Sample records for ca sr substitution

  1. Penta-substituted benzimidazoles as potent antagonists of the calcium-sensing receptor (CaSR-antagonists)

    Microsoft Academic Search

    Marc Gerspacher; Eva Altmann; René Beerli; Thomas Buhl; Ralf Endres; Rainer Gamse; Jacques Kameni-Tcheudji; Michaela Kneissel; Karl Heinz Krawinkler; Martin Missbach; Alfred Schmidt; Klaus Seuwen; Sven Weiler; Leo Widler

    2010-01-01

    A series of novel benzimidazole derivatives has been designed via a scaffold morphing approach based on known calcilytics chemotypes. Subsequent lead optimisation led to the discovery of penta-substituted benzimidazoles that exhibit attractive in vitro and in vivo calcium-sensing receptor (CaSR) inhibitory profiles. In addition, synthesis and structure–activity relationship data are provided.

  2. Structural evolution in lead substituted Bi--Sr--Ca--Cu--O superconductors

    Microsoft Academic Search

    R. Ramesh; K. Remschnig; J. M. Tarascon; S. M. Green

    1991-01-01

    The structural evolution and cationic stoichiometry of Bi(Pb)--Sr--Ca--Cu--O superconductors have been studied using transmission electron microscopy and x-ray microanalysis. The nature of the incommensurate modulation changes systematically as increasing amounts of lead are added. X-ray microanalysis studies reveal that lead replaces Bi in the structure. Pb addition improves the microstructural homogeneity leading to the formation of a nearly homogeneous sample

  3. 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 [Yale Univ., New Haven, CT (United States); Ertem, Mehmed Z. [Yale Univ., New Haven, CT (United States); Brookhaven National Lab. (BNL), Upton, NY (United States); Pal, Rhitankar [Yale Univ., New Haven, CT (United States); Brudvig, Gary W. [Yale Univ., New Haven, CT (United States); Batista, Victor S. [Yale Univ., New Haven, CT (United States)

    2015-01-27

    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.

  4. Structural Ordering and Charge Variation Induced by Cation Substitution in (Sr,Ca)AlSiN3:Eu Phosphor.

    PubMed

    Tsai, Yi-Ting; Chiang, Chang-Yang; Zhou, Wuzong; Lee, Jyh-Fu; Sheu, Hwo-Shuenn; Liu, Ru-Shi

    2015-07-22

    Nitride phosphors are suitable for white light-emitting diode applications. In this study, the structure of phosphor has been modified through cation substitution to induce charge variation and a rearrangement of neighboring nitride clusters, and consequently enhance its luminescent behavior. Substitution of Ca(2+) by Sr(2+) cations expanded the lattice volume and the bc plane, but shortened the distance between the layers along the a axis. Lattice distortion of the framework introduced high-coordination sites in the Sr/Eu centers and adequate space, thereby facilitating charge variation of activators under reduced atmosphere, as detected through X-ray absorption near-edge structure spectroscopy. As such, the photoluminescent intensity of the phosphors increased by more than 10% and a blue shift occurred. The microstructures of the samples were also analyzed using high-resolution transmission electron microscopy. Cation substitution induced a special change in the anion environment, as indicated in the solid-state Raman spectra. Moreover, typical ordering variations in the SiN4 and AlN4 clusters are generated in the lattice. Meanwhile, neighbor sequence of (Si/Al)N4 around the divalent centers were observed through solid-state nuclear magnetic resonance spectroscopy. The modified ordering distribution resulted in a rigid structure and improved the thermal quenching behavior. Thermal stability has been enhanced by 10% at 473 K when x = 0.9 in SrxCa0.993-xAlSiN3:Eu(2+)0.007 compared with that at x = 0. This study promotes the research of neighbor sequence for selective tetrahedral sites such as Li, Mg, Al, and Si coordinated by N atoms in contact with cation sites. PMID:26161898

  5. Enhancement of the superconducting transition temperature of TlSr2CaCu2O7 by yttrium and vanadium substitutions

    Microsoft Academic Search

    R. S. Liu; P. P. Edwards

    1991-01-01

    Superconductivity at 105 K has recently been observed in a family of compounds (Tl1-xMx)Sr2(Ca1-yYy)Cu2O7-delta (M = Ti, Zr, Hf, V, Nb, and Ta). An interesting feature is the enhancement of Tc in the parent TlSr2CaCu2O7 compound via substitution of high-valent 3d transition metals; this is in contrast to other high-Tc cuprates investigated so far. The effects on crystal structure and

  6. Superconductivity in Bi-Ca-Y-Sr-Cu-O (2122) and Tl-Ca-Y-Ba-Cu-O (1122) systems; Effect of substitution of Ca BY Y/sup +/

    SciTech Connect

    Ganguli, A.K.; Nagarajan, R.; Nanjundaswamy, K.S.; Rao, C.N.R. (Indian Inst. of Science, Bangalore (India). Solid State and Structural Chemistry Unit)

    1989-01-01

    Effect of substitution of Ca by Y on the properties of T1CaBa/sub 2/Cu/sub 2/O/sub 7/ (1122) and Bi/sub 2/CaSr/sub 2/O/sub 8+{delta}/ (2122) has been studied. Lattice parameters vary progressively with increase in Y concentration in both the systems. In T1Ca/sub 1/1-chi//Y/sub chi/Ba/sub 2/Cu/sub 2/O/sub 7+{delta}/, compositions with chi{le} 0.5 are superconducting. In Bi/sub 2/Ca/sub 1-chi/Y/sub chi/Sr/sub 2/Cu/sub 2/O/sub 8+{delta}/, compositions with chi {le} 0.5 are superconducting; oxides of both these systems become semiconducting for higher values of chi. In Bi-(Ca, Y, Sr)/sub 3/ Cu/sub 2/O/sub /8+{delta}//, T/sub c/ decreases with the increasing Y/Ca ratio becoming zero at a finite value of the ratio.

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

    NASA Astrophysics Data System (ADS)

    Jaiganesh, G.; Jaya, S. Mathi

    2015-06-01

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

  8. Cation substitution dependent bimodal photoluminescence in whitlockite structural Ca(3-x)Sr(x)(PO4)2:Eu(2+) (0 ? x ? 2) solid solution phosphors.

    PubMed

    Ji, Haipeng; Huang, Zhaohui; Xia, Zhiguo; Molokeev, Maxim S; Atuchin, Victor V; Huang, Saifang

    2014-10-20

    Cation substitution dependent tunable bimodal photoluminescence behavior was observed in the Ca3-xSrx(PO4)2:Eu(2+) (0 ? x ? 2) solid solution phosphors. The Rietveld refinements verified the phase purity and whitlockite type crystal structure of the solid solutions. The tunable photoluminescence evolution was studied as a function of strontium content, over the composition range 0.1 ? x ? 2. In addition to the emission band peak at 416 nm in Ca3(PO4)2:Eu(2+), the substitution of Ca(2+) by Sr(2+) induced the emerging broad-band peak at 493-532 nm. A dramatic red shift of the emission peak located in the green-yellow region was observed on an increase of x in the samples with 0.75 ? x ? 2.00. The two emission bands could be related to the EuOn-Ca9 and EuOn-Ca9-xSrx emitting blocks, respectively. The values for the two kinds of emitting blocks in the solid solutions can be fitted well with the observed intensity evolution of the two emission peaks. PMID:25268559

  9. 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.

    2015-01-27

    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

  10. Anisotropic scattering rate in Fe-substituted Bi 2 Sr 2 Ca ( Cu 1 - x Fe x ) 2 O 8 + ?

    DOE PAGESBeta

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

    2015-05-01

    We measured the electronic structure of Fe-substituted Bi2212 using angle-resolved photoemission spectroscopy. 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 suppresses very strongly the coherence weight around the antinodes.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We measured the electronic structure of Fe-substituted Bi2212 using angle-resolved photoemission spectroscopy. 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 suppresses very strongly the coherence weight around the antinodes.

  12. Effect of Divalent Ions (A = Ca, Ba and Sr) Substitution in La-A-Mn-O Manganite on Structural, Magnetic and Electrical Transport Properties

    Microsoft Academic Search

    K. P. Lim; S. W. Ng; S. A. Halim; S. K. Chen; J. K. Wong

    2009-01-01

    Problem statement: Microstructure of the grain will influence the prop erties of a polycrystalline manganites when different dopant is introduced. In this work, an effort had been made to investigate the influence of Ca, Ba and Sr subst itution in La site. Approach: Polycrystalline manganites compound of La 0.67 A0.33 MnO 3 where A = Ba, Sr and Ca had

  13. Enhancing T/sub c/ in Bi/sub 2. 1/CaSr/sub 2/Cu/sub 2/O/sub 8+//sub delta/ from 90 to 101 K by yttrium substitution

    SciTech Connect

    Tallon, J.L.; Buckley, R.G.; Staines, M.P.; Presland, M.R.; Gilberd, P.W.

    1989-04-17

    The Y and rare-earth substitution for Ca in Bi/sub 2.1/CaSr/sub 2/Cu/sub 2/O/sub 8+//sub delta/ is described with particular emphasis on Y substitution. We have prepared single phase, fully substituted material which exhibits an 8.0 x b-axis incommensurate structure, rather larger than the 4.75 x structure in the parent superconductor. The infrared absorption spectra of the insulating fully substituted material are shown to have features very similar to that for YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/. A solubility range is observed only at substitutions up to 5% at which point zero-resistance T/sub c/ is raised from 90 to 101 K. This is shown to arise from 2 copper-layer material and not from 3 copper-layer material. Combined Y and Pb substitution yields n = 2 material for which T/sub c/ remains fixed at 90 K, insensitive to annealing temperature and oxygen loading.

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

    PubMed

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

    2011-03-16

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

  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. [Universite Mentouri. Laboratoire Couches Minces et Interfaces. Route de Ain el Bey - 25017 Constantine (Algeria); Abant Izzet Baysal University. Department of Physics. 14280 Bolu. (Turkey)

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

    SciTech Connect

    Al-Sharabi, Annas; Abd-Shukor, R. [School of Applied Physics, Universiti Kebangsaan Malaysia 43600 Bangi, Selangor (Malaysia)

    2013-11-27

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

  17. Effect of Cu substitution on magnetic behaviour and electrical properties of bilayered manganite La1.2Sr1.5Ca0.3Mn2O7

    NASA Astrophysics Data System (ADS)

    Saxena, A.; Krishnamurthy, A.; Srivastava, B. K.

    2015-02-01

    DC magnetization and electrical resistance measurements have been made on 0.5 atomic% Cu substituted bi-layered system La1.2Sr1.5Ca0.3Mn1.99Cu0.01O7 for studying the effect of low level substitution of Cu at Mn site. Rietveld analysis of X-Ray diffraction pattern of the sample confirms the single phase Sr3Ti2O7 type structure. On cooling below room temperature the system shows magnetic orderings – ferromagnetic (FM) ordering in ab plane below ~270K and 3D FM ordering below ~45K. Also at an intermediate temperature of ~2i0K there is a signature of another transition which could be attributed to onset of an antiferromagnetic state. Substitution of Cu weakens ferromagnetism and the system shows 96% magnetoresistance (MR) at the field of 8 Tesla. The system remains electrical insulator down to 8K. Resistance versus temperature curves has been fitted following Variable range hopping and semiconducting models. Estimated values of density of states at Fermi energy and of Debye temperature are in reasonably good agreement with those reported for other perovskites. Magnetoresistance versus field curves show hysteresis and discontinuities.

  18. Magnetic Behaviour of Fe Substituted Bilayered Manganite La{sub 1.2}Sr{sub 1.5}Ca{sub 0.3}Mn{sub 2}O{sub 7}

    SciTech Connect

    Saxena, Arpita; Krishnamurthy, Anjali; Srivastava, Bipin K. [Department of Physics, University of Rajasthan, Jaipur 302 055 (India)

    2010-12-01

    For studying the effect of low level substitution of Fe (at Mn site) on magnetic behaviour in the bilayered system La{sub 1.2}Sr{sub 1.5}Ca{sub 0.3}Mn{sub 2}O{sub 7}, dc magnetization measurements have been made on La{sub 1.2}Sr{sub 1.5}Ca{sub 0.3}Mn{sub 1.99}Fe{sub 0.01}O{sub 7}. Cooling from 300 K downwards, the system shows transition to ferromagnetic (FM) ordering in ab plane (at {approx}250 K), to antiferromagnetic state (at {approx}195 K) and to 3D FM order (at {approx}70 K). Magnetization--temperature measurements in zero field cooling and field cooling modes, made under different external magnetic fields, and the observed long time evolution of magnetization with time, are suggestive of FM disorder and high magnetic anisotropy. Substitution of Fe weakens ferromagnetism.

  19. 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.

  20. 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

  1. 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.

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

    SciTech Connect

    Patapis, S.K.; Sideridis, L.; Apostolopoulos, G. [Athens Univ. (Greece). Dept. of Physics; Ausloos, M. [Liege Univ. (Belgium). Inst. de Physique; Luo, H.L. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Electrical and Computer Engineering; Politis, C. [Kernforschungszentrum Karlsruhe GmbH (Germany). Inst. fuer Nukleare Festkoerperphysik; Puig, T.; Pont, M.; Munoz, J.S. [Universidad Autonoma de Barcelona (Spain). Dept. of Physics; Balachadran, U. [Argonne National Lab., IL (United States)

    1991-12-31

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

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

    SciTech Connect

    Patapis, S.K.; Sideridis, L.; Apostolopoulos, G. (Athens Univ. (Greece). Dept. of Physics); Ausloos, M. (Liege Univ. (Belgium). Inst. de Physique); Luo, H.L. (California Univ., San Diego, La Jolla, CA (United States). Dept. of Electrical and Computer Engineering); Politis, C. (Kernforschungszentrum Karlsruhe GmbH (Germany). Inst. fuer Nukleare Festkoerperphysik); Puig, T.; Pont, M.; Munoz, J.S. (Univ

    1991-01-01

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

  4. Effect of Ce Substitution on the Magnetoresistivity and Flux Pinning Energy of the Bi2Sr2Ca1- x Ce x Cu2O8+ ? Superconductors

    NASA Astrophysics Data System (ADS)

    Özçelik, B.; Kaya, C.; Gündo?mu?, H.; Sotelo, A.; Madre, M. A.

    2014-02-01

    In this study, the effect of Ce doping on the properties of Bi2Sr2Ca1- x Ce x Cu2O8+ ? ceramic superconductors, with x=0.0, 0.01, 0.05, 0.1, and 0.25, has been investigated. Samples' precursors were prepared using the conventional solid state method and subsequently textured using the Laser Floating Zone technique. The magnetoresistance measurements were studied under various applied magnetic fields. The activation energies, irreversibility fields ( H irr ), upper critical fields ( H c2) and coherence lengths at 0 K ( ?(0)) were calculated from the resistivity versus temperature ( ?- T) curves, under DC magnetic fields up to 5 T. The thermally activated flux flow model has been applied in order to calculate the flux pinning energies. The results indicated that H c2(0) varied from 416.19 to 115 T and the flux pinning energies varied from 1.46 to 0.042 eV at 0 T.

  5. Effect of Hydrostatic Pressure on the Phase Transitions in Acetate-Substituted Dicalcium Strontium Propionate, Ca2Sr[(C2H5COO)1-x(CH3COO)x]6

    NASA Astrophysics Data System (ADS)

    Gesi, Kazuo; Takashige, Masaaki

    1992-06-01

    The effect of hydrostatic pressure on phase transitions has been studied by dielectric measurements for acetate-substituted dicalcium strontium propionate, Ca2Sr[(C2H5COO)1-x(CH3COO)x]6 with x{=}0.045, 0.10, 0.14. The I-II and II-III transition temperatures of x{=}0.045 crystal (256 K and 120 K at 0 MPa, respectively) increase linearly with increasing pressure. The ferroelectric II phase of x{=}0.10 crystal narrows with application of pressure and disappears at 110 MPa. In the x{=}0.14 crystal, which does not show ferroelectricity, the temperature at which the dielectric constant shows a broad maximum increases with increasing pressure. The pressure dependence of the peak value \\varepsilonmax is expressed by \\varepsilonmax{=}\\varepsilon0+C/(p-pc) where C{=}225 MPa and pc{=}-27 MPa. There is a parallelism between the effects of hydrostatic pressure and acetate-substitution on the phase transitions.

  6. High-concentration Na doping of SrRuO3 and CaRuO3.

    PubMed

    Seki, Hayato; Yamada, Ryuta; Saito, Takashi; Kennedy, Brendan J; Shimakawa, Yuichi

    2014-05-01

    The Na-doped perovskite-structure ruthenates Sr(1-x)Na(x)RuO3 and Ca(1-y)Na(y)RuO3 were prepared by high-pressure synthesis, which enables us to go beyond the previously reported Na doping limits and substitute Na for over 50% of the Sr in SrRuO3 and the Ca in CaRuO3. Gradual and systematic changes in the crystal structures were observed, and the decreases in the Ru-O bond lengths confirmed the Na substitution at the A site caused hole doping to Ru(4+) at the B site. In contrast to what has been previously reported, Sr(1-x)Na(x)RuO3 showed metallic conductivity. Magnetic properties were influenced by the Na substitution, but no long-range antiferromagnetic behavior was observed in Ca(1-y)Na(y)RuO3. PMID:24731152

  7. 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.

  8. A precise, high-throughput method for determining Sr/Ca, Sr/Ba, and Ca/Ba ratios in marine barite

    E-print Network

    Paytan, Adina

    A precise, high-throughput method for determining Sr/Ca, Sr/Ba, and Ca/Ba ratios in marine barite for determining Sr/Ca, Sr/Ba, and Ca/Ba ratios of discrete marine barite separates. Marine barite, separated from, and G. Li, A precise, high-throughput method for determining Sr/Ca, Sr/Ba, and Ca/Ba ratios in marine

  9. 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.

  10. Modulation of agonist-induced Ca2+ release by SR Ca2+ load: direct SR and cytosolic Ca2+ measurements in rat uterine myocytes.

    PubMed

    Shmygol, Anatoly; Wray, Susan

    2005-03-01

    Release of Ca2+ from sarcoplasmic reticulum (SR) is one of the most important mechanisms of smooth muscle stimulation by a variety of physiologically active substances. Agonist-induced Ca2+ release is considered to be dependent on the Ca2+ content of the SR, although the mechanism underlying this dependence is unclear. In the present study, the effect of SR Ca2+ load on the amplitude of [Ca2+]i transients elicited by application of the purinergic agonist ATP was examined in uterine smooth muscle cells isolated from pregnant rats. Measurement of intraluminal Ca2+ level ([Ca2+]L) using a low affinity Ca indicator, mag-fluo-4, revealed that incubation of cells in a high-Ca2+ (10 mM) extracellular solution leads to a substantial increase in [Ca2+]L (SR overload). However, despite increased SR Ca2+ content this did not potentiate ATP-induced [Ca2+]i transients. Repetitive applications of ATP in the absence of extracellular Ca2+, as well as prolonged incubation in Ca2+-free solution without agonist, depleted the [Ca2+]L (SR overload). In contrast to overload, partial depletion of the SR substantially reduced the amplitude of Ca2+ release. ATP-induced [Ca2+]i transients were completely abolished when SR Ca2+ content was decreased below 80% of its normal value indicating a steep dependence of the IP3-mediated Ca2+ release on the Ca2+ load of the store. Our results suggest that in uterine smooth muscle cells decrease in the SR Ca2+ load below its normal resting level substantially reduces the IP3-mediated Ca2+ release, while Ca2+ overload of the SR has no impact on such release. PMID:15670868

  11. Strong kinetic effects on Sr/Ca ratios in the calcitic bivalve Pecten maximus

    E-print Network

    Brest, Université de

    solution Sr/Ca ratios and shell Mg/Ca ratios have also been proposed as possible covariables of Sr and Lohmann, 1992). In bivalves, Sr/Ca ratios could potentially be a proxy of temperature, salinity, or Sr. (1996) suggested metabolic (i.e., metabolic pumping) and/or salinity control on Sr/Ca ratios, whereas

  12. Thermodynamics modeling of the Mg–Sr and Ca–Mg–Sr systems

    Microsoft Academic Search

    Yu Zhong; Jorge O. Sofo; Alan A. Luo; Zi-Kui Liu

    2006-01-01

    Thermodynamic modeling of the Mg–Sr binary system and the prediction of the Ca–Mg–Sr ternary system were carried out using the CALPHAD technique and a computerized optimization procedure. The thermodynamic descriptions of pure Mg, Ca, and Sr elements were taken from the literature. The first-principles calculations were performed using the computer code VASP based on the pseudo-potentials and a plane wave

  13. Effect of substitution of Cr on magnetic behavior and electrical transport in bi-layered manganite La 1.2Sr 1.5Ca 0.3Mn 2O 7

    NASA Astrophysics Data System (ADS)

    Saxena, Arpita; Krishnamurthy, Anjali; Srivastava, Bipin K.; Nigam, A. K.

    2011-05-01

    DC magnetization and electrical resistance measurements have been made on four samples in the series La 1.2Sr 1.5Ca 0.3Mn 2-xCr xO 7 corresponding to x = 0, 0.01, 0.03 and 0.05. The systems show onset of 3D ferromagnetic (FM) state in the temperature range ˜75-90 K Magnetization-temperature measurements in zero field cooling and field cooling modes, made under different external fields show long time evolution of magnetization with time suggestive of FM disorder and high magnetic anisotropy. At two temperatures above the Curie point of ˜75-90 K, broad discontinuities are seen in the range ˜260-270 K and ˜200-220 K. These might be signatures of transitions to FM order in ab plane and to an AFM state, respectively. An alternative explanation for the two higher temperature discontinuities could be in terms of a possible intergrowth in the ab plane reported in bi-layered systems. Insulator-metal transition temperature lies close to Tc but the system with 2.5 atomic percent Cr ( x = 0.05) does not attain metallic state down to 20 K. Estimated values of density of states at Fermi energy and Debye temperature, for the studied compositions, are in reasonably good agreement with those reported in other perovskites.

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

    NASA Astrophysics Data System (ADS)

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

    1997-11-01

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

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

    E-print Network

    Ertekin, Abdullah

    2001-01-01

    O)~/SrO/CuO~/Ca/CuO~/SrO/(BiO)z/SrO/CuO~/Ca/CuO~/SrO/(BiO)~ These planes can be divided into two layers. One of them consists of SrO/CuO&/Ca/CuOq/SrO, which has a structure of perovskite type. The other 12 one is a SrO/(BiO)2/SrO layer. The (BiO)2 planes contribute as a charge reservoir. Bio Iyy q l2) I, j...

  16. 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.

  17. Interlaboratory study for coral Sr/Ca and other element/Ca ratio measurements

    NASA Astrophysics Data System (ADS)

    Hathorne, Ed C.; Gagnon, Alex; Felis, Thomas; Adkins, Jess; Asami, Ryuji; Boer, Wim; Caillon, Nicolas; Case, David; Cobb, Kim M.; Douville, Eric; deMenocal, Peter; Eisenhauer, Anton; Garbe-Schönberg, Dieter; Geibert, Walter; Goldstein, Steven; Hughen, Konrad; Inoue, Mayuri; Kawahata, Hodaka; Kölling, Martin; Cornec, Florence L.; Linsley, Braddock K.; McGregor, Helen V.; Montagna, Paolo; Nurhati, Intan S.; Quinn, Terrence M.; Raddatz, Jacek; Rebaubier, Hélène; Robinson, Laura; Sadekov, Aleksey; Sherrell, Rob; Sinclair, Dan; Tudhope, Alexander W.; Wei, Gangjian; Wong, Henri; Wu, Henry C.; You, Chen-Feng

    2013-09-01

    The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twenty-one laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7°C. However, most of the data fall within a narrower range and the Porites coral reference material JCp-1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5°C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5°C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1.

  18. Atomic properties of Ca^+, Sr^+, Cd^+, Hg^+, and Ra^+

    NASA Astrophysics Data System (ADS)

    Jiang, Dansha; Safronova, M. S.; Safronova, U. I.

    2006-05-01

    We conducted a systematic study of the transition properties of Ca^+, Sr^+, Cd^+, Hg^+, and Ra^+ ions using a relativistic all-order method. Reduced electric-dipole matrix elements and transition rates are determined for the ns-npj and npj-n^'dj transitions, where ns is a ground state. The electric-quadrupole matrix elements are evaluated for the ns-(n-1)dj transitions in Sr^+ and Ra^+. The theoretical lifetimes for the npj and ndj states are compared with latest available experimental measurements. The energy levels and hyperfine constants are also calculated and compared with experiment. This work is motivated by recent lifetime measurements in Ca^+, Sr^+, and Cd^+.

  19. Itinerant-to-localized electron transition in CaRu1-xSnxO3 and SrRu1-xPbxO3

    Microsoft Academic Search

    G. Cao; S. McCall; J. Bolivar; M. Shepard; F. Freibert; P. Henning; J. E. Crow; T. Yuen

    1996-01-01

    SrRuO3 and CaRuO3 are perovskites with an orthorhombic distortion and are believed to have a narrow itinerant band. SrRuO3 is the only known ferromagnetic conductor in 4d transition-metal oxides, while CaRuO3 is a paramagnetic conductor. Substituting Pb and Sn for Ru in SrRuO3 and CaRuO3, respectively, preserves the crystal structure, while removing electrons from the 4d band, resulting in an

  20. 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.

  1. 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.

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

    SciTech Connect

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

    1999-09-01

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

  3. 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

  4. Voltage-independent changes in L-type Ca(2+) current uncoupled from SR Ca(2+) release in cardiac myocytes.

    PubMed

    Janczewski, A M; Lakatta, E G; Stern, M D

    2000-10-01

    To determine the effect of voltage-independent alterations of L-type Ca(2+) current (I(Ca)) on the sarcoplasmic reticular (SR) Ca(2+) release in cardiac myocytes, we measured I(Ca) and cytosolic Ca(2+) transients (Ca(i)(2+); intracellular Ca(2+) concentration) in voltage-clamped rat ventricular myocytes during 1) an abrupt increase of extracellular [Ca(2+)] (Ca(o)(2+)) or 2) application of 1 microM FPL-64176, a Ca(2+) channel agonist, to selectively alter I(Ca) in the absence of changes in SR Ca(2+) loading. On the first depolarization in higher Ca(o)(2+), peak I(Ca) was increased by 46 +/- 6% (P < 0.001), but the increases in the maximal rate of rise of Ca(i)(2+) (dCa(i)(2+)/dt(max), where t is time; an index of SR Ca(2+) release flux) and the Ca(i)(2+) transient amplitude were not significant. Rapid exposure to FPL-64176 greatly slowed inactivation of I(Ca), increasing its time integral by 117 +/- 8% (P < 0.001) without significantly increasing peak I(Ca), dCa(i)(2+)/dt(max), or amplitude of the corresponding Ca(i)(2+) transient. Prolongation of exposure to higher Ca(o)(2+) or FPL-64176 did not further increase peak I(Ca) but greatly increased dCa(i)(2+)/dt(max), Ca(i)(2+) transient amplitude, and the gain of Ca(2+) release (dCa(i)(2+)/dt(max)/I(Ca)), evidently due to augmentation of the SR Ca(2+) loading. Also, the time to peak dCa(i)(2+)/dt(max) was significantly increased in the continuous presence of higher Ca(o)(2+) (by 37 +/- 5%, P < 0.001) or FPL-64176 (by 63 +/- 5%, P < 0.002). Our experiments provide the first evidence of a marked disparity between an increased peak I(Ca) and the corresponding SR Ca(2+) release. We attribute this to saturation of the SR Ca(2+) release flux as predicted by local control theory. Prolongation of the SR Ca(2+) release flux, caused by combined actions of a larger I(Ca) and maximally augmented SR Ca(2+) loading, might reflect additional Ca(2+) release from corbular SR. PMID:11009494

  5. Magnetocaloric effect at room temperature in powder of La 0.5(CaSr) 0.5MnO 3

    Microsoft Academic Search

    M. Bejar; R. Dhahri; F. El Halouani; E. Dhahri

    2006-01-01

    The series of strontium-substituted calcium La0.5Ca0.5?xSrxMnO3 has been studied and show the effect of strontium substitution. Magnetic studies on La0.5Ca0.5?xSrxMnO3 compounds are reported. The substitution of a bigger cation, Sr2+ for Ca2+ enhances the Curie temperature (TC) from 228K (x=0) to 335K (x=0.5) and we have found a value of TC around room temperature (273K) for x=0.15. Maximum magnetic-entropy change

  6. Mg\\/Ca and Sr\\/Ca in living benthic foraminiferal tests from the northeastern Atlantic

    Microsoft Academic Search

    K. Tachikawa; C. Fontanier; F. Jorissen; E. Bard

    2003-01-01

    Mg\\/Ca in benthic foraminiferal tests has been recently used as an indicator of bottom water temperature (BWT). We analysed Mg\\/Ca and Sr\\/Ca in living (Rose Bengal stained) and dead foraminifera collected at five stations in the Bay of Biscay in NE Atlantic (43˜44^oN, 2^oW) at interval of 3 to 4 months (1997--2000). Four species with different microhabitat were studied: Cibicidoides

  7. Superconductivity at 105 K in Tl0.5Pb0.5CaSr2- xLaxCu2O7

    NASA Astrophysics Data System (ADS)

    Presland, M. R.; Tallon, J. L.

    1991-06-01

    Substitution of La 3+ for Sr 2+ in the lattice Tl 0.5Pb 0.5Sr 2CaCu 2O 7 has been used to reduce the hole carrier concentration on the CuO 2 planes resulting in Tc passing through a maximum at 105 K. This behaviour is similar to the previously reported effect of substitution of Y 3+ for Ca 2+ in the same parent material. However, in the La 3+-substituted series: (a) superconductivity is maintained to higher substitution levels; (b) the c-axis lattice parameter initially contracts at only 30% of the rate; and (c) the a-b-planes lattice parameter expands at 140% of the rate; compared to the Y 3+-substituted series. These effects are consequences of the differing sites of substitution-La 3+ on the Sr-O plane bounding the CuO 2 planes, and hence influencing the bridging oxygen atom; Y 3+ on the bare Ca 2+ site between the CuO 2 planes. The superconducting phase diagrams of Tc versus substitution level are similar to the phase diagram for the CuO 2 planes established for La 2- xSr xCuO 4.

  8. Physiological studies in heterozygous calcium sensing receptor (CaSR) gene-ablated mice confirm that the CaSR regulates calcitonin release in vivo

    Microsoft Academic Search

    Neva J Fudge; Christopher S Kovacs

    2004-01-01

    BACKGROUND: The calcium sensing receptor (CaSR) regulates serum calcium by suppressing secretion of parathyroid hormone; it also regulates renal tubular calcium excretion. Inactivating mutations of CaSR raise serum calcium and reduce urine calcium excretion. Thyroid C-cells (which make calcitonin) express CaSR and may, therefore, be regulated by it. Since calcium stimulates release of calcitonin, the higher blood calcium caused by

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

    NASA Astrophysics Data System (ADS)

    Roselieb, Knut; Jambon, Albert

    2002-01-01

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

  10. Determination of the Bond Lengths in MgCCH, CaCCH and SrCCH

    NASA Astrophysics Data System (ADS)

    Forthomme, D.; Tokaryk, D. W.; Linton, C.; Adam, A. G.

    2011-06-01

    %High resolution spectra have been analyzed for the tilde{A}2E-tilde{X}2A_1 transition of M-12C12CH, M-12C12CD and M-13C13CH, where M refers to Mg, Ca and Sr. All the molecules except CaCCH have been recorded and analyzed in our laboratory in a laser ablation molecular jet source. The rotational constants extracted from the fits allowed us to calculate accurate bond lengths in MgCCH, CaCCH and SrCCH. This study is of particular interest since it shows how the structure of the molecules evolves as we substitute the alkaline earth atom by another one from the same family. The results showed clear trends in how the molecules account for changes in the mass of the metal atom and how the bond lengths in the ligand CCH are significantly different from the bond lengths in HCCH. Surprisingly, the triple bond between the two carbon atoms happens to be the one that experiences the greatest change. To determine the three bond lengths in a linear four atom molecule, one requires spectral data from three isotopologues of that molecule. By combining information from previously published analyses with new high resolution isotopically substituted spectra, we have determined the bond lengths for MgCCH, CaCCH and SrCCH. In each case, the tilde{A}2?-tilde{X}2?^+ spectra of the M-12C12CH, M-12C12CD and M-13C13CH isotopologues were considered, where M refers to Mg, Ca and Sr. This study is of particular interest since it shows how the structure of this family of molecules evolves as we change the alkaline earth atom attached to the CCH ligand. In MgCCH, the structure of the CCH ligand is nearly the same as it is in acetylene, HCCH. Surprisingly, the bonding in the ligand is quite different from that of acetylene for the two heavier acetylide molecules, with the triple bond between the two carbon atoms experiencing the greatest change. M. Li and J. A. Coxon, J. Mol. Spectrosc. 176 (1996) 206-210 M. J. Dick, P. M. Sheridan, J. -G. Wang and P. F. Bernath, J. Mol. Spectrosc. 233 (2005) 197-202 J. Overend, Trans. Faraday Soc. 56 (1960) 310-314

  11. Revision of the thermodynamic descriptions of the Cu–O, Ag–O, Ag–Cu–O, Bi–Sr–O, Bi–Ca–O, Bi–Cu–O, Sr–Cu–O, Ca–Cu–O and Sr–Ca–Cu–O systems

    Microsoft Academic Search

    Bengt Hallstedt; Ludwig J. Gauckler

    2003-01-01

    We have revised the thermodynamic descriptions of several subsystems of the Ag–Bi–Sr–Ca–Cu–O system. In the Cu–O system the description of the liquid phase was changed to remove an inverted miscibility gap at high temperature and to get a better fit of the CuO liquidus. Also the dissolution model for O in fcc-Cu and fcc-Ag was changed from substitutional to interstitial.

  12. Insight on the electronic state of Sr2IrO4 revealed by cationic substitutions

    NASA Astrophysics Data System (ADS)

    Klein, Y.; Terasaki, I.

    2008-07-01

    We report the electrical resistivity, thermoelectric power and magnetization of Sr2-xLaxIrO4 (x = 0 and 0.05) and Sr2Ir1-yRhyO4 (y = 0.05, 0.1 and 0.2) measured below room temperature. In Sr2IrO4, electrons (La substitution) or holes (Rh substitution) can be doped, which lead to a strong decrease of the resistivity. In particular, a nearly-metallic state is realized in the case of Rh doping. The thermoelectric power turns out to be metallic-like for y = 0.2. The presence of a gap in the electronic band structure is robust against these substitutions. From various experimental data, similarities with the 3D charge density wave compound, BaBiO3, are suggested. Nevertheless, rather than a charge density wave, our scenario implies the presence of a spin density wave.

  13. 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.

  14. 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

  15. Structural characterization of Sol-Gel derived Sr-substituted calcium phosphates with anti-osteoporotic and

    E-print Network

    Paris-Sud XI, Université de

    1 Structural characterization of Sol-Gel derived Sr- substituted calcium phosphates with anti to prepare un-doped and Sr-doped calcium phosphate ceramics exhibiting a porous structure. The samples) and Tri Calcium Phosphate (-TCP). Doping with Sr2+ ions has a clear effect on the proportions

  16. 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. (Univ. of Washington, Seattle, WA (United States))

    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.

  17. Improved Figure of Merit of (Ba,Sr)TiO3-Based Ceramics by Sn Substitution

    NASA Astrophysics Data System (ADS)

    Ha, Jong-Yoon; Lin, Liwei; Jeong, Dae-Yong; Yoon, Seok-Jin; Choi, Ji-Won

    2009-01-01

    The dielectric properties of (Ba0.6Sr0.4)(Ti1-xSnx)O3 (0 ?x ?0.3) ceramics were investigated. Single-phase specimens having a cubic perovskite structure could be obtained. As Sn concentration increased, dielectric loss decreased untill a composition of x = 0.15 and slightly increased as Sn concentration increased further. The diffused phase transition appeared owing to substitution of Sn ions. When Sn was substituted at 0.1 mol in (Ba0.6Sr0.4)TiO3 at 1400 °C, the dielectric constant, dielectric loss, tunability, Curie point, and figure of merit (FOM) were 1400, 0.0027, 18%, -40 °C, and 67, respectively. These compositions show excellent dielectric properties than those of (Ba0.5Sr0.5)TiO3 ferroelectrics, which are limelight materials for tunable devices such as varactors, phase shifters, and frequency agile filters.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  20. Bulk thermal expansion studies of BiCaSrCu2O x and Bi2CaSr2Cu2O x

    NASA Astrophysics Data System (ADS)

    Momin, A. C.; Mirza, E. B.; Mathews, M. D.

    1991-05-01

    The compounds BiCaSrCu2O x and Bi2CaSr2Cu2O x were prepared by ceramic techniques and characterized by X-ray powder diffractometry (XRD) and microthermogravimetry ( ?TG) and their bulk thermal expansion measurements were carried out using dilatometry in the temperature range 298? T?1073 K in air. The results have been analyzed and are compared with those obtained earlier for YBa2Cu3O7. The XRD analysis shows that both BiCaSrCu2O x and Bi2CaSr2Cu2O x are single phase in nature, having an orthorhombic symmetry. The ?TG analysis carried out in oxygen, air, and nitrogen shows negligible weight loss (R~0.1%) on heating to 1073 K, indicating that these two compounds, unlike YBa2Cu3O7, are quite stable. The analysis of bulk thermal expansion data reveals that the average linear thermal expansion coefficient ( ? 1) for both BiCaSrCu2O x and Bi2CaSr2Cu2O x is almost the same ( ? 1? 10.5×10-6 K-1) and is found to be nearly half of that for YBa2Cu3O7 ( ? 1? 18×10-6 K-1), suggesting that the interatomic bonding in both BiCaSrCu2O x and Bi2CaSr2Cu2O x is stronger as compared to YBa2Cu3O7.

  1. Physico-chemical changes in Ca, Sr and Al-doped La-Mn-O perovskites upon thermochemical splitting of CO2 via redox cycling.

    PubMed

    Gálvez, M E; Jacot, R; Scheffe, J; Cooper, T; Patzke, G; Steinfeld, A

    2015-03-01

    Thermochemical CO2-splitting via redox cycling of Ca, Sr and Al-doped La-Mn perovskites induces irreversible changes in the texture and chemical composition of these oxides. Though the crystal structure is mostly preserved after high-temperature redox cycling, the chemical stability is detrimentally affected by sintering and by the formation and eventual segregation of a carbonate phase during oxidation by CO2. Carbonation of the Ca and Sr phase was diminished by Al-substitution of the Mn-cation in the B-position. PMID:25666121

  2. Synthesis, structural and vibrational properties of Bi0.8La0.15A0.05FeO3 (A = Ca, Sr)

    NASA Astrophysics Data System (ADS)

    Sharma, Poorva; Kumar, Ashwini; Varshney, Dinesh

    2015-06-01

    The polycrystalline Bi0.8La0.15A0.05FeO3 (A = Ca, Sr) was synthesized by solid state reaction route to study the structural and vibrational properties. X-ray diffraction patterns confirmed the formation of single-phase perovskite structure. Rietveld-refined crystal structure parameters revealed the existence of rhombohedral R3c symmetry in the prepared sample. The blue shift of phonon modes is attributed to lower atomic mass of La3+ and A = (Ca, Sr) substitution at Bi site in BiFeO3.

  3. 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...

  4. An alternate preparation for (Bi, Pb) 2Ca 2Sr 2Cu 3O z

    NASA Astrophysics Data System (ADS)

    Arendt, Ronald H.; Garbauskas, Mary F.; Bednarczyk, Peter J.

    1991-05-01

    An alternative synthetic route for obtaining (Bi, Pb) 2Ca 2Sr 2Cu 3O z (2223), by using Bi 2CaSr 2Cu 2O z, (2122), as a starting material is described. The advantages of this route include lower processing temperatures, shorter reaction times, and improved phase purity over conventional synthetic routes.

  5. Direct Observation of Substitutional Au Atoms in SrTiO3

    SciTech Connect

    Wang, Chong M.; Shutthanandan, V.; Zhang, Yanwen; Thevuthasan, Suntharampillai; Duscher, Gerd

    2004-11-05

    Ion implantation and subsequent high-temperature annealing is an effective way to prepare metal nanoclusters dispersed in a dielectric for useful optical and electrical properties. However, there is very little understanding of the nucleation and growth process of these nanoclusters, their correlations with the sites of the implanted ions, and the behavior of defects (such as vacancies) generated during the ion-implantation process. Using high-angle annular dark-field imaging in aberration-corrected scanning transmission electron microscopy, we have directly observed that, at a dilute concentration, Au atoms implanted in SrTiO3 are in a substitutional lattice position for both Sr and Ti. Congregation of Au atoms by diffusion to a critical concentration leads to the nucleation of a Au lattice within the SrTiO3. The Au nanocluster and SrTiO3 were found to maintain an orientation relationship of Au[001]//SrTiO3[001] and Au(100)//SrTiO3(100), which corroborated the results of a first-principles total-energy calculation. The interface between the Au cluster and SrTiO3 was bridged by an O/Ti plane. The Au-O bond length was found to be 2.2 Å, which is the same as Au-O bond length in AuO. Furthermore, the atomic planes adjacent to the interface in both Au and SrTiO3 were found to be slightly stretched. The high concentration of vacancies generated during the Au implantation aggregated to form cavities in the SrTiO3 lattice, and were faceted mostly along the SrTiO3 {100} and (110) planes. The Au and vacancy clusters were spatially associated, indicating a strong interaction. Thus, the formation of cavities in Au-implanted materials indicates that the vacancy-clustering process prevails over the Frenkel-pair recombination.

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

    SciTech Connect

    Lucas-Girot, Anita [UMR 6226 CNRS-Universite de Rennes 1, Sciences Chimiques de Rennes, Bat. 10B, Campus de Beaulieu, Avenue du General Leclerc, F-35042 Rennes (France)]. E-mail: anita.lucas@univ-rennes1.fr; Hernandez, Olivier [UMR 6226 CNRS-Universite de Rennes 1, Sciences Chimiques de Rennes, Bat. 10B, Campus de Beaulieu, Avenue du General Leclerc, F-35042 Rennes (France); Oudadesse, Hassane [UMR 6226 CNRS-Universite de Rennes 1, Sciences Chimiques de Rennes, Bat. 10B, Campus de Beaulieu, Avenue du General Leclerc, F-35042 Rennes (France)

    2007-06-05

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

  7. 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

  8. Comparison of the EXAFS Spectra of Heteronuclear MnCa/Sr Model Complexes to the Oxygen-Evolving Mn(4)Ca Complex of Photosystem II

    SciTech Connect

    Mishra, A.; Yano, J.; Pushkar, Y.; Abboud, K.A.; Yachandra, V.K.; Christou, G.

    2009-06-03

    Heterometallic Mn-Ca and Mn-Sr complexes have been prepared and employed as model complexes for Ca and Sr EXAFS spectral comparisons with the Oxygen-Evolving Complex (OEC) of Photosystem II (PS II); these have revealed similarities that support the presence of at least one O atom bridge between the Mn and Ca/Sr in the OEC.

  9. Gulf of Alaska and California bamboo corals: Ba/Ca and Sr/Ca records

    NASA Astrophysics Data System (ADS)

    Sauthoff, W.; LaVigne, M.; Hill, T. M.; Roark, E.; Dunbar, R. B.; Guilderson, T. P.; Spero, H. J.

    2012-12-01

    Deep-sea bamboo coral communities form on seamounts and along continental margins with near global distribution. Bamboo [Isididae] corals record surrounding ocean geochemistry presenting reliable proxy records of changes in seawater conditions, including productivity and nutrient content. Here we investigate bamboo coral specimens from the California margin and Gulf of Alaska (634-1288 m water depth; ~37oN-48oN), to provide insight into latitudinal and temporal differences in eastern Pacific Ocean climate processes. Past oceanic conditions were reconstructed in this investigation by trace element analyses (Ba/Ca, Sr/Ca) using laser ablation ICP-MS, using a 85 ?m spot size at 10 ?m/s, 4.45 J/cm2 fluence, and 10 Hz repetition rate. Two California specimens show differences in mean Ba/Ca content: 13.73 compared to 18.55 ?mol/mol, which we attribute to differences in collection depth (T1104 A10: 833 m and T1100 A04: 1288 m, respectively). Gulf of Alaska corals show a more subdued nutrient signal with lower mean Ba/Ca values of 10.56 and 10.05 ?mol/mol across a narrower depth range (ALV3803 #3: 720 m; ALV3803 #5: 634 m, respectively). This trend of increasing Ba/Ca with depth is in consensus with eastern Pacific dissolved barium and California margin bamboo coral depth transects. Sr/Ca content was uniform between four coral specimens with values ranging from 3.01 to 3.06 mmol/mol. Coral chronologies were compared against indices of climate oscillations, including El Niño Southern Oscillation and Pacific Decadal Oscillation, using time series based upon radiocarbon dating. The corals investigated here show a limited connection with El Niño Southern Oscillation; longer-term changes related Pacific Decadal Oscillation may be evidenced in this climate archive.

  10. Neutron diffraction evidence for oxygen dimers in Bi-Ca-Sr-Cu-O superconductors

    NASA Astrophysics Data System (ADS)

    Sequeira, A.; Rajagopal, H.; Nagarajan, R.; Rao, C. N. R.

    1989-06-01

    A comparative neutron diffraction study of Bi 2CaSr 2Cu 2O 8+?, Bi 2Ca 2SrCu 2O 8+? and Bi 2Ca 1.5Y 0.5SrCu 2O 8+? has not only shown the presence of considerable oxygen excess in the Bi layers, but also evidence for oxygen pairing giving rise to O 1-2 or O 2-2 type species, probably the latter. The proportion of the paired species increases when Y partly replaces Ca. Furthermore, the Tc decreases with an increase in paired species.

  11. Intercolony Sr/Ca variability in Palmyra Island corals: Implications for paleo-SST reconstructions

    NASA Astrophysics Data System (ADS)

    Sayani, H. R.; Cobb, K.; Cohen, A. L.; Druffel, E. R.; Monteleone, B. D.

    2013-12-01

    The ratio of strontium to calcium (Sr/Ca) in coral skeletons is widely used to construct continuous, highly-resolved records of past sea-surface temperature (SST) variability. Typically, paleo-SST estimates are derived using Sr/Ca-SST functions created by regressing Sr/Ca from a single modern coral against instrumental SST. However, several studies have found that while coral Sr/Ca may strongly covary with SST, the absolute Sr/Ca values in corals growing on the same reef often differ significantly. As such, the uncertainties associated with coral-derived paleo-SST estimates based on the calibration approach outlined above are poorly constrained. To assess reproducibility of coral Sr/Ca and extent of intercolony variability at Palmyra Island (6°N, 162°W; Cobb et al., 2003; Nurhati et al., 2011), we measure mm- and ?m-scale Sr/Ca in four overlapping modern Porites cores. Conventional mm-scale Sr/Ca records from these modern cores are well correlated with each other (R = 0.65 to 0.68) and with SST (R = -0.73 to -0.85), but the absolute Sr/Ca values of these records exhibit baseline offsets of ×0.11mmol/mol (1?). Secondary ion mass spectrometry (SIMS) is used to generate 2-3 year long, weekly-resolved, Sr/Ca records from 3 overlapping modern coral segments. While the SIMS Sr/Ca analyses from each core exhibit relatively large point-to-point variations of ~0.17mmol/mol (1?), compared to ~0.06mmol/mol (1?) in mm-scale Sr/Ca, their monthly-scale variability resolves the annual SST cycles observed at Palmyra reasonably well (R = -0.46 to -0.64). Furthermore, the intercolony offsets observed in mm-scale Sr/Ca records are reproduced in the SIMS Sr/Ca records. These large offsets imply that paleo-SST estimates derived from a single fossil coral Sr/Ca dataset would be associated with uncertainties of ×1.4°C (1?). We build a coral Sr/Ca 'stack' for Palmyra Island using Sr/Ca records from the 4 modern cores. This composite Sr/Ca record is more strongly correlated with SST (R=-0.86), as intercolony variability is averaged out. In ongoing work, we apply this composite calibration to fossil coral Sr/Ca stacks, generated from multiple overlapping cores, from Palmyra Island to provide robust SST estimates for select intervals of the last millennium. References: Cobb, K. M., et al., Nature 424, 271-276 (2003). Nurhati, I. S., et al., Journal of Climate 24, 3294-3308 (2011).

