.

  17. 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.

  18. Regulation of axonal and dendritic growth by the extracellular calcium-sensing receptor (CaSR)

    PubMed Central

    Vizard, Thomas N.; O'Keeffe, Gerard W.; Gutierrez, Humberto; Kos, Claudine H.; Riccardi, Daniela; Davies, Alun M.

    2009-01-01

    The extracellular calcium-sensing receptor (CaSR) monitors the systemic extracellular free ionized calcium level ([Ca2+]o) in organs involved in systemic [Ca2+]o homeostasis. However, the CaSR is also expressed in the nervous system where its role is unknown. Here we find high levels of the CaSR in perinatal mouse sympathetic neurons when their axons are innervating and branching extensively in their targets. Manipulating CaSR function in these neurons by varying [Ca2+]o, using CaSR agonists and antagonists or expressing a dominant-negative CaSR markedly affects neurite growth in vitro Sympathetic neurons lacking the CaSR have smaller neurite arbors in vitro, and sympathetic innervation density is reduced in CaSR-deficient mice in vivo. Hippocampal pyramidal neurons, which also express the CaSR, have smaller dendrites when transfected with dominant-negative CaSR in postnatal organotypic cultures. Our findings reveal a crucial role for the CaSR in regulating the growth of neural processes in the peripheral and central nervous systems. PMID:18223649

  19. Luminescence Spectroscopy of Eu-doped (Ca,Sr)TiO{sub 3} Nanocrystals Prepared by Using Sonochemical Method

    SciTech Connect

    Kurniawan, C.; Prijamboedi, B.

    2010-10-24

    Perovskite-type compounds (ABO{sub 3}) of (Ca,Sr)TiO{sub 3} doped with trivalent europium (Eu{sup 3+}) were synthesized by sonochemical techniques. Powder X-ray diffraction measurement on (Ca,Sr)TiO{sub 3} were used to identify the perovskite crystal structure. The photoluminescence property in (Ca,Sr)TiO{sub 3} with europium substitution several atoms in the host lattice was also studied. Further, the photoluminescence spectra were taken at room temperature. The structural difference between fourth kinds of doped samples with different heating temperatures accounts for the intensification of the luminescence intensity. The presented measurements monitor the emission wavelengths of the Eu{sup 3+} with emission peaks at 593, 615 and 700 nm. The obtained results were discussed with respect to developed preparation method.

  20. A novel CaSR mutation presenting as a severe case of neonatal familial hypocalciuric hypercalcemia

    PubMed Central

    2012-01-01

    Background Familial Hypocalciuric Hypercalcemia (FHH) is a generally benign disorder caused by heterozygous inactivating mutations in the Calcium-Sensing Receptor (CaSR) gene resulting in altered calcium metabolism. Objective We report a case of unusually severe neonatal FHH due to a novel CaSR gene mutation that presented with perinatal fractures and moderate hypercalcemia. Case overview A female infant was admitted at 2?weeks of age for suspected non-accidental trauma (NAT). Laboratory testing revealed hypercalcemia (3.08?mmol/L), elevated iPTH (20.4 pmol/L) and low urinary calcium clearance (0.0004). Radiographs demonstrated multiple healing metaphyseal and rib fractures and bilateral femoral bowing. The femoral deformity and stage of healing were consistent with prenatal injuries rather than non-accidental trauma (NAT). Treatment was initiated with cholecalciferol, 400?IU/day, and by 6?weeks of age, iPTH levels had decreased into the high-normal range. Follow up radiographs demonstrated marked improvement of bone lesions by 3?months. A CaSR gene mutation study showed heterozygosity for a T>C nucleotide substitution at c.1664 in exon 6, resulting in amino acid change I555T in the extracellular domain consistent with a missense mutation. Her mother does not carry the mutation and the father is unknown. At 18?months of age, the child continues to have relative hyperparathyroidism and moderate hypercalcemia but is otherwise normal. Conclusion This neonate with intrauterine fractures and demineralization, moderate hypercalcemia and hyperparathyroidism was found to have a novel inactivating missense mutation of the CaSR not detected in her mother. Resolution of bone lesions and reduction of hyperparathyroidism was likely attributable to the natural evolution of the disorder in infancy as well as the mitigating effect of cholecalciferol treatment. PMID:22620673

  1. Ankyrin-B reduction enhances Ca spark-mediated SR Ca release promoting cardiac myocyte arrhythmic activity

    PubMed Central

    Camors, Emmanuel; Mohler, Peter J.; Bers, Donald M.; Despa, Sanda

    2012-01-01

    Ankyrin-B (AnkB) loss-of-function may cause ventricular arrhythmias and sudden cardiac death in humans. Cardiac myocytes from AnkB heterozygous mice (AnkB+/?) show reduced expression and altered localization of Na/Ca exchanger (NCX) and Na/K-ATPase (NKA), key players in regulating [Na]i and [Ca]i. Here we investigate how AnkB reduction affects cardiac [Na]i, [Ca]i and SR Ca release. We found reduced NCX and NKA transport function but unaltered [Na]i and diastolic [Ca]i in myocytes from AnkB+/? vs. wild-type (WT) mice. Ca transients, SR Ca content and fractional SR Ca release were larger in AnkB+/? myocytes. The frequency of spontaneous, diastolic Ca sparks (CaSpF) was significantly higher in intact myocytes from AnkB+/? vs. WT myocytes (with and without isoproterenol), even when normalized for SR Ca load. However, total ryanodine receptor (RyR)-mediated SR Ca leak (tetracaine-sensitive) was not different between groups. Thus, in AnkB+/? mice SR Ca leak is biased towards more Ca sparks (vs. smaller release events), suggesting more coordinated openings of RyRs in a cluster. This is due to local cytosolic RyR regulation, rather than intrinsic RyR differences, since CaSpF was similar in saponin-permeabilized myocytes from WT and AnkB+/? mice. The more coordinated RyRs openings resulted in an increased propensity of pro-arrhythmic Ca waves in AnkB+/? myocytes. In conclusion, AnkB reduction alters cardiac Na and Ca transport and enhances the coupled RyR openings, resulting in more frequent Ca sparks and waves although the total SR Ca leak is unaffected. This could enhance the propensity for triggered arrhythmias in AnkB+/? mice. PMID:22406428

  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 ? 18O and ? 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 2?) 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 ? 18O, ? 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. Author's personal copy Sr/Ca and Mg/Ca ratios of ontogenetically old, long-lived bivalve shells (Arctica

    E-print Network

    Schöne, Bernd R.

    Author's personal copy Sr/Ca and Mg/Ca ratios of ontogenetically old, long-lived bivalve shells Keywords: Metal-to-calcium ratio Bivalve shell Vital effect Sea surface temperature Longevity The Sr, it has remained largely impossible to obtain such information from bivalve shells. In the present study

  4. Rh, Ni, and Ca substituted pyrochlore catalysts for dry reforming of methane

    SciTech Connect

    Gaur, Sarthak; Haynes, Daniel J.; Spivey, James J.

    2011-07-01

    Dry reforming of methane (DRM) has been widely investigated, with most studies showing rapid deactivation due to carbon deposition. This suggests a need to develop catalysts that limit carbon formation while avoiding structural changes at the elevated temperatures typical of this reaction. Here, we report CO? reforming of methane on four pyrochlore catalysts. First, rhodium was partially substituted for Zr in lanthanum zirconate (La?Zr?O?) to give La?Zr2?xRhxO7?? (LRZ, x = 0.112, 2 wt% Rh) pyrochlore. A second pyrochlore catalyst was synthesized in which Ca was further substituted into the La-site to give La1.95Ca 0.05Zr2?xRhxO7?? (LCRZ, x = 0.055, 1 wt% Rh). This was done to compare the effect of Ca substitution on the La site along with Rh substitution on Zr site. A third catalyst was synthesized where Ni was substituted in the Zr-site to give La?Zr2-xNixO7?? (LNZ, x = 0.112, 1 wt% Ni). A fourth catalyst, containing no catalytically active metal, La1.97Sr0.03Zr?O7?? (LSZ), was synthesized to provide a direct comparison to the substituted pyrochlores. Effects of substitution and kinetic measurements were examined for dry reforming of methane in a fixed-bed reactor. XRD results prior to reaction showed that all the pyrochlore catalysts had a cubic unit-cell lattice. Results from XPS suggested that there were two oxidic phases (RhO? and Rh?O?) in Rh-substituted LRZ and LCRZ and two phases (NiO and Ni?O?) present in Ni substituted LNZ. TPR of the catalysts confirmed the presence of two reducible Rh species in LCRZ and LRZ, and four reducible Ni species in LNZ. Textural measurements revealed that among the active catalysts, LCRZ had the highest BET surface area (10.0 m²/g) and pore volume (0.10 cm³/g). Temperature programmed surface reaction (TPSR) tests indicated different light-off curves for different catalysts, with LCRZ being the most active by this measure. Steady state tests at 750 °C using an equimolar reactant feed for 450 min showed that the Ni-based pyrochlore (LNZ) deactivated rapidly. LCRZ and LRZ showed similar activity, however, LCRZ showed lower carbon built-up. XRD of the spent catalysts showed that the pyrochlore structure was unchanged during reaction for all catalysts. Carbon deposited on catalyst surface during reaction was characterized by TPO. The Ni-based pyrochlore showed higher carbon deposition (1.4 g/gcat.) than either LCRZ (0.26 g/gcat.) or LRZ (0.44 g/gcat.). These results suggested that Rh substituted into the pyrochlore was more active and selective for synthesis gas compared to a directly comparable atomic loading of Ni. In addition, the replacement of Ca²? for La³? may provide improved oxygen mobility of the catalyst (through the introduction of lattice oxygen defects) resulting in the oxidation of carbonaceous species deposited on the active sites on the catalyst during the reaction. Substitution of metals into the crystal lattice might have also lowered the bond energy of La–O and Zr–O lattice bonds resulting in the release of oxygen from the lattice, which probably oxidized surface carbon thus slowing down carbon accumulation.

  5. 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 CaMKII?c-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

  6. 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.

  7. Patterns of Ca/Sr and 87Sr/ 86Sr variation before and after a whole watershed CaSiO 3 addition at the Hubbard Brook Experimental Forest, USA

    NASA Astrophysics Data System (ADS)

    Nezat, Carmen A.; Blum, Joel D.; Driscoll, Charles T.

    2010-06-01

    Forty-one metric tons of the mineral wollastonite (CaSiO 3) was applied to an 11.8 hectare watershed at the Hubbard Brook Experimental Forest (HBEF; White Mountains, New Hampshire, USA) with the goal of restoring the Ca estimated to have been depleted from the soil exchange complex by acid deposition. This experiment provided an opportunity to gain qualitative information on whole watershed hydrologic flow paths by studying the response of stream water chemistry to the addition of Ca. Because the Ca/Sr and 87Sr/ 86Sr ratios of wollastonite strongly contrast that of other Ca sources in the watershed, the wollastonite-derived Ca can be identified and its amount estimated in various ecosystem components. Stream water chemistry at the HBEF varies seasonally due to shifts in the proportion of base flow and interflow. Prior to the wollastonite application, seasonal variations in 87Sr/ 86Sr ratios indicated that 87Sr/ 86Sr was higher during base flow than interflow, due largely to greater amounts of biotite weathering along deeper flow paths. After the application, Ca/Sr and 87Sr/ 86Sr changed markedly as the high Ca/Sr and low 87Sr/ 86Sr wollastonite dissolved and mixed with stream water. The Ca addition provided information on the response times of various flow paths and ion exchange processes to Ca addition in this small upland watershed. During the first year after the addition, wollastonite applied to the near stream zone dissolved and was partially immobilized by cation exchange sites in the hyporheic zone. In the second and third years after the addition we infer that much of this Ca and Sr was subsequently desorbed from the hyporheic zone and was exported from the watershed in stream flow. In the fourth through ninth years after the addition, Ca and Sr from wollastonite that had dissolved in upland soils was transported to the stream by interflow during wet periods when the ground water table was elevated. Between years three and nine the minimum annual Ca/Sr ratio (in late summer base flow) increased, providing evidence that Ca and Sr had increasingly infiltrated to the deepest flow paths. Strong seasonal variations in Ca/Sr and 87Sr/ 86Sr ratios of stream water resulted from the wollastonite addition to upland forest soils, and these ratios have become sensitive to changing flow paths during the annual cycle. Most notably, high flow events now produce large excursions in stream geochemistry toward the high Ca/Sr and low 87Sr/ 86Sr ratios of wollastonite. Nine years after the application we estimate that ˜360 kg of Ca from wollastonite has been exported from the watershed in stream flow. The rate of export of Ca from wollastonite dissolution has stabilized at about 11 kg of Ca per year, which accounts for ˜30% of the dissolved Ca in the stream water. Given that 19 metric tons of Ca were applied to the watershed, and assuming this current rate of loss, it should take over 1000 years for this added Ca to be transported from the watershed.

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  9. 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.

  10. Effect of doping in Bi-Pb-Sr-Ca-Cu-O superconductor composites 

    E-print Network

    Ertekin, Abdullah

    2001-01-01

    The goal of this thesis is to analyze the solid solubility limit of dopants in Bi-Pb-Sr-Ca-Cu-O superconductors. We have studied the effect of Mn doping Bi-Pb-Sr-Ca-Cu-O. The electrical resistivity and critical temperature were measured for samples...

  11. Transcription factor CREB is involved in CaSR-mediated cytoskeleton gene expression.

    PubMed

    Huang, Shuaishuai; Ren, Yu; Wang, Ping; Li, Yanyuan; Wang, Xue; Zhuang, Haihui; Fang, Rong; Wang, Yuduo; Liu, Ningsheng; Hehir, Michael; Zhou, Jeff X

    2015-03-01

    Our previous studies illustrated that a steady increase of intracellular calcium concentration ([Ca2+]i) was important for maintaining microtubules (MTs) rearrangement in apoptotic cells. However, little is known about the effect of calcium sensing receptor (CaSR)-mediated increase in [Ca2+]i on cytoskeleton gene expression. We examined the impact of taxol or CaSR agonist/antagonist on the regulation of [Ca2+]i concentration, cytoskeleton arrangement, phosphorylated CREB and cytoskeleton gene expressions in HeLa cells with dominant negative plasmid of CREB (PM). This study demonstrated that Gdcl3 (a specific CaSR agonist) evoked a rapid increase of [Ca2+]i, formed a rigid bundle of MTs which surrounded the nucleus and decreased the cytoskeleton gene expressions in HeLa cells. These effects were rescued by addition of NPS2390 (a specific CaSR antagonist). Moreover, CaSR activity affected cytoskeleton gene expression through transcription factor CREB. Histoscores of pCREB immunoreactivity in tissues of cervical adenocarcinoma, renal clear cell carcinoma, and diffuse large B-cell lymphoma were markedly increased compared with non malignant tissue. These data demonstrate, for the first time, that CaSR-mediated increase in [Ca2+]i probably modulate cytoskeleton organization and gene expression via transcription factor. PMID:25382680

  12. Injectability of brushite-forming Mg-substituted and Sr-substituted alpha-TCP bone cements.

    PubMed

    Pina, S; Torres, P M C; Ferreira, J M F

    2010-02-01

    The influence of magnesium- and strontium-substitutions on injectability and mechanical performance of brushite-forming alpha-TCP cements has been evaluated in the present work. The effects of Mg- and Sr-substitutions on crystalline phase composition and lattice parameters were determined through quantitative X-ray phase analysis and structural Rietveld refinement of the starting calcium phosphate powders and of the hardened cements. A noticeable dependence of injectability on the liquid-to-powder ratio (LPR), smooth plots of extrusion force versus syringe plunger displacement and the absence of filter pressing effects were observed. For LPR values up to 0.36 ml g(-1), the percentage of injectability was always higher and lower for Mg-containing cements and for Sr-containing cements, respectively, while all the pastes could be fully injected for LPR > 0.36 ml g(-1). The hardened cements exhibited relatively high wet compressive strength values (~17-25 MPa) being the Sr- and Mg-containing cements the strongest and the weakest, respectively, holding an interesting promise for uses in trauma surgery such as for filling bone defects and in minimally invasive techniques such as percutaneous vertebroplasty to fill lesions and strengthen the osteoporotic bone. PMID:19851845

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

    SciTech Connect

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

    1995-07-01

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

  15. 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

  16. 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 (?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

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

    PubMed

    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 (?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

  18. 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 (?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.

  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. Study on the site preference of Ca in superconducting oxides Bi{sub 2}Sr{sub 2?x}Ca{sub x}CuO{sub 6+?} (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+?} (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 ?} grain, which can be described as an intergrowth structure.

  1. Superconducting and structural properties of epitaxial Bi 2Sr 2CaCu 2O 8-?/Bi 2Sr 2YCu 2O 8-?/Bi 2Sr 2CaCu 2O 8-? heterostructures

    NASA Astrophysics Data System (ADS)

    Bacca, E.; Chacón, M.; Castro, L. F.; Lopera, W.; Gómez, M. E.; Prieto, P.; Heiras, J.

    1994-12-01

    We have prepared Bi 2Sr 2CaCu 2O 8-?/Bi 2Sr 2YCu 2O 8-?/Bi 2Sr 2CaCu 2O 8-? trilayer structures, using a “in situ” DC-sputtering process at high oxygen pressures on (001) SrTiO 3 substrates. Bi 2Sr 2CaCu 2O 8-? films were used for superconducting electrodes and semiconductor-like Bi 2Sr 2YCu 2O 8-? films with thickness down 5 nm were used as barrier layers. Both materials have the same crystalline structures and allowed the epitaxial growth of the heterstructure as shown by X-ray, RBS measurements and cross section TEM analysis. The superconducting properties were examined by resistance, AC-susceptibility and current-voltage characteristics as function of the temperature. For junctions with areas of 120×120?m 2 defined by photolitography a RSJ behavior was found at temperatures below T c.

  2. Low loss Sr{sub 1-x}Ca{sub x}La{sub 4}Ti{sub 5}O{sub 17} microwave dielectric ceramics

    SciTech Connect

    Iqbal, Yaseen; Manan, Abdul; Department of Materials Science and Engineering, Sir Robert Hadfield Building, University of Sheffield, S1 3JD ; Reaney, I.M.

    2011-07-15

    Highlights: {yields} New single phase highly dense (95%) microwave dielectric Sr{sub 1-x}Ca{sub x}La{sub 4}Ti{sub 5}O{sub 17} (0 {<=} x {<=} 1) ceramics were designed and processed. {yields} Theoretical density and molar volume decreased due to the substitution of small Ca{sup 2+} for large Sr{sup 2+}. {yields} As required for microwave dielectric applications, optimum properties (i.e. {epsilon}{sub r} {approx} 53.7, Qf{sub o} {approx} 11,532 GHz and {tau}{sub f} {approx} -1.4 ppm/{sup o}C) were achieved for Sr{sub 0.4}Ca{sub 0.6}La{sub 4}Ti{sub 5}O{sub 17} (x = 0.6). -- Abstract: Microwave dielectric ceramics in the Sr{sub 1-x}Ca{sub x}La{sub 4}Ti{sub 5}O{sub 17} (0 {<=} x {<=} 1) composition series were prepared through a solid state mixed oxide route. All the compositions formed single phase ceramics within the detection limit of in-house X-ray diffraction when sintered in the temperature range 1450-1580 {sup o}C. Theoretical density and molar volume decreased due to the substitution of Ca{sup 2+} for Sr{sup 2+} which was associated with a decrease in the dielectric constant ({epsilon}{sub r}) and temperature coefficient of resonant frequency ({tau}{sub f}) but an increase in quality factor, Qf{sub o}. Optimum properties were achieved for Sr{sub 0.4}Ca{sub 0.6}La{sub 4}Ti{sub 5}O{sub 17} which exhibited, {epsilon}{sub r} {approx} 53.7, Qf{sub o} {approx} 11,532 GHz and {tau}{sub f} {approx} -1.4 ppm/{sup o}C.

  3. Crystal fabrics and element impurities (Sr/Ca, Mg/Ca, and Ba/Ca) in shells of Arctica islandica--Implications for paleoclimate reconstructions

    E-print Network

    Schöne, Bernd R.

    -to-calcium ratio Bivalve shell Crystal fabrics Biomineralization Climate proxy Sr/Ca, Mg/Ca and Ba/Ca values from the metal-to-calcium ratios of bivalve shells. © 2011 Elsevier B.V. All rights reserved. 1 number of taxonomic groups such as brachiopods (Lowenstam, 1961; Mii and Grossman, 1994; Powell et al

  4. Seasonal dripwater Mg/Ca and Sr/Ca variations driven by cave ventilation: Implications for and modeling

    E-print Network

    Banner, Jay L.

    Seasonal dripwater Mg/Ca and Sr/Ca variations driven by cave ventilation: Implications to cool season ventilation of the cave atmosphere, enhancing calcite precipitation and leading where seasonal ventilation of caves is likely: (1) speleothem trace-element records may provide seasonal

  5. Hydrothermal alteration processes at midocean ridges: Experimental and theoretical constraints from Ca and Sr exchange reactions and Sr isotopic ratios

    NASA Astrophysics Data System (ADS)

    Berndt, Michael E.; Seyfried, William E., Jr.; Beck, J. Warren

    1988-05-01

    Diabase and basalt were reacted with Na-Ca-K-Cl fluids of seawater chlorinity at 375-425°C, 375-400 bars, and fluid/rock mass ratios of 0.5-1.0 to assess the role of basalt chemistry and texture on Sr and Ca mobility during high-temperature hydrothermal alteration. An additional experiment, utilizing an 84Sr spiked fluid, was performed to help quantify reaction rates of processes affecting Sr mobility. The experimental results help to constrain reaction processes responsible for the chemistry of hot spring fluids at midocean ridges. Alteration of basalt and diabase is characterized by formation of tremolite-actinolite-smectite-chlorite and clinozoisitic epidote-smectite-chlorite, respectively. Diabase alteration produced dissolved Sr/Ca ratios similar to those observed for ridge crest hot spring fluids, whereas alteration of a mostly crystalline basalt produced significantly lower ratios. This observation supports the premise that the Sr/Ca ratios observed in vent fluids may be produced during deep-seated reaction of the hydrothermal fluids with diabase dikes and/or gabbro at relatively low fluid/rock ratios and suggests that hydrothermal alteration of primary igneous minerals at relatively high temperatures (400°C) leads to formation of a mineral with low DSr/Ca, Possibly hydrothermal plagioclase. Results of the 84Sr spiked experiment indicated that only 4% of the Sr in basalt was mobilized after 800 hours of reaction despite the fact that B and Li were nearly quantitatively leached. It is thus suggested that B and Li are good indicators of the amount of fresh rock encountered by fluids, while Sr concentration and isotopic data can be used to estimate the degree of alteration that the Sr-bearing primary minerals have undergone. The degree of alteration of subsurface reservoirs may be estimated by dividing the fluid/rock ratio obtained for highly mobile elements by the fluid/rock ratio obtained from path-integrated Sr isotope and concentration data. Based on this method, for example, it can be estimated that only 5% of the primary Sr-bearing minerals encountered by fluids in the subsurface at EPR 21°N are actually converted to secondary phases.

  6. Synthesis, characterization and thermochemistry of Cs-, Rb- and Sr-substituted barium aluminium titanate hollandites

    NASA Astrophysics Data System (ADS)

    Xu, H.; Wu, L.; Zhu, J.; Navrotsky, A.

    2015-04-01

    Titanate hollandites are of considerable interest for immobilization of radioactive Cs, its daughter product Ba and related radionuclides Rb and Sr. In this study, we synthesized three hollandites, Ba1.18Cs0.21Al2.44Ti5.53O16, Ba1.17Rb0.19Al2.46Ti5.53O16 and Ba1.14Sr0.10Al2.38Ti5.59O16, using sol-gel methods. Rietveld analysis of synchrotron XRD data shows that they adopt the tetragonal structure (space group I4/m), and their cell parameters increase with increasing cation size (Sr2+ ? Rb+ ? Cs+). Standard enthalpies of formation of these hollandites were determined from drop solution calorimetric measurements with lead borate as the solvent at 973 K. Their formation enthalpies are similar, consistent with the occurrence of extensive cation substitutions in hollandites. Further energetic analysis with respect to BaTiO3 and SrTiO3 perovskites and other oxides reveals decreased thermodynamic stability from Cs- to Rb- to Sr-hollandite. This trend is consistent with the phase assemblage observed in Synroc, where Cs+, Rb+ and Ba2+ enter into hollandite, whereas Sr2+ occurs in perovskite.

  7. Thallium cuprate 1223 type.. I. Its elaboration and dependence of chemical and thermal stability and of superconducting transition temperature on Tl/Pb and Sr/Ba substitutions

    NASA Astrophysics Data System (ADS)

    Lebbou, K.; Trosset, S.; Abraham, R.; Cohen-Adad, M. Th; Ciszek, M.; Liang, W. Y.

    1998-08-01

    The formation of samples with nominal composition (Tl xPb 1- x)(Sr 1- yBa y) 2Ca 2Cu 3O z was followed by X-ray diffraction study. With the chosen elaboration conditions, the 1223 phases were formed in two steps with a 1212 type phase observed as an intermediate compound. From the results, the limits of the 1223 single phase field were determined for temperature below 930°C and under 1 bar of oxygen. Samples with 91% purity were obtained and for compositions located outside the limits of the monophased field, a Tl/Pb-Sr/Ba-1212 and a substituted Tl/Pb and Sr/Ba perovskite were found as the main impurities.

  8. Calcium-sensing receptor (CaSR) as a novel target for ischemic neuroprotection

    PubMed Central

    Kim, Jong Youl; Ho, Hanson; Kim, Nuri; Liu, Jialing; Tu, Chia-Ling; Yenari, Midori A; Chang, Wenhan

    2014-01-01

    Object Ischemic brain injury is the leading cause for death and long-term disability in patients who suffer cardiac arrest and embolic stroke. Excitotoxicity and subsequent Ca2+-overload lead to ischemic neuron death. We explore a novel mechanism concerning the role of the excitatory extracellular calcium-sensing receptor (CaSR) in the induction of ischemic brain injury. Method Mice were exposed to forebrain ischemia and the actions of CaSR were determined after its genes were ablated specifically in hippocampal neurons or its activities were inhibited pharmacologically. Since the CaSR forms a heteromeric complex with the inhibitory type B ?-aminobutyric acid receptor 1 (GABABR1), we compared neuronal responses to ischemia in mice deficient in CaSR, GABABR1, or both, and in mice injected locally or systemically with a specific CaSR antagonist (or calcilytic) in the presence or absence of a GABABR1 agonist (baclofen). Results Both global and focal brain ischemia led to CaSR overexpression and GABABR1 downregulation in injured neurons. Genetic ablation of Casr genes or blocking CaSR activities by calcilytics rendered robust neuroprotection and preserved learning and memory functions in ischemic mice, partly by restoring GABABR1 expression. Concurrent ablation of Gabbr1 gene blocked the neuroprotection caused by the Casr gene knockout. Coinjection of calcilytics with baclofen synergistically enhanced neuroprotection. This combined therapy remained robust when given 6 h after ischemia. Interpretation Our study demonstrates a novel receptor interaction, which contributes to ischemic neuron death through CaSR upregulation and GABABR1 downregulation, and feasibility of neuroprotection by concurrently targeting these two receptors. PMID:25540800

  9. 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, ?44/40Ca 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 ?44/40Ca and Sr/Ca proxy signals.

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

    SciTech Connect

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

    1992-05-01

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

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

    SciTech Connect

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

    1992-05-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  13. Infiltration and Injection of a Ca-Citrate-PO4 Solution to Form Apatite In Situ for Sr-90 Remediation at the Hanford 100N Area – An Update

    SciTech Connect

    Szecsody, James E.; Fruchter, Jonathan S.; Vermeul, Vincent R.; Williams, Mark D.; Fritz, Brad G.; Mendoza, Donaldo P.; McKinley, James P.

    2010-03-11

    Sr-90 present in groundwater and the vadose zone at the Hanford 100N area due to past waste disposal practices has reached the nearby Columbia River, as evidenced by Sr-90 concentrations in near river wells and aquifer tubes and near shore sediments. Sr-90 is currently being remediated by adsorption onto apatite (55 times stronger than Sr-90 adsorption to sediment), followed by incorporation of the Sr-90 into the apatite structure. If the Sr-90 can remain immobilized for 300 years (~ten 29.1-yr half-lives of Sr-90 decay), it will have decayed below regulatory limits to Y-90 and to stable Zr-90. Apatite [Ca10(PO4)6(OH)2] is being precipitated in situ in saturated zone sediments by injection of a aqueous solution of Ca-citrate and Na-phosphate through a series of 16 wells. For the treatability study, field scale demonstration of the technology was implemented through injection of a low-concentration, apatite-forming solution, followed by high concentration solution injections as required to emplace sufficient treatment capacity to meet treatability test objectives. Analysis of field cores collected after the low concentration injections indicates that targeted apatite contents were achieved and that ~25% of the Sr-90 associated with the sediment was incorporated in the apatite structure. Aqueous Sr-90 monitoring in four compliance monitoring wells over a year following the high concentration injections indicates 84% to 95% decrease in Sr-90 concentrations (relative to the low and high end of the baseline range, respectively). Cores are currently being analyzed to confirm the apatite mass and Sr-90 substitution in apatite after these high concentration injections.

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

    SciTech Connect

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

    2008-07-31

    The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2#2;y)O(7-j,) (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2#2;x)SrxRhyZr(2#2;y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had significantly less carbon (0.17 gcarbon/gcatalyst). It is speculated that improved oxygen ion mobility in the LSRZ material, which resulted from Sr substitution, was responsible for the reduction in carbon formation on the surface.

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

    SciTech Connect

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

    2008-01-01

    The catalytic partial oxidation (CPOX) of transportation fuels into synthesis gas (H2 + CO) for fuel cells is complicated by the large quantities of aromatics and sulfur-containing compounds commonly found in these fuels. Traditional supported metal catalysts are easily poisoned by these species which adsorb strongly onto the electron-rich metal clusters. The use of noble metal and/or oxide based catalyst systems may offer higher activity and stability, but only if the metal can be bound into a thermally stable structure. To that end, Rh metal was substituted into the structure of a lanthanum zirconate (LZ) pyrochlore to give La2RhyZr(2#2;y)O(7-j,) (LRZ) to produce a strongly bound, well-dispersed metal which is active for CPOX. A second catalyst was prepared in which Sr was substituted for a portion of La in the LRZ structure, producing La(2#2;x)SrxRhyZr(2#2;y)O(7-j) (LSRZ). Each of these pyrochlore catalysts, including the unsubstituted LZ, were characterized and screened for activity in the CPOX of ntetradecane (TD), which is a surrogate for linear paraffins typical of diesel fuel. Results were compared to a commercial Rh/g-Al2O3 catalyst. X-ray diffraction patterns of both the LZ and LRZ showed that each had the cubic unit-cell pyrochlore structure. However, substitution of Sr resulted in a binary perovskite-pyrochlore phase with a defect SrZrO3 phase. Hydrogen pulse chemisorption and temperature programmed reduction studies confirmed that Rh metal was substituted into the structure of the LRZ and LSRZ, and was reducible. Activity screening with the CPOX of TD showed that the Rh substituted in both LRZ and LSRZ is able to retain activity-producing essentially equilibrium synthesis gas yields, as was the Rh/g-Al2O3. Temperature programmed oxidation experiments performed after the CPOX of TD demonstrated that the amount of carbon was quantitatively similar for each catalyst (roughly 0.3 gcarbon/gcatalyst after each run), with the exception of LSRZ, which had significantly less carbon (0.17 gcarbon/gcatalyst). It is speculated that improved oxygen ion mobility in the LSRZ material, which resulted from Sr substitution, was responsible for the reduction in carbon formation on the surface.

  16. 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.

  17. 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.

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

    USGS Publications Warehouse

    Hedrick, James B.; Sinha, Shyama P.; Kosynkin, Valery 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.

  19. Tunnelling anomalies in Bi 2Sr 2CaCu 2O 8-?/Bi 2Sr 2YCu 2O 8-?/Bi 2Sr 2CaCu 2O 8-? planar junctions

    NASA Astrophysics Data System (ADS)

    Baca, E.; Heiras, J.; Gómez, M. E.; Lopera, W.; Bolaños, G.; Prieto, P.; Cucolo, A. M.; Di Leo, R.; Romano, P.

    1997-05-01

    We have prepared Bi 2Sr 2CaCu 2O 8-?/Bi 2Sr 2YCu 2O 8-?/Bi 2Sr 2CaCu 2O 8-? (2 2 1 {2}/{2} 2 Y {2}/{2} 2 1 2) planar heterojunctions (trilayer structures) using an in situ d.c.-sputtering process at high oxygen pressures onto (0 0 1) SrTiO 3 substrates. Bi 2Sr 2YCu 2O 8-? films (semiconducting-like) 10 and 12 nm thick were used as artificial barriers. Composition and structure of the barrier and the superconducting electrodes are entirely compatible which allows epitaxial growth of the entire heterostructure. Gap-like structures of about 30 mV have been determined from tunnelling characteristics of the junctions. Linear conductance backgrounds as well as Zero Bias Anomalies (ZBA) are reported and discussed in detail.

  20. (Ca/Sr)Au{sub x}Cd{sub 1-x}: Stacking variants of the CrB-FeB series

    SciTech Connect

    Harms, Wiebke; Duerr, Ines; Daub, Michael; Roehr, Caroline

    2010-01-15

    The structural chemistry of binary 1:1 alkaline earth metallides A{sup II}M (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){sub 2}(h{sub 2}c){sub 2}), depending on the proportion of the Cd substitution a successive change to structures with increased hexagonality is observed: In SrAu{sub 0.93}Cd{sub 0.07} (monoclinic, space group P2{sub 1}/m, a=621.3(4), b=472.4(2), c=1216.1(9)pm, beta=96.97(5){sup 0}, Z=6, R1=0.0467) the stacking sequence is h{sub 2c}, i.e. the hexagonality is 66.67%. A slightly more increased Cd content in SrAu{sub 0.78}Cd{sub 0.22} (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 (h{sub 3}c){sub 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/beta-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. - SrAu{sub 0.93}Cd{sub 0.97}, one of the stacking sequences of the CrB/FeB structure type series found in the quasibinary section SrAu-SrCd.

  1. 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.

  2. 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

  3. Superconducting properties of Ca3Ir4Sn13: a ?SR study

    NASA Astrophysics Data System (ADS)

    Biswas, P. K.; Amato, A.; Wang, Kefeng; Petrovic, C.; Khasanov, R.; Luetkens, H.; Morenzoni, E.

    2014-12-01

    Muon spin relaxation and rotation (?SR) measurements have been performed to study the superconducting properties of Ca3Ir4Sn13. Zero-field ?SR data shows no sign of any magnetic anomaly in Ca3Ir4Sn13 at the superlattice transition temperature, T* or in the superconducting ground state. Transverse-field ?SR measurements in the vortex state provided the temperature dependence of the magnetic penetration depth ?. The dependence of ?-2 with temperature is consistent with the existence of a single s-wave energy gap in the superconducting state of Ca3Ir4Sn13 with a gap value of 1.51(5) meV at absolute zero temperature. The magnetic penetration depth at zero temperature ?(0) is 351(4) nm. The ratio ?(0)/kBTc = 2.41(8) indicates that Ca3Ir4Sn13 is a strong-coupling superconductor.

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

    PubMed Central

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

    2012-01-01

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

  5. Controls on shell Mg/Ca and Sr/Ca in cultured planktonic foraminiferan, Globigerinoides ruber (white)

    NASA Astrophysics Data System (ADS)

    K?sakürek, B.; Eisenhauer, A.; Böhm, F.; Garbe-Schönberg, D.; Erez, J.

    2008-09-01

    Mg/Ca and Sr/Ca ratios were determined on a single species of planktonic foraminiferan, Globigerinoides ruber (white), collected from the Gulf of Eilat and cultured in seawater at five different salinities (32 to 44), five temperatures (18 to 30 °C) and four pH values (7.9 to 8.4). The Mg/Ca-temperature calibration of cultured G. ruber (with an exponential slope of 8 ± 3%/°C) agrees well with previously published calibrations from core-tops and sediment traps. However, the dependence of Mg/Ca on salinity (with an exponential slope of 5 ± 3%/psu) is also significant and should be included in the calibration equation. With this purpose, we calculated a calibration equation for G. ruber dependent on both temperature and salinity within the 95% confidence limits: Mg/Ca(mmol/mol)=exp[0.06(±0.02)?S(psu)+0.08(±0.02)?T(°C)-2.8(±1.0)],R=0.95 The influence of pH on Mg/Ca ratios is negligible at ambient seawater pH (8.1 to 8.3). However, we observe a dominating pH control on shell Mg/Ca when the pH of seawater is lower than 8.0. Sr/Ca in G. ruber shows a significant positive correlation with average growth rate. Presumably, part of the variability in shell Sr/Ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions.

  6. 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.

  7. 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.

  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. 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.

  10. High-pressure modifications of CaZn 2, SrZn 2, SrAl 2, and BaAl 2: Implications for Laves phase structural trends

    NASA Astrophysics Data System (ADS)

    Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Häussermann, Ulrich

    2008-11-01

    High-pressure forms of intermetallic compounds with the composition CaZn 2, SrZn 2, SrAl 2, and BaAl 2 were synthesized from CeCu 2-type precursors (CaZn 2, SrZn 2, SrAl 2) and Ba 21Al 40 by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl 2 and BaAl 2), X-ray single-crystal diffraction (CaZn 2), and electron microscopy (SrZn 2). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu 2 (C15) structure, the dizincides adopt the hexagonal MgZn 2 (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions.

  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. 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.

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

    SciTech Connect

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

    2009-01-01

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

  14. Epitaxial deposition and properties of Bi2Sr2CaCu2O8 + delta /Bi2Sr2YCu2O8 + delta /Bi2Sr2CaCu2 O + delta trilayers

    NASA Astrophysics Data System (ADS)

    Cucolo, A. M.; Di Leo, R.; Romano, P.; Bacca, E.; Gomez, M. E.; Lopera, W.; Prieto, P.; Heiras, J.

    1996-01-01

    We have deposited Bi2Sr2CaCu2O8+?/Bi2Sr2YCu2O8+?/Bi2Sr2CaCu2 O+? (2212/22Y2/2212) heterostructures by an in situ dc sputtering technique at high oxygen pressures on (001) SrTiO3 substrates. The formation of highly c-axis oriented trilayers with sharp interfaces is demonstrated by x-ray diffraction and transmission electron microscope (TEM) analysis. Both the top and the bottom 2212 layers are superconducting below 87 K. Tunneling phenomena on junctions fabricated from these trilayers are observed. The conductance versus voltage curves at low temperatures exhibit a change of slope indicative of a gap structure at about 30 mV, a zero-bias peak, as well as linear background at high voltages.

  15. Transmission electron study of heteroepitaxial growth in the BiSrCaCuO system

    SciTech Connect

    Chaiken, A.; Wall, M.A.; Howell, R.H.; Bozovic, I.; Eckstein, J.N.; Virshup, G.F.

    1996-07-01

    Films of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and Bi{sub 2}Sr{sub 2}CuO{sub 6} have been grown using Atomic-Layer-by-Layer Molecular Beam Epitaxy (ALL-MBE) on lattice-matched substrates. These materials have been combined with layers of closely related metastable compounds like Bi{sub 2}Sr{sub 2}Ca{sub 7}Cu{sub 8}O{sub 20} (2278) and rare-earth-doped compounds like Bi{sub 2}Sr{sub 2}Dy{sub {ital x}}Ca{sub 1{minus}{ital x}}Cu{sub 2}O{sub 8} (Dy:2212) to form heterostructures with unique superconducting properties, including superconductor/insulator multilayers and tunnel junctions. Transmission electron microscopy (TEM) has been used to study the morphology and microstructure of these heterostructures. These TEM studies shed light on the physical properties of the films, and give insight into the growth mode of highly anisotropic solids like Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. {copyright} {ital 1996 Materials Research Society.}

  16. 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.

  17. 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.

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

    DOEpatents

    Dorris, Stephen E. (La Grange Park, IL); Poeppel, Roger B. (Glen Ellyn, IL); Prorok, Barton C. (Harrisville, PA); Lanagan, Michael T. (Woodridge, IL); Maroni, Victor A. (Naperville, IL)

    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.

  19. 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 ?C 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.

  20. Structure and Superconductivity of GaSr2(Tm,Ca)Cu2Oz Cuprate Doped with Cobalt

    NASA Astrophysics Data System (ADS)

    Lee, H. K.; Kim, Y. I.

    To address the structural mechanisms associated with Tc variations induced by Co doping, two samples of the nominal composition (Ga1-xCox)Sr2(Tm0.6Ca0.4)Cu2Oz with x = 0.5 and 0.7 have been prepared and studied by using neutron powder diffraction and transport measurements. In contrast to the x = 0.5 sample, which shows superconductivity around 35 K, the x = 0.7 sample does not exhibit superconductivity. The neutron powder diffraction studies indicate that both samples exhibit the 1212 structure with space group Ima2 and the Co atoms exclusively substitute for the Cu atoms located on the chain sites of the 123 parent structure. The depression in Tc of the x = 0.7 sample, compared to that of the x = 0.5 sample, is discussed in connection with oxygen content, disorder, and change in hole concentration on the superconducting planes.

  1. EXAFS spectra of the dilute solutions of Ca2+ and Sr2+ in water and methanol

    SciTech Connect

    Dang, Liem X.; Schenter, Gregory K.; Fulton, John L.

    2003-11-19

    A set of polarizable ion-water intermolecular interactions were developed that accurately described solvation enthalpies and structural properties of the dilute Ca2+ and Sr2+ in aqueous solution. The molecular dynamics (MD), coupled to electron scattering simulations of the Ca2+ and Sr2+ X-ray absorption fine structure spectroscopy (EXAFS) spectra are in good agreement with the corresponding experimental measurements. This work demonstrated that the combination of MD-EXAFS and the corresponding experiment measurement provides a power tool in the analysis of the solvation structure of the aqueous ionic solutions. The Ca2+-methanol interaction was also developed and the dilute Ca2+ MD-EXAFS spectrum in liquid methanol was also predicted using same approaches.

  2. Ferroelectricity in strained Ca0.5Sr0.5TiO3 from first principles

    E-print Network

    Halilov, Samed

    We present a density-functional theory investigation of strained Ca[subscript 0.5]Sr[subscript 0.5]TiO[subscript 3] (CSTO). We have determined the structure and polarization for a number of arrangements of Ca and Sr in a ...

  3. 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.

  4. 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

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

    DOEpatents

    Hinks, David G. (Lemont, IL); Capone, II, Donald W. (Northbridge, MA)

    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.

  6. A coral sr/ca calibration and replication study of two massive corals from the gulf of mexico

    USGS Publications Warehouse

    DeLong, K.L.; Flannery, J.A.; Maupin, C.R.; Poore, R.Z.; Quinn, T.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 8.31mmyear-1, A1, F1, and B3, respectively); however, seasonal Sr/Ca variability in M. faveolata is less than S. siderea (0.323, 0.353, and 0.254mmolmol-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. ?? 2011 Elsevier B.V.

  7. 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 ?g/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 ?g/l. The highest REE concentration (207 ?g/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.

  8. If and SR Ca2+ release both contribute to pacemaker activity in canine sinoatrial node cells

    PubMed Central

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

    2010-01-01

    Increasing evidence suggests that cardiac pacemaking is the result of two sinoatrial node (SAN) cell mechanisms: a ‘voltage clock’ and a Ca2+ dependent process, or ‘Ca2+ clock.’ The voltage clock initiates action potentials (APs) by SAN cell membrane potential depolarization from inward currents, of which the pacemaker current (If) is thought to be particularly important. A Ca2+ dependent process triggers APs when sarcoplasmic reticulum (SR) Ca2+ release activates inward current carried by the forward mode of the electrogenic Na+/Ca2+ exchanger (NCX). However, these mechanisms have mostly been defined in rodents or rabbits, but are unexplored in single SAN cells from larger animals. Here, we used patch-clamp and confocal microscope techniques to explore the roles of the voltage and Ca2+ clock mechanisms in canine SAN pacemaker cells. We found that ZD7288, a selective If antagonist, significantly reduced basal automaticity and induced irregular, arrhythmia-like activity in canine SAN cells. In addition, ZD7288 impaired but did not eliminate the SAN cell rate acceleration by isoproterenol. In contrast, ryanodine significantly reduced the SAN cell acceleration by isoproterenol, while ryanodine reduction of basal automaticity was modest (?14%) and did not reach statistical significance. Importantly, pretreatment with ryanodine eliminated SR Ca2+ release, but did not affect basal or isoproterenol-enhanced If. Taken together, these results indicate that voltage and Ca2+ dependent automaticity mechanisms coexist in canine SAN cells, and suggest If and SR Ca2+ release cooperate to determine baseline and catecholamine-dependent automaticity in isolated dog SAN cells. PMID:20380837

  9. 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.

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

    NASA Astrophysics Data System (ADS)

    Chlan, Vojt?ch; Kou?il, Karel; Uli?ná, Kate?ina; Št?pánková, 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.

  11. Effect of Sr substitution on photoluminescent properties of BaAl 2O 4:Eu 2+, Dy 3+

    NASA Astrophysics Data System (ADS)

    Ryu, H.; Singh, B. K.; Bartwal, K. S.

    2008-01-01

    Phosphor material BaAl 2O 4:Eu 2+, Dy 3+ with varying compositions of Sr substitution were prepared by the solid-state synthesis method. The phosphor compositions were characterized for their phase and crystallinity by XRD, SEM and TEM. Photoluminescence (PL) properties were investigated measuring PL and decay time for varying Ba/Sr compositions. The PL results show the blue shift in the luminescence properties in Sr substituted BaAl 2O 4:Eu 2+, Dy 3+ compared to parent BaAl 2O 4:Eu 2+, Dy 3+. It is probably due to the influence of 5d electron states of Eu 2+ in the crystal field because of atomic size variation causing crystal defects. Dy 3+ ion doping in the phosphor generates deep traps, which results in long afterglow phosphorescence.

  12. 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.

  13. First principles study on the electronic and optical properties of B-site ordered double perovskite Sr2MMoO6 (M=Mg, Ca, and Zn)

    NASA Astrophysics Data System (ADS)

    Zhao, Shuai; Lan, Chunfeng; Ma, Jie; Pandey, Shyam S.; Hayase, Shuzi; Ma, Tingli

    2015-07-01

    Electronic and optical properties of double perovskite Sr2MMoO6 (M=Mg, Ca, and Zn) were studied using density functional theory. The double perovskites Sr2MgMoO6 and Sr2CaMoO6 exhibited the direct band gap whereas Sr2ZnMoO6 was found to be indirect band gap material. The valence band maxima consisted mainly of oxygen 2p orbitals, whereas the conduction band minima was composed of hybridization between the B-site of Mo 4d and O 2p orbitals. The on-site Coulomb interaction was examined in terms of the influence of the transition metals' d orbitals on the electronic properties of the double perovskites. The dielectric functions and the absorption coefficients were studied from the ground electronic states. These results demonstrated that substituting the B-site elements in double perovskites is a potential method to tune the electronic structure for absorbing visible light for applications in inorganic perovskite solar cells.

  14. 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

  15. Site-related near-infrared luminescence in MAl{sub 12}O{sub 19} (M = Ca, Sr, Ba):Fe{sup 3+} phosphors

    SciTech Connect

    Li, Y.J.; Ma, Y.Y.; Ye, S.; Hu, G.P.; Zhang, Q.Y.

    2014-03-01

    Graphical abstract: - Highlights: • Intense 700–850 nm NIR emissions in MAl{sub 12}O{sub 19} (M = Ca, Sr, Ba):1%Fe{sup 3+} has been obtained. • The NIR emissions can be ascribed to the octahedral Fe{sup 3+} sites. • The site symmetry of Fe{sup 3+} in CA{sub 6} and SA{sub 6} may be lower than that in BA{sub 6}. • The phosphors may be potentially applied in the high-resolution bioimaging. - Abstract: Intense and broad near-infrared (NIR) photoluminescence (PL) peaks locating at 777, 808 and 810 nm is observed for BaAl{sub 12}O{sub 19} (BA{sub 6}):1%Fe{sup 3+}, CaAl{sub 12}O{sub 19} (CA{sub 6}):1%Fe{sup 3+} and SrAl{sub 12}O{sub 19} (SA{sub 6}):1%Fe{sup 3+}, respectively. Electron paramagnetic resonance (EPR) spectra show that Fe{sup 3+} ions substitute for the different types of Al{sup 3+} sites simultaneously. Meanwhile, the luminescence of Fe{sup 3+} in MAl{sub 12}O{sub 19} (M = Ca, Sr and Ba) are ascribed to octahedral Fe{sup 3+}. In addition, the site symmetry of Fe{sup 3+} in CA{sub 6}/SA{sub 6} is lower compared with BA{sub 6}, deduced from the photoluminescence excitation (PLE), EPR and Fourier-transform infrared (FT-IR) spectra. These phosphors can be considered as good candidates for the applications in the field of high-resolution bioimaging.

  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. 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.

  18. Synthesis and intercalation chemistry of K[Ca 2(Ca,Sr) n-3 Nb 3Ti n-3 O 3 n+1 ] ( n = 4, 5)

    NASA Astrophysics Data System (ADS)

    Ram, R. A. Mohan; Clearfield, A.

    1991-09-01

    A new series of layered perovskite oxides, K[Ca 2(Ca,Sr) n-3 Nb 3Ti n-3 O 3 n+1 ], has been prepared by the incorporation of Ca(Sr)TiO 3 perovskite slabs into KCa 2Nb 3O 10. With an increase in n, there is a progressive increase in unit cell parameters. Potassium atoms in these compounds can be exchanged by protons and these protonated forms do not show a doubled c axis. Proton-exchanged forms of these layered perovskite oxides are solid acids and react with organic bases such as n-hexylamine, forming n-C 6H 13NH 3[Ca 2(Ca,Sr) n-3 Nb 3Ti n-3 O 3 n+1 ], resulting in large layer separations.

  19. Ca, Sr and Ba stable isotopes reveal the fate of soil nutrientsalong 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.

  20. 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 ?M), 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 ?M), 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

  1. 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.

  2. 110K Bi-Sr-Ca-Cu-O superconductor oxide and method for making same

    DOEpatents

    Veal, Boyd W. (Downers Grove, IL); Downey, John W. (Joliet, IL); Lam, Daniel J. (Orland Park, IL); Paulikas, Arvydas P. (Downers Grove, IL)

    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.

  3. 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.

  4. Thermoelectric properties and electronic structure of the Zintl phase Sr?In?Sb? and the Ca(5-x)Sr(x)In?Sb? solid solution.

    PubMed

    Zevalkink, Alex; Chanakian, Sevan; Aydemir, Umut; Ormeci, Alim; Pomrehn, Gregory; Bux, Sabah; Fleurial, Jean-Pierre; Snyder, G Jeffrey

    2015-01-14

    The Zintl phase Sr5In2Sb6 is isostructural with Ca5In2Sb6-a promising thermoelectric material with a peak zT of 0.7 when the carrier concentration is optimized by doping. Density functional calculations for Sr5In2Sb6 reveal a decreased energy gap and decreased valence band effective mass relative to the Ca analog. Chemical bonding analysis using the electron localizability indicator was found to support the Zintl bonding scheme for this structure type. High temperature transport measurements of the complete Ca(5-x)Sr(x)In2Sb6 solid solution were used to investigate the influence of the cation site on the electronic and thermal properties of A5In2Sb6 compounds. Sr was shown to be fully miscible on the Ca site. The higher density of the Sr analog leads to a slight reduction in lattice thermal conductivity relative to Ca5In2Sb6, and, as expected, the solid solution samples have significantly reduced lattice thermal conductivities relative to the end member compounds. PMID:25479002

  5. Time-resolved Ultrafast Spectroscopy Experiments on High Temperature Superconductor Bi2Sr2CaCu2O8

    NASA Astrophysics Data System (ADS)

    Meng, Jianqiao; Dakovski, Georgi L.; Zhu, Jian-Xin; Riseborough, Peter S.; Gu, Genda; Gilbertson, Steve M.; Rodriguez, George; Qi, Jingbo; Taylor, Antoinette; Durakiewicz, Tomasz

    2013-03-01

    Time-resolved ultrafast spectroscopy experiments have been carried out on various dopings of high temperature superconductor Bi2Sr2CaCu2O8In this talk, we will report our observation and analysis of ultrafast dynamics in Bi2Sr2CaCu2O8, with special emphasis on the quasiparticle dynamics in the pseudogap and SC gap regimes.

