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1

Superconductivity in TlSr 2- xCa xYbCu 2O 7 by isovalent cation substitution  

NASA Astrophysics Data System (ADS)

TlSr 2YbCu 2O 7 was found to be non-superconducting, in harmony with the formal valence of Cu 2+ and Tl 3+. However, isovalent cation substitution of Ca 2+ for Sr 2+ made TlSr 2- xCa xYbCu 2O 7 superconducting for x ? 0.2, although no change would be expected in the formal valence of Cu. These observations strongly suggest that hole carriers are self-doped due to overlap between Tl 6s and Cu 3d x2- y2 bands, which is enhanced by the observed shortening of the Cu? bond length in the CuO 2 sheet by Ca substitution for Sr.

Ohshima, Eriko; Kikuchi, Masae; Syono, Yasuhiko

1996-02-01

2

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

NASA Astrophysics Data System (ADS)

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

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

1996-11-01

3

Magnetic comparison of BaCa and BaSr substituted hexaferrite powders  

NASA Astrophysics Data System (ADS)

Results on magnetic studies of Ba0.5Sr0.5Fe12-2x(ZnTi)xO19 and Ba0.75Ca0.25Fe12-2x(ZnTi)xO19, where x = 0.2 to 0.6, ferromagnetic powders prepared by mechanical alloying are discussed. The structural and magnetic properties of the resulting powders were analyzed by thermo-magnetic analysis, X-ray diffraction, scanning electron microscopy, Mssbauer spectroscopy and magnetic measurements. Curie temperature, Tc decreased dramatically (drop ~ 39%) for BaCa samples, whilst for BaSr samples remained almost without change (diminution ~ 2%) at x <= 0.2. SEM studies showed that all the particles present nearly hexagonal platelet shape.

Gonzlez-Angeles, A.; Lipka, J.; Gruskov, A.; Slma, J.; Jan?rik, V.; Sluge?, V.

2010-03-01

4

Two-dimensional incommensurate structures of (Sr0.13Ca0.87)2CoSi2O7 and Ca2CoSi2O7: Effects of substitution of interlayer cations  

Microsoft Academic Search

The modulated structures of (Sr0.13Ca0.87)2CoSi2O7 at 293K and Ca2CoSi2O7 at 293, 393, 468K are compared to find the peculiarity of the partial substitution of Ca by larger alkaline-earth atoms such as Sr. The similarities in structural effects of this substitution and heating are found.

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

2001-01-01

5

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

Microsoft Academic Search

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

R. S. Liu; P. P. Edwards

1991-01-01

6

Fingerprinting substitution sites in Pb,Dy-Bi_2Sr_2Ca_1Cu_2O8+? using X-ray Photoelectron Diffraction  

NASA Astrophysics Data System (ADS)

The substitution sites of Pb and Dy dopants in the cuprate-type high temperature superconductor Bi2Sr2Ca1Cu2O{8+?} are determined by a direct comparison of the angle-scanned X-ray photoelectron diffraction (XPD) patterns. We demonstrate the power of XPD as a fingerprinting tool and conclude that Pb occupies Bi sites and Dy the Ca sites. The presence of the incommensurate lattice modulation is not visible in XPD, probably due to a Pb-induced, reduced modulation amplitude.

Popovi?, D.; Bovet, M.; Berger, H.; Aebi, P.

2005-06-01

7

Studies on simultaneous substitution of Pb and Y in Bi2Sr2CaCu2O8+delta single crystals  

Microsoft Academic Search

The effect of simultaneous substitution of Pb for Bi and Y for calcium in Bi2Sr2CaCu2O8+delta has been studied. Phase pure single crystals of Bi1.7Pb0.3Ca1-xYxCu2O8+delta have been grown for x = 0 to 0.5. Variation in lattice parameters and the change in superconducting transition temperature for different x values have been studied. The optical micrograph revealed the layer growth mechanism and

C. Subramanian; A. Thamizhavel; R. Jayavel; D. Prabhakaran; D. P. Paul

1997-01-01

8

Studies on simultaneous substitution of Pb and Y in Bi 2Sr 2CaCu 2O 8+ ? single crystals  

Microsoft Academic Search

The effect of simultaneous substitution of Pb for Bi and Y for calcium in Bi2Sr2CaCu2O8+? has been studied. Phase pure single crystals of Bi1.7Pb0.3Ca1?xYxCu2O8+? has been grown for x = 0 to 5. Variation in lattice parameters and the change in superconducting transition temperature for different x values has been studied. The optical micrograph revealed the layer growth mechanism and

A. Thamizhavel; D. P. Paul; D. Prabhakaran; R. Jayavel; C. Subramanian

1997-01-01

9

Dielectric and Polarization Studies of Ca Substituted in Bi4SrTi4O15 Ceramics  

Microsoft Academic Search

The processing conditions, microstructure and dielectric properties of strontium bismuth titanate (SBT) were studied by means of Ca substitution in the strontium site referred to hereinafter as SCBT. The mechano-chemical activation method permits one to reduce the particle size of the initial products, so the surface area of the powder is increased, improving in most cases its reactivity.X-ray diffraction analysis

Gagan Anand; A. R. James; P. Sarah

2010-01-01

10

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

NASA Astrophysics Data System (ADS)

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

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

2008-01-01

11

Hydrothermal removal of Sr2+ in aqueous solution via formation of Sr-substituted hydroxyapatite.  

PubMed

We removed Sr(2+) in simulating wastewater and simultaneously prepared Sr-substituted hydroxyapatite via chemical precipitation and hydrothermal treatment. Both higher initial pH value and higher molar ratio of Sr/(Sr+Ca) contributed to lower residual Sr(2+) concentration and higher removal efficiency. About two thirds of Sr(2+) residual in solution after chemical precipitation were further reduced by hydrothermal treatment. The optimal Sr removal result was 99.66% with an ultimate concentration of 2.0 mg L(-1) when the initial pH was 12 and Sr/(Sr+Ca) was 0.2. Sr-substituted hydroxyapatite phase with hexagonal structure was identified by XRD and EDS results. However, it was found that SrHPO(4) phase was formed in the samples with high Sr composition. The lattice constants became larger with the increase of Sr(2+) and the crystallinity became higher with the increase of pH value. Rod-like particles were observed in SEM images of synthesized Sr-substituted hydroxyapatite samples, with the size of 20-30 nm in width and 70-100 nm in length. With little secondary waste and simple treating procedure, this method is an effective and prospective measure to deal with (90)Sr in nuclear waste and industry wastewater. PMID:20363558

Tan, Sheng-Heng; Chen, Xue-Gang; Ye, Ying; Sun, Jie; Dai, Ling-Qing; Ding, Qian

2010-07-15

12

XANES Study on the Generation and Distribution of Holes via Ca Substitution and O Doping in Cu(Ba 0.8Sr 0.2) 2(Yb 1- xCa x)Cu 2O 6+ z  

NASA Astrophysics Data System (ADS)

Generation of holes is facilitated in the Cu(Ba 0.8Sr 0.2) 2 (Yb 1- xCa x)Cu 2O 6+ z (Cu-1212) system by two independent ways, i.e., by Ca substitution (0? x?0.35) and O doping (0< z<1). The distribution of holes between the CuO 2-(Yb 1- xCa x)-CuO 2 block containing two identical superconductive CuO 2 planes and the "charge-reservoir" block consisting of a single CuO z chain has been quantitatively investigated by means of O K-edge and Cu L2,3-edge X-ray absorption near-edge structure (XANES) spectroscopy. The resultant values for the CuO 2-plane hole concentration are compared with those calculated employing the bond-valence-sum (BVS) method from the neutron powder diffraction (NPD) data previously reported for the same samples. The results of the two methods are in good agreement. The two independent hole-doping ways are found to result in different distributions of holes over the crystal, i.e., different ratios of hole numbers at the CuO 2 plane and the CuO z chain. With Ca substitution holes are directed efficiently into the CuO 2 plane, while for O doping holes are more homogeneously distributed between the CuO 2 plane and the CuO z chain. Moreover, the value of Tc at a fixed CuO 2-plane hole concentration is shown to be higher for Ca-substituted than for O-doped samples.

Karppinen, M.; Yamauchi, H.; Nakane, T.; Fujinami, K.; Lehmus, K.; Nachimuthu, P.; Liu, R. S.; Chen, J. M.

2002-06-01

13

Physical, electrical and dielectric properties of Ca-substituted strontium hexaferrite (SrFe 12O 19) nanoparticles synthesized by co-precipitation method  

NASA Astrophysics Data System (ADS)

Calcium substituted strontium hexaferrite Ca xSr 1- xFe 12O 19 ( x=0.0-0.6) nanoparticles are synthesized by chemical co-precipitation method. The synthesized samples are characterized by Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy, Transmission Electron Microscopy, DC electrical resistivity and dielectric measurements. FTIR data of uncalcined sample shows that nitrate ions are present which disappeared on calcination at 920 C. The XRD data shows that a single hexagonal magnetoplumbite phase is formed in samples in which the calcium content, x, is ?0.20. However, a nonmagnetic phase (?-Fe 2O 3) in addition to the hexagonal phase is also present in samples with x>0.20. The average crystallite size is found between 17 and 29 nm. The DC electrical resistivity increases with increase of calcium content up to level of x=0.2 but decreased on further addition of calcium. The enhanced resistivity of the calcium doped material has potential applications in microwave devices. The variations of dielectric constant and dielectric loss angle are explained on the basis of Maxwell-Wagner and Koops models.

Javed Iqbal, Muhammad; Naeem Ashiq, Muhammad; Hussain Gul, Iftikhar

2010-07-01

14

Substitution effects of barium and calcium on magnetic properties of AxSr1-x(Fe0.5Ru0.5)O3 double perovskites (x=0.05, A=Ba,Ca)  

NASA Astrophysics Data System (ADS)

AxSr1-x(Fe0.5Ru0.5)O3 double perovskites (x=0.05 and A=Ba,Ca) were prepared by a sol-gel method and an effect of the cation substitution at the A site of the crystal structure of SrFe0.5Ru0.5O3 on their magnetic properties was monitored by x-ray diffraction (XRD), magnetic measurements, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and temperature-dependent and in-field 57Fe Mssbauer spectroscopy. Both Ca- and Ba-substituted samples reveal the orthorhombic structure similar to the undoped perovskite; however, the cell volume changes with the substituting ion radius. TEM and SEM micrographs manifest agglomerated nanocrystalline samples with particle sizes of about 20-60, 15-50, and 40-70 nm for the undoped, Ba-doped, and Ca-doped perovskites, respectively. Generally, the magnetic regime of both substituted and undoped perovskites can be described by a spin-glass behavior caused by a spin frustration. Among other factors, this is manifested by a nonsaturation of the hysteresis loops even at a high field of 50 kOe, by a low-temperature divergence of the zero-field-cooled and field-cooled magnetization curves, and by a cusp in the zero-field-cooled magnetization curve. The low-temperature spin-glass state is also supported by the in-field Mssbauer spectra, recorded on these systems. The isomer shift parameters, extracted from the Mssbauer spectra, confirm a high-spin iron(III) state with S=5/2. In contrast to the undoped and Ba-doped samples, the narrower distribution of the hyperfine magnetic fields, observed in the Ca-doped perovskite can be ascribed to the larger particles. Compared to the undoped sample, the field of maximum probability is higher in the Ca-substituted perovskite while it is reduced in the Ba-doped sample because of the effects of the chemical compression and expansion, respectively. In addition, the Ca-doped sample exhibits more negative Weiss temperature (?=-105 K) than that found for the Ba-substituted perovskite (?=-49 K), implying that doping with Ca at Sr sites of SrFe0.5Ru0.5O3 perovskite structure provokes strengthening of antiferromagnetic interactions at the expense of the other ones. Furthermore, both substituted samples reveal significantly reduced coercive fields in the hysteresis loops recorded at 5 K, probably as a result of decreasing magnetocrystalline anisotropy. This is an indirect evidence of the essential influence of the substitution on the crystal growth of the synthesized particles. The role of SrRuO3 and SrFeO3 compounds, which have been detected in magnetic and Mssbauer measurements as admixtures, is discussed.

Nomura, K.; Zboril, R.; Tucek, J.; Kosaka, W.; Ohkoshi, S.; Felner, I.

2007-07-01

15

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

SciTech Connect

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.

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

16

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

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.

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

2010-12-01

17

Superconductivity in Bi-Sr-Ca-Mg-Cu-oxide  

SciTech Connect

This paper reports on a Mg-substituted material with nominal composition Bi{sub 2}Sr{sub 2}Ca{sub 3}Mg{sub 2}Cu{sub 6}O{sub x}, prepared by partial substitution of Ca by isovalent Mg in the 2256 composition of Bi-Sr-Ca-Cu-O, studied by the measurements of electrical resistance, magnetic susceptibility and x-ray diffraction pattern. Results show the existence of a superconducting phase with onset T{sub c} at 112l.5 {plus minus} 1 K along with a minor phase with onset T{sub c} = 88 K. The material retained superconducting characteristics (Meissner effect and T{sub c}{sup onset}) even after a period of six months.

Khan, A.Y.; Mohammad, M.; Shahnaz, M. (Dept. of Chemistry, Quaid-i-Azam Univ., Islamabad (PK)); Hasnain, S.K. (Dept. of Physics, Quaid-i-Azam Univ., Islamabad (PK))

1991-05-10

18

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

PubMed

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

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

2014-01-01

19

Physical properties of A(Cu1/3Nb2/3)O3 (A = Ba, Sr, Ca)-substituted BaTiO3 system grown by using aerosol deposition  

NASA Astrophysics Data System (ADS)

The physical properties of the lead-free piezoelectric material BaTiO3 (BT) with complex perovskite phase additives, i.e., A(Cu1/3Nb2/3)O3 (A = Ba, Sr, Ca), were investigated. The dense and crack-free thick films with thickness of > 5 m were grown on platinized Si(100) wafers by using the aerosol deposition method (AD) at room temperature. Compared to pure BT grown by using AD, complex perovskite-substituted BT thick films showed improved physical properties and film quality even after post annealing. The optimal amount of the additives and the optimal post annealing temperature were determined in accordance with the dielectric and the ferroelectric properties.

Kim, Jong-Woo; Ryu, Jungho; Hahn, Byung-Dong; Choi, Jong-Jin; Yoon, Woon-Ha; Ahn, Cheol-Woo; Choi, Joon-Hwan; Park, Dong-Soo

2013-12-01

20

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

NASA Astrophysics Data System (ADS)

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.

zelik, B.; Kaya, C.; Gndo?mu?, H.; Sotelo, A.; Madre, M. A.

2014-02-01

21

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

NASA Astrophysics Data System (ADS)

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

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

1997-02-01

22

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)

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.

Gesi, Kazuo; Takashige, Masaaki

1992-06-01

23

Substitutions of 3-d transition metal ions for copper in Bi sub 2 Sr sub 2 Ca(n-1)Cu(n)O(2n+4)  

SciTech Connect

Transition metal substitutions in YBa{sub 2}Cu{sub 3}O{sub 7} have contributed to an understanding of the dominant role of copper-oxide planes versus the copper-oxide chains in that material. Since the pairing of carriers in the Cu-O{sub 2} planes is responsible for high temperature superconductivity in all copper-oxide ceramics, it is of interest to alter the electronic structure of, as well as to introduce magnetic impurities into, the CuO{sub 2} planes. The 3-d transition elements were chosen because their valences and ionic radii suggest that they might substitute for the Cu in these materials.

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

1989-07-01

24

Interstitial and substitutional zirconium in SrTiO3  

SciTech Connect

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

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

2012-02-22

25

Effect of Nd-Substitution on Thermally Activated Flux Creep in the Bi1.7Pb0.3- x Nd x Sr2Ca3Cu4O12+ y Superconductors  

NASA Astrophysics Data System (ADS)

The magnetoresistance of Bi1.7Pb0.3- x Nd x Sr2Ca3Cu4O12+ y superconductors with x=0.025, 0.050, 0.075 and 0.10 have been measured for different values of the applied magnetic field. Thermally activated flux creep model has been studied in order to calculate the flux pinning energies. The calculated flux pinning energies decrease with the increasing Nd-content and applied magnetic field.

zkurt, Berdan; zelik, Bekir

2009-07-01

26

High-Concentration Na Doping of SrRuO3 and CaRuO3.  

PubMed

The Na-doped perovskite-structure ruthenates Sr1-xNaxRuO3 and Ca1-yNayRuO3 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, Sr1-xNaxRuO3 showed metallic conductivity. Magnetic properties were influenced by the Na substitution, but no long-range antiferromagnetic behavior was observed in Ca1-yNayRuO3. PMID:24731152

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

2014-05-01

27

Are seawater Sr/Ca variations preserved in Quaternary foraminifera?  