  12. Intercolony Sr/Ca variability in Palmyra Island corals: Implications for paleo-SST reconstructions

    NASA Astrophysics Data System (ADS)

    Sayani, H. R.; Cobb, K.; Cohen, A. L.; Druffel, E. R.; Monteleone, B. D.

    2011-12-01

    The ratio of strontium to calcium (Sr/Ca) in coral skeletons is widely used to construct continuous, highly-resolved records of past sea-surface temperature (SST) variability. Typically, paleo-SST estimates are derived using Sr/Ca-SST functions created by regressing Sr/Ca from a single modern coral against instrumental SST. However, several studies have found that while coral Sr/Ca may strongly covary with SST, the absolute Sr/Ca values in corals growing on the same reef often differ significantly. As such, the uncertainties associated with coral-derived paleo-SST estimates based on the calibration approach outlined above are poorly constrained. To assess reproducibility of coral Sr/Ca and extent of intercolony variability at Palmyra Island (6°N, 162°W; Cobb et al., 2003; Nurhati et al., 2011), we measure mm- and ?m-scale Sr/Ca in four overlapping modern Porites cores. Conventional mm-scale Sr/Ca records from these modern cores are well correlated with each other (R = 0.65 to 0.68) and with SST (R = -0.73 to -0.85), but the absolute Sr/Ca values of these records exhibit baseline offsets of ×0.11mmol/mol (1?). Secondary ion mass spectrometry (SIMS) is used to generate 2-3 year long, weekly-resolved, Sr/Ca records from 3 overlapping modern coral segments. While the SIMS Sr/Ca analyses from each core exhibit relatively large point-to-point variations of ~0.17mmol/mol (1?), compared to ~0.06mmol/mol (1?) in mm-scale Sr/Ca, their monthly-scale variability resolves the annual SST cycles observed at Palmyra reasonably well (R = -0.46 to -0.64). Furthermore, the intercolony offsets observed in mm-scale Sr/Ca records are reproduced in the SIMS Sr/Ca records. These large offsets imply that paleo-SST estimates derived from a single fossil coral Sr/Ca dataset would be associated with uncertainties of ×1.4°C (1?). We build a coral Sr/Ca 'stack' for Palmyra Island using Sr/Ca records from the 4 modern cores. This composite Sr/Ca record is more strongly correlated with SST (R=-0.86), as intercolony variability is averaged out. In ongoing work, we apply this composite calibration to fossil coral Sr/Ca stacks, generated from multiple overlapping cores, from Palmyra Island to provide robust SST estimates for select intervals of the last millennium. References: Cobb, K. M., et al., Nature 424, 271-276 (2003). Nurhati, I. S., et al., Journal of Climate 24, 3294-3308 (2011).

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

    E-print Network

    Oh, Se-Jung

    Electronic structure of epitaxial ,,Sr,Ca...RuO3 films studied by photoemission and x 2003; published 25 February 2004 Electronic structures of epitaxial Sr,Ca RuO3 thin films are studied in both SrRuO3 and CaRuO3. However the electron correlation effect seems more important in CaRuO3 than Sr

  14. Otolith Sr:Ca and Ba:Ca may give inconsistent indications of estuarine habitat use for American eels ( Anguilla rostrata )

    Microsoft Academic Search

    Brian M. Jessop; Chia-Hui Wang; Wann-Nian Tzeng; Chen-Feng You; Jen-Chieh Shiao; Shih-Huan Lin

    Temporal patterns in otolith Sr:Ca and Ba:Ca ratio values of American eels Anguilla rostrata from two sites in western Newfoundland gave insight into the use of freshwater and saline habitats. Mean Sr:Ca and Ba:Ca\\u000a values at the core zone did not differ between sites, indicative of a common oceanic origin. At the otolith edge, representing\\u000a continental life, both Sr:Ca and

  15. 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. [College of Science, Northeastern University, Shenyang 110819 (China); Qi, Y., E-mail: qiyang@imp.neu.edu.cn [College of Science, Northeastern University, Shenyang 110819 (China); Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China)

    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.

  16. Fe doping effect on structural properties of Bi1.6Pb0.4Sr2CaCu2-xFexO8+?

    NASA Astrophysics Data System (ADS)

    Bouaïcha, F.; Mosbah, M.-F.; Amira, A.; Chamekh, S.; Boussouf, N.

    2009-11-01

    Since the discovery of the high temperature superconductivity in the Bi-Sr-Ca-Cu-O system , many investigations have focused on it to understand its properties and to improve them. Belonging to this system, the Bi2Sr2CaCu2O8+d (Bi-2212) phase has been widely studied in the recent years in order to understand, by various kinds of substitution, the relation between the structure and the superconductivity. Most of these substitutions have concerned the Cu site in the superconducting layer CuO2. Among these, as showed by G. Ilonca et al., the substitution by Fe kills the superconductivity at a lower concentration than Ni. At our knowledge, nothing has been made when there is in the same time a substitution by lead (Pb) on the Bi site. For that purpose samples of Bi1.6Pb0.4Sr2CaCu2-xFexO8+? with x = 0-0.06, have been prepared using the solid state reaction technique. The samples have been characterized by X-ray diffraction (XRD) and scanning electron microsopy (SEM). Structural analysis shows the influence of the Fe doping on the crystalline lattice structure of the samples.

  17. Structural consideration on the emission properties of Eu²?-doped Ba(Sr, Ca)?MgSi?O?

    SciTech Connect

    Yonesaki, Yoshinori, E-mail: yonesaki@yamanashi.ac.jp [Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Miyamae 7-32, Kofu 400-8511 (Japan)

    2013-05-01

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

  18. Epithelial CaSR deficiency alters intestinal integrity and promotes proinflammatory immune responses.

    PubMed

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

    2014-11-17

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

  19. 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.

  20. 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.

  1. Synthesis of Bi-Ca-Sr-Cu-O superconductive material

    SciTech Connect

    Arendt, R.H.

    1992-03-17

    This patent describes a process for making a sinterable superconductive composition in powder form having the formula Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub x} where x is from about 7.5 to about 8.5. It comprises forming an admixture comprising an alkali metal chloride solvent material selected from the group consisting of sodium chloride and potassium chloride and mixtures thereof, and the oxide or oxide precursors of bismuth, calcium, strontium, and copper in amounts sufficient to form the composition by reaction, heating the admixture to a temperature sufficient to melt the alkali metal chloride, dissolve the oxides of bismuth, calcium, strontium and copper and form the superconductive composition, maintaining the temperature to continuously dissolve reactant oxides or oxide precursors until substantially consumed by formation and precipitation of the composition from the reactant-saturated solvent material; cooling the molten mass to a solid; separating and recovering the superconductive composition by dissolving the alkali metal chloride solvent material in water; and comminuting the superconductive composition to produce powder.

  2. Effects of oxygen partial pressure on the crystallization of amorphous Bi-Sr-Ca-Cu-O and Bi-Sr-Ca-Cu-O + Ag

    NASA Astrophysics Data System (ADS)

    Kramer, M. J.; Margulies, L.; Arrasmith, S. R.; Dennis, K. W.; Lang, J. C.; McCallum, R. W.; Gallagher, P. K.

    1994-07-01

    The temperatures and pathways of crystallization for amorphous Bi-Sr-Ca-Cu-O are strongly dependent on oxygen partial pressure (P(sub O(2))), the oxidation state of the glass, and the presence of Ag. Reducing the P(sub O(2)) from 1 to 0 bar lowers the onset of melting 100 deg C, but does not change the onset of crystallization. Decreasing P(sub O(2)) does inhibit the formation of (CaSr)CuO3 (011). Although Ag appears to be immiscible in Bi-Sr-Ca-Cu-O, finely distributed Ag lowers the onset of melting by 20 to 35 C, depending on P(sub O(2)). In oxygen-deficient glass, two exotherms are observed upon heating.

  3. 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

  4. A Mössbauer study of spinach chloroplasts with substituted functionally active Ca2+ for57Fe

    NASA Astrophysics Data System (ADS)

    Novakova, A. A.; Semin, B. K.; Aleksandrov, A. Yu.; Tsurkina, L. A.

    1992-04-01

    A Mössbauer spectroscopy was used to investigate spinach chloroplasts in which Ca2+ ions localized in photosystem-II (actively involved in the structural-functional organization of the photosynthetic chain) were chemically substituted for57Fe ions.

  5. Wnt5a secretion stimulated by the Extracellular Calcium-sensing Receptor (CaSR) inhibits defective Wnt signaling in colon cancer cells

    Microsoft Academic Search

    R John MacLeod; Madeline Hayes; Ivan Pacheco

    2007-01-01

    ABSTRACT Tounderstand,the role of the colonic extracellular Calcium-sensing Receptor (CaSR) in calcium chemoprotection against colon cancer, we activated the CaSR with 5 mM Ca, stimulated the upregulation (as assessed by RT-PCR) and the secretion of Wnt5a (assessed by Western blot), a non- canonical Wnt family member. I nhibiting CaSR activity with siRNA duplex against the CaSR reduced CaSR protein and

  6. 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.

  7. The extracellular calcium-sensing receptor, CaSR, in fetal development

    PubMed Central

    Riccardi, Daniela; Brennan, Sarah C; Chang, Wenhan

    2015-01-01

    In fetal mammals, serum levels of both total and ionized calcium significantly exceed those in the adult. This relative fetal hypercalcaemia is crucial for skeletal development and is maintained irrespectively of maternal serum calcium levels. Elegant studies by Kovacs and Kronenberg have previously addressed the role of the CaSR in creating and maintaining this relative fetal hypercalcaemia, through the regulation of parathyroid hormone-related peptide secretion. More recently we have shown that the CaSR is widely distributed throughout the developing fetus, where the receptor plays major, unexpected roles in ensuring growth and maturation of several organs. In this article, we present evidence for a role of the CaSR in the control of skeletal development, and how fetal hypercalcaemia, acting through the CaSR, regulates lung development. PMID:23856271

  8. ?SR studies of two-dimensional antiferromagnets CaV 3O 7 and SrV 3O 7

    NASA Astrophysics Data System (ADS)

    Fudamoto, Y.; Gat, I. M.; Larkin, M. I.; Merrin, J.; Nachumi, B.; Savici, A. T.; Uemura, Y. J.; Luke, G. M.; Kojima, K. M.; Isobe, M.; Ueda, Y.; Taniguchi, S.; Sato, M.

    2003-05-01

    A discontinuous change of muon-spin precession frequencies in CaV 3O 7 is observed at T?0.2 K, indicating a possible spin reorientation. Our results suggest that CaV 3O 7 possesses the identical spin direction as isostructural SrV 3O 7 below ?0.2 K, although the spin directions in the two compounds are different at higher temperatures as determined by elastic neutron scattering.

  9. Metal-Insulator Transition in the Bi2Sr2Ca1-xYxCu2O8+y System

    Microsoft Academic Search

    Tsuyoshi Tamegai; Kei-ichi Koga; Kunio Suzuki; Masaki Ichihara; Fumiko Sakai; Yasuhiro Iye

    1989-01-01

    Metal-insulator transition driven by the change of the carrier concentration was investigated in the 80 K superconductor Bi2Sr2CaCu2O8+y. The carrier concentration was controlled by the substitution of yttrium for calcium. Experimental results from structural, transport, and magnetic studies are discussed in comparison with other high-temperature superconductor systems, La2-xSrxCuO4 and YBa2Cu3O7-y.

  10. Magnetism, superconductivity, and the volume collapse transition in (Ca0.67Sr0.33)Fe2As2 under pressure

    NASA Astrophysics Data System (ADS)

    Jeffries, Jason; Butch, N. P.; Saha, S. R.; Kirshenbaum, K.; Weir, S. T.; Vohra, Y. K.; Paglione, J.

    2012-02-01

    The alkaline earth site of CaFe2As2 can be chemically substituted with Sr, forming a homogeneous solid solution series ending with SrFe2As2. It is found that (Ca0.67Sr0.33)Fe2As2 exhibits a pressure-temperature phase diagram intermediate between the two end members of the series, shifting the phase lines for the suppression of magnetism, the development of superconductivity, and the occurrence of a volume collapse transition to higher pressures. The overall shift in the pressure-temperature phase diagram permits the study of each phase field, yielding valuable information about the correlations between local atomic structure, magnetism, superconductivity, and the volume collapse transition. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.

  11. Dimensional 3D–2D cross-over under magnetic field in Bi2Sr2?xLaxCuOy induced by La/Sr substitution

    NASA Astrophysics Data System (ADS)

    Murrills, C. D.; Li, Z. Z.; Raffy, H.

    2015-06-01

    The single CuO2 layer Bi2Sr2CuO6 (Bi-2201) is characterized by a low anisotropy under magnetic field. We show that this anisotropy increases exponentially from 4 to 400 with La/Sr substitution in Bi2Sr2?xLaxCu06 (Bi(La)-2201). We present a phase diagram showing the change in transport properties from 3D to 2D when the La concentration is increased, deduced from angular transport measurements in the mixed state of c-axis oriented epitaxial Bi(La)-2201 thin films with columnar pinning centers parallel to the c-axis. We attribute this anisotropy increase to the decrease of the distortion of CuO2 planes by La/Sr substitution.

  12. A high-resolution calibration of Sr/Ca thermometry using the Caribbean coral Montastraea annularis

    NASA Astrophysics Data System (ADS)

    Swart, P. K.; Elderfield, H.; Greaves, M. J.

    2002-11-01

    A relationship has been established between the Sr/Ca ratio in the skeleton of the scleractinian coral Montastraea annularis and sea surface water temperature in south Florida. In order to obtain this correlation, specimens of Montastraea annularis were transplanted to a site at a local reef where every two to three months throughout a 2-year period the corals were stained with Alizarin-red S and where water temperature, which annually ranges between ˜20° and 30°C, was continually monitored. At the end of the experimental period the coral skeleton was sampled at a rate of ˜50 samples per year, each sample corresponding to only around 20 ?g of calcium carbonate. For the 2.5-year period, the Sr/Ca ratio exhibited excellent correlation in the first year (R2 = 0.83; Sr/Ca (mmol/mol) = 10.11 - 0.0452 × SST (°C)), but a rather poorer correlation in the second year (R2 = 0.68; Sr/Ca (mmol/mol) = 10.09 - 0.0406 × SST (°C)). Averaging the data into monthly values for year 1, we determined a relationship of (Sr/Ca (mmol/mol) = 10.165 - 0.0471 × SST (°C). On the basis of the excellent correlation between temperature and Sr/Ca, we feel that this relationship is the most accurate. Discrepancies in the second year are suggested to arise from slight sampling errors relative to the stain lines.

  13. Electron localization and magnetism in SrRuO3 with non-magnetic cation substitution.

    PubMed

    Tong, W; Huang, F-Q; Chen, I-W

    2011-03-01

    The destruction of the ferromagnetism of alloyed SrRuO(3) can be caused by electron localization at the substitution sites. Among all the non-magnetic cations that enter the B site, Zr(4+) is the least disruptive to conductivity and ferromagnetism. This is because Zr(4+) does not cause any charge disorder, and its empty d electron states which are poorly matched in energy with the Ru t(2g)(4) states cause the least resonance scattering of Ru's d electrons. Conducting Sr(Ru, Zr)O(3) may be used as an electrode for perovskite-based thin film devices, while its insulating counterpart provides unprecedented magnetoresistance, seldom seen in other non-manganite and non-cobaltite perovskites. PMID:21411908

  14. 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.

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

    Microsoft Academic Search

    Stephanie de Villiers; Mervyn Greaves; Henry Elderfield

    2002-01-01

    An inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method for the accurate and precise simultaneous measurement of the Mg\\/Ca and Sr\\/Ca content of carbonates was established. While a precision of <0.3% (1sigma standard deviation (SD)) is easily obtainable for both Mg\\/Ca and Sr\\/Ca analysis, a Ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures. An alternative ratio

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  17. Preparation of superconducting Bi-Ca-Sr-Cu-O thin films by rf magnetron sputtering

    SciTech Connect

    Yang, Y.F.; Dieckmann, G.H.; Nordman, J.E.

    1989-03-01

    Superconducting thin films of Bi-Ca-Sr-Cu oxide, with T/sub c/ onset of approximately 90K, have been prepared by rf magnetron sputtering on sapphire with and without a CaZrO/sub 3/ buffer layer, ZrO/sub 2/-coated silicon (111), as well as on single crystal MgO (100). Sintered pellets of Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8+x/ (2122) and Bi/sub 4/Ca/sub 3/Sr/sub 3/Cu/sub 4/O/sub 16+x/ (4334) were employed as targets. The as-deposited films were amorphous insulators which were then annealed in various ways. Zero resistance at 72K for films on (100) MgO was achieved after annealing in air at 810/sup 0/C for 2 hr. However, the X-ray diffraction pattern showed that two superconducting phases, i.e. Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8+x/ (2122) and Bi/sub 2/Ca/sub x/Sr/sub 2-x/CuO/sub 6+y/ (2021), are present, and that films have preferred orientation with c-axis normal to the substrates.

  18. Synthesis of Bi-Pb-Ca-Sr-Cu-O oriented polycrystal superconductor

    SciTech Connect

    Arendt, R.H.; Garbauskas, M.F.

    1991-10-15

    This patent describes a process for making oriented superconductive crystalline Bi{sub 2{minus}y}Pb{sub y}Ca{sub 2}Sr{sub 2}Cu{sub 3} O{sub 10{plus minus}z} in which y is from 0.1 to 0.5 and z is from zero to less than 1. It comprises forming a slurry comprising an organic liquid vehicle, Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub 8{plus minus}x} where x is from 0 to 0.5, Ca{sub 2}CuO{sub 3}, cupric oxide, and lead oxide; simultaneously removing the liquid vehicle while aligning the Bi{sub 2}CaSr{sub 2}Cu{sub 2} O{sub 8{plus minus}x} with substantially parallel c-axes by means of an external magnetic field; heating the resulting admixture at a temperature between about 820{degrees} C and 860{degrees} C to convert aligned Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub 8{plus minus}x} to aligned Bi{sub 2{minus}y}Pb{sub y}Ca{sub 2}Sr{sub 2}Cu{sub 3}O{sub 10{plus minus}z}.

  19. Magnetic Properties of SrRuO3 and CaRuO3

    Microsoft Academic Search

    J. M. Longo; P. M. Raccah; J. B. Goodenough

    1968-01-01

    Magnetization measurements of SrRuO3 and CaRuO3 confirm that SrRuO3 is ferromagnetic with TC = (160±5) °K and that CaRuO3 has antiferromagnetic exchange interactions dominant. They further identify in CaRuO3 a Ne´el temperature TN = (110±10) °K and parasitic ferromagnetism below TN having a ?0 = (3.2±0.4) × 10?2 emu?g at 4.2°K. High-field (to 125 kOe) magnetization and neutron-diffraction data for

  20. Superconductivity in Pr- and Ce-doped Bi2CaSr2Cu2Oy systems

    NASA Astrophysics Data System (ADS)

    Awana, V. P. S.; Agarwal, S. K.; Narlikar, A. V.; Das, M. P.

    1993-07-01

    We report here a systematic study of Pr and Ce doping (at the Ca site) in Bi2CaSr2Cu2Oy. For both Pr and Ce substitutions Tc decreases with the dopant concentration. Results are interpreted in terms of the hole filling due to aliovalent substitution in the system. At a higher doping level a metal-insulator transition, is observed. Near the transition the localization length (?-1) is calculated and the possibility of having local pairs in the insulating phase is invoked. Around the transition region a dimensional changeover from two to three dimensions is observed in the variable-range hopping (VRH) regime and its consequence on superconductivity is discussed. The lattice parameters have been estimated through x-ray diffractometry and the possibility of Pr and Ce existing in more than the 3+ oxidation state in the system is inferred. Results are also compared with the existing data on other rare-earth dopings (at the Ca site) in the same system.

  1. Ca2+ and Sr2+ activation properties of skinned muscle fibres with different regulatory systems from crustacea and rat.

    PubMed Central

    West, J M; Stephenson, D G

    1993-01-01

    1. The contractile activation properties of long- (sarcomere length (SL) > 6 microns) and short- (SL < 4 microns) sarcomere fibres from the claw muscle of the yabby (freshwater crustacean, Cherax destructor) and the fast- and slow-twitch fibres from the rat have been investigated using single skinned muscle fibres activated in solutions containing Ca2+ or Sr2+ or both Ca2+ and Sr2+. 2. Sr2+ could not fully activate the contractile apparatus of either the long- or the short-sarcomere yabby preparations and the force-pSr curves for both fibre types were biphasic in shape. 3. The long- and short-sarcomere fibres from the yabby differed in their Ca(2+)- and Sr(2+)-activation properties. Thus the long-sarcomere fibres required a significantly lower [Ca2+] to produce 10% maximum force, had Ca(2+)-activation curves which were significantly shallower, and had a significantly higher ratio between maximum Sr(2+)- and maximum Ca(2+)-activated force than the short-sarcomere fibres. 4. Simultaneous activation with Ca2+ and Sr2+ showed a synergistic effect in the rat muscle fibres where Sr2+ could fully replace Ca2+ in activation. In contrast the results with the long- and short-sarcomere fibres from the yabby showed that in some functional states Sr2+ binds but cannot (or can only partially) activate the regulatory system while in others Sr2+ can fully replace Ca2+ in activating contraction. 5. The synergistic effect between Sr2+ and Ca2+ in mammalian muscle could be quantitatively explained if all regulatory sites involved in contractile activation have a similar value for the ratio between their affinity for Ca2+ and Sr2+. 6. Three distinguishable functional states (based on the fibre's ability to be activated by Sr2+ and Ca2+) were identified in the long-sarcomere fibres from the yabby: one where both Ca2+ and Sr2+ were able to activate contraction and had a relatively high sensitivity to Sr2+; one where both Ca2+ and Sr2+ were able to activate contraction but where the sensitivity to Sr2+ was lower and was more sensitive to a decrease in ionic strength; and one where Sr2+ binding to the regulatory system could not activate contraction. Equivalent states of the three described for the long-sarcomere fibres were also found in the short-sarcomere preparations. However, the short-sarcomere fibres had, in addition, a fourth state which was characterized by the ability of Sr2+ to activate contraction at reduced ionic strength but not at standard ionic strength.(ABSTRACT TRUNCATED AT 400 WORDS) PMID:8331593

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  4. Superconducting and magnetic phase boundaries in Bi2Sr2Ca1-xMxCu2O8, with M=Y, Gd, and Pr

    Microsoft Academic Search

    Y. Gao; P. Pernambuco-Wise; J. E. Crow; J. O'reilly; N. Spencer; H. Chen; R. E. Salomon

    1992-01-01

    The temperature dependences of the electrical resistivity, magnetic susceptibility, and specific heat have been measured in Bi2Sr2Ca1-xMxCu2O8, where M=Y, Gd, and Pr, for concentrations 0<=x<=1.0 and temperatures 1.6 K<=T<=300 K. All three dopants substitute a trivalent ion for divalent Ca and cause a depression of Tc observable in the resistivity and susceptibility. Both Pr and Gd retain their free-ion magnetic

  5. 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.

  6. Electron correlation in Sr(Ca)RuO3 by GWA and LSDA+U

    NASA Astrophysics Data System (ADS)

    Hadipour, H.; Akhavan, M.

    2011-11-01

    We have investigated the role of electron-electron correlation in SrRuO3 and CaRuO3 bulk structures. At first, the DOS of SrRuO3 and CaRuO3 is obtained using the full potential linearized augmented plane wave method by LSDA. We have then calculated the electronic structure, dielectric function, self-energy, and spectral function for the bulk SrRuO3 and CaRuO3 by GWA. The shifting of the Ru t 2 g orbitals, broadening in Ru valance bands, and also the enhancement in exchange splitting shows better agreement between the GWA many-body correction with the bulk experimental results. But, in spite of the many-body correction, the GWA results is not completely consistent with the PES experimental results due to small shifting of the Ru t 2 g bands and small broadening of the valance states specially in the Ca-based system. Inclusion of Coulomb correlation by LSDA+ U for both Sr- and Ca-based compounds shows significant difference in the results as compared with the LSDA and GWA calculations, and is consistent with the PES results. So, the discrepancy between the bulk ab-initio calculation and experiment is attributed to the surface effects which is not considered in the both LSDA and GWA bulk calculations. Due to the more distorted structure of CaRuO3, electron correlation at surface in the Ca-based system is more important than that in the Sr-based system. Hence, the bulk character of both SrRuO3 and CaRuO3 experimental results can be well described by GWA.

  7. Pulsed laser deposition and characterization of nitrogen-substituted SrTiO 3 thin films

    NASA Astrophysics Data System (ADS)

    Marozau, I.; Shkabko, A.; Dinescu, G.; Döbeli, M.; Lippert, T.; Logvinovich, D.; Mallepell, M.; Schneider, C. W.; Weidenkaff, A.; Wokaun, A.

    2009-03-01

    Nitrogen-substituted cubic perovskite-type SrTiO 3 thin films were deposited in a one-step process using pulsed reactive crossed beam laser ablation (PRCLA) and RF-plasma assisted pulsed laser deposition (RF-PLD). Both techniques yield preferentially oriented films on SrTiO 3(0 0 1), LaAlO 3(0 0 1) and MgO(0 0 1) substrates with the unit cell parameters within 0.390(5) < a < 0.394(9) nm. The nitrogen content is higher in films deposited by PRCLA (0.84-2.40 at.%) as compared to films deposited by RF-PLD with nitrogen plasma (0.10-0.66 at.%). PRCLA with an ammonia gas pulse leads to a higher nitrogen content compared to the films grown with a nitrogen gas pulse, while films deposited by RF-PLD with ammonia plasma reveal only minor nitrogen contents (<0.10 at.%). The amount of the incorporated nitrogen can be tuned by adjusting the deposition parameters. Films deposited by PRCLA have a lower roughness of 1-3 nm compared to 12-18 nm for the films grown by RF-PLD. PRCLA yields partially reduced films, which exhibit electronic conductivity, while films deposited by RF-PLD are insulating. There is also a pronounced influence of the substrate material on the resistivity of the films deposited by PRCLA: films grown on SrTiO 3 substrates exhibit a metallic-like behaviour, while the corresponding films grown on MgO and LaAlO 3 substrates reveal a metal-to-semiconductor/insulator transition. Nitrogen incorporation into the SrTiO 3 films results in an increased optical absorption at 370-500 nm which is associated with N(2p) localized states with the energy about 0.7 eV higher than the valence band energy in strontium titanate. The optical band gap energies in the studied N-substituted SrTiO 3 films are 3.35-3.40 eV.

  8. Evidence of downstream migration of Sakhalin taimen, Hucho perryi , as revealed by Sr?:?Ca ratios of otolith

    Microsoft Academic Search

    Takaomi Arai; Aya Kotake; Kentaro Morita

    2004-01-01

    The migratory history of Sakhalin taimen, Hucho perryi, was examined in terms of strontium (Sr) and calcium (Ca) uptake in the otolith by using wavelength dispersive X-ray spectrometry on an electron microprobe. Otolioth Sr?:?Ca ratios of freshwater-reared samples remained consistently at low levels throughout the otolith. The Sr?:?Ca ratios of samples from Lake Aynskoye of Sakhalin Island showed a low

  9. A Cenozoic seawater Sr\\/Ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes

    Microsoft Academic Search

    C. H. Lear; H. Elderfield; P. A. Wilson

    2003-01-01

    A Cenozoic multi-species record of benthic foraminiferal calcite Sr\\/Ca has been produced and is corrected for inter-specific offsets (typically less than 0.3 mmol\\/mol) and for the linear relationship between decreasing benthic foraminiferal Sr\\/Ca and increasing water depth. The water depth correction, determined from Holocene, Late Glacial Maximum and Eocene paleowater-depth transects, is ?0.1 mmol\\/mol\\/km. The corrected Cenozoic benthic foraminiferal Sr\\/Ca

  10. Altered photoemission satellites at CaF2-and SrF2-on-Si,,111... interfaces Eli Rotenberg*

    E-print Network

    Olmstead, Marjorie

    Altered photoemission satellites at CaF2- and SrF2-on-Si,,111... interfaces Eli Rotenberg diffraction, are compared for thick, thin, and monolayer films of CaF2 and SrF2 on Si 111 . Intrinsic. The most likely explanation for the new cation satellites at the CaF2/Si 111 SrF2/Si 111 interface

  11. 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

  12. Transport and structural properties of Bi-Sr-Ca-Cu-oxide thin films prepared by reactive magnetron sputtering

    Microsoft Academic Search

    D. W. Face; J. T. Kucera; J. Crain; M. M. Matthiesen; D. Steel; D. A. Rudman; T. P. Orlando; G. Somer

    1989-01-01

    Highly oriented superconducting thin films of Bi-Sr-Ca-Cu-oxides have been reproducibly prepared by reactive magnetically-enhanced triode sputtering using three separate metal targets (Sr, Ca, and Cu-Bi). The as-deposited films had composition ratios of Bi:Sr:Ca:Cu that were very close to either 2:2:1:2 or 2:2:2:3. The films were deposited on SrTiO3, MgO, CaF2, Al2O3, and yttria stabilized zirconia (YSZ) substrates and had thicknesses

  13. 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.

  14. Infrared Hall effect in SrRuO3 and CaRuO3

    Microsoft Academic Search

    M.-H. Yang; G. Acbas; A. Markelz; J. Cerne; I. Ohkubo; P. Khalifah; H. Christen; D. Mandrus; Z. Fang

    2006-01-01

    The mid-infrared (MIR: 115-366 meV) Hall effect is studied in SrRuO3 and CaRuO3 films. In SrRuO3, below 200 meV the MIR Hall response changes sign as a function of temperature near 120 K, similar to the dc Hall effect. Above 200 meV, no sign change occurs and the temperature dependence of the MIR Hall response is similar to the dc

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

  16. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  18. The effect of Pb-doping in Bi-Sr-Ca-Cu-O and Sb-doping in Bi-Pb-Sr-Ca-Cu- superconductors

    Microsoft Academic Search

    Z. J. Yang; H. Bratsberg; T. H. Johansen; N. Norman; J. Taftø; G. Helgesen; I. Lorentzen; A. T. Skjeltorp

    1989-01-01

    A series of samples with nominal starting compositions Bi1.4Pb0.6Sr2Ca3Cu4Oz and Bi2Pb 2Cu4Oz (0.1<=x<=0.4) were prepared using dry and wet methods. X-ray emission studies of SEM and TEM show that most of the Pb-doping is lost during sintering, but Pb apparently acts as a catalyst to form the high-Tc phase. Another series of samples with starting compositions Bi2(1-x)Pb2x(1-y)Sb2xySr2Ca3Cu4Oz (0.2<=x<=0.3 and 0.2<=y<=0.7)

  19. 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.

  20. Critical current in polycrystalline Bi-Ca-Sr-Cu-O films

    NASA Astrophysics Data System (ADS)

    Yang, H. C.; Jao, J. C.; Sung, H. H.; Horng, H. E.; Chen, H. C.

    1989-05-01

    Thin films of Bi-Ca-Sr-Cu-O were prepared by rf magnetron sputtering a sintered Bi2CaSr2Cu2O8-y target. The films were deposited on a MgO(100) substrate. The data reported here have a Tc (50%) of about 86 K and a transition width ?Tc=90-81 K (90%-10%). Temperature-dependent I-V characteristics examined over wide ranges reveal that the critical current is proportional to (1-T/Tc)3/2 near Tc. The implication of the (3/2 power dependence will be discussed.

  1. Spin-glass state induced by cobalt substitution in CaRuO3

    NASA Astrophysics Data System (ADS)

    Bréard, Y.; Hardy, V.; Raveau, B.; Maignan, A.; Lin, H.-J.; Jang, L.-Y.; Hsieh, H. H.; Chen, C. T.

    2007-05-01

    This paper reports on an experimental study of the effects induced by the substitution of Co for Ru in CaRuO3, a prototypical oxide close to a magnetic instability. The L2,3 x-ray absorption spectroscopy (XAS) spectra of Ru and Co in CaRu1-x CoxO3 reveal that Co is in a divalent state for low x values, while the Ru valence increases upon increasing the Co content. The dc and ac magnetic susceptibilities demonstrate that the CaRu1-xCoxO3 compounds can be classified as spin glasses. The origin of this behaviour and its implications are discussed. The effect of Co is also compared with the literature about substitutions by other cations in the magnetic sublattice of CaRuO3.

  2. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: The magnetic and dielectric properties of multiferroic Sr-substituted Zn2-Y hexagonal ferrites

    Microsoft Academic Search

    Fang Xu; Yang Bai; Fen Ai; Li-Jie Qiao

    2008-01-01

    The magnetic and dielectric properties of Sr-substituted Zn2-Y hexagonal ferrites (Ba2-xSrxZn2Fe12O22, 1.0 <= x <= 1.5) are studied in this paper. Sr substitution will lead to the variation of cation occupation, which influences both the magnetic and electric properties. As Sr content x rises from 1.0 to 1.5, magnetic hysteresis loop gets wider gradually and the permeability drops rapidly due

  3. Ferromagnetism induced by chromium substitution in the CaRuO3 perovskite

    Microsoft Academic Search

    A. Maignan; B. Raveau; V. Hardy; N. Barrier; R. Retoux

    2006-01-01

    Chromium has been substituted for ruthenium in CaRuO3 up to 35%. It is found that chromium induces a ferromagnetic contribution showing a maximum fraction for x=0.15 in CaRu0.85Cr0.15O3 with a Curie temperature (TC) of ˜115K . This change of magnetic ground state goes with an electronic localization, the resistivity at 5K increasing by more than 6 orders of magnitude as

  4. Spin-glass state induced by cobalt substitution in CaRuO3

    Microsoft Academic Search

    Y. Bréard; V. Hardy; B. Raveau; A. Maignan; H.-J. Lin; L.-Y. Jang; H. H. Hsieh; C. T. Chen

    2007-01-01

    This paper reports on an experimental study of the effects induced by the substitution of Co for Ru in CaRuO3, a prototypical oxide close to a magnetic instability. The L2,3 x-ray absorption spectroscopy (XAS) spectra of Ru and Co in CaRu1-x CoxO3 reveal that Co is in a divalent state for low x values, while the Ru valence increases upon

  5. Carrier concentration dependence and impurity effects of microwave response in Bi2Sr2CaCu2O8+ y

    NASA Astrophysics Data System (ADS)

    Katase, N.; Shibauchi, T.; Tamegai, T.; Tsukada, I.; Uchinokura, K.

    1996-02-01

    We report the surface impedance ( Z s ) measurements in high quality single crystals of Bi2Sr2CaCu2O8+ y . At relatively low oxygen content, the change of the penetration depth, ??( T) ??( T)-?(0), of the pure single crystals exhibits linear temperature dependence both parallel to the CuO2 planes and in the c direction. In contrast to this behavior, by further oxygenation or 0.6% Zn substitution, the T-linear dependence is disrupted and T 2 dependence of ?? is observed. We also found that 0.9% Ni-substitution induces no pairbreaking effect. The present results suggest that the low-lying excitation spectrum of quasiparticles depends on the carrier concentration and is easily changed by a small amount of Zn substitution.

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

    PubMed

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

    2007-09-01

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

  7. Magnetic and Transport Properties of Na Doped SrRuO3 and CaRuO3 Perovskites

    Microsoft Academic Search

    M. Shepard; G. Cao; S. McCall; F. Freibert; J. E. Crow

    1996-01-01

    The magnetic susceptibility and electrical resistivity of Na doped SrRuO3 and CaRuO3 single crystals have been measured. These two perovskites are orthorhombic with space group Pbnm. While both of them exhibit metallic conductivity, SrRuO3 is a ferromagnet with T_c=160 K whereas CaRuO3 is possibly a paramagnet. When slightly doped with Na (<12 % ), SrRuO3 drastically becomes an insulator with

  8. K-Ca and Rb-Sr dating of two lunar granites: Relative chronometer resetting

    NASA Astrophysics Data System (ADS)

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

    1994-07-01

    K-Ca and Rb-Sr age determinations were made for lunar granite 12033,576. This small fragment is a subsample of soil particle 12033,507, which was collected subsurface at the north rim of Head Crater. The K-Ca mineral isochron is well-defined and yields an age of 3.62 ± 0.11 (2?) Ga for ?( 40K) = 0.5543 Ga-1 and an initial 40Ca /44Ca of 47.160 ? 0.006 (2?) (normalized to 42Ca /44Ca = 0.31221 ). The Rb-Sr mineral isochron is quite disturbed and yields an imprecise young age of 2.20 ± 0.65 Ga for ?( 87Rb) = 0.0139 Ga -1 and a high initial 87Sr /86Sr of 0.775 ? 0.022. Assuming that the granite crystallized ~ 4.0 Ga ago (a modeled formation age), and was shock-heated 0.8 Ga ago ( 39Ar- 40Ar age), the intermediate Rb-Sr and K-Ca ages are interpreted as due to partial resetting by thermal diffusion of strontium and calcium. Diffusion data determined for argon in 12033,507 give a value of D/a 2 ~1 × 10 -6 s -1 for a heating temperature of 700°C; at this temperature it would require a time on the order of days to totally degas argon. The required diffusion coefficients, D, for calcium (7 ~ 9 × 10 -13cm2s-1) and Sr (~8 × 10 -12cm2s-1) that are predicted from the observed age resetting are in good agreement with those determined experimentally in granitic melts. The K-Ca system was about a factor of ten more resistant to resetting than the Rb-Sr system, which in turn was ~ 10 times more resistant to resetting than the K-Ar system. Diffusion data indicate that isotopic exchange of calcium and strontium was responsible for the partial resetting of the K-Ca and Rb-Sr chronometers, rather than elemental exchange of potassium and rubidium among mineral phases. Rb-Sr isotopic data also were obtained for granite 14303,206, a subsample of breccia clast 14303,204, which was collected at the Fra Mauro region about 180 km from the Apollo 12 site. The mineral isochron is quite disturbed and yields an imprecise age of 3.95 ± 0.38 Ga for ?( 87Rb) = 0.0139 Ga -1 and initial 87Sr /86Sr = 0.7046 ? 0.0051 . The Rb-Sr age is comparable to the previously determined K-Ca age of 4.04 ± 0.64 Ga. The Rb-Sr and K-Ca ages of this clast are imprecise and are statistically indistinguishable from the well-defined 39Ar- 40Ar degassing age of 3.83 ± 0.03 Ga or the Rb-Sr and K-Ca model ages of 4.30 ± 0.06 Ga and 4.25 ± 0.12 Ga, respectively. Because these model ages are within error of a reported zircon U-Pb age of 4.31 Ga, we assume this granitic clast crystallized ~ 4.3 Ga ago and was shock-heated ~ 3.83 Ga ago. Using the apparent resetting of the K-Ar, Rb-Sr, and K-Ca isotopic systems, and literature data for relative strontium and calcium diffusivity, we estimate a shock-reheating temperature of ~ 860°C would be necessary to partially reset the Rb-Sr and K-Ca ages to their nominal values. This reheating temperature is uncertain because of the large errors on the ages, but would be consistent with complete resetting of the K-Ar age and partial resetting of the Rb-Sr and K-Ca ages, if the hot clast was buried under ~1 m of the ejecta blanket for ~1 day.

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

    PubMed

    Saparov, Bayrammurad; Sefat, Athena S

    2014-10-28

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

  10. Magnetic structures of the anisotropic Dirac metals AMnBi2 (A = Ca, Sr)

    NASA Astrophysics Data System (ADS)

    Guo, Yanfeng; Princep, Andrew; Manuel, Pascal; Khalyavin, Dimitry; Boothroyd, Andrew; ISIS Facility Collaboration; X-ray neutron scattering group Team

    2014-03-01

    Magnetism is potentially important in the Dirac materials AMnBi2 (A = Sr and Ca) because long-range magnetic order of the Mn spins provides an additional periodic potential that could influence the Fermi surface and hence the behavior of the Dirac fermions. We report powder and single crystal neutron diffacraction measurements of the magnetic order in AMnBi2 (A = Sr and Ca), two layered manganese pnictides with anisotropic Dirac fermions on a Bi square net. Both compounds are found to order in k = 0 antiferromagnetic structures, with ordered Mn moments at T = 10 K of approximately 3.8 ?B aligned along the c axis. The magnetic structures are Néel-type within the Mn-Bi layers, consistent with density functional theory predictions, but the interlayer ordering is different in the two materials, being antiferromagnetic in SrMnBi2 and ferromagnetic in CaMnBi2. This allows a mean-field coupling of the magnetic order to the Dirac fermions in CaMnBi2, but not in SrMnBi2.

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

    E-print Network

    Schrag, Daniel

    ) are primary producers and play key roles in the global carbonate and carbon cycles [West- broeck et al., 1993. Keywords: Geochemistry; carbonate; Sr/Ca; coccoliths; carbon cycle; strontium. Received September 16, 1999 to carbonate carbon, an important control on deep ocean pH and partitioning of CO2 between the atmosphere

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

    PubMed

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

    2015-01-01

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

  13. Thermoelectric Effects in Bi-Pb-Sr-Ca-Cu-O Superconductor

    NASA Astrophysics Data System (ADS)

    Naqvi, S. M. M. R.; Dabir, S.; Rizvi, H.; Fatima, Shabih; Raza, S. Mohsin

    We have prepared the bulk samples of 2223 Bi-Pb-Sr-Ca-Cu-O superconductor with a Tc of 106 K. Temperature dependence of electrical resistivity and thermoelectric power (TEP) measurements were performed on the samples. The behaviour of thermoelectric power near and above the transition temperature can be described on the basis of thermodynamic fluctuations of superconducting order parameter.

  14. Inter- and intragranular properties of Bi 2CaSr 2Cu 2O 2 superconductors

    NASA Astrophysics Data System (ADS)

    Emmen, J. H. P. M.; Brabers, V. A. M.; Steen, C. v. d.; Dalderop, J. H. J.; Lenczowski, S. K. J.; de Jonge, W. J. M.

    1989-12-01

    The granular behaviour of sintered bulk Bi 2CaSr 2Cu 2O y superconductor is investigated by resistivity and ? ac measurements. The observed temperature and magnetic field dependence is discussed within the framework of a granular model. The frequency dependence of the intragranular losses leads to a flux flow or flux creep picture.

  15. Ca 2+ and Sr 2+ activation: Comparison of cardiac and skeletal muscle contraction models

    Microsoft Academic Search

    W. G. L. Kerrick; D. A. Malencik; P. E. Hoar; J. D. Potter; R. L. Coby; S. Pocinwong; E. H. Fischer

    1980-01-01

    The mechanism of contraction in rabbit fast-twitch, and bovine and rabbit cardiac muscle was examined using functionally skinned fibers, ATPase activity of myofibrils, and cardiac or skeletal troponintropomyosin regulated actin heavy meromyosin. The Ca2+ and Sr2+ activation properties for the different measures of contraction were evaluated. (1) Tension in rabbit and bovine cardiac skinned fibers and rabbit cardiac myofibrillar ATPase

  16. 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

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2006-10-01

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

  19. Sr/Ca Sensitivity to Aragonite Saturation in Cultured Coral Measured by NanoSIMS (Invited)

    NASA Astrophysics Data System (ADS)

    Gagnon, A. C.; Adkins, J. F.; Erez, J.

    2010-12-01

    NanoSIMS was used to identify and com¬positionally characterize the micron scale region of skeletal growth resulting from a short coral culture experiment. Using this technique we quantify the sensitivity of Sr/Ca, a proxy for temperature, to aragonite saturation (?), 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 sp. were all grown at 25 °C but at different and near constant carbonate ion concentrations, from 180 to 400 µM (pH of 7.9 to 8.5), yielding a two-fold range in calcification rate. Despite the range of ?s and calcification rates, the average Sr/Ca of nanoSIMS spot measurements corresponding to each condition are within 1.2% (2? std. dev. of the 5 means). Furthermore, the average Sr/Ca measured in this study agrees with two previous coral culture experiments conducted at the same temperature but where ? was not controlled. These results suggest carbonate ion concentration is not a complicating factor to Sr/Ca paleothermometry over this range of ?. Within the framework of a closed system (Rayleigh) model for biomineralization, similar Sr/Ca ratios suggest similar amounts of Rayleigh fractionation. Combined with existing data for low ? conditions, the extent of Rayleigh fractionation is used to test alternative biomineralization models governing the acid-base chemistry of the calcifying fluid. Assuming that coral use alkalinity pumping to increase local calcifying fluid carbonate ion concentration, we try to understand what controls this pumping. Under most conditions, Sr/Ca ratios are consistent with a scenario where calcifying fluid alkalinity increases until reaching a target pH. However, under conditions of very low seawater ?, coral cannot pump enough alkalinity to reach the target pH. Below this threshold value, between approximately 1Sr/Ca sensitivity to ?. This model should improve our understanding of how anthropogenic CO2 will impact coral reefs and can help us better interpret past climate records in coral.

  20. Sintering and characterization of Ca 0.9Sr 0.1TiO 3 ceramics with sintering additive

    Microsoft Academic Search

    R Li; Q Tang; S Yin; H Yamane; T Sato

    2004-01-01

    Ca0.9Sr0.1TiO3 was sintered using Li2Si2O5 as a sintering additive for the first time. Although Ca0.9Sr0.1TiO3 could not be fully sintered even at 1400°C, the densification temperature could be decreased to 1200°C by using Li2Si2O5, which possesses low melting temperature of ca. 1030°C. Consequently, the mechanical and dielectric properties of Ca0.9Sr0.1TiO3 ceramics were improved. The microstructure, mechanical properties, and dielectric properties

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

    PubMed

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

    2012-09-24

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

  2. Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA

    SciTech Connect

    Ingram, B.L.; De Deckker, P.; Chivas, A.R.; Conrad, M.E.; Byrne, A.R.

    2004-10-19

    Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma Marsh over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10-35 {per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5 {per_thousand} between 500 yr BR and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3-4 {per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100-300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600-700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approx} -12{per_thousand}) to CAM ({delta}{sup 13}C = -26 {per_thousand})-type vegetation over time.

  3. Effect of Zn and Ni impurities on the quasiparticle renormalization in Bi2Sr2CaCu2O8+�´

    NASA Astrophysics Data System (ADS)

    Zabolotnyy, V. B.; Borisenko, S. V.; Kordyuk, A. A.; Fink, J.; Geck, J.; Koitzsch, A.; Knupfer, M.; Büchner, B.; Berger, H.; Erb, A.; Lin, C. T.; Keimer, B.; Follath, R.