  6. 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.

  7. Infrared properties of La2x,,Ca,Sr...xCaCu2O6 single crystals N. L. Wang,1,

    E-print Network

    Johnson, Peter D.

    . The reported supercon- ducting transition temperatures for single crystals prepared under high oxygen pressureInfrared properties of La2Àx,,Ca,Sr...xCaCu2O6¿ single crystals N. L. Wang,1, * P. Zheng,1 T. Feng; published 30 April 2003 The in-plane optical properties of two crystals of the bilayer cuprate La2 x

  8. Involvement of palmitate/Ca2+(Sr2+)-induced pore in the cycling of ions across the mitochondrial membrane.

    PubMed

    Mironova, Galina D; Saris, Nils-Erik L; Belosludtseva, Natalia V; Agafonov, Alexey V; Elantsev, Alexander B; Belosludtsev, Konstantin N

    2015-02-01

    The palmitate/Ca2+-induced (Pal/Ca2+) pore, which is formed due to the unique feature of long-chain saturated fatty acids to bind Ca2+ with high affinity, has been shown to play an important role in the physiology of mitochondria. The present study demonstrates that the efflux of Ca2+ from rat liver mitochondria induced by ruthenium red, an inhibitor of the energy-dependent Ca2+ influx, seems to be partly due to the opening of Pal/Ca2+ pores. Exogenous Pal stimulates the efflux. Measurements of pH showed that the Ca2+-induced alkalization of the mitochondrial matrix increased in the presence of Pal. The influx of Ca2+ (Sr2+) also induced an outflow of K+ followed by the reuptake of the ion by mitochondria. The outflow was not affected by a K+/H+ exchange blocker, and the reuptake was prevented by an ATP-dependent K+ channel inhibitor. It was also shown that the addition of Sr2+ to mitochondria under hypotonic conditions was accompanied by reversible cyclic changes in the membrane potential, the concentrations of Sr2+ and K+ and the respiratory rate. The cyclic changes were effectively suppressed by the inhibitors of Ca2+-dependent phospholipase A2, and a new Sr2+ cycle could only be initiated after the previous cycle was finished, indicating a refractory period in the mitochondrial sensitivity to Sr2+. All of the Ca2+- and Sr2+-induced effects were observed in the presence of cyclosporin A. This paper discusses a possible role of Pal/Ca2+ pores in the maintenance of cell ion homeostasis. PMID:25450352

  9. Evidence for the non-influence of salinity variability on the Porites coral Sr/Ca palaeothermometer

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Porites coral-based sea surface temperature (SST) reconstructions are obtained from the measurement of skeleton Sr/Ca ratio. However, the influence of salinity in the incorporation of these trace elements in the Porites aragonitic skeleton is still poorly documented. Laboratory experiments indicate that in three different 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 Porites Sr/Ca-based SST reconstructions at monthly and interannual timescales in open-ocean environmental conditions. We use a large spatial compilation of published Porites data from the Red Sea and Pacific and Indian oceans. Additionally to those published records, we add a new eastern Pacific coral Sr/Ca record from Clipperton Atoll. Using two different salinity products (Simple Ocean Data Assimilation (SODA) SSS reanalyses version 2.2.4, Carton and Giese, 2008; and instrumental SSS from the Institut de Recherche pour le Développement, France (IRD) Delcroix et al., 2011), we find no evidence of salinity bias on the Sr/Ca SST proxy at monthly and interannual timescales. We conclude that Porites Sr/Ca is a reliable palaeothermometer that is not influenced by salinity variability.

  10. Enhancement of redox- and phase-stability of thermoelectric CaMnO3-? by substitution

    NASA Astrophysics Data System (ADS)

    Thiel, Philipp; Populoh, Sascha; Yoon, Songhak; Weidenkaff, Anke

    2015-09-01

    Redox Reactivity and structural phase transitions have a major impact on transport and me-chemical properties of thermoelectric CaMnO3-?. In this study series of Ca1-xAxMn1-yByO3-? (0?x,y?0.8) compounds, each with A-site (Dy3+, Yb3+) or B-site (Nb5+, Ta5+ and Mo6+, W6+) substitution, were synthesized and crystallographically analyzed. It was found that the high-temperature oxygen content is widely independent from the substituent. Subsequently, with increasing temperature the differences in the Seebeck coefficient vanish above 1200 K. With increasing substitution the orthorhombic distortion of the perovskite-like phase increases. The orthorhombic distortion and the upper temperature limit of the stability of the orthorhombic crystal structure show an almost linear dependency. Accordingly, the mechanical stability of all-oxides thermoelectric converters at temperatures exceeding 1000 K will be increased employing materials with high substitution level and substituents inducing a high orthorhombic distortion.

  11. 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-?) 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-? sample with x = y = 0.04 has shown a power factor (S2?) of 176 ?W/m/K2 at 423 K, which is nearly two orders of magnitude higher than that of the pristine sample (2.1 ?W/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).

  12. 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.

  13. 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.

  14. 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 (??) and imaginary part (??) increase with more addition of Ca2+ amount. The imaginary part of complex permittivity (??) increases and the real part (???) goes down after Ca2+ is doped. Furthermore, the Ca2+ ions doped in the ferrite improved microwave absorbency.

  15. Phase equilibria in the CaO-SrO-CuO system ({>=}70 mol % CuO)

    SciTech Connect

    Kosmynin, A.S.; Balashov, V.L.; Garkushin, I.K.

    1995-07-01

    The temperature dependence of interactions between constituent components is among factors responsible for the effect of synthesis temperature on properties of oxide superconductors. The oxides of the CaO-SrO-CuO system are involved in the formation of bismuth-containing superconducting phases. In most works, the CaO-SrO-CuO system was studied in the subsolidus region; the discrepancy between the available results is primarily associated with the difference in synthesis temperatures used. The authors showed that peritectic decomposition of the ternary solid solutions occurs in the ranges 980-985{degrees}C for [(Sr{sub 1-x}Ca{sub x}){sub 3}(Cu{sub 5}){sub n}], 1000-1084{degrees}C for [(Sr{sub 1 - x}Ca{sub x}){sub 2}CuO{sub 3}]. Decomposition of the tetragonal solid solution at 980{degrees}C yields three phases: CuO and two last solid solutions with Ca-rich compositions. In this work, the authors studied the CuO-rich part of the CaO-SrO-CuO system.

  16. Crystallographic analysis of the intermediate phases observed during the conversion of (Bi, Pb) 2Sr 2CaCu 2O 8+? to (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+? in composite tapes

    NASA Astrophysics Data System (ADS)

    Wu, Lijun; Zhu, Yimei; Suenaga, M.

    1998-09-01

    We report our crystallographic analysis of three major intermediate phases during the conversion of (Bi, Pb) 2Sr 2CaCu 2O 8+? (Bi/2212) to (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+? (Bi/2223) phase in Ag-sheathed composite tapes. The intermediate phase (Ca,Sr) 5+ x(Pb, Bi) 3+ yCuO has a c-centered monoclinic lattice with a=1.723 nm, b=0.975 nm, c=0.342 nm, and ?=93.5°; while both (Ca, Sr)CuO 2 and (Ca, Sr) 14Cu 24O 41+? are phase mixtures with nano-precipitates randomly imbedded in their matrix. The structure of the matrix for the former has face-centered monoclinic symmetry with a=1.105 nm, b=0.643 nm, c=0.347 nm, and ?=92.3°; the precipitates for the latter are face-centered orthorhombic with a=1.147 nm, b=1.339 nm, and c=0.277 nm. We discuss the structural evolution of these intermediate phases and their relation to Bi/2212 and Bi/2223.

  17. 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.).

  18. 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.

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

    DOEpatents

    Shi, Donglu (Chicago, IL)

    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. Characterization of MeWO 4 (Me = Ba, Sr and Ca) nanocrystallines prepared by sonochemical method

    NASA Astrophysics Data System (ADS)

    Thongtem, Titipun; Phuruangrat, Anukorn; Thongtem, Somchai

    2008-09-01

    Metal tungstates (MeWO 4, Me = Ba, Sr and Ca) were successfully prepared using the corresponding Me(NO 3) 2·2H 2O and Na 2WO 4·2H 2O in ethylene glycol by the 5 h sonochemical process. The tungstate phases with scheelite structure were detected with X-ray diffraction (XRD) and selected area electron diffraction (SAED). Their calculated lattice parameters are in accord with those of the JCPDS cards. Transmission electron microscopy (TEM) revealed the presence of nanoparticles composing the products. Their average sizes are 42.0 ± 10.4, 18.5 ± 5.1 and 13.1 ± 3.3 nm for Me = Ba, Sr and Ca, respectively. Interplanar spaces of the crystals were also characterized with high-resolution TEM (HRTEM). Their crystallographic planes are aligned in systematic array. Six different vibration wavenumbers were detected using Raman spectrometer and are specified as ?1(A g), ?3(B g), ?3(E g), ?4(B g), ?2(A g) and free rotation. Fourier transform infrared (FTIR) spectra provided the evidence of scheelite structure with W-O anti-symmetric stretching vibration of [WO 4] 2- tetrahedrons at 786-883 cm -1. Photoluminescence emission of the products was detected over the range of 384-416 nm.

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

    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) Å, b = 4.3809(4) and 4.3771(2) Å, c = 12.9430(12) and 12.9378(6) Å, ? = 102.832(2)° and 102.839(1)°, and V = 1207.0(2) and 1204.45(9) Å3, respectively. The composition is described by the general formula Bi4(Ca2- x Sr1.5+ x )O9.5 with x = 0.13(2) for crystal I and x = 0.19(2) for crystal II. The matrix contains intergrowing clusters of the composition Cu2O. 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 Cu2O oxide.

  2. Judd-Ofelt analysis of Pr3+ ions in Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 host matrices

    NASA Astrophysics Data System (ADS)

    Vidyadharan, Viji; Gopi, Subash; Remya, Mohan P.; Thomas, Vinoy; Joseph, Cyriac; Unnikrishnan, N. V.; Biju, P. R.

    2016-01-01

    The spectroscopic properties of Pr3+ doped Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 host matrices have been investigated using optical absorption and emission spectra. The oscillator strengths of observed bands of Pr3+ ions and Judd-Ofelt intensity parameters were calculated by including and excluding the hypersensitive 3H4 ? 3P2 transition using standard and modified Judd-Ofelt (JO) theory. In both the host matrices the JO parameters follow the same trend as ?6 > ?2 > ?4. The JO intensity parameters obtained by using the Modified JO theory was used to compute the radiative properties such as radiative transition probability (AR), branching ratio (?R) and radiative lifetime (?R) for the observed fluorescence bands. The photoluminescence spectrum of Pr3+ doped Sr1.5Ca0.5SiO4 upon 444 nm excitation shows three emission peaks at 489, 608 and 733 nm corresponding to the transitions 3P0 ? 3H4, 3H6 and 3F4 respectively. But in the case of Sr0.5Ca0.5TiO3 host matrix we observed an emission peak at 611 nm corresponding to the 1D2 ? 3H4 transition at ?ex = 336 nm. The experimental branching ratio (?exp) obtained from the fluorescence spectra was compared with the calculated values. The non radiative relaxation rate was calculated from the experimental (?exp) and predicted (?R) lifetimes. Stimulated emission cross section (?e), gain bandwidth (?e × ??eff) and optical gain (?e × ?R) for 0.5 wt% Pr3+ doped Sr1.5Ca0.5SiO4 and Sr0.5Ca0.5TiO3 phosphor samples were also calculated and their high value suggests its candidature as a good optical material.

  3. 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.

  4. Structure of molten CaSiO3: neutron diffraction isotope substitution with aerodynamic levitation and molecular dynamics study.

    PubMed

    Skinner, L B; Benmore, C J; Weber, J K R; Tumber, S; Lazareva, L; Neuefeind, J; Santodonato, L; Du, J; Parise, J B

    2012-11-15

    We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO(3), to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the first 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 redistribution of Ca-O bond lengths, especially toward longer distances in the liquid. The first order neutron difference function provides a test of recent molecular dynamics simulations and supports the MD model which contains 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 CaSiO(3). PMID:23106223

  5. 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 isot

  6. 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.

  7. Superfast contractions without superfast energetics: ATP usage by SR-Ca2+ pumps and crossbridges in toadfish swimbladder muscle

    PubMed Central

    Rome, Lawrence C; Klimov, Andrei A

    2000-01-01

    The rate at which an isometrically contracting muscle uses energy is thought to be proportional to its twitch speed. In both slow and fast muscles, however, a constant proportion (25-40 %) of the total energy has been found to be used by SR-Ca2+ pumps and the remainder by crossbridges. We examined whether SR-Ca2+ pumps account for a larger proportion of the energy in the fastest vertebrate muscle known (the toadfish swimbladder), and whether the swimbladder muscle utilizes energy at the superfast rate one would predict from its mechanics.The ATP utilization rates of the SR-Ca2+ pumps and crossbridges were measured using a coupled assay system on fibres skinned with saponin. Surprisingly, despite its superfast twitch speed, the ATP utilization rate of swimbladder was no higher than that of much slower fast-twitch amphibian muscles.The swimbladder achieves tremendous twitch speeds with a modest steady-state ATP utilization rate by employing two mechanisms: having a small number of attached crossbridges and probably utilizing intracellular Ca2+ buffers (parvalbumin) to spread out the time over which Ca2+ pumping can occur.Finally, although the total ATP utilization rate was not as rapid as expected, the relative proportions used by SR-Ca2+ pumps and the crossbridges were similar to other muscles. PMID:10896717

  8. Theoretical studies of the osmium based perovskites AOsO3 (A=Ca, Sr and Ba)

    NASA Astrophysics Data System (ADS)

    Ali, Zahid; Sattar, Abdul; Asadabadi, S. Jalali; Ahmad, Iftikhar

    2015-11-01

    Osmium based perovskites AOsO3 (A=Ca, Sr and Ba) have been studied theoretically using density functional theory approach. These studies show that CaOsO3 and SrOsO3 are orthorhombic and BaOsO3 is cubic and are consistent with the experiments. The electronic band structures demonstrate that these compounds are metals. The magnetic studies verify the experimental observations at low temperature, where the spin effects are canceled by the orbitals. The stable magnetic phase optimizations and magnetic susceptibilities calculations by the post-DFT treatment confirm that CaOsO3 and SrOsO3 are weak ferromagnetic whereas BaOsO3 is a paramagnetic material. The directional magnetic study shows that these compounds are magnetically anisotropic, and reveals that the easy magnetization axis is [001] direction.

  9. 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.

  10. The Giant Pacific Oyster (Crassostrea gigas) as a modern analog for fossil ostreoids: Isotopic (Ca, O, C) and elemental (Mg/Ca, Sr/Ca, Mn/Ca) proxies

    NASA Astrophysics Data System (ADS)

    Ullmann, Clemens V.; Böhm, Florian; Rickaby, Rosalind E. M.; Wiechert, Uwe; Korte, Christoph

    2013-10-01

    Modern analogs are an essential part of palaeoclimate studies, because they provide the basis for the understanding of geochemical signatures of fossils. Ostreoids are common in many sedimentary sequences and because of their fast growth, high temporal resolution sampling of past seasonal variability is possible. Here, two shell structures of modern Giant Pacific Oysters (Crassostrea gigas), the chalky substance and foliate layers, have been sampled for trace element distributions (Mg, Sr, Mn) and stable isotope variability (C, O, Ca). Oxygen isotopes exhibit a clear seasonal signature. Mean carbon isotope values of different oysters agree within 0.1‰, but ontogenic variability is complicated by shell growth patterns and potential small vital effects. The calcium isotope ratios are found to be constant throughout ontogeny within analytical precision at a value of ?44/40Ca = 0.68 ± 0.16‰ (2 sd) SRM-915a which is consistent with other bivalve species. Calcium isotope ratios in oyster shell material might thus be a possible proxy for palaeo seawater calcium isotope ratios. Element/Ca ratios are significantly higher in the chalky substance than in the foliate layers and especially high Sr/Ca and Mn/Ca ratios are observed for the first growth season of the oysters. Mg/Ca ratios in the chalky substance show a negative correlation with ?18O values, compatible with a temperature dependence, whereas this correlation is absent in the foliate layers. Seasonal changes of Sr/Ca are controlled by metabolic processes, whereas for Mn/Ca an additional environmental control is evident.

  11. 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.

  12. The Solid Solution Sr1-x Bax Ga2 : Substitutional Disorder and Chemical Bonding Visited by NMR Spectroscopy and Quantum Mechanical Calculations.

    PubMed

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

    2015-09-28

    Complete miscibility of the intermetallic phases (IPs) SrGa2 and BaGa2 forming the solid solution Sr1-x Bax 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

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

    SciTech Connect

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

    2006-01-01

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

  14. 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+?} 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.

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

    PubMed

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

    2015-09-28

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

  16. 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}.

  17. Structural, magnetic, and electronic transport properties of ,,Sr0.9Ca0.1...3Ru2O7 single crystal

    E-print Network

    Spinu, Leonard

    of Sr0.9Ca0.1 3Ru2O7 using single crystals grown by a floating-zone technique. The structure analysis underlying physics. Our sample Sr0.9Ca0.1 3Ru2O7 was grown using a floating-zone technique and carefully

  18. First principles studies on the structural, elastic, electronic properties and heats of formation of MgeAE (AE Ca, Sr, Ba) intermetallics

    E-print Network

    Melnik, Roderick

    of states of eight MgeAE (AE ¼ Ca, Sr, Ba) intermetallic compounds. The ob- tained results indicate ¼ Ca, Sr, Ba) systems intermetallic compounds have generated significant interests over the past fewe9] for the eight Mg intermetallic compounds. Moreover, investigations focused on the elastic

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

    SciTech Connect

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

    1996-08-01

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

  20. Thermoelectric Power of (Bi-Pb) SrCaCuO:. Before and after Deoxygenation

    NASA Astrophysics Data System (ADS)

    Chanda, B.; Dey, T. K.

    2000-09-01

    The temperature dependence of thermoelectric power (TEP) of deoxygenated Bi1.6Pb0.4Sr2Ca2Cu3O10+? samples is reported along with the well annealed sample. Tco of the samples is found to decrease with increasing hour of deoxygenation from 102K to 45K. The TEP of all the samples were found to be positive and to increase almost linearly with decrease in temperature down to 120K, before falling to zero. The results are analysed on the basis of two theoretical models and it is concluded that the measured TEP data could be explained extremely well (within 1%) using the modified two-band model proposed by Forro et al.

  1. 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.

  2. Electronic structure of epitaxial ,,Sr,Ca...RuO3 films studied by photoemission and x-ray absorption spectroscopy

    E-print Network

    Oh, Se-Jung

    -temperature conduc- tivity very close to the Mott minimum value. And the cubic pyrochlore structure (Sr,Ca)3Ru2O7 system shows a typical bandwidth-controlled metal-insulator transition MIT .5,6 The Bi-based pyrochlore

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

    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-?, Y0.95Ca0.05Ba2Cu3O7-? and YBa1.75Sr0.25Cu3O7-? 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-? superconductor than the chemical pressure effect promoted by Sr doping.

  4. High angle [001] twist boundaries in platelet colonies of BiSrCaCuO (2223) superconductor.

    PubMed

    Diko, P; Hanic, F

    1999-01-01

    The microstructure of BiPbSrCaCuO (2223) ceramic was studied by polarised light microscopy and the etch-pits technique. The high-angle twist grain boundaries in the platelet colonies were confirmed to be [001] coincidence type twisted boundaries or rotation twin boundaries with the (001) twinning plane. PMID:12558689

  5. 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) .

  6. Systematic study of compositional and synthetic control of vacancy and magnetic ordering in oxygen-deficient perovskites Ca2Fe(2-x)Mn(x)O(5+y)and CaSrFe(2-x)Mn(x)O(5+y) (x = 1/2, 2/3, and 1; y = 0-1/2).

    PubMed

    Ramezanipour, Farshid; Greedan, John E; Cranswick, Lachlan M D; Garlea, V Ovidiu; Donaberger, Ronald L; Siewenie, Joan

    2012-02-15

    Ten compounds belonging to the series of oxygen-deficient perovskite oxides Ca(2)Fe(2-x)Mn(x)O(5) and CaSrFe(2-x)Mn(x)O(5+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 T(d) chain (vacancy) disorder. In the special case of CaSrFeMnO(5) the neutron diffraction peaks broaden, indicating only short-range structural order on a length scale of ~160 Å. This reveals a systematic progression from Ca(2)FeMnO(5) (Pnma, well-ordered tetrahedral chains) to CaSrFeMnO(5) (Icmm, disordered tetrahedral chains, overall short-range order) to Sr(2)FeMnO(5) (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, T(c), decreases for the same x when Sr substitutes for one Ca. A review of the changes in T(c) for the series Ca(2)Fe(2-x)M(x)O(5), taking into account the tetrahedral/octahedral site preferences for the various M(3+) 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 Ca(2)Fe(2-x)Mn(x)O(5) and the CaSrFe(2-x)Mn(x)O(5) series. For the y > 0 phases, while a brownmillerite ordering of oxygen vacancies is preserved for the Ca(2) 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) Å. PMID:22239480

  7. Physical Characterization of Pure and Substituted Tetragonal LaBaCaCu3O7-? Superconductor

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Narlikar, A. V.

    The high Tc superconductor, forming the focus of the present review, presents an interesting situation where, despite its oxygen content close to 7.0, the system prefers to crystallize in tetragonal structure, as distinct from exhaustively studied orthorhombic RE:123 (REBa2Cu3O7, RE = rare earth) compounds. Its optimum Tc is decided by the cation intermixing at various sites, unlike that in case of normal RE:123, where all cationic sites are fully occupied and fixed, leaving the anionic sites free for oxygen filling. In this, we review the rich crystal chemistry of this compound and discuss it in conjunction with its unusual superconducting properties. The article is divided in five parts: (1) first we discuss variously reported interesting finer structural details and superconductivity of pristine LaBaCaCu3O7-? (La:1113) superconductor. The La, Ba and Ca sites are found to be intermixed with respect to their nominal sites of the standard RE:123 structure. (2) We examine the structural aspects and superconductivity of La1-xRExBaCaCu3O7 (RE = Nd, Dy, Sm and Pr). Unlike RE:123 and 124 compounds, the RE:1113 compounds form only with light rare earths such as La, Pr and Nd. Pr:1113 compound is found to be an insulator with Pr moments ordering magnetically at around 8 K, unlike at 17 K for Pr:123. (3) Studies of Pr substitution reveal that relative Tc depression due to Pr in the (La,Nd)1-xPrxBaCaCu3O7 system is less in comparison to that found for La or Nd site Pr substituted (La,Nd)1- xPrxBa2Cu3O7. (4) The results of superconductivity and structural details are reviewed for LaBaCaCu3-xMxO7 (M = Fe, Co, Ni, Ga and Zn) and finally (5) we summarize our conclusions. The results in terms of Tc depression due to these impurities in the parent La:1113 system are seen as similar to those observed for RE:124 (REBa2Cu4O8) and Nd:214 (Nd2-xCexCuO4), but are different from RE:123 and La:214. The results of structural details, superconductivity and magnetic ordering presented in the four parts for La1-xRExBaCaCu3- yMyO7 (RE = Nd, Dy, Sm, Pr with 1.0>=x>=0.0, and M = Fe, Co, Ni, Ga and Zn with 0.24>=y>=0.0 were obtained from X-ray and neutron diffraction and using AC and DC magnetic susceptibility, electrical resitivity and heat capacity data as a function of temperature. This review is mainly a consolidated work of the authors, including their collaboration from various laboratories and the reported data of other workers, all being duly acknowledged in the text.

  8. A Modern Sr/Ca-?18O-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-?18O-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 ?18O annual cycle of 1.1‰ approximates that expected if salinity had little effect on coral ?18O, assuming a previously established conversion of -0.23‰ (?18O)/°C for biogenic aragonite. The average annual salinity amplitude of 0.3 in gridded data from around Heron Island supports our conclusion that ?18O 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.

  9. Structural and Superconducting Properties of Hg 0.75Re 0.25Ba 2- xSr xCa 2Cu 3O 8+ ? Superconductors Grown by Sol-Gel and Sealed Quartz Tube Synthesis

    NASA Astrophysics Data System (ADS)

    Sin, A.; Alsina, F.; Mestres, N.; Sulpice, A.; Odier, P.; Núñez-Regueiro, M.

    2001-11-01

    The structural and superconducting properties of Hg0.75Re0.25Ba2-xSrxCa2Cu3O8+? (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) grown by sol-gel and sealed quartz tube synthesis were investigated through XRD, EDX, and micro-Raman analysis. They show that the efficiency of c-axis reduction caused by the Sr substitution depends on the environment in the (Hg,M)-O layer. The rhenium doping produces a more rigid block that limits the Sr substitution in the Ba site more than other reported doping cations, such as lead. Superconducting properties measurements show that the irreversibility line (IL) values decrease with increasing Sr substitution. Moreover, the IL line measurements also show that the vortex lines have a 3D behavior for all the samples with n values in the range 2.1-1.9. Finally, resistivity measurements under high pressure indicate an overdoped regime for these samples.

  10. 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

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

    NASA Technical Reports Server (NTRS)

    Duncan, R. C., Jr.

    1972-01-01

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

  12. 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.

  13. 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 ?mol 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.

  14. Dielectric and Nonohmic Properties of CaCu3Ti4O12/SrTiO3 Ceramics

    NASA Astrophysics Data System (ADS)

    Xue, Renzhong; Liu, Dewei; Chen, Zhenping; Dai, Haiyang; Chen, Jing; Zhao, Gaoyang

    2015-04-01

    In this work, (1 - x)CaCu3Ti4O12- xSrTiO3 [(1 - x)CCTO/ xST, x = 0% to 2%] ceramic samples were prepared by the solid-state reaction method. The dielectric and electrical properties of CaCu3Ti4O12 (CCTO) and CaCu3Ti4O12/SrTiO3 (CCTO/ST) ceramics were investigated. The results show that a small amount of Sr2+ can enter the lattice of CCTO. The mean grain size of the ceramic samples increased greatly for x = 0.5% and then decreased for x = 0.75% to 2%. ST addition and Sr2+ preferential occupancy in CCTO grains should be responsible for the change of the microstructure. Interestingly, the dielectric constant ( ?) of the 0.5% ST-added sample increased significantly while the dielectric loss (tan ?) remained low. With further increase of the ST content, the ? and tan ? values of the CCTO ceramics decreased monotonically while the nonlinear current-voltage properties were significantly enhanced. The change in the potential barrier height is thought to be the main cause for the opposite behaviors in the dielectric properties and nonohmic characteristics.

  15. Effect of Nd Substitution on PrOs4Sb12 Investigated by ?SR Experiments

    NASA Astrophysics Data System (ADS)

    Ho, P.-C.; Somsanuk, B.; Maclaughlin, D.; Maple, M.; Shu, L.; Bernal, O.; Yanagisawa, T.

    2013-03-01

    The pseudo ternary system Pr1-xNdxOs4Sb12 has been used as a model system to investigate the effect of ferromagnetism (FM) on the unconventional superconductivity (SC) and quantum critical behavior of PrOs4Sb12. SC in this system disappears near a critical concentration xcr , 1 ~ 0 . 58 and FM appears above xcr , 2 ~ 0 . 33. The new ?SR measurements have been performed on samples with x = 0.25, 0.75, and 1. For x = 1 and 0.75, the estimated frozen moments agree with the Nd3+ CEF ground state moment. For x = 0 . 25 , neither time reversal symmetry breaking nor evidence of freezing of Nd3+ spins was observed in zero-field ?SR measurements, the behavior of which is very different than what is observed for x = 0 . 45 - 0 . 55. In the SC state, an unexpected linear T dependence of the Gaussian relaxation rate was also found in the transverse field ?SR data for x = 0 . 25 , which is different than the plateau in PrOs4Sb12 below 1.3K. Research at CSUF is supported by NSF DMR-1104544; at UCSD by NSF DMR-0802478 and US DOE DE-FG02-04ER46105; at UCR by NSF DMR-0801407; at CSULA by NSF DMR-1105380; at Hokkaido U by MEXT, Jpn.

  16. 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).

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

    DOEpatents

    Marshall, Christopher D. (Livermore, CA); Payne, Stephen A. (Castro Valley, CA); Krupke, William F. (Pleasanton, CA)

    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.

  18. 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.

  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 (?) 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 ? at RT is perhaps due to the effect of Jahn-Teller active Mn3+ ions, around which dynamical local lattice distortion may occur.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  1. 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

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

    PubMed Central

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

    2015-01-01

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

  3. 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.

  4. Patterning of Bi 2Sr 2CaCu 2O 8+ x and SrTiO 3 films using lift-off technique combined with MOD

    NASA Astrophysics Data System (ADS)

    Kawata, T.; Iwasaki, H.; Yufune, S.; Ishibashi, T.; Sato, K.

    2006-10-01

    Micrometer size patterns of Bi2Sr2CaCu2O8+x (BSCCO) and SrTiO3 (STO) films were successfully prepared on STO substrates using lift-off technique combined with metal-organic decomposition (MOD) method without any vacuum processes. The minimum size of the pattern obtained was 3 ?m for BSCCO and 5 ?m for STO. The BSCCO film after patterning showed an X-ray diffraction with a c-axis orientation just like the film without patterning. On the other hand, the patterned STO showed an epitaxial relationship with the STO substrate. The BSCCO film with an anti-dot pattern of 3 ?m and 20 ?m in width showed Tc of 50 K and 83 K, respectively.

  5. Crystal structure and resistivity of substituted LaSrYCu{sub 2}O{sub 6}

    SciTech Connect

    Takano, Yoshihiko; Noro, Sumiko; Yamadaya, Tokio; Isobe, Masaaki; Ami, Takaaki; Suzuki, Masayuki; Tanaka, Masahiro

    1995-02-01

    A series of Y-based 2126 compounds, La{sub 1{minus}x}Sr{sub 1+x}YCu{sub 2}O{sub 6} (x = 0 to 0.5), has been prepared. Crystal structure and cation distribution are determined by Rietveld analysis of X-ray powder diffraction data. Small Y ions occupy (2a) site preferentially. All the studied samples including HIP treated ones are semiconducting and no superconducting transition is observed down to 20K. VRH model is applicable as a transport mechanism at low temperatures.

  6. 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.

  7. 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.

  8. 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

  9. Collisional broadening of Mg, Sr, Ca and Na resonance lines by atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Kerkeni, B.; Barklem, P. S.; Spielfiedel, A.; Feautrier, N.

    2004-02-01

    This paper compares different approaches used in the calculation of the broadening of spectral lines by H-atom collisions. Firstly, the validity of the semi-classical approach for the collision versus the quantum one is discussed. It is shown that, at the temperatures typical of stellar atmospheres (from 3000 to 10 000 K), a classical approach (with the advantage of reduced computation times) is sufficient. The dependence of the broadening constants on interatomic potentials is also studied. Two different approaches were used to derive these potentials: in the first approach, the interaction energy is determined by the usual methods of quantum chemistry. The second approach, developed by Anstee, Barklem and O'Mara (ABO potentials), is based on second-order perturbation theory. In the case of Mg H, a hybrid potential obtained from ab initio values for the short distances and from the perturbation method in the asymptotic region was also tested. The results for the Na resonance line show that even significant differences in the potentials lead to relatively small changes in the calculated widths. From the comparison of the results for the Mg, Sr and Ca resonance lines, it appears that ABO potentials give results of the order of 8 20% smaller than results from ab initio and hybrid potentials. This difference is attributed to the presence of an avoided ionic crossing in the upper singlet Sgr states that coincides roughly with the Weisskopf radius.

  10. 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.

  11. 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 ?m 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 ?m-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.

  12. Growth and characterization of (Tl,Pb)(Sr,Ba) 2Ca 2Cu 3O y single crystals

    NASA Astrophysics Data System (ADS)

    Wang, X. L.; Yang, X. M.; Weber, H. W.; Abraham, R.; Lebbou, K.; Cohen-Adad, M. Th.; Halwax, E.; Wiede, P.

    1996-09-01

    (Tl,Pb)(Sr,Ba) 2Ca 2Cu 3O y single crystals were grown by a self flux method. We find that the crystal growth strictly depends on the starting composition, on optimizing the melting temperature by suitable additives and on the choice of the cooling rate. The crystals were characterized by X-ray diffraction, EDX, SEM and SQUID magnetometry. The supercon-ducting transition temperatures and the best transition widths obtained for as-grown crystals are 105.0-111.2 K and 3-6 K, respectively. Layer by layer growth patterns, but no spiral growth, were observed by SEM. Annealing effects were studied in O 2 or Ar atmosphere and led to improvements of Tc and the transition width only following annealing in Ar. Annealing at temperatures above 600°C results in a decomposition of the crystals into the insulating oxides Tl 2O and (Sr,Ba)?Ca?Cu.

  13. Magnetic behavior of nano-crystalline ruthenium perovskites, CaRuO3 and SrRuO3

    NASA Astrophysics Data System (ADS)

    Iyer, K. K.; Mohapatra, Niharika; Sampathkumaran, E. V.

    2012-06-01

    We have investigated the magnetic behavior of the nan-ocrystalline form of the well known ruthenium perovskites, CaRuO3 (paramagnetic, non-Fermi liquid system) and SrRuO3 (ferromagnetic below 160 K), synthesized by high energy ball milling. It is found that the effective moment as well as the magnetization value at high fields (in the magnetically state) decreased for a reduction in particle size for both the compounds. The nano-crystalline form of SrRuO3 appears to be magnetically harder as compared to the bulk material, whereas CaRuO3 remains paramagnetic even in the nano-crystalline form. Otherwise, there is no other qualitative change in the magnetic behavior of both the compounds for the reduced particle-sizes, thereby indicating that the magnetic correlation lengths are small for these compounds.

  14. 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.

  15. Magnetic flux oscillations in partially irradiated Bi2Sr2CaCu2O8+? crystals

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  16. New honeycomb iridium(v) oxides: NaIrO3 and Sr3CaIr2O9.

    PubMed

    Wallace, David C; McQueen, Tyrel M

    2015-12-21

    We report the structures and physical properties of two new iridates, NaIrO3 and Sr3CaIr2O9, both of which contain continuous two-dimensional honeycomb connectivity. NaIrO3 is produced by room temperature oxidative deintercalation of sodium from Na2IrO3, and contains edge-sharing IrO6 octahedra that form a planar honeycomb lattice. Sr3CaIr2O9, produced via conventional solid-state synthesis, hosts a buckled honeycomb lattice with novel corner-sharing connectivity between IrO6 octahedra. Both of these new compounds are comprised of Ir(5+) (5d(4)) and exhibit negligible magnetic susceptibility. They are thus platforms to investigate the origin of the nonmagnetic behavior exhibited by Ir(5+) oxides, and provide the first examples of a J = 0 state on a honeycomb lattice. PMID:26505461

  17. Molecular beam epitaxial growth of high-T{sub c} Bi-Sr-Ca-Cu-O films

    SciTech Connect

    Ray, S.K.; Mishra, S.K.; Sarkar, A.

    1995-06-01

    Molecular beam epitaxy (MBE) has been used to grow high-temperature superconducting Bi-Sr-Ca-Cu-O films with adequate control over growth of number of unit layers. Oxide sources of Sr and Ca used for electron beam evaporation have been found to be useful for epitaxial growth of films. Deposited films show superconducting properties comparable to films deposited by using pure metals with a complicated in situ oxidation technique. Optimum deposition and annealing conditions have been obtained to grow c-axis-oriented 2212 phase BSCCO film. In situ reflection high-energy electron diffraction (RHEED) study of the films has revealed the growth of expitaxial films with atomically smooth surfaces.

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

    E-print Network

    Tomza, Micha?

    2015-01-01

    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. \\textit{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, RCCSD(T), and the multireference configuration interaction method restricted to single and double excitations, MRCISD, are employed. The scalar relativistic effects are included within the small-core energy-consistent pseudopotentials. The leading long-range induction and dispersion interaction co...

  19. Effects of conductor anisotropy on the design of Bi-Sr-Ca-Cu-O sections of 25 T solenoids

    NASA Astrophysics Data System (ADS)

    Weijers, H. W.; Schwartz, J.; ten Haken, B.; Dhallé, M.; ten Kate, H. H. J.

    2003-06-01

    The development of a 25 T superconducting magnet is usually envisioned with the use of an innermost coil wound with high-temperature superconductor (HTS) material. At present, Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox (BSCCO) conductors are the only candidate conductors available with sufficient length and current carrying capability. Unlike NbTi and Nb3Sn conductors, the BSCCO crystal structure and thus properties are strongly anisotropic. In conductor form, various degrees of anisotropy occur. It is often assumed that this anisotropy simply implies that radial field components must be minimized. We show that this assumption can be misleading. Using the average grain colony misalignment angle to parameterize the anisotropy, three regimes are distinguished in the relationship between average grain colony misalignment and critical current limiting field components. The implications of these separate regimes on the design process for 25 T superconducting magnet design are discussed.

  20. 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., TNF? 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 TNF? and IL-13, the transient increase in [Ca2+]mito is blunted despite enhanced [Ca2+]cyt responses. We also found that TNF? 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 TNF? 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

  1. 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 ?l/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 ? 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.

  2. Phase alignment in Ag-clad Bi-Sr-Ca-Cu-O (2:2:1:2) wires

    NASA Astrophysics Data System (ADS)

    Ray, R. D., II; Hellstrom, E. E.

    1990-12-01

    Powder-in-tube wires that contained Bi, Sr, Ca, and Cu in a 2:2:1:2 mole ratio were drawn then rolled flat before processing. The superconducting phase was aligned with its c axis perpendicular to the wide plane of the wire by sintering the wires just below the melting point and by melt processing. Melt processing with slow cooling of the melt yielded the most alignment. Gravity did not influence alignment during melt processing.

  3. 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.

  4. 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.

  5. 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.

  6. Raman microscopy examination of phase evolution in Bi(Pb){endash}Sr{endash}Ca{endash}Cu{endash}O superconducting ceramics

    SciTech Connect

    Wu, K.T.; Fischer, A.K.; Maroni, V.A.; Rupich, M.W.

    1997-05-01

    Raman microspectroscopy (RMS) and imaging Raman microscopy (IRM) were used to probe the composition and spatial distribution of chemical phases in Bi(Pb){endash}Sr{endash}Ca{endash}Cu{endash}O (BSCCO) ceramic superconductor powders and silver-BSCCO composites. The Raman techniques were used to identify various phases, including alkaline earth cuprates, CuO, Bi-2212, Bi-2223, and Pb-containing phases. Changes in the Ca/Sr ratios in (Ca,Sr){sub 2}CuO{sub 3} phases were distinguished by differences in orientation with respect to polarization of the exciting radiation. Variations were observed in the content and distribution of lead in various phases formed during intermediate stages of the thermal processing of composite conductors. The spatial distribution of the various phases detected in powder and composite conductors was established to a resolution of a few microns by collecting images of the Raman scattering at wavelengths corresponding to the signature peaks of the observed phases. Reference Raman spectra of the major phases observed in the BSCCO system are also reported. The Raman techniques, when combined with complimentary techniques, such as x-ray diffraction and electron microscopy, can provide valuable information about the reaction paths and mechanisms of the high temperature BSCCO superconducting ceramics. {copyright} {ital 1997 Materials Research Society.}

  7. 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.

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

    USGS Publications Warehouse

    Takesue, R.K.; VanGeen, A.

    2004-01-01

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

  9. Effect of Eu–Ni substitution on electrical and dielectric properties of Co–Sr–Y-type hexagonal ferrite

    SciTech Connect

    Ali, Irshad; Islam, M.U.; Ashiq, Muhammad Naeem; Khan, Hasan M.; Iqbal, M. Asif; Najam-Ul-Haq, Muhammad

    2014-01-01

    Graphical abstract: - Highlights: • Single phase nanostructured Sr{sub 2}Co{sub 2?x}Ni{sub x} Eu{sub y}Fe{sub 12?y}O{sub 22} were synthesized by the microemulsion method. • The materials show semiconducting behavior. • The high resistivity makes these materials useful for high frequency applications. • The Curie temperature decreases with the substituents. - Abstract: Single phase nanostructured Eu–Ni substituted Y-type hexaferrites with nominal composition Sr{sub 2}Co{sub 2?x}Ni{sub x} Eu{sub y}Fe{sub 12?y}O{sub 22} (x = 0.0–1, y = 0.0–0.1) were synthesized by the normal microemulsion method. X-ray diffraction (XRD) technique was employed for phase analysis and indexing of each pattern corroborates that well defined Y-type crystalline phase is formed. It is observed that DC resistivity enhanced which is accredited to room temperature resistivity differences of dopant and host ions. The hopping of electrons and jumping of holes are responsible for conduction below Curie temperature (T{sub C}), whereas above Curie temperature is due to polaron hopping. The decrease in T{sub C} may be due to the fact that Eu–Fe interactions on the B sites are weaker than Fe–Fe interaction. The dispersion in the dielectric constant ??(f) favor the occurrence of peaks in the tan ?(f). The extraordinary values of resistivity and small dielectric loss make these materials pre-eminent contestant for high frequency applications.

  10. Texture improvements in the high-temperature superconducting Bi?Sr?Ca?Cu?Ox̳/Ag system via surface energy driven grain alignment

    E-print Network

    Vodhanel, Mark E

    2005-01-01

    The relation between processing, microstructure, and material property was investigated in the high-temperature superconducting Bi?Sr?Ca?Cu?Ox̳/Ag system. Experiments were based on a theoretical surface energy model ...

  11. Crystal structure and dielectric properties of complex perovskite (Sr, Ba, Ca)(Ni0.5W0.5)O3

    E-print Network

    Messing, Gary L.

    Crystal structure and dielectric properties of complex perovskite (Sr, Ba, Ca)(Ni0.5W0.5)O3 Takashi + was made for the complex perovskite Sr(Ni0.5W0.5)O3 to correlate with the structure evolution temperatures were studied using high temperature X-ray powder diffractometry. A single phase of the perovskite

  12. Microstructure and magnetic properties of electrospun one-dimensional Al{sup 3+}-substituted SrFe{sub 12}O{sub 19} nanofibers

    SciTech Connect

    Liu, Mingquan; Shen, Xiangqian; Song, Fuzhan; Xiang, Jun; Meng, Xianfeng

    2011-04-15

    SrAl{sub x}Fe{sub 12-x}O{sub 19} (x=0-3.0) nanofibers with diameters about 100 nm have been prepared by electrospinning and subsequent heat treatment. With Al{sup 3+} ion content ranging from 0 to 3.0, the lattice parameters decrease due to Fe{sup 3+} ions substituted by smaller Al{sup 3+} ions and the average grain size calculated by the Scherrer's equation reduces from 65 to 37 nm. The magnetization shows a continuous reduction with the Al content and its value measured at 77 K is higher than at room temperature, which can be explained by Bloch's law. For the coercivity, its value initially increases, reaching a maximum value of 617 (298 K) and 547 kA m{sup -1} (77 K) at x=2.0, and then reduces with the Al content further increase largely arising from the substituted Al{sup 3+} ion arrangement in different interstitial sites of the strontium ferrite unit cell. -- Graphical abstract: Al{sup 3+} ions substituted strontium ferrite nanofibers have been prepared by the electrospinning with a diameter of about 100 nm and the Al{sup 3+} ion substitution has a great effect on the microstructure and magnetic property of SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers. Display Omitted Research highlights: {yields} SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers have been fabricated by the electrospinning. {yields} There is a relation between the Al{sup 3+} ions substitution and microstructure. {yields} The magnetic property can be tuned effectively by Al{sup 3+} ion substitution. {yields} The magnetic property is influenced by measurement temperature.

  13. Single crystal growth and structural characterization of four complex uranium oxides: CaUO4, ?-Ca3UO6, K4CaU3O12, and K4SrU3O12

    NASA Astrophysics Data System (ADS)

    Read, Cory M.; Bugaris, Daniel E.; zur Loye, Hans-Conrad

    2013-03-01

    Single crystals of complex uranium oxides, CaUO4, ?-Ca3UO6, K4CaU3O12 and K4SrU3O12 were grown from carbonate melts. The crystal structures of the four uranates were determined by single crystal X-ray diffraction. CaUO4 crystallizes in the hexagonal space group R-3m, with lattice parameters a = 6.2570(7) Å and ? = 36.04(2)°. The U6+ atom in CaUO4 is 8-coordinate and exhibits hexagonal bipyramidal geometry with six long and two short U-O bonds, typical of a uranyl species. ?-Ca3UO6 forms in the monoclinic space group P21/n, with lattice parameters a = 5.728(1) Å, b = 5.956(1) Å, c = 8.298(2) Å, and ? = 90.55(3)°, and adopts a distorted double perovskite structure. K4CaU3O12 and K4SrU3O12 crystallize in the cubic space group Im-3m with lattice parameters a = 8.483(1) Å and a = 8.582(1) Å, respectively. In all three perovskite-type oxides, the U(VI) cation is located in an octahedral coordination environment and exhibits typical uranyl geometry with four long and two short U-O bonds.

  14. Anisotropic properties of a single superconducting CaCuO2/SrTiO3 interface

    NASA Astrophysics Data System (ADS)

    Salvato, M.; Tieri, G.; Balestrino, G.; Di Castro, D.

    2015-09-01

    The transport properties of CaCuO2/SrTiO3 single interfaces are studied by resistance versus temperature measurements in external magnetic fields. The superconducting anisotropy ? ={? }a-b/{? }c, where {? }a-b and {? }c are the superconducting coherence lengths parallel and perpendicular to the interface, respectively, shows values higher than that previously obtained for CaCuO2/SrTiO3 superlattices deposited in the same conditions. The larger anisotropy, observed for the single interfaces, indicates that the charge carriers are confined inside a thin superconducting layer next to the interface rather than spread throughout the whole CaCuO2 block. The activation energy and the irreversibility line confirm this hypothesis, suggesting that quasi two-dimensional transport is dominant in this system. The interpretation of the experimental data in the framework of the Berezinskii-Kosterlitz-Thouless theory confirms that the thickness of the superconducting sheet layer is about 1 nm, corresponding roughly to two CaCuO2 unit cells.

  15. Voltage clamp methods for the study of membrane currents and SR Ca2+ release in adult skeletal muscle fibres

    PubMed Central

    Hernández-Ochoa, Erick O.; Schneider, Martin F.

    2012-01-01

    Skeletal muscle excitation-contraction (E-C)1 coupling is a process composed of multiple sequential stages, by which an action potential triggers sarcoplasmic reticulum (SR)2 Ca2+ release and subsequent contractile activation. The various steps in the E-C coupling process in skeletal muscle can be studied using different techniques. The simultaneous recordings of sarcolemmal electrical signals and the accompanying elevation in myoplasmic Ca2+, due to depolarization-initiated SR Ca2+ release in skeletal muscle fibres, have been useful to obtain a better understanding of muscle function. In studying the origin and mechanism of voltage dependency of E-C coupling a variety of different techniques have been used to control the voltage in adult skeletal fibres. Pioneering work in muscles isolated from amphibians or crustaceans used microelectrodes or ‘high resistance gap’ techniques to manipulate the voltage in the muscle fibres. The development of the patch clamp technique and its variant, the whole-cell clamp configuration that facilitates the manipulation of the intracellular environment, allowed the use of the voltage clamp techniques in different cell types, including skeletal muscle fibres. The aim of this article is to present an historical perspective of the voltage clamp methods used to study skeletal muscle E-C coupling as well as to describe the current status of using the whole-cell patch clamp technique in studies in which the electrical and Ca2+ signalling properties of mouse skeletal muscle membranes are being investigated. PMID:22306655

  16. 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 ?C/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.

  17. Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy2Ti2O7.

    PubMed

    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 [Formula: see text], dc magnetic susceptibility [Formula: see text], isothermal magnetization M(H) and heat capacity [Formula: see text] measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a spin-glass type freezing behavior near 16 K. Our frequency dependent [Formula: see text] data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly influenced by Ca substitution. The effect of partial nonmagnetic Ca(2+)?substitution for magnetic Dy(3+) is similar to the previous study on nonmagnetic isovalent Y(3+) 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% Ca(2+) substitution for Dy(3+) ions. PMID:26443921

  18. 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 {?\\text{ac}}(T) , dc magnetic susceptibility ? (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 {?\\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.

  19. 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.

  20. Manganite based hetero-junction structure of La0.7Sr(0.7-x)CaxMnO3 and CaMnO(3-?) for cross-point arrays.

    PubMed

    Lee, Hong-Sub; Park, Hyung-Ho

    2015-07-10

    Resistive random access memory and the corresponding cross-point array (CPA) structure have received a great deal of attention for high-density next generation non-volatile memory. However, the cross-talk issue of CPA structure by sneak current should be overcome to realize the highest density integration. To accomplish this, the sneak current can be minimized by high, nonlinear characteristic behaviors of resistive switching (RS). Therefore this study fabricated pnp bipolar hetero-junction structure using the perovskite manganite family, such as La0.7Sr(0.3-x)CaxMnO3 (LSCMO) and CaMnO(3-?) (CMO), to obtain nonlinear RS behavior. The pnp structure not only shows nonlinear characteristics, but also a tunable characteristic with Ca substitution. PMID:26086277

  1. 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

  2. High-Tc Superconductivity at the Interface between the CaCuO2 and SrTiO3 Insulating Oxides

    NASA Astrophysics Data System (ADS)

    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 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 the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 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 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.

  3. Oxygen partial pressure dependence of magnetic, optical and magneto-optical properties of epitaxial cobalt-substituted SrTiO? films.

    PubMed

    Onba?l?, Mehmet C; Goto, Taichi; Tang, Astera; Pan, Annia; Battal, Enes; Okyay, Ali K; Dionne, Gerald F; Ross, C A

    2015-05-18

    Cobalt-substituted SrTiO3 films (SrTi0.70Co0.30O(3-?)) were grown on SrTiO3 substrates using pulsed laser deposition under oxygen pressures ranging from 1 ?Torr to 20 mTorr. The effect of oxygen pressure on structural, magnetic, optical, and magneto-optical properties of the films was investigated. The film grown at 3 ?Torr has the highest Faraday rotation (FR) and magnetic saturation moment (M(s)). Increasing oxygen pressure during growth reduced M(s), FR and optical absorption in the near-infrared. This trend is attributed to decreasing Co2+ ion concentration and oxygen vacancy concentration with higher oxygen partial pressure during growth. PMID:26074589

  4. Magnetic and conductive dead layer at the La0.67Ca0.33MnO3-SrTiO3:Nb interface

    NASA Astrophysics Data System (ADS)

    Liang, S.; Sun, J. R.; Wang, J.; Shen, B. G.

    2009-11-01

    Interfacial properties of the La0.67Ca0.33MnO3 films grown on SrTiO3 and SrTiO3:Nb, respectively, have been experimentally studied. An interface layer, ˜13 or ˜4.4 nm for the films on SrTiO3 or SrTiO3:Nb, with degenerated magnetic/conductive properties is found in the film. The most remarkable result is the significantly different layer width on different substrates. The built-in electric field yielded by charge exchange may be responsible for the layer shrinkage in La0.67Ca0.33MnO3/SrTiO3:Nb. A depression of this layer by magnetic field is also observed and ascribed to field-induced enhancement of the double exchange between Mn ions.