SciTech Connect

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.

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

1999-11-01

28

Controls on Sr/Ca in benthic foraminifera and implications for seawater Sr/Ca during the late Pleistocene  

NASA Astrophysics Data System (ADS)

Changes in the Sr to Ca ratio of sea water have important implications for the interpretation of past climate. It has proven difficult to interpret Sr/Ca of foraminiferal calcite as a measure of seawater Sr/Ca or as reflecting the influence of deep water carbonate ion saturation (?[CO32-]) on the incorporation of Sr into benthic foraminiferal carbonate. Here, we address this issue by measurements of paired benthic foraminiferal Sr/Ca and B/Ca (a proxy for deep water ?[CO32-]) for core-tops from the global ocean and three down cores at different settings during the Last Glacial-interglacial cycle. These new data suggest a significant control of deep water ?[CO32-] on benthic foraminiferal Sr/Ca, and that down-core shell Sr/Ca variations can be largely accounted for by past deep water ?[CO32-] changes. We conclude that seawater Sr/Ca has likely remained near-constant on glacial-interglacial timescales during the late Pleistocene, in agreement with model results. With due caution, benthic Sr/Ca may be used as an auxiliary proxy for deep water ?[CO32-] if seawater Sr/Ca is constant.

Yu, Jimin; Elderfield, Henry; Jin, Zhangdong; Tomascak, Paul; Rohling, Eelco J.

2014-08-01

29

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

PubMed

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

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

2013-02-01

30

Empirical partition coefficients for Sr and Ca in marine barite: Implications for reconstructing seawater Sr and Ca concentrations  

Microsoft Academic Search

A robust record of fluctuations in seawater Sr and Ca concentrations is critical for understanding the long-term global carbon cycle as it is influenced by the history and location of carbonate precipitation, chemical weathering, and hydrothermal activity. Such a record is also necessary for interpretation of paleoceanographic records (temperature, productivity) derived from carbonate sources (e.g. Sr\\/Ca, Mg\\/Ca, Li\\/Ca). Marine barite,

Kristen B. Averyt; Adina Paytan

2003-01-01

31

Geometry and Vibrational Spectra of Alkaline-Earth Dihalides, Ii. CaF2, SrF2 and BaF2.  

National Technical Information Service (NTIS)

The infrared spectra of 40CaF2, 44CaF2, 86SrF2, 88SrF2 and BaF2 trapped in solid krypton matrices at 20K are reported. From precise measurements of the shifts of the vibrational modes on isotopic substitution upper and lower limits for the apex angles of ...

V. Calder D. E. Mann K. S. Seshadri M. Allavena D. White

1969-01-01

32

Measuring Local Gradients of Intra-Mitochondrial [Ca] in Cardiac Myocytes During SR Ca Release  

PubMed Central

Rationale Mitochondrial [Ca2+] ([Ca2+]mito) regulates mitochondrial energy production, provides transient Ca2+buffering under stress and can be involved in cell death. Mitochondria are near the sarcoplasmic reticulum (SR) in cardiac myocytes and evidence for crosstalk exists. However, quantitative measurements of [Ca2+]mito are limited and spatial [Ca2+]mito gradients have not been directly measured. Objective To directly measure local [Ca2+]mito during normal SR Ca release in intact myocytes, and evaluate potential subsarcomeric spatial [Ca2+]mito gradients. Methods and Results We used in-situ calibration of the mitochondrially targeted inverse pericam indicator Mitycam and directly measured [Ca2+]mito during SR Ca2+ release in intact rabbit ventricular myocytes by confocal microscopy. During steady state pacing ?[Ca2+]mito amplitude was 29 3 nM, rising rapidly (similar to cytosolic [Ca2+]i) but declining much more slowly. Taking advantage of the structural periodicity of cardiac sarcomeres, we found that [Ca2+]mito near SR Ca2+ release sites (Z-lines) vs. mid sarcomere (M-line) reached a higher peak amplitude (37 4 vs. 26 4 nM, respectively P < 0.05) which occurred earlier in time. This difference was attributed to ends of mitochondria being physically closer to SR Ca2+ release sites, because the mitochondrial Ca2+ uniporter was homogeneously distributed and elevated [Ca2+] applied laterally did not produce longitudinal [Ca2+]mito gradients. Conclusions We developed methods to measure spatiotemporal [Ca2+]mito gradients quantitatively during excitation-contraction coupling. The amplitude and kinetics of [Ca2+]mito transients differ significantly from those in the cytosol and are higher and faster near the Z- vs. M-line. This approach will help clarify SR-mitochondrial Ca2+ signaling.

Lu, Xiyuan; Ginsburg, Kenneth S.; Kettlewell, Sarah; Bossuyt, Julie; Smith, Godfrey L.; Bers, Donald M.

2013-01-01

33

Correlation of Bone Ba\\/Ca and Sr\\/Ca due to Biological Purification of Calcium  

Microsoft Academic Search

Analyses of more than 1000 samples of soils, plants and bones of many species from a temperate woodland environment confirm the ubiquity of biopurification processes in which Ba\\/Ca and Sr\\/Ca decrease with increasing trophic position. This study reveals that differences among Ba\\/Ca and Sr\\/Ca ratios in soils and plants themselves are comparable to or greater than differences due to biopurification

James H. Burton; T. Douglas Price; William D. Middleton

1999-01-01

34

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

NASA Astrophysics Data System (ADS)

The effect of the isovalent substitution of Sr2+ by Ca2+ on the structure and superconducting properties of Sr2-xCaxVO3FeAs is described in the compositional range 0?x?0.5. SQUID magnetometry measurements reveal that after an initial increase in Tc, which is maximised at 29.5 K in Sr1.95Ca0.05VO3FeAs, a rapid suppression of superconductivity is observed with increasing x. XANES spectra of Sr2-xCaxVO3FeAs collected on the Fe and V absorption K-edges show that the position of both edges are invariant with composition within the experimental uncertainty. A combination of synchrotron X-ray powder diffraction and neutron powder diffraction techniques is used to rationalise the observed changes in Tc with x, in terms of changes to the structure of the FeAs layer upon partial Ca substitution. These findings demonstrate that superconductivity in the Fe-based superconductors is extremely sensitive to the crystal structure with Tc maximised in samples with regular FeAs4-tetrahedra.

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

2014-08-01

35

Heteronuclear Mn-Ca/Sr complexes, and Ca/Sr EXAFS spectral comparisons with the Oxygen-Evolving Complex of Photosystem II  

PubMed Central

Heterometallic MnCa and MnSr 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.

Mishra, Abhudaya; Yano, Junko; Pushkar, Yulia; Yachandra, Vittal K.; Abboud, Khalil A.

2014-01-01

36

Variation of foraminiferal Sr/Ca over Quaternary glacial-interglacial cycles: Evidence for changes in mean ocean Sr/Ca?  

NASA Astrophysics Data System (ADS)

Records of Sr/Ca changes in planktonic and benthic foraminifera from diverse hydrographic settings reveal coherent variability (5 +/- 1%) between ocean basins and between surface and deep waters over the past 300 kyr. There is a general increase in foraminiferal Sr/Ca over the penultimate glaciation declining to minimum values during stage 5 and an increase in Sr/Ca from stage 5 through stage 2. Coincident changes in benthic foraminifera records from the Atlantic and Pacific basins imply that Sr/Ca variations are not dominated by dissolution. Planktonic culturing data provide evidence that the downcore Sr/Ca variations are not controlled by temperature changes and suggest only a small influence of salinity and pH. Variation common to the records is most readily explained by changes in mean ocean Sr/Ca. If fossil foraminifera reliably record higher glacial seawater Sr/Ca, coral Sr paleothermometry would underestimate sea surface temperature during glacialepisodes.

Martin, P. A.; Lea, D. W.; Mashiotta, T. A.; Papenfuss, T.; Sarnthein, M.

1999-12-01

37

Variation of foraminiferal Sr/Ca over Quaternary glacial-interglacial cycles: Evidence for changes in mean ocean Sr/Ca?  

NASA Astrophysics Data System (ADS)

Records of Sr/Ca changes in planktonic and benthic foraminifera from diverse hydrographic settings reveal coherent variability (5 1%) between ocean basins and between surface and deep waters over the past 300 kyr. There is a general increase in foraminiferal Sr/Ca over the penultimate glaciation declining to minimum values during stage 5 and an increase in Sr/Ca from stage 5 through stage 2. Coincident changes in benthic foraminifera records from the Atlantic and Pacific basins imply that Sr/Ca variations are not dominated by dissolution. Planktonic culturing data provide evidence that the downcore Sr/Ca variations are not controlled by temperature changes and suggest only a small influence of salinity and pH. Variation common to the records is most readily explained by changes in mean ocean Sr/Ca. If fossil foraminifera reliably record higher glacial seawater Sr/Ca, coral Sr paleothermometry would underestimate sea surface temperature during glacialepisodes.

Martin, P. A.; Lea, D. W.; Mashiotta, T. A.; Papenfuss, T.; Sarnthein, M.

2000-12-01

38

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2011-11-01

40

CaMKII-dependent SR Ca leak contributes to doxorubicin-induced impaired Ca handling in isolated cardiac myocytes  

PubMed Central

Objective Doxorubicin (DOX) is one of the most effective chemotherapeutic agents, but cardiotoxicity limits DOX therapy. Although the mechanisms are not entirely understood, reactive oxygen species (ROS) appear to be involved in DOX cardiotoxicity. Ca/calmodulin dependent protein kinase II (CaMKII) can be activated by ROS through oxidation and is known to contribute to myocardial dysfunction through Ca leakage from the sarcoplasmic reticulum (SR). Rationale We hypothesized that CaMKII contributes to DOX-induced defects in intracellular Ca ([Ca]i) handling. Methods Cardiac myocytes were isolated from wild-type (WT) adult rat hearts and from mouse hearts lacking the predominant myocardial CaMKII isoform (CaMKII??/?, KO) vs. WT. Isolated cardiomyocytes were investigated 30 min after DOX (10 mol/L) superfusion, using epifluorescence and confocal microscopy. Intracellular ROS-generation ([ROS]i) and [Ca]i handling properties were assessed. In a subset of experiments, KN-93 or AIP (each 1 mol/L) were used to inhibit CaMKII. Melatonin (Mel, 100 mol/L) served as ROS-scavenger. Western blots were performed to determine the amount of CaMKII phosphorylation and oxidation. Results DOX increased [ROS]i and led to significant diastolic [Ca]i overload in rat myocytes. This was associated with reduced [Ca]i transients, a 5.8-fold increased diastolic SR Ca leak and diminished SR Ca content. ROS-scavenging partially rescued Ca handling. Western blots revealed increased CaMKII phosphorylation, but not CaMKII oxidation after DOX. Pharmacological CaMKII inhibition attenuated diastolic [Ca]i overload after DOX superfusion and led to partially restored [Ca]i transients and SR Ca content, presumably due to reduced Ca spark frequency. In line with this concept, isoform-specific CaMKII?-KO attenuated diastolic [Ca]i overload and Ca spark frequency. Conclusions DOX exposure induces CaMKII-dependent SR Ca leakage, which partially contributes to impaired cellular [Ca]i homeostasis. Pharmacological and genetic CaMKII inhibition attenuated but did not completely abolish the effects of DOX on [Ca]i. In light of the clinical relevance of DOX, further investigations seem appropriate to determine if CaMKII inhibition could reduce DOX-induced cardiotoxicity.

Sag, Can M.; Kohler, Anne C.; Anderson, Mark E.; Backs, Johannes; Maier, Lars S.

2011-01-01

41

Nonmagnetic Sc Substitution in a Perovskite Ferromagnetic Insulator Pr0.8Ca0.2MnO3  

NASA Astrophysics Data System (ADS)

The effect of nonmagnetic substitution in a perovskite ferromagnetic insulator Pr0.8Ca0.2MnO3 was studied in epitaxial Pr0.8Ca0.2Mn1-yScyO3 thin films grown on SrTiO3 substrates. An increasing Sc substitution level weakened the ferromagnetic order, resulting in a decrease of saturation magnetization and the ferromagnetic transition temperature. Analysis of transport properties and Raman spectra indicates that besides simple spin dilution, weakening of both the double-exchange interaction and orbital order contributes to the reduction of ferromagnetic order.

Harada, Takayuki; Takahashi, Ryota; Lippmaa, Mikk

2013-01-01

42

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

SciTech Connect

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.

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

1999-09-01

43

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

NASA Astrophysics Data System (ADS)

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 7C. 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 1.5C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5C. 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.

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-Schnberg, Dieter; Geibert, Walter; Goldstein, Steven; Hughen, Konrad; Inoue, Mayuri; Kawahata, Hodaka; Klling, Martin; Cornec, Florence L.; Linsley, Braddock K.; McGregor, Helen V.; Montagna, Paolo; Nurhati, Intan S.; Quinn, Terrence M.; Raddatz, Jacek; Rebaubier, Hlne; Robinson, Laura; Sadekov, Aleksey; Sherrell, Rob; Sinclair, Dan; Tudhope, Alexander W.; Wei, Gangjian; Wong, Henri; Wu, Henry C.; You, Chen-Feng

2013-09-01

44

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

PubMed

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

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

2000-10-01

45

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

SciTech Connect

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

Stevenson, J.W.; Armstrong, T.R.; Pederson, L.R. [and others

1995-04-01

46

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

SciTech Connect

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

Kurniawan, C. [Chemistry Department of Semarang State University, Jl. Raya Sekaran Semarang (Indonesia); Prijamboedi, B. [Chemistry Department of Bandung Institute of Technology, Jl. Ganesha 10 Bandung (Indonesia)

2010-10-24

47

Luminescence Spectroscopy of Eu-doped (Ca,Sr)TiO3 Nanocrystals Prepared by Using Sonochemical Method  

NASA Astrophysics Data System (ADS)

Perovskite-type compounds (ABO3) of (Ca,Sr)TiO3 doped with trivalent europium (Eu3+) were synthesized by sonochemical techniques. Powder X-ray diffraction measurement on (Ca,Sr)TiO3 were used to identify the perovskite crystal structure. The photoluminescence property in (Ca,Sr)TiO3 with europium substitution several atoms in the host lattice was also studied. Further, the photoluminescence spectra were taken at room temperature. The structural difference between fourth kinds of doped samples with different heating temperatures accounts for the intensification of the luminescence intensity. The presented measurements monitor the emission wavelengths of the Eu3+ with emission peaks at 593, 615 and 700 nm. The obtained results were discussed with respect to developed preparaton method.

Kurniawan, C.; Prijamboedi, B.

2010-10-01

48

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

PubMed

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

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

2013-03-01

49

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

PubMed Central

Oxygen-evolving complex of photosystem II (PSII) is a tetra-manganese calcium penta-oxygenic cluster (Mn4CaO5) catalyzing light-induced water oxidation through several intermediate states (S-states) by a mechanism that is not fully understood. To elucidate the roles of Ca2+ in this cluster and the possible location of water substrates in this process, we crystallized Sr2+-substituted PSII from Thermosynechococcus vulcanus, analyzed its crystal structure at a resolution of 2.1 , and compared it with the 1.9 structure of native PSII. Our analysis showed that the position of Sr was moved toward the outside of the cubane structure of the Mn4CaO5-cluster relative to that of Ca2+, resulting in a general elongation of the bond distances between Sr and its surrounding atoms compared with the corresponding distances in the Ca-containing cluster. In particular, we identified an apparent elongation in the bond distance between Sr and one of the two terminal water ligands of Ca2+, W3, whereas that of the Sr-W4 distance was not much changed. This result may contribute to the decrease of oxygen evolution upon Sr2+-substitution, and suggests a weak binding and rather mobile nature of this particular water molecule (W3), which in turn implies the possible involvement of this water molecule as a substrate in the O-O bond formation. In addition, the PsbY subunit, which was absent in the 1.9 structure of native PSII, was found in the Sr-PSII structure.