    2007-09-01

    The Cu substitution by Zn and Ni impurities and its influence on the mass renormalization effects in angle resolved photoelectron spectra (ARPES) of Bi 2Sr 2CaCu 2O 8+ ? is addressed. We show that the nonmagnetic Zn atoms have much stronger effect both in nodal and antinodal parts of the Brillouin zone than magnetic Ni. The observed changes are consistent with the behaviour of the spin resonance mode as seen by inelastic neutron scattering in YBCO-123. This strongly suggests that the “peak-dip-hump” and the “kink” in ARPES on the one side and neutron resonance on the other are closely related features.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

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

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

    PubMed

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

    2013-04-21

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

  7. BN-coated Ca(1-x)Sr(x)S:Eu solid-solution nanowires with tunable red light emission.

    PubMed

    Lin, Jing; Huang, Yang; Mi, Jiao; Zhang, Xinghua; Lu, Zunming; Xu, Xuewen; Fan, Ying; Zou, Jin; Tang, Chengchun

    2013-10-11

    We report on the controlled growth of novel BN-coated Ca(1-x)Sr(x)S:Eu nanowires via a solid-liquid-solid process. The Ca(1-x)Sr(x)S solid solution forms as one-dimensional nanowires and has been coated with homogeneous protective BN nanolayers. The structure and luminescence properties of this new nanocomposite have been systematically investigated. High-spatial-resolution cathodoluminescence investigations reveal that effective red color tuning has been achieved by tailoring the composition of the Ca(1-x)Sr(x)S nanowires. Moreover, codoping of Ce(3+) and Eu(2+) in the CaS nanowire can induce energy transfer in the matrix and make it possible to obtain enhanced orange color in the nanowires. The BN-coated Ca(1-x)Sr(x)S:Eu solid-solution nanowires are envisaged to be valuable red-emitting nanophosphors and useful in advanced nanodevices and white LEDs. PMID:24029011

  8. Involvement of CaSR in hyperglycemia-induced macroangiopathy and related mechanism.

    PubMed

    Lu, Jin-ping; Ren, Jiang-hua; Chen, Ling; Li, Xia; Chen, Hui-li

    2015-02-01

    In order to clarify the potential role of calcium sensing receptor (CaSR), a typical G protein coupled receptor (GPCR), in hyperglacemia-induced macroangiopathy, experimental hyperglycemia models in vivo and in vitro were prepared. Firstly, SD rats were divided into control group (n=10) and diabetes group (n=10), and diabetic model was induced via high-fat diet feeding and streptozotocin (STZ, 30 mg/kg) injection. Hydroxyproline level, determined via Choramnie T oxidation method, in vessel wall in diabetic rats was 30% more than that in control group. The gene transcription and expression levels were detected by real-time PCR and Western blotting, respectively. Both of collagen I and III mRNA levels in diabetic aorta were nearly twice those in normal aorta. The cleaved caspase-3 and -9 were elevated 1.5 and 2.5 times respectively in diabetic vascular cells. As compared with controls, mRNA and protein levels of CaSR in aorta were increased by 3 and 1.5 times in diabetes group. The expression levels of Bax as well as pro-apoptotic kinases (phospho-p38 and phosphor-JNK) were also increased 2, 0.5 and 0.5 times respectively in diabetic rats. To further validate the involvement of CaSR in cell apoptosis and explore the potential mechanism, the endothelial cell line (human umbilical vascular endothelial cells, HUVECs) was stimulated with high concentration of glucose (33 mmol/L) to mimic hyperglycemia in vitro. Cell-based assays also showed that the CaSR level and key apoptotic proteins (cleaved caspase-3 and -9, Bax, phospho-p38 and phosphor-JNK) were elevated in response to stimulation, and inhibition of CaSR by using specific inhibitor (NPS-2143, 10 ?mol/L) could protect cells against apoptosis. Our results demonstrated that CaSR might take important part in the development of diabetic macroangiopathy through promoting cell apoptosis induced by hyperglycemia. PMID:25673191

  9. Substitutional and positional disorder in Sr(2.88)Cu(3.12)(PO4)4.

    PubMed

    Karanovi?, Ljiljana; Sutovi?, Sabina; Poleti, Dejan; Dordevi?, Tamara; Pacevski, Aleksandar

    2010-04-01

    The title compound, a hydrothermally synthesized strontium copper(II) phosphate(V) (2.88/3.12/4), is isotypic with Sr(3)Cu(3)(PO(4))(4), obtained previously by solid-state reaction, but not with Sr(3)Cu(3)(PO(4))(4), obtained previously by the hydrothermal method. A surplus of copper was observed by both structural and chemical analysis, and the formula obtained by the structural analysis is in full agreement with results of the EDX (energy-dispersive X-ray diffraction) analysis. The structure consists of layers of Cu(3)O(12) groups which are linked via the PO(4) tetrahedra. The Cu(3)O(12) groups are formed by one Cu1O(4) and two Cu2O(5) coordination polyhedra sharing corners. The central Cu1 atom of the Cu(3)O(12) group is located at an inversion centre (special position 2a). The unique structural feature of the title compound is the presence of 12% Cu in the Sr1 site (special position 2b, site symmetry 1). Moreover, disordered Sr2 atoms were observed: a main site (Sr2a, 90%) and a less occupied site (Sr2b, 10%) are displaced by 0.48 (3) A along the b axis. Such substitutional and positional disorder was not observed previously in similar compounds. PMID:20354287

  10. 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. [State Key Laboratory of Luminescent Materials and Devices, and Institute of Optical Communication Materials, South China University of Technology, Guangzhou 510641 (China); Ye, S., E-mail: msyes@scut.edu.cn [State Key Laboratory of Luminescent Materials and Devices, and Institute of Optical Communication Materials, South China University of Technology, Guangzhou 510641 (China); Hu, G.P. [School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Zhang, Q.Y., E-mail: qyzhang@scut.edu.cn [State Key Laboratory of Luminescent Materials and Devices, and Institute of Optical Communication Materials, South China University of Technology, Guangzhou 510641 (China)

    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.

  11. The properties of V-substituted La 1.85Sr 0.15CuO 4+ ? superconductor

    NASA Astrophysics Data System (ADS)

    Liu, Lihua; Che, Guangcan; Liu, Guodong; Dong, Cheng; Chen, Hong; Jia, Shunlian; Ni, Yongming; Zhao, Zhongxian

    2003-01-01

    The effect of replacement Cu by V in La 2- xSr xCuO 4+ ? system has been studied in this paper. XRD analysis shows that La 1.85Sr 0.15Cu 1- xV xO 4+ ? keeps tetragonal structure with the concentration of V increasing from 0.0 to 0.15. Resistance and Meissner measurement show that the substitution of V will destroy the superconductivity in this system. The well-defined “ Tc-onset” systematically shifts to lower temperature with increasing V concentration and disappears at x=0.15. It is much higher than that of the La 1.85Sr 0.15Cu 1- xM xO 4+ ? (M=Fe, Co, Ni, Zn, Mg, Al and Ga) systems, in which Tc’s disappear when x are small ( x=0.04 at most). A possible explanation for this phenomenon is presented.

  12. (Sr ,Na ) (Zn,Mn ) 2As2 : A diluted ferromagnetic semiconductor with the hexagonal CaAl2Si2 type structure

    NASA Astrophysics Data System (ADS)

    Chen, B. J.; Zhao, K.; Deng, Z.; Han, W.; Zhu, J. L.; Wang, X. C.; Liu, Q. Q.; Frandsen, B.; Liu, L.; Cheung, S.; Ning, F. L.; Munsie, T. J. S.; Medina, T.; Luke, G. M.; Carl, J. P.; Munevar, J.; Uemura, Y. J.; Jin, C. Q.

    2014-10-01

    A new diluted ferromagnetic semiconductor (Sr ,Na ) (Zn,Mn ) 2As2 is reported, in which charge and spin doping are decoupled via Sr/Na and Zn/Mn substitutions, respectively, being distinguished from classic (Ga ,Mn )As , where charge and spin doping are simultaneously integrated. Different from the recently reported ferromagnetic (Ba ,K ) (Zn,Mn ) 2As2 , this material crystallizes into the hexagonal CaAl2Si2 type structure. Ferromagnetism with a Curie temperature up to 20 K has been observed from magnetization. The muon spin relaxation measurements suggest that the exchange interaction between Mn moments of this new system could be different from the earlier diluted magnetic semiconductors (DMS) systems. This system provides an important means for studying ferromagnetism in DMS.

  13. X-ray photoelectron spectroscopy analysis of Bi sub 2 Sr sub 2 Ca sub 1 minus x Y sub x Cu sub 2 O sub y

    SciTech Connect

    Shichi, Y.; Inoue, Y.; Munakata, F.; Yamanaka, M. (Central Engineering Laboratories, Nissan Motor Company, Limited, 1, Natsushima-cho, Yokosuka, Kanagawa 237 (Japan))

    1990-07-01

    Experiments on x-ray photoelectron spectroscopy of Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}{ital x}}Y{sub {ital x}}Cu{sub 2}O{sub {ital y}} were performed to investigate the change of valence of each atom and the distribution of Y atoms on the cation sites. The core-level binding energies of Sr and Y increased with increasing Y content and that of Bi did not change. The average valence of Cu was above 2 for 0.0{le}{ital x}{le}0.5 and below 2 for 0.8{le}{ital x}{le}1.0. Y atoms were substituted for the cations between the adjacent Cu-O planes.

  14. Effect of Ge 4+ and Mg 2+ doping on superconductivity, fluctuation induced conductivity and interplanar coupling of TlSr 2CaCu 2O 7-? superconductors

    NASA Astrophysics Data System (ADS)

    Ali Yusuf, A.; Yahya, A. K.; Khan, Nawazish A.; Salleh, F. Md.; Marsom, E.; Huda, N.

    2011-06-01

    Substitution of Ge 4+ in place of Cu in Tl 0.85Cr 0.15Sr 2CaCu 2-xGe xO 7-? ( x = 0-0.6) showed initial increase in zero critical temperature value, T czero from 98 K ( x = 0) to 100 K ( x = 0.1) and in the range of 85-86 K for x = 0.2-0.3. The slow decrease in T czero is unexpected as tetravalent Ge 4+ substitution is expected to strongly reduce hole concentration in the samples and suppress T czero. Excess conductivity analyses of resistance versus temperature data based on Asmalazov-Larkin (AL) theory revealed that the substitution induced 2D-to-3D transition of fluctuation induced conductivity with the highest transition temperature, T 2D-3D observed at x = 0.1. FTIR spectroscopy analysis indicates Ge 4+ substitution cause reduction in CuO 2/GeO 2 interplanar distance while our calculation based on Lawrence-Doniach model revealed highest superconducting coherence length, ? c(0) and interplanar coupling, J at x = 0.3. On the other hand, substitution of divalent Mg 2+ for Ca 2+ in (Tl 0.5Pb 0.5)(Sr 1.8Yb 0.2)(Ca 1-yMg y)Cu 2O 7 ( y = 0-1.0), which is not expected to directly vary hole concentration, surprisingly caused T czero to increase from 89.6 K ( y = 0) to an optimum value of 95.9 K ( y = 0.6) before decreasing with further increase in y. Excess conductivity analyses showed 2D-to-3D transition of fluctuation induced conductivity for all samples where the highest T 2D-3D was at y = 0.4. Similar calculation revealed highest values of ? c(0) and J also at y = 0.4. FTIR analysis of the samples indicates inequivalent Cu(1) sbnd O(2) sbnd Pb/Tl lengths and possible tilting of CuO 2 plane as a result of Mg 2+ substitution. The increased ? c(0) and J as a result of the Ge 4+ and Mg 2+ substitutions are suggested to contributed to sustenance of superconductivity above 80 K in the samples.

  15. Small-scale recombination He - Sr{sup +}(Ca{sup +}) lasers

    SciTech Connect

    Latush, Evgeny L; Chebotarev, Gennady D; Sem, M F [Department of Physics, Chair of Quantum Radiophysics, Rostov State University, Rostov-on-Don (Russian Federation)

    2000-06-30

    A review of specific features and output characteristics of small-scale (l{<=}30 cm, d{<=}1.1cm) gas-discharge recombination He-Sr{sup +} ({lambda}=430.5 nm) and He- Ca{sup +} ({lambda}=373.7nm) lasers is provided. Such compact lasers are characterised by a relatively high reliability and durability. These lasers are easy to operate and are capable of generating laser pulses with high repetition rates f, a high specific mean power P{sub sp}, and an improved quality of output radiation. A typical mean power P of self-heating sealed-off He-Sr{sup +} (Ca{sup +}) laser tubes with l{approx} 30 cm and d{approx} 1 cm is {approx} 0.5 W. The best specific characteristics of a He-Sr{sup +} laser with tubes of this type were achieved with l=20 cm and d=0.6 cm (P{sub sp}=73 mW cm{sup -3}) and l=9 cm and d=0.55 cm (P{sub sp}=65 W cm{sup -3}). The best specific characteristics for a He-Ca{sup +} laser were achieved with l=26.5 cm and d=0.7 cm (P{sub sp}=50 mW cm{sup -3}). The use of forced water cooling in a He-Sr{sup +}(Ca{sup +}) laser allowed the powers P=3.9 W and P{sub sp}=137 mW cm{sup -3} to be achieved with a tube with l=30 cm and d=1.1 cm for f=29 kHz. A new method of inputting metal vapours based on cataphoresis is considered in detail. Using this method allowed the output characteristics of a He-Sr{sup +} laser to be considerably improved and a record specific power P{sub sp}=277 mW cm{sup -3} to be achieved for a tube with l=26 cm and d=0.3 cm with f=30 kHz and P=510 mW. A record gain, 0.15 cm{sup -1}, was also achieved under these conditions. Some possible areas of applications of small-scale He-Sr{sup +}(Ca{sup +}) lasers in semiconductor microtechnology, holography, ecology, and medicine are outlined. (invited paper)

  16. Critical current in polycrystalline Bi-Ca-Sr-Cu-O films

    SciTech Connect

    Yang, H.C.; Jao, J.C.; Sung, H.H.; Horng, H.E.; Chen, H.C.

    1989-05-01

    Thin films of Bi-Ca-Sr-Cu-O were prepared by rf magnetron sputtering a sintered Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8-//sub y/ target. The films were deposited on a MgO(100) substrate. The data reported here have a T/sub c/ (50%) of about 86 K and a transition width ..delta..T/sub c/ = 90--81 K (90%--10%). Temperature-dependent I-V characteristics examined over wide ranges reveal that the critical current is proportional to (1-T/T/sub c/)/sup 3/2/ near T/sub c/. The implication of the 3/2 power dependence will be discussed.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1992-01-01

    X-ray powder patterns for the phases in the CaO-SrO-CuO ternary system, along with the corresponding crystal structures, were obtained from the literature and from the Powder Diffraction File (PDF). Available X-ray diffraction (XRD) patterns were compared with each other and, when possible, with a simulated pattern for each phase, yielding a recommended reference pattern. The simulated powder patterns presented here deal with the phases found within the (Ca, Sr)O, (Ca,Sr)2CuO3, (Ca,Sr)14Cu24O41, (Ca,Sr)CuO2, (Ca,Sr)Cu2O3, and (Ca,Sr)Cu2O2 solid solution series and are recommended for the PDF.

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

    SciTech Connect

    Reardon, B.J. [Alfred Univ., NY (United States); Hubbard, C.R. [Oak Ridge National Lab., TN (United States)

    1992-01-01

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

  20. Computer modelling of divalent, trivalent and tetravalent ion doping in LiCaAlF6 and LiSrAlF6

    NASA Astrophysics Data System (ADS)

    Amaral, J. B.; Lewis, A. C.; Valerio, M. E. G.; Jackson, R. A.

    2004-12-01

    This paper describes a computational study of the mixed metal fluorides LiCaAlF6 and LiSrAlF6, doped with divalent (Pb2+, Co2+ and Ni2+), trivalent (Cr3+, Fe3+ and Y3+) and tetravalent (Si4+) ions. For each of the frameworks, all three cation sites were considered, as well as a range of charge compensation mechanisms. For the divalent dopants, substitution at the divalent host site is preferred, whilst for the trivalent dopants, Co3+ and Fe3+ prefer the Al3+ site, and Y3+ shows behaviour similar to the rare earths. Finally, it is found that Al3+ is the preferred site for substitution by Si4+ in both host frameworks.

  1. Systematic studies on Bi-Sr-Ca-Cu-O glasses and glass ceramics

    Microsoft Academic Search

    R. Singh; E. Zacharias

    1990-01-01

    Bi-Sr-Ca-Cu-O glasses and glass ceramics of various compositions have been synthesised. The glass transition temperature varies from 396 to 422 degrees C depending on the glass composition. DC electrical conductivity, measurements on these glasses show a sharp change in slope of the plot of logarithm of conductivity against reciprocal of temperature at a characteristic temperature that depends on the glass

  2. Phase separation in Bi-Sr-Ca-Cu-O melts during quenching

    Microsoft Academic Search

    S. J. Kim; D. P. Birnie; A. Aruchmay; D. R. Uhlmann; O. H. El-Bayoumi; M. J. Suscavage

    1992-01-01

    Phase separation is found for the first time in quenched samples of amorphous Bi2Sr2Ca1Cu2Ox (often called ``2212'' composition). Clear evidemce for metastable phase separation is found using X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential thermal analysis (DTA). This has serious implications for possible fabrication of high current density devices from these compositions, especially via glass-ceramic processing routes.

  3. Deviations from Matthiessen's Rule for SrRuO3 and CaRuO3

    Microsoft Academic Search

    L. Klein; Y. Kats; N. Wiser; M. Konczykowski; J. W. Reiner; T. H. Geballe; M. R. Beasley; A. Kapitulnik

    We have measured the change in the resistivity of thin films of SrRuO3 and CaRuO3 upon introducing point defects by electron irradiation at low temper- atures, and we find significant deviations from Matthiessen's rule. For a fixed irradiation dose, the induced change in resistivity decreases with increasing temperature. Moreover, for a fixed temperature, the increase in resistivity with irradiation is

  4. Optimal scaling of He - Sr{sup +}(Ca{sup +}) recombination lasers

    SciTech Connect

    Chebotarev, Gennady D; Latush, Evgeny L [Department of Physics, Chair of Quantum Radiophysics, Rostov State University, Rostov-on-Don (Russian Federation)

    2000-05-31

    A method for scaling optimal parameters of the discharge-heated He - Sr{sup +}(Ca{sup +}) recombination lasers is suggested. The method can be used for calculating the optimal excitation parameters and output characteristics of laser tubes of arbitrary dimensions from the known parameters of the optimised laser tube. The experimental verification of the scaling relations showed reasonable agreement between calculations and the experimental data, which is acceptable for practical applications. (lasers)

  5. Photoluminescence in the CaSr{sub 1-x}WO system at room temperature

    Microsoft Academic Search

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

    2008-01-01

    In this work, a study was undertaken about the structural and photoluminescent properties, at room temperature, of powder samples from the CaSr{sub 1-x}WO (x=0-1.0) system, synthesized by a soft chemical method and heat treated between 400 and 700 deg. C. The material was characterized using Infrared, UV-vis and Raman spectroscopy and XRD. The most intense PL emission was obtained for

  6. Lattice vibrations in Bi 2CaSr 2Cu 2O 2

    NASA Astrophysics Data System (ADS)

    Ramakrishnan, Chellam; Rajaram, R. K.; Krishnamurthy, N.

    1989-11-01

    The lattice dynamics of Bi 2CaSr 2Cu 2O 8 is worked out employing the conventional central force model. The nearest neighbour interactions within a radius of 4 Å are taken into account. The force constants for these interactions are calculated from the already available crystal data and from the vibrational frequencies of diatomic molecules. The calculated values of zone centre phonon frequencies compare reasonably with the available Raman scattering data.

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

    Microsoft Academic Search

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

    1996-01-01

    Taking advantage of the availability of a continuous sea surface temperature (SST) record at Kenting, southern Taiwan, we have carried out a calibration of D[Sr\\/Ca]-SST (D: distribution coefficient) relationships for Porites lobata and P. lutea. Between 22°C ? 28°C, the best fitting linear relationships for the two species agree within their respective errors with a maximum deviation less than 0.3°C.

  8. Hydrothermal preparation and luminescence property of MWO 4:Sm 3+ (M = Ca, Sr, Ba) red phosphors

    Microsoft Academic Search

    Jinsheng Liao; Liangbin Liu; Hangying You; Haiping Huang; Weixiong You

    MWO4:Sm3+ (M=Ca, Sr and Ba) red phosphors with spherical microparticles were successfully prepared via a mild and facile hydrothermal route. The crystal structure and particle morphology were investigated by the X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Photoluminescence excitation and emission spectra and decay curve were used to characterize the luminescence properties of the MWO4:Sm3+ phosphors. The excitation

  9. Rheology and Microstructure of (Ca,Sr)TiO3 Perovskite Deformed in Compression and Torsion

    NASA Astrophysics Data System (ADS)

    Mecklenburgh, J.; Heidelbach, F.; Mackwell, S.; Seifert, F.

    2002-12-01

    (Mg,Fe)SiO3 perovskite is considered to be the most abundant phase in the Earth's lower mantle, along with magnesiowüstite and other minor high pressure phases. Therefore knowledge of the rheological properties of (Mg,Fe)SiO3 is crucial to the understanding of the rheology of the lower mantle. Presently, deformation experiments, yeilding reliable rheological data, cannot be performed within the stabiltiy field of (Mg,Fe)SiO3 perovskite. Fortunately, many elements can combine to form the perovskite structure and hence an analog for (Mg,Fe)SiO3 perovskite that is stable at experimentally tractable conditions can be found. (Ca,Sr)TiO3 is one such material, which is stable at atmospheric pressure, and undergoes two structural phase transitions between 100 and 1600 K depending on the Ca:Sr ratio. By studying the deformation behavior of (Ca,Sr)TiO3 some insight can be gained in to the rheological properties of (Mg,Fe)SiO3 perovskite. Polycrystalline samples of (Ca0.9,Sr0.1)TiO3 have been synthesized from high purity oxides yielding samples with <3% porosity and a grainsize of ca. 100 ?m. These samples have been used to study the rheological properties of the tetragonal and cubic phases. Data from compression experiments performed over a temperature range spanning the orthorhombic to cubic phase transition show a power-law rheology with a stress exponent of ~4 and an activation energy of ~600 kJmol-1. A crystallographic preferred orientation develops in the compression experiments that is consistent with [110] slip. (Ca0.9,Sr0.1)TiO3 samples deformed in the cubic stability field to high strain in torsion show a comparable strength to compression tests under the same conditions. In these high-strain torsion experiments there is no shape preferred orientation of the grains consistent with the shear strain. Despite this lack of a shape fabric a crystallographic preferred orientation develops that is consistent with [100] slip. Lattice rotations towards the rims of grains are observed to be about an axis perpendicular to the shear direction. It is thought that these samples are deforming by grain boundary sliding, probably accommodated by components of both diffusion and dislocation creep.

  10. 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

  11. 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.

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

    DOEpatents

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

    1992-12-22

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

  13. High Tc Superconductivity and Substructure of Bi-Sr-Ca-Cu-O System

    NASA Astrophysics Data System (ADS)

    Xing, Zhu; Sunqi, Feng; Guo, Lu; Chongde, Wei; Hang, Zhang; Zhaohui, Shen; Wenbin, Zhang; Hui, Gu; Jian, Zhang; Qingzhe, Wen; Kaixuan, Chen; Lixin, Xue; Daole, Yin; Zizhao, Gan; Jing, Zhu; Xiwei, Lin

    BixSr1Ca1CuyOz(x, y=1, 2 or 3) high Tc superconductors were synthesized by solid state reaction method. There are two superconducting phases in Bi-Sr-Ca-Cu-O system: 110 K phase and 80 K phase. The relative portion of the two phases and the state of superconducting connection are closely related to chemical compositions and the conditions of processing. X-ray powder diffraction shows that there exists a main phase with orthorhombic symmetry in the samples of different compositions and conditions of processing. According to X-ray diffraction data, the lattice constants of the main phase in the sample of nominal composition Bi1Sr1Ca1Cu2Oz have been determined as a?=5.44Å, b?=5.35Å and co=30.66Å. Electron diffraction shows complicated modulation structure along b- and c- axes. High resolution image along [001] zone axis indicates the modulation structure along b- axis.

  14. 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

  15. The use of strontium-to-calcium (Sr/Ca) ratios in otoliths is becoming a standard

    E-print Network

    Kurapov, Alexander

    , 1995; Tzeng et al. 1997; Volk et al., 2000; Zimmerman, 2000; Zimmerman and Reeves, 2000, 2002-to-calcium (Sr/Ca) ratios in otoliths of anadromous salmonids Christian E. Zimmerman Oregon State University

  16. Synthesis, structural analysis, mechanical, antibacterial and hemolytic activity of Mg²? and Cu²? co-substitutions in ?-Ca?(PO?)?.

    PubMed

    Singh, Ram Kishore; Kannan, S

    2014-12-01

    The present study reports the synthesis, structural, mechanical and in vitro characterization of a series of Mg(2+) and Cu(2+) co-substitutions in ?-Ca3(PO4)2. Aqueous precipitation technique ensured the formation of calcium deficient apatite with substituted ions in the as prepared conditions and their subsequent heat treatments at 1000°C resulted in the formation of crystalline ?-Ca3(PO4)2. The combined substitutions of lower sized Mg(2+) and Cu(2+) in the structural lattice of ?-Ca3(PO4)2 led to the significant contraction in a=b-axis and c-axis lattice parameters of ?-Ca3(PO4)2. The results from Rietveld refinement confirmed the occupancy of Mg(2+) and Cu(2+) at the Ca(5) site of ?-Ca3(PO4)2. The results from mechanical tests proved that Mg(2+) and Cu(2+) substitutions are not hindering the mechanical properties of ?-Ca3(PO4)2. The antibacterial and hemolytic results determined for the Mg(2+) and Cu(2+) co-substituted ?-Ca3(PO4)2 ensured their good activity against the investigated microbes and also confirmed their blood biocompatibility. PMID:25491861

  17. Invalidity Of A Localized Spin Mechanism For SrRuO3 and CaRuO3

    Microsoft Academic Search

    Srimanta Middey; Priya Mahadevan; D. D. Sarma

    2008-01-01

    We have calculated the electronic structure for CaRuO3 and SrRuO3 within first principles electronic structure calculations. We find that the experimentally observed ferromagnetic state is favoured in the case of SrRuO3, while our calculations also suggest that no state with long range magnetic order will be stabilised for CaRuO3. Mapping the total energies for different magnetic configurations to an extended

  18. LDA+DMFT study of Ru-based perovskite SrRuO3 and CaRuO3

    Microsoft Academic Search

    E. Jakobi; S. Kanungo; S. Sarkar; S. Schmitt; T. Saha-Dasgupta

    2011-01-01

    We carried out a LDA+DMFT study of perovskite ruthenates SrRuO3 and CaRuO3, compounds which have been discussed in great detail in recent literature. Our results reproduced the observed mass enhancements and magnetic properties, and were in reasonable agreement with the measured photoemission spectra. Our calculations produced rather different coherence temperatures for SrRuO3 and CaRuO3, providing a possible explanation for the

  19. 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.

  20. Superconductivity and crystal structure of high T/sub c/ Bi-Ca-Sr-Cu-O compounds

    SciTech Connect

    Pan, V.M.; Dovgopol, V.P.; Popov, A.G.; Spivakovskij, V.B.; Flis, V.S.; Zhalko-Titarenko, A.V.; Barjakhter, V.G.; Melinikov, V.S.; Pshencova, N.P.

    1989-03-01

    Superconducting properties, phase chemical composition and crystal structure of Bi-Ca-Sr-Cu-O system sintered samples were investigated. Two-step resistive superconducting transitions with 120 K T/sub c/ onset were observed. The dominant phase composition might be formulated as Bi/sub 2/CaSr/sub 2/Cu/sub 2 + x/O/sub y/ where x = 0.4 - 1.0 depends upon heat treatment procedure.

  1. Identification of calcium sensing receptor (CaSR) mRNA-expressing cells in normal and injured rat brain

    Microsoft Academic Search

    Giuseppa Mudò; Angela Trovato-Salinaro; Vincenza Barresi; Natale Belluardo; Daniele F. Condorelli

    2009-01-01

    Calcium sensing receptor (CaSR), isolated for the first time from bovine and human parathyroid, is a G-protein-coupled receptors that has been involved in diverse physiological functions. At present a complete in vivo work on the identification of CaSR mRNA-expressing cells in the adult brain lacks and this investigation was undertaken in order to acquire more information on cell type expressing

  2. Atomic-size effects on the growth of SrF sub 2 and (Ca,Sr)F sub 2 on Si(111)

    SciTech Connect

    Denlinger, J.D.; Olmstead, M.A.; Rotenberg, E. (Department of Physics, University of California, Berkeley, California 94720 (USA)); Patel, J.R.; Fontes, E. (AT T Bell Laboratories, Murray Hill, New Jersey 07974 (USA))

    1991-03-15

    Strain-induced lattice relaxation during overlayer growth is investigated by {ital in} {ital situ} monitoring of SrF{sub 2} and Ca{sub {ital x}}Sr{sub 1{minus}{ital x}}F{sub 2} growth on Si(111) with x-ray standing-wave fluorescence and low-energy electron diffracton. Submonolayer films show both intrinsic lateral disorder and variable interface stoichiometry with discommensuration parallel to the surface after completion of the first monolayer. In contrast, local commensuration is observed for Ca-rich alloy films. In the alloy, Sr and Ca occupy different sites in the first monolayer, but have similar average positions in subsequent layers.

  3. Synthesis of Bi-Pb-Ca-Sr-Cu-O superconductive material

    SciTech Connect

    Arendt, R.H.; Garbauskas, M.F.

    1991-10-15

    This patent describes a process for producing a solid superconductive material in powder form containing superconductive Bi{sub 2{minus}y}Pb{sub y}Ca{sub 2}Sr{sub 2}Cu{sub 3}P{sub 10{plus minus}Z} phase, in which y ranges from 0.1 to 0.5 and z ranges from zero to less than 1. It comprises: providing a particulate mixture of reactants consisting essentially of Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub 8{plus minus}y}, x being between zero and 0.5, Ca{sub 2}CuO{sub 3}, cupric oxide, and lead oxide, in proportions for forming the superconductive phase, the Ca{sub 2}CuO{sub 3} and cupric oxide in the mixture being present in approximately equal molar amounts; heating the mixture in an oxidizing atmosphere at a temperature ranging from about 820{degrees}C to about 860{degrees} C to form a reaction product comprising superconductive phase; cooling the reaction product in an oxidizing atmosphere; and comminuting the reaction product to produce powder.

  4. Double transition in calcium-123 (CaSr 2Cu 3O y) superconductor

    NASA Astrophysics Data System (ADS)

    Fei, Xin; Lu, D. F.; Sun, G. F.; Wong, K. W.; Chan, F. T.; Sheng, Z. Z.; Xin, Ying; Fung, P. C. W.; Lam, C. C.; Ching, W. Y.; Xu, Y.

    1990-12-01

    The Ca 2+ is successfully substituted for the 3+ rare earth element in the 123 ceramic structure. A double phase transition is observed in oxygen deficient samples. A superconducting transition onset occurs at 90 K, and all resistivity vanishes at 73 K. However, at a lower temperature of 50 K the sample exhibits a superconducting to insulating transition. The double transition in R-T is accompanied by a corresponding double magnetic transition in ?- T.

  5. Manipulating magnetic properties of SrRuO3 and CaRuO3 with epitaxial and uniaxial strains

    Microsoft Academic Search

    A. T. Zayak; X. Huang; J. B. Neaton; Karin M. Rabe

    2008-01-01

    Using density-functional theory within the local spin-density approximation, SrRuO3 and CaRuO3 are investigated under epitaxial and uniaxial strains. Strains of the order of 2% 3% are predicted to radically alter the magnetic properties of SrRuO3 and CaRuO3 ultrathin films, indicating a large magnetostructural coupling in these systems. In particular, SrRuO3 is shown to become nonmagnetic for sufficient tensile epitaxial and

  6. Broadband microwave study of SrRuO3 and CaRuO3 thin films

    NASA Astrophysics Data System (ADS)

    Geiger, Diana; Scheffler, Marc; Dressel, Martin; Schneider, Melanie; Gegenwart, Philipp

    2012-12-01

    We study the microwave properties of SrRuO3 and CaRuO3 thin films in the frequency range 45 MHz to 40 GHz, and at temperatures between 80 K and 300 K, using a broadband Corbino technique. The films are grown on SrTiO3 and MgO substrates, and we discuss how dielectric substrate resonances complicate the study of the film properties, in particular in the case of SrTiO3 with its large dielectric constant. For SrRuO3 on MgO substrate we find signatures of the ferromagnetic transition throughout our spectral range.

  7. Crystal structure comparison between conductive SrRuO 3 and CaRuO 3 thin films

    Microsoft Academic Search

    N. Higashi; T Watanabe; K Saito; I Yamaji; T Akai; H Funakubo

    2001-01-01

    About 70nm-thick SrRuO3 and CaRuO3 thin films were deposited by metalorganic chemical vapor deposition (MOCVD) on (001)SrTiO3 and (001)[(LaAlO3)0.3-(SrAl0.5Ta0.5O3)]0.7 (LSAT) substrates at 750°C. SrRuO3 and CaRuO3 thin films were epitaxially grown on both substrates. All films had very smooth surfaces. The detailed crystal structure was investigated by using high-resolution X-ray reciprocal space mapping. The in-plane lattice parameter of SrRuO3 thin

  8. Infrared Hall effect in SrRuO3 and CaRuO3

    NASA Astrophysics Data System (ADS)

    Yang, M.-H.; Acbas, G.; Markelz, A.; Cerne, J.; Ohkubo, I.; Khalifah, P.; Christen, H.; Mandrus, D.; Fang, Z.

    2006-03-01

    The mid-infrared (MIR: 115-366 meV) Hall effect is studied in SrRuO3 and CaRuO3 films. In SrRuO3, below 200 meV the MIR Hall response changes sign as a function of temperature near 120 K, similar to the dc Hall effect. Above 200 meV, no sign change occurs and the temperature dependence of the MIR Hall response is similar to the dc magnetization. On the other hand, in CaRuO3, the MIR Hall effect is nearly independent of frequency above 100 meV, has a similar temperature dependence as the dc magnetic susceptibility, and does not change sign, unlike the dc Hall effect. In SrRuO3, the complex Faraday and Kerr angles measured in the MIR at 10 K are in good qualitative and quantitative agreement with first-principles band calculations [Z. Fang et al., Science 2003].

  9. Phase transformation in Bi-Ca-Sr-Cu-O thin films

    NASA Astrophysics Data System (ADS)

    Lin, W. T.; Chu, H. C.; Fang, Y. K.; Chang, C. Y.; Wu, P. T.; Kung, J. H.

    1990-04-01

    Bi-Ca-Sr-Cu-O thin films were deposited on MgO and yttrium stabilized zirconia (YSZ) substrates using DC sputtering. The formation temperatures of Bi 2Sr 2CuO 6 (221) and Bi 2CaSr 2Cu 2O 8 (2122) phases are about 600 and 800°C respectively. The 2122 phase comes from the transformation of the 221 phase. The calcium content in thin films plays an important role in the formation of the 2122 phase. The transformation between the 2122 and 221 phases depending upon the annealing time and temperature range from 800 to 880°C is observed. The ratio of 2122/221 progressively decreases throughout the cyclic heat treatments. In this study the optimum annealing condition for obtaining the purer 2122 phase in thin films is first annealed at 870°C for 10 min, then annealed at 800°C for 10 min. A thin film with zero resistance temperature ( T0) of 85 K can be obtained under this condition.

  10. Next neighbors effect along the Ca–Sr–Ba-åkermanite join: Long-range vs. short-range structural features

    SciTech Connect

    Dondi, Michele [Institute of Science and Technology for Ceramics (ISTEC—CNR), via Granarolo 64, 48018 Faenza (Italy); Ardit, Matteo, E-mail: rdtmtt@unife.it [Department of Physics and Earth Sciences, University of Ferrara, via Saragat 1, 44100 Ferrara (Italy); Cruciani, Giuseppe [Department of Physics and Earth Sciences, University of Ferrara, via Saragat 1, 44100 Ferrara (Italy)

    2013-06-15

    An original approach has been developed herein to explore the correlations between short- and long-range structural properties of solid solutions. X-ray diffraction (XRD) and electronic absorption spectroscopy (EAS) data were combined on a (Ca,Sr,Ba){sub 2}(Mg{sub 0.7}Co{sub 0.3})Si{sub 2}O{sub 7} join to determine average and local distances, respectively. Instead of varying the EAS-active ion concentration along the join, as has commonly been performed in previous studies, the constant replacement of Mg{sup 2+} by a minimal fraction of a similar size cation (Co{sup 2+}) has been used to assess the effects of varying second-nearest neighbor cations (Ca, Sr, Ba) on the local distances of the first shell. A comparison between doped and un-doped series has shown that, although the overall symmetry of the Co-centered T1-site was retained, greater relaxation occurs at the CoO{sub 4} tetrahedra which become increasingly large and more distorted than the MgO{sub 4} tetrahedra. This is indicated by an increase in both the quadratic elongation (?{sub T1}) and the bond angle variance (?{sup 2}{sub T1}) distortion indices, as the whole structure expands due to an increase in size in the second-nearest neighbors. This behavior highlights the effect of the different electronic configurations of Co{sup 2+} (3d{sup 7}) and Mg{sup 2+} (2p{sup 6}) in spite of their very similar ionic size. Furthermore, although the overall symmetry of the Co-centered T1-site is retained, relatively limited (<10 deg) angular variations in O–Co{sup 2+}–O occur along the solid solution series and large changes are found in molar absorption coefficients showing that EAS Co{sup 2+}-bands are highly sensitive to change in the local structure. - Graphical abstract: Average (Mg–O) vs. local (Co–O{sub local}) tetrahedral bond distances in function of the average X cation radius in the (Ca,Sr,Ba){sub 2}(Mg{sub 0.7}Co{sub 0.3})Si{sub 2}O{sub 7} join. - Highlights: • New method to assess short- vs. long-range properties of non-ideal solid solutions. • Constant Co{sup 2+}-for-Mg replacement turns the Ca–Sr–Ba-åkermanite join EAS-active. • Co?Mg substitution does not produce any alteration in the average structure. • Relaxation around Co-tetrahedra scales with second-nearest neighbor cation radius. • Different electronic configurations of Co and Mg cause different local structures.

  11. Substitution at the Ru site in the itinerant ferromagnet SrRuO3

    Microsoft Academic Search

    Li Pi; A. Maignan; R. Retoux; B. Raveau

    2002-01-01

    The doping of SrRuO3 at the Ru sites with various cations was investigated, controlling the oxygen composition in sealed tubes (STs). For these ST samples SrRu1-xMx O3, it is shown that doping with cations containing eg electrons, M = Zn2+, Ni2+, Co2+, Mn3+, decreases TC significantly from 166 K for SrRuO3 down to 105 K, whereas in contrast, doping with

  12. Altered photoemission satellites at CaF{sub 2}- and SrF{sub 2}-on-Si(111) interfaces

    SciTech Connect

    Rotenberg, E. [Department of Physics, University of Oregon, Eugene, Oregon 97403 (United States)] [Department of Physics, University of Oregon, Eugene, Oregon 97403 (United States); Denlinger, J.D. [Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53211 (United States)] [Department of Physics, University of Wisconsin, Milwaukee, Wisconsin 53211 (United States); Olmstead, M.A. [Department of Physics, P.O. Box 351560, University of Washington, Seattle, Washington 98195-1560 (United States)] [Department of Physics, P.O. Box 351560, University of Washington, Seattle, Washington 98195-1560 (United States)

    1996-01-01

    Bulk and interface photoemission satellite excitations, measured with x-ray photoelectron spectroscopy and x-ray photoelectron diffraction, are compared for thick, thin, and monolayer films of CaF{sub 2} and SrF{sub 2} on Si(111). Intrinsic satellites are observed for excitation of atoms in the first monolayer, both uncovered and at the buried interface, that differ from those associated with bulk atoms. For F 1{ital s} excitation, the bulk and interface satellites differ only in width and amplitude; for the cation core excitations (Ca 2{ital p}, Sr 3{ital p}, and Sr 3{ital d}), the observed excitation energies and intensities differ both from the equivalent bulk satellites and among the various core hole states. The results yield new information on the nature of the interface bonding, as well as on the origin of both bulk and interface satellites. Several models are considered, including differential screening, dielectric losses, crystal-field and multiplet effects, and interface excitation. The most likely explanation for the new cation satellites at the CaF{sub 2}/Si(111) [SrF{sub 2}/Si(111)] interface is localized excitation of the interface bond, where the interface band gap is controlled by the collapse of the Ca 3{ital d} (Sr 4{ital d}) level in the presence of the Ca (Sr) core hole. {copyright} {ital 1996 The American Physical Society.}

  13. Seasonal Variability of Riverine Geochemistry (87Sr/86Sr, ?13CDIC, ?44/40Ca, and major ions) in Permafrost Watersheds on the North Slope of Alaska

    NASA Astrophysics Data System (ADS)

    Lehn, G. O.; Jacobson, A. D.; Douglas, T. A.; McClelland, J. W.; Khosh, M. S.; Barker, A. J.

    2014-12-01

    Global climate models predict amplified warming at high latitudes, where permafrost soils have historically acted as a carbon sink. As warming occurs, the seasonally thawed active layer will propagate downward into previously frozen mineral-rich soil, releasing carbon and introducing unique chemical weathering signatures into rivers. We use variations in the 87Sr/86Sr, ?13CDIC, ?44/40Ca, and major ion geochemistry of rivers to track seasonal active layer dynamics. We collected water from six streams on the North Slope of Alaska between May and October, 2009 and 2010. All rivers drain continuous permafrost but three drain tussock tundra-dominated watersheds and three drain steeper bedrock catchments with minor tundra coverage. In tundra streams, elevated 87Sr/86Sr ratios, low ?13CDIC values and major ions ([Na+]+[K+]/ [Ca+2]+[Mg+2]) in spring melt runoff suggest flushing of shallow soils with relatively low carbonate content. By July, 87Sr/86Sr ratios stabilize at relatively low values and ?13CDIC at relatively higher values, indicating the active layer thawed into deeper carbonate-rich soils. In bedrock streams, elevated 87Sr/86Sr ratios correlate with high discharge. By late fall, bedrock stream 87Sr/86Sr ratios decrease steadily, consistent with increased carbonate weathering. Nearly constant ?13CDIC values and high [SO4-2] for most of the melt season imply significant sulfuric acid-carbonate weathering in bedrock streams. ?13CDIC values suggest a shift to carbonic acid-carbonate weathering in late 2010, possibly due to limited oxygen for pyrite oxidation during freezing of the active layer. ?44/40Ca values in both tundra and bedrock streams increase during the seasons, suggesting increased uptake of 40Ca by plants. ?44/40Ca values of rivers are at least 0.1-0.2‰ higher than their watershed soils, rocks and sediments, suggesting significant plant uptake. Our findings show how seasonal changes in mineral weathering have potential for tracking active layer dynamics.

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

    PubMed

    Stashans, Arvids; Chamba, Gaston; Pinto, Henry

    2008-02-01

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

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

    SciTech Connect

    Kosmynin, A.S.; Balashov, V.L.; Garkushin, I.K. [Samara Technical Univ. (Russian Federation)] [and others

    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. Mid-Infrared Hall effect in Ca_xSr_1-xRuO_3

    NASA Astrophysics Data System (ADS)

    Stephens, Anthony; Arroyo, A.; Cho, S. R.; Markelz, Andrea; Cerne, John; Ohkubo, I.; Christen, H.; Khalifah, P.; Mandrus, D.

    2004-03-01

    Ca_xSr_1-xRuO3 compounds exhibit unusual properties, such as metamagnetism, quantum criticality, non-Fermi liquid behavior and an anomalous Hall effect that continue to challenge the condensed matter community. The MIR (115-238 meV) complex Hall angle is studied in Ca_xSr_1-xRuO3 films. A sensitive polarization modulation technique (J. Cerne et al., Rev. Sci. Instr. 2003) using discrete lines from CO2 (115-135 meV)and CO (207-238 meV) lasers probes the samples at temperatures in the range (300 K>T>7 K) and magnetic fields up to 7 T. By probing the energy scales of the system and reducing the effects of impurity scattering, these dynamic Hall effect measurements in the MIR provide qualitatively new information on these materials. For example, while the dc Hall response in CaRuO3 changes sign from electron-like to hole-like at 40 K, and the magnitude of the Hall response decreases with temperature, the MIR Hall response does not change sign, remaining hole-like, and both the real and imaginary parts of the MIR Hall angle increase in strength. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-ACO5-00OR22725.

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

    SciTech Connect

    Porto, S.L. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil); Longo, E. [CMDMC/LIEC, Instituto de Quimica, UNESP-Araraquara, Rua Prof. Francisco Degni s/n, Araraquara, SP, CEP 14800-900 (Brazil); Pizani, P.S.; Boschi, T.M. [Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos, Rodovia Washington Luiz km 235, SP, CEP 13565-905 (Brazil); Simoes, L.G.P. [Centro Multidisciplinar de Desenvolvimento de Materiais Ceramicos (LIEC/DQ), Universidade Federal de Sao Carlos, Rodovia Washington Luiz km 235, Sao Carlos, SP, CEP 13565-905 (Brazil); Lima, S.J.G. [Laboratorio de Solidificacao Rapida, Departamento de Tecnologia Mecanica (LSR/DTM/CT), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil); Ferreira, J.M. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil); COAMA, Area de Meio Ambiente, Centro Federal de Educacao Tecnologica da Paraiba, Av. 1o de Maio 720, Jaguaribe, Joao Pessoa, PB, CEP 58015-430 (Brazil); Soledade, L.E.B.; Espinoza, J.W.M.; Cassia-Santos, M.R.; Maurera, M.A.M.A. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil); Paskocimas, C.A. [Departamento de Engenharia Mecanica, Universidade Federal do Rio Grande do Norte, Natal, RN, CEP 59072-970 (Brazil); Santos, I.M.G. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil)], E-mail: ieda@quimica.ufpb.br; Souza, A.G. [Laboratorio de Combustiveis e Materiais (LACOM/DQ/CCEN), Universidade Federal da Paraiba, Campus I, Cidade Universitaria, Joao Pessoa, PB, CEP 58059-900 (Brazil)

    2008-08-15

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

  18. High resolution windows into early Holocene climate: Sr/(Ca) coral records from the Huon Peninsula

    NASA Astrophysics Data System (ADS)

    McCulloch, Malcolm; Mortimer, Graham; Esat, Tezer; Xianhua, Li; Pillans, Brad; Chappell, John

    1996-02-01

    High-precision measurements of Sr/Ca ratios are reported for Porites corals from the uplifted Holocene coral terraces at Huon Peninsula, Papua New Guinea. The early Holocene Porites have U?Th mass spectrometric ages of 8920 ± 60 yr and 7370 ± 50 yr, and ? 234U(t) values of 145 ± 2, similar to modern seawater. The Sr/Ca coral records provide 5-6 year high resolution (near weekly) time windows into early Holocene sea surface temperatures. Seasonal temperature fluctuations are generally in the range of ± 1°C, with occasional excursions of ± 2°C, which may indicate the more frequent recurrence of very strong ENSO (El Niño-Southern Oscillation) events. Mean annual Sr/Ca temperatures of 24.2 ± 1.1°C and 22.9 ± 0.8°C have been obtained, which are ˜ 2-3°C cooler than that exhibited by a modern Porites. These results indicate that, during the early Holocene, the equatorial western Pacific ocean was at least several degrees cooler than present-day temperatures. This is consistent with late glacial coral records from the Caribbean that indicate lower (˜ 6°C) sea surface temperatures for the equatorial oceans. The Huon Peninsula corals also indicate that SSTs were several degrees cooler than those in the Caribbean during the early Holocene. Thus, although the northern hemisphere summer radiation maximum occurred at ˜ 10 ka, there appears to have been a significant lag in the response of the equatorial western Pacific ocean to this warming. Cooler early Holocene sea surface temperatures in the western Pacific may have been due to changing patterns of ocean-atmosphere circulation, resulting from the exposure of large areas of continental shelf in the southeast Asia region, a consequence of lower glacial sea levels. It is likely that ocean temperatures in the Huon Peninsula were influenced by the opening at ˜ 7 ka of the Torres Strait, that now separates New Guinea from the Australian mainland.