  5. Characterization of hot isostatically pressed Bi-Sr-Ca-Cu-O as a function of consolidation variables

    SciTech Connect

    Goretta, K.C.; Miller, D.J.; Poeppel, R.B. ); Nash, A.S. )

    1991-11-01

    Fully dense, bulk Bi{sub 2}Sr{sub 1.7}CaCu{sub 2}O{sub x} (2212) superconductor pellets were made by hot isostatic pressing in an inert atmosphere. Electron microscopy revealed that rotation and bending of the platelike 2212 grains were responsible for much of the densification. Under processing conditions of 825{degrees}C and 105 MPa, dense pellets were obtained in 15 min. Many dislocations, planar faults, and, perhaps, intergrowths of the Bi{sub 2}Sr{sub 2}CuO{sub x} phase were produced during pressing. The dislocations were largely present in subgrain boundaries when the pressing times were increased to 45--120 min.

  6. 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 (?M) 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.

  7. Crystallography, chemistry and structural disorder in the new high-Tc Bi-Ca-Sr-Cu-O superconductor

    NASA Technical Reports Server (NTRS)

    Veblen, D. R.; Heaney, P. J.; Angel, R. J.; Finger, L. W.; Hazen, R. M.

    1988-01-01

    Diffraction experiments are reported which indicate that the new Bi-Ca-Sr-Cu-O layer-structure superconductor possesses a primitive orthorhombic unit cell with probable space group Pnnn. The material exhibits severe structural disorder which is primarily related to stacking within the layers. The apparent orthorhombic structure is an average resulting from orthorhombic material mixed with monoclinic domains in two twinned orientations. Two distinct types of structural disorder that are common in materials synthesized to date are also described. This disorder complicates the crystallographic analysis and suggests that X-ray and neutron diffraction methods may yield only an average structure.

  8. 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.

  9. Quasiparticles in the superconducting state of Bi(2)Sr(2)CaCu(2)O(8+delta)

    PubMed

    Kaminski; Mesot; Fretwell; Campuzano; Norman; Randeria; Ding; Sato; Takahashi; Mochiku; Kadowaki; Hoechst

    2000-02-21

    Recent improvements in momentum resolution lead to qualitatively new angle-resolved photoemission spectroscopy results on the spectra of Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) along the (pi,pi) direction, where there is a node in the superconducting gap. We now see the intrinsic line shape, which indicates the presence of true quasiparticles at all Fermi momenta in the superconducting state, and lack thereof in the normal state. The region of momentum space probed here is relevant for charge transport, motivating a comparison of our results to conductivity measurements by infrared reflectivity. PMID:11017626

  10. The GW electronic structure of cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Syrotyuk, Stepan V.; Shved, Vira M.

    2015-09-01

    The electronic energy band spectra of cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba) have been evaluated within the projector augmented waves (PAW) approach by means of the ABINIT code. The Kohn-Sham single-particle states have been found in the LDA framework. Our parameters of the electron energy bands obtained in the LDA are in good agreement with the published results of other authors. The calculated GW band gaps and dielectric constants are well compared with the available experimental data. The quasiparticle energies and density of states of electrons as well as the dielectric constants were obtained in the approximation GW for the first time.

  11. Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La,Sr)MnO3.

    PubMed

    Tsekouras, George; Boudoire, Florent; Pal, Banabir; Vondrá?ek, Martin; Prince, Kevin C; Sarma, D D; Braun, Artur

    2015-09-21

    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. PMID:26395726

  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; Vondrá?ek, 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. Mechanical relaxation in thermoelectric oxide Ca{sub 3?x}Sr{sub x}Co{sub 4}O{sub 9+?} (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+?} 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+?} 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+?} 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+?} (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+?}. 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+?}. ? 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.

  14. Substitution of H- for O- and H- emissions of 12CaO•7Al2O3

    NASA Astrophysics Data System (ADS)

    Huang, F.; Li, J.; Xian, H.; Tu, J.; Sun, J. Q.; Yu, S. Q.; Li, Q. X.; Torimoto, Y.; Sadakata, M.

    2005-03-01

    By using an anion-exchanging method, about 90% of the O- anions in the C12A7-O - microporous crystal ([Ca24Al28O64]4+•4O-) have been substituted primarily by the H- anions, leading to the successful formation of a new H- emission material, C12A7-H -([Ca24Al28O64]4+•4H-). A sustainable and stable emission of H-, in a current density of ?A /cm2 level, has been obtained by supplying H2 and electrons on the backside of the C12A7-H - sample. The emission features of C12A7-H -, including temperature and field effects, have been investigated. It is expected that the present material could be practically used as an H- anion generator.

  15. Influence of the network modifier on the characteristics of MSnO3 (M=Sr and Ca) thin films synthesized by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Alves, M. C. F.; Marinho, R. M. M.; Casali, G. P.; Siu-Li, M.; Députier, S.; Guilloux-Viry, M.; Souza, A. G.; Longo, E.; Weber, I. T.; Santos, I. M. G.; Bouquet, V.

    2013-03-01

    CaSnO3 and SrSnO3 alkaline earth stannate thin films were prepared by chemical solution deposition using the polymeric precursor method on various single crystal substrates (R- and C-sapphire and 100-SrTiO3) at different temperatures. The films were characterized by X-ray diffraction (?-2?, ?- and ?-scans), field emission scanning electron microscopy, atomic force microscopy, micro-Raman spectroscopy and photoluminescence. Epitaxial SrSnO3 and CaSnO3 thin films were obtained on SrTiO3 with a high crystalline quality. The long-range symmetry promoted a short-range disorder which led to photoluminescence in the epitaxial films. In contrast, the films deposited on sapphire exhibited a random polycrystalline growth with no meaningful emission regardless of the substrate orientation. The network modifier (Ca or Sr) and the substrate (sapphire or SrTiO3) influenced the crystallization process and/or the microstructure. Higher is the tilts of the SnO6 octahedra, as in CaSnO3, higher is the crystallization temperature, which changed also the nucleation/grain growth process.

  16. The effect of light on intrashell trace metal variability (Mg/Ca and Sr/Ca) in the planktic foraminifer Orbulina universa

    NASA Astrophysics Data System (ADS)

    Fehrenbacher, J. S.; Spero, H. J.; Russell, A. D.; Gagnon, A. C.; Vetter, L.; Snyder, J.; Naumann, E.; Grimm, B. L.; Holland, K.

    2012-12-01

    The shell walls of many planktic foraminifers contain alternating bands of high and low Mg/Ca calcite. These bands have been attributed to chamber formation, light-modulated (circadian-like) biological effects, and light (e.g. pH change in the calcifying environment driven by the photosynthesis/respiration of photosynthetic symbionts). Previous experiments on the living planktic foraminifer Orbulina universa confirm a diurnal nature in the banding of O. universa: a wide band of low-Mg calcite forms during the day (12-hour light) and a narrower band of high Mg calcite forms at night (12-hour dark) (Spero et al., in prep). During the summer of 2011, we explored the response of Mg banding to light by culturing foraminifera at constant temperature, salinity, and ambient seawater pH, but with different light schedules: reverse light cycles (day/night cycle shifted by 12 hours), constant (24-hour) light, and constant (24-hour) dark conditions. We used an artificial Ba spike to mark 12-hour intervals of growth, regardless of the imposed light regime. In specimens grown with a reversed day/night light/dark cycle, we observe an immediate shift in the timing of Mg/Ca banding. The timing of high and low Mg/Ca bands in these specimens is indistinguishable from specimens grown under a normal day/night light/dark cycle. Mg/Ca bands are present in some of the specimens cultured in constant light and in all specimens grown in constant dark conditions. Banding in the constant light and constant dark specimens is not paced by a diurnal cycle. The amplitude of the banding in these specimens is diminished and the average Mg/Ca ratios are 30% lower in comparison to those kept on a 12-hour light/dark cycle. Additionally, we find the Sr/Ca ratios are similar in both the constant light and reverse light/dark specimens, but are statistically significantly lower in the constant dark specimens (8% lower, p-value << 0.05). These results indicate that changes in microenvironment pH due to symbiont photosynthesis are not pacing Mg/Ca banding in Orbulina universa, although photosymbiont/pH activity could modify Mg/Ca band amplitude. The presence of Mg/Ca banding in some specimens of both the constant light and constant dark experiments are consistent with a light-modulated biological mechanism that is disrupted by the absence of a day/night cycle and is no longer paced by a 24-hour cycle.

  17. Physical and chemical effects of silver additions to Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 and (Bi,Pb) sub 2 Sr sub 2 Ca sub 2 Cu sub 3 O sub 10

    SciTech Connect

    Jones, T.E.; Schindler, J.W.; Boss, R.D.; Thibado, P.M.; McGinnis, W.C. )

    1990-04-01

    Silver in the form of silver peroxide has been added prior to the sintering step in the preparation of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}. X-ray-diffraction analysis and microscopic examination show no evidence for chemical reaction between the silver and the ceramic superconductors. However, the presence of the silver can affect the phase purity of the final product---the amount of the three-layered high-{ital T}{sub {ital c}} (110-K) phase can either be increased or decreased depending on the sintering conditions and the starting composition. No evidence can be seen in the x-ray spectra to indicate that the silver is going into either phase. The only effect of the silver is on the thermodynamics and kinetics of the sintering process.

  18. 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.

  19. High-pressure modifications of CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2}: Implications for Laves phase structural trends

    SciTech Connect

    Kal, Subhadeep; Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L.; Norrestam, Rolf; Haeussermann, Ulrich

    2008-11-15

    High-pressure forms of intermetallic compounds with the composition CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}, and BaAl{sub 2} were synthesized from CeCu{sub 2}-type precursors (CaZn{sub 2}, SrZn{sub 2}, SrAl{sub 2}) and Ba{sub 21}Al{sub 40} by multi-anvil techniques and investigated by X-ray powder diffraction (SrAl{sub 2} and BaAl{sub 2}), X-ray single-crystal diffraction (CaZn{sub 2}), and electron microscopy (SrZn{sub 2}). Their structures correspond to that of Laves phases. Whereas the dialuminides crystallize in the cubic MgCu{sub 2} (C15) structure, the dizincides adopt the hexagonal MgZn{sub 2} (C14) structure. This trend is in agreement with the structural relationship displayed by sp bonded Laves phase systems at ambient conditions. - Graphical abstract: CeCu{sub 2}-type polar intermetallics can be transformed to Laves phases upon simultaneous application of pressure and temperature. The observed structures are controlled by the valence electron concentration.

  20. 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. Elastic Anomalies Accompanying Phase Transitions in (CaSr)TiO3 Perovskite III: Experimental Investigation of Polycrystalline Samples

    SciTech Connect

    Carpenter,M.; Li, B.; Liebermann, R.

    2007-01-01

    Bulk and shear moduli of polycrystalline samples of perovskites with different compositions across the CaTiO3-SrTiO3 solid solution have been measured at ambient conditions and in-situ at high pressures by pulse-echo ultrasonic methods. The samples were prepared as dense pellets by hot pressing synthetic powders at {approx}7.5 GPa and {approx}1000 C. Any variations of bulk modulus due to phase transitions are small, but significant anomalies have been observed in the shear modulus at ambient conditions. These are associated with a sequence of symmetry changes PmFormulam -> I4/mcm -> Pbcm -> Pnma with increasing CaTiO3 content. Comparison with variations in elastic properties predicted using Landau theory suggests that a substantial part of the elastic softening observed in tetragonal samples could be due to anelastic contributions from transformation twin walls. This additional softening does not occur in orthorhombic samples, and the transition from tetragonal to orthorhombic symmetry results in a stiffening of the shear modulus. No overt evidence was found for a phase transition I4/mcm {leftrightarrow} Pnma at high pressures in Ca0.35Sr0.65TiO3 but small changes in the trends of both bulk and shear moduli in the range 2.5-3 GPa could be due either to a different transition or a change in compression mechanism. A PmFormulam {leftrightarrow} I4/mcm transition at {approx}2 GPa in Ca0.05Sr0.95TiO3 shows the same form of softening as observed for the transition as a function of composition. A simple model of twin wall contributions to the compliance of tetragonal samples failed to match the observed variations that, alternatively, seem to follow {Delta}G {proportional_to} q4 where {Delta}G is the change in shear modulus and q4 the driving order parameter for the PmFormulam {leftrightarrow} I4/mcm transition. Analogous elastic behavior is expected to occur in (Mg,Fe)SiO3 and CaSiO3 perovskites at high pressures and temperatures.

  2. 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

    2015-10-28

    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 Nd1-xCaxFeO3 (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

  3. Assessing the impact of diagenesis on ?11B, ?13C, ?18O, 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 ?11B of planktic foraminiferal calcite is a promising ocean pH-proxy but the effect of diagenesis is still poorly known. Here we present new ?11B, ?13C, ?18O, 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 ?18O and ?13C 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, ?11B values indicate no large differences between well-preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the ?11B 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 ?11B 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.

  4. Influence of tungsten substitution and oxygen deficiency on the thermoelectric properties of CaMnO{sub 3??}

    SciTech Connect

    Thiel, Philipp; Eilertsen, James; Populoh, Sascha Saucke, Gesine; Shkabko, Andrey; Sagarna, Leyre; Karvonen, Lassi; Döbeli, Max; Weidenkaff, Anke

    2013-12-28

    Polycrystalline tungsten-substituted CaMn{sub 1?x}W{sub x}O{sub 3??} (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.

  5. X-ray diffraction analysis of the modulated structure of Bi2Sr2CaFe2O y

    NASA Astrophysics Data System (ADS)

    Narymbetov, B. Zh.; Shekhtman, V. Sh.; Dubovitskii, A. V.; Sedykh, V.; Smirnova, I. S.

    1996-03-01

    The modulated structure of the Bi2Sr2CaFe2O y compound isomorphous with the Bi2Sr2CaCu2O y phase was refined by the method of the full profile analysis on the basis of the powder X-ray diffraction data. The analysis was carried out in the superspace group of N: Abmm: 1 11 using the parameters of the unit cell of the basic structure a = 5.466(3), b = 5.446(5) and c = 31.25(9) Å and the modulation vector q = 0.220(5) b* + c*. The model of excess oxygen interstitials into the BiO plane was used by applying a saw-tooth-type function of the form: U = 2 U 0 [( X 4 - X {4/0}/?)] [1]. The results point to a strong displacement of the atoms from their positions in the basic structure. An essential improvement of the R factors was obtained by taking into account the modulation waves of the higher harmonics.

  6. Persistent Photoconductivity in Y-doped Bi_2Sr_2CaCu_2O_8+x Thin Films

    NASA Astrophysics Data System (ADS)

    Prieto, P.; Lopera, W.; Girata, D.; Hoffmann, A.; Schuller, Ivan K.

    1998-03-01

    Persistent Photoconductivity (PPC) is characterized by a long term increase in the conductivity due to illumination, and has been observed in oxygen deficient YBa_2Cu_3O_7-x thin films(For a brief review see: A. Hoffmann, D. Reznik, and I.K. Schuller, Adv. Mater. 9), 271 (1997).. A possible mechanism for PPC in these materials is that the electron of a photogenerated electon-hole pair is trapped at an oxygen vacancy in the Cu-O chains. We measured PPC in epitaxial Y doped Bi_2Sr_2CaCu_2O_8-x thin films, prepared in situ by a high-pressure sputtering process. The relaxation of the photoinduced conductivity changes as a function of time have been analyzed using the Kohlrauch relation. The values of the relaxation times and the dispertion parameters have been obtained as a function of temperature. This observation of PPC in the Y-doped Bi_2Sr_2CaCu_8+x high-Tc compounds without Cu-O chains, together with recently measured PPC in Tl_2Ba_2CuO_6+x(A. Hoffmann, I.K. Schuller, Z.F. Ren, J.Y. Lao, and J.H. Wang, to be published in: Phys. Rev. B, 1 December 1997.) indicates that PPC might be a common phenomena in high-Tc materials.

  7. Nonlinear-optical susceptibility of hilgardite-like borates MBOX(M=Pb,Ca,Sr,Ba; X=Cl,Br)

    NASA Astrophysics Data System (ADS)

    Plachinda, Paul A.; Dolgikh, Valery A.; Stefanovich, Sergey Yu.; Berdonosov, Petr S.

    2005-10-01

    Usage of non-centrosymmetric boron oxide derivative crystals as nonlinear elements may be a key solution of pressing problem of obtaining powerful radiation at shorter wavelengths via frequency multiplication of solid state laser radiations. It is shown that Pb 2B 5O 9Br and some other members of hilgardite-like borohalogenides demonstrate in powder form, high non-linear optical activity in the SHG experiments. An attempt is made using the Philips-Van Vechten-Levine-Xue bond theory to calculate second-order nonlinear coefficients for isostructural to mineral hilhardite noncentrosymmetric crystals MBOX with M=Pb, Sr, Ba, Eu, Ca and X=Cl, Br. Theoretically obtained values of nonlinear optical coefficients d only partly correlate with the results of SHG measurements. In particular, the experiments distinctively show sharp increase of nonlinear activity along the series Ca < Sr < Ba < Pb and Cl < Br of metal boro-halogenides, while theoretical estimations give substantially more slack composition dependences. Analysis of contribution of different boron-oxygen bonds to optical nonlinearities of the compounds reveals important role of planar BO 3 triangles, though this factor is yet unable to explain enormously high SHG output from Pb 2B 5O 9Br.

  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. Structural evolution of (Ca 0.35Sr 0.65)TiO 3 perovskite at high pressures

    NASA Astrophysics Data System (ADS)

    Carpenter, Michael A.; Rios, Susana; Sondergeld, Peter; Crichton, Wilson; Bouvier, Pierre

    2007-01-01

    Lattice parameters of a synthetic powder sample of Ca 0.35Sr 0.65TiO 3 perovskite have been determined by the method of Le Bail refinement, using synchrotron X-ray diffraction patterns collected at pressures up to 15.5 GPa with a membrane-driven diamond anvil cell. At ambient conditions, diffraction data were consistent with the I4/ mcm structure reported previously in the literature for the same composition. Diffraction data collected at high pressures were consistent with tetragonal (or, at least, pseudo-tetragonal) lattice geometry, and no evidence was found for the development of any of the orthorhombic structures identified in other studies of (Ca, Sr)TiO 3 perovskites. Additional weak reflections, which could not be accounted for by the normal I4/ mcm perovskite structure, were detected in diffraction patterns collected at pressures of 0.9-2.5 GPa, and above ˜13.5 GPa, however. Small anomalies in the evolution of unit cell volume and tetragonal strain were observed near 3 GPa, coinciding approximately with breaks in slope with increasing pressure of bulk and shear moduli for a sample with the same composition which had previously been reported. The anomalies could be due either to new tetragonal?tetragonal/pseudo-tetragonal phase transitions or to subtle changes in compression mechanism of the tetragonal perovskite structure.

  10. New ordered perovskites containing bismuth (v) [BaLaMBiO{sub 6} (M = Mg, Ca, Sr)

    SciTech Connect

    Subramanian, M.A.

    1995-03-01

    New Bi (V) containing perovskites oxides of the type, BaLaMBiO{sub 6} (M = Mg, Ca, Sr) have been synthesized under high oxygen pressure conditions using the thermal decomposition of peroxides in a tetrahedral anvil apparatus. These compounds have been characterized by X-ray powder diffraction and iodometric titration. All the BaLaMBiO{sub 6} (M + Mg, Ca, Sr) compounds show 1:1 type ordering of cations at the octahedral sites of the perovskite structure. In the case of magnesium and calcium containing perovskites, comparison of the observed and the calculated X-ray powder diffraction intensities show that the A sites are occupied by barium and lanthanum in a disordered manner, and the octahedral sites are occupied by an ordered arrangement of bismuth and magnesium or bismuth and calcium. This is in contrast to the strontium containing phase, where the A sites are found to be occupied by barium and strontium in a disordered arrangement and the octahedral sites are occupied by lanthanum and bismuth. The oxygen content, hence the oxidation state of Bi, in the samples depends on the synthetic conditions employed. The electrical properties of the synthesized materials are discussed briefly.

  11. 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

  12. Calcilytic Ameliorates Abnormalities of Mutant Calcium-Sensing Receptor (CaSR) Knock-In Mice Mimicking Autosomal Dominant Hypocalcemia (ADH).

    PubMed

    Dong, Bingzi; Endo, Itsuro; Ohnishi, Yukiyo; Kondo, Takeshi; Hasegawa, Tomoka; Amizuka, Norio; Kiyonari, Hiroshi; Shioi, Go; Abe, Masahiro; Fukumoto, Seiji; Matsumoto, Toshio

    2015-11-01

    Activating mutations of calcium-sensing receptor (CaSR) cause autosomal dominant hypocalcemia (ADH). ADH patients develop hypocalcemia, hyperphosphatemia, and hypercalciuria, similar to the clinical features of hypoparathyroidism. The current treatment of ADH is similar to the other forms of hypoparathyroidism, using active vitamin D3 or parathyroid hormone (PTH). However, these treatments aggravate hypercalciuria and renal calcification. Thus, new therapeutic strategies for ADH are needed. Calcilytics are allosteric antagonists of CaSR, and may be effective for the treatment of ADH caused by activating mutations of CaSR. In order to examine the effect of calcilytic JTT-305/MK-5442 on CaSR harboring activating mutations in the extracellular and transmembrane domains in vitro, we first transfected a mutated CaSR gene into HEK cells. JTT-305/MK-5442 suppressed the hypersensitivity to extracellular Ca(2+) of HEK cells transfected with the CaSR gene with activating mutations in the extracellular and transmembrane domains. We then selected two activating mutations locating in the extracellular (C129S) and transmembrane (A843E) domains, and generated two strains of CaSR knock-in mice to build an ADH mouse model. Both mutant mice mimicked almost all the clinical features of human ADH. JTT-305/MK-5442 treatment in vivo increased urinary cAMP excretion, improved serum and urinary calcium and phosphate levels by stimulating endogenous PTH secretion, and prevented renal calcification. In contrast, PTH(1-34) treatment normalized serum calcium and phosphate but could not reduce hypercalciuria or renal calcification. CaSR knock-in mice exhibited low bone turnover due to the deficiency of PTH, and JTT-305/MK-5442 as well as PTH(1-34) increased bone turnover and bone mineral density (BMD) in these mice. These results demonstrate that calcilytics can reverse almost all the phenotypes of ADH including hypercalciuria and renal calcification, and suggest that calcilytics can become a novel therapeutic agent for ADH. © 2015 American Society for Bone and Mineral Research. PMID:25967373

  13. Ca, Sr, Mo and U isotopes evidence ocean acidification and deoxygenation during the Late Permian mass extinction

    NASA Astrophysics Data System (ADS)

    Silva-Tamayo, Juan Carlos; Payne, Jon; Wignall, Paul; Newton, Rob; Eisenhauer, Anton; Weyer, Stenfan; Neubert, Nadja; Lau, Kim; Maher, Kate; Paytan, Adina; Lehrmann, Dan; Altiner, Demir; Yu, Meiyi

    2014-05-01

    The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, ca. 252 Mya. Ocean acidification and global oceanic euxinia have each been proposed as causes of this biotic crisis, but the magnitude and timing of change in global ocean chemistry remains poorly constrained. Here we use multiple isotope systems - Ca, Sr, Mo and U - measured from well dated Upper Permian- Lower Triassic sedimentary sections to better constrain the magnitude and timing of change in ocean chemistry and the effects of ocean acidification and de-oxygenation through this interval. All the investigated carbonate successions (Turkey, Italy and China) exhibit decreasing ?44/40Ca 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 ?88/86Sr 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 ?44/40Ca and ?88/86Sr 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.

  14. 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.

  15. Fluorescence and phosphorescence properties of the low temperature forms of the MAl 2Si 2O 8:Eu 2+ ( M=Ca, Sr, Ba) compounds

    NASA Astrophysics Data System (ADS)

    Clabau, Frédéric; Garcia, Alain; Bonville, Pierre; Gonbeau, Danielle; Le Mercier, Thierry; Deniard, Philippe; Jobic, Stéphane

    2008-06-01

    The fluorescence and phosphorescence properties of Europium-doped MAl 2Si 2O 8 ( M=Ca, Sr, Ba) are reinvestigated and discussed on the basis of the propensity of an activator to agglomerate with an oxygen vacancy. Due to a stronger attraction of the anion vacancy towards Eu 2+ cations going from BaAl 2Si 2O 8 to SrAl 2Si 2O 8 and CaAl 2Si 2O 8 host lattices, the interpretation of the fluorescence spectra turns out to be less trivial in the Ca and Sr host lattices than in the Ba one and requests the account for Eu 2+ cations lying at alkaline-earth sites with or without vacancy in their neighborhood. Phosphorescence in these compounds is highlighted.

  16. 4f and 5d energy levels of the divalent and trivalent lanthanide ions in M{sub 2}Si{sub 5}N{sub 8} (M=Ca, Sr, Ba)

    SciTech Connect

    Kate, O.M. ten; Zhang, Z.; Dorenbos, P.; Hintzen, H.T.; Kolk, E. van der

    2013-01-15

    Optical data of Sm, Tb and Yb doped Ca{sub 2}Si{sub 5}N{sub 8} and Sr{sub 2}Si{sub 5}N{sub 8} phosphors that have been prepared by solid-state synthesis, are presented. Together with luminescence data from literature on Ce{sup 3+} and Eu{sup 2+} doping in the M{sub 2}Si{sub 5}N{sub 8} (M=Ca, Sr, Ba) hosts, energy level schemes were constructed showing the energy of the 4f and 5d levels of all divalent and trivalent lanthanide ions relative to the valence and conduction band. The schemes were of great help in interpreting the optical data of the lanthanide doped phosphors and allow commenting on the valence stability of the ions, as well as the stability against thermal quenching of the Eu{sup 2+}d-f emission. Tb{sup 3+} substitutes on both a high energy and a low energy site in Ca{sub 2}Si{sub 5}N{sub 8}, due to which excitation at 4.77 eV led to emission from both the {sup 5}D{sub 3} and {sup 5}D{sub 4} levels, while excitation at 4.34 eV gave rise to mainly {sup 5}D{sub 4} emission. Doping with Sm resulted in typical Sm{sup 3+}f-f line absorption, as well as an absorption band around 4.1 eV in Ca{sub 2}Si{sub 5}N{sub 8} and 3.6 eV in Sr{sub 2}Si{sub 5}N{sub 8} that could be identified as the Sm{sup 3+} charge transfer band. Yb on the other hand was incorporated in both the divalent and the trivalent state in Ca{sub 2}Si{sub 5}N{sub 8}. - Graphical abstract: Energy level schemes showing the 4f ground states of the trivalent ( Black-Down-Pointing-Small-Triangle ) and divalent ( Black-Up-Pointing-Small-Triangle ) lanthanide ions and lowest energy 5d states of the trivalent ({nabla}) and divalent ({Delta}) ions with respect to the valence and conduction bands of Ca{sub 2}Si{sub 5}N{sub 8} (left) and Sr{sub 2}Si{sub 5}N{sub 8} (right). Highlights: Black-Right-Pointing-Pointer Construction of energy level schemes of all lanthanides within the M{sub 2}Si{sub 5}N{sub 8} hosts. Black-Right-Pointing-Pointer Construction was done by analyzing existing as well as new spectroscopic data. Black-Right-Pointing-Pointer Tb{sup 3+}d-f emission from two different Ca sites in Ca{sub 2}Si{sub 5}N{sub 8} has been observed. Black-Right-Pointing-Pointer Observation of the Sm{sup 3+} charge transfer band in Ca{sub 2}Si{sub 5}N{sub 8} and Sr{sub 2}Si{sub 5}N{sub 8}. Black-Right-Pointing-Pointer Ytterbium has been found in the divalent and trivalent state in Ca{sub 2}Si{sub 5}N{sub 8}.

  17. Variations in the Sr/Ca, ?44Ca and ?18O 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.

  18. 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.

  19. Crystal structure and magnetic properties of Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Rangi, Manisha; Agarwal, Ashish; Sanghi, Sujata; Singh, Ripandeep; Meena, S. S.; Das, A.

    2014-08-01

    Bi0.8A0.2FeO3 (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 A2+ results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe4+ 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 Bi0.8Ba0.2FeO3 sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

  20. 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.

  1. High-T_{c} Superconductivity at the Interface between the CaCuO_{2} and SrTiO_{3} 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

  2. Thermoelectric properties and electronic structure of the Zintl phase Sr5In2Sb6 and the Ca5-xSrxIn2Sb6 solid solution

    NASA Astrophysics Data System (ADS)

    Zevalkink, Alex; Chenakian, Sevan; Aydemir, Umut; Ormeci, Alim; Pomrehn, Gregory; Bux, Sabah; Fleurial, Jean-Pierre; Snyder, G. Jeffrey

    2015-01-01

    The Zintl phase Sr5In2Sb6 is isostructural with Ca5In2Sb6—a promising thermoelectric material with a peak zT of 0.7 when the carrier concentration is optimized by doping. Density functional calculations for Sr5In2Sb6 reveal a decreased energy gap and decreased valence band effective mass relative to the Ca analog. Chemical bonding analysis using the electron localizability indicator was found to support the Zintl bonding scheme for this structure type. High temperature transport measurements of the complete Ca5-xSrxIn2Sb6 solid solution were used to investigate the influence of the cation site on the electronic and thermal properties of A5In2Sb6 compounds. Sr was shown to be fully miscible on the Ca site. The higher density of the Sr analog leads to a slight reduction in lattice thermal conductivity relative to Ca5In2Sb6, and, as expected, the solid solution samples have significantly reduced lattice thermal conductivities relative to the end member compounds.

  3. Superconductivity in epitaxial Bi sub 2 Sr sub 2 CuO sub 6 /Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8 superlattices: The superconducting behavior of ultrathin cuprate slabs

    SciTech Connect

    Bozovic, I.; Eckstein, J.N.; Klausmeier-Brown, M.E.; Virshup, G. )

    1992-02-01

    Utilizing atomic layer-by-layer molecular beam epitaxy (ALL-MBE), the authors have synthesized a series of high-quality superlattices in which ultrathin slabs (one-half unit cell thick) of the high-{Tc} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} alternate with up to five such layers of the low-{Tc} Bi{sub 2}Sr{sub 2}Cu{sub 1}O{sub 6}phase. In all these superlattices they found {Tc} to be essentially equal to that of the high-{Tc} Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} phase itself, which indicates that this cuprate is a 2D superconductor insofar as the interslab coupling plays at best a secondary role. Furthermore, it is demonstrated that {Tc} need not be reduced at heterostructure interfaces.

  4. Magnetic hysteresis and relaxation in Ag-sheathed TlBaCaCuO (1223) and Bi(Pb)SrCaCuO (2223) superconducting tapes

    SciTech Connect

    Kung, P.J.; Maley, M.P.; Coulter, J.Y.; Willis, J.O.; Peterson, D.E.; McHenry, M.E.; Wahlbeck, P.G.

    1992-05-01

    Magnetic hysteresis (7--75 K in magnetic fields up to 5 T) and relaxation characteristics (5--50 K in magnetic fields up to 2 T) have been measured with the field perpendicular to the surface of Ag-sheathed TlBaCaCuO (1223 phase) and Bi(Pb)SrCaCuO (2223 phase) superconducting tapes. A study of the difference in the magnetic hysteresis between precursor powders and as-processed tapes was also carried out. The relaxation data were curve-fit using a rate equation for thermally activated flux motion, U{sub eff}/[kG(T)] = {minus}T[ln(dM/dt) {minus} ln (H{omega}{sub o} a/2{pi}d)] with the temperature dependence of U{sub eff} scaled by the functional form G(T) = 1 {minus} (T/Tx){sup 2}. By comparing the results obtained from magnetic characterization with those from transport current measurement, these observations suggest that (1) Tl-1223 tapes have a weaker field dependence for J{sub c} at T > 35 K than Bi-2223 tapes due to the special crystal structure of the 1223 phase, and (2) weak links limit the transport critical current densities in Tl-1223 tapes to 10{sup 3} A/cm{sup 2} at 5 T and 35 K, for instance.

  5. Magnetic hysteresis and relaxation in Ag-sheathed TlBaCaCuO (1223) and Bi(Pb)SrCaCuO (2223) superconducting tapes

    SciTech Connect

    Kung, P.J.; Maley, M.P.; Coulter, J.Y.; Willis, J.O.; Peterson, D.E. ); McHenry, M.E. . Dept. of Metallurgical Engineering and Materials Science); Wahlbeck, P.G. . Dept. of Chemistry)

    1992-01-01

    Magnetic hysteresis (7--75 K in magnetic fields up to 5 T) and relaxation characteristics (5--50 K in magnetic fields up to 2 T) have been measured with the field perpendicular to the surface of Ag-sheathed TlBaCaCuO (1223 phase) and Bi(Pb)SrCaCuO (2223 phase) superconducting tapes. A study of the difference in the magnetic hysteresis between precursor powders and as-processed tapes was also carried out. The relaxation data were curve-fit using a rate equation for thermally activated flux motion, U{sub eff}/(kG(T)) = {minus}T(ln(dM/dt) {minus} ln (H{omega}{sub o} a/2{pi}d)) with the temperature dependence of U{sub eff} scaled by the functional form G(T) = 1 {minus} (T/Tx){sup 2}. By comparing the results obtained from magnetic characterization with those from transport current measurement, these observations suggest that (1) Tl-1223 tapes have a weaker field dependence for J{sub c} at T > 35 K than Bi-2223 tapes due to the special crystal structure of the 1223 phase, and (2) weak links limit the transport critical current densities in Tl-1223 tapes to 10{sup 3} A/cm{sup 2} at 5 T and 35 K, for instance.

  6. 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.

  7. 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 ?mol L-1, which was about 130 times higher than that of the site furthest upstream (site 1, 0.35 ?mol 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 ?mol 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.

  8. Gap-Inhomogeneity-Induced Electronic States in Superconducting Bi2Sr2CaCu2O8+delta

    SciTech Connect

    Fang, A.C.

    2010-02-25

    In this Letter, we analyze, using scanning tunneling spectroscopy, the density of electronic states in nearly optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} in zero magnetic field. Focusing on the superconducting gap, we find patches of what appear to be two different phases in a background of some average gap, one with a relatively small gap and sharp large coherence peaks and one characterized by a large gap with broad weak coherence peaks. We compare these spectra with calculations of the local density of states for a simple phenomenological model in which a 2{zeta}{sub 0} x 2{zeta}{sub 0} patch with an enhanced or suppressed d-wave gap amplitude is embedded in a region with a uniform average d-wave gap.

  9. Reinforced fluropolymer nanocomposites with high-temperature superconducting Bi2Sr2CaCu2Oy

    NASA Astrophysics Data System (ADS)

    Jayasree, T. K.

    2014-10-01

    Bismuth Strontium Calcium Copper Oxide (Bi2Sr2CaCu2Oy)/Polyvinylidene fluoride (PVDF) nanocomposite was prepared and their thermal properties were analyzed. The composite consists of the polyvinylidene fluoride (PVDF) as an insulating polymer matrix, and homogenously distributed Bismuth strontium calcium copperoxide (2212) nanoparticles. SEM data shows flaky grains of the superconductor coated and linked by polymer. Differential scanning calorimetry (DSC) results indicated that the melting point was not affected significantly by the addition of BSCCO. However, the addition of superconducting ceramic resulted in an extra melting peak at a lower temperature (145°C). Thermogravimetric analysis of the samples shows that the onset decomposition temperature of the PVDF matrix was decreased by the addition of SC filler.

  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. Theory of Bi2Sr2CaCu2O8+? cross-whisker Josephson junctions

    NASA Astrophysics Data System (ADS)

    Klemm, Richard A.

    2003-05-01

    Takano et al. [Phys. Rev. B 65, 140513 (2002); J. Low Temp. Phys. 131, 533 (2003)] made Josephson junctions from single crystal whiskers of Bi2Sr2CaCu2O8+? crossed an angle ?0 about the c axis. From the mesa structures that formed at the cross-whisker interface, they inferred a critical current density Jc(?0). As with the single crystal results of Li et al. [Phys. Rev. Lett. 83, 4160 (1999)], we show that the whisker data are unlikely to result from a predominantly d-wave order parameter. However, unlike the single crystals, these results, if correct, require the whisker c-axis transport to be coherent.

  12. Theory of Bi_2Sr_2CaCu_2O_8+x Cross-Whisker Josephson Junctions

    NASA Astrophysics Data System (ADS)

    Klemm, Richard

    2003-03-01

    Takano et al. [Phys. Rev. B 65, 140513 (2002) and unpublished] made c-axis Josephson junctions from crossed single crystal whiskers of Bi_2Sr_2CaCu_2O_8+x. >From the mesa structures that formed at the the cross-whisker interface, they measured the critical current density J_c(?_0) as a function of the cross angle ?_0. Like the single crystal results of Li et al. [Phys. Rev. Lett. 83, 4160 (1999)], the whisker results are shown to rule out most d-wave order parameter forms, and are consistent with a pure s-wave order parameter. However, unlike the single crystals, the whisker results, if correct, require the c-axis transport to be coherent.

  13. Microfilamentary Bi sub 2 Sr sub 2 Ca sub 1 Cu sub 2 O sub 8 fibers

    SciTech Connect

    Miller, T.A.; Sanders, S.C.; Finnemore, D.K. Iowa State Univ. of Science and Technology, Ames, IA . Dept. of Physics); LeBeau, S.E.; Righi, J. . Research Center)

    1990-01-01

    Techniques have been developed for the fabrication of superconducting microfilaments of Bi{sub 2}Sr{sub 2}Ca{sub 1}CU{sub 2}O{sub 8} as part of a larger project to produce microfilamentary composites. The process is based on a gas jet fiberization of a viscous liquid melt to form long slender amorphous fibers. A subsequent anneal then converts the fibers to the superconducting crystalline phase. Fiber diameters range from 1 to 6{mu}m and length to diameter ratios range between 10{sup 3}and 10{sup 4} so the dimensions are favorable for composite formation. The details of grain growth are reviewed with special emphasis on the role of the filament diameter on the morphology of the grain growth. 4 refs., 7 figs.

  14. 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.

  15. Reconstructed Fermi Surface of Underdoped Bi2Sr2CaCu2O8 Cuprate Superconductors

    SciTech Connect

    H Yang; J Rameau; Z Pan; G Gu; P Johnson; H Claus; D Hinks; T Kidd

    2011-12-31

    The Fermi surface topologies of underdoped samples of the high-T{sub c} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} have been measured with angle resolved photoemission. By examining thermally excited states above the Fermi level, we show that the observed Fermi surfaces in the pseudogap phase are actually components of fully enclosed hole pockets. The spectral weight of these pockets is vanishingly small at the magnetic zone boundary, creating the illusion of Fermi 'arcs.' The area of the pockets as measured in this study is consistent with the doping level, and hence carrier density, of the samples measured. Furthermore, the shape and area of the pockets is well reproduced by phenomenological models of the pseudogap phase as a spin liquid.

  16. Towards a high thermoelectric performance in rare-earth substituted SrTiO3: effects provided by strongly-reducing sintering conditions.

    PubMed

    Kovalevsky, A V; Yaremchenko, A A; Populoh, S; Thiel, P; Fagg, D P; Weidenkaff, A; Frade, J R

    2014-12-28

    Donor-substituted strontium titanate ceramics demonstrate one of the most promising performances among n-type oxide thermoelectrics. Here we report a marked improvement of the thermoelectric properties in rare-earth substituted titanates Sr0.9R0.1TiO3±? (R = La, Ce, Pr, Nd, Sm, Gd, Dy, Y) to achieve maximal ZT values of as high as 0.42 at 1190 K < T < 1225 K, prepared via a conventional solid state route followed by sintering under strongly reducing conditions (10%H2-90%N2, 1773 K). As a result of complex defect chemistry, both electrical and thermal properties were found to be dependent on the nature of the rare-earth cation and exhibit an apparent correlation with the unit cell size. High power factors of 1350-1550 ?W m(-1) K(-2) at 400-550 K were observed for R = Nd, Sm, Pr and Y, being among the largest reported so far for n-type conducting bulk-ceramic SrTiO3-based materials. Attractive ZT values at high temperatures arise primarily from low thermal conductivity, which, in turn, stem from effective phonon scattering in oxygen-deficient perovskite layers formed upon reduction. The results suggest that highly-reducing conditions are essential and should be employed, whenever possible, in other related micro/nanostructural engineering approaches to suppress the thermal conductivity in target titanate-based ceramics. PMID:25377924

  17. Preparation of BiSrCaCuO Multilayers by Use of Slower Q-switched 266 nm YAG Laser

    NASA Astrophysics Data System (ADS)

    Kaneko, Satoru; Shimizu, Yoshitada; Ohya, Seishiro

    2001-08-01

    Multilayers of Bi2Sr2Ca1Cu2Ox{\\slash}Bi2Sr2Cu1Ox were prepared by pulsed laser deposition (PLD) using the fourth harmonic 266 nm YAG. Compared to an excimer laser, YAG PLD required the higher oxygen atmosphere. The higher oxygen pressure together with the lower energy generated by YAG laser collapsed the region of plume emission. In order to produce the same energy density as an excimer, only Q-switch was modulated by 2 Hz while the flash lamp kept the original repetition rate of 10 Hz. With the rate of 2 Hz, we obtained the higher energy density per pulse, and more stable laser output of the fourth harmonics, 266 nm. To characterize the multilayers, reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) were employed, and indicative of epitaxial layers with limited in-plane order. The resistivities of multilayers were measured by the Van der Pauw method, and showed the temperatures of superconducting transition, Tc0 (R=0), around 65 K on the multilayers.

  18. 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 (?) 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 ?mol m-2 min-1 at r = 0.0315 to a maximum rate of 74.5 ± 4.8 ?mol m-2 min-1 at r = 0.306 followed by a decrease to 46.3 ± 9.6 ?mol 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 (? = 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

  19. 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.

  20. 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.

  1. Structural, electronic and magnetic properties of the series of double perovskites (Ca,Sr){sub 2?x}La{sub x}FeIrO{sub 6}

    SciTech Connect

    Bufaiçal, L.; Adriano, C.; Lora-Serrano, R.; Duque, J.G.S.; Mendonça-Ferreira, L.; Rojas-Ayala, C.; Baggio-Saitovitch, E.; Bittar, E.M.; Pagliuso, P.G.

    2014-04-01

    Polycrystalline samples of the series of double perovskites Sr{sub 2?x}La{sub x}FeIrO{sub 6} were synthesized. Their structural, electronic and magnetic properties were investigated by X-ray powder diffraction, Mössbauer spectroscopy, magnetic susceptibility, heat capacity and electrical resistivity experiments. The compounds crystallize in a monoclinic structure and were fitted in space group P2{sub 1}/n, with a significant degree of Fe/Ir cationic disorder. As in Ca{sub 2?x}La{sub x}FeIrO{sub 6} the Sr-based system seems to evolve from an antiferromagnetic ground state for the end members (x=0.0 and x=2.0) to a ferrimagnetic order in the intermediate regions (x?1). Since Mössbauer spectra indicate that Fe valence remains 3+ with doping, this tendency of change in the nature of the microscopic interaction could be attributed to Ir valence changes, induced by La{sup 3+} electrical doping. Upon comparing both Ca and Sr series, Sr{sub 2?x}La{sub x}FeIrO{sub 6} is more structurally homogenous and presents higher magnetization and transition temperatures. Magnetic susceptibility measurements at high temperatures on Sr{sub 1.2}La{sub 0.8}FeIrO{sub 6} indicate a very high ferrimagnetic Curie temperature T{sub C}?700K. For the Sr{sub 2}FeIrO{sub 6} compound, electrical resistivity experiments under applied pressure suggest that this material might be a Mott insulator. - Graphical abstract: The Weiss constant as a function of La doping for the (Ca,Sr){sub 2?x}La{sub x}FeIrO{sub 6} series, indicating changes in Fe–Ir magnetic coupling on both families. - Highlights: • The double perovskite series (Ca,Sr){sub 2?x}La{sub x}FeIrO{sub 6} were synthesized. • Changes in the Fe-Ir magnetic coupling due to La doping on both series. • Evidence of high T{sub C} on Sr{sub 1.2}La{sub 0.8}FeIrO{sub 6}. • Indication of Mott insulator behavior on Sr{sub 2}FeIrO{sub 6}.

  2. PII S0016-7037(01)00836-5 Climate proxies from Sr/Ca of coccolith calcite: Calibrations from continuous culture of

    E-print Network

    Falkowski, Paul G.

    PII S0016-7037(01)00836-5 Climate proxies from Sr/Ca of coccolith calcite: Calibrations from.5 divisions per day and calcification rate increased from 1.5 to 50 pg calcite per cell per day. When foraminifera and abiogenic calcites, suggesting that it is controlled by thermodynamic processes. However

  3. Heating-compensated constant-temperature tunneling measurements on stacks of Bi2Sr2CaCu2O8+x intrinsic junctions

    E-print Network

    Lee, Hu-Jong

    of Science and Technology, Pohang 790-784, Republic of Korea Received 10 January 2005; accepted 22 April 2005; published online 1 June 2005 In highly anisotropic layered cuprates such as Bi2Sr2CaCu2O8+x tunneling of interest "sample stack" SmS including self-heating, which was then compensated using the proportional

  4. Dielectric properties of layered perovskite Sr1xAxBi2Nb2O9 ferroelectrics ,,ALa,Ca and x0,0.1...

    E-print Network

    Cao, Guozhong

    Dielectric properties of layered perovskite Sr1ÀxAxBi2Nb2O9 ferroelectrics ,,AÄLa,Ca and xÄ0 in air. X-ray diffraction analysis indicated that single-phase layered perovskite ferroelectrics were of full polarization switching.3 Bismuth layered perovskite materi- als have high fatigue resistance

  5. 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.

  6. Photoluminescence Properties of Red-Emitting Ca3Sr3-x(PO4)4:xEu3+ Phosphors for White Light-Emitting Diodes.

    PubMed

    Hakeem, D A; Park, K

    2015-07-01

    The photoluminescent properties of the Eu(3+)-activated Ca3Sr3(PO4)4 phosphors prepared by a solution combustion method were investigated. The excitation spectra of Ca3Sr3-x(PO4)4:xEu3+ (0.05 ? x ? 0.6) phosphors under 614 nm wavelength showed a broad band centered at 266 nm along with other peaks at 320, 362, 381, 394, 414, 464, and 534 nm. The emission spectra observed in the range of 450 to 750 nm under excitation at 394 nm were ascribed to the 5D0-7F1-4 transitions of Eu3+ ions. The Ca3Sr3-x(PO4)4:xEu3+ phosphors showed the strongest red emission at 614 nm due to the electric dipole 5DO -->7F2 transition of Eu3+. The strongest emission intensity was obtained for the Eu3+ ions of x = 0.5. The prepared Ca3Sr3-x(PO4)4:xEu3+ can be used as an efficient red phosphor for UV-based white LEDs. PMID:26373096

  7. 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.

  8. Methods for estimating a critical value for determining the freshwater/estuarine habitat residence of American eels from otolith Sr:Ca data

    NASA Astrophysics Data System (ADS)

    Jessop, B. M.; Shiao, J. C.; Iizuka, Y.

    2013-11-01

    Linear discriminant analysis (LDA) and habitat discrimination critical value (HDCV) methods are alternatives for evaluating the migratory history, such as the proportion of residence in freshwater (%fwr) and estuarine/marine habitats, of individual American eels (Anguilla rostrata) via the analysis of otolith Sr:Ca data. The LDA process requires Sr:Ca data from both freshwater and estuarine/marine groups while the mean + cSD method requires only a freshwater standard. For the two group (freshwater, estuarine/marine), single predictor variable (Sr:Ca) case, the LDA process defaults to Fisher's linear discriminant where the HDCV equals the average of the group mean Sr:Ca values. The difference between freshwater and estuarine resident eel mean otolith Sr:Ca values, based on 13 published studies and the current study (n = 14), decreased with increasing freshwater group otolith mean (r = 0.80, p < 0.001), reflecting a relatively constant estuarine group mean (r = 0.38, p = 0.17). A process is proposed for estimating a HDCV from freshwater group otolith Sr:Ca mean and SD values based on empirical linear relations between the LDA, HDCV and freshwater mean (n = 14, r = 0.90, p < 0.0001) and c and SD (n = 14, r = -0.89, p < 0.0001) from the equation HDCV = mean + cSD. Variation in the sample sizes of otolith Sr:Ca values used in the discriminant process of estimating a HDCV, while statistically significant, had trivial effect sizes that were likely of little biological consequence. However, larger sample sizes are preferred over smaller sample sizes. Estimates of %fwr increased with increases in the HDCV. Differences in %fwr estimates over a range of HDCVs were highly statistically significant and effect sizes increased with increased HDCV difference. As HDCV levels increased, growth rate estimates increased for a given %fwr value. A HDCV difference of ?0.5 × 10-3 produced a small effect size. Accurate estimation of a HDCV is fundamental to the assessment of the habitat residence and inter-habitat movement of American eels and perhaps of other diadromous fishes and helps minimize bias in dependent estimates of other useful statistics such as the percentage of freshwater residence (%fwr) and growth rate.

  9. Coccolith Sr/Ca as a new indicator of coccolithophorid calcification and growth rate

    E-print Network

    Schrag, Daniel

    . Stoll Department of Geology, Universidad de Oviedo, Oviedo, Asturias 33005, Spain (heather.stoll/Ca of coccolith sediments are similar to variations in primary productivity and alkenone; Revised February 21, 2000; Accepted March 10, 2000; Published May 30, 2000. Stoll, H. M., and D. P. Schrag

  10. Effect of La{sup 3+} substitution with Gd{sup 3+} on the resistive switching properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films

    SciTech Connect

    Lee, Hong-Sub; Park, Chang-Sun; Park, Hyung-Ho

    2014-05-12

    This study demonstrated that the resistive switching voltage of perovskite manganite material could be controlled by A-site cation substitution in “A” MnO{sub 3} perovskite manganite structure. A partial substitution of La{sup 3+} in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} with smaller cation Gd{sup 3+} induced A-site vacancy of the largest Sr{sup 2+} cation with surface segregation of SrO{sub y} due to ionic size mismatch, and the induced vacancies reduced migration energy barrier. The operating voltage decreased from 3.5?V to 2.5?V due to a favorable condition for electrochemical migration and redox of oxygen ions. Moreover, surface-segregated SrO{sub y} was enhanced with Gd-substitution and the SrO{sub y} reduced Schottky-like barrier height and resistive switching ratio from the potential drop and screening effect. The relationship between A-site vacancy generation resulting in surface segregation of SrO{sub y} and resistive switching behavior was also investigated by energy resolved x-ray photoelectron spectroscopy, O 1s near edge x-ray absorption spectroscopy, and current voltage measurement.

  11. 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.

  12. A kinetic mechanism for formation of aligned (Bi, Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} in a powder-in-tube processed tape

    SciTech Connect

    Wang, Y.L.; Bian, W.; Zhu, Y.

    1995-12-31

    A kinetic mechanism for formation of the c-axis aligned (Bi, Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} platelets from a powder mixture of (Bi, Pb){sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and CaCu{sub 2}O{sub 3} + CuO in a silver sheath is proposed.

  13. Suppression of structural phase transition by Sr substitution in the improper ferroelectric BaAl2O4

    NASA Astrophysics Data System (ADS)

    Mori, Shigeo; Ishii, Yui; Tanaka, Eri; Tsukasaki, Hirofumi; Kawaguchi, Shogo

    2015-10-01

    To clarify lattice fluctuations and precursor phenomena accompanied by structural phase transition in stuffed tridymite compounds, changes in diffuse scattering as a function of temperature in Ba0.6Sr0.4Al2O4 have been carefully investigated by powder X-ray diffraction using synchrotron radiation, electron diffraction and transmission electron microscopy (TEM) experiments. In situ electron diffraction experiments revealed that Ba0.6Sr0.4Al2O4 exhibits lattice fluctuation manifested as a unique honeycomb-shaped diffuse scattering in the wide temperature range between 298 and 100 K. Unlike in the case of BaAl2O4, Ba0.6Sr0.4Al2O4 shows no structural phase transition to the ferroelectric structure with the hexagonal P63 space group in the temperature range. In contrast, it is revealed that the electron beam irradiation to the Ba0.6Sr0.4Al2O4 sample inside the transmission electron microscope induced structural change from the hexagonal P6322 structure to the modulated structure with double periodicity in the three equivalent <110> directions in the low-temperature region. This implies that the total energy difference between these two structures is small. The hexagonal P6322 structure transforms into the modulated one with short correlation length owing to some small external perturbations.