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

2013-01-01

50

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

PubMed Central

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

2012-01-01

51

Reactions of Ca and Sr with CH 3X and CF 3X (X ? Br, I). A laser-induced fluorescence study on nascent CaBr, SrBr, and SrI  

Microsoft Academic Search

Continuous-wave laser-induced fluorescence (LIF) spectra have been measured of nascent SrBr, SrI, and CaBr, formed in the reactions of Sr with CH3X and CF3X (X ? Br,I), and of Ca with CH3Br and CF3Br. The bandhead spectra measured for the reactions involving Sr can be attributed to the formation of highly vibrationally excited SrX; for the reaction with CF3I vibrational

F. Keijzer; J. M. Teule; J. Bulthuis; G. J. de Graaff; M. H. Hilgeman; M. H. M. Janssen; E. H. van Kleef; J. J. van Leuken; S. Stolte

1996-01-01

52

Bi-Sr-Ca-Cu-O and Pb-Bi-Sr-Ca-Cu-O superconductor films via an electrodeposition process  

NASA Astrophysics Data System (ADS)

A novel electrochemical process has been developed for the formation of superconducting films. Using this process, superconducting films of Bi2Sr2Ca1Cu2O8 and (Pb,Bi)2Sr2Ca1Cu2O8 have been formed. The process consists of simultaneously depositing the metallic constituents of the superconductor from a single electrolyte, and thermally oxidizing the resulting precursors film to form the superconducting phase. Application of -4 to -5 V vs Ag/Ag(+) to a conductive cathode substrate which is immersed in an electrolyte containing salts of all of the metals reduces the metal cations, causing then to deposit on the cathode as a metallic film precursor. Precursor films having desired stoichiometries were obtained by regulating the electrolyte bath composition.

Maxfield, M.; Eckhardt, H.; Iqbal, Z.; Reidinger, F.; Baughman, R. H.

1989-05-01

53

Structure, nonstoichiometry and magnetic properties of the perovskites Sr 1- xCa xMnO 3- ?  

NASA Astrophysics Data System (ADS)

The structural, thermal and magnetic properties of the perovskite-type alkaline-earth manganites of the series Sr 1- xCa xMnO 3- ? (0? x?1) were investigated. SrMnO 3- ? forms a hexagonal perovskite lattice and shows a first-order transformation to a highly defective cubic high-temperature modification. By substituting Ca for Sr ( x>0.25) the hexagonal perovskite is suppressed and a cubic (or orthorhombic) lattice becomes stabilized for all temperatures. For x=0.5 and 0.75 cubic perovskites with a large nonstoichiometry (e.g., ?=0.25 for x=0.5) are obtained at 1400 C. The defective perovskites are prepared by either quenching from high temperature or by cooling in an inert atmosphere. The oxygen vacancies are easily filled by subsequent reoxidation at low temperature (400-600 C) and stoichiometric samples are obtained. Orthorhombic perovskites are formed at T?1200 C with the nonstoichiometry ? increasing with increasing temperature (e.g., ?=0.06 at 1000 C and ?=0.14 at 1200 C for x=0.5). Slow cooling in air results in almost complete reoxidation ( ?=0). CaMnO 3- ? is an orthorhombic perovskite with a large range of nonstoichiometry (0? ??0.30). The cubic to hexagonal phase transformation of the Sr-rich samples is accompanied by a large expansion of the lattice that is reduced by Ca substitution. The Ca/Sr-manganites are antiferromagnets with TN of 170 K for x=0.5 and ?=0.02 and 120 K for x=1 and ?=0.05.

Tpfer, Jrg; Pippardt, Ute; Voigt, Ingolf; Kriegel, Ralf

2004-07-01

54

Variation of foraminiferal Sr\\/Ca over Quaternary glacial-interglacial cycles: Evidence for changes in mean ocean Sr\\/Ca?  

Microsoft Academic Search

Records of Sr\\/Ca changes in planktonic and benthic foraminifera from diverse hydrographic settings reveal coherent variability (51%) between ocean basins and between surface and deep waters over the past 300 kyr. There is a general increase in foraminiferal Sr\\/Ca over the penultimate glaciation declining to minimum values during stage 5 and an increase in S r\\/ Ca from stage 5

P. A. Martin; D. W. Lea; T. A. Mashiotta; T. Papenfuss; M. Sarnthein

1999-01-01

55

Bi-Sr-Ca-Cu-O superconducting films fabricated using metal alkoxides  

Microsoft Academic Search

Superconducting films in the Bi--Sr--Ca--Cu--O systems were made using metal alkoxides. To prepare a dip-coating solution using a mixed alkoxide solution, insoluble Cu and Bi alkoxides were dissolved by modification with 2-dimethylaminoethanol and formation of a double alkoxide, respectively. Formation of the double alkoxides of Bi with Ca or Sr was confirmed using FT-IR and ¹H-NMR. Bi--Sr--Ca--Cu--O films on yttria-stabilized

Shingo Katayama; Masahiro Sekine

1991-01-01

56

X-ray Quantitative Analysis of High-Tc Phase in the Pb-Contained Bi-Sr-Ca-Cu-O Superconductor.  

National Technical Information Service (NTIS)

The authors determined the relative amount of high-T(c) phase in the Pb-contained Bi-Sr-Ca-Cu-O superconductor by the universal method of standardless X-ray quantitative phase analysis. The experimental results showed that the partial substitution of Pb f...

C. Wang H. Ren L. Xiao X. Wang Y. Wang

1993-01-01

57

High critical current superconducting Bi-Sr-Ca-Cu-O films by sputtering  

Microsoft Academic Search

Superconducting thin films of Bi-Sr-Ca-Cu-O with Tc onsets at 84 K and full superconductivity at 72.5 K were prepared by RF magnetron sputtering. A single-compound target with a composition of BiSrCaCu2O(x) was used. The films contain a mixture of the superconducting phase Bi(2.2)Sr2Ca(0.8)Cu2O(8+x) and the semiconducting phase Bi2(Sr,Ca,Bi)2CuO6. Structural analysis by X-ray diffraction shows a strong preferred orientation with the

M. Hong; J. Kwo; J.-J. Yeh

1988-01-01

58

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

NASA Astrophysics Data System (ADS)

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.

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

2009-01-01

59

Sr 2+ uptake and leachability study on cured aluminum-substituted tobermoriteOPC admixtures  

Microsoft Academic Search

Synthetic calcium silicate hydrate (C-S-H), which is similar to 1.1 nm tobermorite mineral, has demonstrated capacity to selectively pick up Sr2+ cations from mixed cationic solutions in the presence of 1000 times concentration of Na+, K+, Ca2+ and Ba2+ ions. The selective uptake of Sr2+ from mixed cationic solution has been quantified as distribution coefficient (Kd) and decontamination factor (Df).

O. P Shrivastava; Rashmi Shrivastava

2001-01-01

60

Thermodynamics and Constitution of Mg-Al-Ca-Sr-Mn Alloys: Part II. Procedure for Multicomponent Key Sample Selection and Application to the Mg-Al-Ca-Sr and Mg-Al-Ca-Sr-Mn Systems  

Microsoft Academic Search

A procedure is suggested to identify key sample compositions in n-component alloys, providing the most crucial information with limited experimental effort. The proposed algorithm furthermore\\u000a establishes the exact type of reaction equation of the (n+1) phase invariant equilibria. Predictive calculations of phase equilibria in quaternary Mg-Al-Ca-Sr and quinary Mg-Al-Ca-Sr-Mn\\u000a alloys are performed based on elaborate binary and ternary thermodynamic descriptions.

A. Janz; J. Grbner; R. Schmid-Fetzer

2009-01-01

61

Controls on Mg/Ca and Sr/Ca in Planktonic Foraminifera: Results From Culturing Experiments  

NASA Astrophysics Data System (ADS)

Culturing experiments were carried out on Globigerinoides ruber (white) and Globigerinella siphonifera, collected from the Gulf of Eilat and grown in seawater (i) at constant salinity but varying temperatures of 18 to 31 degC, (ii) at constant temperature but varying salinities of 32 to 44 psu, (iii) at constant salinity, temperature and dissolved inorganic carbon but varying pH of 7.9 to 8.4. Temperature response of Mg/Ca in cultured G. ruber (with an exponential constant of 11 +/- 2% per degC) agrees well with previous calibrations from core tops and net catches. Mg/Ca in G. ruber shows secondary dependence on salinity (6 +/- 2% per salinity unit). This compares well with the salinity response of Mg/Ca in cultured G. sacculifer (approx. 7% per salinity unit; Nuernberg et al., 1996), implying a similar salinity effect for shallow dwelling species. Mg/Ca in G. ruber shows no dependence on pH at ambient seawater range (8.1 to 8.3; NBS scale), but demonstrates considerable variation below and above the normal range of seawater pH. We observe no significant control of seawater temperature or pH on Sr/Ca in G. ruber. However, there is a significant correlation between Sr/Ca ratios and salinity (approx. 0.016 mmol/mol per salinity unit). Multiple regression analysis on Mg/Ca data of cultured G. ruber gives a calibration equation as a function of temperature and salinity [Mg/Ca = 0.29(+/-0.13)Sal + 0.46(+/- 0.13)Temp - 17.0(+/-5.9), R2=0.96, p=0.05]. Salinity can be independently derived from the regression for Sr/Ca [Sr/Ca = 0.016(+/-0.015)Sal + 0.72(+/-0.55), R2=0.91, p<0.05]. Nuernberg, D. et al., 1996. Assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures. Geochimica et Cosmochimica Acta, 60: 803-814.

Kisakurek, B.; Eisenhauer, A.; Erez, J.; Boehm, F.; Garbe-Schoenberg, D.

2007-12-01

62

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

PubMed

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

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

2014-02-01

63

Potential and limitations of Paleoproxies from Sr/Ca Ratios in Coccolith Carbonate  

NASA Astrophysics Data System (ADS)

The Sr/Ca ratio of coccoliths was recently proposed as a potential indicator of past growth rates of coccolithophorids, marine algae which play key roles in both the global carbonate and carbon cycles. We discuss recent calibrations of this proxy through culture studies and work with polyspecific and monospecific coccolith assemblages from surface sediments. Culture experiments with several species demonstrate that coccolith Sr/Ca ratios depend not only on calcification rate but also on temperature. Sr/Ca increases about 1% per oC, similar to published relationships in planktonic foraminifera and abiogenic calcites. At constant temperature and variable illumination, coccolith Sr/Ca ratios vary by 10 - 15% across the range of possible growth and calcification rates for a given species. In field studies, coccolith Sr/Ca shows a much larger response to productivity variations than to temperature. In core top sediments across the Somali upwelling zone, a more dynamic response to upwelling intensity and productivity is observed in larger coccoliths like Calcidiscus leptoporus (55% variation in Sr/Ca) than smaller coccoliths of Gephyrocapsa oceanica (15% variation in Sr/Ca). Numerical models of Sr partitioning during crystal growth are used to evaluate possible mechanisms for coccolith Sr/Ca variability and discrepancies over the relative influence of temperature and growth rate in field and culture studies.

Stoll, H. M.; Ziveri, P.; Rosenthal, Y.; Geisen, M.; Probert, I.

2001-12-01

64

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

SciTech Connect

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

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

1991-08-01

65

Impact of Zn substitution on phase formation and superconductivity of Bi1.6Pb0.4 Sr2Ca2Cu3-xZnxO10 with x = 0.0, 0.015, 0.03, 0.06, 0.09 and 0.12  

Microsoft Academic Search

Samples of series Bi1.6Pb0.4Sr2Ca2Cu3-xZnxO10 with x = 0.0, 0.015, 0.03,\\u000a0.06, 0.09 and 0.12 are synthesized by solid-state reaction route. All the\\u000asamples crystallize in tetragonal structure with majority (> 90%) of Bi-2223\\u000a(Bi2Sr2Ca2Cu3O10) phase (c-lattice parameter ~ 36 A0). The proportion of\\u000aBi-2223 phase decreases slightly with an increase in x. The lattice parameters\\u000aa and c of main

R. B. Saxena; Rajiv Giri; V. P. S. Awana; H. K. Singh; M. A. Ansari; B. V. Kumaraswamy; Anurag Gupta; Rashmi Nigam; K. P. Singh; H. Kishan; O. N. Srivastava

2005-01-01

66

Ca\\/Sr and Sr isotope systematics of a Himalayan glacial chronosequence: carbonate versus silicate weathering rates as a function of landscape surface age  

Microsoft Academic Search

We explored changes in the relative importance of carbonate vs. silicate weathering as a function of landscape surface age by examining the Ca\\/Sr and Sr isotope systematics of a glacial soil chronosequence located in the Raikhot watershed within the Himalaya of northern Pakistan. Bedrock in the Raikhot watershed primarily consists of silicate rock (Ca\\/Sr ? 0.20 ?mol\\/nmol, 87Sr\\/86Sr ? 0.77

ANDREW D. JACOBSON; J OEL D. BLUM; C. Page Chamberlain; MICHAEL A. POAGE; VALERIE F. SLOAN

2002-01-01

67

Structure and luminescence of (Ca,Sr)2SiS4 : Eu2+ phosphors  

Microsoft Academic Search

Sr2SiS4 : Eu2+, Ca2SiS4 : Eu2+ and the solid solution of both, europium-doped (Ca,Sr)2SiS4, were investigated as UV-VIS excitable green to red powder phosphors. Sr2SiS4 : Eu2+ shows two emission bands, peaking at 480 and 550 nm. By changing the ratio between Ca2+ and Sr2+, the photoluminescent emission spectrum can be tuned. Using x-ray diffraction, the phase composition and lattice

Anthony B. Parmentier; Philippe F. Smet; Frank Bertram; Jrgen Christen; Dirk Poelman

2010-01-01

68

Fermi Surface Topology of Ca1.5Sr0.5RuO4 Determined by Angle-Resolved Photoelectron Spectroscopy  

NASA Astrophysics Data System (ADS)

We report angle-resolved photoelectron spectroscopy results of the Fermi surface of Ca1.5Sr0.5RuO4, which is at the boundary of magnetic/orbital instability in the phase diagram of the Ca-substituted Sr ruthenates. Three t2g energy bands and the corresponding Fermi surface sheets are observed, which are also present in the Ca-free Sr2RuO4. We find that while the Fermi surface topology of the ?,? (dyz,zx) sheets remains almost the same in these two materials, the ? (dxy) sheet exhibits a holelike Fermi surface in Ca1.5Sr0.5RuO4 in contrast to being electronlike in Sr2RuO4. Our observation of all three volume conserving Fermi surface sheets clearly demonstrates the absence of orbital-selective Mott transition, which was proposed theoretically to explain the unusual transport and magnetic properties in Ca1.5Sr0.5RuO4.

Wang, S.-C.; Yang, H.-B.; Sekharan, A. K.; Souma, S.; Matsui, H.; Sato, T.; Takahashi, T.; Lu, Chenxi; Zhang, Jiandi; Jin, R.; Mandrus, D.; Plummer, E. W.; Wang, Z.; Ding, H.

2004-10-01

69

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

SciTech Connect

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.

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

2009-06-03

70

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

USGS Publications Warehouse

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

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

2004-01-01

71

Structures and self-activating photoluminescent properties of Sr{sub 3-x}A{sub x}GaO{sub 4}F (A=Ba, Ca) materials  

SciTech Connect

The synthesis, structures and photoluminescent properties of mixed oxyfluorides of the type Sr{sub 3-x}A{sub x}GaO{sub 4}F are compared to Sr{sub 3-x}A{sub x}AlO{sub 4}F (A=Ca, Ba) materials. In these compounds the F{sup -} and O{sup 2-} ions are ordered and located on two distinct crystallographic sites. When substituting Sr{sup 2+} by Ba{sup 2+} and Ca{sup 2+}, we find in Sr{sub 3-x}A{sub x}GaO{sub 4}F materials an ordering of the alkaline earth cations over the two crystallographic sites. The amount of Ba{sup 2+} ions that can be substituted into Sr{sub 3-x}A{sub x}GaO{sub 4}F is x{<=}1.2, which is slightly more than can be incorporated into the previously reported Al-analog Sr{sub 3-x}A{sub x}AlO{sub 4}F (x=1.0). Conversely, the amount of Ca{sup 2+} ions that can be substituted into Sr{sub 3-x}Ca{sub x}GaO{sub 4}F (x=0.3) is significantly less than in Sr{sub 3-x}Ca{sub x}AlO{sub 4}F (x=1.0). A post-synthesis reduction step causes these materials to exhibit self-activating broad band photoluminescence where the emitted colors vary with the amount of ions substituted into the host lattice. - Graphical abstract: TOC Statement The structures of the self-activating phosphors Sr{sub 3-x}A{sub x}MO{sub 4}F (A=Ba, Ca and M=Al, Ga) can be rationalized as alternating layers of bond compression and elongation, which impact the photoluminescence. Highlights: Black-Right-Pointing-Pointer Comparison of the structural changes in Sr{sub 3-x}A{sub x}AlO{sub 4}F and Sr{sub 3-x}A{sub x}GaO{sub 4}F (A=Ba, Ca) and its influence on the photoluminescence of these self-activating phosphors. Black-Right-Pointing-Pointer Analysis of the Global Instability Index of the Sr{sub 3-x}A{sub x}AlO{sub 4}F and Sr{sub 3-x}A{sub x}GaO{sub 4}F (A=Ba, Ca). Black-Right-Pointing-Pointer Comparison of the photoluminescence between the self-activating phosphors Sr{sub 3-x}A{sub x}AlO{sub 4}F and Sr{sub 3-x}A{sub x}GaO{sub 4}F (A=Ba, Ca).