  19. Anisotropic thermal expansion in LiCaAlF6 and LiSrAlF6

    NASA Astrophysics Data System (ADS)

    Grzechnik, Andrzej; Dmitriev, Vladimir; Weber, Hans-Peter; Gesland, Jean-Yves; Friese, Karen

    2004-08-01

    The high-temperature behaviour of LiSrAlF6 and LiCaAlF6, both P\\overline {3} 1c and Z = 2, was studied with high-resolution synchrotron angle-dispersive x-ray powder diffraction in the temperature ranges 150-823 and 298-723 K, respectively. No phase transitions were detected. The temperature dependencies of structural parameters and octahedral distortions are obtained with the Rietveld method. Both materials have highly anisotropic thermal expansion, with the c parameter in LiSrAlF6 decreasing with increasing temperature. Our observations on the temperature evolution of various structural parameters, like interatomic distances, angles, distortions and polyhedral volumes indicate that the negative thermal expansion along the c axis in LiSrAlF6 arises from concerted angular distortions around the Sr and Al atoms and diminished {\\mathrm {F\\cdots F}} interatomic distances in the SrF6 slabs. The SrF6 slab contracts with increasing temperatures because of the diminishing F-Sr-F octahedral angles. The CaF6 layer becoming thicker and relatively temperature insensitive angular distortions do not result in anomalous negative thermal expansion in LiCaAlF6.

  20. 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.

  1. Surface dynamics of Bi 2CaSr 2Cu 2O 8

    NASA Astrophysics Data System (ADS)

    de Wette, F. W.; Paltzer, U.; Schröder, U.

    1996-02-01

    We interpret the inelastic He-scattering results for the Bi-O(0 0 1) surface of Bi 2CaSr 2Cu 2O 8, which exhibits an anisotropic superstructure. With a shell model calculation, which takes account of the superstructure, we account for the measurements and show that the appearance of rather dispersionless surface modes and the great similarity between the surface mode spectra in the <1 1 0> and <1 0 0> directions are direct results of the anisotropic superstructure. These features are some of the first examples of unexpected manifestations of a superstructure of a surface in the dynamics of that surface.

  2. Tunneling measurements on Bi2CaSr2Cu2O8

    NASA Astrophysics Data System (ADS)

    Johnson, Robert E.

    1989-03-01

    Measurements have been made of the differential resistance dV/dI versus voltage of point contacts between polycrystalline samples of the high-temperature superconductor Bi2Ca1Sr2Cu2O8 and tungsten points. The spectra exhibited tunneling structure on a nearly symmetric background that decreased with increasing bias voltages. The potential difference between two minima in the dV/dI spectra was used to obtain an estimate of 25+/-3 mV for the gap parameter 2?. The zero-bias minimum characteristic of a no-barrier metal-superconductor junction was never observed.

  3. Ferromagnetism induced by chromium substitution in the CaRuO3 perovskite

    NASA Astrophysics Data System (ADS)

    Maignan, A.; Raveau, B.; Hardy, V.; Barrier, N.; Retoux, R.

    2006-07-01

    Chromium has been substituted for ruthenium in CaRuO3 up to 35%. It is found that chromium induces a ferromagnetic contribution showing a maximum fraction for x=0.15 in CaRu0.85Cr0.15O3 with a Curie temperature (TC) of ˜115K . This change of magnetic ground state goes with an electronic localization, the resistivity at 5K increasing by more than 6 orders of magnitude as x increases from x=0.06 to x=0.35 . Concomitantly, a negative magnetoresistance is induced by the chromium substitution. In order to explain the chromium effect, it is suggested that each trivalent chromium couples antiferromagnetically to its Ru4+/5+ nearest neighbors. When surrounded by six ruthenium cations, this creates “ferrimagnetic” polarons in which TC is governed by the Ru4+/5+-O-Cr3+ antiferromagnetic exchange (TC˜115K) . However, as the Cr3+ concentration increases, the Cr3+-O-Cr3+ antiferromagnetic exchange (energy) (TN˜290K) creates an antagonistic effect. This explains the existence of an optimum chromium content at x=0.15 .

  4. Preparation and Characterizations of High-K (Ca, Sr)ZrO3 Gate Dielectric Thin Films by Sol-Gel Technology

    Microsoft Academic Search

    W. ZHU; T. YU; C. H. CHEN; X. F. CHEN; R. G. KRISHNAN

    2004-01-01

    We have very recently prepared perovskite high-K dielectric thin films in the CaZrO3-SrZrO3 solid solution system using the sol-gel wet chemical technology for CMOS gate and nanoelectronics applications. Such sol-gel prepared (Ca, Sr)ZrO3 thin films with various compositional ratios of Ca\\/Sr on Pt coated (001) Si substrates are annealed in flowing O2 at different temperatures from 550 to 700°C. Based

  5. Luminescence and photoionization processes of Yb2+ in CaF2, SrF2 and BaF2

    E-print Network

    Paris-Sud XI, Université de

    2105 Luminescence and photoionization processes of Yb2+ in CaF2, SrF2 and BaF2 B. Moine, B les propriétés de fluorescence et de photoconductivité de Yb2+ dans CaF2, SrF2 et BaF2. On présente In this paper, we analyze the fluorescence and the photoconductivity properties of Yb2+ in CaF2, SrF2 and BaF2

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

    SciTech Connect

    Skinner, Lawrie [State University of New York, Stony Brook; Benmore, Chris J [Argonne National Laboratory (ANL); Weber, Richard [Argonne National Laboratory (ANL); Santodonato, Louis J [ORNL; Tumber, Sonia [Materials Development, Inc., Evanston, IL; Neuefeind, Joerg C [ORNL; Lazareva, Lena [State University of New York, Stony Brook; Du, Jincheng [University of North Texas; Parise, John B [Stony Brook University (SUNY)

    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.

  7. Superconducting Bi-Ca-Sr-Cu oxide thin films by spray pyrolysis of metal acetates

    NASA Astrophysics Data System (ADS)

    Vaslow, Dale F.; Dieckmann, Gunter H.; Elli, David Dawson; Ellis, Arthur B.; Holmes, D. Scott; Lefkow, Anthony; MacGregor, Mark; Nordman, James E.; Petras, Michael F.; Yang, Yifeng

    1988-07-01

    Superconducting Bi-Ca-Sr-Cu oxide thin films have been prepared on ZrO2-coated silicon (111) wafers by spray pyrolysis of metal acetate precursors followed by rapid annealing to 850 °C in air. Resistivity measurements indicate a broad superconducting transition with Tc onset near 90 K and zero resistivity below 60 K. The films are highly oriented with the c axis normal to the substrate surface and can be indexed to a tetragonal structure with lattice parameters of a=3.832(1) Å and c=30.78(5) Å. Both x-ray photoelectron spectroscopy and x-ray diffraction measurements indicate the loss of Ca to the ZrO2 buffer layer.

  8. Crystalline Phases Precipitated by Heat-Treatment of Rapidly-Quenched Glasses in the Bi-Ca-Sr-Cu-O System

    NASA Astrophysics Data System (ADS)

    Tohge, Noboru; Tsuboi, Shinzo; Tatsumisago, Masahiro; Minami, Tsutomu

    1989-10-01

    The precipitation process of the superconducting phases from the rapidly-quenched glasses has been studied as a function of both heat-treatment temperature and time for the three main compositions in the Bi-Ca-Sr-Cu-O system: Bi2Ca2Sr2Cu3Ox, BiCaSrCu2Ox, and Bi2CaSr2Cu2Ox. The temperature-time-transformation diagram for each composition has been constructed and a difference has been found between those for the former two compositions and that for the last one.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    Stable Ca and radiogenic Sr isotope compositions were measured in different compartments (stream water, soil solutions, rocks, soils and soil leachates and vegetation) of a small permafrost-dominated watershed in the Central Siberian Plateau. The Sr and Ca in the area are supplied by basalt weathering and atmospheric depositions, which significantly impact the Sr isotopic compositions. Only vegetation significantly fractionates the calcium isotopes within the watershed. These fractionations occur during Ca uptake by roots and along the transpiration stream within the larch trees and are hypothesised to be the result of chromatographic processes and Ca oxalate crystallisations during Ca circulation or storage within plant organs. Biomass degradation significantly influences the Ca isotopic compositions of soil solutions and soil leachates via the release of light Ca, and organic and organo-mineral colloids are thought to affect the Ca isotopic compositions of soil solutions by preferential scavenging of 40Ca. The imprint of organic matter degradation on the ?44/40Ca of soil solutions is much more significant for the warmer south-facing slope of the watershed than for the shallow and cold soil active layer of the north-facing slope. As a result, the available stock of biomass and the decomposition rates appear to be critical parameters that regulate the impact of vegetation on the soil-water system in permafrost areas. Finally, the obtained ?44/40Ca patterns contrast with those described for permafrost-free environments with a much lower ?44/40Ca fractionation factor between soils and plants, suggesting specific features of organic matter decomposition in permafrost environments. The biologically induced Ca isotopic fractionation observed at the soil profile scale is not pronounced at the scale of the streams and large rivers in which the ?44/40Ca signature may be controlled by the heterogeneity of lithological sources.

  10. Effect of Electron Irradiation on isovalenly substituted SrFe2(As1-xPx)2, x = 0 . 35

    NASA Astrophysics Data System (ADS)

    Strehlow, C. P.; Murphy, Jason; Tanatar, Makariy; Prozorov, Ruslan; Konczykowski, M.; Salovich, N.; Giannetta, R. W.; Kobayashi, T.; Miyasaka, S.; Tajima, S.

    2014-03-01

    The effects of electron irradiation on the termperature-dependent London penetration depth, ?(T), have been investigated in annealed optimally doped single crystals of isovalently substituted SrFe2(As1-xPx)2, x = 0 . 35 , using the tunnel diode resonator technique. The low temperature behavior of ?(T) changes under electron irradiation from almost T - linear to practically exponentially saturated behavior, similar to the observations in another isovalently substituted 122 pnictide, BaFe2(As1-xPx)2. Furthermore, aluminum - coating technique was used to measure the absolute values of the London penetration depth, ?(0), which allowed calculations of the superfluid density, ?s. We conclude that, similar to BaFe2(As1-xPx)2, the superconducting properties of SrFe2(As1-xPx)2 are compatible with s+/- pairing with accidental line nodes that are lifted by pair-breaking disorder. This work was supported by the Department of Energy Office of Science, Basic Energy Sciences under Contract No. DE-AC02-O7CH11358.

  11. 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.

  12. Crystal growth and characterization of two-leg spin ladder compounds: Sr 14Cu 24O 41 and Sr 2Ca 12Cu 24O 41

    NASA Astrophysics Data System (ADS)

    Vanishri, S.; Marin, C.; Bhat, H. L.; Salce, B.; Braithwaite, D.; Regnault, L. P.

    2009-07-01

    Single crystals of Sr 14-xCa xCu 24O 41 ( x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr 14Cu 24O 41 show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. Tc onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with Tc max=9.4 K and TN=5 K at 56 kbars.

  13. Effect of oxygen concentration on superconductivity of Bi-Sr-Ca-K-Cu-O compounds

    SciTech Connect

    Han Zhiyi; Mao Zhiqiang; Wang Yu; Chen Qun; Zhang Ning; Zhou Zhe; Chao LieZhao; Cheng Zhaojia; Zhou Guien; Zhang Yuheng (Univ. of Science and Technology of China, Anhui (China))

    1991-02-01

    In order to study the relation between the oxygen content and superconductivity samples of Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}x}K{sub x}Cu{sub 2}O{sub y} (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were prepared and treated under different conditions. It was found that the superconducting properties are sensitive to the oxygen concentration and the T{sub c,zero} of Bi{sub 2}Sr{sub 2}Ca{sub 1{minus}x}K{sub x}Cu{sub 2}O{sub y} can be shifted over a range of about 22 K by the changing oxygen concentration; no structural difference induced by oxygen were observed. The change in superconducting properties may be the result of a change in Cu average valence state. In addition, the change in superconducting phase with K{sup +} concentration is also studied.

  14. 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.

  15. Formation of La{sub 4-x}M{sub x}Ni{sub 3}O{sub y} solid solutions (M = Ca, Sr, Ba)

    SciTech Connect

    Vashuk, V.V.; Ol`shevskaya, O.P.; Savchenko, V.F.; Puchkaeva, E.Ya. [Institute of General and Inorganic Chemistry, Minsk (Belarus)

    1994-11-01

    Doping of mixed oxides is known to be capable of substantially modifying their physicochemical properties. For example, partial substitution of strontium for lanthanum in semiconducting La{sub 2}CuO{sub 4} results in the formation of the La{sub 1.85}Sr{sub 0.15}CuO{sub 4} solid solution, which exhibits superconducting properties. Over the past few years, significant effort has been devoted to the investigation of La{sub 2-x}Sr{sub x}NiO{sub y} nickelates, which are isostructural to high-temperature cuprate superconductors and can be used as parent compounds for producing superconductors. The formation of La{sub 4-x}Mg{sub x}Ni{sub 3}O{sub y} solid solutions was reported. At the same time, no data are available on the possibility of preparing analogous solid solutions with other alkaline-earth elements. In this work, the authors report the results on the synthesis of La{sub 4-x}M{sub x}Ni{sub 3}O{sub y} solid solutions (M = Ca, Sr, Ba), their composition ranges, and some physicochemical properties. The choice of subject for the investigation was determined by the chemical and structural similarity of the solid solutions in question to the well-known high-temperature cuprate superconductors and by the high metallic conductivity of La{sub 4}Ni{sub 3}O{sub 10}.

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

    Microsoft Academic Search

    Satoru Kaneko; Yoshitada Shimizu; Seishiro Ohya

    2001-01-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  18. Improved Figure of Merit of (Ba,Sr)TiO3-Based Ceramics by Sn Substitution Jong-Yoon Ha, Liwei Lin, Dae-Yong Jeong1

    E-print Network

    Lin, Liwei

    for Ti4þ , up to 30 mol %, on ferroelectric properties and dielectric tunability of ceramics in the Ba0Improved Figure of Merit of (Ba,Sr)TiO3-Based Ceramics by Sn Substitution Jong-Yoon Ha, Liwei Lin properties of (Ba0:6Sr0:4)(Ti1Àx Snx )O3 (0 x 0:3) ceramics were investigated. Single-phase specimens having

  19. Cr:LiSr(0.8)Ca(0.2)AlF(6) tunable laser.

    PubMed

    Chai, B H; Lefaucheur, J L; Stalder, M; Bass, M

    1992-11-15

    A new congruent melting compound intermediate between the solid solutions of LiCaAIF(6) and LiSrAlF(6) is reported. When doped with Cr(3+) ion, the new compound (Cr:LiSr(0.8)Ca(0.2)AlF(6)) has demonstrated roomtemperature lasing in the spectral region from 750 to 950 nm. This material has mechanical properties similarto those of Cr:LiCaAlF(6) and a broadband laser tuning range similar to that of Cr:LiSrAlF(6). Long-pulse, flash-lamp-pumped lasing with 1.25% overall efficiency is reported by using a rod cut from an earlier boule. PMID:19798253

  20. Thermophysical characteristics of Ca1- x Sr x F2 solid-solution Crystals (0 ? x ? 1)

    NASA Astrophysics Data System (ADS)

    Popov, P. A.; Moiseev, N. V.; Karimov, D. N.; Sorokin, N. I.; Sulyanova, E. A.; Sobolev, B. P.; Konyushkin, V. A.; Fedorov, P. P.

    2015-01-01

    The thermal conductivity of crystals of a continuous series of isovalent Ca1 - x Sr x F2 solid solutions has been experimentally investigated in the temperature ranges of 50-300 K (0 ? x ? 1) and 54-303 K ( x = 0.743). The concentration dependence k( x) of the thermal conductivity has been revealed for Ca1- x Sr x F2 crystals. It is shown that k > 3 W/(m K) at 300 K for any x. Being extrapolated to the melting temperature range, the phonon mean free path l( T) in Ca0.257Sr0.743F2 crystal approaches to the unit-cell parameter a.

  1. Manipulating magnetic properties of SrRuO3 and CaRuO3 with epitaxial and uniaxial strains

    NASA Astrophysics Data System (ADS)

    Zayak, A. T.; Huang, X.; Neaton, J. B.; Rabe, Karin M.

    2008-06-01

    Using density-functional theory within the local spin-density approximation, SrRuO3 and CaRuO3 are investigated under epitaxial and uniaxial strains. Strains of the order of 2% 3% are predicted to radically alter the magnetic properties of SrRuO3 and CaRuO3 ultrathin films, indicating a large magnetostructural coupling in these systems. In particular, SrRuO3 is shown to become nonmagnetic for sufficient tensile epitaxial and compressive uniaxial strains; in contrast, CaRuO3 is predicted to become ferromagnetic for tensile epitaxial strains. These results suggest routes for the manipulation of the magnetic order of perovskite oxides ultrathin films via coherent epitaxial growth.

  2. Solid-state combinatorial screening of (Sr,Ca,Ba, Mg)?Si?N?:Eu(2+) phosphors.

    PubMed

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

    2011-03-14

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

  3. Effects of Cr/Zn Substitutions on Dielectric Properties of CaCu3Ti4O12 (CCTO) Ceramics

    NASA Astrophysics Data System (ADS)

    Rajmi, R.; Yahya, A. K.; Deni, M. S. M.

    2010-07-01

    Effects of Zn and Cr substitutions on dielectric properties of CaCu3-xZnxTi4-yCryO12 ceramics are reported. Dielectric measurements at room temperature for un-substituted CaCu3-xZnxTi4-yCryO12 (x = 0, y = 0) between 102-106 Hz showed dielectric constant of 2.7×104 at 102 Hz. Substitution of Zn for Cu in CaCu3-xZnxTi4-yCryO12 (y = 0, x = 0.10, 0.50)caused dielectric constant to drop with increasing x. Cr substitution at Ti-site in CaCu3-xZnxTi4-yCryO12 (x = 0, x = 0,) also caused decrease in dielectric constant. However, at x = 0.50, the dielectric constant at low frequency was enhanced compared to the un-substituted sample. Our results indicate that Cu and Ti sites play an important role in the formation of Internal Barrier Layer Capacitance (IBLC) in CCTO.

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

    Microsoft Academic Search

    Sarah J. Brown; Henry Elderfield

    1996-01-01

    A comparative study has been made of two species of planktonic foraminifera, G. tumida and G. sacculifer, in a depth transect on the Ontong Java Plateau, western equatorial Pacific. G. tumida tests from core-top sediments showed decreasing Mg\\/Ca (2.65-1.25 mmol\\/mol) and Sr\\/Ca (1.50-1.16 mmol\\/mol) ratios with increasing water depth (1600-4400 m), while no such variation was found in G. sacculifer

  5. Sr\\/Ca and Mg\\/Ca ratios in Niger Delta sediments: Implications for authigenic carbonate genesis in cold seep environments

    Microsoft Academic Search

    G. Bayon; C. Pierre; J. Etoubleau; M. Voisset; E. Cauquil; T. Marsset; N. Sultan; E. Le Drezen; Y. Fouquet

    2007-01-01

    We report on a reconnaissance analysis of the geochemical composition of authigenic carbonates and sediment samples collected from various seepage sites on the Niger deep-sea fan. Our aim has been to investigate whether evidence for the presence of authigenic carbonates and gas hydrates within sediments is discernible from solid-phase sediment geochemistry. We show that sedimentary Sr\\/Ca and Mg\\/Ca ratios can

  6. An anion substitution route to low loss colossal dielectric CaCu 3Ti 4O 12

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

    An anion substitution route was utilized for lowering the dielectric loss in CaCu 3Ti 4O 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 °C. In particular, CaCu 3Ti 4O 11.7F 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 °C. Fluorine analysis confirmed the presence of fluorine in all samples measured.

  7. Nature of the ferromagnetism induced by nonmagnetic substitutions on the Ru site of CaRuO3

    NASA Astrophysics Data System (ADS)

    Hardy, V.; Raveau, B.; Retoux, R.; Barrier, N.; Maignan, A.

    2006-03-01

    In spite of many efforts, the magnetic ground state of CaRuO3 remains enigmatic to date and is still the subject of intense controversy. Among the peculiarities of this ruthenate is the puzzling fact that small levels of substitution on the magnetic Ru4+ sublattice by nonmagnetic cations were found to induce the development of a ferromagnetic transition. The present paper addresses this issue by combining magnetization, resistivity, and heat capacity measurements in CaRu1-xMxO3 for 0?x<1 and M=Ti , Zr, Ga, and Al. It is suggested that this substitution-induced ferromagnetism is basically heterogeneous and itinerant in nature.

  8. 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.

  9. Structural and electronic role of lead in (PbBi) sub 2 Sr sub 2 CaCu sub 2 O sub 8 superconductors by STM

    SciTech Connect

    Wu, Xian Liang; Zhang, Zhe; Wang, Yue Li; Lieber, C.M. (Columbia Univ., New York, NY (USA))

    1990-06-08

    The structural and electronic effects of lead substitution in the high-temperature superconducting materials Pb{sub x}Bi{sub 2{minus}x}Sr{sub 2}CaCu{sub 2}O{sub 8} have been characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Large-area STM images of the Bi(Pb)-O layers show that lead substitution distorts and disorders the one-dimensional superlattice found in these materials. Atomic-resolution images indicate that extra oxygen atoms are present in the Bi(Pb)-O layers. STS data show that the electronic structure of the Bi(Pb)-O layers is insensitive to lead substitution within {plus minus}0.5 electron volt of the Fermi level; however, a systematic decrease in the density of states is observed at {approx}1 electron volt above the Fermi level. Because the superconducting transition temperatures are independent of x(Pb) (x {le} 0.7), these microscopic STM and STS data suggest that the lead-induced electronic and structural changes in the Bi(Pb)-O layer do not perturb the electronic states critical to forming the superconducting state in this system. 28 refs., 4 figs.

  10. Calibración de los paleotermómetros de Sr\\/Ca y Mg\\/Ca en el coral Porites sp. de Isla San Benedicto, Archipiélago Revillagigedo, México Calibration of Sr\\/Ca and Mg\\/Ca paleothermometers in coral Porites sp. from San Benedicto Island, Revillagigedo Archipelago, Mexico

    Microsoft Academic Search

    J. A. Villaescusa; J. D. Carriquiry

    2004-01-01

    A better understanding of the global climate system depends on our ability to expand the limited instrumental records of sea surface temperature (SST) of tropical regions. The Sr\\/Ca and Mg\\/Ca ratios contained in the growth bands of corals have proved to be an accurate tool to reconstruct SST variability. In this study we show the calibration obtained from the seasonal

  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. Magnetic and transport properties of Na doped SrRuO3 and CaRuO3

    Microsoft Academic Search

    M. Shepard; G. Cao; S. McCall; F. Freibert; J. E. Crow

    1996-01-01

    The magnetic susceptibility ?(T) (2?T?400 K) and electrical resistivity &rgr;(T) (2?T?300 K) of undoped and Na doped SrRuO3 and CaRuO3 single crystals were measured. These two perovskites are orthorhombic with space group Pbnm. While both of the undoped systems exhibit metallic conductivity, SrRuO3 is ferromagnetic with Tc?160 K, but CaRuO3 is paramagnetic. When a small concentration of Na (?12%) replaces

  13. Invalidity Of A Localized Spin Mechanism For SrRuO3 and CaRuO3

    NASA Astrophysics Data System (ADS)

    Middey, Srimanta; Mahadevan, Priya; Sarma, D. D.

    2008-04-01

    We have calculated the electronic structure for CaRuO3 and SrRuO3 within first principles electronic structure calculations. We find that the experimentally observed ferromagnetic state is favoured in the case of SrRuO3, while our calculations also suggest that no state with long range magnetic order will be stabilised for CaRuO3. Mapping the total energies for different magnetic configurations to an extended Heisenberg model, we find that a localized spin model is found to be invalid to describe the magnetic state of these systems.

  14. LDA+DMFT study of Ru-based perovskite SrRuO3 and CaRuO3

    NASA Astrophysics Data System (ADS)

    Jakobi, E.; Kanungo, S.; Sarkar, S.; Schmitt, S.; Saha-Dasgupta, T.

    2011-01-01

    We carried out a LDA+DMFT study of perovskite ruthenates SrRuO3 and CaRuO3, compounds which have been discussed in great detail in recent literature. Our results reproduced the observed mass enhancements and magnetic properties, and were in reasonable agreement with the measured photoemission spectra. Our calculations produced rather different coherence temperatures for SrRuO3 and CaRuO3, providing a possible explanation for the observed differences between these compounds. We also present k-resolved spectra for the sake of comparison with future angle-resolved photoemission experiments.

  15. Electronic and structural properties of the Cu - Bi 2CaSr 2Cu 2O 8 interface

    NASA Astrophysics Data System (ADS)

    Bernhoff, H.; Qvarford, M.; Söderholm, S.; Flodström, A. S.; Andersen, J. N.; Nyholm, R.; Karlsson, U. O.; Lindau, I.

    1991-09-01

    The formation of the Cu-Bi 2CaSr 2Cu 2O 8 interface has been studied by photoelectron spectroscopy using synchrotron radiation. Photon energies in the range 20-1000 eV were utilized in order to probe both the valence band and to monitor chemical changes upon Cu deposition, as revealed by the core-level shifts. A strong chemical reaction between Bi 2CaSr 2Cu 2O 8 and Cu is manifested by the formation of metallic Bi. From theb density variations as a function of electron emission angle it is shown that the metallic Bi segregates to the top surface layer.

  16. Vibrating-reed studies on non-single-phase Bi-Ca-Sr-Cu-O superconducting ceramics

    NASA Astrophysics Data System (ADS)

    Gupta, A.; Esquinazi, P.; Braun, H. F.

    1989-06-01

    The resonance frequency ? and damping ? of two selected reeds of Bi-Ca-Sr-Cu-O ceramics were measured between 4.2 and 100 K in different applied magnetic fields up to 0.3 T. The samples showed large anomalies in ? and ? at ~=60 and ~=45 K indicating the existence of different superconducting phases. These anomalies can be interpreted in terms of pinning and hysteretic motion of flux lines. Within experimental resolution x-ray-powder patterns resemble that of the 85-K superconductor Bi2CaSr2Cu2O8.

  17. Vibrating-reed studies on non-single-phase Bi-Ca-Sr-Cu-O superconducting ceramics

    SciTech Connect

    Gupta, A.; Esquinazi, P.; Braun, H. F.

    1989-06-01

    The resonance frequency ..omega.. and damping GAMMA of two selected reeds of Bi-Ca-Sr-Cu-O ceramics were measured between 4.2 and 100 K in different applied magnetic fields up to 0.3 T. The samples showed large anomalies in ..omega.. and GAMMA at /congruent/60 and /congruent/45 K indicating the existence of different superconducting phases. These anomalies can be interpreted in terms of pinning and hysteretic motion of flux lines. Within experimental resolution x-ray-powder patterns resemble that of the 85-K superconductor Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8/.

  18. Preparation of Bi-Sr-Ca-Cu-O High-Tc Superconducting Fibers by Pyrolysis of Organic Acid Salts

    NASA Astrophysics Data System (ADS)

    Nasu, Hiroyuki; Shoyama, Masashi; Nozue, Akiyoshi; Kamiya, Kanichi; Shiono, Takeo

    1990-06-01

    Bi-Sr-Ca-Cu-O high Tc superconducting solid fibers were successfully obtained by pyrolysis of organic acid salts. The addition of oxide powder and the covering of fibers with hydroxypropylcellulose were necessary to prevent the deformation of fibers drawn from the liquid. The Tc (end) of the fibers was 60 K and the strength was 7.5 MPa after the fibers were heated at 800°C for 24 h. X-ray diffraction patterns showed the formation of the Bi:Sr:Ca:Cu=2:2:1:2 phase.

  19. Luminescence properties of double-perovskite Sr 2 Ca 1?2 x Eu x Na x MoO 6 red-emitting phosphors prepared by the citric acid-assisted sol–gel method

    Microsoft Academic Search

    Zhiguo Xia; Jianfeng Sun; Haiyan Du; Daimei Chen; Jiayue Sun

    2010-01-01

    Double-perovskite Sr2Ca1?2x\\u000a Eu\\u000a x\\u000a Na\\u000a x\\u000a MoO6 red-emitting phosphors were prepared by the citric acid-assisted sol–gel method, and their luminescence properties were investigated\\u000a as a function of sintering temperature and Eu3+-doping concentration. B-site substituted Sr2Ca0.8Eu0.1Na0.1MoO6 phosphor, in which Na+ ions act as charge compensators, was selected to study the thermal behavior, phase structure, microstructure, and photoluminescence\\u000a property under different sintering

  20. The effect of skeletal mass accumulation in Porites on coral Sr/Ca and ?18O paleothermometry

    NASA Astrophysics Data System (ADS)

    Gagan, Michael K.; Dunbar, Gavin B.; Suzuki, Atsushi

    2012-03-01

    Paleotemperature estimates based on coral Sr/Ca have not been widely accepted because the reconstructed glacial-Holocene shift in tropical sea-surface temperature (˜4-6°C) is larger than that indicated by foraminiferal Mg/Ca (˜2-4°C). We show that corals over-estimate changes in sea-surface temperature (SST) because their records are attenuated during skeletogenesis within the living tissue layer. To quantify this process, we microprofiled skeletal mass accumulation within the tissue layer of Porites from Australasian coral reefs and laboratory culturing experiments. The results show that the sensitivity of the Sr/Ca and ?18O thermometers in Porites will be suppressed, variable, and dependent on the relationship between skeletal growth rate and mass accumulation within the tissue layer. Our findings help explain why ?18O-SST sensitivities for Porites range from -0.08‰/°C to -0.22‰/°C and are always less than the value of -0.23‰/°C established for biogenic aragonite. Based on this observation, we recalibrated the coral Sr/Ca thermometer to determine a revised sensitivity of -0.084 mmol/mol/°C. After rescaling, most of the published Sr/Ca-SST estimates for the Indo-Pacific region for the last ˜14,000 years (-7°C to +2°C relative to modern) fall within the 95% confidence envelope of the foraminiferal Mg/Ca-SST records. We conclude that two types of calibration scales are required for coral paleothermometry; an attenuated Porites-specific thermometer sensitivity for studies of seasonal to interannual change in SST and, importantly, the rescaled -0.084 mmol/mol/°C Sr/Ca sensitivity for studies of 20th-century trends and millennial-scale changes in mean SST. The calibration-scaling concept will apply to the development of transfer functions for all geochemical tracers in corals.

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

    SciTech Connect

    Kanai, Masaki; Kawai, Tomoji [Osaka Univ., Mihogaoka, Osaka (Japan). Inst. of Scientific and Industrial Research

    1996-12-31

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

  2. Interfacial magnetism in CaRuO3\\/CaMnO3 superlattices grown on (001) SrTiO3

    Microsoft Academic Search

    C. He; X. Zhai; V. V. Mehta; F. J. Wong; Y. Suzuki

    2011-01-01

    We have studied epitaxially grown superlattices of CaRuO3\\/CaMnO3 as well as an alloy film of CaMn0.5Ru0.5O3 on (001) SrTiO3 substrates. In contrast to previous experiments, we have studied CRO\\/CMO superlattices with a constant CRO thickness and variable CMO thickness. All superlattices exhibit Curie temperatures (TC) of 110 K. The saturated magnetization per interfacial Mn cation has been found to be

  3. Partial antiferromagnetism in spin-chain Sr5Rh4O12 , Ca5Ir3O12 , and Ca4IrO6 single crystals

    NASA Astrophysics Data System (ADS)

    Cao, G.; Durairaj, V.; Chikara, S.; Parkin, S.; Schlottmann, P.

    2007-04-01

    We report a structural, thermodynamic, and transport study of the newly synthesized Sr5Rh4O12 , Ca5Ir3O12 , and Ca4IrO6 single crystals. These quasi-one-dimensional insulators consist of a triangular lattice of spin chains running along the c axis, and are commonly characterized by a partial antiferromagnetic (AFM) order, a small entropy removal associated with the phase transitions, and a sizable low-temperature specific heat linearly proportional to temperature. Sr5Rh4O12 is antiferromagnetically ordered below 23K with strong evidence for an Ising character. Isothermal magnetization of Sr5Rh4O12 exhibits two steplike transitions leading to a ferrimagnetic state at 2.4T and a ferromagnetic state at 4.8T , respectively. Ca5Ir3O12 and Ca4IrO6 are also antiferromagnetically ordered below 7.8 and 12K , respectively, and show an unusually large ratio of the Curie-Weiss temperature to the Néel temperature. In particular, Ca5Ir3O12 , which includes both Ir4+ and Ir5+ ions, reveals that only S=1/2 spins of the Ir4+ ions are involved in the magnetic ordering, whereas S=1 spins of the Ir5+ ions remain disordered. All results suggest the presence of a geometrical frustration that causes incomplete long-range AFM order in these quasi-one-dimensional compounds.

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  5. Energy gaps in Bi2Sr2CaCu2O8+? cuprate superconductors

    PubMed Central

    Ren, J. K.; Zhu, X. B.; Yu, H. F.; Tian, Ye; Yang, H. F.; Gu, C. Z.; Wang, N. L.; Ren, Y. F.; Zhao, S. P.

    2012-01-01

    The relationship between the cuprate pseudogap (?p) and superconducting gap (?s) remains an unsolved mystery. Here, we present a temperature- and doping-dependent tunneling study of submicron Bi2Sr2CaCu2O8+? intrinsic Josephson junctions, which provides a clear evidence that ?s closes at a temperature Tc0 well above the superconducting transition temperature Tc but far below the pseudogap opening temperature T*. We show that the superconducting pairing first occurs predominantly on a limited Fermi surface near the node below Tc0, accompanied by a Fermi arc due to the lifetime effects of quasiparticles and Cooper pairs. The arc length has a linear temperature dependence, and as temperature decreases below Tc it reduces to zero while pairing spreads to the antinodal region of the pseudogap leading to a d-wave superconducting gap on the entire Fermi surface at lower temperatures. PMID:22355760

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

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  7. Magnetic impurity induced states in superconducting Bi2Sr2CaCuO8+?

    NASA Astrophysics Data System (ADS)

    Choubey, Peayush; Kreisel, Andreas; Berlijn, Tom; Andersen, Brian; Hirschfeld, Peter

    2015-03-01

    We revisit the Ni impurity problem in superconducting Bi2Sr2CaCu2O8+? (BSCCO-2212) using the Bogoliubov- de Gennes (BdG)-Wannier approach. We solve the self-consistent BdG equations on a square lattice and use first principle-based Wannier function to compute the local density of states (LDOS) with sub-atomic resolution in the vicinity of a magnetic impurity. We find two spin-resolved virtual bound states localized around the impurity position. The spatial LDOS patterns at the resonance energies are found to be in excellent agreement with STM experiment, and can be understood by accounting for the tails of Cu Wannier function.

  8. Surface dynamics of Bi 2CaSr 2Cu 2O 8

    NASA Astrophysics Data System (ADS)

    Paltzer, U.; de Wette, F. W.; Schröder, U.; Rampf, E.

    1998-05-01

    The high- Tc superconductor Bi 2CaSr 2Cu 2O 8 (Bi 2:1:2:2) exhibits a superstructure in the bulk which is manifested at the surface. Helium atom scattering (HAS) from the (001) Bi-O surface has revealed unusual features of the surface phonons, such as the occurrence of apparently rather dispersionless surface modes and an only weak dependence of surface mode dispersion on direction in the surface. We report lattice dynamical calculations of a (001) slab of Bi 2:1:2:2 material, bounded by Bi-O surfaces. The calculations are based on shell model interactions, and take proper account of surface relaxation. We find that the above mentioned features of the surface phonon modes are direct consequences of the anisotropic surface structure.

  9. Critical behaviour and irreversibility in Ca xSr 1- xRuO 3

    NASA Astrophysics Data System (ADS)

    Roshko, R. M.; Viddal, C.; Li, W.

    2004-01-01

    Measurements of the field and temperature dependence of the frequency-dependent susceptibility ?( ?) the thermoremanent magnetization (TRM) and the isothermal remanent magnetization (IRM) have been performed on a series of mixed ruthenates with chemical formula Ca xSr 1- xRuO 3. The susceptibility data are analysed within the framework of a static scaling theory. Estimates for the critical exponents ?, ?, and ? are consistent with a second-order transition from a paramagnetic to a ferromagnetic state, with exchange bond disorder. The remanence data are analysed within the framework of a Preisach model, which incorporates an explicit reference to the critical temperature TC. The analysis shows that, under certain conditions, the TRM and the IRM yield independent scans of the Preisach distribution along two orthogonal directions in the Preisach plane, the TRM along the bias field axis Hs and the IRM along the dissipation field axis Hd.

  10. Light impurities in HTC BiSrCaCuO superconductor films

    NASA Astrophysics Data System (ADS)

    Matsunami, Noriaki; Onoue, O.; Noguchi, M.; Nozaki, J.; Takai, Y.

    1998-03-01

    We have measured the H concentrations in Bi 2Sr 2Ca 2Cu 3O 10- X films (80 nm thick) on MgO. For the detection of H, 2.5 MeV He elastic recoil detection (ERD) was employed and the ERD cross section was calibrated with VH 6. Samples of Bi-2223 films were prepared by the RF sputter deposition method and have a critical temperature ( Tc) for superconductivity of 70-90 K. Hydrogen contamination of 40-160 × 10 15/cm 2 was found at the surface. It appears that in the film, the H concentration NH is nearly constant and the ratio {N H}/{N Bi} ranges from 0.09 to 0.43, where NBi is the Bi concentration. No appreciable H was detected at the interface between the film and MgO substrate. It is found that Tc is higher for lower {N H}/{N Bi}.

  11. Powerful terahertz emission from Bi2Sr2CaCu2O8+? mesa arrays

    NASA Astrophysics Data System (ADS)

    Benseman, T. M.; Gray, K. E.; Koshelev, A. E.; Kwok, W.-K.; Welp, U.; Minami, H.; Kadowaki, K.; Yamamoto, T.

    2013-07-01

    Stacks of intrinsic Josephson junctions in high-temperature superconductors enable the fabrication of compact sources of coherent terahertz radiation. Here, we demonstrate that multiple stacks patterned on the same Bi2Sr2CaCu2O8+? crystal can—under optimized conditions—be synchronized to emit high-power THz-radiation. For three synchronized stacks, we achieved 610 ?W of continuous-wave coherent radiation power at 0.51 THz. We suggest that synchronization is promoted by THz-waves in the base crystal. We note that synchronization cannot be achieved in all samples. However even in these cases, powers on the 100-?W scale can be generated.

  12. 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.

  13. 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

  14. 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 [McMaster University; Greedan, John E [McMaster University; Cranswick, Lachlan M.D. [Canadian Neutron Beam Centre, National Research Council, Chalk River Laboratorie; Donaberger, R. L. [National Research Council of Canada; Garlea, Vasile O [ORNL; Siewenie, Joan [Los Alamos National Laboratory (LANL)

    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) .

  15. Nicotinic Acid Adenine Dinucleotide Phosphate Analogs Containing Substituted Nicotinic Acid: Effect of Modification on Ca2+ Release

    PubMed Central

    Jain, Pooja; Slama, James T.; Perez-Haddock, LeRoy A.; Walseth, Timothy F.

    2011-01-01

    Analogs of nicotinic acid adenine dinucleotide phosphate (NAADP) with substitution at either the 4- or the 5-position position of the nicotinic acid moiety have been synthesized from NADP enzymatically using Aplysia californica ADP-ribosyl cyclase or mammalian NAD glycohydrolase. Substitution at the 4-position of the nicotinic acid resulted in the loss of agonist potency for release of Ca2+-ions from sea urchin egg homogenates and in potency for competition ligand binding assays using [32P]NAADP. In contrast, several 5-substituted NAADP derivatives showed high potency for binding and full agonist activity for Ca2+ release. 5-Azido-NAADP was shown to release calcium from sea urchin egg homogenates at low concentration and to compete with [32P]NAADP in a competition ligand binding assay with an IC50 of 18 nM, indicating that this compound might be a potential photoprobe useful for specific labeling and identification of the NAADP receptor. PMID:20942470

  16. 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.

  17. Van Hove singularities in the parent superconductor Ca 1 - xSr xCuO 2

    NASA Astrophysics Data System (ADS)

    Yadav, P. S.; Kumar, Sudhir; Agrawal, Savitri; Agrawal, Bal K.

    1996-02-01

    We have investigated for the first time the electronic structure and the van Hove singularities of the ordered Ca 1 - xSr xCuO 2 structures for five values of the concentration x = 0.0, 0.25, 0.50, 0.75 and 1.0 by employing a first-principles full potential self-consistent linear muffin tin orbital (LMTO) method without invoking any rigid-band approximation. The scalar relativistic effects have been considered. We observed that the vHs peak at the ? point shows a shifting towards the Fermi energy with the Sr concentration and is closest to the Fermi energy for the ordered structure CaSr 3Cu 4O 8 in agreement with the experimentally observed maximum value for Tc.

  18. 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.

  19. 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.

  20. Geochemistry of alkaline earth elements (Mg, Ca, Sr, Ba) in the surface sediments of the Yellow Sea

    Microsoft Academic Search

    Guebuem Kim; Han-Soeb Yang; Thomas M. Church

    1999-01-01

    The concentrations of alkaline earth elements were measured in the surface sediments of the Yellow Sea in an attempt to establish their sources from horizontal distributions. The maximum concentrations of Mg are found in the central Yellow Sea, and its horizontal distribution is mainly controlled by quartz dilution. The concentrations of Ca and Sr increase toward the southeastern Yellow Sea

  1. Neonatal severe hyperparathyroidism due to compound heterozygous mutation of calcium sensing receptor (CaSR) gene presenting as encephalopathy.

    PubMed

    Kulkarni, Abhishek; Mohite, Mahesh; Vijaykumar, Ramaa; Bansode, Prasanna; Murade, Sachin; Tamhankar, Parag M

    2014-11-01

    The authors report a 14-d-old neonate who presented with lethargy, polyuria and dehydration and was found to have severe hypercalcemia with hyperparathyroidism. This neonate was treated with saline hydration, diuresis and injection pamidronate. Genetic analysis revealed a compound heterozygous mutation of CaSR. PMID:24763815

  2. Preparation of 95 K Bi2CaSr2Cu2O8+? Superconductor from Citrate Precursors

    NASA Astrophysics Data System (ADS)

    Wang, N. H.; Wang, C. M.; Kao, H.-C. I.; Ling, D. C.; Ku, H. C.; Lii, K. H.

    1989-09-01

    Highly crystalline single phase “2122”, Bi2CaSr2Cu2O8+?, sample with ?{=}0.25 has been prepared from citrate precursors with pyrolysis. Stable and bulk superconductivity with Tc(onset){=}99 K and Tc(zero){=}95 K was reproducibly detected by the magnetic susceptibility and electrical resistivity measurements, respectively.

  3. High sensitivity torque magnetometry of small Bi 2CaSr 2Cu 2O 8 single crystals

    NASA Astrophysics Data System (ADS)

    Steinmeyer, F.; Kleiner, R.; Müller, P.

    1991-12-01

    We have developed a very sensitive torsion wire magnetometer with in situ variation of the sample orientation. In Bi 2CaSr 2Cu 2O 8 at field orientations close to the CuO planes, we observe torque jumps directed to perfect alignment. We interpret this as lock-in of the vortices to the interlayer space.

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

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  5. 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.

  6. Spin fluctuations in the ruthenium oxides RuO2, SrRuO3, CaRuO3, and Sr2RuO4 probed by Ru NMR

    Microsoft Academic Search

    H. Mukuda; K. Ishida; Y. Kitaoka; K. Asayama; R. Kanno; M. Takano

    1999-01-01

    By means of Ru NMR, magnetic properties in three-dimensional (3D) perovskites SrRuO3 (ferromagnet) and CaRuO3 (exchange enhanced paramagnet) were investigated and compared with those in the two-dimensional (2D) layered perovskite Sr2RuO4 (superconductor), RuO2, and Ru metal (Pauli paramagnet). We found that 4d-spin contributions in the Knight shift and 101(1\\/T1) of Ru are predominant in SrRuO3, CaRuO3, and Sr2RuO4, but not

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

    SciTech Connect

    Napolsky, Ph.S.; Drozhzhin, O.A. [Department of Chemistry, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Istomin, S.Ya., E-mail: istomin@icr.chem.msu.ru [Department of Chemistry, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Kazakov, S.M.; Antipov, E.V. [Department of Chemistry, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Galeeva, A.V.; Gippius, A.A. [Department of Physics, Moscow State University, Leninskie Gory, Moscow 119991 (Russian Federation); Svensson, G. [Department of Materials and Environmental Chemistry, Stockholm University, Stockholm S-10691 (Sweden); Abakumov, A.M.; Van Tendeloo, G. [EMAT, University of Antwerp, Groenenborgerlaan, Antwerp 171, B-2020 (Belgium)

    2012-08-15

    Oxygen deficient perovskites Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a={radical}(2) Multiplication-Sign a{sub per}, b=2 Multiplication-Sign a{sub per}, c={radical}(2) Multiplication-Sign a{sub per} (a{sup 0}b{sup -}b{sup -} tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}x{<=}0.6 and compound Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92} were prepared in air at 1573 K for 48 h. The crystal structure of Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92} was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) A, R{sub p}=0.057, R{sub wp}=0.056, {chi}{sup 2}=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 and Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92(1)} are 15.5, 15.1, and 13.8 ppm K{sup -1}, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr{sub 0.15}Ca{sub 0.6}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} and Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 2.92}. Conductivity of Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}y{<=}0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the {sigma} value from {approx}1 to {approx}50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E{sub p}) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6. - Graphical abstract: The substitution of cobalt in the 314-phase Sr{sub 0.75}Y{sub 0.25}CoO{sub 2.62} by manganese leads to the formation of oxygen deficient compounds Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5 and 0.75, with the cubic and orthorhombic perovskite structures. The conductivity of the x=0.5 sample (110 S/cm) at 1173 K is substantially higher in comparison with x=0.75 (44 S/cm). Together with comparable TEC values for x=0.5 (15.5 ppm K{sup -1}) and 0.75 (15.1 ppm K{sup -1}) samples this makes the former one a promising cathode material for IT-SOFC. Partial replacement of Sr by Ca in Sr{sub 0.75}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y} leads to the formation of the solid solution with the orthorhombic perovskite structure, Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, 0.1{<=}y{<=}0.6. Along with Sr{sub 0.75}Y{sub 0.25}Co{sub 0.5}Mn{sub 0.5}O{sub 3-y}, novel perovskite Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} represent promising cathode material for IT-SOFC due to low TEC value (13.8 ppm K{sup -1}) and high conductivity of 135 S/cm at 1173 K. Highlights: Black-Right-Pointing-Pointer Mn-doped 314-phases Sr{sub 0.75}Y{sub 0.25}Co{sub 1-x}Mn{sub x}O{sub 3-y}, x=0.5, 0.75 were synthesized. Black-Right-Pointing-Pointer Sr{sub 0.75-x}Ca{sub x}Y{sub 0.25}Co{sub 0.25}Mn{sub 0.75}O{sub 3-y}, x=0.1--0.6, Ca{sub 0.75}Y{sub 0.25}Mn{sub 0.85}Co{sub 0.15}O{sub 3-y} were made. Black-Right-Pointing-Pointer High-temperature conductivity properties and crystal structure were studied. Black-Right-Pointing-Point

  8. Dense and strong plasma initiated by Ca0.7Sr0.3TiO3 ceramic

    NASA Astrophysics Data System (ADS)

    Li, Ruixing; Tang, Qing; Yin, Shu; Yamaguchi, Yukishige; Sato, Tsugio

    2004-08-01

    In order to find a kind of material that is able to initiate plasma avalanches, Ca0.7Sr0.3TiO3 ceramic, which possesses high permittivity, was prepared by liquid phase sintering and used as a dielectric barrier to decompose CO2 in order to investigate the efficiency and characteristics of this ceramic. The results were compared with commercial alumina and silica glass, which possess lower permittivities, but however, were widely used in previous studies. The mechanical and dielectric properties of Ca0.7Sr0.3TiO3 were greatly enhanced by adding 0.5 wt. % Li2Si2O5 as a sintering additive. Although Ca0.7Sr0.3TiO3 without an additive was fractured before the arcing plasma, that which was sintered with 0.5 wt. % Li2Si2O5 successfully generated a dielectric barrier discharge (DBD) plasma and the CO2 conversion was much higher than with those using an alumina or silica glass barrier. The plasma behaviors of using different dielectric materials were studied during the processes of the DBD plasma burst. It was found that the density and strength of current pulses increased with increasing permittivity, and as a consequence, very dense and strong current pulses were initiated by this Ca0.7Sr0.3TiO3 with 0.5 wt. % Li2Si2O5 ceramic because of its high permittivity; likewise, they were efficient in reducing CO2. The density and strength of current pulses are also found to be the dominative parameters of the plasma reaction. This Ca0.7Sr0.3TiO3 ceramic was sintered using Li2Si2O5 as a sintering additive and used as a dielectric barrier of DBD for the first time.