  14. 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.

  15. 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.

  16. 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.

  17. 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

  18. An anion substitution route to low loss colossal dielectric CaCu{sub 3}Ti{sub 4}O{sub 12}

    SciTech Connect

    Smith, Andrew E.; Calvarese, T.G.; Sleight, A.W.; Subramanian, M.A.

    2009-02-15

    An anion substitution route was utilized for lowering the dielectric loss in CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) by partial replacement of oxygen by fluorine. This substitution reduced the dielectric loss, and retained a high dielectric constant that was essentially temperature independent from 25 to 200 deg. C. In particular, CaCu{sub 3}Ti{sub 4}O{sub 11.7}F{sub 0.3} exhibited a giant dielectric constant over 6000 and low dielectric loss below 0.075 at 100 kHz within a temperature range of 25-200 deg. C. Fluorine analysis confirmed the presence of fluorine in all samples measured. - Grapical Abstract: An anion substitution route was utilized for lowering the dielectric loss in CaCu{sub 3}Ti{sub 4}O{sub 12} (CCTO) by partial replacement of oxygen by fluorine. This substitution, confirmed by fluorine analysis, reduced tan {delta}, and retained a high dielectric constant that was essentially temperature independent from 25 to 200 deg. C at 100 kHz.

  19. 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.

  20. 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}.

  1. 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].

  2. Effect of electron correlation in Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3}: Density functional calculation

    SciTech Connect

    Hadipour, H.; Akhavan, M.

    2010-07-15

    We have investigated the electronic structure of Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3} using the full potential linearized augmented plane wave method by different approximation such as LSDA and LSDA+U. The LSDA calculation suggest that Cr{sup 4+}-Ru{sup 4+} hybridization is responsible for the high Curie temperature T{sub C} in SrRu{sub 1-x}Cr{sub x}O{sub 3}, but it cannot completely describe its physical behavior. Our LSDA+U DOS results for SrRu{sub 1-x}Cr{sub x}O{sub 3} clearly establishes renormalization of the intra-atomic exchange strength at the Ru sites, arising from the Cr-Ru hybridization. The antiferromagnetic coupling of Cr{sup 3+} with Ru{sup 4+,5+} lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The more distorted Ca-based compounds as compared to the Sr-based systems shows that the hybridization mechanism is not relevant for these compounds. The bigger exchange splitting of Ru 4d and Cr 3d at the Fermi level with Ru{sup 4+,5+} and Cr{sup 3+,4+} orbital occupancies of CaRu{sub 0.75}Cr{sub 0.25}O{sub 3} in the LSDA+U calculation, compared with that of the LSDA calculation, shows that repulsion between electrons tend to keep the localized spins from overlapping. The low screening of the Ru t{sub 2g} electrons increases T{sub C} in the Ca-based systems, which is consistent with the both high Ru exchange splitting and magnetic moment. The insulating behavior of the high Cr-doped systems can be explained by considering the Ru{sup 4+}+Cr{sup 4+{yields}}Ru{sup 5+}+Cr{sup 3+} charge transfer. - Graphical Abstract: We have investigated the electronic structure of Sr(Ca)Ru{sub 1-x}Cr{sub x}O{sub 3} using different ab-initio calculation such as LSDA and LSDA+U approximation. The antiferromagnetic hybridization of Cr{sup 3+} with Ru{sup 4+,5+} lattice increases the screening, which is consistent with the low magnetic moment of the Ru ions. The LSDA+U calculation for the more distorted Cr impurity doped Ca-based ruthenate compounds as compared to the Sr-based systems shows repulsion between electrons, which tends to keep the localized spins from overlapping.

  3. Sr/Ca sensitivity to aragonite saturation state in cultured subsamples from a single colony of coral: Mechanism of biomineralization during ocean acidification

    NASA Astrophysics Data System (ADS)

    Gagnon, Alexander C.; Adkins, Jess F.; Erez, Jonathan; Eiler, John M.; Guan, Yunbin

    2013-03-01

    Using a new and rapid NanoSIMS-based method, we quantified the sensitivity of skeletal Sr/Ca in coral to the aragonite saturation state of seawater (?SW). Skeletal Sr/Ca is a common proxy for temperature while ?SW is a parameter that varied in the past ocean and is predicted to change with continued ocean acidification. Five adult branches of the surface coral Stylophora pistillata were grown at different ?SW from 2.7 to 4.9 (pH of 7.9-8.5) but at a constant temperature of 25 °C. Despite a large range of growth parameters and a twofold range in calcification rates, the average skeletal Sr/Ca of coral exposed to each condition are within 1.2% of each other (2? std. dev. of the 5 means). Furthermore, the average skeletal Sr/Ca measured in this study agrees with the results of two previous coral culture experiments conducted at the same temperature but where ?SW was not controlled. These results suggest that aragonite saturation has little or no influence on Sr/Ca paleothermometry over the range of ?SW investigated. Combined with existing data for low ?SW conditions, our results were used to elucidate the mechanisms controlling calcifying fluid acid-base chemistry during coral biomineralization. Assuming that coral drive precipitation through alkalinity pumping, our data suggest that this pumping occurs until the calcifying fluid reaches a target pH. Below a threshold ?SW bounded by 1 < ?SW < 2.4, however, coral do not pump enough alkalinity to reach the target pH and instead pump a maximal but finite amount of alkalinity. In this low ?SW regime, calcifying fluid pH is expected to decrease with ?SW. The interplay between these two alkalinity pumping regimes and external seawater composition explain the full range of observed Sr/Ca sensitivity to ?SW and suggest that surface coral may become increasingly sensitive to ocean acidification below a threshold ?SW bounded by 1 < ?SW < 2.4.

  4. Effect of La-Co substitution on the crystal structure and magnetic properties of hot press sintered Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites for use in LTCC technology

    NASA Astrophysics Data System (ADS)

    Peng, Long; Li, Lezhong; Wang, Rui; Hu, Yun; Tu, Xiaoqiang

    2015-10-01

    The La3+ and Co2+ substituted Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites with Bi2O3 additive were prepared by hot press sintering method at a low sintering temperature of 870 °C compatible with LTCC (low temperature co-fired ceramics) systems, and their crystal structure and magnetic properties were mainly investigated. The results show that the pure M-type crystal phase is successfully obtained for the ferrites with La-Co substitution amount x not higher than 0.3. When the substitution amount further increases to 0.4 and 0.5, the ?-Fe2O3 phase and La2O3 phase are found to coexist with the M-type phase, thus the multiphase structure is formed. Besides, the saturation magnetization Ms, intrinsic coercivity Hci, and Curie temperature TC of the ferrites are strongly correlated with the La-Co substitution amount. Enhanced Ms and Hci are obtained when the substitution amount varies from 0.2 to 0.4, which can exceed 3600 Gs and 4000 Oe, respectively. However, the TC decreases rapidly when the substitution amount exceeds 0.3, and a value under 410 °C is observed. It is suggested that the La3+-Co2+ ions can partially substitute the Sr2+-Fe3+ ions for the hot press sintered ferrites at low sintering temperatures, leading to improved Ms and Hci for use in microwave LTCC ferrite devices.

  5. Transformation of AeIn4 Indides (Ae = Ba, Sr) into an AeAu2In2 Structure Type Through Gold Substitution

    SciTech Connect

    Dai, Jing-Cao; Corbett, John D.

    2007-04-17

    The title compounds were prepared from the elements by high-temperature solid-state synthesis techniques. X-ray structural analyses shows that BaAu{sub 2}In{sub 2} (1) and SrAu{sub 2}In{sub 2} (2) crystallize in a new orthorhombic structure, Pnma, Z = 4 (a = 8.755(2), 8.530(2) {angstrom}; b = 4.712(1), 4.598(1) {angstrom}; c = 12.368(3), 12.283(4) {angstrom}, respectively). Gold substitutes for 50% of the indium atoms in the tetragonal BaIn{sub 4} and monoclinic SrIn{sub 4} parents to give this new and more flexible orthorhombic structure. The Ae atoms in this structure are contained within chains of hexagonal prisms built of alternating In and Au that have additional augmenting atoms around their waists from further condensation of parallel displaced chains. The driving forces for these structural changes are in part the shorter Au-In distances (2.72 and 2.69 {angstrom}) relative to d(In-In) in the parents, presumably because of relativistic contractions with Au. Generalities about such centered prismatic building blocks and their condensation modes in these and related phases are described. Band structure calculations (EHTB) demonstrate that the two compounds are metallic, which is confirmed by measurements of the resistivity of 1 and the magnetic susceptibilities of both.

  6. Enhancing photoluminescence performance of SrSi2O2N2:Eu(2+) phosphors by Re (Re = La, Gd, Y, Dy, Lu, Sc) substitution and its thermal quenching behavior investigation.

    PubMed

    Lü, Wei; Jiao, Mengmeng; Shao, Baiqi; Zhao, Lingfei; You, Hongpeng

    2015-09-21

    Eu(2+)-doped SrSi2O2N2 has recently been identified as a viable green phosphor that in conjunction with a blue-emitting diode can be used in solid-state white-lighting sources. In this study, we attempt to improve the photoluminescence and thermal quenching behavior by codoping Re(3+) (Re = La, Gd, Y, Dy, Lu, Sc) and Li(+) instead of Sr(2+). Trivalent cation substitution at the Sr(2+) site enhances the photoluminescence intensities and also achieves better thermal stability at high temperature. The lifetime decay properties in the related substituted phosphors are investigated. Furthermore, under the 460 nm blue light irradiation, this green phosphor exhibits excellent luminescence properties with absorption and internal/external efficiencies. High-color-rendition warm-white LEDs using the phosphor have the color temperature and color rendition of 4732 K and 91.2, respectively, validating its suitability for use in solid-state white lighting. PMID:26331531

  7. ab-plane optical spectra of iodine-intercalated Bi1.9Pb0.1Sr2CaCu2O8 : Normal and superconducting properties

    E-print Network

    Tanner, David B.

    ab-plane optical spectra of iodine-intercalated Bi1.9Pb0.1Sr2CaCu2O8 : Normal and superconducting of an iodine-intercalated Bi1.9Pb0.1Sr2CaCu2O8 single crystal in the 80­40 000 cm 1 10 meV­5 eV frequency range and at temperatures between 10 and 300 K. As compared to the iodine-free Bi2Sr2CaCu2O8 , we find that the visible

  8. Effect of La-CO substitution on the crystal structure and magnetic properties of low temperature sintered Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites

    NASA Astrophysics Data System (ADS)

    Peng, Long; Li, Lezhong; Wang, Rui; Hu, Yun; Tu, Xiaoqiang; Zhong, Xiaoxi

    2015-11-01

    The La-Co substituted Sr1-xLaxFe12-xCoxO19 (x=0-0.5) ferrites with appropriate Bi2O3 additive were prepared at a low sintering temperature of 890 °C compatible with LTCC (low temperature co-fired ceramics) systems, and the effect of La-Co substitution on their crystal structure and magnetic properties was investigated. The results show that the pure M-type phase is successfully obtained when the La-Co substitution amount x does not exceed 0.3. However, the single M-type phase structure transforms to multiphase structure with further increased x, where the ?-Fe2O3 phase and La2O3 phase coexist with the M-type phase. Moreover, the saturation magnetization Ms, magnetic anisotropy field Ha, intrinsic coercivity Hci, and Curie temperature TC of the ferrites depend on the La-Co substitution amount strongly, which are suggested to be determined by the partially substitution of La3+-Co2+ ions for Sr2+-Fe3+ ions with x not higher than 0.3. It is found that the obtained Sr1-xLaxFe12-xCoxO19 (x=0.2 and 0.3) ferrites can provide improved magnetic properties (Ms>62 emu/g, Ha>1400 kA/m, and Hci>320 kA/m) as low temperature sintered M-type hexaferrites for microwave LTCC applications.

  9. Hydrothermal syntheses and low temperature magnetic behaviors of ACo{sub 3}(P{sub 2}O{sub 7}){sub 2} (A=Ca, Sr, Ba, Pb)

    SciTech Connect

    Yang, Tao; Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871 ; Lin, Jianhua

    2013-02-15

    ACo{sub 3}(P{sub 2}O{sub 7}){sub 2} (A=Ca, Sr, Ba, Pb) has been synthesized hydrothermally. Dc and ac magnetic susceptibilities are measured at various conditions. The magnetic interactions in all four compounds are dominantly ferromagnetic. All four compounds has a ferromagnetic-like long-range ordering at 8.0 K for CaCo, 6.4 K for SrCo, 7.6 K for PbCo, 8.0 K for BaCo. The ordering of PbCo at 7.6 K may contain a glassy component. Moreover, there is an additional phase transition for PbCo at 3.6 K. Once enhancing the external field to 3 kOe, the second phase transition is suppressed. Isothermal magnetizations of SrCo, PbCo and BaCo are quite similar, showing a field-induced metamagnetic transition at 2 K. For PbCo, the low-field ground state is weak ferromagnetic, and the critical filed is 10 kOe. Differently, CaCo is a typical soft weak ferromagnet. - Graphical abstract: Dc and ac magnetic susceptibilities were measured on ACo{sub 3}P{sub 4}O{sub 14} (A=Ca, Sr, Ba, Pb). At 2 K, PbCo{sub 3}P{sub 4}O{sub 14} is a field-induced metamagnet, while CaCo{sub 3}P{sub 4}O{sub 14} is a soft ferromagnet. Highlights: Black-Right-Pointing-Pointer Pure ACo{sub 3}(P{sub 2}O{sub 7}){sub 2} (A=Ca, Sr, Ba, Pb) samples are hydrothermally prepared. Black-Right-Pointing-Pointer Dc and ac magnetic data shows they all have a FM-like ordering at 6-8 K. Black-Right-Pointing-Pointer CaCo{sub 3}(P{sub 2}O{sub 7}){sub 2} is a typical soft ferromagnet. Black-Right-Pointing-Pointer PbCo{sub 3}(P{sub 2}O{sub 7}){sub 2} has a metamagnetic transition at 2 K with a critical field of 10 kOe.

  10. Fabrication and microwave properties of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films

    SciTech Connect

    Sobolewski, R.; Konopka, J.; Kula, W.; Gierlowski, P.; Konopka, A.; Lewandowski, S.J.

    1989-03-01

    The authors report their studies on the interaction of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films with microwaves. The films were prepared on cubic zirconia and magnesium oxide substrates using a modified spray deposition technique. The tested films were about 1-3 /mu/m thick and exhibited good superconducting properties (e.g. for YBCO-on zirconia films the 10-90% transition width was 2 K, and the zero resistance was reached at 89 K). Several test structures have been designed by spraying a mixture of nitrate precursors on heated substrates through very thin stencil masks. The supercurrent dependence on millimeter wavelength microwave illumination was measured, and microwave detection and mixing experiments were performed. The films of both materials exhibited proper ties characteristic for granular superconductors, with Josephson-type coupling at the intergrain connections. The studies also demonstrated that these materials can be successfully used as very sensitive millimeter radiation detectors operational at liquid nitrogen temperatures.

  11. Heat Capacity of Zn and Ni Doped Bi_2Sr_2CaCu_2O8 Single Crystals

    NASA Astrophysics Data System (ADS)

    Jaime, M.; Movshovich, R.; Sarrao, J.; Yoshizaki, R.

    1998-03-01

    The consequences of low non-magnetic and magnetic impurity doping were studied in Bi-2212 single crystals by means of the experimental resistivity, magnetization, heat capacity and thermal conductivity. The effect of the impurities includes, but it is not restricted to, a suppression of the superconducting transition temperature T_C. The heat capacity of Zn (0.3 %) and Ni (0-2.4 %) doped Bi_2Sr_2CaCu_2O8 crystals prepared by the floating solvent traveling zone method has been measured between 0.050 and 2 K in zero and applied magnetic fields up to several tesla. Both pure and doped samples display identical low-temperature nuclear Schottky anomaly tail at T <= 200 mK. The difference between specific heat of the Ni-doped sample and that of the pure Bi-2212 is a broad peak centered at about 1K, with an entropy associated with this feature of about 0.08 J/mol-K or 20% of full Rln (2S+1) spin entropy of Ni impurities (assuming S=1). Freezing of magnetic impurities may be related to observation of a second low-temperature transition in several of the Ni-doped samples.(R. Movshovich et al., preprint. Also A.V. Balatsky et al., preprint.) R. Movshovich et al., preprint

  12. 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.

  13. Photoinduced changes of the chemical potential in superconducting Bi2Sr2CaCu2O8 +?

    NASA Astrophysics Data System (ADS)

    Miller, Tristan L.; Smallwood, Christopher L.; Zhang, Wentao; Eisaki, Hiroshi; Orenstein, Joseph; Lanzara, Alessandra

    2015-10-01

    The chemical potential of a superconductor is of critical importance since, at equilibrium, it is the energy where electrons pair and form the superconducting condensate. However, in nonequilibrium measurements, there may be a difference between the chemical potential of the quasiparticles and that of the pairs. Here we report a systematic time- and angle-resolved photoemission study of the pump-induced change in the chemical potential of an optimally doped Bi2Sr2CaCu2O8 +? (Bi2212) sample in both its normal and superconducting states. The change in chemical potential can be understood by separately considering the change in the valence band energy relative to the vacuum and the change in chemical potential relative to the valence band energy. We attribute the former effect to a changing potential barrier at the sample surface and the latter effect to the conservation of charge in an asymmetrical density of states. The results indicate that the pair and quasiparticle chemical potentials follow each other even on picosecond timescales.

  14. Optimization of intergrain connection in high-temperature superconductor Bi2Sr2CaCu2Ox

    NASA Astrophysics Data System (ADS)

    Li, Cheng-Shan; Zhang, Sheng-Nan; Hao, Qing-Bin; Ma, Xiao-Bo; Lu, Tian-Ni; Zhang, Ping-Xiang

    2015-07-01

    A modified spark plasma sintering (SPS) technique was developed for the fabrication of Bi2Sr2CaCu2Ox (Bi-2212) superconducting bulks with better intergrain connections. The influences of the modified SPS process on the microstructures, intergrain connections, and related superconducting properties were systematically analyzed. The modified SPS process can not only increase the final density of the bulk samples but also enhance the texture structures. Clean grain boundaries were obtained instead of the intergrain amorphous layers. Therefore the intergranular properties were obviously improved. Due to the better intergrain connections and the stronger flux pinning properties, the critical current densities of the Bi-2212 bulks obtained via the modified SPS process were greatly increased. The obtained improvements imply the possibility for the modified SPS technique to be used for enhancing the superconducting properties of the Bi-2212 tapes. Project supported by the National Basic Research Program of China (Grant No. 2011CBA00104), the National Natural Science Foundation of China (Grant No. 51472206), the ITER Project of China (Grant No. 2013GB110001), and the Program for Innovative Research Team in Shaanxi Province, China (Grant No. 2013KCT-07).

  15. c -axis transport in naturally grown Bi2 Sr2 CaCu2 O8+? cross-whisker junctions

    NASA Astrophysics Data System (ADS)

    Latyshev, Yu. I.; Orlov, A. P.; Nikitina, A. M.; Monceau, P.; Klemm, R. A.

    2004-09-01

    We studied the c -axis transport of Bi2Sr2CaCu2O8+? (Bi2212) cross-whisker junctions formed by annealing “naturally” formed whisker crosses. These frequently appear during growth when the ab faces of neighboring whiskers come in contact. We obtained Fraunhofer patterns of the cross-junction critical currents in a parallel magnetic field, and found a sharp increase in the quasiparticle tunneling conductance at Vg=50-60mV , indicating high junction quality. For our weak junctions, the interface critical current density is about 3% of the critical current density across the stack of bulk intrinsic junctions, as is the room-temperature conductivity, and both are independent of the twist angle, in contrast to most of the data reported on “artificial” cross-whisker junctions [Y. Takano , Phys. Rev. B PRBMDO65, 140513(R) (2002)]. As a minimum, our results provide strong evidence for incoherent tunneling at least at the interface, and for at least a small s -wave order-parameter component in the bulk of Bi2212 for T?Tc . They are also consistent with the bicrystal twist experiments of Li [Phys. Rev. Lett. 83, 4160 (1999)].

  16. 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.

  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. Comparison of luminescent and scanning laser thermal micro-imaging of self-heating in Bi2Sr2CaCu2O8 mesa THz sources

    NASA Astrophysics Data System (ADS)

    Benseman, Timothy; Koshelev, Alexei; Vlasko-Vlasov, Vitalii; Hao, Yang; Kwok, Wai-Kwong; Welp, Ulrich; Keiser, Courtney; Gross, Boris; Lange, Matthias; Koelle, Dieter; Kleiner, Reinhold; Kadowaki, Kazuo

    2015-03-01

    Scanning laser thermal microscopy of stacked Bi2Sr2CaCu2O8 Josephson junction terahertz sources has revealed both electromagnetic cavity resonance modes and strongly non-uniform self-heating in these devices. However, this technique - in which a modulated laser beam is rastered across the surface of a device - excites a number of physical phenomena, and thus the resulting images can be difficult to interpret. Here we compare scanning laser images taken on Bi2Sr2CaCu2O8 mesa THz sources with micro-images collected via a thermoluminescent technique under identical conditions. The latter technique directly measures the device surface temperature, and we find excellent agreement with the scanning laser results, confirming that scanning laser thermal microscopy is indeed primarily probing device temperature. This research was supported by the Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

  19. Rapid formation of the 110 K phase in Bi-Pb-Sr-Ca-Cu-O through freeze-drying powder processing

    SciTech Connect

    Song, K.H.; Liu, H.K.; Dou, S.X.; Sorrell, C.C. )

    1990-06-01

    This paper reports three techniques for processing Bi-Pb-Sr-Ca-Cu-O (BPSCCO) powders investigated: dry-mixing, sol-gel formation, and freeze-drying. It was found that sintering for 120 h at 850{degrees}C is required to form nearly single-phase (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10{minus}{ital y}} by dry-mixing, whereas sintering for 30 h at 840{degrees}C was sufficient to form the 110 K (2223) phase when freeze-drying was used. The sol-gel route was found to be intermediate in efficiency between these two techniques. Freeze-drying provided highly reactive, intimately mixed, and carbon-free precursors. The presence of carbonates in the uncalcined powders was the major cause of phase segregation and sluggishness of the 110 K phase formation.

  20. Formation of superconducting Bi sub 2-y Pb sub y Sr sub 2 Ca sub 2 Cu sub 3 O sub x from coprecipitated oxalates

    SciTech Connect

    Bernhard, K.; Gritzner, G.; Wang, Xianzhong; Baeuerle, D. )

    1990-06-01

    The conditions for the coprecipitation of Bi{sup 3+}, Pb{sup 2+}, Ca{sup 2+} as oxalates are reported. These oxalates were used as precursors for the formation of Bi{sub 2-y}Pb{sub y}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconducting ceramics. The behavior of the oxalates upon heat treatment was studied by thermogravimetry. Both the oxalates and the superconducting oxides were analyzed and characterized by atomic absorption spectroscopy and by X-ray diffraction.

  1. Stoichiometry control of magnetron sputtered Bi2Sr2Ca1xYxCu2Oy (0 6 x 6 0.5) thin film, composition

    E-print Network

    Hewitt, Kevin

    that the energy of oxygen anions that strike the film is reduced [1,5­11]. Off-axis sputtering greatly reduces is to use an off-axis deposition method, where the substrate is not directly across from the target. RatherStoichiometry control of magnetron sputtered Bi2Sr2Ca1ÀxYxCu2Oy (0 6 x 6 0.5) thin film

  2. Terahertz emission from a stack of intrinsic Josephson junctions in Pb-doped Bi2Sr2CaCu2O8+?

    NASA Astrophysics Data System (ADS)

    Tsujimoto, M.; Maeda, Y.; Kambara, H.; Elarabi, A.; Yoshioka, Y.; Nakagawa, Y.; Wen, Y.; Doi, T.; Saito, H.; Kakeya, I.

    2015-10-01

    We observe continuous terahertz-wave emission from a stack of intrinsic Josephson junctions made of slightly Pb-doped Bi2Sr2CaCu2O{}8+? . We investigate how Pb doping affects the c-axis current-voltage and emission characteristics. The terahertz emission spectra are measured by Fourier-transform infrared spectroscopy and reveal that the emission frequency is remarkably increased by Pb doping, an effect that we attribute to cavity resonance.

  3. Superconductivity up to 114 K in the Bi-Al-Ca-Sr-Cu-O compound system without rare-earth elements

    NASA Technical Reports Server (NTRS)

    Chu, C. W.; Bechtold, J.; Gao, L.; Hor, P. H.; Huang, Z. J.

    1988-01-01

    Stable superconductivity up to 114 K has been reproducibly detected in Bi-Al-Ca-Sr-Cu-O multiphase systems without any rare-earth elements. Pressure has only a slight positive effect on T(c). These observations provide an extra material base for the study of the mechanism of high-temperature superconductivity and also the prospect of reduced material cost for future applications of superconductivity.

  4. Metal-semiconductor-transition observed in Bi{sub 2}Ca(Sr, Ba){sub 2}Co{sub 2}O{sub 8+?} single crystals

    SciTech Connect

    Dong, Song-Tao; Zhang, Bin-Bin; Zhang, Lun-Yong; Yao, Shu-Hua E-mail: shyao@nju.edu.cn; Zhou, Jian; Zhang, Shan-Tao; Gu, Zheng-Bin; Chen, Yan-Feng; Chen, Y. B. E-mail: shyao@nju.edu.cn

    2014-07-28

    Electrical property evolution of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+?} single crystals (AE?=?Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+?} and Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+?} demonstrates semiconductor-like properties. But Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+?} shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+?} to semiconductor-like Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+?} can be attributed to Anderson localization. However the semiconductor behaviour of Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+?} and Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+?} is related to electronic correlations effect that is inferred by large negative magnetoresistance (?70%). The theoretical electronic structures and valence X-ray photoemission spectroscopy substantiate that there is a relative large density of state around Fermi level in Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+?} compared with other two compounds. It suggests that Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+?} is more apt to be metal in this material system.

  5. Structural refinements on high-Tc superconductor Tl0.5Pb0.5Sr2-xBaxCa2Cu3O9-?

    NASA Astrophysics Data System (ADS)

    Gladyshevskii, Roman E.; Galez, Philippe; Lebbou, Kheirreddine; Bellingeri, Emilio; Couach, Michel; Flüklger, René; Jorda, Jean-Louis; Cohen-Adad, Marie Thérèse

    1996-03-01

    Samples of nominal composition Tl0.5Pb0.5Sr2-xBaxCa2Cu3O9-? with 0?x?0.6 were characterized by structural refinements on X-ray powder diffraction data. The weight fraction of the 1223 phase ranged from 85% (x=0) to 91% (x=0.4); 1212 phase, (Ca, Sr)2PbO4, (Ca, Sr)2CuO3 and BaPbO3 being detected in small quantities. The refined Ba content in the 1223 phase corresponded to the nominal compositions and the cell parameters increased with increasing x. The distance between the Cu atom and the apical O atom of the square pyramid increased from 2.29 to 2.50 Å as the Ba content was raised. A displacement (up to 0.26 Å) of the Tl atoms from the ideal position on the 4-fold axis was observed for all samples. Structural refinements on neutron diffraction data indicated related displacement of the O atoms in the TlO layer. Tc was not significantly affected by the changes in composition and structure and ranged from 118 K (x=0) to 116 K (x=0.6).

  6. Effect of local environment on crossluminescence kinetics in SrF2:Ba and CaF2:Ba solid solutions

    NASA Astrophysics Data System (ADS)

    Terekhin, M. A.; Makhov, V. N.; Lebedev, A. I.; Sluchinskaya, I. A.

    2015-10-01

    Spectral and kinetic properties of extrinsic crossluminescence (CL) in SrF2:Ba(1%) and CaF2:Ba(1%) are compared with those of intrinsic CL in BaF2 and are analyzed taking into account EXAFS data obtained at the Ba LIII edge and results of first-principles calculations. The CL decay time was revealed to be longer in SrF2:Ba and CaF2:Ba compared to BaF2. This fact contradicts the expected acceleration of luminescence decay which could result from an increased overlap of wave functions in solid solutions due to shortening of the Ba-F distance obtained in both EXAFS measurements and first-principles calculations. This discrepancy is explained by the effect of migration and subsequent non-radiative decay of the Ba(5p) core holes in BaF2 and by decreasing of the probability of optical transitions between Ba(5p) states and the valence band in SrF2:Ba and CaF2:Ba predicted by first-principles calculations.

  7. Enhanced flux pinning in Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconductors tapes with addition of magnetic nanorod ?-Fe2O3

    NASA Astrophysics Data System (ADS)

    Lau, K. T.; Yahya, S. Y.; Abd-Shukor, R.

    2006-06-01

    The pinning strength of the Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O tapes with the addition of magnetic nanorod ?-Fe2O3 is studied using the exponent n values obtained from power law current-electric field (I-E) characteristics. The starting composition of the ?-Fe2O3 added samples is Bi1.6Pb0.4Sr2Ca2Cu3O10-(?-Fe2O3)0.01. The rate of decrease of n values in applied fields for the tapes with nano-?-Fe2O3 is found lower than the tapes without nano-?-Fe2O3. This indicates that the pinning strength for the tapes with nano ?-Fe2O3 is relatively higher than the tapes prepared without nano ?-Fe2O3. The results are supported by two conventional methods which are normally used to compare the pinning strength of superconductor tapes. Magnetic impurities generally suppress superconductivity. However, our study shows that magnetic nanorod ?-Fe2O3 enhanced the pinning strength of Ag-sheathed Bi-Sr-Ca-Cu-O superconductor tapes. This is consistent with previous calculations on frozen flux superconductor with magnetic nanorod as pinning centers.

  8. Strong Anisotropy of Dirac Cones in SrMnBi2 and CaMnBi2 Revealed by Angle-Resolved Photoemission Spectroscopy

    PubMed Central

    Feng, Ya; Wang, Zhijun; Chen, Chaoyu; Shi, Youguo; Xie, Zhuojin; Yi, Hemian; Liang, Aiji; He, Shaolong; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Chen, Chuangtian; Xu, Zuyan; Dai, Xi; Fang, Zhong; Zhou, X. J.

    2014-01-01

    The Dirac materials, such as graphene and three-dimensional topological insulators, have attracted much attention because they exhibit novel quantum phenomena with their low energy electrons governed by the relativistic Dirac equations. One particular interest is to generate Dirac cone anisotropy so that the electrons can propagate differently from one direction to the other, creating an additional tunability for new properties and applications. While various theoretical approaches have been proposed to make the isotropic Dirac cones of graphene into anisotropic ones, it has not yet been met with success. There are also some theoretical predictions and/or experimental indications of anisotropic Dirac cone in novel topological insulators and AMnBi2 (A = Sr and Ca) but more experimental investigations are needed. Here we report systematic high resolution angle-resolved photoemission measurements that have provided direct evidence on the existence of strongly anisotropic Dirac cones in SrMnBi2 and CaMnBi2. Distinct behaviors of the Dirac cones between SrMnBi2 and CaMnBi2 are also observed. These results have provided important information on the strong anisotropy of the Dirac cones in AMnBi2 system that can be governed by the spin-orbital coupling and the local environment surrounding the Bi square net. PMID:24947490

  9. Endohedral and exohedral metalloborospherenes: M@B40 (M=Ca, Sr) and M&B40 (M=Be, Mg).

    PubMed

    Bai, Hui; Chen, Qiang; Zhai, Hua-Jin; Li, Si-Dian

    2015-01-12

    The recent discovery of the all-boron fullerenes or borospherenes, D(2d) B40(-/0), paves the way for borospherene chemistry. Here we report a density functional theory study on the viability of metalloborospherenes: endohedral M@B40 (M=Ca, Sr) and exohedral M&B40 (M=Be, Mg). Extensive global structural searches indicate that Ca@B40 (1, C(2v), (1)A1) and Sr@B40 (3, D(2d), (1)A1) possess almost perfect endohedral borospherene structures with a metal atom at the center, while Be&B40 (5, C(s), (1)A') and Mg&B40 (7, C(s), (1)A') favor exohedral borospherene geometries with a ?(7)-M atom face-capping a heptagon on the waist. Metalloborospherenes provide indirect evidence for the robustness of the borospherene structural motif. The metalloborospherenes are characterized as charge-transfer complexes (M(2+)B40(2-)), where an alkaline earth metal atom donates two electrons to the B40 cage. The high stability of endohedral Ca@B40 (1) and Sr@B40 (3) is due to the match in size between the host cage and the dopant. Bonding analyses indicate that all 122 valence electrons in the systems are delocalized as ? or ? bonds, being distributed evenly on the cage surface, akin to the D(2d) B40 borospherene. PMID:25418022

  10. Color tunable and thermally stable luminescence of Tb{sup 3+} doped Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors

    SciTech Connect

    Zhang, Xinmin; Seo, Hyo Jin

    2012-08-15

    Highlights: ? Lowest spin-allowed and spin-forbidden f–d transitions locate at 250 and 280 nm. ? Cross relaxation shortens lifetime of {sup 5}D{sub 3} level, while that of {sup 5}D{sub 4} are unaffected. ? Cross-relaxation can explain concentration quenching of the {sup 5}D{sub 3} emission. ? Dipole–quadrupole interaction is responsible for the non-radiative relaxation. ? Li{sub 4}SrCa(SiO{sub 4}){sub 2}:Tb{sup 3+} is thermally stable and color tunable phosphor. -- Abstract: Tb{sup 3+} ions activated Li{sub 4}SrCa(SiO{sub 4}){sub 2} phosphors were synthesized using a solid state reaction method. The phase impurity was checked by XRD. The photoluminescence (PL) excitation spectrum, emission spectra at room and high temperature, decay curves of samples with different Tb{sup 3+} ions concentration were studied in detail. Cross-relaxation and the Inokuti–Hirayama model were used to analyze the experimental results. Li{sub 4}SrCa(SiO{sub 4}){sub 2}:xTb{sup 3+} are thermally stable and color tunable phosphors.

  11. Reduction of Eu 3+ to Eu 2+ in MAl 2Si 2O 8 ( M=Ca, Sr, Ba) in air condition

    NASA Astrophysics Data System (ADS)

    Zhang, Cuimiao; Yang, Jun; Lin, Cuikun; Li, Chunxia; Lin, Jun

    2009-07-01

    In general, the reduction of Eu 3+ to Eu 2+ in solids needs an annealing process in a reducing atmosphere. In this paper, it is of great interest and importance to find that the reduction of Eu 3+ to Eu 2+ can be realized in a series of alkaline-earth metal aluminum silicates MAl 2Si 2O 8 ( M=Ca, Sr, Ba) just in air condition. The Eu 2+-doped MAl 2Si 2O 8 ( M=Ca, Sr, Ba) powder samples were prepared in air atmosphere by Pechini-type sol-gel process. It was found that the strong band emissions of 4 f65 d1-4 f7 from Eu 2+ were observed at 417, 404 and 373 nm in air-annealed CaAl 2Si 2O 8, SrAl 2Si 2O 8 and BaAl 2Si 2O 8, respectively, under ultraviolet excitation although the Eu 3+ precursors were employed. In addition, under low-voltage electron beam excitation, Eu 2+-doped MAl 2Si 2O 8 also shows strong blue or ultraviolet emission corresponding to 4 f65 d1-4 f7 transition. The reduction mechanism from Eu 3+ to Eu 2+ in these compounds has been discussed in detail.

  12. The role of Eu2+ concentration on the phase formation and spectroscopic properties of MZr4(PO4)6 (M2+ = Ca2+, Sr2+)

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi-Jun; Yang, Woochul

    2015-10-01

    The electronic structures of MZr4(PO4)6 (M2+ = Ca2+, Sr2+) were calculated using the CASTEP and the band gaps for CaZr4(PO4)6 and SrZr4(PO4)6 can reach up to 4.30 and 4.45 eV, respectively. Eu2+ doped MZr4(PO4)6 were prepared by solid-state reaction method. The XRD patterns, luminescence, decay curves and thermal quenching properties of the samples were investigated. The Eu2+ ion can be totally incorporated into MZr4(PO4)6 forming complete solid solutions. M1-xEuxZr4(PO4)6 (0.01 ? x ? 1) shows typical broad band emission in energy range from 1.91 to 3.11 eV originating from the 4f65d1 ? 4f75d0 transition of Eu2+. With increasing Eu2+ concentration, there is an abnormal blue-shift of the emission for CaZr4(PO4)6:Eu2+ due to the decreasing crystal field strength and Stokes shift. However, there is no significant change in the position of the emission spectra in Eu2+-activated SrZr4(PO4)6. M0.97Eu0.03Zr4(PO4)6 shows the abnormal blue shift with decreasing emission intensity as an increase in temperature.

  13. Polymorphisms in CaSR and CLDN14 Genes Associated with Increased Risk of Kidney Stone Disease in Patients from the Eastern Part of India

    PubMed Central

    Ghosh, Sudakshina; Pattanayak, Arup Kumar; Ghosh, Saurabh; Pal, Dilip Kumar; Puri, Anurag; Kundu, Anup Kumar; Das, Madhusudan

    2015-01-01

    Kidney stone disease (KSD) is a major clinical problem imposing a large burden for both healthcare and economy globally. In India, the prevalence of kidney stone disease is rapidly increasing. This study aimed to evaluate the association between genetic defects in vitamin D receptor (VDR), calcium sensing receptor (CaSR) and claudin 14 (CLDN14) genes and kidney stone disease in patients from eastern India. We enrolled 200 consecutive kidney stone patients (age 18–60 years) (cases) and their corresponding sex and age matched 200 normal individuals (controls). To identify genetic variants responsible for KSD, we performed sequence analysis of VDR, CaSR and CLDN14 genes. Four non-synonymous (rs1801725, rs1042636, rs1801726 and rs2228570), one synonymous (rs219780) and three intronic single nucleotide polymorphisms (SNPs) (rs731236, rs219777 and rs219778) were identified. Genotype and allele frequency analysis of these SNPs revealed that, rs1801725 (Ala986Ser), rs1042636 (Arg990Gly) of CaSR gene and rs219778, rs219780 (Thr229Thr) of CLDN14 gene were significantly associated with KSD. Serum calcium levels were significantly higher in subjects carrying 986Ser allele and calcium excretion was higher in subjects bearing 990Gly allele. In conclusion, rs1801725, rs1042636, rs219778 and rs219780 SNPs were associated with kidney stone risk in patients from the eastern part of India. PMID:26107257

  14. RF plasma deposition and in-situ property enhancement of Bi 2Sr 2Ca n-1Cu nO x thin films

    NASA Astrophysics Data System (ADS)

    Shah, A.; Patel, S.; Narumi, E.; Shaw, D. T.

    1993-06-01

    An atmospheric pressure, inductively coupled, argon-oxygen RF plasma process has been used to prepare, in-situ, superconducting Bi 2Sr 2Ca n-1 Cu nO x thin films. Film properties have been enhanced by exposing the grown film, in-situ, to the same argon-oxygen plasma used for its deposition. This is achieved by switching off the atomized precursor nitrate solution to the plasma torch. Tc's of 76 K and Jc's of 1.3 × 10 5 A/cm 2 at 60 K and zero field have been achieved in the in-situ, Bi 2Sr 2Ca 1Cu 2O x films. Bi 2Sr 2Ca 2Cu 3O x films with Tc's of 100 K and Jc's of 1 × 10 5 A/cm 2 at 77 K and zero field have also been grown. The effects of film exposure to the plasma for different time periods and RF power levels are discussed. The effects of deposition parameters, such as substrate temperature, bismuth content, solution concentration and phase control, are analyzed. Finally, the critical current behavior of the films under a external magnetic field of up to 5 T is reported.

  15. Controls on stable strontium isotope fractionation in coccolithophores with implications for the marine Sr cycle

    NASA Astrophysics Data System (ADS)

    Stevenson, Emily I.; Hermoso, Michaël; Rickaby, Rosalind E. M.; Tyler, Jonathan J.; Minoletti, Fabrice; Parkinson, Ian J.; Mokadem, Fatima; Burton, Kevin W.

    2014-03-01

    The controls on stable Sr isotope fractionation into the calcite produced by the coccolithophore species Emiliania huxleyi, Coccolithus pelagicus spp. braarudii and Gephyrocapsa oceanica are investigated. Each species has been cultured under controlled laboratory conditions at a range of temperatures (10-25 °C) to test the potential of ?88/86Sr as a proxy for growth rate and/or sea surface temperature. Coccolithophores are one of the most abundant pelagic calcifiers; since Sr substitutes to some degree for Ca in their calcite coccoliths, coccolithophores represent a significant output of Sr from seawater, potentially influencing the ?88/86Sr mass balance in the modern oceans. The coccoliths are investigated for their ?88/86Sr, Sr/Ca, and ?18O measured as function of temperature. As temperature is increased all species show a negative stable Sr isotopic fractionation, related to a temperature controlled growth rate. We infer the shift of ?88/86Sr to lighter values as indicative of a kinetic control on the isotope fractionation, revealing the potential of ?88/86Sr as a proxy for growth rate, which in these experiments is primarily dictated by temperature. The results from these experiments indicate that coccolithophore calcite incorporates Sr with a very light ?88/86Sr isotope composition as low as ˜0‰.

  16. Low loss composition of BaxSryCa1-x-yTiO3: Ba0.12-0.25Sr0.35-0.47Ca0.32-0.53TiO3

    DOEpatents

    Xiang, Xiao-Dong (Alameda, CA); Chang, Hauyee (Berkeley, CA); Takeuchi, Ichiro (Albany, CA)

    2001-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  17. Zintl phase Yb{sub 1-x}Ca{sub x}Cd{sub 2}Sb{sub 2} with tunable thermoelectric properties induced by cation substitution

    SciTech Connect

    Cao Qigao; Zhang Hui; Tang Meibo; Chen Haohong; Yang Xinxin; Zhao Jingtai; Grin, Yuri

    2010-03-15

    It has been shown previously that the thermoelectric properties of the Zintl phase compound YbCd{sub 2}Sb{sub 2} can be finely tuned via Zn substitution at the Cd-site in the anionic (Cd{sub 2}Sb{sub 2}){sup 2-} framework. Here we report the results of the investigation of isoelectronic substitution of Yb by Ca. The p-type Yb{sub 1-x}Ca{sub x}Cd{sub 2}Sb{sub 2} (0.2{<=}x{<=}0.8) samples have been synthesized via a solid-state reaction followed by suitable cooling, annealing, grinding, and spark plasma sintering densification processes. In samples with x=0.2, 0.4, 0.5, 0.6, 0.8, the electrical conductivity, Seebeck coefficient, and thermal conductivity measurements have been carried out in the temperature range from 300 to 650 K. It is found that the Ca substitution effectively lowers the thermal conductivity for all samples at high temperature, while it significantly increases the Seebeck coefficient. As a result, the dimensionless figure of merit ZT of 0.96 has been attained at 650 K for samples with x=0.4, while the value is 0.78 for the unsubstituted YbCd{sub 2}Sb{sub 2}

  18. Enantiomorphism of the Ca3Ga2Ge4O14 compound and comparison of the Ca3Ga2Ge4O14 and Sr3Ga2Ge4O14 structures

    NASA Astrophysics Data System (ADS)

    Mill, B. V.; Klimenkova, A. A.; Maximov, B. A.; Molchanov, V. N.; Pushcharovsky, D. Yu.

    2007-09-01

    The absolute crystal structures of two enantiomorphic forms of the Ca3Ga2Ge4O14 crystals ( a = 8.075(1) Å, c = 4.9723(6) Å, space group P321) with the positive and negative senses of the optical activity are determined using X-ray diffraction analysis. The final R factors are as follows: R = 1.75% and R w = 2.57% for the crystal with the positive sense of the optical activity and R = 1.86% and R w = 2.78% for the crystal with the negative sense of the optical activity. The replacement of the Ca2+ ions by larger Sr2+ ions (with the formation of the Sr3Ga2Ge4O14 compound) leads to an anisotropic expansion of the crystal lattice (with a more considerable increase in the lattice parameter a as compared to the lattice parameter c), a change in the occupation of the 1 a and 3 f positions by the Ga3+ and Ge4+ ions, and symmetrization of the octahedra and tetrahedra forming the structural framework. The shape of the dodecahedron changes so that its size along the polar electric axis 2 increases significantly. This change is the main factor responsible for the increase in the piezoelectric activity of the Sr3Ga2Ge4O14 compound as compared to the piezoelectric activity of the Ca3Ga2Ge4O14 compound.

  19. Structural variation and recovery of superconductivity by Ca substitution in Y{sub 0.4}Pr{sub 0.6}Ba{sub 2-x}Ca{sub x}Cu{sub 3}O{sub 7-{sigma}}

    SciTech Connect

    Cao, G.; Qian, Y.; Wu, H.

    1996-02-01

    Y{sub 0.4}Pr{sub 0.6}Ba{sub 2{minus}x}Ca{sub x}Cu{sub 3}O{sub 7{minus}{delta}} polycrystalline samples were prepared and investigated. The Ca substitution led to a structural variation toward tetragonal symmetry, possibly due to the structural modification within the Cu(1)O layer. Superconductivity and metallic conduction were recovered when x{>=}0.2, giving one more evidence for the existence of the ion-size effect at the Ba site.

  20. Neutron diffraction study of the crystal structure and structural phase transition of La{sub 0.7}Ca{sub 0.3-x}Sr{sub x}CrO{sub 3} (0<=x<=0.3)

    SciTech Connect

    Omoto, Kazuki; Norberg, Stefan T.; Hull, Steve; Aoto, Akimitsu; Hashimoto, Takuya

    2010-02-15

    The crystal structure of the La{sub 0.7}Ca{sub 0.3-x}Sr{sub x}CrO{sub 3} series, including the compositional and temperature dependence of the structural parameters, has been studied by variable temperature neutron diffraction measurements. The extent of the distortions from the ideal cubic perovskite structure has been evaluated quantitatively using the average bond lengths and the mean volumes of the [CrO{sub 6}] octahedron and [(La/Ca/Sr)O{sub 12}] polyhedron, and has been shown to decrease with increase of Sr content or temperature. At the structural phase transition from the orthorhombic (Pnma) structure to the rhombohedral (R3-barc) one, the volume of the [CrO{sub 6}] octahedron decreases whereas that of the [(La/Ca/Sr)O{sub 12}] polyhedron shows little difference, resulting in an overall decrease in the level of distortion. The change in the degree of distortion at the phase transition decreases with increase of Sr content, in agreement with the smaller variation of the enthalpy and volume for the specimens with higher Sr content. - Graphical abstract: Temperature dependence of parameter, PHI, representing the extent of distortion from the ideal cubic perovskite structure, for La{sub 0.7}Ca{sub 0.3}CrO{sub 3} (diamonds) and La{sub 0.7}Ca{sub 0.15}Sr{sub 0.15}CrO{sub 3} (circles) calculated from neutron diffraction patterns.

  1. Investigating the influence of Na+ and Sr2+ on the structure and solubility of SiO2-TiO2-CaO-Na2O/SrO bioactive glass.

    PubMed

    Li, Y; Placek, L M; Coughlan, A; Laffir, F R; Pradhan, D; Mellott, N P; Wren, A W

    2015-02-01

    This study was conducted to determine the influence that network modifiers, sodium (Na+) and strontium (Sr2+), have on the solubility of a SiO2-TiO2-CaO-Na2O/SrO bioactive glass. Glass characterization determined each composition had a similar structure, i.e. bridging to non-bridging oxygen ratio determined by X-ray photoelectron spectroscopy. Magic angle spinning nuclear magnetic resonance (MAS-NMR) confirmed structural similarities as each glass presented spectral shifts between -84 and -85 ppm. Differential thermal analysis and hardness testing revealed higher glass transition temperatures (Tg 591-760 °C) and hardness values (2.4-6.1 GPa) for the Sr2+ containing glasses. Additionally the Sr2+ (~250 mg/L) containing glasses displayed much lower ion release rates than the Na+ (~1,200 mg/L) containing glass analogues. With the reduction in ion release there was an associated reduction in solution pH. Cytotoxicity and cell adhesion studies were conducted using MC3T3 Osteoblasts. Each glass did not significantly reduce cell numbers and osteoblasts were found to adhere to each glass surface. PMID:25644099

  2. Elastic and anelastic anomalies in (Ca,Sr)TiO 3 perovskites: Analogue behaviour for silicate perovskites

    NASA Astrophysics Data System (ADS)

    Walsh, J. N.; Taylor, P. A.; Buckley, A.; Darling, T. W.; Schreuer, J.; Carpenter, M. A.

    2008-03-01

    Values of bulk modulus ( K), shear modulus ( G) and mechanical quality factor ( Q) have been determined for polycrystalline samples across the CaTiO 3 (CST0)-SrTiO 3 (CST100) solid solution by resonant ultrasound spectroscopy. Because of similarities with low frequency elastic and anelastic anomalies due to twin wall motion reported in previous studies, a working hypothesis is developed in which dissipation processes are interpreted in terms of twin wall displacements. At high temperatures in CST50 the stability field of the I4/ mcm structure is marked by the disappearance of all resonance peaks (superattenuation). This is attributed to anelastic domain wall sliding. At room temperature the I4/ mcm phase of CST70 and CST80 has values of G which are lower than those of cubic or orthorhombic phases, and a concomitant drop in Q is interpreted as implying that the domain wall pinning process reported elsewhere to occur below ˜400-450 K is only partial. A similar drop in G and Q was found in CST95 below the Pm3¯m?I4/mcm transition at ˜238 K. The I4/ mcm ? Pbcm transition in CST70 at ˜230 K is marked by an abrupt increase in Q, suggesting that mobile twins in crystals with the I4/ mcm structure become effectively immobile in antiferroelectric crystals with the Pbcm structure. The I4/ mcm ? Pnma transition in CST50 is marked by a similarly abrupt increase in Q, consistent with twin walls becoming effectively immobile also in crystals with the Pnma structure. A fall in Q below ˜800 K in CST0, however, could imply that a degree of twin wall mobility might develop in Pnma crystals if the tetragonal spontaneous strain departs significantly from zero. The remarkable attenuation behaviour of crystals with the I4/ mcm structure at the relatively low stress conditions which apply during resonances of a parallelepiped with edge dimensions of ˜2-4 mm, is consistent with the view that a characteristic signature for tetragonal CaSiO 3 in the Earth's lower mantle should be a marked attenuation of seismic waves.

  3. Synthesis and structure of alkaline earth silicon nitrides: BaSiN(2), SrSiN(2), and CaSiN(2).

    PubMed

    Gál, Zoltán A; Mallinson, Phillip M; Orchard, Heston J; Clarke, Simon J

    2004-06-28

    The alkaline earth silicon nitrides AESiN(2) (AE = Ca, Sr, Ba) are reported, synthesized as clear, colorless, single crystals from molten sodium at 900-1100 degrees C or, in the cases of BaSiN(2) and SrSiN(2), as white powders by reacting powdered intermetallics AESi with flowing anhydrous ammonia at 550-1000 degrees C. Structures were determined from single-crystal X-ray diffraction measurements at 150 K: BaSiN(2) crystallizes in space group Cmca (No. 64) with a = 5.6046(1) A, b = 11.3605(3) A, c = 7.5851(2) A, and Z = 8. The structure consists of pairs of SiN(4) tetrahedra edge-linked to form bow-tie-shaped Si(2)N(6) dimers which share vertexes to form layers and has no analogue in oxide chemistry. SrSiN(2) has a distorted form of this structure (SrSiN(2): space group P2(1)/c (No. 14), a = 5.9750(5) A, b = 7.2826(7) A, c = 5.4969(4) A, beta = 113.496(4) degrees, Z = 4). The structure of CaSiN(2) contains only vertex-sharing SiN(4) tetrahedra, linked to form a three-dimensional stuffed-cristobalite type framework isostructural with KGaO(2) (CaSiN(2): space group Pbca (No. 61), a = 5.1229(3) A, b = 10.2074(6) A, c = 14.8233(9) A, Z = 16). PMID:15206881

  4. Calcium EXAFS Establishes the Mn-Ca Cluster in the Oxygen-Evolving Complex of Photosystem II†

    PubMed Central

    Cinco, Roehl M.; Holman, Karen L. McFarlane; Robblee, John H.; Yano, Junko; Pizarro, Shelly A.; Bellacchio, Emanuele; Sauer, Kenneth; Yachandra, Vittal K.