Green, Robert [Nanocenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States)] [Nanocenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States); Vogt, Thomas, E-mail: tvogt@mailbox.sc.edu [Nanocenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States)] [Nanocenter and Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208 (United States)

2012-10-15

72

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

Microsoft Academic Search

The destruction of the ferromagnetism of alloyed SrRuO3 can be caused by electron localization at the substitution sites. Among all the non-magnetic cations that enter the B site, Zr4 + is the least disruptive to conductivity and ferromagnetism. This is because Zr4 + does not cause any charge disorder, and its empty d electron states which are poorly matched in

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

2011-01-01

73

Magnetic order changes in Al substituted Sr 2FeMoO 6 double perovskites  

Microsoft Academic Search

We have studied the effect of Al substituting for Fe in Sr2(Fe1?xAlx)MoO6 (x?0.3) double perovskites. X-ray diffraction, magnetic measurements at low and room temperature and Mssbauer spectroscopy have been used to determine the structural and magnetic properties of these compounds. The main observed effect is an increase with respect to the undoped composition, of the cationic order with Al doping

J. Gutirrez; L. M Rodr??guez-Mart??nez; J. M Barandiarn; T. Hernndez; T. Rojo

2003-01-01

74

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

NASA Astrophysics Data System (ADS)

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 Nio Southern Oscillation and Pacific Decadal Oscillation, using time series based upon radiocarbon dating. The corals investigated here show a limited connection with El Nio Southern Oscillation; longer-term changes related Pacific Decadal Oscillation may be evidenced in this climate archive.

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

2012-12-01

75

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

NASA Astrophysics Data System (ADS)

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 (6N, 162W; 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 1.4C (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).

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

2011-12-01

76

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

PubMed

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

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

2010-01-28

77

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

PubMed

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

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

2014-01-21

78

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

SciTech Connect

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.

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

2008-07-31

79

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

SciTech Connect

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.

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

2008-01-01

80

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

NASA Astrophysics Data System (ADS)

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

Moreau, M.; Corrge, T.; Dassi, E. P.; Le Cornec, F.

2014-04-01

81

Electrical transport and magnetoresistive properties of nanophasic La1-XAXMnO3 (A = Ca, Sr and Na) manganites  

NASA Astrophysics Data System (ADS)

With a view to understand the electrical transport and magnetoresistance behavior of divalent (Ca & Sr) and monovalent (Na) substituted nanophasic lanthanum manganites, a series of materials were prepared using co-precipitation route by sintering at 800 C. The effect of doping has been investigated in terms of structural, grain size, metal-insulator transition and variation in magnetoresistance properties for La0.7Ca0.3MnO3 (LCMO), La0.7Sr0.3MnO3 (LSMO) and La0.8Na0.2MnO3 (LNMO) samples. The X-ray diffraction data were analyzed using Rietveld refinement technique. It has been found that the samples doped with Sr and Na having rhombohedral structure with R-3c space group. The sample with Ca doping crystallizes into orthorhombic structure with Pnma space group. From resistivity measurements, it is found that all the samples exhibit metal-insulator transition (TMI) in the range of 201-261 K, which is low as compared to the samples prepared by ceramic route. The electrical resistivity data were analyzed using various theoretical models.

Mankadia, S. R.; Bhalodia, J. A.

2013-06-01

82

Thermodynamic modelling of the BCa, BSr and BBa systems  

Microsoft Academic Search

The boron-alkaline earth metal binary systems BCa, BSr and BBa have been modelled by means of the calculation of phase diagram (CALPHAD) technique, wherein the thermodynamic properties of the alkaline-earth hexaborides CaB6, SrB6, BaB6, and the elements ?-B, ?-B, fcc-Ca, fcc-Sr and bcc-Ba are obtained on the basis of the previous first-principles quasiharmonic phonon calculations. The temperaturecomposition (Tx) phase diagrams

Shunli Shang; Tao Wang; Zi-Kui Liu

2007-01-01

83

Extracellular calcium and CaSR drive osteoinduction in mesenchymal stromal cells.  

PubMed

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

Gonzlez-Vzquez, Arlyng; Planell, Josep A; Engel, Elisabeth

2014-06-01

84

First principles study of magnetic properties of Zn-Sn substituted M-type Sr-hexaferrite  

NASA Astrophysics Data System (ADS)

Site occupancy and magnetic properties of Zn-Sn substituted M-type Sr-hexaferrite SrFe12-x(Zn0.5Sn0.5)xO19 with x=1 were studied using density functional theory and generalized gradient approximation (GGA). Using the GGA+U method the description of strongly correlated 3d electrons of Fe was improved. Our results show that Zn and Sn atoms prefer to occupy 4f1 and 4f2 sites respectively. Favorable Zn-Sn substituted configurations show an increase in saturation of magnetization (Ms), and a decrease in magnetic anisotropy energy (MAE), over the pure M-type Sr-hexaferrite (x=0). Experimental observations agree with the decrease of MAE and the increase of Ms for Zn-Sn substituted Sr-hexaferrite.

Kim, Seong-Gon; Liyanage, Laalitha; Houze, Jeff; Kim, Sungho

2012-02-01

85

Superconductivity in Bi-Sr-Ca-Cu-O (invited)  

SciTech Connect

We report on the structure and superconducting properties of a single phase polycrystalline composition given by Bi/sub 2.2/Sr/sub 1.7/Ca/sub 1.2/Cu/sub 2/O/sub 8+//sub delta/ as well as measurements on single crystals. X-ray and electron diffraction analyses of both single-crystal and single phase materials show an incommensurately modulated orthorhombic superlattice, derivable from a pseudotetragonal substructure. The various compositions have the common feature that the major portion of the superconductivity disappears above 85 K but there is a small tail in the diamagnetic susceptibility extending to 110 K, above which the sample becomes paramagnetic. Single crystals, grown by the flux method, exhibit the same incommensurately modulated pseudotetragonal structure as the ceramic, but show a higher diamagnetic shielding and in some cases also have tails. The critical currents in the (ab) plane are only about one-fifth of the value found for YBa/sub 2/Cu/sub 3/O/sub 7/ crystals and the anisotropy is smaller. These reduced values may be an intrinsic property of the modulated superlattice but more likely are due to stacking faults and other defects in the crystals.

McGuire, T.R.; Shivashankar, S.A.; La Placa, S.J.; Chandrashekhar, G.V.; Boehme, R.F.; Shaw, T.M.; Yee, D.S.; Shafer, M.W.; Cuomo, J.J.

1988-11-15

86

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

87

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

88

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

PubMed

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

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

2013-07-01

89

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

Microsoft Academic Search

Thirteen laboratories from the USA and Europe participated in an intercomparison study of Mg\\/Ca and Sr\\/Ca measurements in foraminifera. The study included five planktonic species from surface sediments from different geographical regions and water depths. Each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples. Analysis of solutions of known Mg\\/Ca

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

2004-01-01

90

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

PubMed

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

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

2011-03-01

91

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

NASA Astrophysics Data System (ADS)

The destruction of the ferromagnetism of alloyed SrRuO3 can be caused by electron localization at the substitution sites. Among all the non-magnetic cations that enter the B site, Zr4 + is the least disruptive to conductivity and ferromagnetism. This is because Zr4 + does not cause any charge disorder, and its empty d electron states which are poorly matched in energy with the Ru t2g4 states cause the least resonance scattering of Ru's d electrons. Conducting Sr(Ru, Zr)O3 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.

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

2011-03-01

92

Effect of crystalline quality and substitution on magnetic anisotropy of SrRuO3 thin films  

Microsoft Academic Search

Magnetic anisotropy of pure and substituted laser-ablated SrRuO3 and SrRu0.9Cr0.1O3 thin films has been studied by rotational magnetization experiments in a superconducting quantum interference device (SQUID) magnetometer. The magnetic easy axis for epitaxial (single domain) SrRuO3 and SrRu0.92O3 thin films lies in the (001) plane and is tilted away from the normal to the surface by 23-26. Its direction lies

S. Kolesnik; Y. Z. Yoo; O. Chmaissem; B. Dabrowski; T. Maxwell; C. W. Kimball; A. P. Genis

2006-01-01

93

Improving SST reconstructions from coral Sr\\/Ca records: multiple corals from Tahiti (French Polynesia)  

Microsoft Academic Search

We reconstruct SST from coral Sr\\/Ca ratios measured at three coral cores taken from the lagoon of Tahiti (French Polynesia).\\u000a Two coral cores were drilled from the same coral colony (one horizontally and one vertically), and a third core was drilled\\u000a vertically from another coral growing at a different site. We evaluate several Sr\\/Ca records as proxies for regional SST

Sri Yudawati Cahyarini; Miriam Pfeiffer; W.-Chr. Dullo

2009-01-01

94

Room temperature transport properties of new BiSrCaCuO compounds  

Microsoft Academic Search

New compounds belonging to the BiSrCaCuO cuprate family have been synthesized by sequentially imposed layer epitaxy. The Cu\\/Ca ratio in these compounds is typically twice the value for conventional Bi2Sr2Can?1CunO2n 4. A second characteristic of the new compounds is a Bi deficiency relative to conventional BSCCO. The room temperature electrical resistivity of these compounds reaches extremely low values, orders of

Michel Lagus; Claire Partiot; Vincent Mairet; Christophe Hatterer; Xiang Zhen Xu; Catherine Deville Cavellin; Cristian Florin Beuran; Betty Eustache; Jean-Baptiste Moussy

1997-01-01

95

Reversibility between the Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3Q10 superconducting phases. (Reannouncement with new availability information)  

SciTech Connect

The Bi2Sr2Ca2Cu3O10 phase is kinetically favored over the Bi2Sr2CaCu2O8 phase. Starting compositions used to produce Bi2Sr2Ca2Cu3O10 even with lead added, always result in the formation of mostly Bi2Sr2CaCu2O8, along with by-products, after short sintering times. Prolonged sintering in the range of 850 to 860 C can result in nearly single phase Bi2Sr2Ca2Cu3O10. When Bi2Sr2Ca2Cu3O10 is then melted at 1000 C and slowly cooled, one finds all Bi2Sr2CaCu2O8 again plus impurities. Long-term sintering results in the regrowth of Bi2Sr2Ca3Cu3O10, provide that the stoichiometry was not changed too much by the melting and that contamination with containment vessels has been minimized. Thus, there is a reversibility between Bi2Sr2Ca2Cu3O10 and Bi2Sr2CaCu2O8 plus impurities. This phase reversibility will be demonstrated for bulk sintered materials. The implications for melt-processed thick films cast components will be discussed.

Jones, T.E.; McGinnis, W.C.; Briggs, J.S.

1991-03-01

96

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

NASA Astrophysics Data System (ADS)

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

Iqbal, Y.; Muhammad, R.

2013-03-01

97

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

NASA Astrophysics Data System (ADS)

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.

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

2012-02-01

98

Are SR Ca content fluctuations or SR refractoriness the key to atrial cardiac alternans?: insights from a human atrial model.  

PubMed

Despite the important role of electromechanical alternans in cardiac arrhythmogenesis, its molecular origin is not well understood. The appearance of calcium alternans has often been associated to fluctuations in the sarcoplasmic reticulum (SR) Ca loading. However, cytosolic calcium alternans observed without concurrent oscillations in the SR Ca content suggests an alternative mechanism related to a dysfunction in the dynamics of the ryanodine receptor (RyR2). We have investigated the effect of SR release refractoriness in the appearance of alternans, using a mathematical model of a single human atrial cell, based on the model by Nygren et al. (30), where we modified the dynamics of the RyR2 and of SR Ca release. The genesis of calcium alternans was studied stimulating the cell for different periods and values of the RyR2 recovery time from inactivation. At fast rates cytosolic calcium alternans were obtained without concurrent SR Ca content fluctuations. A transition from regular response to alternans was also observed, changing the recovery time from inactivation of the RyR2. This transition was found to be hysteretic, so for a given set of parameters different responses were observed. We then studied the relevance of RyR2 refractoriness for the generation of alternans, reproducing the same protocols as in recent experiments. In particular, restitution of Ca release during alternans was studied with a S1S2 protocol, obtaining a different response if the S2 stimulation was given after a long or a short release. We show that the experimental results can be explained by RyR2 refractoriness, arising from a slow RyR2 recovery from inactivation, stressing the role of the RyR2 in the genesis of alternans. PMID:24610921

Lugo, Carlos A; Cantalapiedra, Inma R; Pearanda, Angelina; Hove-Madsen, Leif; Echebarria, Blas

2014-06-01

99

Non-traditional stable Ca, Sr isotopic composition in rainwater from Guiyang city, southwest China  

NASA Astrophysics Data System (ADS)

The major ions, strontium concentrations, ?[44/40]Ca, [87]Sr/^[86]Sr and ?[88/86]Sr ratios were measured in rainwater samples collected at an urban site in Guiyang, southwest China, over a period of one year. The pH values ranged between 4.2 and 8.6, with a volume-weighted mean (VWM) of 6.2. About 30% of the rainwater studied were acidic rain with pH values less than 5.6. Ca[2+] was the most dominant cation in rainwater samples and the VWM value was175?mol/L (21-1631 ?mol/L). SO[4][2-] was the predominant anion with VWM value of 137 ?mol/L (5-2019 ?mol/L), next was NO3- with VWM value of 26 ?mol/L(1.4-444 ?mol/L).Using Na as an indicator of marine origin, and Al for the terrestrial inputs, the proportions of sea salt and terrestrial elements were estimated from elemental ratios. More than 99% of Ca[2+] and 98% of SO[4][2-] in rainwater samples are non-sea-salt origin. The ?[44/40]Ca values of rainwater samples from Guiyang city, ranged from 0.510.18to 1.090.14, are very similar to the range of ?[44/40]Ca values in natural rivers. The [87]Sr/^[86]Sr ratios spanned a range of 0.70800 to 0.72742, with a mean value of 0.71080. The ?[88/86]Sr of rainwater samples ranged from 0.2150.004 to 0.3330.004, with a mean ?88/86Sr of rainwater is 0.2960.01. The radiogenic strontium isotope data ([87]Sr/^[86]Sr) can infer the sources of Sr of the rainwater samples. The [87]Sr/^[86]Sr vs. Cl/Na suggests that the sources of rainwater samples come from dissolved carbonate minerals and anthropogenic inputs. The ?[44/40]Ca values and the stable Sr isotope (?[88/86]Sr) may be affected by biological processes.

Han, G.; Tang, Y.

2013-12-01

100

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

SciTech Connect

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

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

2007-10-01

101

Hydrothermal Preparation and Characterization of Ultralong Strontium-Substituted Hydroxyapatite Whiskers Using Acetamide as Homogeneous Precipitation Reagent  

PubMed Central

The ultralong strontium- (Sr-) substituted hydroxyapatite (SrHAp) whiskers were successfully prepared using acetamide as homogeneous precipitation reagent. The effect of the Sr substitution amount on the lattice constants and proliferation of human osteoblast cells (MG-63) was further investigated. The results showed that the SrHAp whiskers with diameter of 0.212??m and ultralong length up to 200??m were obtained and the Sr substitution level could be facilely tailored by regulating the initial molar ratio of Sr/(Sr + Ca) in raw materials. The Sr2+ replaced part of Ca2+ and the lattice constants increased apparently with the increase of the Sr substitution amount. Compared with the pure HAp whiskers, the Sr substitution apparently stimulated the proliferation of MG-63 at certain extracted concentrations. Our study suggested that the obtained SrHAp whiskers might be used as bioactive and mechanical reinforcement materials for hard tissue regeneration applications.

Xu, Jianqiang; Yang, Yaoqi; Wan, Rong; Zhang, Weibin

2014-01-01

102

Hydrothermal preparation and characterization of ultralong strontium-substituted hydroxyapatite whiskers using acetamide as homogeneous precipitation reagent.  