  9. Equilibrium phase relations in the Bi-Ca-Sr-Cu-O system at 850 and 900 degree C

    SciTech Connect

    Lee, C.; Chen, J.; Wen, W.; Perng, T.; Wu, J.; Wu, T.; Chin, T. (Department of Materials Science Engineering, National Tsing Hua University, Hsinchu, Taiwan (Republic of China)); Liu, R.; Wu, P. (Industrial Technology Research Institute, Hsinchu, Taiwan (Republic of China))

    1990-07-01

    The phase relations of equilibrium compounds in the pseudoternary system Bi{sub 2}O{sub 3}-(Ca,Sr)O-CuO at 850 and 900 {degree}C were studied. The ratio of Ca:Sr was fixed at 1:2. Starting materials of Bi{sub 2}O{sub 3}, CaCO{sub 3}, SrCo{sub 3} and CuO with various ratios were mixed, pressed into pellets, and heated at or above and then brought back to 850 or 900 {degree}C for different durations to ensure that equilibrium had been reached. The products were cooled in air or quenched in liquid nitrogen and then identified by x-ray powder diffraction. At 850 {degree}C, only the superconducting phase, Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub {ital x}}(2122), was observed inside the triangle. The other stable phases were all positioned on the boundary lines, and included CuO{center dot}3/5MO, CuO{center dot}MO, CuO{center dot}2MO, 1.1/2Bi{sub 2}O{sub 3}{center dot}0.9MO, Bi{sub 2}O{sub 3}{center dot}4MO, Bi{sub 2}O{sub 3}{center dot}9MO, and a solid solution, Bi{sub 2}O{sub 3}{center dot}xMO, where 0.16 {le} x {le} 0.82 and MO represents 1/3(CaO{center dot}2SrO). At 900 {degree}C, the above boundary line phases remained stable but the 2122 phase was not observed. The tie lines among the stable phases in the two isotherms were established.

  10. Multiferroicity in geometrically frustrated ?-MCr2O4 systems (M = Ca, Sr, Ba)

    NASA Astrophysics Data System (ADS)

    Zhao, Li.; Lan, Tian-Wey; Wang, Kuen-Jen; Chien, Chia-Hua; Hung, Tsu-Lien; Luo, Jiu-Yong; Chao, Wei-Hsiang; Chang, Chung-Chieh; Chen, Yang-Yuan; Wu, Maw-Kuen; Martin, Christine

    2012-08-01

    We have successfully synthesized three quasi-two-dimensional geometrically frustrated magnetic compounds (?-MCr2O4, M= Ca, Sr, Ba) using the spark-plasma-sintering technique. All these members of the ?-MCr2O4 family consist of the stacking planar triangular lattices of Cr3+ spins (S=3/2), separated by nonmagnetic alkaline-earth ions. Their corresponding magnetic susceptibility, specific heat, dielectric permittivity, and ferroelectric polarization are systematically investigated. A long-range magnetic ordering arises below the Néel temperature (around 40 K) in each member of the ?-MCr2O4 family, which changes to the quasi-120? proper-screw-type helical spin structure at low temperature. A very small but confirmed spontaneous electric polarization emerges concomitantly with this magnetic ordering. The direction of electric polarization is found within the basal triangular plane. The multiferroicity in ?-MCr2O4 can not be explained within the frameworks of the magnetic exchange striction or the inverse Dzyaloshinskii-Moriya interaction. The observed results are more compatible with the newly proposed Arima mechanism that is associated with the d-p hybridization between the ligand and transition-metal ions, modified by the spin-orbit coupling. The evolution of multiferroic properties with the increasing interplanar spacing (as M changes from Ca to Ba) reveals the importance of interlayer interaction in this new family of frustrated magnetic systems.

  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. Combinatorial pulsed laser deposition of Fe, Cr, Mn, and Ni-substituted SrTiO3 films on Si substrates.

    PubMed

    Kim, Dong Hun; Bi, Lei; Aimon, Nicolas M; Jiang, Peng; Dionne, Gerald F; Ross, C A

    2012-03-12

    Combinatorial pulsed laser deposition (CPLD) using two targets was used to produce a range of transition metal-substituted perovskite-structured Sr(Ti(1-x)M(x))O(3-?) films on buffered silicon substrates, where M = Fe, Cr, Ni and Mn and x = 0.05-0.5. CPLD produced samples whose composition vs distance fitted a linear combination of the compositions of the two targets. Sr(Ti(1-x)Fe(x))O(3-?) films produced from a pair of perovskite targets (SrTiO(3) and SrFeO(3) or SrTiO(3) and SrTi0(0.575)Fe(0.425)O(3)) had properties similar to those of films produced from single targets, showing a single phase microstructure, a saturation magnetization of 0.5 ?(B)/Fe, and a strong out-of-plane magnetoelastic anisotropy at room temperature. Films produced from an SrTiO(3) and a metal oxide target consisted of majority perovskite phases with additional metal oxide (or metal in the case of Ni) phases. Films made from SrTiO(3) and Fe(2)O(3) targets retained the high magnetic anisotropy of Sr(Ti(1-x)Fe(x))O(3-?), but had a much higher saturation magnetization than single-target films, reaching for example an out-of-plane coercivity of >2 kOe and a saturation magnetization of 125 emu/cm(3) at 24%Fe. This was attributed to the presence of maghemite or magnetite exchange-coupled to the Sr(Ti(1-x)Fe(x))O(3-?). Films of Sr(Ti(1-x)Cr(x))O(3-?) and Sr(Ti(1-x)Mn(x))O(3-?) showed no room temperature ferromagnetism, but Sr(Ti(1-x)Ni(x))O(3-?) did show a high anisotropy and magnetization attributed mainly to the perovskite phase. Combinatorial synthesis is shown to be an efficient process for enabling evaluation of the properties of epitaxial substituted perovskite films as well as multiphase films which have potential for a wide range of electronic, magnetic, optical, and catalytic applications. PMID:22353232

  13. An alternate preparation for grain aligned structures of (Bi, Pb) 2Ca 2Sr 2Cu 3O z

    NASA Astrophysics Data System (ADS)

    Arendt, R. H.; Garbauskas, M. F.; Lay, K. W.; Tkaczyk, J. E.

    1991-05-01

    A unique process for the preparation of bulk, grain aligned (Bi, Pb) 2Ca 2Sr 2Cu 3O z (2223), is presented. The process starts with the magnetic alignment of Bi 2CaSr 2Cu 2O z (2122), in a heptane slurry with sufficient particulate PbO, Ca 2CuO 3 and CuO necessary to form the (2223). Following evaporation of the heptane to physically set the alignment, the compacts are reacted and sintered at high temperature, for long times, to generate the final (2223) product. Critical currents, Jc on the order of 700 A cm -2 at 77 K and zero magnetic field have been obtained. The severe degradation of Jc with increasing fields suggests that grain alignment alone is not sufficient criterion for achieving large values of Jc and that other factors, such as bulk density and connectivity between grains, are of equal or greater importance.

  14. Prostate cancer metastatic to bone has higher expression of the calcium-sensing receptor (CaSR) than primary prostate cancer

    PubMed Central

    Feng, Jie; Xu, Xiaojun; Li, Bo; Brown, Edward; Farris, Alton B.; Sun, Shi-Yong; Yang, Jenny J.

    2015-01-01

    The calcium-sensing receptor (CaSR) is the principal regulator of the secretion of parathyroid hormone and plays key roles in extracellular calcium (Ca2+o) homeostasis. It is also thought to participate in the development of cancer, especially bony metastases of breast and prostate cancer. However, the expression of CaSR has not been systematically analyzed in prostate cancer from patients with or without bony metastases. By comparing human prostate cancer tissue sections in microarrays, we found that the CaSR was expressed in both normal prostate and primary prostate cancer as assessed by immunohistochemistry (IHC). We used two methods to analyze the expression level of CaSR. One was the pathological score read by a pathologist, the other was the positivity% obtained from the Aperio positive pixel count algorithm. Both of the methods gave consistent results. Metastatic prostate cancer tissue obtained from bone had higher CaSR expression than primary prostate cancer (P <0.05). The expression of CaSR in primary prostate cancers of patients with metastases to tissues other than bone was not different from that in primary prostate cancer of patients with or without bony metastases (P >0.05). The expression of CaSR in cancer tissue was not associated with the stage or status of differentiation of the cancer. These results suggest that CaSR may have a role in promoting bony metastasis of prostate cancer, hence raising the possibility of reducing the risk of such metastases with CaSR-based therapeutics.

  15. 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.

  16. [Fabrication and luminescent properties of Dy3+ doped Sr(1-x)Ca(x)MoO4].

    PubMed

    Guan, Li; Li, Xu; Tian, Xiao-dong; Jin, Li-tao; Yang, Yan-min; Li, Pan-lai; Yang, Zhi-ping

    2011-03-01

    Dy3+ doped Sr(1-x)CaxMoO4 phosphors were prepared by solid state method in the present paper. The crystal structure, luminescent properties and the effect of x on the luminescent properties were studied by XRD, SEM, excitation, emission and color parameters. The XRD patterns indicated that the samples were single phase of CaMoO4 and SrMoO4 when x=1 and x=0. It can be seen that the crystal size of samples prepared at 750 degrees C for 3 h were 0.2-1.0 microm, which was matched with solid state luminescent device. The excitation spectra monitored at 576 nm were composed of a broad band at 250-340 nm and a series of narrow band at 340-460 nm. The excitation peaks situation of CT transition and the excitation peaks intensity of narrow bands varied with Sr/Ca. The emission spectra excited by 350 nm were composed of two broad bands at 470 and 576 nm, which were attributed to the transition of 4F(9/2)-->(6)H(15/2) and (4)F(9/2)-->(6)H(13/2). The emission intensity of yellow and blue emission varied with the value of Sr/Ca. PMID:21595204

  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. Synthesis and characterization of glass-ceramic Bi2- xGaxSr2Ca2Cu3O10+y superconductors

    NASA Astrophysics Data System (ADS)

    Aksan, M. A.; Yakinci, M. E.; Balci, Y.

    2000-07-01

    We have melt quenched a series of Ga substituted Bi2- xGaxSr2Ca2Cu3O10+y samples with the compositions with x = 0.2, 0.4, 0.6, 0.8 and 1.0. Microstructure, thermal properties including crystallization activation energy, magnetic and superconducting properties were investigated. We have found that Ga3+ ions have a solid solubility limit in the BSCCO system and this limit was passed at x = 0.6. Below this limit HTc BSCCO n = 3 phase was obtained, but after the solid solubility limit samples yield multiphase superconducting properties. Extended heat treatment at 840°C displayed no suppression of the solid solubility limit. The crystallization kinetic studies were investigated using non-isothermal kinetic models of Kissinger and Augis-Bennet. Higher crystallization activation energies, Ea, were obtained compared to unsubstituted BSCCO materials, glassification improved and glass handling time increased. The substitution had a slight effect on Jc, the flux pinning in the material was improved and better Jc values were obtained below the solid solubility limit.

  20. Influence of substitution on dielectric and impedance spectroscopy of Sr 1 - xBi 2 + yNb 2O 9 ferroelectric ceramics synthesized by chemical route

    NASA Astrophysics Data System (ADS)

    Dhak, D.; Dhak, P.; Pramanik, P.

    2008-03-01

    Nanocrystalline powders of Sr 1 - xBi 2 + yNb 2O 9 (SBN, x = 0.0, 0.1, 0.2, 0.3, and 0.4; y = 0, 0.066, 0.133, 0.200, and 0.266) were prepared by aqueous solution method using water-soluble Sr-EDTA, Bi-EDTA and Nb-tartarate as the starting materials. XRD showed that the samples were free from fluorite or pyrochlore phase within heat-treatment temperature from 550 to 600 °C. Average crystallite size and particle diameter were observed to be between 10 and 25 nm, which were analyzed through XRD and TEM, respectively. Bi-substitution has substantially improved the sinterability of SBN and enabled to achieve high density (96%), which was otherwise difficult in the case of pure SBN. The dielectric properties of SBN ceramics were significantly enhanced by the partial replacement of Sr 2+ ions by the trivalent bismuth ions. The complex impedance diagrams of Bi-substituted SBN, x = 0.4 ceramics exhibited only one semicircle indicating a significant contribution from the grains. In contrast, the impedance plots for pure and other substituted SBN ceramics show an additional low-frequency semicircle, which was attributed to the blocker size effects. The dielectric behavior of pure and Bi-substituted SBN ceramics was rationalized using the impedance and modulus data.

  1. 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., E-mail: otto.haas@bluewin.ch [Energy and Material Research Consulting, CH-6648 Minusio (Switzerland); Ludwig, Chr. [General Energy Research, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Ecole Polytechnique Federale de Lausanne, ENAC-IIE, CH-1015 Lausanne (Switzerland); Bergmann, U. [Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025 (United States); Singh, R.N. [Banaras Hindu University, Chemistry Department, Varanasi 221005 (India); Braun, A.; Graule, T. [Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for High Performance Ceramics, CH-8600 Duebendorf (Switzerland)

    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.

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

    USGS Publications Warehouse

    Flannery, Jennifer A.; Poore, Richard Z.

    2013-01-01

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

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

    PubMed Central

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

    2010-01-01

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

  4. Superconducting properties of Bi 2Sr 2CaCu 2O y/Bi 2Sr 2CuO x multilayer thin films

    NASA Astrophysics Data System (ADS)

    Matsushima, T.; Ichikawa, Y.; Adachi, H.; Setsune, K.; Wasa, K.

    1990-12-01

    We have prepared Bi 2Sr 2CaCu 2O y(BSCCO)/Bi 2Sr 2CuO x(BSCO) multilayer thin films using a multitarget RF magnetron sputtering technique. Our BSCO films exhibit a semiconductor-like transport property, and BSCCO/BSCO multilayers are supposed as superconductor/nonsuperconductor multilayers. The x-ray diffraction measurements showed that all of the multilayers with various thicknesses have the c-axis normal to the substrate surface. In the multilayer films with the constant BSCO layer thickness of 100Å, an T c onset slightly decreases from 85 K to 75 K with decreasing the BSCCO layer thickness from 250Å to 31Å. From this result it seems that interlayer coupling in BSCCO/BSCO multilayers is weaker than in YBaCuO/PrBaCuO multilayers.

  5. Phase equilibria in the pseudo-binary systems LiF-CaAlF 5 and LiF-SrAlF 5

    NASA Astrophysics Data System (ADS)

    Chen, H. B.; Fan, Shiji; Xia, Haiping; Fei, Yiting

    2002-02-01

    The phase equilibria in pseudo-binary systems LiF-CaAlF 5 and LiF-SrAlF 5 have been studied by means of differential thermal analysis and X-ray diffraction. The two analogous phase diagrams show that the compounds LiCaAlF 6 and LiSrAlF 6 melt congruently with the composition of LiF:CaAlF 5=1:1 and LiF:SrAlF 5=1:1 at 814°C and 765°C, respectively. There are two eutectic relationships in the system LiF-CaAlF 5, one between the compounds LiF and LiCaAlF 6 with the eutectic temperature of 705°C, the other between LiCaAlF 6 and CaAlF 5 with the eutectic temperature of 781°C. The system LiF-SrAlF 5 also has two eutectic relationships at the left or right side of the compound LiSrAlF 6 with the eutectic temperatures of 673°C and 705°C, respectively. Using the feed materials with the stoichiometry compositions, large-size fluoride laser crystals Cr 3+:LiCaAlF 6 and Cr 3+:LiSrAlF 6 with high quality have been grown successfully by the vertical Bridgman method.

  6. 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. [Ames Laboratory; Gulo, Fakhili [Ames Laboratory; Corbett, John D. [Ames Laboratory

    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.

  7. Temperature dependence of the positron annihilation parameters in Bi2-xPbxCa2Sr2Cu3Oy and Bi2CaSr2Cu2Oy superconductors

    NASA Astrophysics Data System (ADS)

    Pujari, P. K.; Datta, T.; de, Udayan; Ghosh, B.

    1994-08-01

    We report the results of temperature dependence of S-parameter and lifetime (?) measurements on the normal and superconducting states of Bi2CaSr2Cu2Oy (Bi-2:1:2:2) and Bi2-xPbxCa2Sr2Cu3Oy (Bi-2:2:2:3) superconductors. A decrease of the S parameter as well as ? below Tc is seen for both compounds. These observations are interpreted qualitatively considering a reported positron-density-distribution calculation and invoking the local charge-transfer process from CuO2 to Bi-O planes at the onset of the superconducting transition. The possible influence of sample preparation conditions and structural changes on the temperature dependencies of the positron annihilation parameters across Tc is also discussed.

  8. Development of anode material based on La-substituted SrTiO 3 perovskites doped with manganese and\\/or gallium for SOFC

    Microsoft Academic Search

    M. J. Escudero; J. T. S. Irvine; L. Daza

    2009-01-01

    Materials based on La-substituted SrTiO3 perovskites doped with manganese and\\/or gallium for SOFC have been studied as novel anodes for solid oxide fuel cell. La4Sr8Ti11Mn1?xGaxO38?? (0?x?1) oxides were synthesized by solid state reaction and the influences of the manganese and\\/or gallium content on the structure, morphology, thermal properties and electrical conductivity of these materials has been investigated. All compounds show

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

    SciTech Connect

    Ali, Irshad, E-mail: irshadalibzu@gmail.com [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan); Islam, M.U. [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan); Ashiq, Muhammad Naeem, E-mail: naeemashiqqau@yahoo.com [Institute of Chemical Sciences, Bahauddin Zakariya University, Multan 60800 (Pakistan); Khan, Hasan M. [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan); Iqbal, M. Asif [Department of Physics, Bahauddin Zakariya University, Multan 60800 (Pakistan); Nust College of Electrical and Mechanical Engineering, Islamabad (Pakistan); Najam-Ul-Haq, Muhammad [Institute of Chemical Sciences, Bahauddin Zakariya University, Multan 60800 (Pakistan)

    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. 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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  12. 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.

  13. Nature of the ferromagnetism induced by nonmagnetic substitutions on the Ru site of CaRuO3

    Microsoft Academic Search

    V. Hardy; B. Raveau; R. Retoux; N. Barrier; A. Maignan

    2006-01-01

    In spite of many efforts, the magnetic ground state of CaRuO3 remains enigmatic to date and is still the subject of intense controversy. Among the peculiarities of this ruthenate is the puzzling fact that small levels of substitution on the magnetic Ru4+ sublattice by nonmagnetic cations were found to induce the development of a ferromagnetic transition. The present paper addresses

  14. Mean-field analysis of La_1-x(CaSr)_xMnO3 films

    NASA Astrophysics Data System (ADS)

    O'Donnell, J. O.; Rzchowski, M.; Onellion, M.; Eckstein, J. N.; Bozovic, I.

    1996-03-01

    We have measured the magnetoresistance and magnetization of thin La_1-x (CA,Sr)_xMnO3 films. The film microstructure was determined by atomic force microscopy and scanning tunneling microscopy. The lattice parameters were measured using x-ray diffraction. We found that the growth morphology could be controlled by stoichiometry, and was either single crystal films under biaxial strain or films with strain relief obtained by incorporating defects. We suceeded in growing both types of films with tetragonal symmetry, rather than the bulk orthorhombic symmetry. By lowering the point group symmetry, we obtained anisotropic magnetoresistance results. We analyzed the results using a mean field theory and obtained excellent agreement with experimental results. In particular, we explained the change in magnetoresistance from positive for field applied perpendicular to the film plane to negative for field applied in the film plan.[1] In addition, the change of resistivity with applied field at both low (0-200 Oe) and high (0-7 Tesla) applied field can be explained within a mean field model.

  15. Vortex motion and energy dissipation in single crystal (Bi?Pb)?Sr?Ca?Cu?O

    NASA Astrophysics Data System (ADS)

    Pradhan, A. K.; Hazell, S. J.; Hodby, J. W.; Chen, C.; Hu., Y.; Wanklyn, B. M.

    1993-01-01

    We have measured the magnetoresistance and I- V characteristics both in with and without magnetic fields, applied parallel to the ab-plane at different temperatures in single crystal Bi 1.6Pb 0.4Sr 2Ca 2Cu 3O y. The I- V characteristics in both cases obey the power law behaviour, V? I?( T) . The zero-field power law exponents clearly show the existence of a Nelson-Kosterlitz jump confirming the transition to be KT-type. The observation of a clear power law in the I- V characteristics, an abrupt change in the magnetic field dependent power law exponent at 2 T along with a non-linear behaviour in the magnetoresistance predicts a Lorentz-force independent dissipation which can be explained in terms of two-dimensional vortex-antivortex pair breaking because of the c-axis misalignment within the crystal. The effect of a magnetic field on the KT transition has been explained in terms of excessive vortices induced by the magnetic field.

  16. Molecular beam epitaxy growth and microstructure of thin superconducting Bi 2Sr 2CaCu 2O x films

    NASA Astrophysics Data System (ADS)

    Brazdeikis, A.; Vailionis, A.; Flodseröm, A. S.; Træholt, C.; Flodström, A. S.

    1995-02-01

    The microstructure of molecular beam epitaxy (MBE) grown Bi 2Sr 2CaCu 2O x films has been studied by reflection high-energy electron diffraction (RHEED), high-resolution electron microscopy (HREM) and X-ray diffraction (XRD). In situ recorded RHEED images of as-grown films show two-dimensional growth, 90° oriented domains (twist domains) and an incommensurate superstructure. For the first time, the presence of both 2201 and 2223 stacking faults in Bi 2Sr 2CaCu 2O x thin films is reported. These local structural defects are not easily observed by standard XRD techniques. To examine the structure of the films quantitatively, a general one-dimensional XRD model was fitted to the experimental XRD data. The model considered changes in peak intensities, positions and line-widths, and thus allowed a quantitative determination of the structural properties of the high- Tc superconducting thin films.

  17. Characterization of the intra-unit-cell magnetic order in Bi2Sr2CaCu2O8+?

    NASA Astrophysics Data System (ADS)

    Mangin-Thro, L.; Sidis, Y.; Bourges, P.; De Almeida-Didry, S.; Giovannelli, F.; Laffez-Monot, I.

    2014-03-01

    As in YBa2Cu3O6+x and HgBa2CuO8+?, the pseudogap state in Bi2Sr2CaCu2O8+? is characterized by the existence of an intra-unit-cell magnetic order revealed by polarized neutron scattering technique. We report here a supplementary set of polarized neutron scattering measurements for which the direction of the magnetic moment is determined and the magnetic intensity is calibrated in absolute units. These data allow a close comparison between bilayer systems YBa2Cu3O6+x and Bi2Sr2CaCu2O8+? and raise important questions concerning the range of the magnetic correlations and the role of disorder around optimal doping.

  18. Superconductivity induced by carrier injection into non-superconducting Bi2Sr2CaCu2O8 + ?

    NASA Astrophysics Data System (ADS)

    Simsek, Y.; Koval, Y.; Gieb, K.; Müller, P.

    2014-09-01

    Doping by carrier injection was investigated in strongly oxygen-depleted Bi2Sr2CaCu2O8 + ?. In order to perform four point c-axis measurements in non-superconducting samples, a new fabrication technique was developed. We were able to show that non-superconducting Bi2Sr2CaCu2O8 + ? can be converted into a superconducting, even overdoped state only by applying a large bias current along the c-axis. A critical temperature of 91 K and a c-axis critical current density of 2000 A cm-2 were achieved. Moreover, the doping effect is persistent and reversible resembling the resistive-memory switching effect observed earlier in various oxides. The mutual influence of oxygen doping and change of the charge carrier concentration by carrier injection is discussed.

  19. Role of electron correlation and long range magnetic order in the electronic structure of Ca(Sr)RuO3

    NASA Astrophysics Data System (ADS)

    Singh, Ravi Shankar; Medicherla, V. R. R.; Maiti, Kalobaran

    2008-04-01

    The room temperature photoemission spectra collected at different surface sensitivities reveal qualitatively different surface and bulk electronic structures in CaRuO3 and SrRuO3. The extracted bulk spectra are dominated by the coherent feature intensity with a weak correlation induced feature at higher binding energies. The First principle calculations provide a wonderful representation of the bulk spectra for the effective electron correlation strength, U/W?0.2 as expected for highly extended 4d systems. This resolves a long-standing issue that arose due to the prediction of large U/W similar to 3d systems. Photoemission spectra across the magnetic phase transition reveal unusual evolution exhibiting a large reduction in the coherent feature intensity in the bulk spectrum of SrRuO3, while the bulk spectrum in CaRuO3 remains almost the same down to the lowest temperature studied.

  20. 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.

  1. A new superconducting material in a Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O mixed system

    SciTech Connect

    Tennekone, K.; Samarappuli, S.H.S.P.; DissanaYake, M.A.; Ileperuma, O.A.

    1989-04-10

    A new superconducting phase has been found in a mixed system prepared from the YBa/sub 2/Cu/sub 3/O/sub 7-/delta// and Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 9-/delta// high-T/sub c/ materials. The new compound shows an onset of resistivity transition at --100 K and zero resistivity below --50 K. Powder X-ray diffraction pattern of the new compound differs completely from those of YBa/sub 2/Cu/sub 3/O/sub 7-/delta// and Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 9-/delta//. The materials prepared using a mixture of the oxides and carbonates with identical cation stoichiometric ratios, on the other hand, does not exhibit superconductivity.

  2. Effects of the substitution of Pb for Ba in (Ba,Sr)TiO3 films on the temperature stability of the tunable properties

    NASA Astrophysics Data System (ADS)

    Xia, Yidong; Cai, Cong; Zhi, Xiaoyuan; Pan, Bai; Wu, Di; Meng, Xiangkang; Liu, Zhiguo

    2006-05-01

    The tunable property and thermal stability of (Ba0.25Pb0.25)Sr0.5TiO3 films derived by pulsed laser deposition have been investigated. The substitution of Pb for Ba in (Ba,Sr)TiO3 (BST) system has been revealed to raise the transition temperature close to room temperature (RT) and enhance the tuning property. It is proposed that nanopolar regions would occur in the films in the paraelectric state at RT, arising from the addition of Pb2+ into the A site of pervoskite structure of BST. This induces the relaxor behavior and diffuse phase transition. Hence, low temperature-dependent tunability is obtained due to the broadening of dielectric constant peak. These results demonstrated that Pb substitution could be a simple and effective method to obtain high tunability and good temperature stability simultaneously.

  3. Improvement in current density of bulk Bi-Sr-Ca-Cu-O superconductors through a modified preparation condition

    NASA Astrophysics Data System (ADS)

    Sen, A.; Das Sharma, A.; Maiti, H. S.

    1989-05-01

    The critical current density of Bi-Sr-Ca-Cu-O superconductors of 1112 nominal composition can be improved appreciably by giving them a flash heat treatment at 1050°C for 5 minutes followed by sintering at 860°C for 18 hours. The results of XRD, TEM, magnetic susceptibility and four probe electrical measurements indicate that the grain boundary weak links are improved by this flash treatment.

  4. Conduction-cooled Bi 2Sr 2Ca 2Cu 3O x (Bi2223) magnet for magnetic separation

    Microsoft Academic Search

    H. Kumakura; T. Ohara; H. Kitaguchi; K. Togano; H. Wada; H. Mukai; K. Ohmatsu; H. Takei

    2001-01-01

    A prototype of a conduction-cooled Bi2Sr2Ca2Cu3Ox (Bi-2223) magnet system for magnetic separation was constructed. The magnet system has a 200 mm room temperature bore and generates fields higher than 1 T in an 11-liter room temperature space. The magnet axis of the system was designed to be horizontal in order to attain effective magnetic separation. The magnet consisted of 42

  5. Dense and strong plasma initiated by Ca0.7Sr0.3TiO3 ceramic

    Microsoft Academic Search

    Ruixing Li; Qing Tang; Shu Yin; Yukishige Yamaguchi; Tsugio Sato

    2004-01-01

    In order to find a kind of material that is able to initiate plasma avalanches, Ca0.7Sr0.3TiO3 ceramic, which possesses high permittivity, was prepared by liquid phase sintering and used as a dielectric barrier to decompose CO2 in order to investigate the efficiency and characteristics of this ceramic. The results were compared with commercial alumina and silica glass, which possess lower

  6. Photoluminescence and photocurrent characteristics of Eu 2 + activated MAl 2 O 4 (M = Ba, Ca, Sr) phosphors

    Microsoft Academic Search

    Sei-Ki Kim; Mi-Jae Lee; Jong-Hoo Paik; Byung-Hyun Choi

    2006-01-01

    Photoluminescence and photocurrent characteristics of Eu2 + activated MAl2O4 (M = Ba, Ca, Sr) phosphors during and after Ultraviolet ray and visible light irradiation have been investigated. The photoluminescence\\u000a (PL) and the photocurrent (PC) of the phosphors, in order to elucidate the relationship between the PL and the PC, were measured\\u000a simultaneously on the same samples within a specially designed

  7. Fermi arc in the superconducting state of impurity-doped Bi2Sr2CaCu2O8

    Microsoft Academic Search

    T. Sato; K. Terashima; K. Nakayama; S. Souma; T. Takahashi; T. Yamamoto; K. Kadowaki

    2008-01-01

    We have performed ultrahigh energy- and momentum-resolved angle-resolved photoemission spectroscopy of impurity-doped Bi2Sr2CaCu2O8 . We found that the point node of the superconducting gap near the (pi\\/2,pi\\/2) point in a pristine sample gradually evolves into a small gapless Fermi arc upon Zn or Ni doping. The shape of impurity-induced density of states inside the superconducting gap shows a marked difference

  8. Scanning tunneling spectroscopy of a superlattice superconductor: Bi 2Sr 2CaCu 2O 8

    Microsoft Academic Search

    E. L. Wolf

    1996-01-01

    It is clear that many of the cuprate superconductors are truly superlattices, composed of sheets whose individual superconducting critical temperatures may approach bulk values. Such a cuprate is Bi2Sr2CaCu2O8, often referred to as BSCCO-2212. Scanning tunneling spectroscopy (vacuum tunneling) applied toa-bBiO cleavage planes ofTc?90K BSCCO single crystals under liquid helium simultaneously provides topography and local dI\\/dVspectra (superconducting density of states:

  9. Thermodynamic investigation of the magnetic phase transitions of CaMnO3 and SrRuO3

    Microsoft Academic Search

    J. J. Neumeier; A. L. Cornelius; K. Andres

    2001-01-01

    Measurements of the linear thermal expansion Deltal\\/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 alpha and CP are used to calculate the influence of pressure on the magnetic ordering temperatures Tc through the Ehrenfest relation. Good

  10. Bi 2Sr 2Ca 1Cu 2O X film prepared using 266 nm YAG laser

    Microsoft Academic Search

    Satoru Kaneko; Yoshitada Shimizu; Hiroyasu Yuasa; Seishiro Ohya

    2002-01-01

    Epitaxial growth of Bi2Sr2Ca1Cu2OX (Bi-2212) was achieved on MgO(100) substrate using the fourth harmonics of Nd:YAG pulsed laser. The repetition rates of both 10 and 2 Hz were used to deposit Bi-2212. In order to change the repetition rate without any optical adjustment, another function generator was employed to modulate only the Q-switch (slower Q-switched). The axis of plume was

  11. Hall-effect sign reversal in CaRuO3 and SrRuO3 thin films

    Microsoft Academic Search

    S. C. Gausepohl; Mark Lee; R. A. Rao; C. B. Eom

    1996-01-01

    Hall-effect measurements on epitaxial thin films of the metallic oxides CaRuO3 and SrRuO3 show a sign change from negative to positive as temperature is increased through ~50 K. The presence of both signs together with the low- and high-temperature magnitudes of the Hall coefficients indicate that these materials are highly compensated metals. The sign change with temperature suggests that large

  12. Negative deviations from Matthiessen's rule for SrRuO3 and CaRuO3

    Microsoft Academic Search

    L. Klein; Y. Kats; N. Wiser; M. Konczykowski; J. W. Reiner; T. H. Geballe; M. R. Beasley; A. Kapitulnik

    2001-01-01

    We have measured the change in the resistivity of thin films of SrRuO3 and CaRuO3 upon introducing point defects by electron irradiation at low temperatures, and we find significant negative deviations from Matthiessen's rule. For a fixed irradiation dose, the induced change in resistivity decreases with increasing temperature. Moreover, for a fixed temperature, the increase in resistivity with irradiation is

  13. Late Neogene marine temperatures reconstruction of the Florida Platform from molluscan stable isotopic and Sr\\/Ca records

    Microsoft Academic Search

    K. Tao; E. L. Grossman

    2009-01-01

    Molluscan delta18O records provide valuable information for understanding global climate change, but their applications are limited due to uncertainty in the delta18O of ancient seawater. This uncertainty can be constrained by introducing a salinity-independent paleotemperature proxy. It has been demonstrated that seasonal Sr\\/Ca variations correlate with temperature variations in modern gastropod shells (Sosdian et al., 2006, G3 7, Q11023; Tripati

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

    Microsoft Academic Search

    M. A. Carpenter; B. Li; R. C. Liebermann

    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 7.5 GPa and 1000 C. Any variations of bulk modulus due to phase transitions are

  15. The effect of oxygen doping on the superconductivity of Bi 2CaSr 2Cu 2O 8+?

    NASA Astrophysics Data System (ADS)

    Kao, Huey-Chuen I.; Wang, Nien-Hour; Wang, Chi-Ming

    1991-12-01

    Parent Bi 2CaSr 2Cu 2O 8+? superconductor was doped with oxygen by annealing powder sample at 500 °C in the flowing oxygen atmosphere with intermittent grinding. The amount of amorphous phase and insulating layer found on the sample surface was increased with more oxygen doping. As a consequence, the sharpness and intensity of the XRD peaks were reduced, and the room temperature conductivity, T c, as well as the magnetic susceptibility were decreased.

  16. Dissociation energies of CaI, SrI, and BaI from high temperature mass spectrometry

    Microsoft Academic Search

    P. D. Kleinschmidt; D. L. Hildenbrand

    1978-01-01

    Equilibrium effusion beams containing the gaseous molecules CaI, SrI, and BaI were generated by the reaction of HI with the corresponding metal oxides at 1500 to 1900 K. Beam composition data obtained by mass spectrometry were used to determine the equilibrium constants of gaseous reactions involving the monoiodides and certain reference molecules. Reaction enthalpies then were evaluated by second and

  17. Annealing Effects on Transition Temperature of Superconductiong Bi-Sr-Ca-Cu-O Films after Ion Irradiation

    Microsoft Academic Search

    Taiji Hoshiya; Saburo Takamura; Takeo Aruga; Mamoru Kobiyama

    1989-01-01

    The effect of annealing after irradiation on the transition temperature is studied for polycrystalline Bi-Sr-Ca-Cu-O films irradiated by He ions at room temperature. The temperatures of the out-diffusion and the in-diffusion of oxygen are obtained by annealing in air and a vacuum. There is a large recovery stage around 200˜ 500°C on annealing in air after irradiation. The 110 K

  18. Sintering and hot isostatic pressing of Bi2Sr2CaCu2O(x)

    NASA Astrophysics Data System (ADS)

    Nash, A. S.; Nash, P.; Poeppel, R. B.; Goretta, K. C.

    1991-01-01

    The Bi2Sr2CaCu2O(x) phase was synthesized by solid-state reaction of oxides and carbonates. Initial compositions of Bi:Sr:Ca:Cu were 4:3:3:6 and 2:1.7:1:2. Pellets of the pure powder and powder containing 2.5, 5, or 15 wt percent Ag were cold-pressed and either sintered or hot isostatically pressed (HIPped). For HIPping, the pellets were encased in thin Ag sheets, canned in steel, and pressed at 105 MPa in argon at 800 or 850 C. HIPping produced dense specimens, but sintering did not. HIPping induced very little decomposition of the Bi2Sr2CaCu2O(x), but a post-HIP anneal was needed to raise the transition temperature above 80 K. The Ag additions appeared to minimize microcracking during HIPping at 800 C. Little microcracking was evident in any of the specimens HIPped at 850 C.

  19. 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.

  20. 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 ...

  1. Interfacial magnetism in CaRuO3/CaMnO3 superlattices grown on (001) SrTiO3

    NASA Astrophysics Data System (ADS)

    He, C.; Zhai, X.; Mehta, V. V.; Wong, F. J.; Suzuki, Y.

    2011-04-01

    We have studied epitaxially grown superlattices of CaRuO3/CaMnO3 as well as an alloy film of CaMn0.5Ru0.5O3 on (001) SrTiO3 substrates. In contrast to previous experiments, we have studied CRO/CMO superlattices with a constant CRO thickness and variable CMO thickness. All superlattices exhibit Curie temperatures (TC) of 110 K. The saturated magnetization per interfacial Mn cation has been found to be 1.1 ?B/Mn ion. The TC's of the superlattices are much lower than the TC of the alloy film while the saturated magnetization values are larger than that of the alloy film. These observations suggest that interdiffusion alone cannot account for ferromagnetism in the superlattices and that double exchange induced FM must play a role at the interfaces.

  2. 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

  3. Oxygen partial pressure dependence of magnetic, optical and magneto-optical properties of epitaxial cobalt-substituted SrTiO3 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 (SrTi0.70Co0.30O3-?) 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 (Ms). Increasing oxygen pressure during growth reduced Ms, 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. 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.

  5. Phase transitions and equations of state of alkaline earth fluorides CaF2, SrF2, and BaF2 to Mbar pressures

    E-print Network

    Duffy, Thomas S.

    Phase transitions and equations of state of alkaline earth fluorides CaF2, SrF2, and BaF2 to Mbar received 28 April 2010; published 27 May 2010 Phase transitions and equations of state of the alkaline at ambient conditions for the alkaline earth fluorides CaF2, SrF2, and BaF2. Fluorides are widely used

  6. Application of Sr Isotopic Data to Tuolumne Intrusive Series, Sierra Nevada, CA

    NSDL National Science Digital Library

    Jeff Tepper

    In this problem set students are given Rb/Sr and 87Sr/86Sr data for whole rock and mineral samples from three granitic intrusions in the Sierra Nevada. They use these data (in EXCEL) to calculate isochron ages and initial ages for the intrusions and then interpret their results. This problem is intended to teach some spreadsheet skills (linear regressions, graphing) as well as having them think about the use of radiogenic isotopes.

  7. Effect of P(O 2) and Ag content on the decompisition pathway of Bi 2Sr 2CaCu 2O x

    NASA Astrophysics Data System (ADS)

    Margulies, L.; Dennis, K. W.; Kramer, M. J.; McCallum, R. W.

    1996-02-01

    The decomposition pathway of Bi 2Sr 2CaCu 2O x (Bi2212) with 0, 2 and 10 wt.% Ag added has been examined at 0.01, 0.21, and 1 bar P(O 2) by performing scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and microprobe analysis on oil quenched samples. A series of pseudo-ternary phase diagrams at each P(O 2) was constructed to describe the evolution of the phase assemblage with temperature. Ag sdhowed limited solubility (2-3 wt.%) in the ceramic melt which depressed the reaction temperature of each step along the decomposition pathway. The first solid phases to form upon the peritectic decomposition of Bi2212 were Bi 9Sr 11Ca 5O x (9 115) and (Sr 1- xCa x) 14Cu 24O 41 (14,24) in 1 bar O 2, (9 115) and (Sr 1- xCa x)CuO 2 (11) in 0.21 bar O 2, and (11), (Sr 1- xCa x) 2CuO 3 (21) and Bi 2(Sr 1- xCa x) 3O x (23 x) in 0.01 bar O 2.

  8. Manganite based hetero-junction structure of La0.7Sr0.7-xCaxMnO3 and CaMnO3-? 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 La0.7Sr0.3-xCaxMnO3 (LSCMO) and CaMnO3-? (CMO), to obtain nonlinear RS behavior. The pnp structure not only shows nonlinear characteristics, but also a tunable characteristic with Ca substitution. PMID:26086277

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

    NASA Astrophysics Data System (ADS)

    Lee, Hong-Sub; Park, Hyung-Ho

    2015-07-01

    Resistive random access memory and the corresponding cross-point array (CPA) structure have received a great deal of attention for high-density next generation non-volatile memory. However, the cross-talk issue of CPA structure by sneak current should be overcome to realize the highest density integration. To accomplish this, the sneak current can be minimized by high, nonlinear characteristic behaviors of resistive switching (RS). Therefore this study fabricated pnp bipolar hetero-junction structure using the perovskite manganite family, such as La0.7Sr0.3?xCaxMnO3 (LSCMO) and CaMnO3?? (CMO), to obtain nonlinear RS behavior. The pnp structure not only shows nonlinear characteristics, but also a tunable characteristic with Ca substitution.

  10. Effects of a 21-day expedition to 6,194 m on human skeletal muscle SR Ca2+-ATPase.

    PubMed

    Green, H; Roy, B; Grant, S; Tupling, R; Otto, C; Pipe, A; McKenzie, D; Ouyang, J

    2000-01-01

    We investigated the effects of a 21-day expedition to the summit of Mount Denali, Alaska (6,194 m) on selected Ca2+ sequestration properties of sarcoplasmic reticulum (SR) calcium pump in vastus lateralis muscle. Muscle samples were obtained by biopsy from 5 male climbers (peak oxygen consumption, VO2peak = 52.3 +/- 2.1 mL.kg(-1).min(-1)) approximately 7 days prior to (PRE) and 4 days following (POST) the expedition. A comparison of PRE versus POST measures of maximal Ca2+-ATPase activities (117 +/- 8.5 vs. 97.6 +/- 5.6 nmol.mg protein(-1).min(-1)) and Ca2+-uptake (204 +/- 15 vs. 161 +/- 11 nmol.mg protein(-1).min(-1)) measured in crude homogenates obtained from pre-exercised muscle, indicated only an effect (p < 0.05) of the expedition on Ca2+-uptake. The reduction in Ca2+-ATPase activity, representing 16.6%, was not significant (p = 0.089). The sarco endoplasmic reticulum calcium (SERCA)-ATPase isoforms, measured using Western blotting techniques, revealed a small reduction (p < 0.05) in SERCA 1 (-4.6 +/- 1.9%), but not in SERCA 2a (+2.0 +/- 1.4%). Prior to the expedition, both Ca2+-ATPase activity and Ca2+-uptake were reduced (p < 0.05) by approximately 34 and 18%, respectively, following 40 min of a two-step continuous cycling task (20 min at 59% VO2peak and 20 min at 74% VO2peak). The exercise-induced reduction in Ca2+-ATPase activity was independent of fiber type. Only in the case of Ca2+-uptake was a lower exercise response (p < 0.05) observed following the expedition, an effect that was due to the lower resting value. It is concluded that acclimatization as experienced during a mountaineering expedition induces changes in the properties of the SR Ca2+-pump, and particularly to Ca2+-sequestering function. PMID:11256466

  11. Polyanionic hydrides from polar intermetallics AeE2 (Ae = Ca, Sr, Ba; E = Al, Ga, In).

    PubMed

    Björling, Thomas; Noréus, Dag; Häussermann, Ulrich

    2006-01-25

    The hydrogenation behavior of the polar intermetallic systems AeE2 (Ae = Ca, Sr, Ba; E = Al, Ga, In) has been investigated systematically and afforded the new hydrides SrGa2H2 and BaGa2H2. The structure of these hydrides was characterized by X-ray powder diffraction and neutron diffraction of the corresponding deuterides. Both compounds are isostructural to previously discovered SrAl2H2 (space group P3m1, Z = 1, SrGa2H2/D2: a = 4.4010(4)/4.3932(8) A, c = 4.7109(4)/4.699(1) A; BaGa2H2/D2: a = 4.5334(6)/4.5286(5) A, c = 4.9069(9)/4.8991(9) A). The three hydrides SrAl2H2, SrGa2H2, and BaGa2H2 decompose at around 300 degrees C at atmospheric pressure. First-principles electronic structure calculations reveal that H is unambiguously part of a two-dimensional polyanion [E2H2]2- in which each E atom is tetrahedrally coordinated by three additional E atoms and H. The compounds AeE2H2 are classified as polyanionic hydrides. The peculiar feature of polyanionic hydrides is the incorporation of H in a polymeric anion where it acts as a terminating ligand. Polyanionic hydrides provide unprecedented arrangements with both E-E and E-H bonds. The hydrogenation of AeE2 to AeE2H2 takes place at low reaction temperatures (around 200 degrees C), which suggests that the polyanion of the polar intermetallics ([E2]2-) is employed as precursor. PMID:16417371

  12. Influence of strontium for calcium substitution in bioactive glasses on degradation, ion release and apatite formation

    PubMed Central

    Fredholm, Yann C.; Karpukhina, Natalia; Brauer, Delia S.; Jones, Julian R.; Law, Robert V.; Hill, Robert G.

    2012-01-01

    Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO2–P2O5–CaO–Na2O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions. PMID:21993007

  13. Structure, magnetic and dielectric properties in Mn-substituted Sm1.5Sr0.5NiO4 ceramics

    NASA Astrophysics Data System (ADS)

    Wen Jia, Bo; Qiang Liu, Xiao; Ming Chen, Xiang

    2011-09-01

    The crystal structures, magnetic and dielectric properties were evaluated for Sm1.5Sr0.5Ni1-xMnxO4 (x = 0.03, 0.05, 0.1) ceramics. The Rietveld results of X-ray diffraction patterns confirmed single orthorhombic phase with the space group of Bmab (64) were obtained in Sm1.5Sr0.5Ni1-xMnxO4 (x = 0.03, 0.05) ceramics, while in Sm1.5Sr0.5Ni0.9Mn0.1O4 ceramics, apart from the main orthorhombic phase, a tiny secondary phase was detected. A magnetism characteristic of a spin glass was found in Sm1.5Sr0.5NiO4, while a complicated magnetic phenomenon was observed in Sm1.5Sr0.5Ni0.9Mn0.1O4 ceramics. The giant dielectric response was observed in these ceramics, and dielectric loss decreased with increasing the content of manganese ions. After comparing the activation energies of dielectric relaxation and electrical conduction, the low-temperature giant dielectric response should be attributed to the adiabatic small polaronic hopping process, while at high-temperature, the low frequency relaxation was mainly attributed to the grain boundary effect. The suppression of dielectric loss should be benefited from the various polar region caused by Mn-substitution.