    2014-01-01

    The proximity of Ca to the Mn cluster of the photosynthetic water-oxidation complex is demonstrated by X-ray absorption spectroscopy. We have collected EXAFS data at the Ca K-edge using active PS II membrane samples that contain approximately 2 Ca per 4 Mn. These samples are much less perturbed than previously investigated Sr-substituted samples, which were prepared subsequent to Ca depletion. The new Ca EXAFS clearly shows backscattering from Mn at 3.4 Å, a distance that agrees with that surmised from previously recorded Mn EXAFS. This result is also consistent with earlier related experiments at the Sr K-edge, using samples that contained functional Sr, that show Mn is ~ 3.5 Å distant from Sr. The totality of the evidence clearly advances the notion that the catalytic center of oxygen evolution is a Mn-Ca heteronuclear cluster. PMID:12390018

  5. Electronic correlations, magnetism, and Hund's rule coupling in the ruthenium perovskites SrRuO3 and CaRuO3

    NASA Astrophysics Data System (ADS)

    Dang, Hung T.; Mravlje, Jernej; Georges, Antoine; Millis, Andrew J.

    2015-05-01

    A comparative density functional plus dynamical mean field theory study of the pseudocubic ruthenate materials CaRuO3 and SrRuO3 is presented. Phase diagrams are determined for both materials as a function of Hubbard repulsion U and Hund's rule coupling J . Metallic and insulating phases are found, as are ferromagnetic and paramagnetic states. The locations of the relevant phase boundaries are determined. Based on the computed phase diagrams, Mott dominated and Hund's dominated regimes of strong correlation are distinguished. Comparison of calculated properties to experiments indicates that the actual materials are in the Hund's coupling dominated region of the phase diagram so can be characterized as Hund's metals, in common with other members of the ruthenate family. Comparison of the phase diagrams for the two materials reveals the role played by rotational and tilt (GdFeO3-type) distortions of the ideal perovskite structure. The presence of magnetism in SrRuO3 and its absence in CaRuO3 despite the larger mass and larger tilt/rotational distortion amplitude of CaRuO3 can be understood in terms of density of states effects in the presence of strong Hund's coupling. Comparison of the calculated low-T properties of CaRuO3 to those of SrRuO3 provides insight into the effects of magnetic order on the properties of a Hund's metal. The study provides a simultaneous description of magnetism and correlations and explicates the roles played by band theory and Hubbard and Hund's interactions.

  6. Massive production of A2SiO4:Eu3+ and A2SiO4:Eu2+ (A = Ca, Sr, Ba) microspheres and luminescent properties

    NASA Astrophysics Data System (ADS)

    Wei, Fengjun; Jia, Qiuli

    2015-06-01

    A2SiO4:Eu3+ and A2SiO4:Eu2+ (A = Ca, Sr, Ba) microspheres with dense structure were synthesized by the modified spray-drying process. The obtained samples were characterized by XRD, SEM, and spectrophotometer. The XRD results reveal that all samples are isostructure. The SEM results show that the obtained samples are microspheres with size in the range of 0.6-2.2 ?m. Dextrin plays an important role in the formation of spherical morphology. The excitation and emission spectra of the samples indicate that Eu3+ (or Eu2+) ions doped into different alkaline earth silicates will give different emission bands in different color regions and with different emission intensities. A2SiO4:Eu3+ samples show characteristic emission bands originating from 5D0 ? 7Fj transitions of Eu3+ ions. A2SiO4:Eu2+ samples show different emission bands. The two emission bands for Sr2SiO4:Eu2+ relate to the two Eu2+ activator sites locating at two Sr2+ sites in Sr2SiO4 host. The difference of luminescent properties relates to the different sites of Eu3+ (or Eu2+) ions in the A2SiO4 hosts.

  7. Structure, Crystallographic Sites, and Tunable Luminescence Properties of Eu(2+) and Ce(3+)/Li(+)-Activated Ca1.65Sr0.35SiO4 Phosphors.

    PubMed

    Xia, Zhiguo; Miao, Shihai; Chen, Mingyue; Molokeev, Maxim S; Liu, Quanlin

    2015-08-17

    Eu(2+) and Ce(3+)/Li(+) singly doped and Eu(2+)/Ce(3+)/Li(+)-codoped Ca1.65Sr0.35SiO4 phosphors have been synthesized by a solid-state reaction method. The crystal structure was determined by Rietveld refinement to verify the formation of the ?L?-Ca2SiO4 phase with the Sr addition into Ca2SiO4, and the preferred crystallographic positions of the Eu(2+) and Ce(3+)/Li(+) ions in Ca1.65Sr0.35SiO4 were analyzed based on a comparison of the unit-cell volumes and the designed chemical compositions of undoped isostructural compounds Ca(2–x)Sr(x)SiO4 (x = 0.25, 0.35, 0.45, 0.55 and 0.65). Ce(3+)/Li(+) singly activated Ca1.65Sr0.35SiO4 phosphors exhibit strong absorption in the range of 250–450 nm and a blue emission peak centered at about 465 nm. When Eu(2+) ions are codoped, the emission colors of Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphors under the irradiation of 365 nm can be finely tuned from blue to green through the energy transfer from Ce(3+) to Eu(2+). The involved energy-transfer process between Ce(3+) and Eu(2+) and the corresponding mechanism are discussed in detail. The reported Ca1.65Sr0.35SiO4:Ce(3+)/Li(+),Eu(2+) phosphor might be a candidate for color-tunable blue-green components in the fabrication of near-ultraviolet-pumped white-light-emitting diodes (WLEDs). PMID:26062769

  8. The Calcilytic Agent NPS 2143 Rectifies Hypocalcemia in a Mouse Model With an Activating Calcium-Sensing Receptor (CaSR) Mutation: Relevance to Autosomal Dominant Hypocalcemia Type 1 (ADH1)

    PubMed Central

    Hannan, Fadil M.; Walls, Gerard V.; Babinsky, Valerie N.; Nesbit, M. Andrew; Kallay, Enikö; Hough, Tertius A.; Fraser, William D.; Cox, Roger D.; Hu, Jianxin; Spiegel, Allen M.

    2015-01-01

    Autosomal dominant hypocalcemia type 1 (ADH1) is caused by germline gain-of-function mutations of the calcium-sensing receptor (CaSR) and may lead to symptomatic hypocalcemia, inappropriately low serum PTH concentrations and hypercalciuria. Negative allosteric CaSR modulators, known as calcilytics, have been shown to normalize the gain-of-function associated with ADH-causing CaSR mutations in vitro and represent a potential targeted therapy for ADH1. However, the effectiveness of calcilytic drugs for the treatment of ADH1-associated hypocalcemia remains to be established. We have investigated NPS 2143, a calcilytic compound, for the treatment of ADH1 by in vitro and in vivo studies involving a mouse model, known as Nuf, which harbors a gain-of-function CaSR mutation, Leu723Gln. Wild-type (Leu723) and Nuf mutant (Gln723) CaSRs were expressed in HEK293 cells, and the effect of NPS 2143 on their intracellular calcium responses was determined by flow cytometry. NPS 2143 was also administered as a single ip bolus to wild-type and Nuf mice and plasma concentrations of calcium and PTH, and urinary calcium excretion measured. In vitro administration of NPS 2143 decreased the intracellular calcium responses of HEK293 cells expressing the mutant Gln723 CaSR in a dose-dependent manner, thereby rectifying the gain-of-function associated with the Nuf mouse CaSR mutation. Intraperitoneal injection of NPS 2143 in Nuf mice led to significant increases in plasma calcium and PTH without elevating urinary calcium excretion. These studies of a mouse model with an activating CaSR mutation demonstrate NPS 2143 to normalize the gain-of-function causing ADH1 and improve the hypocalcemia associated with this disorder. PMID:26052899

  9. Concurrent Sr/Ca Ratios and Bomb Test 14C Records from a Porites evermanni Colony on Kure Atoll: SST, Climate Change, Ocean Circulation and Management Applications

    NASA Astrophysics Data System (ADS)

    Covarrubias, S.; Potts, D.; Siciliano, D.; Andrews, A.; Franks, R.

    2013-12-01

    Coral reefs near their latitudinal and ecological limits may be affected disproportionately by global climate changes, especially by changing sea surface temperatures (SST's). One such reef is Kure Atoll, the northernmost reef in the Hawaiian chain. Kure Atoll experiences dramatic temperature and seasonal differences throughout the year. Tracking these fluctuations is important for understanding recent physical forces affecting coral growth in such marginal reefs, and for predicting likely responses to future climate and oceanic changes. We used Sr/Ca ratios of a 50cm Porites evermanni coral core collected in Kure (September 2002) as a SST proxy for reconstructing a temperature timescale spanning the length of the core (~62 years). After cutting a 5 mm thick slab through the center growth axis and X-raying it to identify annual density banding, we extracted 4 equally-spaced samples from each annual increment to quantify, seasonal, inter-annual, and decadal SST patterns. We measured Sr and Ca concentrations by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). We then converted Sr/Ca ratios (mmol/mol) to SST using published equations, and calibrated the more recent SST estimates against satellite-based SST imagery and instrumental records from Midway Atoll (ca. 90 km to SE). We coupled the ICP-OES data with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) scans along the core to provide higher temporal resolution for interpreting intra-seasonal and inter-seasonal trends. Higher resolution of temperature dating can help us interpret strong inter-seasonal changes not readily seen with low resolution measurements, giving us the ability to track temperature anomalies at interannual and decadal timescales, such as El Niño/Southern Oscillation or La Niña/North Pacific Decadal Oscillation. Further, the SST signature from the Sr/Ca analyses are being used in conjunction with bomb radiocarbon signals in order to establish a complete timeline of when carbon isotope spikes appear in this region from large scale atomic testing. Changes in 14C along the length of our core have important implications for understanding regional oceanic circulation, and for the life history age validation of marine organisms, including long-lived fishes whose calcareous otoliths retain a 14C signal. These results have direct application for improved management of commercially important reef and bottom fishes of Hawaii. By tracing the bomb 14C signal in the otolith (ear bone) of regional fishes, important population parameters can be validated (e.g. age of maturity and longevity). At present, the bomb 14C record is incomplete for the Hawaiian Archipelago, but the work presented will fill the void.

  10. Effects on structural, optical, and magnetic properties of pure and Sr-substituted MgFe2O4 nanoparticles at different calcination temperatures

    NASA Astrophysics Data System (ADS)

    Loganathan, A.; Kumar, K.

    2015-07-01

    In the present work, pure and Sr2+ ions substituted Mg ferrite nanoparticles (NPs) had been prepared by co-precipitation method and their structural, optical, and magnetic properties at different calcination temperatures were studied. On this purpose, thermo gravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy, UV-Visible diffused reflectance spectroscopy, impedance spectroscopy, and vibrating sample magnetometer were carried out. The exo- and endothermic processes of synthesized precursors were investigated by TG-DTA measurements. The structural properties of the obtained products were examined by XRD analysis and show that the synthesized NPs are in the cubic spinel structure. The existence of two bands around 578-583 and 430-436 cm-1 in FT-IR spectrum also confirmed the formation of spinel-structured ferrite NPs. The lattice constants and particle size are estimated using XRD data and found to be strongly dependent on calcination temperatures. The optical, electrical, and magnetic properties of ferrite compositions also investigated and found to be strongly dependant on calcination temperatures.

  11. Dielectric properties and substitution mechanism of samarium-doped Ba{sub 0.68}Sr{sub 0.32}TiO{sub 3} ceramics

    SciTech Connect

    Li Yuanliang Qu Yuanfang

    2009-01-08

    Ba{sub 0.68}Sr{sub 0.32}TiO{sub 3} ceramics of perovskite structure are prepared by solid state reaction method with addition of x mol% Sm{sub 2}O{sub 3}, and their dielectric properties are investigated. It is found that, integrating with the lattice parameters and tolerance factor t, there is an alternation of substitution preference of Sm{sup 3+} for the host cations in perovskite lattice. Owing to the replacement of Sm{sup 3+} ions for Ba{sup 2+} ions in the A site, T{sub c} rises with the increase of Sm{sub 2}O{sub 3} doping when the doping content is below 0.1 mol%; meanwhile, when the content is more than 0.1 mol%, Sm{sup 3+} ions tend to occupy the B-site, causing a drop of T{sub c}. Owing to the modifications of Sm{sup 3+} doping, dielectric constant, dissipation factor and temperature stability of dissipation factor are influenced remarkably, making it a superior candidate for environment-friendly applications. Moreover, the creation of oxygen vacancies controls the dielectric constant when the addition is above 0.1 mol%, so the dielectric constant decreases with increasing of samarium.

  12. Surface Topography on Epitaxial HoBa2Cu3O7-? and Bi2Sr2CaCu2O8+? Thin Films

    NASA Astrophysics Data System (ADS)

    Lopera, W.; Giratá, D.; Pérez, F.; Castro, L. F.; Baca, E.; Prieto, P.; Mendoza, A.

    Surface topography on epitaxial HoBa2Cu3O7-? (HBCO) and Bi2Sr2CaCu2O8+? (BSCCO) thin films analysis by using the atomic force microscopy (AFM) technique was carried out. The films were deposited in situ on SrTiO3 substrates with thicknesses ranging from 100 to 300 nm by a high-pressure sputtering process. Chemical etching with a nonaqueous solution of Br-ethanol was used to modify the surface of the samples. HBCO films showed spiral grains, while BSCCO samples exhibited a terraced growth. Etching with Br-ethanol has different effects on HBCO and BSCCO. In HBCO, etching produces clean surfaces with light changes on the surface morphology, whereas in BSCCO it conduces to strong changes in the structure and the roughness of the film surface.

  13. Effect of Bi Substitution on Microstructure and Thermoelectric Properties of Polycrystalline [Ca2CoO3] pCoO2

    NASA Astrophysics Data System (ADS)

    Mikami, Masashi; Ando, Naoko; Guilmeau, Emmanuel; Funahashi, Ryoji

    2006-05-01

    Partially Bi-substituted [Ca2CoO3] pCoO2 ceramics were synthesized using a hot-forging technique. Then, the effects of Bi-substitution on microstructure and thermoelectric properties were evaluated. The average grain size of the precursor powder prepared by a solid-state reaction increased concomitant with the increase in Bi content. Furthermore, the electrical resistivity (?) of the hot-forged sample was decreased accordingly. Seebeck coefficient (S) was increased slightly by Bi-substitution and was less affected by grain size. Therefore, power factor (\\mathit{PF}=S2/?) was improved. On the other hand, the ? of the hot-forged sample was reduced using a large-grained precursor powder prepared by a solution growth method. Different from the case of the former samples made from as-sintered powder, the ? of the sample made from large-grained powder was increased slightly with the increase in Bi content. These results indicate that the main advantage of Bi-substitution for the decrease in the ? of the hot-forged sample is the enhanced grain growth during the heat treatment processes.

  14. Phase stability in the systems AeAl(2-x)Mgx (Ae = Ca, Sr, Ba): electron concentration and size controlled variations on the laves phase structural theme.

    PubMed

    Amerioun, Shahrad; Yokosawa, Tadahiro; Lidin, Sven; Häussermann, Ulrich

    2004-07-26

    The systems AeAl(2-x)Mgx (Ae = Ca, Sr, Ba) display electron concentration induced Laves phase structural changes. However, the complete sequence MgCu2 --> MgNi2 --> MgZn2 with increasing x (decreasing electron count) is only observed for Ae = Ca. Compounds SrAl(2-x)Mgx (0 < x < or = 2) and BaAl(2-x)Mgx (x = 0.85 and 2.0) were synthesized and structurally characterized by X-ray diffraction experiments. For the Sr system the structural sequence CeCu2 --> MgNi2 --> MgZn2 occurs with increasing Mg content x. Thus, larger Sr does not allow the realization of the MgCu2 structure at low x. For Ae = Ba a binary compound BaAl2 does not exist, but more Ba-rich Ba7Al13 forms. The reinvestigation of the crystal structure of Ba7Al13 by selected area and convergent beam electron diffraction in a transmission electron microscope revealed a superstructure, which subsequently could be refined from single X-ray diffraction data. The formula unit of the superstructure is Ba21Al40 (space group P31m, Z = 1, a = 10.568(1) angstroms, c = 17.205(6) angstroms). In Ba21Al40 a size match problem between Ba and Al present in Ba7Al13 is resolved. The structure of Ba7Al13 (Ba21Al40) can be considered as a Ba excess variant of the hexagonal MgNi2 Laves phase type structure. An incommensurately modulated variant of the MgNi2 structure is obtained for phases BaAl(2-x)Mgx with x = 0.8-1. At even higher Mg concentrations a structural change to the proper MgZn2 type structure takes place. PMID:15257605

  15. High strength kiloampere Bi2Sr2CaCu2Ox cables for high-field magnet applications

    NASA Astrophysics Data System (ADS)

    Shen, Tengming; Li, Pei; Jiang, Jianyi; Cooley, Lance; Tompkins, John; McRae, Dustin; Walsh, Robert

    2015-06-01

    Multifilamentary Ag-sheathed Bi2Sr2CaCu2Ox (Bi-2212) wire can carry sufficient critical current density Jc for the development of powerful superconducting magnets. However, the range of its applications is limited by the low mechanical strength of the Ag/Bi-2212 strand. A potential solution is to cable Ag/Bi-2212 wire with high-strength materials that are compatible with the Bi-2212 heat treatment in an oxygen atmosphere. Past attempts have not always been successful, because the high-strength materials reacted with Bi-2212 wires, significantly reducing their Jc. We examined the nature of reactions occurring when Ag/Bi-2212 wires are heat-treated in direct contact with several commonly used high-strength alloys and a new Fe-Cr-Al alloy. INCONEL X750 and INCONEL 600 resulted in significant Jc loss, whereas Ni80-Cr caused little or no Jc loss; however, all of them formed chromium oxide that subsequently reacted with silver, creating cracks in the silver sheath. We found that Fe-Cr-Al did not show significant reactions with Ag/Bi-2212 strands. Scanning electron microscopy (SEM) and energy dispersive x-ray (EDS) examinations revealed that the Fe-Cr-Al alloy benefits from the formation of a uniform, crack-free, continuous alumina layer on its surface that does not react with Ag and that helps minimize the Cu loss found with INCONEL X750 and INCONEL 600. We fabricated prototype 6-around-1 cables with six Bi-2212 strands twisted and transposed around an Fe-Cr-Al alloy core coated with TiO2. After standard 1 bar melt processing, the cable retained 100% of the total current-carrying capability of its strands, and, after a 10 bar overpressure processing, the cable reached a total current of 1025 A at 4.2 K and 10 T. Tensile tests showed that Fe-Cr-Al becomes brittle after being cooled to 4.2 K, whereas INCONEL X750 remains ductile and retains a modulus of 183 GPa. We proposed new cable designs that take advantage of the chemical compatibility of Fe-Cr-Al and high strength of INCONEL X750 for various high-field magnet applications.

  16. The effect of Ca-substitution in La-site on the magnetic properties of La{sub 2}CoMnO{sub 6}

    SciTech Connect

    Li, Qiu-hang; Li, Na; Hu, Jian-zhong; Han, Qi; Ma, Qing-shan; Ge, Lei; Xiao, Biao; Xu, Ming-xiang

    2014-07-21

    Double perovskite La{sub 2-x}Ca{sub x}CoMnO{sub 6} (x?=?0, 0.1, 0.2, 0.5) ceramics samples were synthesized by the standard solid-state reaction method. The crystal structures have been confirmed to be monoclinic perovskite structure with space group of P2{sub 1}/n at room temperature by the powder x-ray diffraction (Cu-K?). The grains of the samples are relatively dense and distribute in random directions from the scanning electron microscope patterns. Holes are doped into La{sub 2}CoMnO{sub 6} with the substitution of the Ca{sup 2+} ions in La-site, and further lead to the valences of Mn ions and Co ions transforming from Mn{sup 4+} and Co{sup 2+} to Mn{sup 3+} and Co{sup 3+}, respectively. Ferromagnetic coupling of Mn{sup 4+}-O{sup 2–}-Co{sup 2+} and antiferromagnetic coupling of Mn{sup 3+}-O{sup 2–}-Co{sup 3+} are coexistent in La{sub 2-x}Ca{sub x}CoMnO{sub 6} system, which correspond to two transitions existed in field-cooling magnetization versus temperature curves. Curie temperature of La{sub 2-x}Ca{sub x}CoMnO{sub 6} system decreases with the increasing of Ca-substitution amount. The coexistence of different magnetic phases leads to the exchange bias effect.

  17. Substitutional disorder in Sr2-yEuyB2-2xSi2+3xAl2-xN8+x (x ? 0.12, y ? 0.10).

    PubMed

    Funahashi, Shiro; Michiue, Yuichi; Takeda, Takashi; Xie, Rong-Jun; Hirosaki, Naoto

    2014-05-01

    A novel nitride, Sr2-yEuyB2-2xSi2+3xAl2-xN8+x (x ? 0.12, y ? 0.10) (distrontium europium diboron disilicon dialuminium octanitride), with the space group P62c, was synthesized from Sr3N2, EuN, Si3N4, AlN and BN under nitrogen gas pressure. The structure consists of a host framework with Sr/Eu atoms accommodated in the cavities. The host framework is constructed by the linkage of MN4 tetrahedra (M = Si, Al) and BN3 triangles, and contains substitutional disorder described by the alternative occupation of B2 or Si2N on the (0, 0, z) axis. The B2:Si2N ratio contained in an entire crystal is about 9:1. PMID:24816012

  18. Synthesis of homogeneous Ca{sub 0.5}Sr{sub 0.5}FeO{sub 2.5+{delta}} compound using a mirror furnace method

    SciTech Connect

    Mahboub, M.S.; Zeroual, S.; Laboratoire de Cristallographie, Departement de Physique, Faculte des Sciences Exactes, Universite Mentouri, Constantine 25000 ; Boudjada, A.

    2012-02-15

    Graphical abstract: X-ray diffraction pattern indexing of Ca{sub 0.5}Sr{sub 0.5}FeO{sub 2.5+{delta}} powder sample obtained by mirror furnace method after thermal treatment. Highlights: Black-Right-Pointing-Pointer A homogenous compound Ca{sub 0.5}Sr{sub 0.5}FeO{sub 2.5+{delta}} has been synthesized for the first time by a mirror furnace method. Black-Right-Pointing-Pointer Ca{sub 0.5}Sr{sub 0.5}FeO{sub 2.5+{delta}} powder sample is perfectly homogenous, confirmed by X-ray diffraction, Raman spectroscopy and EDS technique. Black-Right-Pointing-Pointer The thermal treatment of Ca{sub 0.5}Sr{sub 0.5}FeO{sub 2.5+{delta}} powder sample can increase their average grain sizes. -- Abstract: A new synthesis method using melting zone technique via the double mirror furnace around 1600 Degree-Sign C is used to obtain homogenous brownmillerite compounds Ca{sub 1-x}Sr{sub x}FeO{sub 2.5+{delta}} in the range 0.3 {<=} x {<=} 0.7. These compounds play important role in understanding the mystery of the oxygen diffusion in the perovskite-related oxides. We have successfully solved the miscibility gap problem by synthesizing a good quality of homogenous powder samples of Ca{sub 0.5}Sr{sub 0.5}FeO{sub 2.5+{delta}} compound. Our result was confirmed by X-rays diffraction, Raman spectroscopy and energy dispersive spectroscopy analysis. Thermal treatment was also applied until 800 Degree-Sign C under vacuum to confirm again the homogeneity of powder samples, improve its quality and show that no decomposition or return to form Ca- and Sr-enriched microdomains takes place as a result of phase separation.

  19. Strontium-Substituted Hydroxyapatite Thin Films Grown by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Capuccini, C.; Sima, F.; Axente, E.; Boanini, E.; Gazzano, M.; Bigi, A.; Mihailescu, I. N.

    Strontium substitution for calcium in the hydroxyapatite structure has lately attracted growing interest due to its beneficial effects on both bone formation and prevention of bone resorption. Coating Ti implants with Sr2+ substituted hydroxyapatite is expected to enhance the bioactivity of the surface and stimulate bone apposition. To this end, we deposited thin films of hydroxyapatite with different substitutions of Sr2+ for Ca2+ on Ti substrates by Pulsed Laser Deposition (PLD). Solid solutions of Sr-Ca hydroxyapatites [Ca10-xSrxHA(x = 0-1)] were prepared by direct synthesis in aqueous medium at 90°C. Sr2+ insertion led to a decrease of crystallinity degree, which accounted for the simultaneous reduction of the crystal dimensions. For PLD experiments, we used an UV excimer (KrF*) laser source (248 nm, ˜7.4 ns) operating at a repetition rate of 2 Hz. The fluence during target irradiation was set at 2.4 J/cm2, and substrate temperature kept at 400°C. The depositions were performed from HA at different degrees of Sr2+ substitution for Ca2+ (x = 0; 0.1; 0.5; 1). All structures were post-treated in a H2O enriched atmosphere for 6 h. The results of structural and morphological characterizations carried out on the obtained structures indicated that the coatings, which adhered well to the substrates, were made of crystalline HA and contained strontium with a (Ca + Sr)/P molar ratio close to the stoichiometric value of HA.

  20. Rb-Sr, Sm-Nd, K-Ca, O, and H isotopic study of Cretaceous-Tertiary boundary sediments, Caravaca, Spain: evidence for an oceanic impact site

    USGS Publications Warehouse

    DePaolo, D.J.; Kyte, F.T.; Marshall, B.D.; O'Neil, J.R.; Smit, J.

    1983-01-01

    Isotopic ratios and trace element abundances were measured on samples of Ir-enriched clay at the Cretaceous-Tertiary boundary, and in carbonate and marl from 5 cm below and 3 cm above the boundary. Samples were leached with acetic acid to remove carbonate, and with hydrochloric acid. Leachates and residues were measured. The Sr, Nd, O and H isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials. The data indicate that most of the clay material was derived from a terrestrial source with relatively low 87Sr/86Sr and high 143Nd/144Nd ratios. The ??18O data suggest that the detritus has been modified by submarine weathering. K-Ca and Rb-Sr systematics, as well as O isotope ratios of K-feldspar spherules within the boundary clay, suggest that they are predominantly authigenic and may have formed after the time of deposition. However, Sm-Nd and Rb-Sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus. The isotopic evidence for foreign terrestrial detritus in the boundary clay, the low rare earth element concentrations and high Ni concentration, support the hypothesis of a terminal Cretaceous asteroidal impact that produced a global layer of fallout. The data are most easily explained if the impact site was on oceanic crust rather than continental crust, and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere (>3 km). This would probably require a single large impactor. ?? 1983.

  1. Superconducting Bi1.5Pb0.5Sr2Ca2Cu3O(x) ceramics by rapid melt quenching and glass crystallization

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.

    1989-01-01

    A glass of nominal Bi(1.5)Pb(0.5)Sr2Ca2Cu3O(x) composition, prepared by rapid quenching of the melt, showed a glass transition temperature of 383 C, crystallization temperature of 446 C, melting temperature of 855 C, and bulk density of 5.69 g/cu cm in air. The activation energy for crystallization of the glass was estimated to be 292kJ/mol from non-isothermal DSC. On heating in oxygen, the glass showed a slow and continuous weight gain starting at approximately 530 C which reached a plateau at approximately 820 C. The weight gained during heating was retained on cooling to ambient conditions indicating an irreversible oxidation step. The influence of annealing conditions on the formation of various phases in the glass has been investigated. The Bi(2)Sr(2)Ca(0)Cu(1)O(6) phase crystallized out first followed by formation of other phases at higher temperatures. The high-T(sub c) phase, isostructural with Bi(2)Sr(2)Ca(2)Cu(3)O(10) was not detected below 840 C, but its fraction increased with the annealing time at 840 C. A sample annealed at 840 C for 243h in air and furnace cooled showed the highest T(sub c)(R=0) of 107.2K and a narrow transition width, delta T(sub c)(10 to 90 percent), of approximately 2 K. The high T(sub c) phase does not seem to crystallize out directly from the glass but is rather produced at high temperature by reaction between the phases formed at lower temperatures. The kinetics of 110K phase formation was sluggish. It appears that the presence of lead helps in the formation and/or stabilization of the 110 K phase.

  2. Structural evolution of (Ca{sub 0.35}Sr{sub 0.65})TiO{sub 3} perovskite at high pressures

    SciTech Connect

    Carpenter, Michael A. Rios, Susana; Sondergeld, Peter; Crichton, Wilson; Bouvier, Pierre

    2007-01-15

    Lattice parameters of a synthetic powder sample of Ca{sub 0.35}Sr{sub 0.65}TiO{sub 3} perovskite have been determined by the method of Le Bail refinement, using synchrotron X-ray diffraction patterns collected at pressures up to 15.5 GPa with a membrane-driven diamond anvil cell. At ambient conditions, diffraction data were consistent with the I4/mcm structure reported previously in the literature for the same composition. Diffraction data collected at high pressures were consistent with tetragonal (or, at least, pseudo-tetragonal) lattice geometry, and no evidence was found for the development of any of the orthorhombic structures identified in other studies of (Ca, Sr)TiO{sub 3} perovskites. Additional weak reflections, which could not be accounted for by the normal I4/mcm perovskite structure, were detected in diffraction patterns collected at pressures of 0.9-2.5 GPa, and above {approx}13.5 GPa, however. Small anomalies in the evolution of unit cell volume and tetragonal strain were observed near 3 GPa, coinciding approximately with breaks in slope with increasing pressure of bulk and shear moduli for a sample with the same composition which had previously been reported. The anomalies could be due either to new tetragonal{r_reversible}tetragonal/pseudo-tetragonal phase transitions or to subtle changes in compression mechanism of the tetragonal perovskite structure. - Graphical abstract: Variation of the tetragonal strain, e {sub t} {sub z} , as a function of pressure for Ca{sub 0.35}Sr{sub 0.65}TiO{sub 3}, showing a break in slope in the vicinity of 3-4 GPa.

  3. Preparation and formation mechanism of three-dimensionally ordered macroporous (3DOM) MgO, MgSO 4, CaCO 3, and SrCO 3, and photonic stop band properties of 3DOM CaCO 3

    NASA Astrophysics Data System (ADS)

    Sadakane, Masahiro; Kato, Rika; Murayama, Toru; Ueda, Wataru

    2011-08-01

    Three-dimensionally ordered macroporous (3DOM) magnesium (Mg) oxide (MgO), MgSO 4, calcium (Ca) carbonate (CaCO 3), and strontium (Sr) carbonate (SrCO 3) were prepared using a colloidal crystal of polymer spheres as a template. Ethanol or ethanol-water solution of metal salts (acetate or nitrate) and citric acid was infiltrated into the void of the colloidal crystal template of a monodispersed poly(methyl methacrylate) (PMMA) sphere. Heating of this PMMA-metal salt-citric acid composite produced the desired well-ordered 3DOM materials with a high pore fraction, which was confirmed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ultraviolet-visible (UV-vis) diffuse reflectance spectra. The presence of citric acid is crucial for production of the 3DOM structures. Reaction of citric acid with metal salt produces metal citrate solid in the void of PMMA spheres, which is necessary to maintain the 3DOM structure during the calcination process. 3DOM CaCO 3 shows opalescent colors because of it's photonic stop band properties.

  4. Substitution studies on copper oxide systems

    SciTech Connect

    Grabowski, N.A.

    1991-01-01

    Four different metal oxide systems having the formulas La[sub 2]CuO[sub 4], Ba[sub 2]YCu[sub 3]O[sub 6+x], Ca[sub 0.85]Sr[sub 0.15]CuO[sub 2], and Cu[sub 4]O[sub 3] were prepared at ambient or high pressure using solid state reactions of the appropriate binary oxides. Substitution reactions were performed on these systems in order to examine the structural effects. These substituted products were also examined for superconducting behavior. The critical temperature and magnetic susceptibility were determined for those compounds exhibiting superconducting properties. Fluorine substitution for oxygen in the lanthanum-copper-oxide system produced a superconductor with a critical temperature of 37 K and the formula: La[sub 2]Cu[sup 2+] [sup 1[minus]y]Cu[sup 3+[sub y

  5. Understanding Processing, Microstructure and Transport Relationships of Bi2Sr2CaCu2Ox/Ag Round Wires

    NASA Astrophysics Data System (ADS)

    Naderi, Golsa

    Superconducting magnets generating magnetic fields above 25 T are needed for many scientific applications. Due to fundamental limitations to NbTi and Nb3Sn, such high-field superconducting magnets require alternative high-field conductors. One candidate conductor is round wire composites of Bi2Sr2CaCu2Ox sheathed in an Ag-alloy matrix (Bi2212/Ag). The performance of such wires is sensitive to the heat treatment, so improvements in the critical current density (Jc) require a thorough understanding of the processing-structureproperties relationships. Due to the complex microstructure-transport relationships, their performance is far from optimized, and the potential for further increase in Jc remains. In this research a new heat treatment approach, saw-tooth processing (STP) is introduced based upon previous results showing that Bi2212 nucleation is site-saturation limited. STP increases Jc by 120% and 70% relative to partial-melt processing at 5 T and self-field respectively. The effects of STP heat treatment parameters on the microstructure and transport properties are discussed. It is shown that wires with the highest transport critical current densities primarily have filaments with two types of microstructures, one comprised primarily highly textured Bi2212 grains, and another with a noticeable amount of Bi2Sr2CuOX with the Bi2212. After processing, multifilamentary Bi2212 round wires have complex microstructures. In melt processed Bi2212/Ag wires the primary impurity is Bi2Sr 2CuOx (Bi2201), which forms as mesoscopic grains and nanoscopic intergrowths. Microstructureproperties relationship studies are performed based on the hypothesis that Bi2201 plays critical roles in transport depending on the micron-size length scale. Mesoscopic microstructures are analyzed quantitatively using a statistical approach in which filaments are categorized based on the predominant phases observed by scanning electron microscope (SEM). A Matlab program is created to analyze the SEM micrographs and categorize over 100 filaments within each image. The majority of filaments (78% of all filaments classified) are either predominantly Bi2212 or containing-large-Bi2201 grains. Jc is directly proportional to the percentage of "predominatly-Bi2212" filaments. Although typically 70-90% of the containing-large-Bi2201 filament cross-sections is actually Bi2212 phase, Jc is inversely proportional to the percentage of this type of filament. To study the impact of nanoscale Bi2201 intergrowths on the superconducting properties, Bi2212 grains are extracted from filaments with and without significant Bi2201 grains present. By relating scanning transmission electron microscopy results to the Bi2212 coherence length, anisotropic magnetization behavior and magnetic-field dependent transport the effects of Bi2201 intergrowths on c-axis transport and magnetic flux pinning is studied. Wide Bi2201 (15-25 nm), intergrowths are barrier to c-axis transport within Bi2212 grains, whereas narrow half (1.3 nm wide),- and full-cell (2.5 nm wide) Bi2201 intergrowths are not detrimental to c-axis transport and are likely magnetic flux pinning centers. Microstructural, magnetization and transport studies designate effective contribution of c-axis transport in Bi2212/Ag multifilamentary wires; because the continuous favorable a--b plane current path is obstructed randomly. In addition to conventionally-processed wires, 100 atm over pressured partial melt processed wires (OP-PMP) are studied on different length scales. OP causes grain growth in the preannealing, increases the peritectic melting temperature in the partial melt, improves oxygen uptake during solidification, and enhances the grain connectivity in sintering. The increase in transport of OP-PMP wire is related to increase in filament density. Yet OP-PMP wire shows higher area fraction of filaments with large Bi2201 grains. To even further improve the transport, optimization of OP-PMP is essential. This study confirms that after porosity, Bi2201 grains has the greatest negative impact on Bi2212 wires

  6. Charge-coupled substituted garnets (Y 3–x Ca 0.5x M 0.5x )Fe?O?? (M = Ce, Th): Structure and stability as crystalline nuclear waste forms

    DOE PAGESBeta

    Guo, Xiaofeng; Kukkadapu, Ravi K.; Lanzirotti, Antonio; Newville, Matthew; Engelhard, Mark H.; Sutton, Stephen R.; Navrotsky, Alexandra

    2015-04-20

    The garnet structure has been proposed as a potential crystalline nuclear waste form for accommodation of actinide elements, especially uranium (U). In this study, yttrium iron garnet (YIG) as a model garnet host was studied for the incorporation of U analogs, cerium (Ce) and thorium (Th), incorporated by a charge-coupled substitution with calcium (Ca) for yttrium (Y) in YIG, namely, 2Y³? = Ca²? + M??, where M?? = Ce?? or Th??. Single-phase garnets Y3–xCa0.5xM0.5xFe?O?? (x = 0.1–0.7) were synthesized by the citrate–nitrate combustion method. Ce was confirmed to be tetravalent by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. X-ray diffractionmore »and ??Fe–Mössbauer spectroscopy indicated that M?? and Ca²? cations are restricted to the c site, and the local environments of both the tetrahedral and the octahedral Fe³? are systematically affected by the extent of substitution. The charge-coupled substitution has advantages in incorporating Ce/Th and in stabilizing the substituted phases compared to a single substitution strategy. Enthalpies of formation of garnets were obtained by high-temperature oxide melt solution calorimetry, and the enthalpies of substitution of Ce and Th were determined. The thermodynamic analysis demonstrates that the substituted garnets are entropically rather than energetically stabilized. This suggests that such garnets may form and persist in repositories at high temperature but might decompose near room temperature.« less

  7. A search for disorder in the spin glass double perovskites Sr(2)CaReO(6) and Sr(2)MgReO(6) using neutron diffraction and neutron pair distribution function analysis.

    PubMed

    Greedan, J E; Derakhshan, Shahab; Ramezanipour, F; Siewenie, J; Proffen, Th

    2011-04-27

    The geometrically frustrated, B-site ordered, S = 1/2, double perovskites Sr(2)CaReO(6) and Sr(2)MgReO(6), which show spin frozen magnetic ground states, have been investigated using neutron powder diffraction (ND) and neutron pair distribution function (NPDF) analysis in a search for evidence for atomic positional disorder. For both materials, data were taken above and below the spin freezing temperatures of ? 14 K and ? 45 K for the CaRe and MgRe phases, respectively. In both cases the fully B-site ordered model was in excellent agreement with the data, both ND and NPDF, at all temperatures studied. Thus, the structure of these materials, from the average and the local perspectives, is very well described by the fully B-site ordered model, which raises questions concerning the origin of the spin glass ground state. These results are compared with those for the spin glass pyrochlore Y(2)Mo(2)O(7) and other B-site ordered double perovskites. PMID:21471633

  8. Spectral Evolution in (Ca,Sr)RuO[sub 3] near the Mott-Hubbard Transition

    SciTech Connect

    Ahn, J.S.; Bak, J.; Choi, H.S.; Noh, T.W. ); Han, J.E. ); Bang, Y. ); Cho, J.H. ); Jia, Q.X. )

    1999-06-01

    We investigated optical properties of (Ca,Sr)RuO [sub 3] films on the borderline of a metal-insulator transition. Our results show all of the predicted characteristics for a metallic Mott-Hubbard system, including (i) a mass enhancement in dc limit, (ii) a U/2 excitation, and (iii) a U excitation. Also, self-consistency is exploited within the Gutzwiller-Brinkman-Rice picture for the Mott transition. Our finding displays that electron correlation should be important even in 4d materials. However, low frequency behaviors of electrodynamic quantities suggest extra scattering mechanisms in addition to the Mott-Hubbard correlation. [copyright] [ital 1999] [ital The American Physical Society

  9. Spectral Evolution in (Ca,Sr)RuO{sub 3} near the Mott-Hubbard Transition

    SciTech Connect

    Ahn, J.S.; Bak, J.; Choi, H.S.; Noh, T.W.; Han, J.E.; Bang, Y.; Cho, J.H.; Jia, Q.X.

    1999-06-01

    We investigated optical properties of (Ca,Sr)RuO {sub 3} films on the borderline of a metal-insulator transition. Our results show all of the predicted characteristics for a metallic Mott-Hubbard system, including (i) a mass enhancement in dc limit, (ii) a U/2 excitation, and (iii) a U excitation. Also, self-consistency is exploited within the Gutzwiller-Brinkman-Rice picture for the Mott transition. Our finding displays that electron correlation should be important even in 4d materials. However, low frequency behaviors of electrodynamic quantities suggest extra scattering mechanisms in addition to the Mott-Hubbard correlation. {copyright} {ital 1999} {ital The American Physical Society }

  10. High critical current densities in (Tl0.5Pb0.5)Sr2-xBaxCa2Cu3O9-?

    NASA Astrophysics Data System (ADS)

    Pugnat, P.; Lebbou, K.; Cohen-Adad, M. T.; Jorda, J. L.; Couach, M.; Fillion, G.

    1996-03-01

    A high quality of (Tl0.5Pb0.5)Sr1.8Ba0.2Ca2Cu3O9-? ceramic with Tc?120 K has been prepared and studied by magnetic measurements. The field and temperature dependence of the intragranular critical current are deduced from the Bean model. For this single (insulating) Tl-O layer material, Jc has a value of the order of 2.105 A/cm2 at 80 K and in a field of 1 T. The mean irreversible line determined from hysteresis loops is also compared to the ones obtained from ac susceptibility measurements.

  11. The features of structural transformations in lanthanum manganites La{sub 1?x}A{sub x}MnO{sub 3+?} (A = Ca, Sr, Ba)

    SciTech Connect

    Sedykh, Vera D.

    2014-10-27

    In this work, the effect of the ionic radius and concentration of a doping element on the features of the structural transformations in polycrystalline lanthanum manganites, La{sub 1?x}A{sub x}MnO{sub 3+?} (A = Ca, Sr, Ba), has been studied by Mössbauer spectroscopy and X-ray diffraction analysis. For Mössbauer investigations, a small amount of {sup 57}Fe (2 at%) Mössbauer isotope was introduced into the samples. It follows from the analysis of the obtained data that both common features of the structural transformations and differences between them exist in lanthanum manganites depending on ionic radius and concentration of a doping element.

  12. Sequestration of Sr-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of a Ca-Citrate-Phosphate Solution

    SciTech Connect

    Szecsody, James E.; Rockhold, Mark L.; Oostrom, Martinus; Moore, R. C.; Burns, Carolyn A.; Williams, Mark D.; Zhong, Lirong; Fruchter, Jonathan S.; McKinley, James P.; Vermeul, Vincent R.; Covert, Matthew A.; Wietsma, Thomas W.; Breshears, Andrew T.; Garcia, Ben J.

    2009-03-01

    The objective of this project is to develop a method to emplace apatite precipitate in the 100N vadose zone, which results in sorption and ultimately incorporation of Sr-90 into the apatite structure. The Ca-citrate-PO4 solution can be infiltrated into unsaturated sediments to result in apatite precipitate to provide effective treatment of Sr-90 contamination. Microbial redistribution during solution infiltration and a high rate of citrate biodegradation for river water microbes (water used for solution infiltration) results in a relatively even spatial distribution of the citrate biodegradation rate and ultimately apatite precipitate in the sediment. Manipulation of the Ca-citrate-PO4 solution infiltration strategy can be used to result in apatite precipitate in the lower half of the vadose zone (where most of the Sr-90 is located) and within low-K layers (which are hypothesized to have higher Sr-90 concentrations). The most effective infiltration strategy to precipitate apatite at depth (and with sufficient lateral spread) was to infiltrate a high concentration solution (6 mM Ca, 15 mM citrate, 60 mM PO4) at a rapid rate (near ponded conditions), followed by rapid, then slow water infiltration. Repeated infiltration events, with sufficient time between events to allow water drainage in the sediment profile can be used to buildup the mass of apatite precipitate at greater depth. Low-K heterogeneities were effectively treated, as the higher residual water content maintained in these zones resulted in higher apatite precipitate concentration. High-K zones did not receive sufficient treatment by infiltration, although an alternative strategy of air/surfactant (foam) was demonstrated effective for targeting high-K zones. The flow rate manipulation used in this study to treat specific depths and heterogeneities are not as easy to implement at field scale due to the lack of characterization of heterogeneities and difficulty tracking the wetting front over a large subsurface area. However, the use of real-time surface and cross-borehole geophysics can be used to track the infiltrating Ca-citrate-PO4 front so some adjustments can be made in the infiltration rate to precipitate apatite in desired zones. In addition, the reactive transport code used in this study with field scale physical parameters for sediments can be used to evaluate infiltration strategies along with preliminary water infiltration tests at field scale.

  13. Unexpected behavior of diamagnetic signal in polycrystalline Bi 2Sr 2Ca 1- xY xCu 2O 8+ ?

    NASA Astrophysics Data System (ADS)

    Kim, G. C.; Kim, H.; Kim, Y. C.

    2007-07-01

    The effect of superconductivity and inhomogeneity on the phase coherence between superconducting grains for Bi 2Sr 2CaCu 2O 8+ ? (Bi-2212) is discussed. We find that in the UD regime, inhomogeneity plays a central role in establishing the phase coherence between superconducting grains. By decreasing hole concentration, p, the phase stiffness for the thermal fluctuations is suppressed, whereas the phase coherence between the superconducting grains is enhanced. In particular, the phase coherence between the superconducting grains is established almost immediately as the superconductivity for Bi-2212 with p ? 0.075 appears.

  14. Surface currents and bulk pinning in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}

    SciTech Connect

    Majer, D.; Zeldov, E.; Konczykowski, M.; Geshkenbein, V.B.; Larkin, A.I. |; Burlachkov, L.; Vinokur, V.M.; Chikumoto, N.

    1994-05-01

    The mechanisms giving rise to the irreversibility line (IL) in the phase diagram of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and the mechanism behind the second maximum in the magnetization loops were determined using a novel Hall-sensor array. The IL is caused by bulk pinning at lower temperatures and by irreversible shielding currents above 22K. The second maximum is caused by vortex lattice melting, taking place at the same local magnetic induction B{sub m} throughout the sample.

  15. Manipulation of subsurface carbon nanoparticles in Bi2Sr2CaCu2O8+? using a scanning tunneling microscope

    DOE PAGESBeta

    Stollenwerk, A. J.; Hurley, N.; Beck, B.; Spurgeon, K.; Kidd, T. E.; Gu, G.

    2015-03-19

    In this study, we present evidence that subsurface carbon nanoparticles in Bi?Sr?CaCu?O8+? can be manipulated with nanometer precision using a scanning tunneling microscope. High resolution images indicate that most of the carbon particles remain subsurface after transport observable as a local increase in height as the particle pushes up on the surface. Tunneling spectra in the vicinity of these protrusions exhibit semiconducting characteristics with a band gap of approximately 1.8 eV, indicating that the incorporation of carbon locally alters the electronic properties near the surface.

  16. The non-centrosymmetric borate oxides, MBi{sub 2}B{sub 2}O{sub 7} (M=Ca, Sr)

    SciTech Connect

    Barbier, J. . E-mail: barbier@mcmaster.ca; Cranswick, L.M.D.

    2006-12-15

    Two novel noncentrosymmetric borates oxides, MBi{sub 2}B{sub 2}O{sub 7} or MBi{sub 2}O(BO{sub 3}){sub 2} (M =Ca, Sr), have been synthesized by solid-state reactions in air at temperatures in the 600-700 {sup o}C range. r crystal structures have been determined ab initio and refined using powder neutron diffraction data. CaBi{sub 2}B{sub 2}O{sub 7} crystallizes in the orthorhombic Pna2{sub 1} space group with a=8.9371(5) A, b=5.4771(3) A, c=12.5912(7) A, Z=4, R {sub wp}=0.118, {chi} {sup 2}=2.30. SrBi{sub 2}B{sub 2}O{sub 7} crystallizes in the hexagonal P6{sub 3} space group with a=9.1404(4) A, c=13.0808(6) A, Z=6, R {sub wp}=0.115, {chi} {sup 2}=4.15. Large displacement parameters suggest the presence of disorder in SrBi{sub 2}B{sub 2}O{sub 7} as also revealed by diffuse 2xa superstructure reflections in electron diffraction patterns. Both structures are built of identical (001) neutral layers of corner-sharing BO{sub 3} triangles and MO{sub 6} trigonal prisms forming six-membered rings in which Bi{sub 2}O groups are located. Adjacent layers are stacked in a staggered configuration and connected through weak Bi-O bonds. A moderate efficiency for second harmonic generation (SHG) has been measured for a powder sample of CaBi{sub 2}B{sub 2}O{sub 7} (d {sub eff}=2d {sub eff}(KDP)). - Graphical abstract: The new borate oxides, MBi{sub 2}O(BO{sub 3}){sub 2} (M=Ca, Sr), belong to the same layer structure-type built of MO{sub 6} trigonal prisms, BO{sub 3} triangles and Bi{sub 2}O groups.

  17. Bilayer Splitting in the Electronic Structure of Heavily Overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O

    SciTech Connect

    Feng, D. L.; Armitage, N. P.; Lu, D. H.; Damascelli, A.; Hu, J. P.; Bogdanov, P.; Lanzara, A.; Ronning, F.; Shen, K. M.; Eisaki, H.

    2001-06-11

    The electronic structure of heavily overdoped Bi{sub 2}Sr {sub 2}CaCu{sub 2}O{sub 8+{delta}} is investigated by angle-resolved photoemission spectroscopy. The long-sought bilayer band splitting in this two-plane system is observed in both normal and superconducting states, which qualitatively agrees with the bilayer Hubbard model calculations. The maximum bilayer energy splitting is about 88meV for the normal state feature, while it is only about 20meV for the superconducting peak.

  18. The Phase-sensitive c-Axis Twist Experiments on Bi2Sr2CaCu2O8+? and Their Implications

    NASA Astrophysics Data System (ADS)

    Klemm, Richard A.

    2006-09-01

    There are presently three sets of c-axis twist experiments on Bi2Sr2CaCu2O8+? (Bi2212): The bicrystal experiments of Li et al., the artificial cross-whisker experiments of Takano et al., and the natural cross-whisker experiments of Latyshev et al.. We summarize these experiments and the extensive theoretical analyses of their possible implications. All three experiments can only be understood in terms of a substantial s-wave superconducting order parameter component for T ? Tc. The Li and Latyshev experiments are also consistent most other data that the c-axis tunneling is strongly incoherent.

  19. Free-standing epitaxial La{sub 1-x}(Sr,Ca){sub x}MnO{sub 3} membrane on Si for uncooled infrared microbolometer

    SciTech Connect

    Kim, J.-H.; Grishin, A.M.

    2005-07-18

    Ar ion beam etching and inductively coupled SF{sub 6} and C{sub 4}F{sub 8} plasma-etching processes have been employed to fabricate free standing membrane from the heteroepitaxial La{sub 1-x}(Sr,Ca){sub x}MnO{sub 3}(50 nm)/Bi{sub 4}Ti{sub 3}O{sub 12}(100 nm)/CeO{sub 2}(40 nm)/YSZ(30 nm) film structure pulsed laser deposited on Si(001) wafer. We demonstrate feasibility to use epitaxial colossal magnetoresistive manganite film as thermally isolated self-supporting membrane for uncooled infrared microbolometer applications.