PubMed

The ultralong strontium- (Sr-) substituted hydroxyapatite (SrHAp) whiskers were successfully prepared using acetamide as homogeneous precipitation reagent. The effect of the Sr substitution amount on the lattice constants and proliferation of human osteoblast cells (MG-63) was further investigated. The results showed that the SrHAp whiskers with diameter of 0.2-12??m and ultralong length up to 200??m were obtained and the Sr substitution level could be facilely tailored by regulating the initial molar ratio of Sr/(Sr + Ca) in raw materials. The Sr(2+) replaced part of Ca(2+) and the lattice constants increased apparently with the increase of the Sr substitution amount. Compared with the pure HAp whiskers, the Sr substitution apparently stimulated the proliferation of MG-63 at certain extracted concentrations. Our study suggested that the obtained SrHAp whiskers might be used as bioactive and mechanical reinforcement materials for hard tissue regeneration applications. PMID:24592192

Xu, Jianqiang; Yang, Yaoqi; Wan, Rong; Shen, Yuhui; Zhang, Weibin

2014-01-01

103

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

SciTech Connect

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) LaRhZr (LRZ) and LaSr RhZr (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.

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

2009-01-01

104

A skeletal Sr/Ca record preserved in Dipsastraea (Favia) speciosa and implications for coral Sr/Ca thermometry in mid-latitude regions  

NASA Astrophysics Data System (ADS)

A core (900 mm long) of the scleractinian coral Dipsastraea (Favia) speciosa was collected from Iki Island (3348'N), Japan, one of the highest latitude coral reefs known to exist at present, where winter monthly mean sea surface temperature (SST) drops to 13C. The Sr/Ca profile was constructed using a bulk sampling method for the uppermost 280 mm interval of the core, which grew between 1966 and 2007, to test whether it could act as a suitable proxy for SST in a harsh environmental setting where reef-building coral do not usually survive. The Sr/Ca-SST relationship derived from the annual Sr/Ca and SST extremes predicted the observed monthly averaged summer SST extremes within an error range of 1.1C (1 s.d., n = 40). The obtained Sr/Ca-SST calibration was also found to be valid for subtropical Dipsastraea (Favia) corals, proving its broad applicability. However, low-amplitude winter peaks were observed in the slow-growing intervals, which we confirmed (using individual spot analysis along a continuous growth line) result from the mixing of theca grown at different times. Our bulk sampling approach, across multiple growth lines in the skeleton of D. (F.) speciosa, led to the mixing of asynchronous skeletal part. At the study site, D. (F.) speciosa grows continuously, even during the cold season, suggesting that the skeletal Sr/Ca obtained from specimens of D. (F.) speciosa can be used as an SST proxy in the northwest Pacific marginal seas.

Seo, Inah; Lee, Yong Il; Watanabe, Tsuyoshi; Yamano, Hiroya; Shimamura, Michiyo; Yoo, Chan Min; Hyeong, Kiseong

2013-08-01

105

Long-range magnetic ordering in bulk Tb1-xMxMnO? (M = Ca, Sr).  

PubMed

Substitution of Ca(2+) and Sr(2+) at the A-site of multiferroic TbMnO3 bulk results in an increased average ionic radius and ionic-size mismatch, and was found to reduce the orthorhombic distortion. Signatures of long-range ferromagnetic-like ordering at 78 K in Tb0.67Ca0.33MnO3 and at 87 K in Tb0.67Sr0.33MnO3 samples are clearly observed in both the dc and ac susceptibility data. A compensation temperature is also observed in Tb0.67Ca0.33MnO3, indicating the antiparallel alignment of Tb(3+) moments to the Mn(3+)-Mn(4+) moments. The canted antiferromagnetic ordering coexists with antiferromagnetic clusters, resulting in spin-glass-like behavior at low temperatures. An increased average ionic radius and ionic-size mismatch at the A-site are determined to be critical factors in determining the magnetic properties of the hole-doped manganites. PMID:23807807

Staruch, M; Jain, M

2013-07-24

106

ESR study of (Sr,La,Ca)_{14}Cu_{24}O_{41}  

Microsoft Academic Search

We report an electron spin resonance (ESR) study of single crystals of the\\u000aspin-chain spin-ladder compound (Sr,La,Ca)_{14}Cu_{24}O_{41}. The data suggest\\u000athat in intrinsically hole doped Sr_{14-x}Ca_xCu_{24}O_{41} only a small amount\\u000aof holes is transferred from the chains to the ladders with increasing x,\\u000aresulting in a crossover from spin dimerized to uniform spin chains. In the\\u000asamples of La_{14-x}Ca_xCu_{24}O_{41} with

V. Kataev; K.-Y. Choi; M. Grueninger; U. Ammerahl; B. Buechner; A. Freimuth; A. Revcolevschi

2001-01-01

107

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

PubMed Central

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

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

1990-01-01

108

44/40Ca and 87Sr/86Sr isotopes as tracers of silicate weathering in small catchments of the Massif Central, France  

NASA Astrophysics Data System (ADS)

We present calcium stable isotope and strontium radiogenic isotope data for soils and sediments developed on volcanic and igneous rocks forming small catchments in the Massif Central (France). Measurements of 44/40Ca isotope ratios (44/40Ca measured by the double spike method on TIMS and normalized to the value for seawater Ca in delta units) in rocks, sediments and soils from silicate catchments (e.g. granite and basalts) together with 87Sr/86Sr isotope ratios permit an examination of the relationships of these isotope systematics during weathering of silicate rocks. We have analysed the granite, weathered granite (arene) and saprolite, sediment and soil overlying the granite on one hand and the basanite, sediment and soil overlying the basanite on the other. The main bedrock in the volcanic zone (e.g. Allanche catchment) is 11 to 2.5 Ma basanite (nephelinitic to leucitic basalts) having SiO2 between 41-45 wt. %, Na2O + K2O <5%, modal or normative nepheline or leucite and a ground mass of clinopyroxene and plagioclase. Surrounding rocks are feldspathic basalts having SiO2 between 46-49 wt. %, Na2O + K2O <5%, normative nepheline, hyperstene and olivine, with plagioclase as the main crystalline phase. The granite massif (e.g. Margeride, 332 12Ma) consists of light and dark facies as a result of the fractional crystallisation of a crustal magma in a sub-horizontal laccolith, with leucogranites dated at 2982 Ma intruding this granite. The average mineral composition is 37% quartz, 30% oligoclase, 23% K-feldspar and 10% biotite (light facies) and 31% quartz, 30% andesine, 20% K-feldspar and 19% biotite (dark facies). Sr isotope ratios in the arene, sediment and soil diverge strongly from those in the granite bedrock and are positively correlated with Rb/Sr ratios. The 87Sr/86Sr and Rb/Sr ratios both increase from the whole rock to the arene, reflecting the weathering of low 87Sr/86Sr, low-Rb/Sr minerals such as plagioclase and apatite. Sediments collected on a river bank have 87Sr/86Sr ratios greater than that of the arene with values increasing in the sediment from the surface down to soil. The 87Sr/86Sr vs. Rb/Sr variation observed in the volcanic area likewise confirms the weathering of low 87Sr/86Sr, low Rb/Sr phases in the bedrock, and there is a linear increase in 87Sr/86Sr and Rb/Sr ratios from those in the sediment up to the values observed in the soils. In the volcanic area, the basanite bedrock has 44/40Ca = -0.94 0.05 (n = 7), while the soils and sediments have 44/40Ca of -0.75 to -1.13 and -0.79 to -1.01, respectively. These results suggest that Ca isotopes are not strongly fractionated during weathering of the basalt. The granite whole-rock has 44/40Ca of -1.29, while the soil and sediments have 44/40Ca of -1.93 to -2.07 and -1.98 to -2.81, respectively, with values decreasing as the Ca content decreases. The 44/40Ca ratios of arene, soil and sediment are similar to or less than that of K- feldspar, reflecting complete loss of the relatively heavy Ca from plagioclase and apatite during weathering. Comparison of the 44/40Ca and 87Sr/86Sr ratios further revealed the role of mineralogical assemblage in sediments and soils, particularly for the lesser 44/40Ca - greater 87Sr/86Sr samples, when compared to the bedrock.

Ngrel, Philippe; Guerrot, Catherine; Millot, Romain; Petelet-Giraud, Emmanuelle; Bullen, Thomas

2013-04-01

109

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

Microsoft Academic Search

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

Takaomi Arai; Aya Kotake; Kentaro Morita

2004-01-01

110

Effect of fe Doping on Superconductivity in the Bi-Pb-Sr-Ca-Cu-O System  

NASA Astrophysics Data System (ADS)

The effects of Fe substitution for Cu in Bi1.6Pb0.4Sr1.6Ca2Cu3O10-y were investigated. The superconducting transition, phase assemblage, and lattice parameters were studied for samples with up to ~1/4 of the Cu replaced by Fe. With increasing levels of Fe, the superconducting transition gradually degenerated to that of semiconducting behaviour, the phase assemblage underwent the reaction series 2223?2221?2201, and the c-axis of the 2212 phase decreased monotonically when the doped samples were heat treated in air. These results can be explained in terms of structural changes rather than magnetic effects, where the higher valence and smaller size of Fe3+ compared Cu2+ alter the nature of the oxygen co-ordination and bonding. When the Fe-doped samples were treated in nitrogen, the effect of destabilisation of the superconducting phase was minimised. In contrast to the effect of Fe on the structure, the depression in Tc is attributed mainly to the magnetic effects of Fe doping. The critical concentration of the Fe dopant at which superconductivity was completely destroyed, is at ~13% Cu replacement.

Dou, S. X.; Sheng, Y. J.; Liu, H. K.; Sorrell, C. C.; Savvides, N.

111

Synchrony of cardiomyocyte Ca(2+) release is controlled by T-tubule organization, SR Ca(2+) content, and ryanodine receptor Ca(2+) sensitivity.  

PubMed

Recent work has demonstrated that cardiomyocyte Ca(2+)release is desynchronized in several pathological conditions. Loss of Ca(2+) release synchrony has been attributed to t-tubule disruption, but it is unknown if other factors also contribute. We investigated this issue in normal and failing myocytes by integrating experimental data with a mathematical model describing spatiotemporal dynamics of Ca(2+) in the cytosol and sarcoplasmic reticulum (SR). Heart failure development in postinfarction mice was associated with progressive t-tubule disorganization, as quantified by fast-Fourier transforms. Data from fast-Fourier transforms were then incorporated in the model as a dyadic organization index, reflecting the proportion of ryanodine receptors located in dyads. With decreasing dyadic-organization index, the model predicted greater dyssynchrony of Ca(2+) release, which exceeded that observed in experimental line-scan images. Model and experiment were reconciled by reducing the threshold for Ca(2+) release in the model, suggesting that increased RyR sensitivity partially offsets the desynchronizing effects of t-tubule disruption in heart failure. Reducing the magnitude of SR Ca(2+) content and release, whether experimentally by thapsigargin treatment, or in the model, desynchronized the Ca(2+) transient. However, in cardiomyocytes isolated from SERCA2 knockout mice, RyR sensitization offset such effects. A similar interplay between RyR sensitivity and SR content was observed during treatment of myocytes with low-dose caffeine. Initial synchronization of Ca(2+) release during caffeine was reversed as SR content declined due to enhanced RyR leak. Thus, synchrony of cardiomyocyte Ca(2+) release is not only determined by t-tubule organization but also by the interplay between RyR sensitivity and SR Ca(2+) content. PMID:23601316

yehaug, Leiv; Loose, Kristian ; Jlle, Guro F; Re, smund T; Sjaastad, Ivar; Christensen, Geir; Sejersted, Ole M; Louch, William E

2013-04-16

112

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

PubMed Central

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

?yehaug, Leiv; Loose, Kristian ?.; J?lle, Guro F.; R?e, Asmund T.; Sjaastad, Ivar; Christensen, Geir; Sejersted, Ole M.; Louch, William E.

2013-01-01

113

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

NASA Astrophysics Data System (ADS)

Magnesium (Mg) and Calcium (Ca) isotopes are fractionated by aqueous precipitation and incongruent silicate weathering, resulting in sedimentary reservoirs with characteristic isotopic compositions. Limestones and dolomites are isotopically light in both elements, whereas shales/pelites can have heavy Mg and light Ca. The isotopic character of these reservoirs may persist through anatexis (Shen, et al., PNAS 106(49), 2009). Mg and Ca isotopes could therefore be used to gain new insights into the sources of granitic magmas and hence the mechanisms by which the continental crust forms and evolves. Radiogenic 40Ca gives additional information about the K/Ca ratios of magma sources, and Sr and Nd isotopes provide complementary age and lithology information. To evaluate the potential of Ca and Mg isotopes for studying granite petrogenesis we made measurements on a suite of granitic intrusive rocks of Jurassic to Miocene age in southern Tibet that exhibit large variations in Nd (?Nd = +5 to -12) and Sr isotopes (87Sr/86Sr = 0.704 to 0.722). Our samples represent a transect northward from the Indus-Yalu Suture (IS), west of Lhasa. Rocks close to the IS have mantle-like Nd and Sr isotopic compositions, whereas those farther to the north have low ?Nd and higher 87Sr/86Sr, and include Mesozoic, Paleogene and Neogene peraluminous (2-mica) granites (DePaolo, et al., Goldschmidt, 2008; Kapp, et al., JGR 110, 2005; Hou et al., EPSL 220, 2004). Radiogenic 40Ca is detectable in peraluminous (2-mica) granites and correlates with high 87Sr/86Sr, but does not correlate with Nd isotopes, indicating that 2-mica granite magmas come from both low-K and high-K sources. Stable isotopes of both Ca and Mg show substantial variation. Relative to bulk silicate Earth (BSE, which we define as ?=0 for discussion) ?44Ca values vary from 0 to -0.7, and ?26Mg varies from -0.3 to +0.6. Thus to first order Ca is light and Mg is heavy relative to BSE. For samples with mantle-like Nd and Sr, ?44Ca values cluster between -0.2 and -0.3; we have few Mg data for these rocks so far, but they appear to be in a similar range. Hence the mantle-derived granitoids have relatively homogeneous Ca and Mg that is slightly enriched in light isotopes relative to mantle rocks. For samples with strong crustal Nd and Sr isotope signatures, there is a wide range of both Ca and Mg isotope ratios, from heavier to lighter than BSE. The ?44Ca values suggest that Ca from ancient marine limestones is a major component of the magma source regions, whereas the ?26Mg values require that pelites provide a substantial amount of the Mg. Considering that both Ca and Mg are minor components of granitic magmas, this result can be understood in terms of the involvement of carbonate-bearing pelitic rock as a major component of the crustal granitic source regions.

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

2010-12-01

114

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

USGS Publications Warehouse

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

Patchett, P. J.

1980-01-01

115

Percolation behaviour in intergrowth BiSrCaCuO structures grown by molecular beam epitaxy  

Microsoft Academic Search

BiSrCaCuO thin films and specially Bi-2212 compounds were grown on (100) SrTiO3 substrates by molecular beam epitaxy (MBE). The growth mechanism was controlled in real time by monitoring the RHEED intensity. The deposition sequence of the elements was also varied in order to induce intergrowth structures at nanometer scale. The resulting high density of stacking faults is in contrast with

J. B. Moussy; J. Y. Laval; X. Z. Xu; F. C. Beuran; C. Deville Cavellin; M. Lagus

2000-01-01

116

Reduced pressure MOCVD of C-axis oriented BiSrCaCuO thin films  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

117

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

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

118

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

NASA Technical Reports Server (NTRS)

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.

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

119

An approach to achieve layered spintronics material using brownmillerite compound Ca2.5Sr0.5GaMn2O8  

NASA Astrophysics Data System (ADS)

Magnetic and magnetotransport properties of the naturally occurring layered compounds Ca2.5- x La x Sr0.5GaMn2O8 ( x = 0, 0.05, 0.075, and 0.1) have been reported. We have succeeded to introduce ferromagnetic ordering in the pure antiferromagnetic system Ca2.5Sr0.5GaMn2O8 by varying the ratio between Mn3+ and Mn4+ ions. The experimental results of magnetization, magnetoresistance, and neutron diffraction were interpreted on the basis of an electronic phase separation model, where a formation of ferromagnetic clusters (due to DE interactions) inside the layered antiferromagnetic matrix (due to superexchange interactions) in the La-substituted compounds is proposed. Significantly, the present study shows that the magnetic and electronic properties of the layered system Ca2.5Sr0.5GaMn2O8 can be tuned/optimized by appropriate chemical substitution to achieve a new spintronic material based on naturally occurring layered system for practical applications.

Yusuf, S. M.; Bera, A. K.