  14. Investigations on the Structural, Electrical and Magnetic Properties of Sr Substituted Ln2NiO 4 ( Ln = Pr, Sm, Gd)

    NASA Astrophysics Data System (ADS)

    Chen, S. C.; Ramanujachary, K. V.; Greenblatt, Martha

    1993-08-01

    Solid solutions of Ln2- x Sr xNiO 4±? ( Ln = Pr, Sm) and GdSrNiO 4 were synthesized in air using conventional solid state methods and were characterized by powder X-ray diffraction, TGA, electrical resistivity, DSC, Seebeck coefficient, and magnetic susceptibility measurements. A structural transition from orthorhombic to tetragonal was observed at x ˜ 0.2 for Pr and 0.8 for Sm. For both series of compounds ( Ln = Pr, Sm), the tetragonal unit cell parameters at and c as functions of x display sharp minima and maxima, respectively, at x ˜ 0.6. The tetragonality ratio, c/at, shows a maximum at x ˜ 0.6. All the compounds are semiconducting from room temperature down to 25 K, except SmSrNiO 4 and GdSrNiO 4, which exhibit a degenerate semiconductor to semiconductor transition at ˜292 K and ˜260 K, respectively. Seebeck measurements indicate that electrons are the dominant carriers of conductivity at ambient temperature in all the compounds. The magnetic susceptibility data for all the samples, except Sm 2- xSr xNiO 4±? for x = 0.8 and 1.0, follow Curie-Weiss behavior in the temperature range 100-300 K with no evidence of long range magnetic ordering. The effect of Sr 2+ substitution on the structural, electrical, and magnetic properties of Ln2- x Sr xNiO 4±? ( Ln = Pr, Sm) is discussed in terms of the mixed-valent character of Ni 2+/3+ ions, the Ln-O vs Ni-O bond competition along the crystallographic c-axis, the size effect, the local distortion of NiO 6 octahedra, and a configurational transition in the d -manifold or nickel ions.

  15. Positron annihilation studies of Bi 2CaSr 2Cu 2O x and Bi 1.6Pb 0.4Ca 2Sr 2Cu 3O y in the region of the superconducting transition

    NASA Astrophysics Data System (ADS)

    Pujari, P. K.; Datta, T.; Manohar, S. B.; Prakash, Satya; Sastry, P. V. P. S. S.; Yakhmi, J. V.; Iyer, R. M.

    1990-03-01

    Doppler broadened annihilation radiation (DBAR) spectral parameters have been reported- for the first time- between 77 K and 300 K, for several Bi-based oxide superconductors, viz. A: single phase (2122) Bi 2CaSr 2Cu 2O x with Tc=85 K (R=0), B: a mixed phase lead doped sample containing both 2122 and 2223 with a nominal composition Bi 1.6Pb 0.4Ca 2Sr 2Cu 3O y, and, C: another 2122+2223 sample with same nominal composition as that of B but synthesised under a different heat-treatment schedule so as to yield a Tc=85 K (R=0). Analyses of these spectra using PAACFIT program yielded two components, of which the intensity of the narrow component, I N, and, the width of the broad component, T B, were seen to be the only temperature dependent parameters. At the onset of superconducting transition both T B and I N were seen to increase to a maximum value and decrease on further cooling. A double peak structure in T B vs temperature profile were observed in sample B and C, similar to one reported by us in Tl-Ca-Ba-Cu-O systems. In addition, presence of a magnetic field (1 KG) yielded no significant change in the DBAR spectral parameters. The results are discussed.

  16. Thermal expansion behaviour in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Competing effects of water and oxygen ordering

    SciTech Connect

    Zhou Qingdi [School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia); Kennedy, Brendan J., E-mail: b.kennedy@chem.usyd.edu.au [School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia); Avdeev, Maxim [Bragg Institute, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234 (Australia)

    2011-09-15

    Neutron diffractions studies reveal the presence of oxygen disorder in the oxygen deficient perovskites Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba). Synchrotron X-ray studies demonstrate that these oxides have a double perovskite-type structure with the cell size increasing as the size of the B cation increases from 8.2114(2) A for B=Ca to 8.4408(1) A for B=Ba. It is postulated that a combination of local clustering of the anions and vacancies together with water-water and water-host hydrogen bonds plays a role in defining the volume of the encapsulated water clusters and that changes in the local structure upon heating result in anomalous thermal expansion observed in variable temperature diffraction measurements. - Graphical abstract: The oxides Sr{sub 2}BSbO{sub 5.5} (B=Ca, Sr, Ba) have unusual anion disorder. There is a lag in the contraction in the cell size of Sr{sub 2}CaSbO{sub 5.5}nH{sub 2}O established from X-ray diffraction measurements following the loss of water suggesting changes on the local structure are important. Highlights: > The average structures of the defect perovskites Sr{sub 2}MSbO{sub 5.5} established. > Anion and cation disorder quantified by neutron and synchrotron X-ray diffraction. > Anomalous thermal expansion due to local clustering of anions and vacancies observed.

  17. Functional Expression of the Extracellular Calcium Sensing Receptor (CaSR) in Equine Umbilical Cord Matrix Size-Sieved Stem Cells

    PubMed Central

    Martino, Nicola Antonio; Lange-Consiglio, Anna; Cremonesi, Fausto; Valentini, Luisa; Caira, Michele; Guaricci, Antonio Ciro; Ambruosi, Barbara; Sciorsci, Raffaele Luigi; Lacalandra, Giovanni Michele; Reshkin, Stephan Joel; Dell'Aquila, Maria Elena

    2011-01-01

    Background The present study investigates the effects of high external calcium concentration ([Ca2+]o) and the calcimimetic NPS R-467, a known calcium-sensing receptor (CaSR) agonist, on growth/proliferation of two equine size-sieved umbilical cord matrix mesenchymal stem cell (eUCM-MSC) lines. The involvement of CaSR on observed cell response was analyzed at both the mRNA and protein level. Methodology/Principal Findings A large (>8 µm in diameter) and a small (<8 µm) cell line were cultured in medium containing: 1) low [Ca2+]o (0.37 mM); 2) high [Ca2+]o (2.87 mM); 3) NPS R-467 (3 µM) in presence of high [Ca2+]o and 4) the CaSR antagonist NPS 2390 (10 µM for 30 min.) followed by incubation in presence of NPS R-467 in medium with high [Ca2+]o. Growth/proliferation rates were compared between groups. In large cells, the addition of NPS R-467 significantly increased cell growth whereas increasing [Ca2+]o was not effective in this cell line. In small cells, both higher [Ca2+]o and NPS R-467 increased cell growth. In both cell lines, preincubation with the CaSR antagonist NPS 2390 significantly inhibited the agonistic effect of NPS R-467. In both cell lines, increased [Ca2+]o and/or NPS R-467 reduced doubling time values.Treatment with NPS R-467 down-regulated CaSR mRNA expression in both cell lines. In large cells, NPS R-467 reduced CaSR labeling in the cytosol and increased it at cortical level. Conclusions/Significance In conclusion, calcium and the calcimimetic NPS R-467 reduce CaSR mRNA expression and stimulate cell growth/proliferation in eUCM-MSC. Their use as components of media for eUCM-MSC culture could be beneficial to obtain enough cells for down-stream purposes. PMID:21437284

  18. Tilting structures in inverse perovskites, M3TtO (M = Ca, Sr, Ba, Eu; Tt = Si, Ge, Sn, Pb).

    PubMed

    Nuss, Jürgen; Mühle, Claus; Hayama, Kyouhei; Abdolazimi, Vahideh; Takagi, Hidenori

    2015-06-01

    Single-crystal X-ray diffraction experiments were performed for a series of inverse perovskites, M3TtO (M = Ca, Sr, Ba, Eu; Tt = tetrel element: Si, Ge, Sn, Pb) in the temperature range 500-50 K. For Tt = Sn, Pb, they crystallize as an `ideal' perovskite-type structure (Pm\\bar 3m, cP5); however, all of them show distinct anisotropies of the displacement ellipsoids of the M atoms at room temperature. This behavior vanishes on cooling for M = Ca, Sr, Eu, and the structures can be regarded as `ideal' cubic perovskites at 50?K. The anisotropies of the displacement ellipsoids are much more enhanced in the case of the Ba compounds. Finally, their structures undergo a phase transition at ??150?K. They change from cubic to orthorhombic (Ibmm, oI20) upon cooling, with slightly tilted OBa6 octahedra, and bonding angles O-Ba-O ? 174° (100?K). For the larger Ba(2+) cations, the structural changes are in agreement with smaller tolerance factors (t) as defined by Goldschmidt. Similar structural behavior is observed for Ca3TtO. Smaller Tt(4-) anions (Si, Ge) introduce reduced tolerance factors. Both compounds Ca3SiO and Ca3GeO with cubic structures at 500?K, change into orthorhombic (Ibmm) at room temperature. Whereby, Ca3SiO is the only representative within the M3TtO family where three polymorphs can be found within the temperature range 500-50?K: Pm\\bar 3m-Ibmm-Pbnm. They show tiny differences in the tilting of the OCa6 octahedra, expressed by O-Ca-O bond angles of 180° (500?K), ??174° (295?K) and 170° (100?K). For larger M (Sr, Eu, Ba), together with smaller Tt (Si, Ge) atoms, pronounced tilting of the OM6 octahedra, and bonding angles of O-M-O ? 160° (295?K) are observed. They crystallize in the anti-GdFeO3 type of structure (Pbnm, oP20), and no phase transitions occur between 500 and 50?K. The observed phase transitions are all accompanied by multiple twinning, in terms of pseudo-merohedry or reticular pseudo-merohedry. PMID:26027006

  19. Disorder effects in (LaTb)0.5(CaSr)0.5MnO3 compounds

    NASA Astrophysics Data System (ADS)

    Rana, D. S.; Mavani, K. R.; Thaker, C. M.; Kuberkar, D. G.; Kundaliya, D. C.; Malik, S. K.

    2004-06-01

    Electrical, magnetotransport, and magnetization measurements have been carried out on half-doped (La0.5-xTbx)(Ca0.38-ySr0.12+y)MnO3 (0.025?x?0.125; y=0.8x) compounds. The increase in Tb3+ and Sr2+ contents keeps the average A-site ionic radius constant at ˜1.215 Å but introduces increasing size disorder. The insulator-metal transition temperature (Tp) falls from 191 to 107 K and the Curie temperature (TC) falls from 230 to 106 K as x increases from 0.025 to 0.125. Interestingly, with increasing size disorder, the disparity between TC and Tp disappears and magnetoresistance increases around Tp but decreases at low temperatures. This is discussed in the light of phase segregation.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  1. Effect of partial substitution of Ni and Zn for Cu in CaBaLaCu 3O 7-? superconductor

    NASA Astrophysics Data System (ADS)

    Gunasekaran, R. A.; Gopalakrishnan, I. K.; Yakhmi, J. V.; Iyer, R. M.; Tomy, C. V.; Malik, S. K.

    1991-09-01

    Superconducting behaviour of the tetragonal superconductor CaBaLaCu 3O 7-? ( Tc = 70 K) has been studied as a function of substitution of Ni and Zn for Cu. Both electrical resistivity and AC susceptibility measurements show that Tc decreases monotonically with increasing concentration of the substituent ion, within the composition range where the samples remain single phase, although Zn suppresses Tc more strongly than Ni for equivalent concentrations. It is argued that the suppression of Tc in this system cannot be explained by the Abrikosov-Gorkov mechanism alone.

  2. The series Bi2Sr2Ca(n-1) Cu(n)O(2n+4) (1 less than or equal to n less than or equal to 5): Phase stability and superconducting properties

    NASA Technical Reports Server (NTRS)

    Deguire, Mark R.; Bansal, Narottam P.; Farrell, David E.; Finan, Valerie; Kim, Cheol J.; Hills, Bethanie J.; Allen, Christopher J.

    1989-01-01

    Phase relations at 850 and 870 C, melting transitions in air, oxygen, and helium were studied for Bi(2.1)Sr(1.9) CuO6 and for the Bi2Sr2Ca(n-1) Cu(n)O(2n+4) for n = 1, 2, 3, 4, 5, and infinity (CaCuO2). Up to 870 C, the n = 2 composition resides in the compatibility tetrahedron bounded by Bi(2+x)(Sr,Ca)(3-y) Cu2O8, (Sr,Ca)14 Cu24O41, Ca2CuO3, and a Bi-Sr-Ca-O phase. The n is greater than or equal to 3 compositions reside in the compatibility tetrahedron Bi(2+x)(Sr,Ca)(3-y) Cu2O8 - (Sr,Ca)14 Cu24O41 - Ca2CuO3 - CuO up to 850 C. However, Bi(2+x)Sr(4-y) Cu3O10 forms for n is greater than or equal to 3 after extended heating at 870 C. Bi(2+x)Sr(2-y) CuO6 and Bi(2+x)(Sr,Ca)(3-y) Cu2O8 melt in air at 914 C and 895 C respectively. During melting, all of the compositions studied lose 1 to 2 percent by weight of oxygen from the reduction of copper. Bi(2+x)Sr(2-y) CuO6, Bi(2+n)(Sr,Ca)(3-y) Cu2O8, and Bi(2+x)(Sr,Ca)(4-y) Cu3O10 exhibit crystallographic alignment in a magnetic field, with the c-axes orienting parallel to the field.

  3. Overcoming phase instability of RBaCo2O5+ (R = Y and Ho) by Sr substitution for application as cathodes in solid oxide fuel cells

    SciTech Connect

    Kim, Jung-Hyun [ORNL; Young Nam, Kim [University of Texas at Austin; Bi, Zhonghe [ORNL; Manthiram, Arumugam [University of Texas at Austin; Paranthaman, Mariappan Parans [ORNL; Huq, Ashfia [ORNL

    2013-01-01

    Phase instabilities of the RBaCo2O5+ (R = Y and Ho) layered-perovskites and their decompositions into RCoO3 and BaCoO3-z at 800 oC in air were investigated. This will restrict their high temperature applications such as cathodes in solid oxide fuel cell (SOFC). However, appropriate amount of Sr substitution ( 60 % for R = Y and 70 % for R = Ho) for Ba successfully stabilized the R(Ba1-xSrx)Co2O5+ phase at elevated temperatures. This can be explained by decreasing oxygen vacancies at R-O layer, decreasing R-O bonding length, and consequent improvement of structural integrity. In addition, the Sr substitution (x = 0.6 - 1.0) for Ba provided added benefit with respect to the chemical stability against Ce0.8Gd0.2O1.9 (GDC) electrolyte, which is a critical requirement for the cathodes in SOFC. Among the various compositions investigated, the Y(Ba0.3Sr0.7)Co2O5+ + GDC composite cathode delivered the optimum electrochemical performances with a stable phase demonstrating the potential as a cathode in SOFC.

  4. Functional Expression of the Extracellular Calcium Sensing Receptor (CaSR) in Equine Umbilical Cord Matrix Size-Sieved Stem Cells

    Microsoft Academic Search

    Nicola Antonio Martino; Anna Lange-Consiglio; Fausto Cremonesi; Luisa Valentini; Michele Caira; Antonio Ciro Guaricci; Barbara Ambruosi; Raffaele Luigi Sciorsci; Giovanni Michele Lacalandra; Stephan Joel Reshkin; Maria Elena Dell'Aquila; Maurizio Pesce

    2011-01-01

    BackgroundThe present study investigates the effects of high external calcium concentration ([Ca2+]o) and the calcimimetic NPS R-467, a known calcium-sensing receptor (CaSR) agonist, on growth\\/proliferation of two equine size-sieved umbilical cord matrix mesenchymal stem cell (eUCM-MSC) lines. The involvement of CaSR on observed cell response was analyzed at both the mRNA and protein level.Methodology\\/Principal FindingsA large (>8 µm in diameter)

  5. Indications of a Quantum Critical Point in Bi2Sr2CaCu2O8+? Using a Local Kondo Effect

    NASA Astrophysics Data System (ADS)

    Calleja, Eduardo; Dai, Jixia; Arnold, Gerald; Gu, Genda; McElroy, Kyle

    2014-03-01

    A complete understanding of the complex phase diagrams that are present in high temperature superconductors remains elusive. While there is an overwhelming amount of experimental data on the existence and interplay of the phases present in high Tc superconductors from local probes, much of the existing data only looks at the charge degree of freedom of the material. By substituting Fe atoms for Cu atoms in the CuO plane of Bi2Sr2CaCu2O8+? (Bi2212), we gain the ability to access the spin degree of freedom since the Fe atoms retain their magnetization below the superconducting transition temperature. This leads to a local Kondo effect which can be observed using Spectroscopic-Imaging Scanning Tunneling Microscopy (SI-STM) and the local Kondo temperature can be extracted from spectra via a theoretical model. We show that the examination of this local Kondo temperature across local and sample average doping leads to the observation of a change in the quasiparticle spin degree of freedom at a quantum critical point (QCP) with a nominal hole doping of roughly 0.22, in agreement with other probes. The observation of the QCP in Bi2212 with this new method to access the spin degree of freedom helps to unravel some of the mystery behind the complex phase diagram of Bi2212.

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

    SciTech Connect

    Nakamura, J.; Karppinen, M.; Yamauchi, H. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Karen, P. [Department of Chemistry, University of Oslo, N-0315 Oslo (Norway); Linden, J. [Department of Physics, Aabo Akademi, FIN-20500 Turku (Finland)

    2004-10-01

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

  7. Mechanochemical Synthesis and Electrical Conductivity of Bi 1.6 M 0.4 O 3 – x (M = Ca, Ca 0.5 Sr 0.5 ?, In, Y, La) Metastable Fluorite Solid Solutions

    Microsoft Academic Search

    V. V. Zyryanov; N. F. Uvarov

    2004-01-01

    Metastable fluorite solid solutions with the nominal composition Bi1.6Mo0.4O3 – x (M = Ca, Ca0.5Sr0.5?, In, Y, La) are prepared by mechanochemical synthesis, and their structure is studied by x-ray diffraction. The oxygen ion conductivity of dense samples prepared by hot pressing is measured in air.

  8. Correlations between bond lengths, Tc, and O vibration frequencies: Raman-scattering and infrared-absorption study of the 1:2:1:2 structure (Ca1-yYy)Sr2(Tl0.5Pb0.5)Cu2O7 as a function of doping

    Microsoft Academic Search

    T. Mertelj; D. Mihailovic; F. C. Matacotta; R. S. Liu; J. R. Cooper; I. Gameson; P. P. Edwards

    1993-01-01

    Raman-scattering and infrared-absorption measurements on optical phonons are used to investigate the doping-induced changes in the electronic structure of (Ca1-yYy)Sr2(Tl0.5Pb0.5)Cu2O7 (Tl\\/Pb-1:2:1:2). In contrast to YBa2Cu3O7-delta (YBCO), the doping of the CuO2 planes is achieved by direct substitution of Ca2+ for Y3+ in between the CuO2 planes, enabling the effects of the dynamic out-of-plane charge transfer and doping to be separated.

  9. Transversal thermovoltages of (1 1 9) Bi2Sr2CaCu2O8+delta thin-films on vicinal (1 1 0) SrTiO3 substrates

    Microsoft Academic Search

    P. Haibach; U. Frey; H. Adrian; K. F. Renk; F. Lankes

    1997-01-01

    Biaxial textured (1 1 9) oriented Bi2Sr2CaCu2O8+delta thin films were fabricated by DC-Magnetron sputtering on vicinal (1 1 0) SrTiO3 substrates. The crystal orientation and stochiometry of the films were obtained from precise X-ray diffraction measurements in four-circle geometry. According to anisotropic transport measurements, the superconducting transition temperature is approximately 47 K and the normal state resistivities along two perpendicular

  10. Transversal thermovoltages of (1 1 9) Bi 2Sr 2CaCu 2O 8+? thin films on vicinal (1 1 0) SrTiO 3 substrates

    Microsoft Academic Search

    P. Haibach; U. Frey; H. Adrian; F. Lankes; K. F. Renk

    1997-01-01

    Biaxial textured (1 1 9) oriented Bi2Sr2CaCu2O8+? thin films were fabricated by DC-Magnetron sputtering on vicinal (1 1 0) SrTiO3 substrates. The crystal orientation and stochiometry of the films were obtained from precise X-ray diffraction measurements in four-circle geometry. According to anisotropic transport measurements, the superconducting transition temperature is approximately 47 K and the normal state resistivities along two perpendicular

  11. Manipulation of subsurface carbon nanoparticles in Bi?Sr?CaCu?O8+? using a scanning tunneling microscope

    DOE PAGESBeta

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

    2015-03-01

    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.

  12. LiCaAlF 6 and LiSrAlF 6: tunable solid state laser host materials

    NASA Astrophysics Data System (ADS)

    Samtleben, Till A.; Hulliger, Jürg

    2005-03-01

    Tunable all-solid-state lasers find more and more applications in different fields. Chromium-doped ternary colquiriites, LiCaAlF 6 (LiCAF) and LiSrAlF 6 (LiSAF), show a tunable laser activity in the region of 720-840 nm and 780-1010 nm, respectively. Other interesting properties enable them to be used as scintillators and window materials. Single crystals of LiCAF and LiSAF have been grown by various methods, including the Czochralski, Bridgeman, zone melting and top-seeded solution growth techniques. Vertical gradient freezing (VGF) is proposed for producing high optical quality crystals.

  13. Magnetic field dependence of the resistivity and susceptibility of the above-100-K Bi-Sr-Ca-Cu superconductor

    NASA Astrophysics Data System (ADS)

    Parkin, S. S. P.; Engler, E. M.; Lee, V. Y.; Nazzal, A. I.; Tokura, Y.; Torrance, J. B.; Grant, P. M.

    1988-10-01

    The magnetic field dependence of the resistivity and susceptibility of multiphase Bi-Sr-Ca-Cu-O compounds exhibiting transport and diamagnetic anomalies at ~=115 and ~=75 K are reported. The field dependence of the latter yields values of Hc and dHc2/dT(T=Tc) very similar to those found for the Y(R)Ba2Cu3O7-x family of Cu Perovskitelke superconductors. The field dependence of the above-100-K region strongly suggests that bulk superconductivity, as opposed to filamentary or fluctuation behavior, dominates at these temperatures.

  14. Redox intercalation of iodine into Bi 2Sr 2Ca n - 1 Cu nO x ( n = 2, 3)

    NASA Astrophysics Data System (ADS)

    Xenikos, D. G.; Müller, H.; Strobel, P.

    1996-02-01

    The conditions for the solid-state reaction between iodine and Bi 2Sr 2Ca n - 1 Cu nO x ( n = 2, 3) have been studied. Only oxygen-deficient host lattices reacted with halogen to yield stage- one intercalation compounds, whereas oxygen-enriched hosts underwent decomposition. The difference in reactivity has been correlated to relative changes in the oxygen concentrations of the host lattices by ac-susceptibility measurements and X-ray powder diffraction. The charge transfer caused by intercalation is estimated to be 0.04 < ?Nc < 0.1.

  15. Partially Disordered Structure of Ca2Sr(C2H5CO2)6 in the Ferroelectric Phase

    NASA Astrophysics Data System (ADS)

    Mishima, Naoyuki; Itoh, Kazuyuki; Nakamura, Eiji

    1982-12-01

    The crystal structure of Ca2Sr(C2H5CO2)6 in the ferroelectric phase was determined at -40°C by X-ray reflection data from a monodomain crystal. The least-squares calculation was converged with the R-factor of 0.044. Among the six independent propionate ions in a formula unit, four ones which are disordered perfectly in the paraelectric phase are in partially disordered states with two equilibrium atomic positions. Correlation between the positions of methyl groups in the disordered propionate ions is discussed on the basis of the van der Waals version.

  16. Photoelectron energy-loss study of the Bi2CaSr2Cu2O8 superconductor

    NASA Astrophysics Data System (ADS)

    Shen, Z.-X.; Lindberg, P. A. P.; Dessau, D. S.; Lindau, I.; Spicer, W. E.; Mitzi, D. B.; Bozovic, I.; Kapitulnik, A.

    1989-03-01

    Using energy-loss spectroscopy of photoelectrons from a single crystal of Bi2CaSr2Cu2O8, we show that the electronic structure of the near-surface region is the same as that of the bulk. Utilizing the fact that photoelectrons of different elements are excited at different locations in the unit cell, we identify the energy-loss features as due to valence plasmon excitations, and one-electron excitations by comparing the photoelectron energy-loss spectra of the different elements.

  17. Long-time relaxation of low energy excitations in Bi 2CaSr 2O 8

    NASA Astrophysics Data System (ADS)

    Sahling, S.; Sievert, J.

    1990-07-01

    The long-time power release typical of amorphous solids was observed after rapid cooling of a superconducting polycrystalline ceramic Bi 2CaSr 2Cu 2O 8 from various equilibrium temperatures T1 (2.24 K ? T1 ? 13.68 K) to 1.5 K. The resulting distribution parameter of two-level systems P = 12.5 × 10 44 Jm -3 is close to the values of the other high temperature superconductors and amorphous solids. The upper limit of the relaxation time spectrum was found.

  18. Thermal expansion measurements using neutron diffraction of Bi 2CaSr 2Cu 2O x

    NASA Astrophysics Data System (ADS)

    Arendt, Ronald H.; Garbauskas, Mary F.; Meyer, Charles A.; Rotella, Frank J.; Jorgensen, James D.; Hitterman, Richard L.

    1991-10-01

    The differential thermal expansion of Bi 2CaSr 2Cu 2O x, Bi-(2122), has been measured using high-temperature neutron powder diffraction in air, 0.980% oxygen in nitrogen, and pure argon. Thermal expansion in the c-axis direction is greater by a factor of about 1.4 than that in either the a- or b-axis direction for all sample environments. The neutron results for Bi-(2122) in air are compared with results from similar X-ray powder diffraction measurements.

  19. Magnetic behaviour of the MTbF{sub 6} fluoroterbates (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba)

    SciTech Connect

    Josse, M. [Laboratoire des Materiaux Inorganiques, UMR 6002 CNRS, Universite Blaise Pascal, 63171 Aubiere (France); CNRS, Universite de Bordeaux, ICMCB, Pessac (France); El-Ghozzi, M., E-mail: Malika.EL-GHOZZI@univ-bpclermont.fr [Laboratoire des Materiaux Inorganiques, UMR 6002 CNRS, Universite Blaise Pascal, 63171 Aubiere (France); Avignant, D. [Laboratoire des Materiaux Inorganiques, UMR 6002 CNRS, Universite Blaise Pascal, 63171 Aubiere (France); Andre, G.; Bouree, F. [Laboratoire Leon Brillouin, CEA-CNRS, CEA-Saclay, 91191 Gif-sur-Yvette (France); Isnard, O. [Institut Neel, CNRS/Universite Joseph Fourier, UPR2940, 38042 Grenoble (France)

    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.

  20. Structure of high-T c superconducting Bi-Sr-Ca-Cu-O films prepared by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Roul, B. K.; Pramanik, P.; Chopra, K. L.

    1989-10-01

    High- Tc superconducting films of Bi-Sr-Ca-Cu-O have been synthesized by spray pyrolysis of nitrate precursors onto yttria stabilized zirconia (YSZ), followed by rapid annealing at 840°C in air/oxygen. The films are preferentially oriented with c-axis parallel to the plane of the substrate surface. The diffraction patterns of the films correspond to a mixed phase orthorhombic structure, with different c-values of 24.49 Å, 30.78 Å and 37.25 Å. These films exhibit superconductivity at 91 K and zero resistance at 77 K.

  1. Renormalized non-linear flux-flow and phase-slip resistivity in polycrystalline Bi?Sr?Ca?Cu?O

    NASA Astrophysics Data System (ADS)

    Blackstead, H. A.; Pulling, D. B.; Keiffer, D. G.; Sankararaman, M.; Sato, H.

    1992-10-01

    Flux-flow in polycrystalline Bi?Sr?Ca?Cu?O, identified by rotation of an applied field relative to the rf current in the sa plane, is observed superimposed on an isotropic background phase-slip resistivity. Flux-flow resistivity varies as sin 2 (?), where ? is the angle between the applied magnetic field and the rf current, vanishes as T? Tc, and is a non-linear function of the applied field. The phase-slip resistivity is seen to vary approximately with field and temperature as {? n}/{I 20}( {?}/{2}) with ? 3=A T × {(1- {T}/{T c}) {3}/{2}}/{(H+H 0) }.

  2. Crystal chemistry of Ca-doped and Ca-free Pb$\\\\sb2$Sr$\\\\sb2$RCu$\\\\sb3$O$\\\\sb{8+\\\\delta}$ (R = rare earth): Synthesis, structure and physical properties

    Microsoft Academic Search

    Jiayu Simon Xue

    1992-01-01

    A novel PbO\\/NaCl flux growth method has been developed to grow single crystals of Ca-doped Pb$\\\\sb2$Sr$\\\\sb2$(R\\/Ca)Cu$\\\\sb3$O$\\\\sb{8 + \\\\delta}$ with R = Nd, Sm, Gd, Dy, Er, Tm, Yb, Lu and Y. The absence of CuO flux enables the crystals to be extracted nondestructively from the melt using an ultrasonic bath and methanol. The as grown Pb$\\\\sb2$Sr$\\\\sb2$(Y\\/Ca)Cu$\\\\sb3$O$\\\\sb{8 + \\\\delta}$ crystals are

  3. 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, E-mail: viktor.hlukhyy@lrz.tu-muenchen.de; 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.

  4. The temporal and spatial expression of Claudins in epidermal development and the accelerated program of epidermal differentiation in K14-CaSR transgenic mice

    Microsoft Academic Search

    Tammy-Claire Troy; Yuhua Li; Lauren O’Malley; Kursad Turksen

    2007-01-01

    The importance of the epidermal permeability barrier (EPB) in protecting the mammalian species against harmful UV irradiation, microorganism invasion and water loss is well recognized, as is the role of calcium (Ca2+) in keratinocyte differentiation, cell–cell contact and the EPB. In a previous study, we reported that the overexpression of the Ca2+-sensing receptor (CaSR) in the undifferentiated basal cells of

  5. 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 [Department of Chemistry and Biochemistry, Arizona State University, P.O. Box 871604 Tempe, AZ 85287-1604 (United States); Department of Chemistry, Indian Institute of Technology, Kharagpur 721302 (India); Stoyanov, Emil; Belieres, Jean-Philippe; Groy, Thomas L. [Department of Chemistry and Biochemistry, Arizona State University, P.O. Box 871604 Tempe, AZ 85287-1604 (United States); Norrestam, Rolf [Structural Chemistry, Stockholm University, 10691 Stockholm (Sweden); Haeussermann, Ulrich [Department of Chemistry and Biochemistry, Arizona State University, P.O. Box 871604 Tempe, AZ 85287-1604 (United States)], E-mail: Ulrich.Haussermann@asu.edu

    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.

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

    Microsoft Academic Search

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

    2011-01-01

    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 CO2 reforming of methane on four pyrochlore catalysts. First, rhodium was partially substituted for Zr

  7. Pd-substituted (La,Sr)CrO3-?-Ce0.9Gd0.1O2-? solid oxide fuel cell anodes exhibiting regenerative behavior

    NASA Astrophysics Data System (ADS)

    Bierschenk, David M.; Potter-Nelson, Elizabeth; Hoel, Cathleen; Liao, Yougui; Marks, Laurence; Poeppelmeier, Kenneth R.; Barnett, Scott A.

    2011-03-01

    Composite anodes consisting of Pd-substituted (La,Sr)CrO3-? mixed with 50 wt% Ce0.9Gd0.1O2-? were tested in La0.9Sr0.1Ga0.8Mg0.2O3-?-electrolyte supported fuel cells at 800 °C with humidified H2 fuel. Low anode polarization resistance was observed during the first several hours of operation, explained by the nucleation of Pd nano-particles on perovskite particle surfaces. Anode performance then degraded gradually before stabilizing. Redox cycling repeatedly restored the anodes to their initial peak performance, followed again by degradation. This regenerative behavior was explained by the observation that the Pd nano-particles were removed by oxidation, and then re-nucleated upon reduction.

  8. 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.

  9. Reactions between oxides and Ag-sheathed Bi2Sr2CaCu2Ox conductors

    NASA Astrophysics Data System (ADS)

    Wesolowski, D. E.; Rikel, M. O.; Jiang, J.; Arsac, S.; Hellstrom, E. E.

    2005-07-01

    We studied reactions between Ag-sheathed Bi2Sr2CaCu2Ox (2212) conductors and a variety of oxides. We identified two intrinsic reactions: solid-state diffusion of a metallic species from the 2212 melt through the Ag sheath to react with an oxide, and direct reaction between Ag and an oxide. The dominant species that diffused through the Ag sheath was Cu because its solubility in Ag and diffusivity through Ag under 2212 melt processing conditions are the highest of the BSCCO metallic species. Al2O3, CeO2, pure SiO2, Y2O3, ZrO2, CaZrO3, and SrZrO3 were identified as non-reactive when heat treated in contact with Ag-sheathed 2212 tape. Fe2O3, MgO, and NiO reacted with Cu that diffused through Ag during the heat treatment. Cr2O3 and SiO2-based Pyrex glass reacted directly with Ag in the sheath during the heat treatment, which can create cracks and pinholes in the Ag sheath through which liquid can flow. Based on thermodynamic estimates, we calculated the Cu concentration in Ag at the 2212/Ag interface at 900 °C and 1 bar O2 to be between 0.15 and 0.22 at.%, which is consistent with 0.19 ± 0.02 at.% deduced from the experimentally measured diffusion flux.

  10. Polarization-dependent infrared reflectivity study of Sr???Ca????Cu??O?? under pressure: Charge dynamics, charge distribution, and anisotropy

    DOE PAGESBeta

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

    2014-12-01

    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. The optical data suggest that Sr???Ca????Cu??O?? remains electronically highly anisotropic up to high pressure, also at low temperatures.« less

  11. The effect of silver doping on the critical current density of Bi-Pb-Sr-Ca-Cu-O ceramic superconductor

    NASA Astrophysics Data System (ADS)

    Zargar Shoushtari, M.; Bahrami, Amir; Farbod, Mansoor

    2006-09-01

    In this research, the effect of silver doping on Bi1.6Pb0.4Sr2Ca2Cu3Oy ceramic superconductor has been investigated. The solid-state reaction method and two different silver doping methods has been used, namely, doping during making processes of samples (batch 1) and doping after making Bi1.6Pb0.4Sr2Ca2Cu3Oy superconductor (batch 2). We observed that by adding silver to BPSCCO compound, partial melting temperature of the compound is decreased. The critical current density (Jc) in both batches is affected by Ag doping. The investigation of SEM images of samples has shown that the all surfaces of the samples are porous and the grains are plate like. It seems that the BPSCCO grains in batch 1 samples are coated with silver but in the samples of batch 2, the silver also sits between the BPSCCO grains. The XRD patterns studies indicated that the silver peaks form separate phase and also by adding silver to BSCCO, the BPSCCO peaks do not show considerable shift.

  12. Effect of high Xe-concentration in a plasma display panel with a SrCaO cold cathode

    SciTech Connect

    Uchida, Giichiro; Kajiyama, Hiroshi; Shinoda, Tsutae [Graduate School of Advanced Science of Matter, Hiroshima University, Higashi-Hiroshima 739-8530 (Japan); Uchida, Satoshi [Graduate School of Science and Engineering, Tokyo Metropolitan University, Hachioji 192-0397 (Japan); Akiyama, Toshiyuki [Advanced PDP Development Center Corporation, Ibaraki 567-0026 (Japan)

    2010-05-15

    We present here measurements of high Xe-contents plasma display panel (PDP) with SrCaO cold cathode. Luminous efficacy ({eta}) shows a two-step increase with Xe-concentration in Ne/Xe gas mixture: {eta} drastically increases up to Xe-concentration of 30% (Xe: 30%), and then attains 5 lm/W at the highest Xe-concentration of Xe: 100%. The high performance PDP with Xe: 100% can be operated at low applied voltage between 230 and 377 V due to the high secondary electron emission from the SrCaO cathode. Emission measurements clearly show the change in discharge characteristics at Xe: 30%, where the discharge changes from a Ne/Xe mixture discharge to an almost pure Xe discharge, and the vacuum ultraviolet (VUV) radiation from the combination of resonance and excimer radiations to only excimer radiation. Theoretical analysis solving Boltzmann equation for electron demonstrates that increasing Xe-concentration enhances the collision frequency for electron impact excitation directly from ground state to lower levels concerned with the VUV radiation, resulting in a drastic increase in luminous efficacy up to Xe: 30%. Also, one-dimensional fluid simulation of a Ne/Xe dielectric barrier discharge clearly shows that a combination of high secondary electron emission cathode and high Xe-concentration is quite effective for high VUV radiation efficiency because it induces a drastic increase in electron-heating efficiency.

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

    NASA Astrophysics Data System (ADS)

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

    1989-11-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

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

    SciTech Connect

    Davis, M.F.; Wosik, J.L.; Wolfe, J.C. (Department of Electrical Engineering, University of Houston, Houston, Texas 77004 (US))

    1989-11-15

    An electron beam flash evaporation technique is described which reproduces the stoichiometry of superconducting YBa{sub 2}Cu{sub 3}O{sub {ital x}} (123), Bi{sub 2}CaSr{sub 2}Cu{sub 2}O{sub {ital y}} (2122), and Bi{sub 2}Ca{sub 2}Sr{sub 2}Cu{sub 3}O{sub {ital z}} (2223) source powders. Films of each material deposited with this technique exhibit zero resistance temperatures of 78 K or above when furnace annealed; 75 K zero temperatures are obtained for 123 films {ital in} {ital situ} annealed with atomic oxygen at 775 {degree}C. Transport critical current densities are 1{times}10{sup 4} A/cm{sup 2} in 25-{mu}m stripes patterned from 123 films, and 6{times}10{sup 4} A/cm{sup 2} in 1-mm stripes of 2122 and 2223 films using a 1-{mu}V/mm measurement criteria. Typical normal state resistivities are 700 {mu}{Omega} cm for 2122 and 2223 films and 5 m{Omega} cm for 123 films. The 2122 films are highly textured with the {ital c} axis normal to the substrate. All results are for films deposited on MgO.

  16. Influence of IIA metals (Mg, Ca, Sr, Ba) on the Co modification of ?-Fe2O3 particles

    NASA Astrophysics Data System (ADS)

    Fukumoto, Yuji; Matsumoto, Kazuyoshi; Matsui, Yasushi

    1991-04-01

    In the reaction of Co modification of ?-Fe2O3, we found a very interesting phenomenon. When cations of Ca2+, Sr2+, or Ba2+ belonging to IIA metals are adsorbed on the surface of ?-Fe2O3 prior to Co2+ ion adsorption, the coercivity of Co modified ?-Fe2O3 is signifcantly increased compared to ?-Fe2O3 modified only with Co2+. In contrast, when the Mg2+ ion is adsorbed prior to Co2+ ion adsorption, the coercivity is rarely increased. In this paper, we made the following hypotheses in order to interpret these phenomena: (1) Co2+ ions are adsorbed both on the tetrahedral (A) site and the octahedral (B) site in the spinel structure of ?-Fe2O3. When Co2+ ion occupies the B site and forms cobalt ferrite, the coercivity increases as a result of the surface magnetic anisotropy. (2) Because cations of alkaline earth metals (Ca,Sr,Ba) are easily adsorbed on the A site, adding alkaline earth metal before cobalt addition results in an increase in adsorption selectivity of Co2+ ion on the B site. (3) On the other hand, Mg2+ ion which is easily adsorbed on the B site prevents Co2+ ion occupancy of the B site and as a result the coercivity does not increase.

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

    E-print Network

    Zheng, Yufeng

    In vitro and in vivo studies on biodegradable CaMgZnSrYb high-entropy bulk metallic glass q H.F. LiZn20Sr20Yb20 alloy High-entropy alloys Bulk metallic glasses Biodegradable metals Bone a b s t r a c metallic glass did not show any obvious degradation after 4 weeks of implantation, and they can promote

  18. Raman spectrum of the double-layer superconductor La 2- xSr xCaCu 2O 6- ?(0.2? x?0.4)

    NASA Astrophysics Data System (ADS)

    Mateev, D. M.; Iliev, M. N.; Bozukov, L. N.; Hadjiev, V. G.; Stastny, P.

    1991-09-01

    The Raman spectra of micro-crystals of the double-layer superconductor La 2- xSr xCaCu 2O 6- ? ( x=0.2, 0.3 and 0.4) have been measured for samples prepared at 1 atm oxygen. Six Raman lines have been observed at 138, 195-200, 265-270, 425-430, 445-450 and 585 cm -1. The assignment of these lines to certain atomic vibrations is discussed in close comparison with the Raman modes of La 2CuO 4, Bi 2CaSr 2Cu 2O 8 and YBa 2Cu 3O 6. The presence of a small amount of (LaCaSr) 14Cu 24O 41 (2-4 wt.%) as a main “impurity” phase has been established by means of Raman and electron microprobe and X-ray analysis.

  19. Superconducting properties of Tl 1-yPb yCaSr 2Cu 2O 7: Role of Pb and oxygen stoichiometry

    NASA Astrophysics Data System (ADS)

    Vijayaraghavan, R.; Rao, C. N. R.

    1992-07-01

    In the Tl 1-yPb yCaSr 2Cu 2O 7 system, monophasic superconducting compositions are formed in the range 0.25 < y < 0.60 and the minimum Pb content required to stabilize the tetragonal 1122 phase is about 25%. Maximum T c is found when y = 0.5, at which composition the hole concentration is optimal. Metallic compositions of Tl 1-yPb yCaSr 2Cu 2O 7 ( y = 0.25) and Tl 0.75Pb 0.25Y 1-xCa xSr 2Cu 2O 7 (0.80 ? X ? 1.0) become superconducting on decreasing the oxygen content by vacuum annealing.

  20. Doppler Imaging of the Ap star epsilon Ursae Majoris: Ca, Cr, Fe, Mg, Mn, Ti, Sr

    Microsoft Academic Search

    T. Lueftinger; R. Kuschnig; N. E. Piskunov; W. W. Weiss

    2003-01-01

    The surface abundance structure of seven elements of the brightest chemically peculiar A-type star, epsilon Ursae Majoris (epsilon UMa, HD 112185, HR 4905) has been determined. Cr, Fe and, Mn are enhanced at the magnetic polar region of epsilon UMa while they avoid the magnetic equator. Sr seems to behave like Cr, Fe, and Mn, but is concentrated only at

  1. Activity of Ni Substituted Ca-La-hexaaluminate Catalyst in Dry Reforming of Methane

    Microsoft Academic Search

    K. Ikkour; D. Sellam; A. Kiennemann; S. Tezkratt; O. Cherifi

    2009-01-01

    Ca1?x\\u000a La\\u000a x\\u000a NiAl11O19??(O ? x?1) hexaaluminate oxydes were synthesized starting from nitrate salts of Ca, La, Ni and Al precipitated by citric acid. After\\u000a calcination they were used as catalysts precursors in dry reforming of methane to synthesis gas at atmospheric pressure (600–800 °C)\\u000a with a mixture of CH4\\/CO2\\/Ar:1\\/1\\/3. The solids were characterized by X-ray diffraction (XRD), BET surface area, temperature programmed

  2. Effects of Cr/Zn Substitutions on Dielectric Properties of CaCu{sub 3}Ti{sub 4}O{sub 12}(CCTO) Ceramics

    SciTech Connect

    Rajmi, R.; Yahya, A. K.; Deni, M. S. M. [Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selangor (Malaysia)

    2010-07-07

    Effects of Zn and Cr substitutions on dielectric properties of CaCu{sub 3-x}Zn{sub x}Ti{sub 4-y}Cr{sub y}O{sub 12} ceramics are reported. Dielectric measurements at room temperature for un-substituted CaCu{sub 3-x}Zn{sub x}Ti{sub 4-y}Cr{sub y}O{sub 12}(x = 0, y = 0) between 10{sup 2}-10{sup 6} Hz showed dielectric constant of 2.7x10{sup 4} at 10{sup 2} Hz. Substitution of Zn for Cu in CaCu{sub 3-x}Zn{sub xTi{sub 4{sub -{sub yCr{sub yO{sub 1{sub 2}}}}}}}(y = 0, x = 0.10, 0.50)caused dielectric constant to drop with increasing x. Cr substitution at Ti-site in CaCu{sub 3-x}Zn{sub xTi{sub 4{sub -{sub yCr{sub yO{sub 1{sub 2}}}}}}}(x = 0, x = 0,) also caused decrease in dielectric constant. However, at x = 0.50, the dielectric constant at low frequency was enhanced compared to the un-substituted sample. Our results indicate that Cu and Ti sites play an important role in the formation of Internal Barrier Layer Capacitance (IBLC) in CCTO.

  3. Arsenate Substitution in Hydroxylapatite: Structural Characterization of the Ca5(PxAs1-xO4)3OH Solid Solution

    SciTech Connect

    Lee, Y.; Stephens, P; Tang, Y; Li, W; Phillips, B; Parise, J; Reeder, R

    2009-01-01

    Arsenate (As{sup 5+}) substitution in the hydroxylapatite structure was examined using a combination of crystallographic and spectroscopic techniques. Samples of hydroxylapatite, the As{sup 5+}-substituted analog (synthetic johnbaumite), and five intermediate compositions were synthesized from solution. Synchrotron X-ray diffraction data show that all samples are single-phase, confirming complete substitution. No evidence is found for lowering of symmetry below P6{sub 3}/m. Rietveld structure refinements show progressive expansion of the unit cell with increasing As substitution, which can be accounted for primarily by an average expansion of the tetrahedral site. Sizes of Ca polyhedra show little variation as a result of As substitution. NMR results show no evidence for local clustering of PO{sub 4} tetrahedra. EXAFS confirms that the size of As-centered tetrahedra remains constant across the solid-solution series.

  4. 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

  5. Dy3+-activated NaM4(VO4)3 (M = Ca, Ba, Sr) phosphor for near-UV solid-state lighting.

    PubMed

    Singh, Roshani; Dhoble, S J

    2011-01-01

    We report the photoluminescence characterization of Dy(3+)-activated NaM(4)(VO(4))(3) (M = Ca, Ba, Sr) phosphors prepared by a solid-state method. The synthesis was confirmed by X-ray diffraction (XRD) characterization and photoluminescence (PL) emission results showed sharp blue and yellow bands for NaM(4)(VO(4))(3) (M = Ca, Ba, Sr):Dy(3+) phosphors at the excitation wavelength of 323 nm, which is near-UV excitation. Thus, these phosphors could be applicable for near-UV excited solid-state lighting devices. PMID:21618681

  6. CW and self-mode-locking performance of a red pumped Cr 3+: LiSr 0.8Ca 0.2AlF 6 laser

    NASA Astrophysics Data System (ADS)

    Wang, H. S.; Li Kam Wa, P.; Lefaucheur, J. L.; Chai, B. H. T.; Miller, A.