  20. Nanoscale phase separation in deeply underdoped Bi2Sr2CuO6 +? and Ca2CuO2Cl2

    NASA Astrophysics Data System (ADS)

    Mistark, Peter; Markiewicz, Robert S.; Bansil, Arun

    2015-04-01

    We demonstrate that the tunneling spectra from deeply underdoped Bi2Sr2CuO6 +? (Bi2201) and Ca2CuO2Cl2 (CCOC) provide clear evidence for a nanoscale phase separation (NPS), which causes the gap to fill rather than close with doping. The phase separation extends from half-filling to a doping of x ˜0.09 . Assuming that the NPS is in the form of stripes, the nodal gap, which we model as a Coulomb gap, arises from impurity pinning of the charged stripes, and ultimately drives a metal-insulator transition.

  1. Nanoscale phase separation in deep underdoped Bi2Sr2CuO6+? and Ca2CuO2Cl2

    NASA Astrophysics Data System (ADS)

    Mistark, Peter; Markiewicz, Robert; Bansil, Arun

    2015-03-01

    We demonstrate that the tunneling spectra from deeply underdoped Bi2Sr2CuO6+? (Bi2201) and Ca2CuO2Cl2 (CCOC) provide clear evidence for a nanoscale phase separation (NPS), which causes the gap to fill rather than close with doping. The phase separation extends from half-filling to a doping of x ~ 0 . 09 . Assuming that the NPS is in the form of stripes, the nodal gap, which we model as a Coulomb gap, arises from impurity pinning of the charged stripes, and ultimately drives a metal-insulator transition. This work is supported by the U.S.D.O.E.

  2. A mechanism for resistive dissipation in Ag sheathed Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}

    SciTech Connect

    Suenaga, M.; Li, Q.; Sabatini, R.L.; Shibutani, K.; Hayoashi, S.; Ogawa, R.; Kawate, Y.; Motowidlo, L.

    1993-11-01

    Detailed measurements of the V-I curves for a number of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} and Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}/Ag composite tapes were made at 4.2, 27, and 64-77 K as a function of applied magnetic field as well as the angle between the tape face and the direction of applied field. Results suggest that the weak vortex-pinning strength, and the amount of the weakly coupled grain boundaries and of the non-superconducting volume are primary limiting factors for critical current densities in Bi(2212)/Ag and Bi(2223)/Ag, respectively. Furthermore, in both cases, the dissipative voltages arise from the interior of the gains.

  3. Influence of strontium on structure, sintering and biodegradation behaviour of CaO-MgO-SrO-SiO2-P2O5-CaF2 glasses

    SciTech Connect

    Goel, Ashutosh; Rajagopal, Raghu R.; Ferreira, Jose M.

    2011-11-01

    The present study investigates the influence of SrO on structure, apatite forming ability, physico-chemical degradation and sintering behaviour of melt-quenched bioactive glasses with composition: mol.% (36.07 – x) CaO – x SrO - 19.24 MgO – 5.61 P2O5 – 38.49 SiO2 – 0.59 CaF2, where x varies between 0 – 10. The detailed structural analysis of glasses has been made by infra red spectroscopy (FTIR) and magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). Silicon was predominantly present as Q2 (Si) species while phosphorus was found in orthophosphate type environment in all the investigated glasses. The apatite forming ability of glasses was investigated by immersion of glass powders in simulated body fluid (SBF) for time durations varying between 1 h – 7 days. While increasing Sr2+/Ca2+ ratio in glasses did not affect the structure of glasses significantly, their apatite forming ability was decreased considerably. Further, physico-chemical degradation of glasses has been studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris HCl and citric acid buffer and the possible implications of ion release profile from glasses in different solutions has been discussed. The addition of strontium in glasses led to a 7-fold decrease in chemical degradation of glasses in Tris-HCl. The sintering of glass powders rendered glass-ceramics (GCs) with varying degree of crystallinity and good flexural strength (98-131 MPa) where the mechanical properties depend on the nature and amount of crystalline phases present in GCs.

  4. Method of forming a dielectric thin film having low loss composition of Ba.sub.x Sr.sub.y Ca.sub.1-x-y TiO.sub.3 : Ba.sub.0.12-0.25 Sr.sub.0.35-0.47 Ca.sub.0.32-0.53 TiO.sub.3

    DOEpatents

    Xiang, Xiao-Dong (Alameda, CA); Chang, Hauyee (Berkeley, CA); Takeuchi, Ichiro (Albany, CA)

    2000-01-01

    A dielectric thin-film material for microwave applications, including use as a capacitor, the thin-film comprising a composition of barium strontium calcium and titanium of perovskite type (Ba.sub.x Sr.sub.y Ca.sub.1-x-y)TiO.sub.3. Also provided is a method for making a dielectric thin film of that formula over a wide compositional range through a single deposition process.

  5. Electronic study of Al substituted La{sub 0.7}Ca{sub 0.3}MnO{sub 3} using photoemission spectroscopy

    SciTech Connect

    Phase, D. M. Kumar, Manish Wadikar, A. D. Choudhary, R. J.

    2014-04-24

    Polycrystalline samples of La{sub 0.7}Ca{sub 0.3}Mn{sub 1?X}Al{sub X}O{sub 3} (X=0, 0.05, 0.15) are prepared using solid state reaction route. Photoemission spectroscopy measurements were performed on these samples to investigate their electronic properties. Al shows 3+ oxidation state in both Al doped samples while no effect of Al doping is found on the core level spectrum of La 4d and Ca 2p orbitals and they were found in 3{sup +} and 2{sup +} oxidation state respectively in all the samples . Mn 2p core level photoemission measurements indicates that for 5% Al doped sample (lower doping) Al ions replaces the Mn{sup 3+} ions while they substitute Mn{sup 4+} in 15 % Al doped sample ((higher doping)

  6. Fabrication and texture characterization of bulk (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} superconductors

    SciTech Connect

    Goretta, K.C.; Chen, Nan; Biondo, A.C.; Fisher, B.L.; Lanagan, M.T.; Kallend, J.S.

    1995-05-01

    Bulk (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) and Bi{sub 2}Sr{sub 2}CaCU{sub 2}0{sub x} (Bi-2212) superconductors were fabricated by sinter forging. Bi-2223 ({approx}90% Bi-2223, 10% (Bi,Pb){sub 2}Sr{sub 2}CaCU{sub 2}0. + other phases) and Bi-2212 (nearly phase pure) powders were first synthesized and then cold pressed into bars that were -50% dense. These bars were surrounded by Ag foil, heated in air to {approx}845{degrees}C, and compressed for 3--6 h. The resultant bars were dense and highly textured. At 77 K, the Bi-2223 exhibited transport critical current density (J{sub c}) values of 2000--8000 A/cm{sup 2}; the Bi-2212 exhibited very low J{sub c}. Extent of texture was evaluated by three X-ray diffraction methods: 2{theta} scans, rocking curves, and orientation distribution functions. It was found that J{sub c} correlated best with the orientation distribution functions.

  7. Controllable synthesis of hierarchical nanostructures of CaWO{sub 4} and SrWO{sub 4} via a facile low-temperature route

    SciTech Connect

    Chen, Z.; Gong, Q.; Zhu, J.; Yuan, Y.P.; Qian, L.W.; Qian, X.F.

    2009-01-08

    CaWO{sub 4} and SrWO{sub 4} nanostructures have been synthesized via a simple microemulsion-mediated route. With careful control of the fundamental experimental parameters including the concentration of reactants, the reaction time and the temperature, the products with different morphologies of dumbbell, coral, rod and dendrite have been obtained, respectively. The possible formation mechanism of these unique morphologies has been proposed based on surfactant self-assembly under different experimental conditions. The as-synthesized CaWO{sub 4} samples with various morphologies exhibit different photoluminescence properties. X-ray powder diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and luminescence spectroscopy were used to characterize these products.

  8. Mapping the Electronic Structure of Each Ingredient Oxide Layer of High-T_{c} Cuprate Superconductor Bi_{2}Sr_{2}CaCu_{2}O_{8+?}.

    PubMed

    Lv, Yan-Feng; Wang, Wen-Lin; Peng, Jun-Ping; Ding, Hao; Wang, Yang; Wang, Lili; He, Ke; Ji, Shuai-Hua; Zhong, Ruidan; Schneeloch, John; Gu, Gen-Da; Song, Can-Li; Ma, Xu-Cun; Xue, Qi-Kun

    2015-12-01

    Understanding the mechanism of high transition temperature (T_{c}) superconductivity in cuprates has been hindered by the apparent complexity of their multilayered crystal structure. Using a cryogenic scanning tunneling microscopy (STM), we report on layer-by-layer probing of the electronic structures of all ingredient planes (BiO, SrO, CuO_{2}) of Bi_{2}Sr_{2}CaCu_{2}O_{8+?} superconductor prepared by argon-ion bombardment and annealing technique. We show that the well-known pseudogap (PG) feature observed by STM is inherently a property of the BiO planes and thus irrelevant directly to Cooper pairing. The SrO planes exhibit an unexpected van Hove singularity near the Fermi level, while the CuO_{2} planes are exclusively characterized by a smaller gap inside the PG. The small gap becomes invisible near T_{c}, which we identify as the superconducting gap. The above results constitute severe constraints on any microscopic model for high T_{c} superconductivity in cuprates. PMID:26684137

  9. Momentum-space Electronic Structures and Charge Orders of the High-temperature Superconductors Ca2?xNaxCuO2Cl2 and Bi2Sr2CaCu2O8+?

    SciTech Connect

    Meng, J.Q.; Xu, Z.; Brunner, M.; Kim, K.-H.; Lee, H.-G.; Lee, S.-I.; Wen, J.S.; Gu, G.D.; Gweon, G.-H.

    2011-08-24

    We study the electronic structure of Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} samples in a wide range of doping, using angle-resolved photoemission spectroscopy, with emphasis on the Fermi surface (FS) in the near antinodal region. The 'nesting wave vector,' i.e., the wave vector that connects two nearly flat pieces of the FS in the antinodal region, reveals a universal monotonic decrease in magnitude as a function of doping. Comparing our results to the charge order recently observed by scanning tunneling spectroscopy (STS), we conclude that the FS nesting and the charge order pattern seen in STS do not have a direct relationship. Therefore, the charge order likely arises due to strong-correlation physics rather than FS nesting physics.

  10. Momentum-space electronic structures and charge orders of the high-temperature superconductors Ca2-xNaxCuO?Cl? and Bi?Sr?CaCu?O8+?

    DOE PAGESBeta

    Meng, Jian-Qiao; Brunner, M.; Kim, K.-H.; Lee, H.-G.; Lee, S.-I.; Wen, J. S.; Xu, Z. J.; Gu, G. D.; Gweon, G.-H.

    2011-08-24

    We study the electronic structure of Ca2-xNaxCuO?Cl? and Bi?Sr?CaCu?O8+? samples in a wide range of doping, using angle-resolved photoemission spectroscopy, with emphasis on the Fermi surface (FS) in the near antinodal region. The “nesting wave vector,” i.e., the wave vector that connects two nearly flat pieces of the FS in the antinodal region, reveals a universal monotonic decrease in magnitude as a function of doping. Comparing our results to the charge order recently observed by scanning tunneling spectroscopy (STS), we conclude that the FS nesting and the charge order pattern seen in STS do not have a direct relationship. Therefore,more »the charge order likely arises due to strong-correlation physics rather than FS nesting physics« less

  11. Momentum-space electronic structures and charge orders of the high-temperature superconductors Ca2-xNaxCuO?Cl? and Bi?Sr?CaCu?O8+?

    SciTech Connect

    Meng, Jian-Qiao; Brunner, M.; Kim, K.-H.; Lee, H.-G.; Lee, S.-I.; Wen, J. S.; Xu, Z. J.; Gu, G. D.; Gweon, G.-H.

    2011-08-24

    We study the electronic structure of Ca2-xNaxCuO?Cl? and Bi?Sr?CaCu?O8+? samples in a wide range of doping, using angle-resolved photoemission spectroscopy, with emphasis on the Fermi surface (FS) in the near antinodal region. The “nesting wave vector,” i.e., the wave vector that connects two nearly flat pieces of the FS in the antinodal region, reveals a universal monotonic decrease in magnitude as a function of doping. Comparing our results to the charge order recently observed by scanning tunneling spectroscopy (STS), we conclude that the FS nesting and the charge order pattern seen in STS do not have a direct relationship. Therefore, the charge order likely arises due to strong-correlation physics rather than FS nesting physics

  12. Polarization-dependent infrared reflectivity study of Sr2.5Ca11.5Cu24O41 under pressure: Charge dynamics, charge distribution, and anisotropy

    DOE PAGESBeta

    Frank, S.; Huber, A.; Ammerahl, U.; Hücker, M.; Kuntscher, C. A.

    2014-12-18

    We present a polarization-dependent infrared reflectivity study of the spin-ladder compound Sr???Ca????Cu??O?? under pressure. The optical response is strongly anisotropic, with the highest reflectivity along the ladders/chains (E?c) revealing a metallic character. For the polarization direction perpendicular to the ladder plane, an insulating behavior is observed. With increasing pressure the optical conductivity for E?c shows a strong increase, which is most pronounced below 2000cm?¹. According to the spectral weight analysis of the E?c optical conductivity the hole concentration in the ladders increases with increasing pressure and tends to saturate at high pressure. At ~7.5 GPa the number of holes permore »Cu atom in the ladders has increased by ??=0.09(±0.01), and the Cu valence in the ladders has reached the value +2.33. Thus, the optical data suggest that Sr???Ca????Cu??O?? remains electronically highly anisotropic up to high pressure, also at low temperatures.« less

  13. Synthesis, spectroscopic characterization, thermal analysis and electrical conductivity studies of Mg(II), Ca(II), Sr(II) and Ba(II) vitamin B2 complexes

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; Moussa, Mohamed A. A.; Mohamed, Soha F.

    2011-05-01

    Riboflavin (RF) complexes of Mg(II), Ca(II), Sr(II) and Ba(II) were successfully synthesized. Structures of metal complexes obtained were confirmed and characterized by elemental analysis, molar conductance, and infrared spectra. DC electrical conductivity measurements indicated that the alkaline earth metal (II) complexes of RF ligand are non-electrolytes. Elemental analysis of chelates suggest that the metal(II) ligand ratio is 1:2 with structure formula as [M(RF) 2( X) 2]· nH 2O. Infrared assignments clearly show that RF ligand coordinated as a bidentate feature through azomethine nitrogen of pyrazine ring and C dbnd O of pyrimidine-2,4-dione. Thermal analyses of Mg(II), Ca(II), Sr(II) and Ba(II) complexes were investigated using (TG/DSC) under atmospheric nitrogen between 30 and 800 °C. The surface morphology of the complexes was studied by SEM. The electrical conductivities of RF and its metal complexes were also measured with DC electrical conductivity in the temperature range from room to 483 K.

  14. ARPES EVIDENCE FOR A QUASIPARTICLE LIQUID IN OVERDOPED Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+delta}.

    SciTech Connect

    WELLS,B.O.; YUSOF,Z.; VALLA,T.; FEDOROV,A.V.; JOHNSON,P.; KENDZIORA,C.; JIAN,S.; HINKS,D.

    2001-07-23

    High resolution angle-resolved photoemission spectroscopy of highly overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} with a T{sub c} = 51K indicates that the basic transport processes in this material are fundamentally different from both the lesser doped cuprates as well as model metallic compounds. The overdoped sample has sharp ARPES peaks at the Fermi energy throughout the Brillouin zone even in the normal state, unlike the lesser-doped compounds. In particular, the spectra near ({pi},0) point show the presence of a sharp peak well above T{sub c}. The ARPES lineshapes, and thus the self energy, at a given energy are almost independent of k. Further, the quasiparticle scattering rate at the Fermi energy seems to be closely tied to direct resistivity measurements. This leads us to the conclusion that overdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} is best described as a quasiparticle liquid. However, the energy dependence of the scattering rates is quite similar to that found in the lesser-doped compounds and quite different from that seen in a typical metal.

  15. Comparison of the electronic band structures of LiCaAlF6 and LiSrAlF6 ultraviolet laser host media from ab initio calculations

    NASA Astrophysics Data System (ADS)

    Viet Luong, Mui; Cadatal-Raduban, Marilou; Empizo, Melvin John F.; Arita, Ren; Minami, Yuki; Shimizu, Toshihiko; Sarukura, Nobuhiko; Azechi, Hiroshi; Pham, Minh Hong; Nguyen, Hung Dai; Kawazoe, Yoshiyuki

    2015-12-01

    We report the electronic structures and density of states (DOS) of perfect LiCAF and LiSAF crystals calculated from density functional theory (DFT) with local density approximation (LDA) using optimized lattice constants. DOS calculations reveal that the valence band is mainly derived from F 2p, thereby resulting to a very narrow valence band manifold. Meanwhile, the conduction band is mainly derived from Ca 4s or Sr 5s resulting to Sr having a broader band dispersion compared to Ca. Both fluoride compounds have indirect band gaps with LiCAF having a band gap of 8.02 eV and LiSAF a band gap of 7.92 eV. This is, to the best of our knowledge, the first report on the electronic structure of LiSAF calculated using DFT with LDA. Our results suggest that when doped with Ce3+, the shorter 5d-conduction band distance in Ce:LiSAF combined with the difficulty of growing high-purity crystals lead to the more pronounced excited state absorption (ESA) and solarization effect experimentally observed in Ce:LiSAF, limiting its potential as a laser material compared with Ce:LiCAF.

  16. Strong Coupling Superconductivity in the Vicinity of the Structural Quantum Critical Point in (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13}.

    PubMed

    Yu, Wing Chi; Cheung, Yiu Wing; Saines, Paul J; Imai, Masaki; Matsumoto, Takuya; Michioka, Chishiro; Yoshimura, Kazuyoshi; Goh, Swee K

    2015-11-13

    The family of the superconducting quasiskutterudites (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13} features a structural quantum critical point at x_{c}=0.9, around which a dome-shaped variation of the superconducting transition temperature T_{c} is found. Using specific heat, we probe the normal and the superconducting states of the entire series straddling the quantum critical point. Our analysis indicates a significant lowering of the effective Debye temperature on approaching x_{c}, which we interpret as a result of phonon softening accompanying the structural instability. Furthermore, a remarkably large enhancement of 2?/k_{B}T_{c} and ?C/?T_{c} beyond the Bardeen-Cooper-Schrieffer values is found in the vicinity of the structural quantum critical point. The phase diagram of (Ca_{x}Sr_{1-x})_{3}Rh_{4}Sn_{13} thus provides a model system to study the interplay between structural quantum criticality and strong electron-phonon coupling superconductivity. PMID:26613465

  17. Electrical and Structural Properties of Ex-situ Annealed Superconducting Bi2Sr2CaCu2O8 Thin Films Obtained by Coevaporation of Components

    NASA Astrophysics Data System (ADS)

    Baštürk, Necdet

    2005-03-01

    Bi2Sr2CaCu2O8 system superconducting thin films were obtained by synchronized deposition of Bi, Cu, CaF2 and SrF2 components onto cleaved MgO (100) single crystal substrates after annealing in the temperature range 600--840 °C. The films were annealed in H2O and O2, then dry O2 atmosphere for the removal of fluorine from the structure and to attain superconducting properties. X-ray powder diffraction patterns were used to characterize the obtained film structure. The films were observed to grow along c-axis perpendicular to the substrate surface with the identified reflection on the (00l, l = 6, 8, 10...) planes. The films having the critical temperature higher than liquid nitrogen were obtained when Bi and the other components were evaporated from separate sources. DC resistance in the films were measured in the temperature range 77--300 K. of those films having good superconducting properties, metallic behaviors were seen in the normal state and zero resistance at 79 K was obtained following a transition in the resistance.

  18. Photoluminescence and phosphorescence properties of MAl 2O 4:Eu 2+, Dy 3+ (M=Ca, Ba, Sr) phosphors prepared at an initiating combustion temperature of 500 °C

    NASA Astrophysics Data System (ADS)

    Mothudi, B. M.; Ntwaeaborwa, O. M.; Botha, J. R.; Swart, H. C.

    2009-12-01

    Eu 2+ and Dy 3+ co-doped calcium aluminate, barium aluminate and strontium aluminate phosphors were synthesized at an initiating combustion temperature of 500 °C using urea as an organic fuel. The crystallinity of the phosphors was investigated by using X-ray diffraction (XRD) and the morphology was determined by a scanning electron microscope (SEM). The low temperature monoclinic structure for both CaAl 2O 4 and SrAl 2O 4 and the hexagonal structure of BaAl 2O 4 were observed. The effect of the host materials on the photoluminescence (PL) and phosphorescence properties were investigated by using a He-Cd Laser and a Cary Eclipse fluorescence spectrophotometer, respectively. The broad band emission spectra observed at 449 nm for CaAl 2O 4:Eu 2+, Dy 3+, 450 nm (with a shoulder-peak at 500 nm) for BaAl 2O 4:Eu 2+, Dy 3+ and 528 nm for SrAl 2O 4:Eu 2+, Dy 3+ are attributed to the 4f 65d 1 to 4f 7 transition in the Eu 2+ ion in the different hosts.

  19. High-performance tellurium-free thermoelectrics: all-scale hierarchical structuring of p-type PbSe-MSe systems (M = Ca, Sr, Ba).

    PubMed

    Lee, Yeseul; Lo, Shih-Han; Androulakis, John; Wu, Chun-I; Zhao, Li-Dong; Chung, Duck-Young; Hogan, Timothy P; Dravid, Vinayak P; Kanatzidis, Mercouri G

    2013-04-01

    We present a systematic study of the characterization and thermoelectric properties of nanostructured Na-doped PbSe embedded with 1-4% MSe (M = Ca, Sr, Ba) phases as endotaxial inclusions. The samples were powder-processed by the spark plasma sintering technique, which introduces mesoscale-structured grains. The hierarchical architectures on the atomic scale (Na and M solid solution), nanoscale (MSe nanoprecipitates), and mesoscale (grains) were confirmed by transmission electron microscopy. These structures produce a great reduction in the lattice thermal conductivity relative to pristine PbSe without appreciably affecting the power factor. The lattice thermal conductivity can be reduced by up to ?29% when the second phase is added. The highest ZT value achieved was ?1.3 at 923 K for both 2% SrSe-and 3% BaSe-containing samples, while the sample containing 4% CaSe showed a ZT value of ?1.2 at 923 K. The optimal samples have hole carrier concentration of 1-2 × 10(20) cm(-3). We attribute the high ZT values to the combination of broad-based phonon scattering on multiple length scales and favorable charge transport through coherent interfaces between the PbSe matrix and MSe. PMID:23521562

  20. High-temperature electrical and thermal transport properties of fully filled skutterudites RFe4Sb12 (R = Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb)

    NASA Astrophysics Data System (ADS)

    Qiu, P. F.; Yang, J.; Liu, R. H.; Shi, X.; Huang, X. Y.; Snyder, G. J.; Zhang, W.; Chen, L. D.

    2011-03-01

    Fully filled skutterudites RFe4Sb12 (R = Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb) have been prepared and the high-temperature electrical and thermal transport properties are investigated systematically. Lattice constants of RFe4Sb12 increase almost linearly with increasing the ionic radii of the fillers, while the lattice expansion in filled structure is weakly influenced by the filler valence charge states. Using simple charge counting, the hole concentration in RFe4Sb12 with divalent fillers (R = Ca, Sr, Ba, Eu, and Yb) is much higher than that in RFe4Sb12 with trivalent fillers (R = La, Ce, Pr, and Nd), resulting in relatively high electrical conductivity and low Seebeck coefficient. It is also found that RFe4Sb12 filled skutterudites having similar filler valence charge states exhibit comparable electrical conductivity and Seebeck coefficient, and the behavior of the temperature dependence, thereby leading to comparable power factor values in the temperature range from 300 to 800 K. All RFe4Sb12 samples possess low lattice thermal conductivity. The correlation between the lattice thermal resistivity WL and ionic radii of the fillers is discussed and a good relationship of WL ˜ (rcage-rion)3 is observed in lanthanide metal filled skutterudites. CeFe4Sb12, PrFe4Sb12, and NdFe4Sb12 show the highest thermoelectric figure of merit around 0.87 at 750 K among all the filled skutterudites studied in this work.

  1. Effects of midlatitude westerlies on the paleoproductivity at the Agulhas Bank slope during the penultimate glacial cycle: Evidence from coccolith Sr/Ca ratios

    NASA Astrophysics Data System (ADS)

    Mejia, Luz Maria; Ziveri, Patrizia; Cagnetti, Marilisa; Bolton, Clara; Zahn, Rainer; Marino, Gianluca; Martinez Mendez, Gema; Stoll, Heather

    2015-04-01

    Because modern primary productivity on the Agulhas Bank, off South Africa, is linked to the mid-latitude westerlies, a paleoproductivity record from this area could be used to investigate past may changes in the westerlies dynamics. Coccolith Sr/Ca is a suitable productivity indicator to explore paleoproductivity from the penultimate glacial-interglacial cycle because it is independent of preservation changes that may accompany changes in deepwater circulation. In the Agulhas Bank slope core MD96-2080, the coccolith Sr/Ca record shows that phases of depressed productivity coincided with periods of stratification in the same core, indicated by high relative abundances of the coccolithophore Florisphaera profunda, and with low relative abundances of the upwelling indicator G. bulloides in the Cape Basin. This coherence suggests that upwelling regulated productivity throughout this region. As in the present, we infer that periods of low productivity result from northward positions of the westerlies which block the upwelling-promoting easterlies. Productivity minima also coincide with periods of increased ice-rafted detritus (IRD) deposition on the Agulhas Plateau, which also indicates extreme northward positions of the westerlies. The influence of the westerlies appears to be obliquity-conditioned, as productivity minima occur during low obliquity intervals. The dynamic connection between productivity and the westerlies is supported by coeval salinity changes in the South Indian Gyre that likewise respond sensitively to a poleward contraction of the westerlies.

  2. Dielectric and ferroelectric properties of Sr4CaSmTi3Nb7O30 with tetragonal tungsten bronze structure

    NASA Astrophysics Data System (ADS)

    Gong, Gao-Shang; Fang, Yu-Jiao; Huang, Shuai; Yin, Chong-Yang; Yuan, Song-Liu; Wang, Li-Guang

    2014-09-01

    Sr4CaSmTi3Nb7O30 ceramics are synthesized and indexed as tetragonal tungsten bronze structure. The dielectric behavior and ferroelectric nature are investigated. Three dielectric anomalies are observed. The phase transition is a displacive phase transition with some diffusive characteristics, which indicates possible compositional variations within the materials on the microscopic scale. The weak distortion disappears in cooling process for differential scanning calorimetry measurement, and the large depression of Curie—Weiss temperature T0 indicates the difficulty in forming macroferroelectric domain. The ferroelectric nature in these filled tungsten bronze niobates originates from the off-center displacement of B-site cations, but they are primarily dominated by A-site cation occupation. Both the radius and the valence of A1-site cations play an important role on ferroelectric properties of the filled tungsten bronze compounds. Existence of spontaneous polarization with a remanent polarization of 0.16 ?C/cm2 a coercive field of Ec = 11.74 kV/cm confirms the room-temperature ferroelectric nature of Sr4CaSmTi3Nb7O30 ceramics.

  3. Sequence of phase transitions induced by chemical composition and high temperature in [Ba2CaWO6](1-x)[Sr2CaWO6]x double perovskite tungsten oxides

    NASA Astrophysics Data System (ADS)

    Mirinioui, F.; Manoun, Bouchaib; Tamraoui, Y.; Lazor, P.

    2015-12-01

    [Ba2CaWO6]1-x[Sr2CaWO6]x (0?x?1) materials were synthesized by the high temperature solid state reaction and firing methods, and characterized using techniques of X-ray diffraction and Raman spectroscopy. The crystal structures were determined by Rietveld refinements on the laboratory X-ray powder diffraction data. As a function of composition, upon increasing the strontium content, the samples exhibit a sequence of three phase transitions: from cubic (Fm 3 ?m) to tetragonal (I4/m) to monoclinic structural phases (I2/m, P21/n). These transitions have been confirmed by Raman studies Fm 3 bar m x = 0 ? I 4 / m 0.1 ? x ? 0.2 ? I 2 / m 0.3 ? x ? 0.5 ? P21 / n 0.6 ? x ? 1 Furthermore, increasing the temperature for the compositions [Ba2CaWO6]1-x[Sr2CaWO6]x (0.1?x<1), manifests the P21/n to I2/m, the I2/m to I4/m and the I4/m to Fm 3 ?m phase transitions. For the compositions (0.1?x?0.2) the tetragonal to cubic phase transition is well illustrated. For the room temperature I2/m monoclinic compositions, two phase transitions were observed for all the compositions with x ranging from 0.3 to 0.5: from the monoclinic (I2/m) to tetragonal (I4/m), and from I4/m to Fm 3 ?m structures. Finally, for the room temperature P21/n monoclinic compositions, only two phase transitions are observed in the temperature range probed by Raman spectroscopy, the temperature was not high enough to reach the tetragonal-to-cubic phase transition.

  4. Double MITs and magnetoresistance: an intrinsic feature of Ru substituted La0.67Ca0.33MnO3

    NASA Astrophysics Data System (ADS)

    Seetha Lakshmi, L.; Sridharan, V.; Sukumar, A. A.; Kamruddin, M.; Sastry, V. S.; Raju, V. S.

    2006-05-01

    In this paper, we examine the possible influence of extrinsic factors on the electrical and magnetotransport of La0.67Ca0.33Mn1-xRuxO3 (x<=0.10). Ru substitution results in double metal-insulator transitions (MITs) at TMI1 and TMI2, both exhibiting magnetoresistance (MR). No additional magnetic signal corresponding to a second low-temperature maximum (LTM) at TMI2 could be observed, either in ac susceptibility (?') or in specific heat (Cp). Typical grain sizes of ~18 000-20 000 nm, as estimated from the scanning electron microscope (SEM) micrographs, are not so small as to warrant an LTM. The absence of additional peaks in the high statistics powder x-ray diffraction (XRD), a linear systematic increase of the unit cell parameters, close matching of the transition temperatures in resistivity, ?' and Cp and their linear systematic decrease with x, and an homogeneous distribution of Mn, Ru and O at arbitrarily selected regions within and across the grains exclude chemical inhomogeneity in the samples. The insensitivity of grain boundary MR at 5 K to Ru composition indicates that the grain boundary is not altered to result in an LTM. Oxygen stoichiometry of all the compounds is close to the nominal value of 3. These results not only exclude the extrinsic factors, but also establish that double MITs, both exhibiting MR, are intrinsic to Ru substituted La0.67Ca0.33MnO3.

  5. Structure, solvation, and dynamics of Mg{sup 2+}, Ca{sup 2+}, Sr{sup 2+}, and Ba{sup 2+} complexes with 3-hydroxyflavone and perchlorate anion in acetonitrile medium: A molecular dynamics simulation study

    SciTech Connect

    Agieienko, Vira N.; Kolesnik, Yaroslav V.; Kalugin, Oleg N.

    2014-05-21

    Molecular dynamics simulations of complexes of Mg{sup 2+}, Ca{sup 2+}, Sr{sup 2+}, and Ba{sup 2+} with 3-hydroxyflavone (flavonol, 3HF) and ClO {sub 4}{sup ?} in acetonitrile were performed. The united atoms force field model was proposed for the 3HF molecule using the results of DFT quantum chemical calculations. 3HF was interpreted as a rigid molecule with two internal degrees of freedom, i.e., rotation of the phenyl ring and of the OH group with respect to the chromone moiety. The interatomic radial distribution functions showed that interaction of the cations with flavonol occurs via the carbonyl group of 3HF and it is accompanied with substitution of one of the acetonitrile molecules in the cations’ first solvation shells. Formation of the cation–3HF complexes does not have significant impact on the rotation of the phenyl ring with respect to the chromone moiety. However, the orientation of the flavonol's OH-group is more sensitive to the interaction with doubly charged cations. When complex with Mg{sup 2+} is formed, the OH-group turns out of the plane of the chromone moiety that leads to rupture of intramolecular H-bond in the ligand molecule. Complexation of Ca{sup 2+}, Sr{sup 2+}, and BaClO {sub 4}{sup +} with 3HF produces two structures with different OH-positions, as in the free flavonol with the intramolecular H-bond and as in the complex with Mg{sup 2+} with disrupted H-bonding. It was shown that additional stabilization of the [MgClO{sub 4}(3HF)]{sup +} and [BaClO{sub 4}(3HF)]{sup +} complexes is determined by strong affinity of perchlorate anion to interact with flavonol via intracomplex hydrogen bond between an oxygen atom of the anion and the hydrogen atom of the 3-hydroxyl group. Noticeable difference in the values of the self-diffusion coefficients for Kt{sup 2+} from one side and ClO {sub 4}{sup ?}, 3HF, and AN in the cations’ coordination shell from another side implies quite weak interaction between cation, anion, and ligands in the investigated complexes.

  6. Structural characterization and superconducting properties of (Tl 0.5Pb 0.5)(Sr 2- xBa x)Ca 2Cu 3O 9-?

    NASA Astrophysics Data System (ADS)

    Gladyshevskii, R. E.; Galez, Ph.; Lebbou, K.; Allemand, J.; Abraham, R.; Couach, M.; Flükiger, R.; Jorda, J.-L.; Cohen-Adad, M. Th.

    1996-02-01

    Samples of nominal composition (Tl 0.5Pb 0.5)(Sr 2- xBa x)Ca 2Cu 3O 9-?, 0 ? x ? 0.6, and (Tl 0.6Pb 0.2Bi 0.2)(Sr 1.8Ba 0.2)-Ca 2Cu 3O 9-? were characterized by X-ray powder diffraction, scanning electron microscopy and AC susceptibility measurements. In the Bi-free samples, the highest weight fraction of the 1223 phase, 91.3%, was observed for x = 0.4. Above this Ba content, BaPbO 3 perovskite appeared as main impurity phase. In the Bi-containing sample the weight fraction was even higher, 92.6%. The Ba content of the 1223 phase, as determined from X-ray diffraction data, was in agreement with the nominal composition of the samples. The unit cell parameters increased when the Sr atoms were progressively replaced by the larger Ba atoms. The refinement of the crystal structure of the 1223 phase revealed a significant off-centering of the Tl site. The distance from the splitted site to the ideal position on the four-fold axis was found to be ? 0.26 Å for the Ba-containing samples, but only 0.07 Å for the Ba-free sample. The distance from the Cu atom to the apical atom of the square pyramid formed by the oxygen atoms increased from 2.29 to 2.50 Å as the Ba content was raised. The critical temperature remained between 116 and 120.5 K and was not significantly affected by changes in composition or structure.

  7. Hydrothermal preparation of tobermorite from blast furnace slag for Cs+ and Sr2+ sorption.

    PubMed

    Tsutsumi, Takuma; Nishimoto, Shunsuke; Kameshima, Yoshikazu; Miyake, Michihiro

    2014-02-15

    Al-substituted 11?-tobermorite was formed by alkaline hydrothermal treatment of blast furnace slag with sodium silicate added at 180°C for 2-48 h. Effects of the hydrothermal treatment time were characterized by XRD, SEM, and isothermal adsorption of N2. Sorption characteristics of the obtained samples were examined for Cs(+) and Sr(2+). The sample obtained by hydrothermal treatment for 48 h (HT-48 h) consisted of calcium silicate hydrate (C-S-H), and Al-substituted 11?-tobermorite. The HT-48 h showed the highest performance for Cs(+) and Sr(2+) selectivity in the presence of Na(+). The interlayer Na(+) of Al-substituted 11?-tobermorite and surface Ca(2+) played an important role in selective Cs(+) and Sr(2+). PMID:24412625

  8. Phonon Raman scattering in R1 xAxMnO3 ,,R La,Pr; A Ca,Sr... E. Granado, N. O. Moreno, A. Garcia, J. A. Sanjurjo, C. Rettori, and I. Torriani

    E-print Network

    of La0.78Ca0.22MnO3 and La0.7Sr0.3MnO3 were grown by the optical floating zone method. Typical rotation/h. The Pr0.625Sr0.375MnO3 single crystals were also grown by the floating zone method, using a lamp zone under lattice deformation. For the orthorhombic LaMnO3.0 , the Raman spectra are consistent

  9. Optical investigation of the electronic structures of Y2Ru2O7 , CaRuO3 , SrRuO3, and Bi2Ru2O7

    E-print Network

    Oh, Se-Jung

    metal. Y2Ru2O7 has the pyrochlore structure and shows an insulat- ing behavior. Both CaRuO3 and SrRuO3RuO3, and that SrRuO3 becomes fer- romagnetic below 160 K. Bi2Ru2O7 has the pyrochlore structure and behaves as a Pauli paramagnetic metal. All of the above pyrochlore and perovskite ruthenates have four 4d

  10. Electrical-transport, magnetoresistance and magnetic properties of La0.7Ca0.3MnO3 and La0.7Ca0.24Sr0.06MnO3 single crystals

    NASA Astrophysics Data System (ADS)

    Tank, Tejas M.; Bodhaye, Ashish; Mukovskii, Ya. M.; Sanyal, S. P.

    2015-06-01

    We report the electrical-transport, magnetoresistance and magnetic properties of the hole doped La0.7Ca0.3MnO3 (LCMO) and La0.7Ca0.24Sr0.06MnO3 (LCSMO) single crystals. It was prepared using floating zone technique. The resistivity data shows the metal to insulator transition (TMI) occurs at 211 K along c-axis and TMI = 185 K the ab-plane for LCMO and TMI = 290 K along the c-axis and TMI = 280 K along the ab-plane for LCSMO single crystals. It is observed that the TMI is higher along the c-axis as compared to that in the ab-plane, consequently signifying more favorable hoping of electrons is along the c-axis. The ac-susceptibility measurement shows that this material exhibits ferromagnetic to paramagnetic transition temperature (TC) at 206 K for LCMO and TC = 277 K for LCSMO single crystals. For magnetic memory device application point of view, the sample shows the maximum MR of 98% for LCMO and 80% for LCSMO single crystals at 8T applied magnetic field. Doping small amount of Sr (0.06%) reveals that the electronic and magnetic phase transition in CMR single crystal increases substantially and useful for device application. This is first time such type of comparative study in these manganite single crystals.

  11. Properties of freeze-dried Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+d} : effects of Ag doping and analysis of powder-in-tubetapes.

    SciTech Connect

    Deis, T. A.; Eror, N. G.; Lelovic, M.; Prorok, B. C.; Balachandran, U.; Energy Technology; Univ. of Pittsburgh

    1997-06-01

    Low level doping (⩽1 atomic%) of Ag in Bi2Sr2CaCu2O8+d was performed via freeze-drying of nitrate solutions. Effects of Ag doping on the c-axis lattice parameter, oxygen content and critical temperature were monitored, Powder-in-tube tapes were fabricated using both Ag-doped and undoped Bi2Sr2CaCu2O8+d powders. Tapes were processed using a partial melt heat treatment in flowing oxygen. The effects of Ag doping on the critical current and microstructure were investigated, specifically the Ag-Bi2Sr2CaCu2O8+d interface region.

  12. Effects of Nb doping level on the electronic transport, photoelectric effect and magnetoresistance across La{sub 0.5}Ca{sub 0.5}MnO{sub 3}/Nb:SrTiO{sub 3} junctions

    SciTech Connect

    Wang, J. F.; Jiang, Y. C.; Gao, J.; Chen, M. G.

    2013-12-16

    Heterojunctions composed of La{sub 0.5}Ca{sub 0.5}MnO{sub 3} and Nb doped SrTiO{sub 3} were fabricated, and the effects of the Nb doping level on their electronic transport, photoelectric effect, and magnetoresistance were investigated. A lower doping concentration of Nb led to better rectifying properties and higher open circuit voltages. The I-V curves for La{sub 0.5}Ca{sub 0.5}MnO{sub 3}/0.7?wt.?% Nb-SrTiO{sub 3} showed a negligible response to magnetic fields for all temperatures, whereas La{sub 0.5}Ca{sub 0.5}MnO{sub 3}/0.05?wt.?% Nb-SrTiO{sub 3} exhibited distinct magnetoresistance, which depended on both the bias voltage and temperature. These results are discussed with the assistance of conventional semiconductor theories.

  13. Ages and Nd, Sr isotopic systematics in the Sierran foothills ophiolite belt, CA: the Smartville and Feather River complexes

    SciTech Connect

    Shaw, H.F.; Niemeyer, S.

    1985-01-01

    Sm-Nd dating has shown the Kings-Kaweah ophiolite to be approx. 480 My old. Its Nd, Sr, and Pb isotopic compositions require an unusually old depleted mantle source. Samples from the Smartville and Feather River complexes have been analyzed in a search for similar highly depleted, early Paleozoic ophiolites in the northern foothills ophiolite belt. Six whole rocks from Smartville, encompassing representative lithologies, plus plagioclase and pyroxene mineral separates define a 183 +/- 22 My Sm-Nd isochron. This age, interpreted as the igneous age, is older than, but within error of, approx. 160 My U-Pb ages previously obtained from plagiogranite zircon analyses. One diabase with unusually high Rb/Sr yields a depleted mantle Sr model age of 200 +/- 25 My, consistent with the Sm-ND age. These compositions are clearly oceanic in character but do not discriminate among possible tectonic settings for the formation of the Smartville complex. Sm-Nd data for flaser gabbros and related rocks from Feather River scatter about an approx. 230 My errorchron with element of/sub Nd/(T) = +6.3 to +8.7. Initial /sup 87/Sr//sup 86/Sr ranges from 0.7028 to 0.7031. These results indicate a complex history with initial isotopic heterogeneities and/or disturbances of the isotopic systems. If primary, the element of/sub Nd/ (T) values are somewhat low, suggesting a possible arc origin for these rocks. Neither the Smartville nor Feather R. complexes appear to be related to the Kings-Kaweah ophiolite which, so far, is unique among foothill ophiolites in having an early Paleozoic age and a clear MORB, as opposed to arc or marginal basin, isotopic signature.

  14. Enhanced electrical and magnetic properties in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films deposited on CaTiO{sub 3}-buffered silicon substrates

    SciTech Connect

    Adamo, C.; Méchin, L.; Guillet, B.; Wu, S.; Routoure, J.-M.; Heeg, T.; Katz, M.; Pan, X. Q.; Mercone, S.; Schubert, J.; Zander, W.; Misra, R.; Schiffer, P.; and others

    2015-06-01

    We investigate the suitability of an epitaxial CaTiO{sub 3} buffer layer deposited onto (100) Si by reactive molecular-beam epitaxy (MBE) for the epitaxial integration of the colossal magnetoresistive material La{sub 0.7}Sr{sub 0.3}MnO{sub 3} with silicon. The magnetic and electrical properties of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} films deposited by MBE on CaTiO{sub 3}-buffered silicon (CaTiO{sub 3}/Si) are compared with those deposited on SrTiO{sub 3}-buffered silicon (SrTiO{sub 3}/Si). In addition to possessing a higher Curie temperature and a higher metal-to-insulator transition temperature, the electrical resistivity and 1/f noise level at 300 K are reduced by a factor of two in the heterostructure with the CaTiO{sub 3} buffer layer. These results are relevant to device applications of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} thin films on silicon substrates.

  15. Effects of midlatitude westerlies on the paleoproductivity at the Agulhas Bank slope during the penultimate glacial cycle: Evidence from coccolith Sr/Ca ratios

    NASA Astrophysics Data System (ADS)

    Mejía, Luz María.; Ziveri, Patrizia; Cagnetti, Marilisa; Bolton, Clara; Zahn, Rainer; Marino, Gianluca; Martínez-Méndez, Gema; Stoll, Heather

    2014-07-01

    Modern primary productivity on the Agulhas Bank, off South Africa, has been proposed to be linked to the midlatitude westerlies. A paleoproductivity record from this area may therefore resolve temporal changes in the westerly dynamics. Accordingly, we produced a coccolith Sr/Ca-based paleoproductivity record from core MD96-2080 (Agulhas Bank slope) during the penultimate glacial-interglacial cycle. Deriving the productivity signal from Sr/Ca requires a correction for a temperature effect, here constrained using Mg/Ca sea surface temperatures from the foraminifer Globigerina bulloides from core MD96-2080. Phases of depressed productivity coincided with periods of stratification in the same core, indicated by high relative abundances of the coccolithophore Florisphaera profunda and with low relative abundances of the upwelling indicator G. bulloides in the nearby Cape Basin. These observations collectively suggest that productivity was regulated by upwelling throughout this region. We infer that, as in the present, periods of low productivity result from a more northerly position of the westerlies, potentially accompanied by subtropical front displacements, and blockage of upwelling promoting easterlies. Productivity minima also coincide with periods of increased ice-rafted detritus (IRD) deposition on the Agulhas Plateau, which also indicates extreme northward positions of the westerlies. The influence of the westerlies appears to be obliquity conditioned, as productivity minima (and IRD maxima) occur during low-obliquity intervals. The dynamic connection between productivity and the westerlies is supported by coeval salinity changes in the South Indian Gyre that likewise respond sensitively to a poleward contraction of the westerlies.

  16. Correlation between upconversion photoluminescence and dielectric response in Ba-substituted (Sr{sub 1?x}Ba{sub x}){sub 4}(La{sub 0.85}Ho{sub 0.025}Yb{sub 0.125}){sub 2}Ti{sub 4}Nb{sub 6}O{sub 30}

    SciTech Connect

    Wei, T.; Wang, X. D.; Zhao, C. Z.; Liu, M. F.; Liu, J. M.

    2014-06-30

    The filled tetragonal tungsten bronze (Sr{sub 1?x}Ba{sub x}){sub 4}(La{sub 0.85}Ho{sub 0.025}Yb{sub 0.125}){sub 2}Ti{sub 4}Nb{sub 6}O{sub 30} (SBLTNx: Ho-Yb) ceramics with different Ba substitution levels (x) are prepared. The upconversion photoluminescence (UC-PL) and dielectric permittivity are investigated. The substitution of Sr{sup 2+} ions at the A{sub 2}-sites by larger Ba{sup 2+} ions results in substantial variation of the UC-PL intensity as a function of substitution level x. Furthermore, the dielectric response to the substitution of Sr{sup 2+} by Ba{sup 2+} suggests a close correlation between the UC-PL intensity and dielectric permittivity. The origin for this correlation is discussed based on the random stress field (RSF) model.

  17. [Preparation of chitosan/strontium-substituted hydroxyapatite films on titanium and its FTIR characteristics].

    PubMed

    Huang, Yong; Han, Shu-guang; Ding, Qiong-qiong; Yan, Ya-jing; Pang, Xiao-feng

    2013-09-01

    Chitosan/strontium-substituted hydroxyapatite (CHI/SrHAP) coatings were prepared on titanium substrate by electrochemical deposition technique containing Sr2+, Ca2+, PO4(3-) and Chitosan. The as-prepared coatings were examined by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) tests. The results indicate that the CHI/SrHAP coatings take the morphology of flake-like rather than the needle-like crystal , and the composite coating becomes more compact. The FTIR test indicates that the typical vibration absorption peaks of chitosan (amide I and amide II) emerged, simulated body fluid immersion test proved that the CHI/SrHAP coatings had induced carbonate-apatite formation, indicating that the composite coating possesses excellent biocompatibility. In the electrochemical corrosion testing, that the CHI/SrHAP coatings showed stronger corrosion resistance than pure Ti. PMID:24369635

  18. Magnetoresistance of substituted lanthanum manganites La0.7Ca0.3MnO3 upon nonequilibrium overheating of carriers

    NASA Astrophysics Data System (ADS)

    Shaykhutdinov, K. A.; Semenov, S. V.; Popkov, S. I.; Balaev, D. A.; Bykov, A. A.; Dubrovskiy, A. A.; Petrov, M. I.; Volkov, N. V.

    2011-04-01

    Current-voltage characteristics of the polycrystalline substituted lanthanum manganite La0.7Ca0.3MnO3 were experimentally studied at T = 77.4 K in magnetic fields up to 13 kOe. In these characteristics, a portion of negative differential resistivity was observed above a certain threshold value of critical current density j caused, in our opinion, by nonequilibrium heating of the electron gas due to low thermal conductivity of the manganite material. Because of the nonlinearity of the current-voltage characteristics, the field dependences of resistivity ?(H) appear extremely sensitive to the value of a transport current. In this case, the ?(H) dependences reveal both ordinary negative and positive magnetoresistance.

  19. Low-temperature synthesis of homogeneous solid solutions of scheelite-structured Ca1-xSrxWO4 and Sr1-xBaxWO4 nanocrystals.

    PubMed

    Culver, Sean P; Greaney, Matthew J; Tinoco, Antonio; Brutchey, Richard L

    2015-09-01

    A series of compositionally complex scheelite-structured nanocrystals of the formula A1-xAWO4 (A = Ca, Sr, Ba) have been prepared under benign synthesis conditions using the vapor diffusion sol-gel method. Discrete nanocrystals with sub-20 nm mean diameters were obtained after kinetically controlled hydrolysis and polycondensation at room temperature, followed by composition-dependent thermal aging at or below 60 °C. Rietveld analysis of X-ray diffraction data and Raman spectroscopy verified the synthesis of continuous and phase-pure nanocrystal solid solutions across the entire composition space for A1-xAWO4, where 0 ? x ? 1. Elemental analysis by X-ray photoelectron and inductively coupled plasma-atomic emission spectroscopies demonstrated excellent agreement between the nominal and experimentally determined elemental stoichiometries, while energy dispersive X-ray spectroscopy illustrated good spatial elemental homogeneity within these nanocrystals synthesized under benign conditions. PMID:26228527

  20. The Impact of an Oxygen Dopant in an ideal Bi_2Sr_2CaCu_2O_8 delta Crystal

    SciTech Connect

    Johnston, S.

    2010-05-04

    Recent scanning tunneling microscopy studies have shown that local nanoscale pairing inhomogenities are correlated with interstitial oxygen dopants in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}. Combining electrostatic and cluster calculations, in this paper the impact of a dopant on the local Madelung and charge transfer energies, magnetic exchange J, Zhang-Rice mobility, and interactions with the lattice is investigated. It is found that electrostatic modifications locally increases the charge transfer energy and slightly suppresses J. It is further shown that coupling to c-axis phonons is strongly modified near the dopant. The combined effects of electrostatic modifications and coupling to the lattice yield broadened spectral features, reduced charge gap energies, and a sizable local increase of J. This implies a strong local interplay between antiferromagnetism, polarons, and superconducting pairing.

  1. Induced superconductivity in noncuprate layers of the Bi2Sr2CaCu2O8+? high-temperature superconductor: Modeling of scanning tunneling spectra

    NASA Astrophysics Data System (ADS)

    Suominen, Ilpo; Nieminen, Jouko; Markiewicz, R. S.; Bansil, A.

    2011-01-01

    We analyze how the coherence peaks observed in scanning tunneling spectroscopy (STS) of cuprate high-temperature superconductors are transferred from the cuprate layer to the oxide layers adjacent to the STS microscope tip. For this purpose, we have carried out a realistic multiband calculation for the superconducting state of Bi2Sr2CaCu2O8+? (Bi2212) assuming a short-range d-wave pairing interaction confined to the nearest-neighbor Cu dx2-y2 orbitals. The resulting anomalous matrix elements of the Green’s function allow us to monitor how pairing is then induced not only within the cuprate bilayer but also within and across other layers and sites. The symmetry properties of the various anomalous matrix elements and the related selection rules are delineated.

  2. Microwave microstrip resonator measurements of Y1Ba2Cu3O(7-x) and Bi2Sr2Ca1Cu2O(8-y) thin films

    NASA Technical Reports Server (NTRS)

    Lichtenberg, Christopher L.; Wosik, Jaroslaw; Davis, Matthew; Wolfe, J. C.