2013-05-01

120

Correlation between magnetism and crystal symmetry in the mixed valence system of Sr1- x Ca x Ru0.5Mn0.5O3  

NASA Astrophysics Data System (ADS)

The crystallographic, magnetic and transport properties of Sr1- x Ca x Ru0.5Mn0.5O3 were studied to reveal the effects of crystal symmetry on the magnetism and the transport properties of antiferromagnetic SrRu1- y Mn y O3 ( y > 0.2). The Ca-content dependences of the lattice constants and volume suggest that the mixed valence state of Mn3+, Mn4+, Ru4+, and Ru5+ ions in SrRu0.5Mn0.5O3 is held for Ca substitution. However, a structural transformation from tetragonal to orthorhombic symmetry occurs at a Ca content of x 0.2, and a ferromagnetic state appears simultaneously. The Weiss temperature of all samples has a positive value regardless of the magnetic state. The resistivity decreases as the Ca content increases, and the high temperature part of the resistivity could be fitted by using the variable range hopping (VRH) model. The localization length increases as soon as ferromagnetism appears. The Curie temperature seems to depend on the distance between transition metal ions. The antiferromagnetic state was explained by using the competition between a ferromagnetic interaction along the c-axis and an antiferromagnetic interaction in the ab-plane, and the orthorhombic ferromagnetic state was explained by using a three-dimensional ferromagnetic interaction between Mn ions.

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

2013-06-01

121

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

SciTech Connect

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

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

1993-12-01

122

Ionic conductivity of congruently melting Ca0.6Sr0.4F2 and Ca1 - x - y Sr y R x F2 + x ( R = La, Ce, Pr, Nd) single crystals with fluorite structure  

NASA Astrophysics Data System (ADS)

Single crystals of congruently melting compositions of the Ca0.6Sr0.4F2 and Ca1 - x - y Sr y R x F2 + x ( R = La, Ce, Pr, Nd; x = 0.16-0.21; y = 0.07-0.16) solid solutions with fluorite structure have been grown by the Bridgman-Stockbarger method. Their electrical properties have been investigated in the range from 473 to 823 K, and it is shown that they are ionic conductors. For Ca0.6Sr0.4F2 crystals, the ionic conductivity ? = 2 10-6 S/cm at 673 K, and the ion transport activation energy E a = 1.1 eV. For Ca0.77Sr0.07La0.16F2.16, Ca0.70Sr0.11Ce0.19F2.19, Ca0.65Sr0.15Pr0.20F2.20, and Ca0.58Sr0.21Nd0.21F2.21 crystals, the values of ? lie in the range from 9 10-7 to 2 10-6 S/cm at 500 K, and the activation energy E a is 0.88-0.93 eV. The concentration and mobility of ionic charge carriers in Ca1 - x - y Sr y R x F2 + x crystals have been calculated.

Sorokin, N. I.; Karimov, D. N.; Krivandina, E. A.; Zhmurova, Z. I.; Komar'kova, O. N.

2008-03-01

123

Bulk superconductivity up to 122 K in the Tl-Pb-Sr-Ca-Cu-O system  

Microsoft Academic Search

The preparation of high-temperature superconductors based on oxides of thallium and copper, but not containing barium, is discussed. Two materials are examined. It is found that (Tl\\/0.5\\/Pb\\/0.5\\/)Sr2CaCu2O7 has a transition temperature of about 85 K, and a tetragonal symmetry with a = 3.80 A, and c = 12.05 A. The other material, (Tl\\/0.5\\/Pb\\/0.5\\/)Sr2Ca2Cu3O9, has a transition temperature of about 120

M. A. Subramanian; C. C. Torardi; J. Gopalakrishnan; P. L. Gai; J. C. Calabrese; T. R. Askew; R. B. Flippen; A. W. Sleight

1988-01-01

124

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

DOEpatents

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

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

1994-01-01

125

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

DOEpatents

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.

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

1994-10-11

126

Eect of Sintering Time On Sb Added BiPbSrCaCuO Superconducting Ceramics  

NASA Astrophysics Data System (ADS)

In this study, superconducting Sb doped BiPbSrCaCuO ceramics with a fixed nominal composition were prepared and sintered at 850oC for different periods. The structural phases of the sintered ceramics were determined by means of the measurements of the resistivity-temperature behaviour and of the XRD analysis. Sb doping along with Pb doping in the BiSrCaCuO ceramics was observed to increase the volume fraction of the high Tc phase, the onset temperature and the critical temperature Tc. The critical temperature for the 100 hour sintered sample was 4K higher than that of the 60 hour sintered sample.

Kocabas, K.

1998-05-01

127

Crystal structures of the double perovskites Ba 2Sr 1? x Ca x WO 6  

Microsoft Academic Search

Structures of the double perovskites Ba2Sr1?xCaxWO6 have been studied by the profile analysis of X-ray diffraction data. The end members, Ba2SrWO6 and Ba2CaWO6, have the space group I2\\/m (tilt system a0b?b?) and Fm3m (tilt system a0a0a0), respectively. By increasing the Ca concentration, the monoclinic structure transforms to the cubic one via the rhombohedral R3 phase (tilt system a?a?a?) instead of

W. T. Fu; S. Akerboom; D. J. W. IJdo

2007-01-01

128

Strain relaxation in buried SrRuO3 layer in (Ca1-xSrx)(Zr1-xRux)O3\\/SrRuO3\\/SrTiO3 system  

Microsoft Academic Search

A novel relaxation phenomenon occurs in buried SrRuO3 layers in strained (Ca1-xSrx)(Zr1-xRux)O3\\/SrRuO3\\/SrTiO3 (001) thin film system. The lightly strained SrRuO3 buried layer is initially clamped by the SrTiO3 substrate. After a heavily strained (Ca1-xSrx)(Zr1-xRux)O3 overlayer is deposited, localized strain relaxation develops in the buried layer. This is manifested by a crosshatch pattern of corrugations on the surface, due to the

Soo Gil Kim; Yudi Wang; I.-Wei Chen

2006-01-01

129

Strain relaxation in buried SrRuO3 layer in (Ca1?xSrx)(Zr1?xRux)O3?SrRuO3?SrTiO3 system  

Microsoft Academic Search

A novel relaxation phenomenon occurs in buried SrRuO3 layers in strained (Ca1?xSrx)(Zr1?xRux)O3?SrRuO3?SrTiO3 (001) thin film system. The lightly strained SrRuO3 buried layer is initially clamped by the SrTiO3 substrate. After a heavily strained (Ca1?xSrx)(Zr1?xRux)O3 overlayer is deposited, localized strain relaxation develops in the buried layer. This is manifested by a crosshatch pattern of ?100? corrugations on the surface, due to

Soo Gil Kim; Yudi Wang; I-Wei Chen

2006-01-01

130

Modulation of the local SR Ca2+ release by intracellular Mg2+ in cardiac myocytes.  

PubMed

In cardiac muscle, Ca(2+)-induced Ca(2+) release (CICR) from the sarcoplasmic reticulum (SR) defines the amplitude and time course of the Ca(2+) transient. The global elevation of the intracellular Ca(2+) concentration arises from the spatial and temporal summation of elementary Ca(2+) release events, Ca(2+) sparks. Ca(2+) sparks represent the concerted opening of a group of ryanodine receptors (RYRs), which are under the control of several modulatory proteins and diffusible cytoplasmic factors (e.g., Ca(2+), Mg(2+), and ATP). Here, we examined by which mechanism the free intracellular Mg(2+) ([Mg(2+)](free)) affects various Ca(2+) spark parameters in permeabilized mouse ventricular myocytes, such as spark frequency, duration, rise time, and full width, at half magnitude and half maximal duration. Varying the levels of free ATP and Mg(2+) in specifically designed solutions allowed us to separate the inhibition of RYRs by Mg(2+) from the possible activation by ATP and Mg(2+)-ATP via the adenine binding site of the channel. Changes in [Mg(2+)](free) generally led to biphasic alterations of the Ca(2+) spark frequency. For example, lowering [Mg(2+)](free) resulted in an abrupt increase of spark frequency, which slowly recovered toward the initial level, presumably as a result of SR Ca(2+) depletion. Fitting the Ca(2+) spark inhibition by [Mg(2+)](free) with a Hill equation revealed a K(i) of 0.1 mM. In conclusion, our results support the notion that local Ca(2+) release and Ca(2+) sparks are modulated by Mg(2+) in the intracellular environment. This seems to occur predominantly by hindering Ca(2+)-dependent activation of the RYRs through competitive Mg(2+) occupancy of the high-affinity activation site of the channels. These findings help to characterize CICR in cardiac muscle under normal and pathological conditions, where the levels of Mg(2+) and ATP can change. PMID:19029377

Gusev, Konstantin; Niggli, Ernst

2008-12-01

131

Effect of crystalline quality and substitution on magnetic anisotropy of SrRuO3 thin films  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy of pure and substituted laser-ablated SrRuO3 and SrRu0.9Cr0.1O3 thin films has been studied by rotational magnetization experiments in a superconducting quantum interference device (SQUID) magnetometer. The magnetic easy axis for epitaxial (single domain) SrRuO3 and SrRu0.92O3 thin films lies in the (001) plane and is tilted away from the normal to the surface by 23-26. Its direction lies between the [110] and [010] axes. For the lower oxygen pressure grown SrRuO3 thin film, which consists of intertwined crystal nanodomains the magnetic easy axis is no longer locked-in to the (001) plane but is oriented closer to the normal to the surface that is the resultant orientation of easy axes for different domains. Similar effect is observed in single-domain SrRu0.9Cr0.1O3 thin film with random Cr substitution on the RuO6 octahedra. A role of ruthenium deficiency observed in all the studied thin films is also discussed.

Kolesnik, S.; Yoo, Y. Z.; Chmaissem, O.; Dabrowski, B.; Maxwell, T.; Kimball, C. W.; Genis, A. P.

2006-04-01

132

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

NASA Astrophysics Data System (ADS)

Analysis of aragonite from sea shells and coral skeletons showed a clear correlation between the strontium and calcium concentrations for these crystals (Sr/Ca ratio) and seawater temperature obtained by satellites and ship readings. In this work we present the results of a study that correlates Sr/Ca ratio with formation temperature of another calcium crystal, the hydroxyapatite (Ca 10(PO 4) 6(OH) 2), main mineral compound of teeth and bones from vertebrates. These animals, independent of its thermoregulation pattern (endothermic or ectothermic) have variations of internal temperature along the body. One interesting application of this work is to differentiate warm-blooded animals from cold-blooded ones just by measuring Sr/Ca ratio in their bones. Bones from a crocodile from Caiman yacare species and two dogs, a poodle and a non defined race, were analyzed using PIXE technique and thick target correction. A 1.78 (18) MeV external proton beam was used in LAMFI-USP with an accumulated charge of about 10 ?C for probing the samples. Emitted X-rays were collected using Si-PIN detectors (140 keV for Fe). As in coral skeletons, the Sr/Ca ratio of animals is lower in the body's warmer parts and higher in colder parts.

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

2008-04-01

133

Low-temperature thermoelectric properties of the electron-doped perovskites Sr1- x Ca x Ti1- y Nb y O3  

NASA Astrophysics Data System (ADS)

We have investigated the thermoelectric (TE) properties for single crystals of the perovskites Sr1- x Ca x Ti1- y Nb y O3 for 0 ? x ? 0.4 and 0 ? y ? 0.03 at temperatures below room temperature (RT). We found that SrTi0.99Nb0.01O3 showed a large power factor at low temperatures ( PF = 50 W/K2cm at 100 K 90 W/K2cm at 50 K) and the largest dimensionless TE figure-ofmerit at temperatures below 40 K ( ZT 0.07) among the reported materials. Such a large low-temperature TE response around a carrier concentration of 1020 cm-3 is due to a distinct phonon drag effect. We also found that the Ca2+ substitution for Sr2+ increased the ZT at 300 K for Sr1- x Ca x Ti0.97Nb0.03O3 from 0.08 to 0.105. The enhancement of the ZT around RT originates both from a large reduction of a thermal conductivity due to a randomness introduced into the crystal structure and from an unexpected enhancement of a Seebeck coefficient.

Okuda, Tetsuji; Fukuyado, Junichi; Narikiyo, Kurahito; Akaki, Mitsuru; Kuwahara, Hideki

2013-08-01

134

Properties of the infrared-transmitting Bi-Ca-Sr-(Cu, Zn)-O glasses doped with lead oxide  

NASA Astrophysics Data System (ADS)

The glass forming regions of the Bi015-CuO-Ca05Sr05O superconducting system have been explored by the addition of PbO. The glass froming regions expand with PbO addition and shrink with the substitution of copper oxide by zinc oxide. The glass transition temperature of these glasses ranges from 300C to 420C. These glasses have high refractive index of about 2. 8 and density from 6 to 9 g/cm3 they are infrared transmitting with cutoff wavelength farther than 7 tm. The high polarizability of Bi3 ions gives these glasses high non-linear optical coefficient of 4 * lO13. 1.

Zheng, Haixing; Lin, Patrick; Mackenzie, John D.

1990-10-01

135

Doping control and thermoelectric properties in R1-xAxZnSbO (R = La, Ce; A = Ca, Sr)  

NASA Astrophysics Data System (ADS)

As the two-dimensional analogues of a conventional thermoelectric semiconductor ZnSb, we investigated the thermoelectric properties of layer-structured R1-xAxZnSbO (R = La, Ce; A = Ca, Sr) using the polycrystalline samples with compaction density around 55%, combining with the electronic band-structure calculation. We found that the carrier concentration of RZnSbO can be controlled by substituting A2+ for R3+ in the charge-reservoir layers without lowering the carrier mobility. The hole-doped materials exhibited relatively low thermal conductivity and a moderately high Seebeck coefficient, whose temperature and doping dependence were well reproduced by the calculation. ZT values were found to increase without showing saturation up to 390 K, and even higher values would be expected along the conducting ZnSb layers for a single crystal. These results indicate the potential of the hole-doped RZnSbO as a good thermoelectric material.

Suzuki, T.; Bahramy, M. S.; Arita, R.; Taguchi, Y.; Tokura, Y.

2011-01-01

136

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

Microsoft Academic Search

The high precision measurement of the Sr\\/Ca ratio in corals has the potential for measuring past sea surface temperatures at very high accuracy. However, the veracity of the technique has been questioned on the basis that there is both a spatial and temporal variation in the Sr\\/Ca ratio of seawater, and that kinetic effects, such as the calcification rate, can

JOHN F. MARSHALL; MALCOLM T. MCCULLOCH

2002-01-01

137

Directional Solidification and Superconductive Transition of Bi2Sr2CaCu2O8+delta.  

National Technical Information Service (NTIS)

By laser heated pedestal growth method, Bi2Sr2CaCu2O(8 + delta) as-grown fibers with different morphologies were solidified in non-equilibrium condition at the rates of 0.1 to about 14 mm/min. At low rates, a (Sr(1-x)Ca(x))CuO2 phase with long and straigh...

C. Zhang J. Zhang Y. Ge Z. Hu

1994-01-01

138

First-Principles Study on the Surfaces of Transition-Metal Perovskites: Sr_2RuO4 and Sr_1-xCa_xVO_3  

Microsoft Academic Search

Trying to bridge the gap between the rich experiment data, which are surface sensitive, and the little understanding about the surface phases of transition metal perovskites, we study the surfaces of Sr_2RuO4 and Sr_1-xCa_xVO3 as examples of 214 and 113 compounds respectively by first-principles calculations based on the density function theory. For layered perovskite Sr_2RuO_4, we found the surface is

Zhong Fang; Priya Mahadevan; Kiyoyuki Terakura

2000-01-01

139

Effects of A-site substitution on the structure and magnetic properties of Bi 0.15Sr 0.85- yAe yCo 1- xFe xO 3- ? perovskites  

NASA Astrophysics Data System (ADS)

The effects of partial substitution of Sr 2+ by Ca 2+ and Ba 2+ on the A-site of oxygen-deficient perovskites, Bi 0.15Sr 0.85- yAe yCo 1- xFe xO 3- ?, where y = 0.28 for Ae = Ba and y = 0.17 for Ae = Ca, and 0.0 ? x ? 1.0, have been investigated. The differing ionic size of the Ca 2+ and Ba 2+ cations influences both the crystal structure and the properties of the materials. The smaller Ca 2+ cation favoured formation of an oxygen vacancy ordered perovskite superstructure ( I4/ mmm, a = 2 ap, c = 4 ap), meanwhile the presence of the larger Ba 2+ cation promoted a disordered simple cubic structure ( Pm3m, a = ap) that was also found for all Fe containing samples, i.e. x ? 0.25. The samples were studied with PXRD, NPD, TGA, electron microscopy and magnetic susceptibility measurements. All as-prepared samples exhibited long range G-type antiferromagnetic ordering. The effect of oxygen annealing was dramatic for the Bi 0.15Sr 0.68Ca 0.17Co 1- xFe xO 3- ? series, with a disappearance of magnetic order for x ? 0.25 linked to increasing spin-glass properties. The oxygen content of the Bi 0.15Sr 0.57Ba 0.28Co 1- xFe xO 3- ? as-prepared materials was generally higher than their Ca substituted counterparts, and the long range antiferromagnetic order was more resistant to oxygen annealing.