    1994-09-01

    Reported is cw lasing and sub-100 femtosecond pulse generation in end-pumped Cr 3+: LiSr 0.8Ca 0.2AlF 6, a congruently melting compound intermediate between Cr 3+: LiSrAlF 6 and Cr 3+: LiCaAlF 6. Using a dispersion compensated cavity with no active or passive mode-locking elements in the cavity, self-sustained stable modelocked pulses of 90 fs duration at 140 MHz repetition frequency were initiated by rocking of the output coupler.

  7. High-temperature resistance behavior of Bi2Sr2CaCu2O(8+y) and YBa2Cu3O(7-x) superconductors

    Microsoft Academic Search

    T. K. Bansal; Sadhana Bansal; R. L. McGreevy; S. H. Smith; G. Garton

    1988-01-01

    High- and low-temperature resistance measurements have been carried out on Bi2Sr2CaCu2O(8+y) and YBa2Cu3O(7-x) in air and in vacuum. Both ceramics exhibit a significant change in oxygen content during annealing between 350 and 450 C. The Bi2Sr2CaCu2O(8+y) sample exhibits an increase in resistance with increased oxygen content resulting in deterioration of superconductivity, whereas YBa2Cu3O(7-x) shows improvement in superconducting behavior with increase

  8. High-temperature resistance behavior of Bi2Sr2CaCu2O8+y and YBa2Cu3O7?x superconductors

    Microsoft Academic Search

    T. K. Bansal; Sadhana Bansal; R. L. McGreevy; S. H. Smith; G. Garton

    1988-01-01

    High- and low-temperature resistance measurements have been carried out on Bi2Sr2CaCu2O8+y and YBa2Cu3O7?x in air and in vacuum. Both the ceramics exhibit a significant change in oxygen content during annealing between 350 and 450 °C. The Bi2Sr2CaCu2O8+y sample exhibits an increase in resistance with increased oxygen content resulting in deterioration of superconductivity, whereas YBa2Cu3O7?x shows improvement in superconducting behavior with

  9. Orbital orderings and optical conductivity of SrRuO3 and CaRuO3: first-principles studies

    Microsoft Academic Search

    Guang-Tao Wang; Min-Ping Zhang; Zong-Xian Yang; Zhong Fang

    2009-01-01

    The Jahn-Teller (JT) distortion induced orbital order and optical conductivity in SrRuO3 and CaRuO3 are investigated by first-principles calculations. The total energy and optical conductivity of all the spin ordering states of SrRuO3 and CaRuO3 are calculated in the LDA+U scheme with Ueff = 2.5 eV. The down-spin t2g of Ru show antiferromagnetic-like orbital order in the a-b plane. We

  10. Bi 2- xPb x(Ca, Sr) n+1 Cu nO 2 n+4+ ? ( n = 1, 2, 3, and 4) family of superconductors

    NASA Astrophysics Data System (ADS)

    Rao, C. N. R.; Vijayaraghavan, R.; Ganapathi, L.; Bhat, S. V.

    1989-03-01

    Superconducting oxides of the Bi 1.5Pb 0.5(Ca, Sr) n+1 Cu nO 2 n+4+? series with n = 1, 2, 3 and 4 have been characterized. The superconducting transition temperature increases markedly with n up to n = 3, but the Tc of the n = 4 member is not much higher than that of the n = 3 member. The Tc does not change significantly in Bi 2- xPb xCaSr 2Cu 2O 8+? with x (0.1 < x ? 0.5).

  11. Interband optical conductivity of Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8/

    SciTech Connect

    Ching, W.Y.; Zhao, G.L.; Xu, Y.N.; Wong, K.W.

    1989-03-10

    The band structure and interband optical conductivity of Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8/ superconductor in the body-centered tetragonal sub-unit is calculated self-consistently using orthogonalized linear combination of atomic orbitals method. The result shows Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8/ has both semi-metal-like and semiconductor-like features with small band gap and band overlap. The interband optical conductivity shows strong anisotropy between the in-plane and z-direction components. A plasmon frequency at 6 eV is predicted.

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

    SciTech Connect

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

    1992-02-01

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

  13. 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.

  14. Effects of A1 site occupation on dielectric and ferroelectric properties of Sr4CaRTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics

    NASA Astrophysics Data System (ADS)

    Fang, Yu-Jiao; Gong, Gao-Shang; Gebru, Zerihun; Yuan, Song-Liu

    2014-12-01

    Sr4CaRTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr4CaRTi3Nb7O30 (R = Ce, Eu) tetragonal tungsten bronzes are investigated. The Sr4CaCeTi3Nb7O30 shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. Sr4CaEuTi3Nb7O30 ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between Ca2+ and Eu3+ could lead to the uneven distribution of Ca2+ and Eu3+ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarization—electric field (P—E) curves are evaluated at room temperature and both of them show hysteresis loops. Sr4CaCeTi3Nb7O30 shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current density—electric field (J—E) curves are measured at room temperature with a largest leakage current density of ~ 10?6 A/cm2, indicating that their leakage currents are rather low.

  15. A Langmuir isotherm-based prediction of competitive sorption of Sr, Cs, and Co in Ca-montmorillonite

    SciTech Connect

    Gutierrez, M. (New Mexico State Univ., Las Cruces, NM (United States). Dept. of Geological Sciences); Fuentes, H.R. (Florida International Univ., Miami, FL (United States). Dept. of Civil and Environmental Engineering)

    1993-01-01

    An accurate determination of parameters such as the distribution coefficient K[sub d] (for low concentrations) and the maximum adsorption capacity S[sub T] (for high concentrations) is desirable, as these values can be used in contaminant transport modeling. Considering that contaminants would more likely be found as mixtures and not as single components, the effects on K[sub d] and S[sub T] values resulting from competitive interactions between the target cation and other cations present in the system were estimated. This study focused on the determination of K[sub d] and S[sub T] for suspensions of Ca-montmorillonite and mixtures of the solutes strontium (Sr), cesium (Cs), and cobalt (Co) as analogs of a possible release of contaminants from radioactive waste repositories. Batch experiments were conducted for mixtures of the above solutes at intermediate concentrations at varying pH values and for two background electrolytes, NaCl and CaCl[sub 2]. The Langmuir isotherm adequately fitted the experimental data and was used to determine K[sub d] and S[sub T]. Maximum K[sub d] values were obtained for Sr at pH 6 and for Co at pH 8, while for Cs the pH did not affect the resulting K[sub d] value. The presence of competing ions resulted in a decrease of K[sub d] values depending on the type and concentration of ions in the original mixture. For clay preconditioned with NaCl electrolyte solution, the Na[sup +] partially saturated surface attracted more solutes, leading to greater K[sub d] values than for suspensions preconditioned with a CaCl[sub 2] solution. Although the total amount of adsorbed cations (S[sub cum]) in either electrolyte solution was nearly constant, a difference in the adsorption of individual cations was observed as an increased percentage of adsorbed Sr and Co in systems preconditioned with NaCl solution.

  16. Core level x-ray photoemission of the high T sub c CaSr sub 2 Bi sub 2 Cu sub 2 O sub x superconductor

    SciTech Connect

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

    1988-04-01

    The x-ray photoemission spectroscopy (XPS) signatures of Cu core levels in CaSr{sub 2}Bi{sub 2}Cu{sub 2}O{sub x} are distinctly different from those of Bi and of Ca in this high {Tc} superconductor. The Cu signatures are very similar to those of Cu in YBa{sub 2}Cu{sub 3}O{sub 6.9}. The Cu 2p spectra, in both cases, indicate that the photoexcited ion has poor (ionic) coupling to screening electrons. In contrast, the spectra of Bi and Ca in CaSr{sub 2}Bi{sub 2}Cu{sub 2}O{sub x} are indicative of good (metallic) coupling between the ion and screening electrons. These observations illuminate the connection between high {Tc} superconductivity and the coupling of Cu ions with conduction electrons. 15 refs., 4 figs.

  17. 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. [Los Alamos National Lab., NM (United States); McHenry, M.E. [Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Metallurgical Engineering and Materials Science; Wahlbeck, P.G. [Wichita State Univ., KS (United States). Dept. of Chemistry

    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.

  18. 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. (Los Alamos National Lab., NM (United States)); McHenry, M.E. (Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Metallurgical Engineering and Materials Science); Wahlbeck, P.G. (Wichita State Univ., KS (United States). 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.

  19. Phase relations in the composition(Pb 1- yCu y)Sr 2(Ln 1- xCa x)Cu 2O 7 and the crystal structure of La 8- xSr xCu 8- yO 20

    NASA Astrophysics Data System (ADS)

    Lee, J. Y.; Kim, J. S.; Swinnea, J. S.; Steinfink, H.

    1990-02-01

    The compound (Pb 0.71Cu 0.29)Sr 2(Ln 1-xCa x)Cu 2O 7 (1212) has been synthesized as single phase material for La, Pr, Nd, Gd, Er, and Y from the proper starting compositions fired above 950°C. Calcium can be substituted up to x = 0.5. When this limit is exceeded the 1212 phase, SrCuO 2, and a hexagonal phase are formed. When x = 1 only SrCuO 2 and the hexagonal phase are formed. The hexagonal phase has the general composition Sr 5- xPb 3+ xCu yO 11+ z. When a mixture corresponding to PbSr 2Co 0.5Cu 0.5O z is fired above 960°C a tetragonal phase isostructural with TlSr 2CuO 5 (121) forms, but below 960°C the hexagonal phase is formed. A nominal mixture of PbSr 2CaCu 2 (1212) fired at 930°C and quenched forms primarily the SrCuO 2 phase and some of the hexagonal compound, but slow cooling in the furnace produces a nearly single phase hexagonal product. The crystal structure of a crystal found in a reaction product from a nominal mixture PbSr 2LaCu 2 (1212) fired at 1050°C was determined from three-dimensional X-ray diffraction data. Its composition is (La 6.16Sr 1.84)Cu 7.66O 20, M r = 1823.6 , tetragonal, P4/mbm, a = 10.7468(8)Å, c = 3.8633(3)Å, V = 446.2(1)Å 3, Z = 1, D x = 6.79g cm -3, ? = 0.71069Å, ? = 288.0 cm -1, R = 0.032, wR = 0.034 for 385 observed reflections. The structure is formed by the articulation of Cu octahedra, square pyramids, and square coplanar nets into a three-dimensional framework. LaSr are in 10-fold coordination to oxygen atoms that are in a perovskite-like arrangement. The octahedral Cul site contains 17% vacancies on the basis of the least-squares refinement of the site occupancy. The two apical Cul sbnd O bond lengths are 1.9317(1)Å, and the four equatorial lengths are 1.978(7)Å. The square Cu2 sbnd O bond lengths are 1.9317(1) and 1.869(6)Å, respectively. The square pyramidal Cu3 sbnd O bond lengths are 2.364(6)Åto the apex and 1.9322(2) and 1.878(7)Å, respectively, to pairs of the four equatorial oxygen ions. Valence bond calculation and the abence of Jahn-Teller distortion around the octahedrally coordinated Cu1 indicate that it is trivalent.

  20. Effect of Ca substitution on some physical properties of nano-structured and bulk Ni-ferrite samples

    NASA Astrophysics Data System (ADS)

    Assar, S. T.; Abosheiasha, H. F.

    2015-01-01

    Nanoparticles of Ni1-xCaxFe2O4 (x=0.0, 0.02, 0.04, 0.06 and 0.10) were prepared by citrate precursor method. A part of these samples was sintered at 600 °C for 2 h in order to keep the particles within the nano-size while the other part was sintered at 1000 °C to let the particles to grow to the bulk size. The effect of Ca2+ ion substitution in nickel ferrite on some structural, magnetic, electrical and thermal properties was investigated. All samples were characterized by using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). A two probe method was used to measure the dc electrical conductivity whereas the photoacoustic (PA) technique was used to determine the thermal diffusivity of the samples. To interpret different experimental results for nano and bulk samples some cation distributions were assumed based on the VSM and XRD data. These suggested cation distributions give logical explanations for other experimental results such as the observed values of the absorption bands in FTIR spectra and the dc conductivity results. Finally, in the thermal measurements it was found that increasing the Ca2+ ion content causes a decrease in the thermal diffusivity of both nano and bulk samples. The explanation of this behavior is ascribed to the phonon-phonon scattering.

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

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

    Calcination behavior of nano-crystalline lanthanum chromites doped with calcium and strontium has been probed by Fourier transform infrared spectroscopy, X-ray diffraction and small-angle neutron scattering as a function of temperature. Infrared spectroscopic results imply that over a range of temperatures, some intermediate phase of dopant chromates evolve and then dissolve back, which has also been confirmed by the XRD. Neutron scattering data reveal a fractal type correlation of building blocks in virgin powders. Increase in fractal dimension and reduction in upper cutoff vis-à-vis the densification of agglomerates were found with increasing calcination temperature. Calcination, beyond 900 °C, results in breaking down of the fractal morphology almost completely. Such shrinkage event also results in a modification of the microscopic structure. These changes have been attributed to the compaction of agglomerates of both Ca- and Sr-doped lanthanum chromites, assisted via liquid state sintering by the melting of the intermediate phases at intermediate calcination stages.

  2. Preparation of superconducting Y-Ba-Cu-O and Bi-Pb-Sr-Ca-Cu-O compounds by chelating method

    NASA Astrophysics Data System (ADS)

    Fujisawa, Tadashi; Takagi, Akira; Honjoh, Tetzuji; Okuyama, Katsuro; Ohshima, Shigetoshi

    1989-08-01

    Superconducting Y-Ba-Cu-O (YBCO) and Bi-Pb-Sr-Ca-Cu-O (BPSCCO) compounds were prepared by a chelating method with various chelating agents, such as nitrilotriacetic acid, hydroxyethylethylene diaminetriacetic acid and ethylenediaminetetraacetic acid. Above 600 C, the precursors YBCO and BPSCCO turned into a mixture of metal oxides and BaCO3, which finally transformed into the almost single phase of YBCO at 850 to 930 C and into the high-Tc phase of BPSCCO at 840 C. The critical current densities of YBCO and BPSCCO in blocks of 1 x 4 x 15 cu mm were estimated to be as high as 350 and 500 A/sq cm at 77 K, respectively.

  3. Unadulterated spectral function of low-energy quasiparticles in Bi2Sr2CaCu2O8+?

    NASA Astrophysics Data System (ADS)

    Evtushinsky, D. V.; Kordyuk, A. A.; Borisenko, S. V.; Zabolotnyy, V. B.; Knupfer, M.; Fink, J.; Büchner, B.; Pan, A. V.; Erb, A.; Lin, C. T.; Berger, H.

    2006-11-01

    Fitting the momentum distribution photoemission spectra to the Voigt profile appears to be a robust procedure to purify the interaction effects from the experimental resolution. In application to Bi2Sr2CaCu2O8+? high- Tc cuprates, the procedure reveals the true scattering rate at low binding energies and temperatures, and consequently, the true value of the elastic scattering. Reaching the minimal value ˜16meV , the elastic scattering does not reveal a systematic dependence on doping level, but is rather sensitive to impurity concentration and can be explained by the forward scattering on out-of-plane impurities. The inelastic scattering is found to form well-defined quasiparticles with the scattering rate ˜?2 and ˜?3 , above and below Tc , respectively.

  4. Pairing modulations and phase separation instabilities in Bi2Sr2CaCu2O8 + ?

    NASA Astrophysics Data System (ADS)

    Fang, Kun; Fernando, G. W.; Balatsky, A. V.; Kocharian, A. N.; Palandage, K.

    2014-01-01

    There is growing evidence that the unconventional spatial inhomogeneities in the doped high-Tc superconductors are accompanied by the pairing of electrons, subsequent phase transitions and condensation into coherent states. We show that such pairing states can be obtained from phase separation instabilities near level crossings. Conditions for coherent pairing instabilities are examined using exact diagonalization of Hubbard-like pyramid structures under variation of coupling and interaction strengths. We also evaluate the behavior of the energy charge gap in the vicinity of level crossings using a parametrization of coupling to the apical site to represent out-of-plane effects. These results provide a simple microscopic explanation of (correlation induced) supermodulation of the coherent pairing gap observed in scanning tunneling microscopy measurements at atomic scale in Bi2Sr2CaCu2O8 + ?.

  5. Tunneling measurements on Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8/

    SciTech Connect

    Johnson, R.E.

    1989-03-01

    Measurements have been made of the differential resistance dV/dI versus voltage of point contacts between polycrystalline samples of the high-temperature superconductor Bi/sub 2/Ca/sub 1/Sr/sub 2/Cu/sub 2/O/sub 8/ and tungsten points. The spectra exhibited tunneling structure on a nearly symmetric background that decreased with increasing bias voltages. The potential difference between two minima in the dV/dI spectra was used to obtain an estimate of 25 +- 3 mV for the gap parameter 2..delta... The zero-bias minimum characteristic of a no-barrier metal-superconductor junction was never observed.

  6. Analysis of large-area twins in Bi2CaSr2Cu2O8 superconductors

    NASA Astrophysics Data System (ADS)

    Han, P. D.; Asthana, A.; Xu, Z.; Chang, L.; Payne, D. A.

    1991-03-01

    We report on large-area twin structures in Bi2CaSr2Cu2O8. Crystal growth was by a self-fluxed method. Twins were extracted from the free surfaces of the resolidified flux. Twinning was characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy and the twins were determined to be growth twins with \\{110\\} twin boundaries. Details of twin morphology and structure are presented in the context of twin formation and growth. Superconducting properties of the twinned specimens were determined by electrical and magnetic measurements. Preliminary results indicate that a single twin boundary did not significantly affect the resistance-temperature characteristics. Growth steps on the (001) face (which necessitated current transport in the c direction) were more important in determining the sharpness and form of the resistive transition.

  7. Raman study of oxygen in the oxide superconductor Bi2CaSr2Cu2O8+?

    NASA Astrophysics Data System (ADS)

    Shi, Y. H.; Lee, M. J. G.; Moskovits, M.; Carpick, R.; Hsu, A.; Statt, B. W.; Wang, Z.

    1992-01-01

    The zero-resistance temperature of the high-Tc oxide superconductor Bi2CaSr2Cu2O8+? (2:1:2:2) can be significantly increased by annealing at 500 °C in an oxygen-reduced environment. Raman spectroscopy of high-density sintered samples shows that processing the material in this way increases the strength of the Raman peak of highest frequency (650 cm-1), leaving the strengths of the other oxygen peaks unchanged. The Raman data confirm that the mobile oxygen atoms are located in the bismuth layer and support those models of oxygen structure in which excess oxygen is incorporated interstitially. They provide evidence that the incommensurate-to-commensurate transition observed in electron diffraction in the vicinity of 500 °C is associated with a loss of oxygen from the bismuth layer.

  8. Single crystal growth of Bi 2CaSr 2Cu 2O 8+ x superconductor by travelling zone method

    NASA Astrophysics Data System (ADS)

    Pandey, R. K.; Hannan, M.; Raina, K. K.

    1994-03-01

    A new method of crystal growth based on the travelling zone technique is successfully used to grow single crystals of Bi 2CaSr 2Cu 2O 8+ x superconductor. Relatively large crystals of the order of 4 × 3× 1 mm 3 dimensions can be grown by using a bridgman type crucible in the traveling zone setup. Identification of crystals is carried out by X-ray powder diffraction and energy dispersive X-ray spectroscopy (EDAX) analysis. Single crystal X-ray diffraction shows a superstrucutre along the b-axis of the crystal grwon from a Bridgman type crucible. Scanning electron microscopy (SEM) studies conducted on these crystals show extensive evidence of layer-growth patterns. Supersonducting properties of these crystals are determined by four-probe direct current (DC) resistance and alternating current (AC) susceptibility measurements.

  9. Normal state magnetoresistance in Bi 2Sr 2CaCu 2O 8+? thin films with different oxygen contents

    NASA Astrophysics Data System (ADS)

    Konstantinovic, Z.; Laborde, O.; Monceau, P.; Li, Z. Z.; Raffy, H.

    1999-01-01

    We report preliminary results obtained in a magneto-transport study in the normal state of overdoped ( Tc?63 K) and underdoped ( Tc?60 K and Tc?30 K) Bi 2Sr 2CaCu 2O 8+? thin films. In all cases the transverse magnetoresistance ( H? c with in-plane current) is positive and proportional to H2 up to 20 T for temperatures above approximately 110 K and does not follow Kohler's rule. No proportionality between the magnetoresistance and the square of the Hall angle ?H is observed, as would be expected if both quantities were governed by the same relaxation time ?H. In the high-temperature range the magnetoresistance of the underdoped samples appears to saturate in the vicinity of the temperature T ? where the resistivity shows a downturn from T-linear dependence.

  10. Exfoliated Bi2Sr2CaCu2O8+x thin flakes for electronic transport experiments

    NASA Astrophysics Data System (ADS)

    Lee, Menyoung; Neumann, Michael; Goldhaber-Gordon, David; Sandilands, Luke; Burch, Kenneth; Xu, Zhijun; Yang, Alina; Gu, Genda

    2013-03-01

    Bismuth-based cuprates are the model high-temperature superconductor of choice for experimental probes that are spectroscopic and sensitive to the surface (STM, ARPES), while studies of transport properties have typically focused on rare-earth element-based compounds. We will first discuss preparation methods for and characterization of tape-exfoliated single crystal thin (few to tens nm) flakes of the Bi2Sr2CaCu2O8+x compound, in particular focusing on protocols designed to produce exposed conducting surfaces that are atomically smooth over several microns, and addressing the factors that influence the surface morphology and Raman scattering properties of BSCCO thin flakes. In addition, data from electronic transport measurements, aimed at observing a modulation of critical temperature and an insulator to superconductor transition as a function of hole density in the compound, will be presented.

  11. The influence of selected metals (Mg, Ca, Sr and Ba) on the electronic system of the p-halogenobenzoic acids

    NASA Astrophysics Data System (ADS)

    Koczo?, P.; Mo?cibroda, P.; Dobrosz-Teperek, K.; Lewandowski, W.

    2001-05-01

    The assignment of the vibrational spectra of p-halogenobenzoic acid complexes with Mg, Ca, Sr and Ba is proposed. The influence of the metals on the electronic system of p-halogenobenzoic acids is the topic of study. The biggest differences in wavenumber of selected bands dependent on metal ion occurred within the spectral range: 1604-1612, 1550-1520, 1440-1410, 1302-1243, 1100-1090 and 875-865 cm -1. The influence of halogen (F, Cl, Br and I) on the electronic system of complexes was also investigated. The effect of halogen was mostly seen within the spectral range: 1610-1580, 1546-1540, 1183-1164, 1019-849 and 688-681 cm -1. The main factor responsible for the changes in the vibrational structure of the molecules was the ionic potential.

  12. 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., E-mail: lbufaical@ufg.br [Instituto de Física, Universidade Federal de Goiás, 74001-970 Goiânia, GO (Brazil); Adriano, C. [Instituto de Física “Gleb Wataghin”, UNICAMP, 13083-859 Campinas, SP (Brazil); Lora-Serrano, R. [Instituto de Física, Universidade Federal de Uberlândia, 38400-902 Uberlândia, MG (Brazil); Duque, J.G.S. [Núcleo de Física, Universidade Federal de Sergipe, Campus Itabaiana, 49500-000 Itabaiana, SE (Brazil); Mendonça-Ferreira, L. [Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, 09210-170 Santo André, SP (Brazil); Rojas-Ayala, C.; Baggio-Saitovitch, E.; Bittar, E.M. [Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, RJ (Brazil); Pagliuso, P.G. [Instituto de Física “Gleb Wataghin”, UNICAMP, 13083-859 Campinas, SP (Brazil)

    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}.

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

    PubMed

    Oh, Yoon Seok; Luo, Xuan; Huang, Fei-Ting; Wang, Yazhong; Cheong, Sang-Wook

    2015-04-01

    On the basis of successful first-principles predictions of new functional ferroelectric materials, a number of new ferroelectrics have been experimentally discovered. Using trilinear coupling of two types of octahedron rotation, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the Ruddlesden-Popper compounds (Ca3Ti2O7, Ca3Mn2O7 and (Ca/Sr/Ba)3(Sn/Zr/Ge)2O7). However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. Here we provide the first experimental demonstration of room-temperature switchable polarization in bulk crystals of Ca3Ti2O7, as well as Sr-doped Ca3Ti2O7. Furthermore, (Ca, Sr)3Ti2O7 is found to exhibit an intriguing ferroelectric domain structure resulting from orthorhombic twins and (switchable) planar polarization. The planar domain structure accompanies abundant charged domain walls with conducting head-to-head and insulating tail-to-tail configurations, which exhibit a conduction difference of two orders of magnitude. These discoveries provide new research opportunities, not only for new stable ferroelectrics of Ruddlesden-Popper compounds, but also for meandering conducting domain walls formed by planar polarization. PMID:25581628

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

    NASA Astrophysics Data System (ADS)

    Oh, Yoon Seok; Luo, Xuan; Huang, Fei-Ting; Wang, Yazhong; Cheong, Sang-Wook

    2015-04-01

    On the basis of successful first-principles predictions of new functional ferroelectric materials, a number of new ferroelectrics have been experimentally discovered. Using trilinear coupling of two types of octahedron rotation, hybrid improper ferroelectricity has been theoretically predicted in ordered perovskites and the Ruddlesden–Popper compounds (Ca3Ti2O7, Ca3Mn2O7 and (Ca/Sr/Ba)3(Sn/Zr/Ge)2O7). However, the ferroelectricity of these compounds has never been experimentally confirmed and even their polar nature has been under debate. Here we provide the first experimental demonstration of room-temperature switchable polarization in bulk crystals of Ca3Ti2O7, as well as Sr-doped Ca3Ti2O7. Furthermore, (Ca, Sr)3Ti2O7 is found to exhibit an intriguing ferroelectric domain structure resulting from orthorhombic twins and (switchable) planar polarization. The planar domain structure accompanies abundant charged domain walls with conducting head-to-head and insulating tail-to-tail configurations, which exhibit a conduction difference of two orders of magnitude. These discoveries provide new research opportunities, not only for new stable ferroelectrics of Ruddlesden–Popper compounds, but also for meandering conducting domain walls formed by planar polarization.

  15. Crystal structure and luminescence of Li 2Ca 0.7Sr 0.3SiO 4:Eu 2+ and its application in multi-phosphor converted white LEDs

    Microsoft Academic Search

    Hong He; Xiufeng Song; Renli Fu; Zhengwei Pan; Xinran Zhao; Zhonghua Deng; Yongge Cao

    2010-01-01

    The crystal structure and photoluminescence properties of Eu2+ doped Li2Ca0.7Sr0.3SiO4 phosphors were investigated. The Li2Ca0.7Sr0.3SiO4 is not an alloy between the tetragonal Li2CaSiO4 and hexagonal Li2SrSiO4 but crystallizes in orthorhombic structure similar to Li2(CaSr)SiO4. Photoluminescence properties of the Li2Ca0.7Sr0.3SiO4:Eu2+ phosphors, summarized in effective excitation in the UV region, strong emission in the blue light range (with a peak at 427nm)

  16. Hybrid density functional study of bulk titanates, ATiO3 (A=Sr, Ba, Ca, La, Sn, Pb)

    NASA Astrophysics Data System (ADS)

    Wadehra, Amita; Wilkins, John W.

    2013-03-01

    Perovskites have been a focus of considerable research attention due to exhibiting a variety of interesting and unique physical properties such as magnetism, ferroelectricity, superconductivity and multiferroicity. Accurate computations are needed to gain insights into the underlying physics of these complex materials. We present a systematic computational study of a series of titanates (ATiO3; A=Sr, Ba, Ca, La, Sn, Pb) using the hybrid functional HSE in density functional theory. HSE surpasses standard DFT and computes properties such as lattice constants, band gaps, structural and magnetic phases in excellent agreement with available experimental data. We also discuss the importance of spin-orbit interaction in determining the electronic structure and magnetic properties of these complex oxides. Perovskites have been a focus of considerable research attention due to exhibiting a variety of interesting and unique physical properties such as magnetism, ferroelectricity, superconductivity and multiferroicity. Accurate computations are needed to gain insights into the underlying physics of these complex materials. We present a systematic computational study of a series of titanates (ATiO3; A=Sr, Ba, Ca, La, Sn, Pb) using the hybrid functional HSE in density functional theory. HSE surpasses standard DFT and computes properties such as lattice constants, band gaps, structural and magnetic phases in excellent agreement with available experimental data. We also discuss the importance of spin-orbit interaction in determining the electronic structure and magnetic properties of these complex oxides. This work was supported by DOE-BES-DMS (DE-FG02-99ER45795). We used computational resources of the NERSC, supported by the U.S. DOE (DE-AC02-05CH11231), and the Ohio Supercomputing Center.

  17. 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.

  18. 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.

  19. Nanosized Cr2O3 as pinning center in (Bi,Pb)-Sr-Ca-Cu-O superconductor tapes

    NASA Astrophysics Data System (ADS)

    Lee, G. H.; Abd-Shukor, R.

    2013-05-01

    Nanosized Cr2O3 (6 nm) has been introduced into (Bi,Pb)-Sr-Ca-Cu-O/Ag tapes fabricated by the powderin-tube method. The starting powder with composition (Bi,Pb)2Sr2Ca2Cu3O10(Cr2O3)0.05 was prepared by the solid state reaction method. The superconductor tapes with thickness of about 0.3 mm and length about 2 cm were heated at 845°C for 96, 144, 192 and 240 h. The samples were characterized by the four point probe electrical measurements, X-ray powder diffraction method and scanning electron microscopy. The transport critical current density, Jc was measured from 30 to 65 K using the 1 ?/cm criterion. The highest Jc was obtained for the tape heated for 240 h with Jc = 1700 A/cm2 at 30 K. XRD patterns showed that the samples consisted of the 2212 and 2223 phase. SEM micrographs showed the plat-like structure. The role of nano-Cr2O3 in the superconductor system is discussed. The size of the nanoparticle (R) was larger than the coherence length, ? but smaller than the penetration depth, ?(?< R

  20. 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

  1. Photoemission study of the Bi 2CaSr 2Cu 2O 8 superconductor with Cu, Ag and Au overlayers

    NASA Astrophysics Data System (ADS)

    Bernhoff, H.; Qvarford, M.; Söderholm, S.; Nyholm, R.; Karlsson, U. O.; Lindau, I.; Flodström, A. S.

    1993-12-01

    In this paper, we present a photoemission study of the interaction of Cu, Ag and Au with clean single-crystal Bi 2CaSr 2Cu 2O 8 superconductor surfaces. Both the valence-band and the Bi 5d, O 1s and Sr 3d core levels were monitored for all overlayers. Cu, Ag and Au were deposited as consecutively thicker layers starting with a third of a monolayer and progressing in steps up to a deposition in the range of eight monolayers. Comparing the results for the different overlayers reveals the Ag overlayers to be less reactive than Au which causes the formation of metallic Bi on cleaved Bi 2CaSr 2Cu 2O 8 surface. Cu is shown to be the most reactive of the three metals. The Au and Ag overlayers display an island-growth mode, while Cu grows in a layer-by-layer fashion.

  2. Creep of polycrystalline (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x}

    SciTech Connect

    Martinez-Fernandez, J.; Dominguez-Rodriguez, A.; Routbort, J.L.; Goretta, K.C.

    2000-04-14

    Plastic deformation has proved to be essential to the manufacture of bulk (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223) superconductors. Compressive creep of dense, forged Bi-2223, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (Bi-2212), and Bi{sub 2}Sr{sub 2}CuO{sub x} (Bi-2201) superconductors has been studied. These previous studies left unanswered questions about the large variation in Q among the Bi-superconductors and the rate-controlling deformation mechanism. The goals of this work were to test high-quality bulk Bi-2223 to determine whether steady state can be established, and if so, to determine the dominant creep mechanism and the values of n and Q.

  3. electrophysiology and immunohistochemistry in the hippocampal ca1 and the dentate gyrus of rats chronically exposed to 1-bromopropane, a substitute for specific chlorofluorocarbons

    Microsoft Academic Search

    Y. Fueta; T. Fukuda; T. Ishidao; H. Hori

    2004-01-01

    1-Bromopropane is a newly introduced substitute for specific chlorofluorocarbons whose production was prohibited because of depletion of ozone layers. In this study, we analyzed disinhibitory effects induced by repetitive inhalation of 1-bromopropane for 12 weeks in the hippocampal CA1 and the dentate gyrus. In addition, reversal of the disinhibitory effects was examined 4 weeks after 1-bromopropane inhalation ceased. Exposure rats

  4. Magnetic properties of Ca-doped SrRuO 3 from full-potential calculations

    Microsoft Academic Search

    R. Vidya; P. Ravindran; A. Kjekshus; H. Fjellvåg; B. C. Hauback

    2004-01-01

    We have carried out accurate generalized-gradient-corrected fully-relativistic full-potential calculations for Sr1?xCaxRuO3 (x=0, 0.25, 0.5, 0.75, and 1) in para-, ferro-, and A-, C-, and G-type antiferromagnetic configurations. We have performed electronic structure calculations for the experimentally observed orthorhombic structure as well as the hypothetical cubic structure. Our results are analyzed with the help of total, site-, spin-, and orbital-projected density

  5. Sr\\/Ca and 13 C\\/ 12 C ratios in skeletal calcite of Mytilus trossulus: Covariation with metabolic rate, salinity, and carbon isotopic composition of seawater

    Microsoft Academic Search

    Robert T. Klein; Kyger C. Lohmann; Charles W. Thayer

    1996-01-01

    Minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity. Although molluscan calcite is secreted at or near oxygen isotope equilibrium, the influence of metabolic activity (i.e., vital effects) on skeletal Sr\\/Ca ratios and 13 C values is not well known. We present measurements of skeletal chemistry from (a) consecutive

  6. Sr Ca and 13C 12C ratios in skeletal calcite of Mytilus trossulus: Covariation with metabolic rate, salinity, and carbon isotopic composition of seawater

    Microsoft Academic Search

    Robert T. Klein; Kyger C. Lohmann; Charles W. Thayer

    1996-01-01

    Minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity. Although molluscan calcite is secreted at or near oxygen isotope equilibrium, the influence of metabolic activity (i.e., vital effects) on skeletal SrCa ratios and ? 13C values is not well known. We present measurements of skeletal chemistry from (a) consecutive

  7. 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.

  8. Eu and Dy activated (Sr0.90Ca0.10)3(PO4)2 phosphors for near- UV LED

    NASA Astrophysics Data System (ADS)

    Shinde, K. N.; Dhoble, S. J.

    2015-02-01

    The new efficient trivalent Eu and Dy activated (Sr0.90Ca0.10)3(PO4)2 phosphors were prepared by the conventional solid state method. X-ray powder diffraction analysis confirmed the formation of (Sr0.90Ca0.10)3(PO4)2 host lattice. The Eu3+ PL emission spectrum was observed in (Sr0.90Ca0.10)3(PO4)2 phosphors at 590 (orange) and 614 nm (red) region, the spectrum due to 5D0-7F1 and 5D0-7F2 transitions at near UV excitation, respectively. (Sr0.90Ca0.10)3(PO4)2: Dy3+ excited by 350 nm near-ultraviolet (NUV) light, the phosphors show an efficient blue and yellow band emissions, which originates from the 4F9/2-6H15/2 and 4F9/2-6H13/2 transitions of Dy3+ ion, respectively. The excitation spectra of the phosphors are broadband extending from 340 to 400 nm, which are characteristics of NUV excited LED. The investigated prepared phosphors are suitable for a NUV excited LED.

  9. Theoretical Calculations of Mechanical, Electronic, and Chemical Bonding in CaN2, SrN2, and BaN2

    NASA Astrophysics Data System (ADS)

    Zhang, Li-Qin; Cheng, Yan; Niu, Zhen-Wei; Piao, Chang-Ge; Ji, Guang-Fu

    2014-12-01

    We present a first-principles density functional theory-based study about the impact of pressure on the structural and elastic properties of bulk CaN2, SrN2, and BaN2. Non-spin and spin polarized calculations indicate that the non-spin polarized ground state was more favourable with magnetic moments of 1.049 ?B, 1.059 ?B, and 1.014 ?B for CaN2, SrN2, and BaN2, respectively, and these were in good agreement with previous experimental and theoretical data. The high bulk modulus of CaN2, SrN2, and BaN2 confirm that those compounds have low compressibility and high hardness. The obtained bulk modulus, N-N bond length, and optimized structure parameters are similar to those from previous studies.With an increase in applied pressure the independent elastic constants of CaN2, SrN2, and BaN2 indicated the presence of mechanical instability at 20, 15, and 10 GPa, which is possibly related to phase transitions in addition to a decrease in N-N bond length.

  10. Depression of the interlayer Josephson coupling in Bi2Sr2CaCu2O8x single crystals by spin-polarized

    E-print Network

    Lee, Hu-Jong

    Depression of the interlayer Josephson coupling in Bi2Sr2CaCu2O8þx single crystals by spin of Science and Technology, Pohang 790-784, South Korea Abstract We studied the effect of spin. Spin- injection through the Co electrode caused pair breaking in the CuO2 double layers, which led

  11. NUCLEAR THERMODYNAMIC DATABASE O-U-Zr-Fe-Cr-Ni-Ag-In-B-C-Ba-La-Ru-Sr-Al-Ca-Mg-Si

    E-print Network

    Paris-Sud XI, Université de

    NUCLEAR THERMODYNAMIC DATABASE « NUCLEA » O-U-Zr-Fe-Cr-Ni-Ag-In-B-C-Ba-La-Ru-Sr-Al-Ca-Mg-Si + Ar - TVA : FR 91 304 441 090 #12;NUCLEA Nuclear Thermodynamic Database Version 2007-01 developed March 1996 on the legal protection of databases. Extraction and/or re-utilization of the whole

  12. 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

    First principles studies on the structural, elastic, electronic properties and heats of formation of MgeAE (AE ¼ Ca, Sr, Ba) intermetallics Zhiwen Yang a , Jinglian Du b , Bin Wen b,*, Chuanzheng Hu Available online 9 October 2012 Keywords: A. Intermetallics, miscellaneous B. Brittleness and ductility B

  13. Observation of Josephson Coupling between CuO double layers in Bi 2CaSr 2Cu 2O 8 single crystals

    NASA Astrophysics Data System (ADS)

    Kleiner, R.; Steinmeyer, F.; Kunkel, G.; Müller, P.

    1991-12-01

    We report on measurements of DC and AC Josephson effects in small sized Bi 2CaSr 2Cu 2O 8 single crystals. The results are consistent with the assumption that adjacent CuO double layers are coupled via Josephson mechanisms.

  14. 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

  15. 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.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

    Margulies, Lawrence

    A variety of experimental techniques were utilized to examine the high temperature phase equilibria in the Bi- Sr-Ca-Cu-O-Ag system. Quenching studies were used to determine the liquid solubility of Ag in the Bi2Sr 2CaCu2O8 (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO2). A liquid immiscibility region between oxide and Ag liquids in the 8-98 at% range was found above 900°C. Two eutectics were found in the Bi2212-Ag pseudo-binary. On the oxide rich side, a eutectic exists at approximately 4 at% Ag. On the Ag rich side, a eutectic exists at approximately 98 at% Ag at a temperature of 15°C below the melting point of pure Ag. Six distinct solid phases were found to be in equilibrium with the partial melt within the Ag content and PO2 range studied. The stability of these solid phases were found to be highly sensitive to PO2, and to a much lesser extent Ag content. High temperature x-ray diffraction (HTXRD) studies of this system are in conflict with these results. It is suggested that these discrepancies are due to experimental artifacts caused by the significant thermal gradients and lack of full bulk sampling which is inherent in conventional HTXRD designs. In part II, a new furnace design compatible with synchrotron radiation sources is introduced to address these problems. This design allows for full bulk sampling in a low thermal gradient environment using Debye- Scherrer transmission geometry. Sample spinning is also introduced in the design to eliminate preferred orientation and incomplete powder averaging and allow for quantitative phase analysis and structural refinement. Studies on model systems are presented to demonstrate the capabilities for high resolution structural studies (Al 2O3) and time resolved phase transformation studies (SrCO 3). Finally, the Bi2212 system is examined to confirm the quenching results of part I, and to demonstrate the degree to which this new HTXRD design solves the problems associated with conventional designs.

  18. Two Ca2+ functions are demonstrated by the substitution of specific divalent and lanthanide cations for the Ca2+ required by the aggregation factor complex from the marine sponge, Microciona prolifera.

    PubMed

    Rice, D J; Humphreys, T

    1983-05-25

    Multivalent cations were tested for their ability to replace the Ca2+ requirements of aggregation factor (AF) complex in activity, stability, and integrity assays. The ability of each cation to replace the Ca2+ required for the cell aggregation-enhancing activity of AF was examined by replacing the usual 10 mM Ca2+ with the test cation at various concentrations in the serial dilution assay of the AF. The other alkaline earth cations, Mg2+, Sr2+, and Ba2+, could not replace Ca2+; two transition elements, Mn2+ and Cd2+, partially replaced calcium. All 15 of the available lanthanides (including La3+ and Y3+) produced normal activity but only at 10-400-fold lower cation concentrations than Ca2+. An AF preparation is stable and remains active for months in 1 mM Ca2+ but decays rapidly when Ca2+ is lowered. Sr2+ and Ba2+ at 20 mM but not at 1 mM could replace 1 mM Ca2+ and give long term stability. AF was not stable in the presence of Mg2+, even at 100 mM. High Mn2+ concentrations did not stabilize AF even though AF was partially active in Mn2+. Cd2+ gave full stability at 75 mM and La3+ at about 0.1 mM. When Ca2+ is chelated, the macromolecular subunits of the AF slowly dissociate. Permeation chromatography and analytical ultracentrifugation showed that the cations that stabilized activity maintained the integrity of AF complex while those that failed to stabilize activity allowed the complex to dissociate into subunits, indicating that these two Ca2+ requirements are related. The cation specificities for activity and for stability-integrity are different indicating that these are separate Ca2+-dependent functions. PMID:6853489

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    the South Pacific Convergence Zone (SPCZ), the variability in a sub-seasonally resolved microatoll Porites colony Sr/Ca record from Tonga and a previously published high-resolution record from Fiji are strongly influenced by sea surface temperature (SST) over the calibration period from 1981 to 2004 (R2 = 0.67-0.68). However, the Sr/Ca-derived SST correlation to instrumental SST decreases back in time. The lower frequency secular trend (~1°C) and decadal-scale (~2-3°C) modes in Sr/Ca-derived SST are almost two times larger than that observed in instrumental SST. The coral Sr/Ca records suggest that local effects on SST generate larger amplitude variability than gridded SST products indicate. Reconstructed ?18O of seawater (?18Osw) at these sites correlate with instrumental sea surface salinity (SSS; r = 0.64-0.67) but not local precipitation (r = -0.10 to -0.22) demonstrating that the advection and mixing of different salinity water masses may be the predominant control on ?18Osw in this region. The Sr/Ca records indicate SST warming over the last 100 years and appears to be related to the expansion of the western Pacific warm pool (WPWP) including an increasing rate of expansion in the last ~20 years. The reconstructed ?18Osw over the last 100 years also shows surface water freshening across the SPCZ. The warming and freshening of the surface ocean in our study area suggests that the SPCZ has been shifting (expanding) southeast, possibly related to the southward shift and intensification of the South Pacific gyre over the last 50 years in response to strengthened westerly winds.

  20. Electrical resistivity and stoichiometry of Ca(x)C60 and Sr(x)C60 films

    NASA Astrophysics Data System (ADS)

    Haddon, R. C.; Kochanski, G. P.; Hebard, A. F.; Fiory, A. T.; Morris, R. C.

    1992-12-01

    The temperature- and concentration-dependent resistivities of annealed Ca(x)C60 and Sr(x)C60 films were measured near room temperature. Resistivity minima were observed at x = 2 and 5. The resistivities of these films were rho (min) of about 1 ohm-centimeter for x = 2 and rho (min) of about 0.01 ohm-centimeter for x = 5. This latter value is comparable to the resistivities found in similar experiments on K3C60 films. There is a maximum in the resistivity between x = 2 and 3, another at x about 7. The conductivity is activated over the whole range of compositions, and the activation energy scales with the logarithm of the resistivity. The results suggest that the conductivity and superconductivity observed in Ca5C60 are associated with the population of bands derived form the (1g) level of C60. ticleCount> 2006 1 Springer-Verlag/Wien 2006 162 10.1007/s00704-005-0162-z 4 Four-dimensional data assimilation method based on SVD: Theoretical aspect 51 57 2005 1 1 2005 1 24 2005 3 14 2005 4 10 2005 7 18 Springer-Verlag/Wien 2005

  1. Synthesis, structure, and properties of four ternary compounds: CaSr Tt, Tt=Si, Ge, Sn, Pb

    NASA Astrophysics Data System (ADS)

    Liu, Shengfeng; Corbett, John D.

    2006-03-01

    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 2-type structure ( Pnma, Z=4, a=8.108(2), 8.124(2), 8.421(2), 8.509(2) Å; b=4.944(1), 4.949(1), 5.168(1), 5.189(1) Å; c=9.170(2), 9.184(2), 9.685(2), 9.740(2) Å, 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 2Si 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 Ae2Tt analogues.

  2. Phase analysis of Bi sbnd Ca sbnd Sr sbnd Cu sbnd O superconducting films at different growth temperatures from KCl supercooled solutions

    NASA Astrophysics Data System (ADS)

    Raina, Kanwal K.; Narayanan, S.; Pandey, R. K.

    1993-03-01

    Films of 80 K phase of BiCaSrCu-oxide superconductor referred as BCSCO have been grown from KCl-Bi2CaSr2Cu2O8+? solutions at different growth temperature regimes by the LPE process. Twin-free single crystal substrates of NdGaO3 with (001) orientation are used for growing these films. The temperature range of 850-830°C is found to be the most favorable region for the formation of the 2122 phase of BCSCO. Above 850°C up to the peritectic melting point of the 2122 phase (885°C), formation of the 2122 phase is highly suppressed with the separation of Bi2CaSr2Cu2O8+? into 2021, calcium copper oxide (Ca2CuO3 and CaCu2O3) and other non-superconducting phases. X-ray powder diffraction analysis is used to identify different phases of BCSCO films. Morphological examination of the films is carried out by scanning electron microscopy. The onset of transition of the 2122 phase films is observed at 90 K and zero resistance is reached at 83 K. Post-growth annealing has an adverse effect on the superconducting properties of the films.

  3. A three step method for synthesis of HTSC Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8+. delta. /

    SciTech Connect

    Kishan, P.; Chatterjee, S.N.; Prakash, C.; Sachar, B.K. (Solid State Physics Lab., Delhi (India))

    1989-02-01

    A method for the preparation of high Tc superconductor (HTSC) Bi/sub 2/CaSr/sub 2/Cu/sub 2/O/sub 8+{delta}/ involving three steps has been adopted. Firstly two compositions namely Bi/sub 2/O/sub 3/ + CaO and SrCO/sub 3/ + CuO were prepared, these were then mixed in the molar ratio 1:2. Short duration heat treatment at temperature approaching melting stage, which here was well above 900{sup 0}C due to pre-conversion of Bi/sub 2/O/sub 3/ into CaBi/sub 2/O/sub 4/, resulted in formation of material rich in the desired phase. Characterisation of samples by XRD, EMPA, electrical and magnetic methods is done.