    1989-01-01

    Radio frequency (RF) surface resistance measurement experiments on high T(sub c) thin films were performed. The method uses a microstrip resonator comprising a top gold conductor strip, an alumina dielectric layer, and a separate superconductivity ground plane. The surface resistance of the superconducting ground plane can be determined, with reference to a gold calibration standard, from the measured quality factor of the half-wave resonator. Initial results near 7 GHz over the temperature range from 25 to 300 K are presented for YBa2Cu3O(7-x) and Bi2Sr2CaCu2O(8-y) thin film samples deposited by an electron beam flash evaporation process. The RF surface resistance at 25 K for both materials in these samples was found to be near 25 milliohms.

  3. Improvement of critical current density in thallium-based (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) superconductors

    NASA Technical Reports Server (NTRS)

    Ren, Z. F.; Wang, C. A.; Wang, J. H.; Miller, D. J.; Goretta, K. C.

    1995-01-01

    Epitaxial (Tl,Bi)Sr(1.6)Ba(0.4)Ca2Cu3O(x) ((Tl,Bi)-1223) thin films on (100) single crystal LaAlO3 substrates were synthesized by a two-step procedure. Phase development, microstructure, and relationships between film and substrate were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Resistance versus temperature, zero-field-cooled and field cooled magnetization, and transport critical current density (J(sub c)) were measured. The zero-resistance temperature was 105-111 K. J(sub c) at 77 K and zero field was greater than 2 x 10(exp 6) A/sq cm. The films exhibited good flux pinning properties.

  4. Single-crystalline Bi2Sr2CaCu2O8+x detectors for direct detection of microwave radiation

    NASA Astrophysics Data System (ADS)

    Li, M.; Winkler, D.; Yurgens, A.

    2015-04-01

    We test radiation detectors made from single-crystalline Bi2Sr2CaCu2O8+x flakes put on oxidized Si substrates. The 100-nm-thick flakes are lithographically patterned into 4 ×12 ?m2 large rectangles embedded in thin-film log-spiral antennas. The SiO2 layer weakens the thermal link between the flakes and the bath. Two modes of radiation detection have been observed. For a bolometric type of sensors a responsivity of ˜300 V/W and a noise equivalent power of 30 nW/ ?{Hz } has been deduced at 70 K. Much more sensitive is the non-bolometric device showing characteristics similar to a Golay-type detector while being at least a thousand times faster. Making smaller (sub-?m) structures is expected to significantly improve the performance of these devices and makes them very competitive among other microwave and terahertz detectors.

  5. On the application of CaF2:Eu and SrF2:Eu phosphors in LED based phototherapy lamp

    NASA Astrophysics Data System (ADS)

    Belsare, P. D.; Moharil, S. V.; Joshi, C. P.; Omanwar, S. K.

    2013-06-01

    In the last few years the interest of scientific community has been increased towards solid state lighting based on LEDs because of their superior advantages over the conventional fluorescent lamps. As the GaN based LEDs are easily available efforts of the researchers are now on making the new phosphors which are excitable in the near UV region (360-400nm) for solid state lighting. This paper reports the photoluminescence characteristics of CaF2:Eu and SrF2:Eu phosphor prepared by wet chemical method. The violet emission of these phosphors with near UV excitation can be useful in making a phototherapy lamp based on LEDs for treating various skin diseases like acne vulgaris and hyperbilirubinemia.

  6. BEAN MODEL AND AC LOSSES IN Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}/Ag TAPES

    SciTech Connect

    SUENAGA,M.; CHIBA,T.; WIESMANN,H.J.; HALDAR,P.

    1997-10-27

    The Bean model is almost solely used to interpret ac losses in the powder-in-tube processed composite conductor, Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10}/Ag. In order to examine the limits of the applicability of the model, a detailed comparison was made between the values of critical current density J{sub c} for Bi(2223)/Ag tapes which were determined by standard four-probe-dc measurement, and which were deduced from the field dependence of the ac losses utilizing the model. A significant inconsistency between these values of J{sub c} were found, particularly at high fields. Possible sources of the discrepancies are discussed.

  7. Solid-liquid interfacial energy of the Bi sub 0. 7 Pb sub 0. 3 SrCaCu sub 1. 8 O sub x glass

    SciTech Connect

    Nishi, Y.; Manabe, T.; Watanabe, S.; Igarashi, A.; Mikagi, K. )

    1991-11-15

    The solid-liquid interfacial energy is estimated by use of the nucleation frequency of isothermal crystallization on aging in Bi{sub 0.7}Pb{sub 0.3}SrCaCu{sub 1.8}O{sub {ital x}} glassy samples above glass transition temperature. The value of solid-liquid interfacial energy {ital Q} is about 74.7 mJ/m{sup 2}. The {ital Q} value is often expressed by use of enthalpy change {Delta}{ital H}{sub {ital f}}, Avogadro's number {ital N} and molar volume {ital V}; {ital Q} = {ital C}{Delta}{ital H}{sub {ital f}}/({ital N}{sup 1/3}{ital V}{sup 2/3}). The constant {ital C} obtained is 0.38, which is between 0.32 for covalent bonded elements and 0.45 for metals.

  8. Ultrasonic studies of textured superconducting Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+y} in magnetic fields

    SciTech Connect

    Wang, Q.; Almond, D.P.; Saunders, G.A.; Palmer, S.B.; Lim, C.M.; Goretta, K.C.

    1996-07-01

    Measurements have been made of ultrasonic shear wave attenuation and sound velocity in highly textured polycrystalline samples of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+y] in magnetic fields up to 9 tesla and at temperatures down to 4.2 K. Magnetic field dependent attenuation peaks and velocity enhancements were found that are in good agreement with theoretical predictions based on the assumptions of the thermally assisted flux flow model of the mixed state. A pinning activation energy of approximately 160 K was deduced from the ultrasonic data. Pinning energy showed little evidence of dependence upon magnetic field magnitude or orientation. The flux-line lattice was found to be pinned fully at lowest temperatures.

  9. Polaronic quasiparticle injection in organic copper (II) phthalocyanine/Bi2Sr2CaCu2O8+? tunnel junctions

    NASA Astrophysics Data System (ADS)

    Kim, Sunmi; E, Jungyoon; Lee, Kiejin; Ishibashi, Takayuki; Sato, Katsuaki; Friedman, Barry

    2002-04-01

    We report the current transport properties of an organic conductor/superconductor tunnel junction as a high-Tc superconducting three terminal device. The organic copper (II) phthalocyanine (Cu-Pc) layer was used for a polaronic quasiparticle (QP) injector. The junction was investigated in the dark and under ultraviolet radiation. The injection of polaronic QP from the Cu-Pc interlayer into a superconductor Bi2Sr2CaCu2O8+? (BSCCO) thin film generated a substantially larger nonequilibrium effect as compared to the normal QP injection current. The tunneling spectroscopy of a Cu-Pc/BSCCO junction exhibited a zero bias conductance peak, which may be interpreted as Andreev reflection at a Cu-Pc/d-wave superconductor junction.

  10. Inferring effective interactions from the local density of states: application to STM data from Bi_2Sr_2CaCu_2O_8 delta

    SciTech Connect

    Jamei, R.

    2010-04-06

    While the influence of impurities on the local density of states (LDOS) in a metal is notoriously non-local due to interference effects, low order moments of the LDOS in general can be shown to depend only on the local structure of the Hamiltonian. Specifically, we show that an analysis of the spatial variations of these moments permits one to 'work backwards' from scanning tunneling microscopy (STM) data to infer the local structure of the underlying effective Hamiltonian. Applying this analysis to STM data from the high temperature superconductor, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}, we find that the variations of the electro-chemical potential are remarkably small (i.e., the disorder is, in a sense, weak) but that there are large variations in the local magnitude of the d-wave gap parameter.

  11. Effect of neutron irradiation on the London penetration depth for polycrystalline Bi(1.8)Pb(0.3)Sr2Ca2Cu3O10 superconductor

    NASA Technical Reports Server (NTRS)

    Ossandon, J. G.; Thompson, J. R.; Sun, Yang Ren; Christen, D. K.; Chakoumakos, B. C.

    1995-01-01

    Magnetization studies of polycrystalline Bi(1.8)Pb(0.3)Sr2Ca2Cu3O10 superconductor, prior to and after neutron irradiation, showed an increase in J(sub c) due to irradiation damage. Analysis of the equilibrium magnetization revealed significant increases in other more fundamental properties. In particular, the London penetration depth increased by approximately 15 percent following irradiation with 8 x 10(exp 16) neutrons/sq cm. Corresponding changes were observed in the upper critical magnetic field H(sub c2). However, the most fundamental thermodynamic property, the superconductive condensation energy F(sub c), was unaffected by the moderate level of neutron-induced damage.

  12. Series resistance effects in La0.5Ca0.5MnO3/SrTiO3:Nb(0?0?1) heterojunctions

    NASA Astrophysics Data System (ADS)

    Wang, J. F.; Cao, D.; Zhou, Y.; Wang, X. Y.; Jiao, Z. W.; Gao, J.

    2015-09-01

    The effects of series resistance in heterojunctions composed of La0.5Ca0.5MnO3 (LCMO) and Nb:SrTiO3 with 0.05 wt.% and 0.7 wt.% of Nb doping (0.05NbSTO and 0.7NbSTO) have been investigated in detail using current-voltage curves with and without light illumination. Two linear plots, namely, dV/dlnJ versus J and H(J)[?V-(nk B T/q)ln(J/A**T 2)] versus J, have been used to extract the series resistance. These two plots give very close values. The extracted series resistance exhibits a monotonous increase with decreasing temperatures, which could explain the observed anomalous temperature dependence of short circuit current in LCMO/0.7NbSTO.

  13. Quantitative Raman Measurement of the Evolution of the Cooper-pair Density with Doping in Bi2Sr2CaCu2O8+? Superconductors

    SciTech Connect

    Blanc, S.; Gu, G.; Gallais, Y.; Sacuto, A.; Cazayous, M.; Méasson, M.A.; Wen, J.S.; Xu, Z.J.

    2009-10-08

    We report Raman measurements on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals that allow us to quantitatively evaluate the doping dependence of the density of Cooper pairs in the superconducting state. We show that the drastic loss of Cooper pairs in the antinodal region as the doping level is reduced is concomitant with a deep alteration of the quasiparticles dynamic above T{sub c} and consistent with a pseudogap that competes with superconductivity. Our data also reveal that the overall density of Cooper pairs evolves with doping, distinctly from the superfluid density above the doping level p{sub c} = 0.2.

  14. Reinforced fluropolymer nanocomposites with high-temperature superconducting Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y}

    SciTech Connect

    Jayasree, T. K.

    2014-10-15

    Bismuth Strontium Calcium Copper Oxide (Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y})/Polyvinylidene fluoride (PVDF) nanocomposite was prepared and their thermal properties were analyzed. The composite consists of the polyvinylidene fluoride (PVDF) as an insulating polymer matrix, and homogenously distributed Bismuth strontium calcium copperoxide (2212) nanoparticles. SEM data shows flaky grains of the superconductor coated and linked by polymer. Differential scanning calorimetry (DSC) results indicated that the melting point was not affected significantly by the addition of BSCCO. However, the addition of superconducting ceramic resulted in an extra melting peak at a lower temperature (145°C). Thermogravimetric analysis of the samples shows that the onset decomposition temperature of the PVDF matrix was decreased by the addition of SC filler.

  15. Angle-resolved photoemission spectroscopy study of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} thin films

    SciTech Connect

    Marshall, D.S.; Dessau, D.S.; King, D.M.; Park, C.; Matsuura, A.Y.; Shen, Z.; Spicer, W.E.; Eckstein, J.N.; Bozovic, I.

    1995-11-01

    We report angle-resolved photoemission spectroscopy (ARPES) results from Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (2212) single-crystal thin films grown with atomic layer-by-layer molecular beam epitaxy (ALL-MBE). This was made possible by adapting the top-post cleaving technique to thin films of 2212. We have observed clear photoemission features from these films that disperse through the Fermi level. We have observed the superconducting energy gap with ARPES in thin films. Both the magnitude of the gap as well as its anisotropy are consistent with the results from bulk crystals. Furthermore, we observe the pile-up and dip in spectral weight associated with the gap. These results open possibilities for future research using thin-film samples in this materials system that take advantage of the ability to grow metastable materials with ALL-MBE.

  16. The Influence of Impurity Doping On the Phase Transition and Morphology Tuning of Sr/CaFCl: Yb3+,Er3+ Nanoparticles

    NASA Astrophysics Data System (ADS)

    Cui, Yue; Zhao, Suling; Huang, Wenxiao; Xu, Zheng; Li, Yuan; Carroll, David; Suling Zhao Team

    2015-03-01

    Upconversion nanoparticles (UCNPs) are well-known for their unique luminescent properties that enable the conversion of low-energy photons into high-energy photons by multiphoton processes. In this work, Sr/CaFCl: Yb3 +,Er3 + NCs with a wide range of ions dopant concentrations were synthesized, and strong green and red upconversion fluorescence were observed under laser excitation at a wavelength of 980 nm. The influence and mechanism of ions dopant are demonstrated and discussed. The ions doped concentration has a significant influence on the phase-transfer of the host material and on the corresponding upconversion emissions, and the mechanism of which was studied. In addition, the optimized concentration represents a good balance between the occurrence of the phase transition and concentration quenching. These high-efficiency nanoparticles have potential applications in the fields of optical nanodevices and biomedicine.

  17. Current Filamentation in Large Bi2Sr2CaCu2O8 +? Mesa Devices Observed via Luminescent and Scanning Laser Thermal Microscopy

    NASA Astrophysics Data System (ADS)

    Benseman, T. M.; Koshelev, A. E.; Vlasko-Vlasov, V.; Hao, Y.; Kwok, W.-K.; Welp, U.; Keiser, C.; Gross, B.; Lange, M.; Kölle, D.; Kleiner, R.; Minami, H.; Watanabe, C.; Kadowaki, K.

    2015-04-01

    We study the self-heating of a large stack of Bi2Sr2CaCu2O8 +? intrinsic Josephson junctions, of a configuration designed for terahertz generation. We find good qualitative agreement between direct thermoluminescent measurements of the device surface temperature and low-temperature scanning laser microscopy images. In particular, the two techniques both reveal a mode of thermal instability through the asymmetric nucleation of a small hot spot near a corner or edge of the sample. This behavior conforms with a theoretical stability analysis, and the radius of the hot spot is in excellent agreement with theoretical predictions, as is its growth with increasing bias current and bath temperature. Narrow hot spots may offer a possible means of enhancing the terahertz emission power from this type of device.

  18. An electron diffraction study of Bi2Sr2(Gd/x/Ca/1-x/)0.8Cu2O(8+delta)

    NASA Technical Reports Server (NTRS)

    Kulik, J.; Xue, Y. Y.; Sun, Y. Y.; Bonvalot, M.

    1990-01-01

    The compound Bi2Sr2(Gd/x/Ca/1-x/)0.8Cu2O(8+delta) is examined by electron diffraction for several values of x. The incommensurate modulation which has been reported for x = 0 persists for all values of x with the wave vector increasing as x increases. A secondary modulation with a wave vector equal to one-half that of the primary is observed for x equal to or greater than 0.85. This modulation manifests itself through satellite reflections that are highly streaked normal to the (001) planes and that flank certain select positions in reciprocal space. The appearance of this secondary modulation is accompanied by a change in the average crystal structure from B-centered to F-centered orthorhombic.

  19. Reconstructed Fermi surface of underdoped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}+{delta} cuprate superconductors.

    SciTech Connect

    Yang, H.-B.; Rameau, J. D.; Pan, Z.-H.; Gu, G. D.; Johnson, P. D.; Claus, H.; Hinks, D. G.; Kidd, T. E.

    2011-07-20

    The Fermi surface topologies of underdoped samples of the high-T{sub c} superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} have been measured with angle resolved photoemission. By examining thermally excited states above the Fermi level, we show that the observed Fermi surfaces in the pseudogap phase are actually components of fully enclosed hole pockets. The spectral weight of these pockets is vanishingly small at the magnetic zone boundary, creating the illusion of Fermi 'arcs.' The area of the pockets as measured in this study is consistent with the doping level, and hence carrier density, of the samples measured. Furthermore, the shape and area of the pockets is well reproduced by phenomenological models of the pseudogap phase as a spin liquid.

  20. First-principles study of the large-gap three-dimensional topological insulators M3Bi2 (M =Ca , Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Li, Ronghan; Xie, Qing; Cheng, Xiyue; Li, Dianzhong; Li, Yiyi; Chen, Xing-Qiu

    2015-11-01

    By means of first-principles calculations in combination with universal evolutionary structure search, we identified the crystalline structure of long-term argued M3Bi2 (M =Sr , Ca, and Ba), which crystallizes in a tubelike structure stacked by buckled graphenelike layers. The analyses of electronic structures revealed that this type of M3Bi2 is a native wide-gap three-dimensional topological insulator with the inverted band order induced mainly by crystal field effect. The spin-orbit coupling effect was found to open the band gap and further enhance the band inversion. Among them, Sr3Bi2 is most attractive due to its largest fundamental gap of about 0.3 eV and the directly inverted band gap of 0.81 eV at ? obtained within the framework of Green functionals (G W ). Moreover, the computation also evidences that their tubelike structure is suitable for further treatment via magnetic dopants, which prefer to occupy 1 b site. Interestingly, the ferromagnetic insulating state has been achieved for V- and Mn-doped cases. This may provide a further opportunity to observe the quantized anomalous Hall effect in its thin films.

  1. Twentieth century sea surface temperature and salinity variations at Timor inferred from paired coral ?18O and Sr/Ca measurements

    NASA Astrophysics Data System (ADS)

    Cahyarini, Sri Yudawati; Pfeiffer, Miriam; Nurhati, Intan Suci; Aldrian, Edvin; Dullo, Wolf-Christian; Hetzinger, Steffen

    2014-07-01

    The Indonesian Throughflow (ITF), which represents the global ocean circulation connecting the Pacific Warm Pool to the Indian Ocean, strongly influences the Indo-Pacific climate. ITF monitoring since the late 1990s using mooring buoys have provided insights on seasonal and interannual time scales. However, the absence of longer records limits our perspective on its evolution over the past century. Here, we present sea surface temperature (SST) and salinity (SSS) proxy records from Timor Island located at the ITF exit passage via paired coral ?18O and Sr/Ca measurements spanning the period 1914-2004. These high-resolution proxy based climate data of the last century highlights improvements and cautions when interpreting paleoclimate records of the Indonesian region. If the seasonality of SST and SSS is not perfectly in phase, the application of coral Sr/Ca thermometry improves SST reconstructions compared to estimates based on coral ?18O only. Our records also underline the importance of ocean advection besides rainfall on local SSS in the region. Although the El Niño/Southern Oscillation (ENSO) causes larger anomalies relative to the Indian Ocean Dipole (IOD), Timor coral-based SST and SSS records robustly correlate with IOD on interannual time scales, whereas ENSO only modifies Timor SST. Similarly, Timor SST and SSS are strongly linked to Indian Ocean decadal-scale variations that appear to lead Timor oceanographic conditions by about 1.6-2 years. Our study sheds new light on the complex signatures of Indo-Pacific climate modes on SST and SSS dynamics of the ITF. This article was corrected on 8 AUG 2014. See the end of the full text for details.

  2. Reconstructing seawater ?18O from paired coral ?18O and Sr/Ca ratios: Methods, error analysis and problems, with examples from Tahiti (French Polynesia) and Timor (Indonesia)

    NASA Astrophysics Data System (ADS)

    Cahyarini, Sri Yudawati; Pfeiffer, Miriam; Timm, Oliver; Dullo, Wolf-Christian; Schönberg, Dieter Garbe

    2008-06-01

    We compare several statistical routines that may be used to calculate ?18Osw and SSS from paired coral Sr/Ca and ?18O measurements. Typically, the ?18Ocoral-SST relationship is estimated by linear regression of coral ?18O vs. SST. If this method is applied, evidence should be given that at a particular site SST and SSS do not co-vary. In the tropical oceans, SST and ?18Osw (SSS) often co-vary, and this will bias the estimate of the regression slope of ?18Ocoral-SST. Using a stochastic model, we show that covariance leads to a bias in the coefficients of the univariate regression equations. As the slope of the ?18Ocoral-SST relationship has known, we propose to insert this value for ?1 in the regression models. This requires that the constants of the regression equations are removed. To omit the constants, we propose to center the regression equations (i.e., to remove the mean values from the variables). The statistical error propagation is calculated to assess our ability to resolve past variations in ?18Osw (SSS). At Tahiti, we find that the combined analytical uncertainties of coral ?18O and Sr/Ca equal the amplitude of the seasonal cycle of ?18Osw (SSS). Therefore, we cannot resolve the seasonal cycle of SSS at Tahiti. At Timor, the error of reconstructed ?18Osw (SSS) is lower than the magnitude of seasonal variations of ?18Osw (SSS), and the seasonal cycle of ?18Osw (SSS) can be resolved.

  3. Reconstructing seawater ? 18O from paired coral ? 18O and Sr/Ca ratios: Methods, error analysis and problems, with examples from Tahiti (French Polynesia) and Timor (Indonesia)

    NASA Astrophysics Data System (ADS)

    Yudawati Cahyarini, Sri; Pfeiffer, Miriam; Timm, Oliver; Dullo, Wolf-Christian; Schönberg, Dieter Garbe

    2008-06-01

    We compare several statistical routines that may be used to calculate ? 18O sw and SSS from paired coral Sr/Ca and ? 18O measurements. Typically, the ? 18O coral-SST relationship is estimated by linear regression of coral ? 18O vs. SST. If this method is applied, evidence should be given that at a particular site SST and SSS do not co-vary. In the tropical oceans, SST and ? 18O sw (SSS) often co-vary, and this will bias the estimate of the regression slope of ? 18O coral-SST. Using a stochastic model, we show that covariance leads to a bias in the coefficients of the univariate regression equations. As the slope of the ? 18O coral-SST relationship has known, we propose to insert this value for ?1 in the regression models. This requires that the constants of the regression equations are removed. To omit the constants, we propose to center the regression equations (i.e., to remove the mean values from the variables). The statistical error propagation is calculated to assess our ability to resolve past variations in ? 18O sw (SSS). At Tahiti, we find that the combined analytical uncertainties of coral ? 18O and Sr/Ca equal the amplitude of the seasonal cycle of ? 18O sw (SSS). Therefore, we cannot resolve the seasonal cycle of SSS at Tahiti. At Timor, the error of reconstructed ? 18O sw (SSS) is lower than the magnitude of seasonal variations of ? 18O sw (SSS), and the seasonal cycle of ? 18O sw (SSS) can be resolved.

  4. Structural, electronic and optical properties of novel carbonate fluorides ABCO{sub 3}F (A=K, Rb, Cs; B=Ca, Sr)

    SciTech Connect

    Narsimha Rao, E.; Appalakondaiah, S.; Yedukondalu, N.; Vaitheeswaran, G.

    2014-04-01

    In the present study, we performed first principles calculations on the electronic and optical properties of layered alkali–alkaline earth carbonate fluorides which attract attention in the domain of nonlinear optics. The calculated lattice parameters and volumes with and without inclusion of van der Waals (vdW) correction methods to standard density functional methods were compared with experiments. We observed that vdW interactions are predominant in RbCaCO{sub 3}F and CsCaCO{sub 3}F as compared with other computed compounds. The calculated bulk modulus from single crystal elastic constants reveals that these materials are all relatively harder than the KH{sub 2}PO{sub 4} (KDP) crystal. We also found that these materials are wide band gap insulators as obtained from Tran–Blaha modified Becke–Johnson potential. The linear optical properties such as dielectric function, refractive indices, birefringence and absorption spectra are presented. Finally, the calculated birefringence values indicate that these crystals could be promising for producing phase matching in the deep ultra-violet region. - Graphical abstract: The co- and anti-parallel alignment of CO{sub 3} groups leads to larger and smaller SHG coefficients in (a) KCaCO{sub 3}F, (b) KSrCO{sub 3}F, (c) RbSrCO{sub 3}F, (d) RbCaCO{sub 3}F, and (e) CsCaCO{sub 3}F. - Highlights: • Effect of van der Waals interactions on structural properties. • Single-crystalline elastic constants and mechanical stability. • Electronic properties. • Linear optical properties. • Comparison of present computed compounds with other well known materials in non-linear optical materials.

  5. Charge-coupled Substituted Garnets (Y3-xCa0.5xM0.5x)Fe5O12 (M = Ce, Th): Structure and Stability as Crystalline Nuclear Waste Forms

    SciTech Connect

    Guo, Xiaofeng; Kukkadapu, Ravi K.; Lanzirotti, Anthony; Newville, Mathew; Engelhard, Mark H.; Sutton , Steven R.; Navrotsky, Alexandra

    2015-04-20

    The garnet structure has been proposed as a potential crystalline nuclear waste form for accommodation of actinide elements, especially uranium (U). In this study, yttrium iron garnet (YIG) as a model garnet host was studied for the incorporation of U analogs, cerium (Ce), and thorium (Th), incorporated by a charge-coupled substitution with calci-um (Ca) for yttrium (Y) in YIG, namely 2Y3+ = Ca2+ + M4+, where M4+ = Ce4+ or Th4+. Single phase garnets Y3-xCa0.5xM0.5xFe5O12, synthesized by the citrate-nitrate combustion method, were obtained up to x = 0.7. Ce was confirmed to be tetravalent by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. X-ray diffraction and 57Fe-Mössbauer spectroscopy indicated that the samples are single phase, M4+ and Ca2+ cations are restricted to the c-site, the nature of M4+ has only a minor effect on the structure, and the local environments of both the tetrahedral and octahedral Fe3+ are systematically affected by the extent of substitution, especially on the tetrahedral sublattice. The charge coupled substitution has advantages in incorporating Ce/Th and in stabilizing the substituted phases, compared to a single substitution strategy. Enthalpies of formation of garnets were obtained by high temperature oxide melt solution calorimetry, and the enthalpies of substitution of Ce and Th were determined. The thermodynamic analysis demonstrates that the substituted garnets are entropically rather than energetically stabilized. This suggests that such garnets may form and persist in repositories at high temperature but might decompose near room temperature. These structural and thermodynamic findings shed light on possible incorporation of U in this garnet system.

  6. Charge-coupled substituted garnets (Y3-xCa0.5xM0.5x)Fe5O12 (M = Ce, Th): structure and stability as crystalline nuclear waste forms.

    PubMed

    Guo, Xiaofeng; Kukkadapu, Ravi K; Lanzirotti, Antonio; Newville, Matthew; Engelhard, Mark H; Sutton, Stephen R; Navrotsky, Alexandra

    2015-04-20

    The garnet structure has been proposed as a potential crystalline nuclear waste form for accommodation of actinide elements, especially uranium (U). In this study, yttrium iron garnet (YIG) as a model garnet host was studied for the incorporation of U analogs, cerium (Ce) and thorium (Th), incorporated by a charge-coupled substitution with calcium (Ca) for yttrium (Y) in YIG, namely, 2Y(3+) = Ca(2+) + M(4+), where M(4+) = Ce(4+) or Th(4+). Single-phase garnets Y3-xCa0.5xM0.5xFe5O12 (x = 0.1-0.7) were synthesized by the citrate-nitrate combustion method. Ce was confirmed to be tetravalent by X-ray absorption spectroscopy and X-ray photoelectron spectroscopy. X-ray diffraction and (57)Fe-Mössbauer spectroscopy indicated that M(4+) and Ca(2+) cations are restricted to the c site, and the local environments of both the tetrahedral and the octahedral Fe(3+) are systematically affected by the extent of substitution. The charge-coupled substitution has advantages in incorporating Ce/Th and in stabilizing the substituted phases compared to a single substitution strategy. Enthalpies of formation of garnets were obtained by high temperature oxide melt solution calorimetry, and the enthalpies of substitution of Ce and Th were determined. The thermodynamic analysis demonstrates that the substituted garnets are entropically rather than energetically stabilized. This suggests that such garnets may form and persist in repositories at high temperature but might decompose near room temperature. PMID:25853274

  7. Shear-induced vortex decoupling in Bi2Sr2CaCu2O8 crystals B. Khaykovich, D. T. Fuchs,* K. Teitelbaum, Y. Myasoedov, and E. Zeldov

    E-print Network

    Zeldov, Eli

    Shear-induced vortex decoupling in Bi2Sr2CaCu2O8 crystals B. Khaykovich, D. T. Fuchs,* K simultaneous transport measurements. The findings are ascribed to a shear-induced decoupling, in which due to surface barriers,9 most of the samples were prepared in a form of large square platelets

  8. Tl/Pb and Sr/Ba cuprates of type 1212: compositional effect on the purity and on the superconducting properties

    NASA Astrophysics Data System (ADS)

    Lebbou, K.; Cohen-Adad, M. Th; Abraham, R.; Trosset, S.; Gladyshevskii, R. E.; Flükiger, R.; Galez, P.; Schulz, G. W.; Weber, H. W.; Couach, M.

    1998-03-01

    The effect of Sr/Ba and Tl/Pb substitutions has been investigated for Tl 1- xPb x(Sr 1- yBa y) 2CaCu 2O 7- ? (0? x and/or y?1) compounds produced by conventional solid state reaction. The observed phases were characterized by X-ray powder diffraction, scanning electron microscopy and their nominal composition has been controlled by plasma emission spectroscopy. A tentative single phase field is proposed at T?960°C. For x=0.5, the highest weight fraction of the (Tl 0.5Pb 0.5)(Sr/Ba)-1212 phase was found to be 96.4% and 94% when Ba increases from 0 to 0.2. It drastically decreases when Ba content is over 0.3. For Ba over 0.3, (Tl/Pb)(Sr/Ba)-1223 and perovskite (Tl/Pb)(Sr/Ba)O 3 are observed as main impurities and their content increases with Ba stoichiometry. The unit cell parameters of (Tl 0.5Pb 0.5)(Sr/Ba)-1212 phase increase when Sr atoms are progressively replaced by Ba atoms. Structural refinement leads to conclude that 10 at% of Tl would be substituted on Ca sites and less than 2 at% of Ca could be substituted on Sr sites. The distance between the Cu atom and the apical O atom of the square pyramid increases only slightly when the Ba content raises. The critical temperature remains between 80 and 90 K and seems to be affected by the substitution Sr/Ba.

  9. SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} - two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)

    SciTech Connect

    Stegmaier, Saskia; Faessler, Thomas F.

    2012-08-15

    SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}, 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 SrZn{sub 2}Sn{sub 2} comprises (anti-)PbO-like {l_brace}ZnSn{sub 4/4}{r_brace} and {l_brace}SnZn{sub 4/4}{r_brace} layers. Ca{sub 2}Zn{sub 3}Sn{sub 6} shows similar {l_brace}ZnSn{sub 4/4}{r_brace} layers and {l_brace}Sn{sub 4}Zn{r_brace} 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. SrZn{sub 2}Sn{sub 2} adopts the SrPd{sub 2}Bi{sub 2} structure type, and Ca{sub 2}Zn{sub 3}Sn{sub 6} is isotypic to the R{sub 2}Zn{sub 3}Ge{sub 6} compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6} 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 {l_brace}Sn{sub 4}Zn{r_brace} layers of Ca{sub 2}Zn{sub 3}Sn{sub 6}. - Graphical abstract: Crystal structures of the new Ae-Zn-Sn polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Highlights: Black-Right-Pointing-Pointer New polar intermetallic phases SrZn{sub 2}Sn{sub 2} and Ca{sub 2}Zn{sub 3}Sn{sub 6}. Black-Right-Pointing-Pointer Obtained by high temperature reactions of the elements. Black-Right-Pointing-Pointer Single crystal XRD structure determination and DFT electronic structure calculations. Black-Right-Pointing-Pointer Closely related crystal and electronic structures. Black-Right-Pointing-Pointer Metallic conductivity coexisting with lone pairs and covalent bonding features.

  10. Structural analysis of xSrO-(50-x)CaO-50P2O5 glasses with x=0, 5, or 10mol% for potential use in a local delivery system for osteomyelitis treatment.

    PubMed

    Comeau, P A; Filiaggi, M J

    2016-01-01

    The introduction of ions into a local delivery matrix is one method of managing degradation and subsequent release of the incorporated therapeutic agents. Of interest in this study was whether we could modify the structural nature of calcium polyphosphate (CPP) glass and the subsequent therapeutic potential of this local delivery matrix with inclusion of strontium (Sr). We found that adding 10mol% Sr significantly increased the density and chain length of the glass. There was no significant impact of Sr doping on the subsequent loading of vancomycin into the matrix, or the matrix porosity. The noted differences in structural stability, ion release, and vancomycin release between the un-doped CPP matrices and 10mol% Sr-doped CPP matrices in vitro are likely a result of a decrease in glass disorder upon Sr addition to the glass and preferential retention of Sr over Ca during matrix degradation. This study has provided further evidence that Sr incorporation may serve to both manipulate antibiotic release from the amorphous CPP matrix and provide a potential source of therapeutic ions for enhanced bone regeneration. PMID:26478355

  11. Synthesis of alkylsulfonyl and substituted benzenesulfonyl curcumin mimics as dual antagonist of L-type Ca(2+) channel and endothelin A/B2 receptor.

    PubMed

    Park, Chong-Bin; Ahn, Chan Mug; Oh, Sangtae; Kwon, Daeho; Cho, Won-Chul; Shin, Woon-Seob; Cui, Yuan; Um, Ye Sol; Park, Byong-Gon; Lee, Seokjoon

    2015-10-15

    We synthesized a library of curcumin mimics with diverse alkylsulfonyl and substituted benzenesulfonyl modifications through a simple addition reaction of important intermediate, 1-(3-Amino-phenyl)-3-(4-hydroxy-3-methoxy-phenyl)-propenone (10), with various sulfonyl chloride reactants and then tested their vasodilatation effect on depolarization (50mM K(+))- and endothelin-1 (ET-1)-induced basilar artery contraction. Generally, curcumin mimics with aromatic sulfonyl groups showed stronger vasodilation effect than alkyl sulfonylated curcumin mimics. Among the tested compounds, six curcumin mimics (11g, 11h, 11i, 11j, 11l, and 11s) in a depolarization-induced vasoconstriction and seven compounds (11g, 11h, 11i, 11j, 11l, 11p, and 11s) in an ET-1-induced vasoconstriction showed strong vasodilation effect. Based on their biological properties, synthetic curcumin mimics can act as dual antagonist scaffold of L-type Ca(2+) channel and endothelin A/B2 receptor in vascular smooth muscle cells. In particular, compounds 11g and 11s are promising novel drug candidates to treat hypertension related to the overexpression of L-type Ca(2+) channels and ET peptides/receptors-mediated cardiovascular diseases. PMID:26386817

  12. Nicotinic Acid Adenine Dinucleotide Phosphate Analogues Substituted on the Nicotinic Acid and Adenine Ribosides. Effects on ReceptorMediated Ca²? Release.

    PubMed

    Trabbic, Christopher J; Zhang, Fan; Walseth, Timothy F; Slama, James T

    2015-04-23

    Nicotinic acid adenine dinucleotide phosphate (NAADP) is a Ca(2+) releasing intracellular second messenger in both mammals and echinoderms. We report that large functionalized substituents introduced at the nicotinic acid 5-position are recognized by the sea urchin receptor, albeit with a 20-500-fold loss in agonist potency. 5-(3-Azidopropyl)-NAADP was shown to release Ca(2+) with an EC50 of 31 ?M and to compete with NAADP for receptor binding with an IC50 of 56 nM. Attachment of charged groups to the nicotinic acid of NAADP is associated with loss of activity, suggesting that the nicotinate riboside moiety is recognized as a neutral zwitterion. Substituents (Br- and N3-) can be introduced at the 8-adenosyl position of NAADP while preserving high potency and agonist efficacy and an NAADP derivative substituted at both the 5-position of the nicotinic acid and at the 8-adenosyl position was also recognized although the agonist potency was significantly reduced. PMID:25826221

  13. The Substitution of CO 3 Groups for Copper in Y 1- xCa xBa 2Cu 3O 7: HREM Study

    NASA Astrophysics Data System (ADS)

    Domengès, B.; Boullay, Ph.; Hervieu, M.; Raveau, B.

    1994-02-01

    The carbonation of the 123-type cuprates (Y 1- xCa x) nBa 2 nCu 3 n-1 CO 3O 7 n-3 has been studied by high-resolution electron microscopy. The investigation of the system, varying x and n, shows that the most stable phase is the n = 2 member. A structural model is proposed from XRD profile analysis for Y 1.3Ca 0.7Ba 4Cu 5CO 3O 11. The contrast of the HREM images was calculated on the basis of the XRD data and is discussed depending on focus values, carbon substitution, and crystal thickness. The study of the distribution of the CO 3 groups versus composition shows that different n members are locally stabilized, from n = 1 to n = ?. Short thermal treatments involve the formation of local ordering, in domains of some tens of angströms width, which correspond to local superstructures along [110] and [031]; 90° oriented domains are frequent phenomena in these materials, and the boundaries are generally parallel to (001). Some intergrowth defects, in the form of "124" members, are observed.

  14. Investigation into the effect of Si doping on the cell symmetry and performance of Sr{sub 1?y}Ca{sub y}FeO{sub 3??} SOFC cathode materials

    SciTech Connect

    Porras-Vazquez, Jose M.; Smith, R.I.; Slater, Peter R.

    2014-05-01

    In this paper we report the successful incorporation of silicon into Sr{sub 1?y}Ca{sub y}FeO{sub 3??} perovskite materials for potential applications as electrode materials for Solid Oxide Fuel Cells. It is observed that Si doping leads to a change from a tetragonal or orthorhombic structure (with partial ordering of oxygen vacancies) to a cubic one (with the oxygen vacancies disordered). The structures of the phases, SrFe{sub 0.85}Si{sub 0.15}O{sub 3??}, Sr{sub 0.75}Ca{sub 0.25}Fe{sub 0.85}Si{sub 0.15}O{sub 3??} and Sr{sub 0.5}Ca{sub 0.5}Fe{sub 0.85}Si{sub 0.15}O{sub 3??}, were analysed using neutron powder diffraction. The data confirmed the cubic unit cell, with no long range oxygen vacancy ordering. Conductivity measurements showed an improvement in the conductivity on Si doping, especially for samples with high Ca content. Composite electrodes comprising 50% Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95} and 50% Sr{sub 1?y}Ca{sub y}(Fe/Si)O{sub 3??} on dense Ce{sub 0.9}Gd{sub 0.1}O{sub 1.95} pellets were therefore examined in air. An improvement in the area specific resistances (ASR) values is observed for the Si-doped samples with respect to the undoped samples. Thus the results show that silicon can be incorporated into Sr{sub 1?y}Ca{sub y}FeO{sub 3??}-based materials and can have a beneficial effect on the performance, making them potentially suitable for use as cathode material in Solid Oxide Fuel Cells (SOFC). - Graphical abstract: X-ray diffraction patterns for: (left) Sr{sub 0.75}Ca{sub 0.25}Fe{sub 1?x}Si{sub x}O{sub 3??} (x=0, 0.05, 0.10 and 0.15) and (right) Sr{sub 0.25}Ca{sub 0.75}Fe{sub 1?x}Si{sub x}O{sub 3??} (x=0, 0.05, 0.10 and 0.15), showing the stabilization of the cubic form of these series through silicon doping. For the latter Sr{sub 0.25}Ca{sub 0.75}Fe{sub 1?x}Si{sub x}O{sub 3??} phase, the stabilisation is not quite complete at 15% Si doping. - Highlights: • In Sr{sub 1?y}Ca{sub y}Fe{sub 1?x}Si{sub x}O{sub 3??} materials Si doping results in a change from tetragonal or orthorhombic symmetry. • An improvement in the conductivity is observed on Si doping. • An improvement in the area specific resistances (ASR) values is observed on Si doping. • Silicon can have a beneficial effect on the performance in perovskite materials.

  15. Rectifying and photovoltaic properties of the heterojunction composed of CaMnO3 and Nb-doped SrTiO3

    NASA Astrophysics Data System (ADS)

    Sun, J. R.; Zhang, S. Y.; Shen, B. G.; Wong, H. K.

    2005-01-01

    A heterojunction composed of CaMnO3 (CMO) and Nb-doped SrTiO3 (STON) was fabricated and its properties were studied and compared with La0.67Ca0.33MnO3/STON and LaMnO3+?/STON p-n, junctions. This CMO/STON junction exhibits an asymmetric current-voltage relation similar to a p-n junction. The most remarkable discovery is that the magnetic state of the manganites has a strong impact on the rectifying behaviors. The diffusion voltage, which is the critical voltage for the current rush, shows a tendency to decrease/increase with the establishment of the antiferromagnetic/ferromagnetic order in the manganites of the junction. Similar to other manganite p-n junctions, CMO/STON also exhibits a significant photovoltaic effect, and the maximum photovoltage is ˜2.2mV under the illumination of ˜7mW light (?=460nm). A qualitative explanation is given based on an analysis on the band diagram of the junctions.

  16. Investigation into the effect of molybdenum-site substitution on the performance of Sr2Fe1.5Mo0.5O6-? for intermediate temperature solid oxide fuel cells

    NASA Astrophysics Data System (ADS)

    Hou, Mingyue; Sun, Wang; Li, Pengfa; Feng, Jie; Yang, Guoquan; Qiao, Jinshuo; Wang, Zhenhua; Rooney, David; Feng, Jinsheng; Sun, Kening

    2014-12-01

    In this paper, niobium doping is evaluated as a means of enhancing the electrochemical performance of a Sr2Fe1.5Mo0.5O6-? (SFM) perovskite structure cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) applications. As the radius of Nb approximates that of Mo and exhibits +4/+5 mixed valences, its substitution is expected to improve material performance. A series of Sr2Fe1.5Mo0.5-xNbxO6-? (x = 0.05, 0.10, 0.15, 0.20) cathode materials are prepared and the phase structure, chemical compatibility, microstructure, electrical conductivity, polarization resistance and power generation are systematically characterized. Among the series of samples, Sr2Fe1.5Mo0.4Nb0.10O6-? (SFMNb0.10) exhibits the highest conductivity value of 30 S cm-1 at 550 °C, and the lowest area specific resistance of 0.068 ? cm2 at 800 °C. Furthermore, an anode-supported single cell incorporating a SFMNb0.10 cathode presents a maximum power density of 1102 mW cm-2 at 800 °C. Furthermore no obvious performance degradation is observed over 15 h at 750 °C with wet H2 (3% H2O) as fuel and ambient air as the oxidant. These results demonstrate that SFMNb shows great promise as a novel cathode material for IT-SOFCs.

  17. The effect of multilayered Bi1.8Pb0.4Ca2.2Sr2Cu3Ox/Ag on superconducting and microstructure properties of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox

    NASA Astrophysics Data System (ADS)

    Akdogan, Mustafa; Terzioglu, Cabir; Belenli, Ibrahim

    2010-03-01

    A precursor powder with a nominal chemical composition of Bi1.8Pb0.4Ca2.2Sr2Cu3Ox was used to fabricate the multilayered Bi1.8Pb0.4Ca2.2Sr2Cu3Ox/Ag samples (number of layers was 2, 4 and 8) using the powder-in-tube method (PIT). The density of powder increases during the drawing procedure and inside the composite wires of the final diameter is 3.54 mm. By an intermediate rolling, pressing and annealing procedure, the wires were rolled to obtain tapes. The rolling process was not effective in obtaining further substantially increase of the powder density, but greatly improved the orientation of ceramic grains inside the silver sheath. The sample is composed of a highly oriented Bi-2223 phase in the region near to the Ag layer. The eight-layered sample exhibits a rather high Ic value of 110 A. Tc and Jc are enhanced by increasing the number of Ag layers. The formation of the dense oriented structure is near the interface between oxide and the Ag layer. This suggests that Ag plays an important role in the improvement of Jc.

  18. 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.

    1993-12-09

    The solid solution region and reaction kinetics of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (2212) superconductor were examined as a function of temperature and oxygen partial pressure. Crystallization studies from the glassy and molten states were undertaken to determine the phase transformation and kinetics associated with the formation of 2212 and other competing phases. Crystallization of nominal 2212 glasses was found to proceed 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. However, its formation below 800 C was kinetically limited. At 800 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. In low oxygen partial pressures, the solidus is reduced to approximately 750 C. Solidification studies revealed an eutectic structure separating the incongruently melting 2212/2201 phases at high oxygen partial pressures from the congruently melting 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. During solidification in various oxygen partial pressures, the separation of CaO in the melt and the initial crystallization of alkaline-earth cuprates leaves behind a Bi-rich liquid from which it is impossible to form single-phase 2212. Hence, significant amounts of 2201 were also present in these samples. These problems could be reduced by melt processing in inert atmospheres. Bulk 2212 material produced in this manner was found to possess high transition temperatures, high intergranular critical current densities below 20K, and modest critical current densities at 77K.

  19. Electrical and thermal conductivities of congruently melting single crystals of isovalent M 1 - x M'xF2 solid solutions ( M, M' = Ca, Sr, Cd, Pb) in relation to their defect fluorite structure

    NASA Astrophysics Data System (ADS)

    Sorokin, N. I.; Karimov, D. N.; Buchinskaya, I. I.; Popov, P. A.; Sobolev, B. P.

    2015-07-01

    The electrical and thermal conductive properties of two-component single crystals of Pb0.67Cd0.33F2, Ca0.59Sr0.41F2, and Cd0.77Sr0.23F2 solid solutions with fluorite-type structure (CaF2), characterized by congruent melting (presence of minima in melting curves) and uniform distribution of components in the crystal bulk. Pb0.67Cd0.33F2 crystals, in contrast to isostructural Ca0.59Sr0.41F2 and Cd0.77Sr0.23F2 crystals, are characterized by high fluorine-ion electrical conductivity (? = 0.02 S/m at 293 K); low ion-transport activation enthalpy (? H ? 0.4 eV); low thermal conductivity ( k = 1.1 W/mK at 300 K); and glassy behavior of heat transfer, which is atypical for crystalline state. This anomalous behavior of the electrical and thermal conductivities of Pb0.67Cd0.33F2 crystals is due to the strong structural disordering of the anionic subsystem (which is retained at room temperature) as a result of isovalent replacements of Pb2+ cations with Cd2+ cations.

  20. Understanding processing-microstructure-properties relationships in Bi2Sr2CaCu2Ox/Ag round wires and enhanced transport through saw-tooth processing

    NASA Astrophysics Data System (ADS)

    Naderi, Golsa; Liu, Xiaotao; Nachtrab, William; Schwartz, Justin

    2013-10-01

    Superconducting magnets generating magnetic fields above 25 T are needed for many scientific applications. Due to fundamental limitations in NbTi and Nb3Sn, such high-field superconducting magnets require alternative high-field conductors. One candidate conductor is round wire composites of Bi2Sr2CaCu2Ox sheathed in a Ag-alloy matrix (Bi2212/Ag). The performance of such wires is sensitive to the heat treatment, so improvements in the critical current density (Jc) require a thorough understanding of the processing-structure-properties relationships. Here we present a two-part study. In part I, a new heat treatment approach, saw-tooth processing (STP), is introduced based upon previous results showing that Bi2212 nucleation is site-saturation limited. The microstructural evolution of Bi2212 filaments during processing is discussed and results from STP are compared with those from other processes. STP is shown to increase Jc by 120% and 70% relative to partial-melt processing at 5 T and self-field respectively, and by 65% and 34% relative to split-melt processing. Yet STP also complicates the heat treatment by introducing a number of new heat treatment variables that affect the grain morphology, phase assemblage and oxygen content of the Bi2212 filaments and thus the transport properties. In part II, the effects of STP heat treatment parameters on the microstructure and transport properties are discussed. It is shown that wires with the highest transport critical current densities primarily have filaments with two types of microstructures, one comprised primarily of highly textured Bi2212 grains, and another with a noticeable amount of Bi2Sr2CuOx with the Bi2212.

  1. Elaboration of Ti{sub 0.5}Pb{sub 0.5}Sr{sub 2}CaCu{sub 2}O{sub x} superconducting phases by an ultrasonic spray-pyrolysis process

    SciTech Connect

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

    1998-02-01

    An ultrasonic spray-pyrolysis process has been used to prepare a homogeneous T{sub 10.5}Pb{sub 0.5}Sr{sub 2}CaCu{sub 2}O{sub x} high-temperature superconductor. Depending on experimental conditions, the grain morphology changes from platelet to cauliflower-like, contrary to the three copper layers series. The (Tl/Pb)-Sr-1212 phase has remarkable stability and does not decompose before melting. The critical temperature onset, about 80 K, is similar to that for samples prepared by the usual sintering methods.

  2. X-ray photoelectron study of Bi{sub 2}Sr{sub 2}CaCu{sub 2{minus}x}Co{sub x}O{sub {approximately}8}

    SciTech Connect

    Man, N.K.; Hien, T.D.; Kumari, K.; Venkatesh, S.; Garg, K.B.; Sinh, N.K.; Phuc, N.X.

    1999-05-30

    An X-ray photoelectron spectroscopy study has been performed on well characterized Bi{sub 2}Sr{sub 2}CaCu{sub 2{minus}x}Co{sub x}O{sup {approximately}8} (x = 0, 0.02 and 0.1) samples. There is a shift in the Sr binding energy with Co concentration, which is related to the change in {Tc}. This relationship can be understood by the change of hole concentration in the CuO{sub 2} planes as a result of Cobalt doping. The results of Bi 4f and Co 2p core level spectra are also discussed in detail.

  3. The decline of winter monsoon velocity in the South China Sea through the 20th century: Evidence from the Sr/Ca records in corals

    USGS Publications Warehouse

    Liu, Yajing; Peng, Z.; Chen, T.; Wei, G.; Sun, W.; Sun, R.; He, J.; Liu, Gaisheng; Chou, C.-L.; Zartman, R.E.

    2008-01-01

    A modern massive Porites coral was collected from the Longwan Bay (19??20???N, 110??39???E) on the east coast of the Hainan Island, China. The coral was sectioned vertical to the growth axis into discs of double density-bands representing annual growth. The samples were analyzed for the Sr/Ca ratio by inductively coupled plasma atomic emission spectrometry. The history of winter sea-surface temperature (SST) is reconstructed using the Sr/Ca ratio in winter bands of corals. The winter SST at Xisha in the middle of the South China Sea (SCS) is weakly correlated with the instrument-measured winter monsoon velocity (WMV) with a correlation coefficient of 0.19. The winter SST data from corals at Longwan Bay, Hainan, in the northern SCS are moderately correlated with the WMV (r = 0.40). Interestingly we found that the difference of winter SSTs between the two sites (Xisha and Longwan Bay, Hainan) (the X-H index) is significantly negatively correlated with the WMV (r = - 0.73). This negative correlation may be related to the intrusion of the warm Kuroshio Current into the SCS through the Luzon Strait promoted by the strong northeastern monsoon winds in the winter. Using the relationship between our coralline data and observed WMV, the calculated winter monsoon velocity (WMVc) was obtained for 87??years. This data set in combination with the instrument-measured data between 1993 and 1998 generate a record of WMVc for a period of 93??years from 1906 to 1998. The WMVc in the 20th century shows significant interannual and decadal variability with a trend of persistent decline in the whole 20th century at the rate of decrease of - 0.02 (m/s)/a. The lowest wind velocity occurred during the last two decades of the 20th century. The WMVc has decreased significantly by about 30% from the early to the late of 20th century. The 20th century decline of winter monsoon velocity evidenced from the SCS coral records is consistent with the atmosphere-ocean general circulation models (AOGCMs) simulations for monsoon response to increasing temperatures. In addition, an obvious decline shift of WMV around 1976 can be seen in both instrumental and proxy records and it coincides with many other Pacific records. This shift is likely to correspond to a Pacific-wide change in the Pacific Decadal Oscillation occurring at the same time. ?? 2008 Elsevier B.V. All rights reserved.