Eriksson, A. K.; Tran, T.; Saxin, S.; Svensson, G.; Svedlindh, P.; Eriksson, S.-G.; Knee, C. S.

2009-11-01

140

Spectroscopic and structural analysis of Ca substituted La orthoferrite  

NASA Astrophysics Data System (ADS)

Samples of orthoferrites La 1- xCa xFeO 3 (0.15? x?0.45) were synthesized by double sintering ceramic technique. X-ray diffraction and infrared spectroscopy experiments were carried out and discussed for the investigated samples. The data showed the formation of single-phase orthorhombic structure of space group Pbnm. The FTIR spectra were performed in the region (1200-200 cm -1). Four main absorption bands were present with some side bands and shoulders in the range (1200-400 cm -1). Another four bands were appeared in the range (400-200 cm -1). The positions, intensities and values of the absorptions bands vary depending on the Ca content in the samples. The first absorption band appeared at about 920 cm -1 was assigned to the La-O stretching vibration.

Ahmed, M. A.; Seoudi, R.; El-dek, S. I.

2005-11-01

141

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

USGS Publications Warehouse

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.

DeLong, K. L.; Flannery, J. A.; Maupin, C. R.; Poore, R. Z.; Quinn, T. M.

2011-01-01

142

Potential and limitations of Sr/Ca ratios in coccolith carbonate: new perspectives from cultures and monospecific samples from sediments.  

PubMed

The Sr/Ca ratio of coccoliths was recently proposed as a potential indicator of past growth rates of coccolithophorids, marine algae, which play key roles in both the global carbonate and carbon cycles. We synthesize calibrations of this proxy through laboratory culture studies and analysis of monospecific coccolith assemblages from surface sediments. Cultures of coccolithophorids Helicosphaera carteri, Syracosphaera pulchra and Algirospira robusta confirm a 1-2% increase in Sr/Ca per degrees C previously identified in Emiliania huxleyi and Gephyrocapsa oceanica. This effect is not due merely to increases in growth rate with temperature and must be considered in palaeoceanographic studies. In light-limited cultures of E. huxleyi, Calcidiscus leptoporus and G. oceanica at constant temperature, coccolith Sr/Ca ratios vary by 10% across the range of possible growth and calcification rates for a given species. Among different species under similar culture conditions, Sr/Ca ratios vary by 30%. Although the highest ratios are in the cells with highest calcification and organic carbon fixation rates, at lower rates there is much scatter, indicating that different mechanisms control interspecific and intraspecific coccolith Sr/Ca variations. In field studies in the Equatorial Pacific and Somalia coastal region, coccolith Sr/Ca correlates with upwelling intensity and productivity. A more dynamic response is observed in larger coccoliths like C. leptoporus (23-55% variation in Sr/Ca) than in smaller coccoliths of G. oceanica or Florisphaera profunda (6-15% variation in Sr/Ca). This response suggests that, despite temperature effects, coccolith Sr/Ca has potential as an indicator of coccolithophorid productivity. If the variable Sr/Ca response of different species accurately reflects their variable productivity response to upwelling (and not different slopes of Sr/Ca with productivity), coccolith Sr/Ca could provide useful data on past changes in coccolith ecology. The mechanism of coccolith Sr/Ca variations remains poorly understood but is probably more closely tied to biochemical cycles during carbon acquisition than to chemical kinetic effects on Sr incorporation in the calcite coccolith crystals. PMID:12804301

Stoll, Heather M; Ziveri, Patricia; Geisen, Markus; Probert, Ian; Young, Jeremy R

2002-04-15

143

Enhanced irreversibility by crystal defects in the Bi-Sr-Ca-Cu-O system  

SciTech Connect

We measured magnetic irreversibility, H*(T), in liquid-quenched Bi-Sr-Ca-Cu-O samples with various microstructures at high applied field (up to 7 T). We found that H*(T) is considerably increased in the Bi{sub 2}Sr{sub 2}Ca{sub 3}Cu{sub 4}O{sub x} (2234) sample with a large amount of crystal defects, including severe lattice distortion and calcium and copper rich precipitates. We argue that the lattice distortion may affect the degree of anisotropy and the Josephson coupling between the Cu-O layers, which in turn enhance the irreversibility in the Bi-Sr-Ca-Cu-O system. A critical current density, J{sub c}, of 8 {times} 10{sup 4} A/cm{sup 2} at 8 kG and 40 K was obtained in the 2234 sample with many defects, while the J{sub c} dropped significantly at the same temperature and field in the near stoichiometry Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (2223) sample with a uniform microstructure.

Salem-Sugui, S. Jr.; Shi, Donglu; McFarland, S.E.

1991-04-01

144

High critical current superconducting Bi-Sr-Ca-Cu-O films by sputtering  

NASA Astrophysics Data System (ADS)

Superconducting thin films of Bi-Sr-Ca-Cu-O with Tc onsets at 84 K and full superconductivity at 72.5 K were prepared by RF magnetron sputtering. A single-compound target with a composition of BiSrCaCu2O(x) was used. The films contain a mixture of the superconducting phase Bi(2.2)Sr2Ca(0.8)Cu2O(8+x) and the semiconducting phase Bi2(Sr,Ca,Bi)2CuO6. Structural analysis by X-ray diffraction shows a strong preferred orientation with the c-axis perpendicular to the film plane. The resistivity shows a linear dependence on temperature with rho(300 K) = 450 microohm cm, and ratio rho(300 K)/(100 K) about 2.4. High critical-current densities of 100,000 A/sq cm, measured by the transport method at 61 K in zero field, and of 10 to the 7th A/sq cm, measured by the magnetic method at 6 K have been obtained.

Hong, M.; Kwo, J.; Yeh, J.-J.

1988-08-01

145

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

SciTech Connect

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

Goretta, K. C.

1998-09-11

146

The effect of oxidant on resputtering of Bi from Bi-Sr-Ca-Cu-O films  

SciTech Connect

The type and partial pressure of oxidant mixed with argon can affect the selective resputtering of Bi in composite-target, magnetron-sputtered Bi-Sr-Ca-Cu-O films. Comparative studies using oxygen and ozone show that ozone is a more potent oxidant, as well as a more potent source of resputterers, than is oxygen. Severe resputtering from ozone is significantly reduced by a {minus}40 V potential on the sample block. We suggest that oxygen causes resputtering by forming O{sub 2}{sup +}, which interacts with the target to produce energetic O{sup {minus}}. In contrast, ozone may form lower-energy O{sup {minus}} by electron impact in the dark space. Negative oxygen ions from the target itself may be responsible for a background resputtering effect. Our results and those found for Y-Ba-Cu-O by others are comparable. Bi in Bi-Sr-Ca-Cu-O behaves as Ba in Y-Ba-Cu-O, with regard to selective resputtering; furthermore, the response of Sr, Ca, and Cu to oxygen in sputtered Bi-Sr-Ca-Cu-O is similar to what is observed for Cu in Y-Ba-Cu-O.

Grace, J.M.; McDonald, D.B.; Reiten, M.T.; Olson, J.; Kampwirth, R.T.; Gray, K.E.

1991-09-01

147

INFRARED PROPERTIES OF CaF, SrF, AND BaF  

Microsoft Academic Search

Reflectivity and transmission measurements on CaF SrF, and ; BaF are studied to obtain information on the lattice vibrations. The ; reflection band in each material is analyzed with classical dispersion theory. ; In order to fit the data, it is necessary to use one strong and one weak ; resonance in each case. The strong resonance is identified as

W. Kaiser; W. G. Spitzer; R. H. Kaiser; L. E. Howarth

1962-01-01

148

The 120K-SUPERCONDUCTING Phase in Bi-Ca-Sr-Cu-O  

NASA Astrophysics Data System (ADS)

The formation of the high temperature superconducting phases in the quinary Bi-Ca-Sr-Cu-O compound system has been investigated. The 120K-superconducting transition appears in samples prepared between 850 and 900C. A certain homogeneity range is found to exist in this superconducting system, suggesting that higher Tc may be achievable in the same system.

Meng, R. L.; Hor, P. H.; Sun, Y. Y.; Huang, Z. J.; Gao, L.; Xue, Y. Y.; Wang, Y. Q.; Bechtold, J.; Chu, C. W.; Hazen, R. M.; Prewitt, C. T.; Angel, R. J.; Ross, N. L.; Finger, L. W.; Hadidiacos, C. G.

149

On the superconductivity in (Sr, Ca) 14Cu 24O 41 towards a chemical standard model  

Microsoft Academic Search

The superconductivity in cuprates has been suggested to result from (a) holes clustering resonances as a means of restoring antiferromagnetic order, and (b) the formation of weak peroxy-chemical bonds. This understanding is employed here to explain the appearance of superconductivity in the ladder compound (Sr, Ca)14Cu24O41 under pressure.

Itai Panas; Refael Gatt

1997-01-01

150

On the superconductivity in (Sr, Ca) 14Cu 24O 41 towards a chemical standard model  

NASA Astrophysics Data System (ADS)

The superconductivity in cuprates has been suggested to result from (a) holes clustering resonances as a means of restoring antiferromagnetic order, and (b) the formation of weak peroxy-chemical bonds. This understanding is employed here to explain the appearance of superconductivity in the 'ladder' compound (Sr, Ca) 14Cu 24O 41 under pressure.

Panas, Itai; Gatt, Refael

1997-05-01

151

Fermi surface of Bi2Sr2CaCu2O8+delta thin film  

Microsoft Academic Search

We present angular resolved photoemission spectroscopy measurements about the Fermi surface of a Bi2Sr2CaCu2O8+delta (Bi2212) thin film. Dispersion curves in two directions are discussed. It is confirmed that the Fermi surface observed on the Bi2212 thin film fits the bulk Fermi surface.

C. J. Hatterer; V. Mairet; F. C. Beuran; X. M. Xie; X. Z. Xu; M. Lagus; C. Coussot; B. Eustache; H. Adrian; P. Wagner; C. D. Cavellin; G. Indlekofer; A. Taleb

1996-01-01

152

Fermi surfaces of Bi 2Sr 2CaCu 2O 8+? thin film  

Microsoft Academic Search

We present angular resolved photoemission spectroscopy measurements about the Fermi surface of a Bi2Sr2CaCu2O8+? (Bi2212) thin film. Dispersion curves in two directions are discussed. It is confirmed that the Fermi surface observed on the Bi2212 thin film fits bulk Fermi surface.

C. J. Hatterer; V. Mairet; F. C. Beuran; X. M. Xie; X. Z. Xu; M. Lagus; C. Coussot; B. Eustache; H. Adrian; P. Wagner; C. Deville Cavellin; G. Indlekofer; A. Taleb

1996-01-01

153

Fermi surfaces of Bi 2Sr 2CaCu 2O 8+? thin film  

NASA Astrophysics Data System (ADS)

We present angular resolved photoemission spectroscopy measurements about the Fermi surface of a Bi 2Sr 2CaCu 2O 8+? (Bi2212) thin film. Dispersion curves in two directions are discussed. It is confirmed that the Fermi surface observed on the Bi2212 thin film fits bulk Fermi surface.

Hatterer, C. J.; Mairet, V.; Beuran, F. C.; Xie, X. M.; Xu, X. Z.; Lagus, M.; Coussot, C.; Eustache, B.; Adrian, H.; Wagner, P.; Deville Cavellin, C.; Indlekofer, G.; Taleb, A.

1996-02-01

154

Hydrogen probe equipped with SrCeO3-based proton conductor and Ca/CaH2 reference electrode  

NASA Astrophysics Data System (ADS)

The protonic transference number of SrCe0.95Yb0.05O3-? (SCYB) ceramic pellets was determined to be above 0.9 in the temperature range of 873 to 1073 K using a hydrogen concentration cell. The density of the ceramic disk and tube is above 96 pct of the theoretical. Highly dense SCYB tube and glass seal improved the reliability and life of an electrochemical hydrogen probe. When the probe was immersed in molten aluminum, a hydrogen concentration cell was established as Mo, Ca/CaH2|SrCe0.95Yb0.05O3-?|[H]in molten Al, Mo The probe under different conditions generated stable electromotive force within 5 minutes after immersion and responded rapidly to the change in the atmosphere. The thermodynamic stability of the solid electrolyte under the testing conditions is also discussed.

Zheng, Minhui; Zhen, Xiuxin

1993-10-01

155

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

NASA Astrophysics Data System (ADS)

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

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

1996-10-01

156

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

PubMed

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

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

2012-09-24

157

Magnetic properties of triangular lattice Ca4IrO6 and Ca2.5Sr1.5IrO6  

NASA Astrophysics Data System (ADS)

We report a structural, thermodynamic, and transport study of single-crystal Ca4IrO6 and Ca2.5Sr1.5IrO6. The isostructural Ca4IrO6 and Ca2.5Sr1.5IrO6 feature a triangular lattice of spin chains running along the c axis. The underlying properties of the two systems are characterized by a partial antiferromagnetic order occuring at 12 K and 9 K for Ca4IrO6 and Ca2.5Sr1.5IrO6, respectively, a small entropy removal associated with the phase transition, and a sizable low-temperature specific heat linearly proportional to temperature. The detailed results will be discussed along with comparisons drawn with other related systems such as Ca5Ir3O12.

Butrouna, K. H.; Li, L.; Qi, T. F.; Korneta, O. B.; Terzic, J.; Akbari, E.; Parkin, S.; Yuan, S. J.; Cao, G.

2013-03-01

158

Structural effects of hydrostatic pressure in Sr1-xMxCuO2 (M=La,Ca) and Sr4Cu6O10  

Microsoft Academic Search

Pressure effects on the tetragonal infinite-layer structure were studied in superconducting Sr0.9La0.1CuO2 (electron-doped) and Sr0.7Ca0.3CuO2 (hole-doped) samples, and in an insulating nonsuperconducting Sr0.14Ca0.86CuO2 sample, using time-of-flight neutron powder diffraction. Neutron-diffraction measurements, with the sample at room temperature, were performed at several hydrostatic pressures up to ~=0.6 GPa on each of the three samples, using a helium-gas pressure cell. The measured

H. Shaked; Y. Shimakawa; B. A. Hunter; P. G. Radaelli; B. Dabrowski; R. L. Hitterman; J. D. Jorgensen; P. D. Han; D. A. Payne; S. Kikkawa; G. Er; F. Kanamaru

1994-01-01

159

Basic Science and Experimental Studies The Na\\/Ca 2 Exchanger\\/SR Ca 2 ATPase Transport Capacity Regulates the Contractility of Normal and Hypertrophied Feline Ventricular Myocytes  

Microsoft Academic Search

Background: Pressure overload leads to cardiac hypertrophy, which is often followed by heart failure. We tested the hypothesis that depressed contractility in this process results from an imbalance in Ca 2 transport by the sarcoplasmic reticulum (SR) Ca 2 ATPase (SERCA) and the sarcolemmal Na\\/Ca 2 exchanger (NCX). Methods and Results: Left ventricular (LV) myocytes (n 79) from 12 normal

JUTTA WEISSER-THOMAS; HAJIME KUBO; COLLEEN A. HEFNER; JOHN P. GAUGHAN; BRIAN S. MCGOWAN; ROBERT ROSS; MARKUS MEYER; WOLFGANG DILLMANN; STEVEN R. HOUSER

160

Redox-Mediated Reciprocal Regulation of SERCA and Na+/Ca2+-Exchanger Contributes to SR Ca2+-Depletion in Cardiac Myocytes  

PubMed Central

Myocardial failure is associated with increased oxidative stress and abnormal excitation-contraction coupling characterized by depletion of sarcoplasmic reticulum (SR) Ca2+-stores and a reduction in Ca2+-transient amplitude. Little is known about the mechanisms whereby oxidative stress affects Ca2+-handling and contractile function; however, reactive thiols may be involved. We used an in vitro cardiomyocyte system to test the hypothesis that short-term oxidative stress induces SR Ca2+-depletion via redox-mediated regulation of sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) and the sodium-Ca2+-exchanger (NCX) and that this is associated with thiol oxidation. Adult rat ventricular myocytes paced at 5 Hz were superfused with H2O2 (100 ?M, 15 min). H2O2 caused a progressive decrease in cell shortening followed by diastolic arrest, which was associated with decreases in SR Ca2+-content, systolic [Ca2+]i and Ca2+-transient amplitude, but no change in diastolic [Ca2+]i. H2O2 caused reciprocal effects on the activities of SERCA (decreased) and NCX (increased). Pretreatment with the NCX inhibitor KB-R7943 prior to H2O2 increased diastolic [Ca2+]i, and mimicked the effect of SERCA inhibition with thapsigargin. These functional effects were associated with oxidative modification of thiols on both SERCA and NCX. In conclusion, redox-mediated SR Ca2+-depletion involves reciprocal regulation of SERCA and NCX, possibly via direct oxidative modification of both proteins.