  4. Study on possible correlation of superconductivity with defects and superparamagnetism in undoped AFe2As2 with A =Ca, Sr and Ba

    NASA Astrophysics Data System (ADS)

    Zhao, Kui; Lv, Bing; Deng, Liangzi; Xue, Yuyi; Chu, Paul; High pressure low temperature lab Team

    2014-03-01

    Extensive studies have been carried out on the induction of bulk superconductivity in the Fe-pnictide 122 system with a Tc up to 38 K through doping and/or pressure. However, non-bulk superconductivity has also been detected unexpectedly in undoped AFe2As2 where A = Ca, Sr, and Ba with Tc = ~12K, ~22K and ~23K, respectively. The reason for the observation remains unknown. Recently, systematic investigation shows that highly anisotropic superconductivity with a Tc up to 49 K and superparamagnetism occur in rare-earth doped Ca122. Further examination reveals slight deviation from the 1:2:2 stoichiometry which correlates closely with the occurrence of non-bulk superconductivity and superparamagnetism in these samples. We have therefore decided to investigate systematically the stoichiometry, defects, magnetism and superconductivity in undoped AFe2As2 single crystals under different synthesis conditions where A = Ca, Sr, and Ba. Results will be presented and discussed.

  5. High Oxygen Pressure and the Preparation of New Iridium (VI) Oxides with Perovskite Structure: Sr 2MIrO 6 ( M = Ca, Mg)

    NASA Astrophysics Data System (ADS)

    Jung, Duk-Young; Demazeau, Gérard

    1995-03-01

    Ir(VI) in an octahedral coordination has been stabilized in Sr 2MlrO 6 ( M = Ca, Mg) oxides with an ordered perovskite structure by use of high oxygen pressure. The structure of Sr 2CaIrO 6 depends strongly on the oxygen pressure and reversibly returns to the original structure according to the heat treatment applied. The oxidation state of iridium in each compound is determined by chemical titration and is correlated with the structural factors and the covalency of M-O bonds. The t32 ge0g electronic configuration of Ir(VI) leads to a high Néel temperature with 55 K ( M = Ca) and 80 K ( M = Mg). The samples are not metallic conductors.

  6. Composition dependences of Tc, Jc, physical property and crystal structure of Bi 1.8Pb 0.3Sr 2.0Ca 0.9Y 0.1Cu 2.0-xM xO y (M = Zr, Zn) superconducting oxide

    NASA Astrophysics Data System (ADS)

    Idemoto, Yasushi; Sekizawa, Oki; Kitamura, Naoto

    2011-03-01

    In this study, we focused on bulks and thin films of Bi 1.8Pb 0.3Sr 2.0Ca 0.9Y 0.1Cu 2.0O y, and replaced Cu by Zr 4+ and Zn 2+. From the electrical conductivity measurements on the bulk samples, it was found that Tc became higher by a partial substitution of Zr 4+, and exhibited a maximum value in the sample with the Zr 4+ content of 0.05. On the other hand, Tc was decreased by the Zn 2+ substitution. These results suggested that it was possible to control a carrier concentration by the Zr- and Zn-substitutions. Indeed, an average valence of the Cu, determined by a chelate titration, was changed by these substitutions. Similar tendency of the superconducting properties was also observed in the case of the film samples. In order to investigate crystal structures in detail, we measured neutron diffraction patterns, and then performed the Rietveld analysis. As a result, it was clarified that the (Cu, Zr)-O2 layers became flat by the Zr-substitution. Such a structure change may be one of the reasons why the substitution improved the superconducting properties.

  7. Effect of Ga doping on the physical properties of La0.7(CaSr)0.3Mn1-xGaxO3 (x = 0, 0.025, 0.05, 0.075 and 0.1)

    NASA Astrophysics Data System (ADS)

    Othmani, S.; Balli, M.

    2012-02-01

    In this paper we report on the structural, magnetic and transport properties of La0.7(CaSr)0.3Mn1-xGaxO3 (x = 0, 0.025, 0.05, 0.075 and 0.1) manganites elaborated by sol-gel method. The substitution of Mn by Ga affects slightly the structural parameters. A decrease of both magnetization M and Curie temperature Tc has been observed with increasing Ga content. The temperature dependence of the resistance shows a metal-insulator transition around TC.

  8. Effect of Ga doping on the physical properties of La0.7(CaSr)0.3Mn1?xGaxO3 (x = 0, 0.025, 0.05, 0.075 and 0.1)

    Microsoft Academic Search

    S Othmani; M Balli

    2012-01-01

    In this paper we report on the structural, magnetic and transport properties of La0.7(CaSr)0.3Mn1?xGaxO3 (x = 0, 0.025, 0.05, 0.075 and 0.1) manganites elaborated by sol-gel method. The substitution of Mn by Ga affects slightly the structural parameters. A decrease of both magnetization M and Curie temperature Tc has been observed with increasing Ga content. The temperature dependence of the

  9. Rolled-up tubes and cantilevers by releasing SrRuO3-Pr0.7Ca0.3MnO3 nanomembranes.

    PubMed

    Deneke, Christoph; Wild, Elisabeth; Boldyreva, Ksenia; Baunack, Stefan; Cendula, Peter; Mönch, Ingolf; Simon, Markus; Malachias, Angelo; Dörr, Kathrin; Schmidt, Oliver G

    2011-01-01

    Three-dimensional micro-objects are fabricated by the controlled release of inherently strained SrRuO3/Pr0.7Ca0.3MnO3/SrRuO3 nanometer-sized trilayers from SrTiO3(001) substrates. Freestanding cantilevers and rolled-up microtubes with a diameter of 6 to 8 ?m are demonstrated. The etching behavior of the SrRuO3 film is investigated, and a selectivity of 1:9,100 with respect to the SrTiO3 substrate is found. The initial and final strain states of the rolled-up oxide layers are studied by X-ray diffraction on an ensemble of tubes. Relaxation of the sandwiched Pr0.7Ca0.3MnO3 layer towards its bulk lattice parameter is observed as the major driving force for the roll-up of the trilayers. Finally, ?-diffraction experiments reveal that a single object can represent the ensemble proving a good homogeneity of the rolled-up tubes.PACS: 81.07.-b; 68.60.-p; 68.37.Lp; 81.16.Dn. PMID:22151894

  10. Rolled-up tubes and cantilevers by releasing SrRuO3-Pr0.7Ca0.3MnO3 nanomembranes

    PubMed Central

    2011-01-01

    Three-dimensional micro-objects are fabricated by the controlled release of inherently strained SrRuO3/Pr0.7Ca0.3MnO3/SrRuO3 nanometer-sized trilayers from SrTiO3(001) substrates. Freestanding cantilevers and rolled-up microtubes with a diameter of 6 to 8 ?m are demonstrated. The etching behavior of the SrRuO3 film is investigated, and a selectivity of 1:9,100 with respect to the SrTiO3 substrate is found. The initial and final strain states of the rolled-up oxide layers are studied by X-ray diffraction on an ensemble of tubes. Relaxation of the sandwiched Pr0.7Ca0.3MnO3 layer towards its bulk lattice parameter is observed as the major driving force for the roll-up of the trilayers. Finally, ?-diffraction experiments reveal that a single object can represent the ensemble proving a good homogeneity of the rolled-up tubes. PACS: 81.07.-b; 68.60.-p; 68.37.Lp; 81.16.Dn. PMID:22151894

  11. Strontianite-aragonite solid solutions Sr/sub x/Ca/sub 1-x/CO/sub 3/: effect of composition on the orthorhombic-rhombohedral phase transition and the conversion to oxide solid solutions Sr/sub x/Ca/sub 1-x/O

    SciTech Connect

    Fubini, B.; Di Renzo, F.; Stone, F.S.

    1988-12-01

    The conversion of orthorhombic Sr/sub x/Ca/sub 1-x/CO/sub 3/ solid solutions to Sr/sub x/Ca/sub 1-x/O has been studied by thermal analysis and X-ray diffraction. The decomposition occurs in two stages. In the first stage, occurring at 950-1150 K in N/sub 2/, the cations demix to produce CaO and leave a Sr-enriched carbonate phase. In the second stage (1150-1350 K) the residual carbonate decomposes and the cations remix to form the oxide solid solution. By heating in CO/sub 2/, thereby displacing decomposition to above 1250 K, the orthorhombic-rhombohedral phase transition characteristic of these carbonates has been studied over the whole range x = O ..-->.. 1. The transition temperature (T/sub tr/) increases progressively with x. For the Sr-enriched carbonate obtained after the first stage of decomposition in N/sub 2/, T/sub tr/ is independent of the initial composition and close to that for SrCO/sub 3/. ..delta..H for the transition, however, is less than that expected for well-crystallized SrCO/sub 3/, suggesting that the demixed carbonate is partly amorphous.

  12. Superconducting ceramics in the Bi1.5SrCaCu2O sub x system by melt quenching technique

    NASA Astrophysics Data System (ADS)

    Bansal, Narottam P.; Deguire, Mark R.

    1989-10-01

    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.

  13. The crystal structures of pressure-induced LiSrAlF6-II and LiCaAlF6-II

    NASA Astrophysics Data System (ADS)

    Grzechnik, Andrzej; Dmitriev, Vladimir; Weber, Hans-Peter; Gesland, Jean-Yves; van Smaalen, Sander

    2004-02-01

    The crystal structures of LiCaAlF6-II and LiSrAlF6-II (both P 21/c, Z = 4) occurring at high pressures and room temperature were studied with synchrotron angle-dispersive x-ray powder diffraction in diamond anvil cells. The structure of LiSrAlF6-II stable between 1.6 and 3.0 GPa was solved with a global optimisation algorithm and group theory considerations, and refined with the Rietveld method in the rigid-body approximation. It is a distorted variant of the ambient pressure polymorph (LiSrAlF6-I, P\\bar 3 1c, Z=2 ), in which each cation occupies a deformed octahedral site. LiCaAlF6 transforms to this monoclinic polymorph II above about 7 GPa. The differences in the high-pressure behaviours of LiCaAlF6 and LiSrAlF6 are discussed by considering the ionic radii.

  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. Ferroelectric and piezoelectric properties of tungsten substituted SrBi{sub 2}Ta{sub 2}O{sub 9} ferroelectric ceramics

    SciTech Connect

    Coondoo, Indrani, E-mail: indrani_coondoo@yahoo.com; Agarwal, S.K. [Superconductivity and Cryogenics Division, National Physical Laboratory, Dr K.S. Krishnan Road, New Delhi 110012 (India); Jha, A.K. [Department of Applied Physics, Delhi College of Engineering, Bawana Road, Delhi 110042 (India)

    2009-06-03

    Tungsten substituted samples of compositions SrBi{sub 2}(W{sub x}Ta{sub 1-x}){sub 2}O{sub 9} (x = 0.0, 0.025, 0.050, 0.075, 0.10 and 0.20) were synthesized by solid-state reaction method and studied for their microstructural, electrical conductivity, ferroelectric and piezoelectric properties. The X-ray diffractograms confirm the formation of single phase layered perovskite structure in the samples with x up to 0.05. The temperature dependence of dc conductivity vis-a-vis tungsten content shows a decrease in conductivity, which is attributed to the suppression of oxygen vacancies. The ferroelectric and piezoelectric studies of the W-substituted SBT ceramics show that the remanent polarization and d{sub 33} values increases with increasing concentration of tungsten up to x {<=} 0.05. Such compositions with low conductivity and high P{sub r} values should be excellent materials for highly stable ferroelectric memory devices.

  16. Fluctuation-conductivity Characterization of Superconducting Bi2Sr2CaCu2O8+d Thin Films Prepared by the Metal-organic Decomposition Method

    NASA Astrophysics Data System (ADS)

    Deguchi, Y.; Kikuchi, H.; Mori, N.; Yamada, Y.; Atsumi, T.; Yoshida, K.; Ishibashi, T.

    We report on the preparation and characterization of Bi2Sr2CaCu2O8+d (Bi2212) thin films. These films on SrTiO3 substrates were fabricated by the metal-organic decomposition method and annealing at a temperature between 810~850 °C. On the basis of the analysis for the fluctuation conductivity ?' above Tc, we characterize properties of Bi2212 films by taking account of overall theoretical ?' terms and momentum cutoff effects. In the analysis we estimate, as a function of Tc, the fluctuation parameters, among which anisotropy and depairing parameters are found to be correlated with Tc.

  17. Superconductivity and normal-state magnetic properties of Bi 2Sr 2Ca 1-xCe xCu 2O y

    NASA Astrophysics Data System (ADS)

    Sawa, Akihito; Han, Tae-Su; Iwamatsu, Takayuki; Uwe, Hiromoto; Sakupido, Tunerato; Yamaguchip, Yuji; Tokumoto, Madoka

    1991-12-01

    The normal-state magnetic susceptivity of Bi 2Sr 2Ca 1-xCe xCu 2O y has been studied. The temperature dependent contribution to the susceptivity, which is attributable to the twp-dimensional square lattice Hesenberg antiferromagnet of the CuO 2 plane, is found to scale with two parameters of X2 Dmax and Tmax, by using a function which was found for La 2-xSr xCuO 4 by D.C.Johnston. The spin fluctuation of Cu-ion estimated from the susceptivity is smaller near the Ce concentration of the highest Tc.

  18. Temperature dependence of electron spin resonance in CaCu 3Ti 4O 12 substituted with transition metal elements

    NASA Astrophysics Data System (ADS)

    Brizé, Virginie; Autret-Lambert, Cécile; Wolfman, Jérôme; Gervais, Monique; Simon, Patrick; Gervais, François

    2009-04-01

    The temperature dependence of the electron spin resonance (ESR) spectrum of copper in CaCu 3Ti 4O 12 (CCTO) polycrystalline samples doped with transition metal elements Mn, Fe, Ni is reported. The frequency dependence of the dielectric constant of the sample is also reported at room temperature. While the dielectric constant of undoped CCTO samples reaches ˜10,000, it is found one hundred times lower in samples doped with only 0.5 or 1% of Mn or Fe. Copper is confirmed to give a g = 2.14 signal at room temperature for substituted and unsubstituted samples. Below the antiferromagnetic transition that occurs near 25 K, the signal is found shifted down to low fields for all samples. However the downshift is 10-20 times more important in Mn and Fe-doped samples compared to undoped or Ni-doped CCTO. ESR results in an undoped CCTO thin film grown by pulse laser deposition are also reported. While in the low-temperature antiferromagnetic phase the spectrum is multi-line and magnetic-field-orientation-dependent, it reduces to a narrow single line, independent of the orientation of the magnetic field, in the upper paramagnetic phase, similar to the undoped polycrystalline sample. All doped samples display much broader response in the upper phase. The results are discussed within the framework of the relationship between the high effective dielectric constant and the electrical conductivity of CCTO bulk.

  19. Morphology and Properties of (Ba, Sr, Ca) Titanates Synthesized by Microwave-Assisted Hydrothermal Method

    NASA Astrophysics Data System (ADS)

    Souza, A. E.; Santos, G. T. A.; Silva, R. A.; Moreira, M. L.; Volante, D. P.; Teixeira, S. R.; Longo, E.

    2011-10-01

    Ba1-xCaxTiO3, Ba1-xSrxTiO3 and Sr1-xCaxTiO3 (x = 0, 0.25, 0.50, 0.75 and 1) nanoparticles were synthesized using the microwave-assisted hydrothermal method. Samples were prepared for 40 minutes at 140°C under a pressure of 3 MPa using an adapted domestic microwave oven. The samples were characterized by X-Ray diffraction (XRD), scanning electron microscopy (FE-SEM), and Raman, photoluminescence (PL) and ultraviolet-visible (UV-Vis) spectroscopies. XRD data show that ceramic powders have crystalline phases associated with a short-range structural disorder. This structural disorder is confirmed by Raman spectral bands indicating multi-phonon processes and the presence of defects or impurities. Such defects account for a broad band in the photoluminescence spectrum in the green light (460 nm) region for all samples. Gap energy variation, obtained from UV-Vis spectra, suggest a non-uniform band structure of these titanates in accordance with the PL results. The morphology of each sample is changed with doping and varies from a spherical to cubic appearance for energy minimization.

  20. Three monthly coral Sr/Ca records from the Chagos Archipelago covering the period of 1950-1995 A.D.: reproducibility and implications for quantitative reconstructions of sea surface temperature variations

    NASA Astrophysics Data System (ADS)

    Pfeiffer, Miriam; Dullo, Wolf-Christian; Zinke, Jens; Garbe-Schönberg, Dieter

    2009-02-01

    In order to assess the fidelity of coral Sr/Ca for quantitative reconstructions of sea surface temperature variations, we have generated three monthly Sr/Ca time series from Porites corals from the lagoon of Peros Banhos (71°E, 5°S, Chagos Archipelago). We find that all three coral Sr/Ca time series are well correlated with instrumental records of sea surface temperature (SST) and air temperature. However, the intrinsic variance of the single-core Sr/Ca time series differs from core to core, limiting their use for quantitative estimates of past temperature variations. Averaging the single-core data improves the correlation with instrumental temperature ( r > 0.7) and allows accurate estimates of interannual temperature variations (~0.35°C or better). All Sr/Ca time series indicate a shift towards warmer temperatures in the mid-1970s, which coincides with the most recent regime shift in the Pacific Ocean. However, the magnitude of the warming inferred from coral Sr/Ca differs from core to core and ranges from 0.26 to 0.75°C. The composite Sr/Ca record from Peros Banhos clearly captures the major climatic signals in the Indo-Pacific Ocean, i.e. the El Niño-southern oscillation and the Pacific decadal oscillation. Moreover, composite Sr/Ca is highly correlated with tropical mean temperatures ( r = 0.7), suggesting that coral Sr/Ca time series from the tropical Indian Ocean will contribute to multi-proxy reconstructions of tropical mean temperatures.

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

    SciTech Connect

    Hadipour, H. [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of); Akhavan, M., E-mail: akhavan@sharif.ed [Magnet Research Laboratory (MRL), Department of Physics, Sharif University of Technology, P.O. Box 11365-9161, Tehran (Iran, Islamic Republic of)

    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.

  2. 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.

  3. 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

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

    E-print Network

    Oh, Se-Jung

    Optical investigation of the electronic structures of Y2Ru2O7 , CaRuO3 , SrRuO3, and Bi2Ru2O7 J. S structures of the bandwidth-controlled ruthenates, Y2Ru2O7 , CaRuO3 , SrRuO3, and Bi2Ru2O7, by optical metal. Y2Ru2O7 has the pyrochlore structure and shows an insulat- ing behavior. Both CaRuO3 and SrRuO3

  5. Normal-state Hall effect measurements for Tl 0.8Hg 0.2Ba 2Ca 2Cu 3O 9-? substituted by Sm and Yb

    NASA Astrophysics Data System (ADS)

    Awad, R.; Abou-Aly, A. I.; Ibrahim, I. H.; Abdeen, W.

    2008-04-01

    The normal-state Hall effect for Tl 0.8Hg 0.2Ba 2Ca 2- xR xCu 3O 9-?, where R=Sm and Yb with 0?x?0.15, is measured above the superconducting transition temperature. The Hall coefficients RH, for all prepared samples, are positive and follow the Curie-Weiss temperature dependence type. Carrier-concentrations nH decrease as the substitution-content x increases, as a result of the hole-filling mechanism. The sample with lower resistivity exhibits higher carrier-concentration. The Hall angle cot ?H increases as the temperature increases and well fitted to the formula cot ?H=?T2+?. The constant ? is found to be strongly dependent on the substitution-content and it is correlated to the residual resistivity ?0. Finally, the variation of Hall mobility with both temperature and substitution-content is reported.

  6. Synthesis, crystal structure, and TEM analysis of Sr19Li44 and Sr3Li2: a reinvestigation of the Sr-Li phase diagram.

    PubMed

    Smetana, Volodymyr; Kienle, Lorenz; Duppel, Viola; Simon, Arndt

    2015-02-01

    Two intermetallic phases in the Sr-Li system have been synthesized and structurally characterized. According to single-crystal X-ray diffraction data, Sr(19)Li(44) and Sr(3)Li(2) crystallize with tetragonal unit cells (Sr(19)Li(44), I-42d, a = 15.9122(7) Å, c = 31.831(2) Å, Z = 4, V = 8059(2) Å(3); Sr(3)Li(2), P42/mnm, a = 9.803(1) Å, c = 8.784(2) Å, Z = 4, V = 844.2(2) Å(3)). The first compound is isostructural with the recently discovered Ba(19)Li(44). Sr in Sr(19)Li(44) can be fully replaced by Ba with no changes to the crystal structure, whereas the substitution of Sr by Ca is only possible within a limited concentration range. Sr(3)Li(2) can be assigned to the Al(2)Zr(3) structure type. The crystal structure determination of Sr(19)Li(44) was complicated by multiple twinning. As an experimental highlight, an electron microscopy investigation of the highly moisture- and electron-beam-sensitive crystals was performed, enabling high-resolution imaging of the defect structure. PMID:24969220

  7. 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).

  8. Dip effect in ?? of ac susceptibility in Bi 2Sr 2CaCu 2O 8 single crystal

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Ren, C.; Ding, S. Y.; Lin, F. Y.; Li, Z. M.; Aruna, S. A.; Qiu, L.; Yao, X. X.; Gu, G. D.

    1999-08-01

    We present a direct evidence of the softening of the shear modulus constant c66 by a measurement of the real part ??( T) of ac susceptibility. A dip in ??( T) for a single crystal of Bi 2Sr 2CaCu 2O 8 has been found at an intermediate field region between 50 and 3000 G. We showed that the dip effect was due to the softening of the shear modulus constant c66, equivalent to the peak effect in resistivity measurement. The dependence of the peak temperature Tp in ?? on magnetic field and current density shows the transition between vortex solid and vortex liquid. Thus, the dip in ??( T) is illustrated as a precursor to vortex lattice melting in this narrow field region, indicative of lattice softening prior to melting. In the region between Td and the melting temperature Tm, the flux lines move by a type of plastic deformation, and the pinning energy barrier U has been obtained as: U?[1-( J/ Jc) ?] H? with ?, ?>0.

  9. Infrared and millimeter wave detection using thin films of Pb doped BiSrCaCuO superconductor

    NASA Astrophysics Data System (ADS)

    Phong, L. Ngo

    1995-01-01

    Thin film detectors made of CuO superconductors were developed in our laboratory. This article reports details of the fabrication and testing of Pb doped BiSrCaCuO detectors. The detector comprises a film sensor housed in a small cryostat with built-in bias supply and temperature control circuitry. The film sensor was first deposited by magnetron rf sputtering and then crystallized under a rapid thermal annealing process. The characteristics of the response of the detector under millimeter wave and infrared illumination were investigated. The millimeter wave response exhibited a Josephson component with a D(*) approximately 10(exp 8) - 10(exp 9) cm.Hz(exp (1/2))/W in the wavelength range of 3 - 8 mm. The transient response to short pulses indicated a time constant tau less than or equal to 10 ns for this component. The response to laser pulses was thermal in origin and inherently compressible, preventing saturation of the detector electronics to intense beams. The wide band characteristic of the responses at both infrared and millimeter wavelengths could be confirmed. The damage threshold of the film sensor was shown to exceed 10 mJ / sq cm per 3 ns pulse. The possible use of these detectors for threat detection and the optimization of their figure of merit are discussed.

  10. Theoretical Study of M(+)-RG2: (M(+) = Ca, Sr, Ba, and Ra; RG = He-Rn).

    PubMed

    Andrejeva, Anna; Gardner, Adrian M; Graneek, Jack B; Breckenridge, W H; Wright, Timothy G

    2015-06-11

    Ab initio calculations were employed to investigate M(+)-RG2 species, where M(+) = Ca, Sr, Ba, and Ra and RG = He-Rn. Geometries have been optimized, and cuts through the potential energy surfaces containing each global minimum have been calculated at the MP2 level of theory, employing triple-? quality basis sets. The interaction energies for these complexes were calculated employing the RCCSD(T) level of theory with quadruple-? quality basis sets. Trends in binding energies, De, equilibrium bond lengths, Re, and bond angles are discussed and rationalized by analyzing the electronic density. Mulliken, natural population, and atoms-in-molecules (AIM) population analyses are presented. It is found that some of these complexes involving the heavier group 2 metals are bent whereas others are linear, deviating from observations for the corresponding Be and Mg metal-containing complexes, which have all previously been found to be bent. The results are discussed in terms of orbital hybridization and the different types of interaction present in these species. PMID:25633369

  11. 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.

  12. Fractional-exponent behavior of magnetization near Tc in Bi2Sr2CaCu2O8

    NASA Astrophysics Data System (ADS)

    Li, Lu; Naughton, M. J.; Ono, S.; Ong, N. P.

    2005-03-01

    Using high-resolution torque magnetometry, we have investigated in detail how long-range phase coherence develops as the critical temperature Tc (88.7 K) is approached in optimally-doped Bi2Sr2CaCuO8+? with field H||c. Three distinct regimes are observed. Above ˜92 K, |M| increases rapidly as T->Tc in step with the vortex Nernst signal. M is strictly linear in H in weak H, but shows strong curvature at large H (5-14 T). The curvature provides a determination of the correlation length ?sc which grows as a power law, viz. ?sc˜1/t^?. In the second regime, 86 < T < 92 K, M becomes nonlinear in H, viz. M˜H^?(T), where the exponent ?(T) decreases from 1 to 0. This interesting fractional-exponent behavior is highly unusual and fits poorly with conventional pictures of `fluctuating diamagnetism.' As previously known, M is virtually H independent below 2 Tesla at the ``crossing temperature'' Tcr = 86 K. Below Tcr, M is a function of H. We compare this behavior with predictions of the 3DXY and Kosterlitz-Thouless theory. Supported by funds from the U.S. National Science Foundation under grant DMR 0213706.

  13. Ternary CaCu{sub 4}P{sub 2}-type pnictides AAg{sub 4}Pn{sub 2} (A=Sr, Eu; Pn=As, Sb)

    SciTech Connect

    Stoyko, Stanislav S.; Khatun, Mansura; Scott Mullen, C. [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada); Mar, Arthur, E-mail: arthur.mar@ualberta.ca [Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada)

    2012-08-15

    Four ternary pnictides AAg{sub 4}Pn{sub 2} (A=Sr, Eu; Pn=As, Sb) were prepared by reactions of the elements at 850 Degree-Sign C and their crystal structures were determined from single-crystal X-ray diffraction studies. These silver-containing pnictides AAg{sub 4}Pn{sub 2} adopt the trigonal CaCu{sub 4}P{sub 2}-type structure (Pearson symbol hR21, space group R3-bar m, Z=3; a=4.5555(6) A, c=24.041(3) A for SrAg{sub 4}As{sub 2}; a=4.5352(2) A, c=23.7221(11) A for EuAg{sub 4}As{sub 2}; a=4.7404(4) A, c=25.029(2) A for SrAg{sub 4}Sb{sub 2}; a=4.7239(3) A, c=24.689(2) A for EuAg{sub 4}Sb{sub 2}), which can be derived from the trigonal CaAl{sub 2}Si{sub 2}-type structure of the isoelectronic zinc-containing pnictides AZn{sub 2}Pn{sub 2} by insertion of additional Ag atoms into trigonal planar sites within [M{sub 2}Pn{sub 2}]{sup 2-} slabs built up of edge-sharing tetrahedra. Band structure calculations on SrAg{sub 4}As{sub 2} and SrAg{sub 4}Sb{sub 2} revealed that these charge-balanced Zintl phases actually exhibit no gap at the Fermi level and are predicted to be semimetals. - Graphical abstract: SrAg{sub 4}As{sub 2} and related pnictides adopt a CaCu{sub 4}P{sub 2}-type structure in which additional Ag atoms enter trigonal planar sites within slabs built from edge-sharing tetrahedra. Highlights: Black-Right-Pointing-Pointer AAg{sub 4}Pn{sub 2} are the first Ag-containing members of the CaCu{sub 4}P{sub 2}-type structure. Black-Right-Pointing-Pointer Ag atoms are stuffed in trigonal planar sites within CaAl{sub 2}Si{sub 2}-type slabs. Black-Right-Pointing-Pointer Ag-Ag bonding develops through attractive d{sup 10}-d{sup 10} interactions.

  14. 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. (School of Materials Science and Engineering, Univ. of New South Wales, Kensington, New South Wales 2033 (AU))

    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.

  15. Raman spectroscopy study of the interface structure in (CaCuO2)n/(SrTiO3)m superlattices

    NASA Astrophysics Data System (ADS)

    Di Castro, D.; Caramazza, S.; Innocenti, D.; Balestrino, G.; Marini, C.; Dore, P.; Postorino, P.

    2013-11-01

    Raman spectra of CaCuO2/SrTiO3 superlattices show clear spectroscopic marker of two structures formed in CaCuO2 at the interface with SrTiO3. For non-superconducting superlattices, grown in low oxidizing atmosphere, the 425 cm-1 frequency of oxygen vibration in CuO2 planes is the same as for CCO films with infinite layer structure (planar Cu-O coordination). For superconducting superlattices grown in highly oxidizing atmosphere, a 60 cm-1 frequency shift to lower energy occurs. This is ascribed to a change from planar to pyramidal Cu-O coordination because of oxygen incorporation at the interface. Raman spectroscopy proves to be a powerful tool for interface structure investigation.

  16. Synthesis, structures and phase transitions in the double perovskites Sr{sub 2-x}Ca{sub x}CrNbO{sub 6}

    SciTech Connect

    Cheah, Melina C.L. [School of Chemistry, University of Sydney, Sydney, NSW 2006 Australia (Australia); Kennedy, Brendan J. [School of Chemistry, University of Sydney, Sydney, NSW 2006 Australia (Australia)]. E-mail: kennedyb@chem.usyd.edu.au; Withers, Ray L. [Research School of Chemistry, Australian National University, Canberra ACT 2600 (Australia); Yonemura, Masao [Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573 (Japan); Kamiyama, Takashi [Institute of Materials Science, University of Tsukuba, Tsukuba 305-8573 (Japan)

    2006-08-15

    The synthesis and crystal structures of nine members of the rock-salt ordered double perovskites Sr{sub 2-x}Ca{sub x}CrNbO{sub 6} is presented. The crystal structures of the end members of the series Sr{sub 2}CrNbO{sub 6} and Ca{sub 2}CrNbO{sub 6} were refined using powder neutron diffraction data and are cubic in Fm3-bar m and monoclinic in P2{sub 1}/n, respectively, in both cases there being considerable anti-site Cr-Nb mixing. Variable temperature and/or composition studies suggest a direct first-order P2{sub 1}/n to Fm3-bar m transition, a suggestion supported by selected area electron diffraction studies.

  17. Orbital orderings and optical conductivity of SrRuO3 and CaRuO3: first-principles studies

    NASA Astrophysics Data System (ADS)

    Wang, Guang-Tao; Zhang, Min-Ping; Yang, Zong-Xian; Fang, Zhong

    2009-07-01

    The Jahn-Teller (JT) distortion induced orbital order and optical conductivity in SrRuO3 and CaRuO3 are investigated by first-principles calculations. The total energy and optical conductivity of all the spin ordering states of SrRuO3 and CaRuO3 are calculated in the LDA+U scheme with Ueff = 2.5 eV. The down-spin t2g of Ru show antiferromagnetic-like orbital order in the a-b plane. We observe a d-d transition peak at an energy of about 1.0 eV in the calculated optical conductivity and analyze the reason for it not being observed in previous experiments.

  18. High-pressure synthesis of Y 1-xCa xSr 2GaCu 2O 7±? (0? x?1.0)

    NASA Astrophysics Data System (ADS)

    Isobe, M.; Matsui, Y.; Takayama-Muromachi, E.

    1994-03-01

    High-pressure synthesis at 6 GPa was performed for a series of compounds, Y 1- xCa xSr 2GaCu 2O 7±? with 0? x?0. The solubility limit extended up to x=1.0 at 6 GPa in contrast to x?0.3 at ambient pressure and the Y-free compound, CaSr 2GaCu 2O 7±?, was prepared successfully. Superconductivity appeared in samples with x?0.4 which showed metallic conductivity above Tc. Tc increased up to 49 K at x=0.6 with increasing x, while Tc decreased to 15 K at x=0.8, probably owing to overdoping of carriers. However, Tc of the Y-free sample was as high as 70 K in spite of the fact that it seems to have larger carrier density. Possible reasons for this “abnormal” result are discussed.

  19. Spin-orbit-induced orbital excitations in Sr2RuO4 and Ca2RuO4 : A resonant inelastic x-ray scattering study

    NASA Astrophysics Data System (ADS)

    Fatuzzo, C. G.; Dantz, M.; Fatale, S.; Olalde-Velasco, P.; Shaik, N. E.; Dalla Piazza, B.; Toth, S.; Pelliciari, J.; Fittipaldi, R.; Vecchione, A.; Kikugawa, N.; Brooks, J. S.; Rønnow, H. M.; Grioni, M.; Rüegg, Ch.; Schmitt, T.; Chang, J.

    2015-04-01

    High-resolution resonant inelastic x-ray scattering (RIXS) at the oxygen K edge has been used to study the orbital excitations of Ca2RuO4 and Sr2RuO4 . In combination with linear dichroism x-ray absorption spectroscopy, the ruthenium 4 d -orbital occupation and excitations were probed through their hybridization with the oxygen p orbitals. These results are described within a minimal model, taking into account crystal field splitting and a spin-orbit coupling ?s o=200 meV. The effects of spin-orbit interaction on the electronic structure and implications for the Mott and superconducting ground states of (Ca,Sr)2RuO 4 are discussed.

  20. Superconductivity in (Pb 0.75Cu 0.25)Sr 2(Y 1- x, Ca x)Cu 2O 7-? without high pressure oxygen annealing

    NASA Astrophysics Data System (ADS)

    Naqvi, S. H. H.; Boyd, I. W.

    1993-08-01

    The effects of annealing (Pb 0.75Cu 0.25)Sr 2(Y 1- xCa x)Cu 2O 7-?, where the calcium content varied from x=0.4 to 0.8, have been investigated. We have found for the first time that superconducting (Pb 0.75Cu 0.25)Sr 2(Y 1- xCa x)Cu 2O 7-? can be formed by adjusting the final oxygen content in a nitrogen ambient instead of using a high-pressure oxygen anneal. The total processing time of only 9 h (including all the calcining, annealing, sintering and cooling steps) is by far the shortest yet reported. This material exhibits a Tc,onset of 82 K and Tc,zero of 76 K.

  1. Composition and magnetic studies of ultrafine Al-substituted Sr hexaferrite particles prepared by citrate sol-gel method

    NASA Astrophysics Data System (ADS)

    Nga, Tran Thi Viet; Duong, Nguyen Phuc; Hien, Than Duc

    2012-03-01

    Ultrafine aluminum-substituted strontium hexaferrite particles have been prepared via citrate sol-gel route. Gels were synthesized with molar ratios [Al3+]:[Fe3+] of 0.4:11.6, 1:11, 1.5:10.5 and 2:10 and the ferrite particles were obtained by annealing the gels at 950 °C for 2 and 24 h. Electron energy dispersive X-ray spectroscopy (EDX) verified the presence of Al in the substituted samples. X-ray diffraction (XRD) confirmed the formation of the M-type hexaferrite phase in the samples with some indication of ?-Fe2O3. Scanning electron microscope showed that the hexaferrite powder consists hexagonal crystals with average diameter Dav (80-186 nm) that decreases with increasing Al content and increases with increasing annealing time. Magnetic properties were determined using a pulsed-field magnetometer and a vibrating sample magnetometer (VSM). The saturation magnetization at room temperature and the Curie temperature were found to decrease while the coercivity increases with increasing the Al content. The highest coercivity of 10.1 kOe was achieved for the sample with the molar ratio [Al3+]:[Fe3+]=2:10 annealed for 24 h. The influences of the particle size, composition and impurity on the magnetic properties were discussed.

  2. Superconductivity in Co and Li Substituted Cu0.5Tl0.5Ba2Ca2Cu3- x Co x O10- ?

    NASA Astrophysics Data System (ADS)

    Mumtaz, M.; Khan, Nawazish A.; Ullah, Anayat

    2011-05-01

    We have tried to explore the possible sources of suppression of superconducting properties in cobalt substituted Cu0.5Tl0.5Ba2Ca2Cu3- x Co x O10- ? ( x=0,0.05,0.1,0.5) superconductor. It can be expected from these studies that Co substitution at Cu sites in the CuO2 planes somehow localizes the carriers and decreases the mobile carriers density. The density of mobile carriers in the CuO2 planes can be restored by partial substitution of Li at Tl sites in Cu0.5Tl0.5Ba2O4- ? charge reservoir layer of Cu0.5Tl0.5Ba2Ca2Cu3- x Co x O10- ? superconductor; since alkali metals are known to lose their outermost "s-orbital" electron easily, which can be supplied to the CuO2 planes. The post-annealing experiments on these samples have been carried out in flowing oxygen and nitrogen and the motivation behind these extreme post-annealing conditions was to optimize the carriers density in the CuO2 planes of Cu0.5Tl0.5Ba2Ca2Cu3- x Co x O10- ? superconductor. The optimized free carrier density in the CuO2 planes enhances the superconducting properties of the final compound.

  3. 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 [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai 200050 (China); Graduate School of Chinese Academy of Science, Beijing 100080 (China); Zhang Hui; Tang Meibo; Chen Haohong; Yang Xinxin; Zhao Jingtai [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai 200050 (China); Grin, Yuri [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Str. 40, 01187 Dresden (Germany)

    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}

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

    Microsoft Academic Search

    B. J. Reardon; C. R. Hubbard

    1992-01-01

    X-ray powder patterns for the phases in the CaO-SrO-CuO ternary system, along with the corresponding crystal structures, were obtained from the literature and from the Powder Diffraction File (PDF). Available X-ray diffraction (XRD) patterns were compared with each other and, when possible, with a simulated pattern for each phase, yielding a recommended reference pattern. The simulated powder patterns presented here

  5. From overdoped to underdoped regime – high temperature in situ studies of Bi 2Sr 2CaCu 2O 8+ X single crystals

    Microsoft Academic Search

    G. Yang; J. S. Abell; C. E. Gough

    2001-01-01

    High temperature in situ study of the physical properties of high Tc cuprates is one of the best ways to investigate the phase diagram, as hole concentration of the CuO2 planes may alter after high temperature thermal cycles in various atmospheres. The in situ c-axis resistivity of Bi2Sr2CaCu2O8+X crystals as a function of the thermal cycle in flowing oxygen and

  6. From overdoped to underdoped regime - high temperature in situ studies of Bi2Sr2CaCu2O8+X single crystals

    Microsoft Academic Search

    G. Yang; J. S. Abell; C. E. Gough

    2001-01-01

    High temperature in situ study of the physical properties of high Tc cuprates is one of the best ways to investigate the phase diagram, as hole concentration of the CuO2 planes may alter after high temperature thermal cycles in various atmospheres. The in situ \\/c-axis resistivity of Bi2Sr2CaCu2O8+X crystals as a function of the thermal cycle in flowing oxygen and

  7. Inhomogeneous transport in heteroepitaxial La0.7Ca0.3MnO3 /SrTiO3 multilayers

    E-print Network

    Jo, Moon-Ho

    to magnetic tunneling as well as transport. Previous studies of ultrathin manganite films have shown strongO3 films up to 1.5 nm thickness. Heteroepitaxial multilayer structures can be uti- lized not onlyInhomogeneous transport in heteroepitaxial La0.7Ca0.3MnO3 /SrTiO3 multilayers Moon-Ho Jo,a) Neil D

  8. Computer modelling of defect structure and rare earth doping in LiCaAlF6 and LiSrAlF6

    NASA Astrophysics Data System (ADS)

    Amaral, J. B.; Plant, D. F.; Valerio, M. E. G.; Jackson, R. A.

    2003-05-01

    This paper describes a computational study of the mixed metal fluorides LiCaAlF6 and LiSrAlF6, which have potential technological applications when doped with a range of elements, especially those from the rare earth series. Potentials are derived to represent the structure and properties of the undoped materials, then defect properties are calculated, and finally solution energies for rare earth elements are calculated, enabling preferred dopant sites and charge compensation mechanisms to be predicted.

  9. Energy transfer in pure and Ce-doped LiCaAlF 6 and LiSrAlF 6 crystals

    NASA Astrophysics Data System (ADS)

    Shiran, N.; Gektin, A.; Neicheva, S.; Weber, M.; Derenzo, S.; Kirm, M.; True, M.; Shpinkov, I.; Spassky, D.; Shimamura, K.; Ichinose, N.

    2005-01-01

    Intrinsic ultra-fast scintillations at pulsed X-ray excitation were found in LiCaAlF 6 and LiSrAlF 6. Radiative recombination features of Ce-doped crystals are explained by differences of lattice properties, defect structure and Ce 3+ ion environment in these crystals. The role of exciton formation, electron and hole traps, and energy transfer to the activator centers are discussed.

  10. Origin of Narrow-band and Broadband Noise in Conduction Noise Spectra of Bi_2Sr_2CaCu_2O_y

    Microsoft Academic Search

    A. Maeda; Y. Togawa; R. Abiru; H. Kitano

    2001-01-01

    Conduction noise spectra were investigated in the driven vortex state of a high-temperature superconductor, Bi_2Sr_2CaCu_2Oy single crystals. Two characteristic noise features, a broad-band noise (BBN) and a narrow-band noise (NBN), were observed in the vortex solid phase. The NBN was found to originate from the washboard modulation of the translational velocity of the driven vortices [1]. To clarifify the origin

  11. Use of microsatellite DNA and otolith Sr:Ca ratios to infer genetic relationships and migration history of four morphotypes of Rhinogobius sp. OR

    Microsoft Academic Search

    Kenichi Ohara; Momoko Hotta; Daisuke Takahashi; Takashi Asahida; Hitoshi Ida; Tetsuya Umino

    2009-01-01

    The genetic diversity and relationship among four morphotypes of Rhinogobius sp. OR, Gobiidae (“T?shoku,” “Shinjiko,” “Gi-t?shoku,” and “Shimahire”) were investigated with seven microsatellite DNA loci,\\u000a and amphidromy of these morphotypes was verified by strontium (Sr) and calcium (Ca) deposition in the otolith. Samples of\\u000a “T?shoku,” “Shinjiko,” “Gi-t?shoku,” and “Shimahire” were collected from, respectively, three, three, two, and four locations\\u000a in

  12. Weak links within a Bi sub 2 Sr sub 2 Ca sub 1 Cu sub 2 O sub x single crystal by magnetizaion and dirct optical observations

    SciTech Connect

    Willis, J.O. (Los Alamos National Lab., NM (United States)); Nakamura, N.; Gotoh, S.; Takamuku, K.; Koshizuka, N.; Tanaka, S. (Superconductivity Research Lab., Tokyo (Japan))

    1991-01-01

    We have performed magnetic susceptibility and direct optical High Contrast Magnetic Flux (HICOM) observations on a single crystal of Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub x}. Low temperature pinning and high temperature flux creep have been observed by HICOM. The results suggest that the breakdown of flux pinning may occur gradually with temperature and may exhibit spatial variation related to sample inhomogeneities. 4 refs., 2 figs.

  13. Evidence against strong correlation in 4d transition-metal oxides CaRuO3 and SrRuO3

    Microsoft Academic Search

    Kalobaran Maiti; Ravi Shankar Singh

    2005-01-01

    We investigate the electronic structure of 4d transition-metal oxides CaRuO3 and SrRuO3 . The analysis of the photoemission spectra reveals significantly weak electron correlation strength (U\\/ Wtilde 0.2) as expected in 4d systems and resolves the long-standing issue that arose due to the prediction of large U\\/W similar to 3d systems. It is shown that the bulk spectra, thermodynamic parameters,

  14. Representations about nature of processes occurring in the material at different stages of Bi(Pb)–Sr–Ca–Cu–O ceramic manufacture

    Microsoft Academic Search

    I. A. Yurchenko

    2006-01-01

    The state of material and processes occurring in material during synthesis of bismuth HTSC ceramic are analyzed in this article.\\u000a Special attention is given to the mechanism of Bi2Sr2Ca2Cu3Oy (2223) phase synthesis and processes resulting in its intensification, as well as to the processes responsible for superconducting\\u000a grain contacts formation. A scheme of structural and phase transformation at sintering is

  15. Tem investigation on the crystal structure of the high-Tc superconductor system Bi-Pb-Sr-Ca-Cu-O doped with Sb

    Microsoft Academic Search

    B. Kabius; M. E. Gòmez; P. Prieto; S. Thierfeldt; R. R. Arons

    1989-01-01

    The effect of antimony on the crystal structure and superconducting properties of the high-Tc superconductor system Bi-Pb-Sr-Ca-Cu-O has been examined by resistivity and susceptibility measurements, electron diffraction and high-resolution electron microscopy. Tc0 as obtained by resistivity measurements was increased by Sb-doping from 85 to 107K. Polytypoid structures adjacent to grain boundaries have not been detected for samples containing Sb. Two

  16. Interpretation of the critical current in Bi2Sr2Ca2Cu3Ox tape conductors as parallel weak-link and strong-link paths

    Microsoft Academic Search

    D. C. van der Laan; H. J. N. van Eck; J. Schwartz; B. Ten Haken; H. H. J. Ten Kate

    2002-01-01

    To better understand the dominant mechanisms that limit the critical current density in high temperature superconductors, the dependence of the critical current density on magnetic field and temperature of Bi2Sr2Ca2Cu3Ox tapes is measured in magnetic fields up to 8 T and temperatures between 4.2 and 100 K. The results were modeled by describing the current in the tape as two

  17. Interpretation of the critical current in Bi 2Sr 2Ca 2Cu 3O x tape conductors as parallel weak-link and strong-link paths

    Microsoft Academic Search

    D. C van der Laan; H. J. N van Eck; J Schwartz; B ten Haken; H. H. J ten Kate

    2002-01-01

    To better understand the dominant mechanisms that limit the critical current density in high temperature superconductors, the dependence of the critical current density on magnetic field and temperature of Bi2Sr2Ca2Cu3Ox tapes is measured in magnetic fields up to 8 T and temperatures between 4.2 and 100 K. The results were modeled by describing the current in the tape as two

  18. Limits to the critical current in Bi2Sr2Ca2Cu3Ox tape conductors: The parallel path model

    Microsoft Academic Search

    D. C. van der Laan; J. Schwartz; B. Ten Haken; M. Dhallé; H. J. N. van Eck

    2008-01-01

    An extensive overview of a model that describes current flow and dissipation in high-quality Bi2Sr2Ca2Cu3Ox superconducting tapes is provided. The parallel path model is based on a superconducting current running in two distinct parallel paths. One of the current paths is formed by grains that are connected at angles below 4° . Dissipation in this strongly linked backbone occurs within

  19. Direct optical visibility of ferroelectric domains of dicalcium strontium propionate, Ca2Sr(C2H5CO2)6

    NASA Astrophysics Data System (ADS)

    Hosokawa, T.; Kobayashi, J.; Uesu, Y.

    1980-06-01

    It has been found that antiparallel domains in a ferroelectric phase of Ca2Sr(C2H5CO2)6 are visible in polarized light traveling along the unique optic axis, although the phase is optically uniaxial. The domains with opposite polarity are discerned as pseudo-octagonal islands with dark and bright contrast. As the most probable origin of the visibility the induced dissymmetry due to growth pyramids is proposed.

  20. Comparative spectroscopic and laser properties of Yb 3+ -doped CaF 2 , SrF 2 and BaF 2 single crystals

    Microsoft Academic Search

    P. Camy; J. L. Doualan; A. Benayad; M. von Edlinger; V. Ménard; R. Moncorgé

    2007-01-01

    We present the spectroscopic properties and room-temperature cw tunable laser operation of Yb3+-doped CaF2, SrF2 and BaF2 single crystals grown and studied in the same conditions. Emission cross sections, lifetimes, laser thresholds, laser slope\\u000a efficiencies and laser wavelength tuning ranges are compared. It appears that Yb3+-doped BaF2 might be more promising for diode-pumped high power laser operation.