  4. Structural and dielectric properties of A(Fe{sub 1/2}Ta{sub 1/2})O{sub 3} [A = Ba, Sr, Ca

    SciTech Connect

    Dutta, Alo

    2011-04-15

    Graphical abstract: FTIR spectra of BFT, SFT and CFT at room temperature. Research highlights: {yields} The structural and dielectric properties of BaFe{sub 1/2}Ta{sub 1/2}O{sub 3}, SrFe{sub 1/2}Ta{sub 1/2}O{sub 3} and CaFe{sub 1/2}Ta{sub 1/2}O{sub 3}. {yields} Fourier transform infrared spectra show two primary phonon modes of the samples at around 450 cm{sup -1} and 620 cm{sup -1}. {yields} The compounds show significant frequency dispersion in its dielectric properties. {yields} The relaxation mechanism of the samples is modelled by Cole-Cole equation. -- Abstract: The complex perovskite oxide barium iron tantalate (BFT), BaFe{sub 1/2}Ta{sub 1/2}O{sub 3}, strontium iron tantalate (SFT), SrFe{sub 1/2}Ta{sub 1/2}O{sub 3} and calcium iron tantalate (CFT), CaFe{sub 1/2}Ta{sub 1/2}O{sub 3} are synthesized by a solid-state reaction technique. Rietveld refinement of the X-ray diffraction data of the samples shows that BFT and SFT crystallize in cubic structure, with lattice parameter a = 4.06 A for BFT and 3.959 A for SFT, whereas CFT crystallizes in orthorhombic structure having lattice parameters a = 5.443 A, b = 5.542 A and c = 7.757 A. Fourier transform infrared spectra show two primary phonon modes of the samples at around 450 cm{sup -1} and 620 cm{sup -1}. The compounds show significant frequency dispersion in its dielectric properties. The complex impedance plane plots of the samples show that the relaxation (conduction) mechanism in these materials is purely a bulk effect arising from the semiconductive grains. The relaxation mechanism of the samples is modelled by Cole-Cole equation. The frequency dependent conductivity spectra are found to follow the power law.

  5. Electronic transport properties of MFe2As2 (M = Ca, Eu, Sr) at ambient and high pressures up to 20 GPa

    NASA Astrophysics Data System (ADS)

    Morozova, Natalia V.; Karkin, Alexander E.; Ovsyannikov, Sergey V.; Umerova, Yuliya A.; Shchennikov, Vladimir V.; Mittal, R.; Thamizhavel, A.

    2015-12-01

    We experimentally investigated the electronic transport properties of four iron pnictide crystals, namely, EuFe2As2, SrFe2As2, and CaFe2As2 parent compounds, and superconducting CaFe1.94Co0.06As2 at ambient and high pressures up to 20 GPa. At ambient pressure we examined the electrical resistivity, Hall and magnetoresistance effects of the samples in a temperature range from 1.5 to 380 K in high magnetic fields up to 13.6 T. In this work we carried out the first simultaneous investigations of the in-plane and out-of-plane Hall coefficients, and found new peculiarities of the low-temperature magnetic and structural transitions that occur in these materials. In addition, the Hall coefficient data suggested that the parent compounds are semimetals with a multi-band conductivity that includes hole-type and electron-type bands. We measured the pressure dependence of the thermoelectric power (the Seebeck effect) of these samples up to 20 GPa, i.e. across the known phase transition from the tetragonal to the collapsed tetragonal lattice. The high-pressure behavior of the thermopower of EuFe2As2 and CaFe2As2 showing the p-n sign inversions was consistent with the semimetal model described above. By means of thermopower, we found in single-crystalline CaFe2As2 direct evidence of the band structure crossover related to the formation of As–As bonds along the c-axis on the tetragonal ? collapsed tetragonal phase transition near 2 GPa. We showed that this feature is distinctly observable only in high-quality samples, and already for re-pressurization cycles this crossover was strongly smeared because of the moderate deterioration of the sample. We also demonstrated by means of thermopower that the band structure crossover that should accompany the tetragonal ? collapsed tetragonal phase transition in EuFe2As2 near 8 GPa is hardly visible even in high-quality single crystals. This behavior may be related to a gradual valence change of the Eu ions under pressure that leads to an injection of free electrons and the steady shift of the conduction to n-type.

  6. Effects of Sr{sup 2+} substitution on photoluminescence characteristics of Ba{sub 1?x?y}Sr{sub y}ZrSi{sub 3}O{sub 9}:xEu{sup 2+} phosphors

    SciTech Connect

    Chiang, Chung-Hao; Gong, Syuan-Jhih; Lin, Han-Yu; Zhan, Ting-Shi; Chu, Sheng-Yuan

    2014-12-14

    In this work, single-phase Ba{sub 1?x?y}Sr{sub y}ZrSi{sub 3}O{sub 9}:xEu{sup 2+} phosphors were synthesized via the solid-state reaction method. The crystal structure and luminescence properties were investigated using X-ray diffraction and photoluminescence measurements, respectively. An increase of the dopant Sr{sup 2+} increased the emission intensity of the phosphors. The peak intensity of the samples was at y?=?0.4 under near-ultraviolet light excitation (397?nm). The wavelength of the emission peaks red-shifts slightly from 477 to 483?nm due to the splitting of the 5d energy level. Sr{sup 2+} ions have a smaller ionic radius than that of Ba{sup 2+} ions, and thus the dopant changes the crystal structure, improving the energy transfer efficiency between luminescence centers. More Eu{sup 2+} solid solubility was found in Ba{sub 0.6?x}Sr{sub 0.4}ZrSi{sub 3}O{sub 9}:xEu{sup 2+} phosphors (10?mol.?%) than in the host BaZrSi{sub 3}O{sub 9} (6?mol.?%), which enhanced the emission intensity. In addition, the thermal reliability of the phosphors was studied.

  7. Structural and electronic properties of Sr{sub 1?x}Ca{sub x}Ti{sub 0.5}Mn{sub 0.5}O{sub 3}

    SciTech Connect

    Qasim, Ilyas; Blanchard, Peter E.R.; Kennedy, Brendan J.; Kamiyama, Takashi; Miao, Ping; Torii, Shuki

    2014-05-01

    The series of Sr{sub 1?x}Ca{sub x}Ti{sub 1/2}Mn{sub 1/2}O{sub 3} perovskites has been prepared using solid state methods and their structures determined using combination of synchrotron X-ray and powder neutron diffraction. At room temperature the crystal structure evolves with increasing Ca content from Pm3{sup ¯}m?tetragonal I4/mcm?orthorhombic Pbnm, as a consequence of the sequential introduction of cooperative tilting of the (Ti/Mn)O{sub 6} octahedra. X-ray absorption measurements show the Mn is tetravalent in all oxides. Magnetic susceptibility measurements demonstrate all the oxides to be paramagnetic at room temperature, with a transition to a spin glass arrangement occurring at low temperatures. Electrical measurements prove that all the members are semiconductors and their activation energy increase with Ca doping amount. - Graphical abstract: Changes in the bond valence sums for the A- and B-sites in Sr{sub 1?x}Ca{sub x}Mn{sub 0.5}Ti{sub 0.5}O{sub 3} reflect changes in the symmetry of the oxides. - Highlights: • Structures of the Sr{sub 1?x}Ca{sub x}Ti{sub 1/2}Mn{sub 1/2}O{sub 3} perovskites studies using synchrotron X-ray and powder neutron diffraction. • Tilting of the octahedra occurs as Ca content increases. • Changes in the bond valence sums for the A- and B-sites cations reflect changes in the crystal symmetry. • Magnetic properties dependent of Ca content.

  8. High-pressure synthesis, crystal structures, and magnetic properties of 5d double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6.

    PubMed

    Yuan, Yahua; Feng, Hai L; Ghimire, Madhav Prasad; Matsushita, Yoshitaka; Tsujimoto, Yoshihiro; He, Jianfeng; Tanaka, Masahiko; Katsuya, Yoshio; Yamaura, Kazunari

    2015-04-01

    Double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 have been synthesized under high-pressure and high-temperature conditions (6 GPa and 1500 °C). Their crystal structures and magnetic properties were studied by a synchrotron X-ray diffraction experiment and by magnetic susceptibility, specific heat, isothermal magnetization, and electrical resistivity measurements. Ca2MgOsO6 and Sr2MgOsO6 crystallized in monoclinic (P21/n) and tetragonal (I4/m) double-perovskite structures, respectively; the degree of order of the Os and Mg arrangement was 96% or higher. Although Ca2MgOsO6 and Sr2MgOsO6 are isoelectric, a magnetic-glass transition was observed for Ca2MgOsO6 at 19 K, while Sr2MgOsO6 showed an antiferromagnetic transition at 110 K. The antiferromagnetic-transition temperature is the highest in the family. A first-principles density functional approach revealed that Ca2MgOsO6 and Sr2MgOsO6 are likely to be antiferromagnetic Mott insulators in which the band gaps open, with Coulomb correlations of ?1.8-3.0 eV. These compounds offer a better opportunity for the clarification of the basis of 5d magnetic sublattices, with regard to the possible use of perovskite-related oxides in multifunctional devices. The double-perovskite oxides Ca2MgOsO6 and Sr2MgOsO6 are likely to be Mott insulators with a magnetic-glass (MG) transition at ?19 K and an antiferromagnetic (AFM) transition at ?110 K, respectively. This AFM transition temperature is the highest among double-perovskite oxides containing single magnetic sublattices. Thus, these compounds offer valuable opportunities for studying the magnetic nature of 5d perovskite-related oxides, with regard to their possible use in multifunctional devices. PMID:25751088

  9. Effect of divalent Ba cation substitution with Sr on coupled ‘multiglass’ state in the magnetoelectric multiferroic compound Ba3NbFe3Si2O14

    PubMed Central

    Rathore, Satyapal Singh; Vitta, Satish

    2015-01-01

    (Ba/Sr)3NbFe3Si2O14 is a magneto-electric multiferroic with an incommensurate antiferromagnetic spiral magnetic structure which induces electric polarization at 26?K. Structural studies show that both the compounds have similar crystal structure down to 6?K. They exhibit a transition, TN at 26?K and 25?K respectively, as indicated by heat capacity and magnetization, into an antiferromagnetic state. Although Ba and Sr are isovalent, they exhibit very different static and dynamic magnetic behaviors. The Ba-compound exhibits a glassy behavior with critical slowing dynamics with a freezing temperature of ~35?K and a critical exponent of 3.9, a value close to the 3-D Ising model above TN, in addition to the invariant transition into an antiferromagnetic state. The Sr-compound however does not exhibit any dispersive behavior except for the invariant transition at TN. The dielectric constant reflects magnetic behavior of the two compounds: the Ba-compound has two distinct dispersive peaks while the Sr-compound has a single dispersive peak. Thus the compounds exhibit coupled ‘multiglass’ behavior. The difference in magnetic properties between the two compounds is found to be due to modifications to super exchange path angle and length as well as anti-site defects which stabilize either ferromagnetic or antiferromagnetic interactions. PMID:25988657

  10. Ca cofactor of the water-oxidation complex: Evidence for a Mn/Ca heteronuclear cluster

    SciTech Connect

    Cinco, Roehl M.; Robblee, John H.; Messinger, Johannes; Fernandez, Carmen; McFarlane, Karen L.; Pizarro, Shelly A.; Sauer, Ken; Yachandra, Vittal K.

    2001-07-25

    Calcium and chloride are necessary cofactors for the proper function of the oxygen-evolving complex (OEC) of Photosystem II (PS II). Located in the thylakoid membranes of green plants, cyanobacteria and algae, PS II and the OEC catalyze the light-driven oxidation of water into dioxygen (released into the biosphere), protons and electrons for carbon fixation. The actual chemistry of water oxidation is performed by a cluster of four manganese atoms, along with the requisite cofactors Ca{sup 2+} and Cl{sup -}. While the Mn complex has been extensively studied by X-ray absorption techniques, comparatively less is known about the Ca{sup 2+} cofactor. The fewer number of studies on the Ca{sup 2+} cofactor have sometimes relied on substituting the native cofactor with strontium or other metals, and have stirred some debate about the structure of the binding site. past efforts using Mn EXAFS on Sr-substituted PSII are suggestive of a close link between the Mn cluster and Sr, within 3.5 {angstrom}. The most recent published study using Sr EXAFS on similar samples confirms this finding of a 3.5 {angstrom} distance between Mn and Sr. This finding was base3d on a second Fourier peak (R {approx} 3 {angstrom}) in the Sr EXAFS from functional samples, but is absent from inactive, hydroxylamine-treated PS II. This Fourier peak II was found to fit best to two Mn at 3.5 {angstrom} rather than lighter atoms (carbon). Nevertheless, other experiments have given contrary results. They wanted to extend the technique by using polarized Sr EXAFS on layered Sr-substituted samples, to provide important angle information. Polarized EXAFS involves collecting spectra for different incident angles ({theta}) between the membrane normal of the layered sample and the X-ray electric field vector. Dichroism in the EXAFS can occur, depending on how the particular absorber-backscatterer (A-B) vector is aligned with the electric field. Through analysis of the dichroism, they extract the average number of scatterers per absorbing atom (N{sub iso}). Constraints on the structural model are then imposed by these parameters. In a complementary and definitive experiment, they use Ca K-edge EXAFS studies to probe the binding site of the native cofactor for any nearby Mn, within {approx} 4 {angstrom}. This is analogous to the Sr EXAFS studies already published, but it focuses on the native cofactor and avoids the treatments involving Ca depletion and Sr substitution. The samples examined were PS II membrane particles from spinach. This new technique promises to be a more sensitive and direct probe of the calcium binding site in PS II than Sr EXAFS. Clarifying whether the Ca cofactor is proximate to the Mn cluster, and finding its coordination environment at the various intermediate S-states of the OEC will reveal its important role in oxygen evolution.

  11. Effect of Cu-site Co, Ni and Ga substitution on the superconductivity of tetragonal LaBaCaCu 3O 7 system

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Horvat, J.; Liu, H. K.; Dou, S. X.; Singh, Rajvir; Narlikar, A. V.; Das, M. P.

    1998-06-01

    X-ray diffraction and AC susceptibility measurements have been carried out on LaBaCaCu 3- xM xO 7 (RE:1113) system, where M=Co, Ni, Ga with x=0.0, 0.06, 0.08, 0.24 and 0.30. X-ray diffraction results show that these cations substitute isostructurally in the tetragonal La:1113 phase, with decreased c-parameter for Co and Ga and nearly unchanged for Ni, at least up to 10 at% of doping level. Superconducting transition temperature ( Tc) of the pristine sample, determined from the measurements of both real and imaginary parts of AC susceptibility, decreases with an increase of x for all the three cations. Tc depression rate with doping concentration (d Tc/d x) follows the order Ga>Ni>Co. These results, in terms of Tc depression due to these impurities in the parent La:1113 system are similar to those observed for RE:124 (REBa 2Cu 4O 8), 247 and Nd:214 (Nd 2- xCe xCuO 4) compounds, but are different from RE:123 and La:214.

  12. New insights into organic-inorganic hybrid perovskite CH3NH3PbI3 nanoparticles. An experimental and theoretical study of doping in Pb2+ sites with Sn2+, Sr2+, Cd2+ and Ca2+

    NASA Astrophysics Data System (ADS)

    Navas, Javier; Sánchez-Coronilla, Antonio; Gallardo, Juan Jesús; Cruz Hernández, Norge; Piñero, Jose Carlos; Alcántara, Rodrigo; Fernández-Lorenzo, Concha; de Los Santos, Desireé M.; Aguilar, Teresa; Martín-Calleja, Joaquín

    2015-03-01

    This paper presents the synthesis of the organic-inorganic hybrid perovskite, CH3NH3PbI3, doped in the Pb2+ position with Sn2+, Sr2+, Cd2+ and Ca2+. The incorporation of the dopants into the crystalline structure was analysed, observing how the characteristics of the dopant affected properties such as the crystalline phase, emission and optical properties. XRD showed how doping with Sn2+, Sr2+ and Cd2+ did not modify the normal tetragonal phase. When doping with Ca2+, the cubic phase was obtained. Moreover, DR-UV-Vis spectroscopy showed how the band gap decreased with the dopants, the values following the trend Sr2+ < Cd2+ < Ca2+ < CH3NH3PbI3 ~ Sn2+. The biggest decrease was generated by Sr2+, which reduced the CH3NH3PbI3 value by 4.5%. In turn, cathodoluminescence (CL) measurements confirmed the band gap obtained. Periodic-DFT calculations were performed to understand the experimental structures. The DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy, with the values calculated following the trend Sn2+ ~ Pb2+ > Cd2+ > Sr2+ for the tetragonal structure and Pb2+ > Ca2+ for the cubic phase. The electron localization function (ELF) analysis showed similar electron localizations for undoped and Sn2+-doped tetragonal structures, which were different from those doped with Sr2+ and Cd2+. Furthermore, when Cd2+ was incorporated, the Cd-I interaction was strengthened. For Ca2+ doping, the Ca-I interaction had a greater ionic nature than Cd-I. Finally, an analysis based on the non-covalent interaction (NCI) index is presented to determine the weak-type interactions of the CH3NH3 groups with the dopant and I atoms. To our knowledge, this kind of analysis with these hybrid systems has not been performed previously.This paper presents the synthesis of the organic-inorganic hybrid perovskite, CH3NH3PbI3, doped in the Pb2+ position with Sn2+, Sr2+, Cd2+ and Ca2+. The incorporation of the dopants into the crystalline structure was analysed, observing how the characteristics of the dopant affected properties such as the crystalline phase, emission and optical properties. XRD showed how doping with Sn2+, Sr2+ and Cd2+ did not modify the normal tetragonal phase. When doping with Ca2+, the cubic phase was obtained. Moreover, DR-UV-Vis spectroscopy showed how the band gap decreased with the dopants, the values following the trend Sr2+ < Cd2+ < Ca2+ < CH3NH3PbI3 ~ Sn2+. The biggest decrease was generated by Sr2+, which reduced the CH3NH3PbI3 value by 4.5%. In turn, cathodoluminescence (CL) measurements confirmed the band gap obtained. Periodic-DFT calculations were performed to understand the experimental structures. The DOS analysis confirmed the experimental results obtained using UV-Vis spectroscopy, with the values calculated following the trend Sn2+ ~ Pb2+ > Cd2+ > Sr2+ for the tetragonal structure and Pb2+ > Ca2+ for the cubic phase. The electron localization function (ELF) analysis showed similar electron localizations for undoped and Sn2+-doped tetragonal structures, which were different from those doped with Sr2+ and Cd2+. Furthermore, when Cd2+ was incorporated, the Cd-I interaction was strengthened. For Ca2+ doping, the Ca-I interaction had a greater ionic nature than Cd-I. Finally, an analysis based on the non-covalent interaction (NCI) index is presented to determine the weak-type interactions of the CH3NH3 groups with the dopant and I atoms. To our knowledge, this kind of analysis with these hybrid systems has not been performed previously. Electronic supplementary information (ESI) available: Elemental analysis obtained by ICP-AES, and XRF (Table S1). XRD patterns of the samples synthesized (Fig. S1). XRD patterns of commercials PbI2 and CdI2 used as reagents (Fig. S2). XRD patterns of MAPb0.5Sn0.5I3 (Fig. S3). UV-Vis spectra, in mode reflectance diffuse, of the samples synthesized (Fig. S4). UV-Vis spectra, in mode reflectance diffuse, of MAPbI3 and MAPb0.5Sn0.5I3 samples (Fig. S5). XPS spectra for MAPbI3 and MAPb1-xBxI3 (B: Sn, Sr, Cd, Ca) with x

  13. Legitional behavior of 5,5-diethylbarbituric acid sodium salt (HL) towards Mg, Ca, Sr, Ba(II), spectral, thermal and biological studies

    NASA Astrophysics Data System (ADS)

    Refat, Moamen S.; El-Metwaly, Nashwa M.

    2011-03-01

    A new series of sodium barbital complexes with Alkaline earth metals (Mg2+, Ca2+, Sr2+ and Ba2+ ions) was prepared. The molecular formulas for the isolated complexes were suggested basically on the elemental analysis data. The binuclear central were proposed for all investigated complexes. The geometry suggested based on knowing the coordination sits for each complex was built on concerning with the shift observed in IR spectra surround the coordinating groups. The shifts in charge transfer bands appeared in the electronic spectra of the complexes supports the coordination process. The presence of solvent molecules coordinately attached with central metal atoms as well as the conjugated anions was supported based on thermogravimetric analysis. The kinetic parameters were calculated for each complex. The theoretical calculations for the molecular modeling structures reflect an insight about their stability in comparing with the free ligand. The XRD studies were performed and concluding the nanocrystalline feature for all complexes. The biochemical effect of all investigated compounds was performed towards Gram-negative and Gram-positive bacteria as well as their degradation effect on calf Thymus DNA. The biological performance is the major goal in this study especially with such essential metal ions.

  14. Magnetoresistance anisotropy and scaling in textured high-temperature superconductor Bi1.8Pb0.3Sr1.9Ca2Cu3O x

    NASA Astrophysics Data System (ADS)

    Gokhfel'd, D. M.; Balaev, D. A.; Semenov, S. V.; Petrov, M. I.

    2015-11-01

    The magnetoresistance of the textured high-temperature superconductor (HTSC) Bi1.8Pb0.3Sr1.9Ca2Cu3O x + Ag has been studied at different directions of the transport current I and external magnetic field H with respect to crystallographic directions of HTSC crystallites. When I and H are oriented along the ab planes of crystallites and ? is the angle between H and I, the anisotropic part of the magnetoresistance follows the functional dependence sin2?, which is characteristic of vortex flows under Lorentz forces. The magnetoresistance R at H parallel to the c axis of crystallites (H || c) is higher than R at H || ab for both cases of I || c and I || ab. The anisotropy coefficient ? ? 2.3 has been estimated from the scaling of the dependences R( H) measured at H || c and H || ab. The inclusion of the magnetic field induced by the transport current allows scaling of the dependences R( H) at different values of I. A qualitative picture of the current flow along the c axis of crystallites in the textured HTSC has been proposed.

  15. In-plane electrodynamics of the superconductivity in Bi2Sr2CaCu2O8+? : ? Energy scales and spectral weight distribution

    NASA Astrophysics Data System (ADS)

    Santander-Syro, A. F.; Lobo, R. P. S. M.; Bontemps, N.; Lopera, W.; Giratá, D.; Konstantinovic, Z.; Li, Z. Z.; Raffy, H.

    2004-10-01

    The in-plane infrared and visible (3meV-3eV) reflectivity of Bi2Sr2CaCu2O8+? (Bi-2212) thin films is measured between 300K and 10K for different doping levels with unprecedented accuracy. The optical conductivity is derived through an accurate fitting procedure. We study the transfer of spectral weight from finite energy into the superfluid as the system becomes superconducting. In the overdoped regime, the superfluid develops at the expense of states lying below 60meV , which is a conventional energy of the order of a few times the superconducting gap. In the underdoped regime, spectral weight is removed from up to 2eV , far beyond any conventional scale. The intraband spectral weight change between the normal and superconducting state, if analyzed in terms of a change of kinetic energy, is ˜1meV . Compared to the condensation energy, this figure addresses the issue of a kinetic-energy driven mechanism.

  16. First-principles KKR-CPA calculation of the magnetic and transport properties of La1-xXxMnO3 (X = Ca, Sr)

    NASA Astrophysics Data System (ADS)

    Ogura, M.; Akai, H.

    2012-11-01

    Electrical transport properties of (La1-xXx)MnO3 (X = Ca, Sr), which exhibits the so-called colossal magnetoresistance (CMR) effect, are investigated in the framework of linear response theory combined with first-principles calculation. The calculation is performed by applying the coherent potential approximation and Kubo-Greenwood formula to the KKR Green’s function method. In order to reveal the mechanism that underlies the CMR effects, the dc conductivities of the system in A (layered)-, C (stripe)-, and G (111)-type antiferromagnetic states as well as the local moment disordered state are calculated as a function of x. It is found that the conductivity of the system strongly depends on the magnetic structure and is highly anisotropic in the cases of A- and C-type antiferromagnetic structures. Also, it is concluded that a drastic change in the conductivity is expected when the system undergoes a magnetic transition, and that this might be closely related to the observed CMR effect. It is pointed out that, for such a drastic change in the conductivity to occur associated with the magnetic transition, the half-metallic nature of the Mn local electronic structure must be essential.

  17. Tunable THz radiation from intrinsic Josephson junctions in Bi2Sr2CaCu2O8+? in a localized phase rotating mode

    NASA Astrophysics Data System (ADS)

    Tsujimoto, Manabu; Delfanazari, Kaveh; Kitamura, Takeo; Sawamura, Masashi; Ishida, Kazuya; Sekimoto, Shunsuke; Watanabe, Chiharu; Yamamoto, Takashi; Kashiwagi, Takanari; Minami, Hidetoshi; Kadowaki, Kazuo

    2013-03-01

    After the first report of intense continuous THz electromagnetic wave radiation from high-Tc superconductor Bi2Sr2CaCu2O8+? [L. Ozyuzer et al., Science 318, 1291 (2007)] with remarkably higher intensity, a great deal of interest has been drawn not only to the physical mechanism of the radiation but also to the possible variety of applications in the vast fields of THz science and technology. Recently, the authors pointed out that the contributions to the output power from the Josephson current source was found to be comparable in magnitude [K. Kadowaki et al., J. Phys. Soc. Jpn. 79, 023703 (2010); M. Tsujimoto et al., Phys. Rev. Lett. 108, 107006 (2012)]. As R. Kleiner et al. observed in 1992 [R. Kleiner et al., Phys. Rev. Lett. 68, 2394 (1992)], the intrinsic junctions in the phase rotating mode produce an equal number of I- V characteristic branches. Here we show clear evidence that the mesas can emit radiation at many frequencies in various localized phase rotating modes, and that the resulting radiation is tunable over a broad range of frequencies, allowing us to construct a powerful THz source device that could fill the THz gap. JST-CREST, WPI-MANA

  18. Electrothermal behavior and terahertz emission properties of a planar array of two Bi2Sr2CaCu2O8+? intrinsic Josephson junction stacks

    NASA Astrophysics Data System (ADS)

    Gross, B.; Rudau, F.; Kinev, N.; Tsujimoto, M.; Yuan, J.; Huang, Y.; Ji, M.; Zhou, X. J.; Y An, D.; Ishii, A.; Wu, P. H.; Hatano, T.; Koelle, D.; Wang, H. B.; Koshelets, V. P.; Kleiner, R.

    2015-05-01

    We report on the investigation of the electrothermal behavior and the terahertz (THz) emission properties of two nearby Bi2Sr2CaCu2O8+? (BSCCO) intrinsic Josephson junction stacks, using a combination of electric transport and THz emission measurements plus low temperature scanning laser microscopy. We start with a compact BSCCO stack (placed in a z-shaped structure between two BSCCO electrodes) with lateral dimensions of 330× 60 ? {{m}2} and 0.7 ? m height, consisting of about 480 junctions. After characterization, a 200 nm wide slit was introduced by focused ion beam milling, splitting the stack into two halves connected by continuous superconducting electrodes. In a third step, the upper electrode was also split, leading to a structure where the two stacks can be biased separately. In all configurations hot-spot formation was observed. Despite the separation into two stacks only a single hot spot formed, which, depending on the bias condition, could either be located in one of the stacks or extend into both stacks with its center in the slit. In none of the structures it was possible to achieve mutual synchronization of the two stacks, indicating that additional synchronizing elements or the presence of a base crystal as for mesa structures may be necessary for the operation of parallel array structures.

  19. Study of Bi2Sr2CaCu2O8/BiFeO3 nano-composite for electrical transport applications

    NASA Astrophysics Data System (ADS)

    Acharya, S.; Biswal, A. K.; Ray, J.; Vishwakarma, P. N.

    2012-09-01

    The Bi2Sr2CaCu2O8/BiFeO3 (BSCCO/BFO) nano composite for various BFO weight percentage is prepared and studied for electrical transport. Double resistive superconducting transition is seen in all composite samples with increasing semiconducting nature as a function of BFO content. Initially, the added BFO goes mainly to the grain boundary and from 10% onwards, it enters grains as well, acting as pinning centers. The conduction mechanism in BSCCO shows weak localization for low BFO, tunneling in intermediate BFO, and power law behavior (similar to metal-insulator boundary) for higher BFO samples. The paraconductivity studies reveal the 2D-3D transition in parent BSCCO and the composites, with a signature of percolative behavior in the composites. The study of critical current density reveals two types of Josephson junction in the composites: (1) thin intrinsic superconductor-insulator-superconductor (SIS) type present in all samples including parent BSCCO and (2) extrinsic type due to BFO added, present only in composite samples. The extrinsic junction is SIS with tunneling for low BFO and goes to proximity SIS type for increasing BFO. The Jc(0) as a function of BFO content, first decreases with increasing BFO, attains minima at 5% BFO, and increases thereafter.

  20. Spark plasma sintering consolidation of Bi1.65Pb0.35Sr2Ca2Cu3010+? ceramic samples

    NASA Astrophysics Data System (ADS)

    Govea-Alcaide, E.; Machado, I. F.; Torikachvili, M. S.; Dilley, N. R.; Jardim, R. F.

    2014-05-01

    Pre-reacted powders of (Bi-Pb)2Sr2Ca2Cu3O10+? (Bi-2223) were consolidated by using the spark plasma sintering (SPS) technique under vacuum and at different consolidated temperatures TD. We have found that the transport properties of SPS samples depend on their oxygen content because the SPS process is performed under vacuum. From these results we have inferred that SPS samples are oxygen deficient and that a post-annealing treatment, performed in air for a brief time interval, is needed to restore such a deficiency. Measurements of temperature dependence of the thermal conductivity, ?(T), were performed in all SPS samples including a reference sample sintered at 845 °C in air. The results indicate that the electronic contribution to the thermal conductivity in all samples is very low. Values of ? were found to be higher in SPS samples mostly because of their high volume density of ~ 5.7 g/cm3. We have also performed measurements of the critical current density as a function of the applied magnetic field, Jc(Ba). All samples display a clear Josephson-like behavior and low values of the superconducting critical current density at zero applied magnetic field. The experimental results indicate that the oxygen deficiency in SPS samples is marked near the grain boundaries. This suggests the occurrence of grains with core-shell morphology, where the width of the shell is consolidation temperature dependent.

  1. High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O8+x down to half-unit-cell thickness by protection with graphene

    NASA Astrophysics Data System (ADS)

    Jiang, Da; Hu, Tao; You, Lixing; Li, Qiao; Li, Ang; Wang, Haomin; Mu, Gang; Chen, Zhiying; Zhang, Haoran; Yu, Guanghui; Zhu, Jie; Sun, Qiujuan; Lin, Chengtian; Xiao, Hong; Xie, Xiaoming; Jiang, Mianheng

    2014-12-01

    High-Tc superconductors confined to two dimension exhibit novel physical phenomena, such as superconductor-insulator transition. In the Bi2Sr2CaCu2O8+x (Bi2212) model system, despite extensive studies, the intrinsic superconducting properties at the thinness limit have been difficult to determine. Here, we report a method to fabricate high quality single-crystal Bi2212 films down to half-unit-cell thickness in the form of graphene/Bi2212 van der Waals heterostructure, in which sharp superconducting transitions are observed. The heterostructure also exhibits a nonlinear current-voltage characteristic due to the Dirac nature of the graphene band structure. More interestingly, although the critical temperature remains essentially the same with reduced thickness of Bi2212, the slope of the normal state T-linear resistivity varies by a factor of 4-5, and the sheet resistance increases by three orders of magnitude, indicating a surprising decoupling of the normal state resistance and superconductivity. The developed technique is versatile, applicable to investigate other two-dimensional (2D) superconducting materials.

  2. Vortex pinning by different angular distributions of columnar defects in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}

    SciTech Connect

    Hebert, S.; Hardy, V.; Villard, G.; Hervieu, M.; Simon, C.; Provost, J.

    1998-01-01

    Different configurations of columnar defects tilted with respect to c have been tailored in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} single crystals by controlling the orientation of a heavy-ion beam: One single direction of tracks yielding parallel defects (n=1), two coplanar directions of tracks (n=2), and three directions of tracks symmetrically distributed around the c axis (n=3). The pinning efficiency has been systematically investigated by magnetic measurements with the field applied along c. We found evidence for a low-T regime where the pinning efficiency is nearly independent of n, and a high-T regime where it essentially increases with n. These features are discussed in the frame of two different but not incompatible approaches: (i) a static approach based on accommodation effects, and (ii) a dynamic approach based on elementary flux-creep processes. Finally, the further comparison of these results with angular measurements performed for n=1 strongly suggests that the symmetry of the track distribution relative to the orientation of the applied field might play a major role in the pinning efficiency of splayed configurations. {copyright} {ital 1998} {ital The American Physical Society}

  3. Relating atomic-scale electronic phenomena to wave-like quasiparticle states in superconducting Bi2Sr2CaCu2O8+delta.

    PubMed

    McElroy, K; Simmonds, R W; Hoffman, J E; Lee, D-H; Orenstein, J; Eisaki, H; Uchida, S; Davis, J C

    2003-04-10

    The electronic structure of simple crystalline solids can be completely described in terms either of local quantum states in real space (r-space), or of wave-like states defined in momentum-space (k-space). However, in the copper oxide superconductors, neither of these descriptions alone may be sufficient. Indeed, comparisons between r-space and k-space studies of Bi2Sr2CaCu2O8+delta (Bi-2212) reveal numerous unexplained phenomena and apparent contradictions. Here, to explore these issues, we report Fourier transform studies of atomic-scale spatial modulations in the Bi-2212 density of states. When analysed as arising from quasiparticle interference, the modulations yield elements of the Fermi-surface and energy gap in agreement with photoemission experiments. The consistency of numerous sets of dispersing modulations with the quasiparticle interference model shows that no additional order parameter is required. We also explore the momentum-space structure of the unoccupied states that are inaccessible to photoemission, and find strong similarities to the structure of the occupied states. The copper oxide quasiparticles therefore apparently exhibit particle-hole mixing similar to that of conventional superconductors. Near the energy gap maximum, the modulations become intense, commensurate with the crystal, and bounded by nanometre-scale domains. Scattering of the antinodal quasiparticles is therefore strongly influenced by nanometre-scale disorder. PMID:12686994

  4. Simulation of the local structure, mixing properties, and stability of Ca x Sr1 - x CO3 solid solutions by the interatomic potential method

    NASA Astrophysics Data System (ADS)

    Dudnikova, V. B.; Urusov, V. S.; Eremin, N. N.

    2015-06-01

    Strontianite (SrCO3)-aragonite (CaCO3) solid solutions have been simulated by the interatomic potential method. The composition dependences of the unit cell parameters, the unit cell volume, and bulk modulus have been constructed. It has been shown that the volume of the unit cell and bulk modulus show small negative deviations from additivity. The local structure of solid solutions has been analyzed. It has been established that the enthalpy of mixing is positive and, for the equimolar composition, reaches a maximum of 2.45 kJ/mol. Based on the composition dependences of the Gibbs free energy for the temperature range of 300-650 K, the solvus of the system has been constructed. According to the obtained data, the solubility of aragonite in strontianite under ambient conditions is 5.5 mol %, while that of strontianite in aragonite is 2.8 mol %. The miscibility gap of the system disappears at around 450 K. The calculated results have been compared with the experimental data.

  5. Processing and properties of Bi 2Sr 2CaCu 2O x thick films on polycrystalline magnesium oxide substrates

    NASA Astrophysics Data System (ADS)

    Köbel, S.; Schneider, D.; Sager, D.; Sütterlin, P.; Fall, L.; Gauckler, L. J.

    2003-12-01

    In this paper we report on the processing parameters and resulting critical current densities of Bi 2Sr 2CaCu 2O x (Bi-2212) thick films on polycrystalline MgO substrates. Bi-2212 tapes were cast by the doctor blade technique and laminated onto flat MgO-ceramic substrates. The tapes were produced via the partial melt-process in a single cycle. Silver(I)oxide (Ag 2O) was added to the powder and the maximum process temperature was varied in order to optimize the transport current density at 77 K in self-field. It was found that both parameters, maximum process temperature during partial melting and amount of Ag 2O added have a strong influence on the critical current density at 77 K. The highest Jc of 1900 A/cm 2 was achieved in the 130 ?m thick films with an addition of 4 wt% Ag 2O processed at a maximum temperature of 900 °C. In addition, large components were processed with 1 cm wide conductors meandering over 150 cm on 20 cm diameter MgO plates.

  6. Observation of superconductivity at 30~46 K in A(x)Fe?Se?(A = Li, Na, Ba, Sr, Ca, Yb, and Eu).

    PubMed

    Ying, T P; Chen, X L; Wang, G; Jin, S F; Zhou, T T; Lai, X F; Zhang, H; Wang, W Y

    2012-01-01

    New iron selenide superconductors by intercalating smaller-sized alkali metals (Li, Na) and alkaline earths using high-temperature routes have been pursued ever since the discovery of superconductivity at about 30?K in KFe?Se?, but all have failed so far. Here we demonstrate that a series of superconductors with enhanced T(c) = 30?46?K can be obtained by intercalating metals, Li, Na, Ba, Sr, Ca, Yb, and Eu in between FeSe layers by the ammonothermal method at room temperature. Analysis on their powder X-ray diffraction patterns reveals that all the main phases can be indexed based on body-centered tetragonal lattices with a?3.755-3.831 Å while c?15.99-20.54 Å. Resistivities show the corresponding sharp transitions at 45?K and 39?K for NaFe?Se? and Ba?.?Fe?Se?, respectively, confirming their bulk superconductivity. These findings provide a new starting point for studying the properties of these superconductors and an effective synthetic route for the exploration of new superconductors as well. PMID:22645642

  7. Bi 2Sr 2CaCu 2O 8+ ? bicrystal c-axis twist Josephson junctions: a new phase-sensitive test of order parameter symmetry

    NASA Astrophysics Data System (ADS)

    Klemm, Richard A.

    2003-05-01

    Li et al. (Phys. Rev. Lett. 83 (1999) 4160) prepared atomically clean Bi 2Sr 2CaCu 2O 8+ ? (BSCCO) Josephson junctions between identical single crystal cleaves stacked and twisted an angle ?0 about the c-axis. For each bicrystal, the ratio JcJ/ JcS of the c-axis twist junction critical current density to that across either single crystal part is unity, independent of ?0 and the ratio AJ/ AS of junction areas. From extensive theoretical studies involving a variety of tunneling and superconducting order parameter (OP) forms, we conclude that the results provide strong evidence for incoherent c-axis tunneling and that the dominant OP is s-wave for T? Tc. Recently, Takano et al. (Phys. Rev. B 65 (2002) 140513(R)) obtained results from BSCCO whisker twist junctions which also rule out a pure d-wave OP, but which are surprisingly suggestive of coherent c-axis tunneling from small Fermi surface hot spots.

  8. Scanning tunneling microscope studies on the atomic structures in Bi 2Sr 2CaCu 2O 8+ ? highly doped with Pb

    NASA Astrophysics Data System (ADS)

    Nishiyama, M.; Ogawa, K.; Chong, I.; Hiroi, Z.; Takano, M.

    1999-03-01

    Highly doped high- Tc Bi compounds, i.e., Bi 2.2- xPb xSr 1.8CaCu 2O 8+ ? ( x=0.7) (denoted by Bi(Pb)-2212) were recently found to have dramatically improved critical current Jc [I. Chong, Z. Hiroi, M. Izumi, J. Shimoyama, Y. Nakayama, K. Kishio, T. Terashima, Y. Bando, and M. Takano, Science 276 (1997) 770; J. Shimoyama, Y. Nakayama, K. Kitazawa, K. Kishio, Z. Hiroi, I. Chong, M. Takano, Physica C 281 (1997) 69]. To elucidate atom structures of the Bi(Pb)-2212, ultrahigh vacuum scanning tunneling microscope (UHV-STM) studies have been performed. We observed, for the first time, defected ?-phase with fragmented modulation of ?=7 nm. Observed defects are amorphous regions of a few nanometer size embedded in the ?-phase and edge dislocations with Burgers vector (1/2) [110]. Both the defects are suggested potentially to be effective pinning centers in Bi(Pb)-2212. Annealing in vacuum at temperatures up to 630°C for 19 h was found sufficient enough to evaporate all the Pb atoms in the surface layers of Bi(Pb)-2212 and consequently to transform Bi(Pb)-2212 with ?=7 nm to pure Bi-2212 with ?=2.7 nm.

  9. Single-crystalline Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} detectors for direct detection of microwave radiation

    SciTech Connect

    Li, M. Winkler, D.; Yurgens, A.

    2015-04-13

    We test radiation detectors made from single-crystalline Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} flakes put on oxidized Si substrates. The 100-nm-thick flakes are lithographically patterned into 4×12??m{sup 2} large rectangles embedded in thin-film log-spiral antennas. The SiO{sub 2} layer weakens the thermal link between the flakes and the bath. Two modes of radiation detection have been observed. For a bolometric type of sensors a responsivity of ?300 V/W and a noise equivalent power of 30 nW/?(Hz) has been deduced at 70?K. Much more sensitive is the non-bolometric device showing characteristics similar to a Golay-type detector while being at least a thousand times faster. Making smaller (sub-?m) structures is expected to significantly improve the performance of these devices and makes them very competitive among other microwave and terahertz detectors.

  10. Seawater temperature seasonality in the South China Sea during the late Holocene derived from high-resolution Sr/Ca ratios of Tridacna gigas

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    Temperature seasonality, the difference between summer and winter temperature, has significant influences on global terrestrial and marine ecosystems. However, most of proxy-based climate records are of limited temporal resolution and thus insufficient to quantify the past temperature seasonality. In this study, high-resolution Sr/Ca ratios of modern (live-caught) and fossil (dead-collected) Tridacna gigas shells from the South China Sea (SCS) were used to reconstruct the seawater temperature seasonality during the late Holocene. The averaged seawater temperature seasonality around 2165 ± 75 BC (4.46 ± 1.41°C, derived from the data of 18 yr) were similar to the seasonality of recent decade (4.41 ± 0.82°C during AD 1994-2005), but the temperature seasonality around AD 50 ± 40 (3.69 ± 1.37°C, derived from the data of 48 yr) and AD 990 ± 40 (3.64 ± 0.87°C, derived from the data of 11 yr) was significantly lower than that during AD 1994-2005. The reduced seasonality around AD 990 ± 40 was attributable to the unusually warm winter during the medieval times, probably caused by the weakening of East Asian Winter Monsoon. Our study highlighted the potential of T. gigas shells in providing high-resolution seasonality climate information during the late Holocene.

  11. Percolation effect in thick film superconductors: Using a Bi(Pb)SrCaCuO based paste to prepare a superconducting planar transformer

    NASA Technical Reports Server (NTRS)

    Sali, Robert; Harsanyi, Gabor

    1995-01-01

    A thick film superconductor paste has been developed to study the properties of granulated superconductor materials, to observe the percolation effect and to confirm the theory of the conducting mechanism in the superconducting thick films. This paste was also applied to make a superconducting planar transformer. Due to the T(sub c) and advantageous current density properties the base of the past was chosen to be of Bi(Pb)SrCaCu) system. For contacts a conventional Ag/Pt paste was used. The critical temperature of the samples were between 110 K and 115 K depending on the printed layer thickness. The critical current density -at the boiling temperature of the liquid He- was between 200 - 300 A/sq cm. The R(T) and V(I) functions were measured with different parameters. The results of the measurements have confirmed the theory of conducting mechanism in the material. The percolation structure model has been built and described. As an application, a superconducting planar thick film transformer was planned and produced. Ten windings of the transformer were printed on one side of the alumina substrate and one winding was printed on the other side. The coupling between the two sides was possible through the substrate. The samples did not need special drying and firing parameters. After the preparation, the properties of the transformer were measured. The efficiency ans the losses were determined. Finally, some fundamental advantages and problems of the process were discussed.

  12. Hot Spot and THz Wave Generation in Bi2Sr2CaCu2O8 Intrinsic Josephson Junction Stacks

    NASA Astrophysics Data System (ADS)

    Kleiner, Reinhold

    2013-03-01

    Stacks of intrinsic Josephson junctions made of the high temperature superconductor Bi2Sr2CaCu2O8 have been shown to emit coherent radiation at THz frequencies. Emission is observed both in a low bias regime and a high bias regime. While at low bias the temperature of the stack is close to the bath temperature, at high bias a hot spot and a standing wave, formed in the ``cold'' part of the stack, coexist. THz radiation is very stable in this regime, exhibiting a linewidth which is much smaller than expected from a purely cavity-induced synchronization mechanism. We investigate the interaction of hot spots and THz waves using a combination of transport measurement, direct electromagnetic wave detection and low temperature scanning laser microscopy (LTSLM). In this talk recent developments will be presented, with a focus on the mechanism of hot spot formation. In collaboration with B. Gross, S. Guénon, M. Y. Li, J. Yuan, N. Kinev, J. Li, A. Ishii, K. Hirata, T. Hatano, R. G. Mints, D. Koelle, V. P. Koshelets, H. B. Wang and P. H. Wu.

  13. Unimolecular and hydrolysis channels for the detachment of water from microsolvated alkaline earth dication (Mg2+, Ca2+, Sr2+, Ba2+) clusters

    SciTech Connect

    Miliordos, Evangelos; Xantheas, Sotiris S.

    2014-02-07

    We examine theoretically the three channels that are associated with the detachment of a single water molecule from the aqueous clusters of the alkaline earth dications, [M(H2O)n]2+, M = Mg, Ca, Sr, Ba, n ? 6. These are the unimolecular water loss (M2+(H2O)n-1 + H2O) and the two hydrolysis channels resulting to the loss of hydronium ([MOH(H2O)n-2]+ + H3O+) and Zundel ([MOH(H2O)n-3]+ + H3O+(H2O)) cations. The Potential Energy Curves (PECs) corresponding to those three channels were constructed at the Møller-Plesset second order perturbation (MP2) level of theory with basis sets of double- and triple-? quality. We furthermore investigated the water and hydronium loss channels from the mono-hydroxide water clusters with up to four water molecules, [MOH(H2O)n]+, 1 ? n ? 4. Our results indicate the preference of the hydronium loss and possibly the Zundel cation loss channels for the smallest size clusters, whereas the unimolecular water loss channel is preferred for the larger ones as well as the mono-hydroxide clusters. Although the charge separation (hydronium and Zundel cation loss) channels produce more stable products when compared to the ones for the unimolecular water loss, they also require the surmounting of high energy barriers, a fact that makes the experimental observation of fragments related to these hydrolysis channels difficult.

  14. Single-crystal growth and size control of three novel polar intermetallics: Eu2.94(2)Ca6.06In8Ge8, Eu3.13(2)Ca5.87In8Ge8, and Sr3.23(3)Ca5.77In8Ge8 with crystal structure, chemical bonding, and magnetism studies.

    PubMed

    Woo, Hyein; Nam, Gnu; Jang, Eunyoung; Kim, Jin; Lee, Yunho; Ahn, Kyunghan; You, Tae-Soo

    2014-05-01

    Three new quaternary polar intermetallic compounds of Eu2.94(2)Ca6.06In8Ge8, Eu3.13(2)Ca5.87In8Ge8, and Sr3.23(3)Ca5.77In8Ge8 have been synthesized by a metal-flux method using molten indium metal as a reactive flux, and the novel isotypic crystal structures have been characterized by both powder and single-crystal X-ray diffractions. All compounds crystallize in the orthorhombic space group Pmmn (Z = 2, Pearson symbol oP50) with 14 crystallographically unique atomic positions in the asymmetric unit. The lattice parameters are refined as follows: a = 36.928(2) Å, b = 4.511(1) Å, and c = 7.506(1) Å for Eu2.94(2)Ca6.06In8Ge8; a = 37.171(19) Å, b = 4.531(2) Å, and c = 7.560(4) Å for Eu3.13(2)Ca5.87In8Ge8; and a = 37.350(2) Å, b = 4.550(3) Å, and c = 7.593(4) Å for Sr3.23(3)Ca5.77In8Ge8. In particular, single crystals of two Eu-containing compounds are obtained as bundles of bar/needle-shaped crystals, and the thicknesses of those crystals can be controlled in the range between ca. 300 ?m and ca. <10 ?m by adjusting several reaction conditions, including the reaction cooling rate and the centrifugation temperature. The overall crystal structure is illustrated as an assembly of (1) the three-dimensional anionic framework, which is formed by the chains of edge-sharing InGe4 tetrahedra and the annulene-like "12-membered anionic rings" connected via Ge2 dimers, and (2) the cationic mixed sites embedded in the space between the anionic frameworks. Theoretical investigations based on tight-binding linear muffin-tin orbital (TB-LMTO) calculations provide a comprehesive understanding of the overall electronic structure and chemical bonding observed among anionic components and between anions and cations. Electron localization function (ELF) and electron density map present chemical bond strengths and polarization within the anionic framework. Magnetic susceptibility measurement proves an antiferromagnetic (AFM) ordering of Eu atoms below 4 K with a reduced effective magnetic moment of 7.12 ?B for the Eu atom. PMID:24754445

  15. Critical current density, irreversibility line, and flux creep activation energy in silver-sheathed Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconducting tapes

    SciTech Connect

    Shi, D.; Wang, Z.; Sengupta, S.; Smith, M.; Goodrich, L.F.; Dou, S.X.; Liu, H.K.; Guo, Y.C.

    1992-08-01

    Transport data, magnetic hysteresis and flux creep activation energy experimental results are presented for silver-sheathed high-{Tc} Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} superconducting tapes. The 110 K superconducting phase was formed by lead doping in a Bi-Sr-Ca-Cu-0 system. The transport critical current density was measured at 4.0 K to be 0.7 {times} 10{sup 5} A/cm{sup 2} (the corresponding critical current is 74 A) at zero field and 1.6 {times} 10{sup 4} A/cm{sup 2} at 12 T for H{parallel}ab. Excellent grain alignment in the a-b plane was achieved by a short-melting method, which considerably improved the critical current density and irreversibility line. Flux creep activation energy as a function of current is obtained based on the magnetic relaxation measurements.

  16. Critical current density, irreversibility line, and flux creep activation energy in silver-sheathed Bi[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub x] superconducting tapes

    SciTech Connect

    Shi, D.; Wang, Z.; Sengupta, S.; Smith, M. ); Goodrich, L.F. , Boulder, CO . Electromagnetic Technology Div.); Dou, S.X.; Liu, H.K.; Guo, Y.C. . School of Materials and Engineering)

    1992-08-01

    Transport data, magnetic hysteresis and flux creep activation energy experimental results are presented for silver-sheathed high-[Tc] Bi[sub 2]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub x] superconducting tapes. The 110 K superconducting phase was formed by lead doping in a Bi-Sr-Ca-Cu-0 system. The transport critical current density was measured at 4.0 K to be 0.7 [times] 10[sup 5] A/cm[sup 2] (the corresponding critical current is 74 A) at zero field and 1.6 [times] 10[sup 4] A/cm[sup 2] at 12 T for H[parallel]ab. Excellent grain alignment in the a-b plane was achieved by a short-melting method, which considerably improved the critical current density and irreversibility line. Flux creep activation energy as a function of current is obtained based on the magnetic relaxation measurements.

  17. Severe Fermi Surface Reconstruction at a Metamagnetic Transition in Ca2-xSrxRuO4 (for 0.2 ? x ? 0.5)

    SciTech Connect

    Balicas, L.; Nakatsuji, S.; Hall, D.; Ohnishi, T.; Fisk, Z.; Maeno, Y.; Singh, David J

    2005-01-01

    We report an electrical transport study in Ca{sub 2-x}Sr{sub x}RuO{sub 4} single crystals at high magnetic fields (B). For x=0.2, the Hall constant R{sub xy} decreases sharply at an anisotropic metamagnetic transition, reaching its value for Sr{sub 2}RuO{sub 4} at high fields. A sharp decrease in the A coefficient of the resistivity T{sup 2} term and a change in the structure of the angular magnetoresistance oscillations for B rotating in the planes confirms the reconstruction of the Fermi surface. Our observations and local-density-approximation calculations indicate a strong dependence of the Fermi surface on Ca concentration and suggest the coexistence of itinerant and localized electronic states in single layered ruthenates.