Kuster, Gabriela M.; Lancel, Steve; Zhang, Jingmei; Communal, Catherine; Trucillo, Mario P.; Lim, Chee C.; Pfister, Otmar; Weinberg, Ellen O.; Cohen, Richard A.; Liao, Ronglih; Siwik, Deborah A.; Colucci, Wilson S.

2010-01-01

161

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

PubMed

Transient changes in intracellular Ca(2+) concentration are essential signals for activation of plant immunity. It has also been reported that Ca(2+) signals suppress salicylic acid-mediated plant defense through AtSR1/CAMTA3, a member of the Ca(2+) /calmodulin-regulated transcription factor family that is conserved in multicellular eukaryotes. How plants overcome this negative regulation to mount an effective defense response during a stage of intracellular Ca(2+) surge is unclear. Here we report the identification and functional characterization of an important component of ubiquitin ligase, and the associated AtSR1 turnover. The AtSR1 interaction protein1 (SR1IP1) was identified by CytoTrap two-hybrid screening. The loss-of-function mutant of SR1IP1 is more susceptible to bacterial pathogens, and over-expression of SR1IP1 confers enhanced resistance, indicating that SR1IP1 acts as a positive regulator of plant defense. SR1IP1 and AtSR1 act in the same signaling pathway to regulate plant immunity. SR1IP1 contains the structural features of a substrate adaptor in cullin3-based E3 ubiquitin ligase, and was shown to serve as a substrate adaptor that recruits AtSR1 for ubiquitination and degradation when plants are challenged with pathogens. Hence, SR1IP1 positively regulates plant immunity by removing the defense suppressor AtSR1. These findings provide a mechanistic insight into how Ca(2+) -mediated actions are coordinated to achieve effective plant immunity. PMID:24528504

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

2014-04-01

162

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

PubMed

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

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

2000-10-01

163

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

NASA Astrophysics Data System (ADS)

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.

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

164

Mssbauer spectrometric study of nonstoichiometric perovskite, A (Co0.8Fe0.2) O3- (A=Ba, Sr, Ca), for oxidative coupling of methane  

NASA Astrophysics Data System (ADS)

Nonstoichiometric perovskites. A(Co0.8Fe0.2)O3-6, were prepared by a pyrolysis of mixed metal citrates, and the catalytic property and structure of these perovskites were investigated. The efficiency of an oxidative coupling of methane increases with the order of Ba. Sr, and Ca substituted in A site and decreases with the amounts of deficient oxygens. The mixed valence of B site ions in the disordering of deficient oxygen is considered to contribute mainly to the oxidative coupling of methane.

Nomura, Kiyoshi; Goda, Takeshi; Ujihira, Yusuke; Hayakawa, Takashi; Takehira, Katsuomi

1992-04-01

165

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

166

Crystalline phases during the melting of Bi2Sr2CaCu2O(x)  

Microsoft Academic Search

The melting of Bi2Sr2CaCu2O(x) material has been studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in order to study the phases that formed in the high temperature regions. Two distinct phases of (Sr(1-x)Ca(x))CuO2 and (Sr(1-x)Ca(x))2CuO3 have been observed in the Bi-rich matrix depending upon quenching temperatures. Crystallization from the melt by fast cooling usually produce the co-existence

Ming Xu; J. Polonka; A. I. Goldman; D. K. Finnemore; Qiang Li; F. C. Laabs

1991-01-01

167

Behavior and Calibration of the Sr/Ca Temperature Proxy in Vesicomyid Clams  

NASA Astrophysics Data System (ADS)

Clams of the Vesicomyidae family populate both hydrothermal vent areas and hydrocarbon cold seep areas. These habitats furnish reduced sulfides that support chemoautotrophic endosymbionts that nourish the clams. Clams of this family all grow aragonitic shells, and can have lifetimes that span many decades. The incorporation of Sr into aragonite in corals has a well-known temperature dependence and the same is true in clams, though the partitioning is reversed from that in corals. Thus the potential exists to use these clams to provide proxy temperatures for both hydrothermal and cold seep environments. Hart and Blusztajn (1998) used ion probe techniques for Sr/Ca analysis of several Calyptogena magnifica specimens from 10N on the East Pacific Rise. Sub-monthly resolution was obtained, and large Sr/Ca variations were observed that could be correlated with known eruptive and venting episodes. The preliminary temperature calibration we reported in 1998 was obtained from an Arctica icelandica (ocean quahog), recovered from a coastal site with a 6 year instrumental temperature record (1.3 - 17.7C). Because this species stops growing in the winter, the low temperature end of the calibration was uncertain. To refine this calibration, we report here Sr/Ca records from 3 cold seep localities (typically with 200+ analysis spots per clam): a Calyptogena ponderosa (Green Canyon, Gulf of Mexico, 720 m, ~ 6C); a C. phaseoliformis? (Aleutian trench, 4922 m, 1.5C); and paired C. pacifica and C. kilmeri (Monterey Canyon, 904 m, 4.2C). All of these samples exhibited significant Sr/Ca variations, suggesting that either the sites were not isothermal (as hoped), or that the clams were processing water with anomalous, pore-water-derived, Sr/Ca. Significant stretches of each record did have low and fairly constant Sr/Ca and, when coupled with the known ambient water temperatures for each locality, substantiated a calibration only ~ 1 higher than the 1998 calibration (new calibration: TC = 18160*(Sr/Ca) - 12.2). The C. kilmeri spent most of its early life at 9-12C, only dropping to ambient a year or so before collection in 1996. In contrast, the nearby C. pacifica spent most of its early life near ambient, with a rapidly increasing temperature over its last few years, reaching almost 20C just before collection in 1994. We also have determined detailed Sr/Ca records for 7 specimens of C. magnifica from a hydrothermal venting region at ~ 10N on the East Pacific Rise. These clams were collected in 1990, 1991, 1992, 1996, 1997, and 1999, and thus provide a time series with at least one known time for each clam. This was a period of active eruption and venting at this site, and the thermal episodes can be matched fairly well across the various clams. Sporadic low temperatures for these clams are in the 3-4C range, but large periods of their lives are spent in the 10-20C range, with short spikes to ~ 40C being common. We thank Colleen Cavanaugh, Lauren Mullineaux, Dan Fornari, Tim Shank, Rich Lutz, Jim Barry and Chuck Fisher for sharing their magnificent Vesicomyids.

Hart, S. R.

2009-12-01

168

Reactions of Ca and Sr with CH 3X and CF 3X (X ? Br, I). A laser-induced fluorescence study on nascent CaBr, SrBr, and SrI  

NASA Astrophysics Data System (ADS)

Continuous-wave laser-induced fluorescence (LIF) spectra have been measured of nascent SrBr, SrI, and CaBr, formed in the reactions of Sr with CH 3X and CF 3X (X ? Br,I), and of Ca with CH 3Br and CF 3Br. The bandhead spectra measured for the reactions involving Sr can be attributed to the formation of highly vibrationally excited SrX; for the reaction with CF 3I vibrational bandheads up to ?? = 42 in SrI are observed. The LIF spectra of CaBr formed in the reactions of Ca with CH 3Br and CF 3Br can be interpreted as a sum of a thermal and a nonthermal spectrum. These two types of spectra originate from the formation of CaBr inside the Ca oven and in the reaction region outside the oven, respectively. In all cases studied, the spectroscopic constants reported in the literature from studies at low t; values need only minor modifications in order to yield a satisfactory fit of the measured spectra, even though products were formed in highly excited vibrational states. The results are compared with those of other studies of reactions of alkaline earth metals with halogenated methanes. A comparison of the energy disposal into the alkaline earth monohalide product as a function of the average available energy is hampered because of the uncertainty of the latter. In the present study the available energy, which is the sum of the internal energy of the molecular reactant, the collision energy, and the bond energies involved, is consistently too low as to give a satisfactory fit of the alkaline earth monohalide bandhead spectrum. The relatively high fraction of the available energy disposed into vibration of the diatomic product is indicative of an early energy release, such as takes place in an electron jump model. The variation of the disposal into vibrational energy of the formed diatom among the various systems is attributed to a variation of the harpooning radius and its magnitude relative to the interatomic distance of the diatomic product.

Keijzer, F.; Teule, J. M.; Bulthuis, J.; de Graaff, G. J.; Hilgeman, M. H.; Janssen, M. H. M.; van Kleef, E. H.; van Leuken, J. J.; Stolte, S.

1996-07-01

169

Temperature and carbonate ion effects on Mg/Ca and Sr/Ca ratios in benthic foraminifera: Aragonitic species Hoeglundina elegans  

NASA Astrophysics Data System (ADS)

Core top samples from Atlantic (Little Bahama Banks (LBB)) and Pacific (Hawaii and Indonesia) depth transects have been analyzed in order to assess the influence of bottom water temperature (BWT) and aragonite saturation levels on Mg/Ca and Sr/Ca ratios in the aragonitic benthic foraminifer Hoeglundina elegans. Both the Mg/Ca and Sr/Ca ratios in H. elegans tests show a general decrease with increasing water depth. Although at each site the decreasing trends are consistent with the in situ temperature profile, Mg/Ca and Sr/Ca ratios in LBB are substantially higher than in Indonesia and Hawaii at comparable water depths with a greater difference observed with increasing water depth. Because we find no significant difference between results obtained on "live" and "dead" specimens, we propose that these differences are due to primary effects on the metal uptake during test formation. Evaluation of the water column properties at each site suggests that in situ CO3 ion concentrations play an important role in determining the H. elegans Mg/Ca and Sr/Ca ratios. The CO3 ion effect is limited, however, only to aragonite saturation levels ([?CO3]aragonite) below 15 ?mol kg-1. Above this level, temperature exerts a dominant effect. Accordingly, we propose that Mg/Ca and Sr/Ca in H. elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships: Mg/Ca = (0.034 0.002)BWT + (0.96 0.03) and Sr/Ca = (0.060 0.002)BWT + (1.53 0.03) (for [?CO3]aragonite > 15 ?mol kg-1). The standard error associated with these equations is about 1.1C. Reconstruction of deeper water temperatures is complicated because in undersaturated waters, changes in Mg/Ca and Sr/Ca ratios reflect a combination of changes in [CO3] and BWT. Overall, we find that Sr/Ca, rather than Mg/Ca, in H. elegans may be a more accurate proxy for reconstructing paleotemperatures.

Rosenthal, Yair; Lear, Caroline H.; Oppo, Delia W.; Linsley, Braddock K.

2006-03-01

170

Europium substitution into intermetallic phases grown in Ca/Zn flux  

SciTech Connect

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

Stojanovic, Milorad [Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390 (United States); Latturner, Susan E., E-mail: latturne@chem.fsu.ed [Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390 (United States)

2009-08-15

171

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

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.

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

1992-01-01

172

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

SciTech Connect

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

Fang Liang; Dong Wen; Zheng Fengang; Shen Mingrong [Jiangsu Key Laboratory of Thin Films and Department of Physics, Soochow University, Suzhou 215006 (China)

2012-08-01

173

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

NASA Astrophysics Data System (ADS)

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

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

2001-06-01

174

INVITED PAPER: Small-scale recombination He Sr+(Ca+ ) lasers  

NASA Astrophysics Data System (ADS)

A review of specific features and output characteristics of small-scale (l<=30 cm, d<=1.1cm) gas-discharge recombination HeSr+ (?=430.5 nm) and He Ca+ (?=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 Psp, and an improved quality of output radiation. A typical mean power P of self-heating sealed-off HeSr+ (Ca+) laser tubes with lapprox 30 cm and dapprox 1 cm is ~ 0.5 W. The best specific characteristics of a HeSr+ laser with tubes of this type were achieved with l=20 cm and d=0.6 cm (Psp=73 mW cm-3) and l=9 cm and d=0.55 cm (Psp=65 W cm-3). The best specific characteristics for a HeCa+ laser were achieved with l=26.5 cm and d=0.7 cm (Psp=50 mW cm-3). The use of forced water cooling in a HeSr+(Ca+) laser allowed the powers P=3.9 W and Psp=137 mW cm-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 HeSr+ laser to be considerably improved and a record specific power Psp=277 mW cm-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-1, was also achieved under these conditions. Some possible areas of applications of small-scale HeSr+(Ca+) lasers in semiconductor microtechnology, holography, ecology, and medicine are outlined.

Latush, Evgeny L.; Chebotarev, Gennady D.; Sem, M. F.

2000-06-01

175

Activation energy and critical current density in Bi-Sr-Ca-Cu-O  

SciTech Connect

Flux creep in a Bi-Sr-Ca-Cu-0 system has been investigated in wide temperature and field regimes. Previously reported studies of the flux-creep activation energy U have been controversial in terms of the temperature and field dependence, and the U values have not been consistent with the macroscopically measured critical current density, J{sub c} We have developed a new approach to obtain the activation energy by considering the nonlinearity between U and J. We find that the activation energy is considerably increased in liquid-quenched Bi-Sr-Ca-Cu-0, as a result of enhanced pinning by finely dispersed precipitates. Our results are consistent with the increased macroscopic parameter J{sub c}.

Shi, Donglu; Sengupta, S.; Smith, M.; Wang, Z.

1992-07-01

176

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

177

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

NASA Technical Reports Server (NTRS)

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.

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

178

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

179

Electronic band structures and photovoltaic properties of MWO 4 ( M=Zn, Mg, Ca, Sr) compounds  

NASA Astrophysics Data System (ADS)

Divalent metal tungstates, MWO 4, with wolframite ( M=Zn and Mg) and scheelite ( M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO 4 and MgWO 4) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO 4 and SrWO 4), which was attributed to their enhanced electron transfer resulting from their appropriate band positions.

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

2011-08-01

180

(Ca,Sr)CO 3 aqueoussolid solution systems: From atomistic simulations to thermodynamic modelling  

Microsoft Academic Search

The uptake of strontium in calcium carbonates is a topic of sustained interest in (radio)geochemistry. The available data on (Ca,Sr)CO3 aqueoussolid solution (AqSS) systems with the calcite (R3c) and aragonite (Pmcn) structures are reconciled using a stepwise approach from atomistic to thermodynamic modelling consisting of: (1) Quantummechanical and force-field calculations aimed at the prediction of standard thermodynamic properties of a

D. A. Kulik; V. L. Vinograd; N. Paulsen; B. Winkler

2010-01-01

181

Studies of New Superconducting Bi-Sr-Ca-Cu-O System by Infrared and Raman Spectroscopy  

Microsoft Academic Search

We report both infrared transmission and Raman scattering results on the new superconducting Bi-Sr-Ca-Cu-O system. Because of its layered structure along c axis, some very thin and transparent slices have been got. In the infrared spectrum there is an absorption band around 500cm-1 with a width of about 300cm-1, and a vibrational mode at 840cm-1, higher frequency than those of

Jingqing Liu; Yifeng Yan; Tang Zhou; Guangcan Che; Dawei Chang; Wei Chen; Yanyun Wang; Zhongxian Zhao

1988-01-01

182

Preparation and properties of Bi-Sr-Ca-Cu-O made by a chemical precipitation method  

SciTech Connect

A chemical precipitation method is utilized to synthesize Bi-Sr-Ca-Cu-O powder. Tetramethyl ammonium hydroxide and tetramethyl ammonium carbonate are used as a precipitant and for pH adjustment. The precursor powder is heat treated in a low pressure oxygen atmosphere. The decomposition of the precursor was studied by using TGA and DTA techniques. The powders were characterized by using XRD and SEM.

Sengupta, S.; Corpus, J.; Chaudhury, Z. [Superconductive Components, Inc., Columbus, OH (United States)] [and others

1997-06-01

183

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

Microsoft Academic Search

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

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

1990-01-01

184

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

Microsoft Academic Search

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 22C ? 28C, the best fitting linear relationships for the two species agree within their respective errors with a maximum deviation less than 0.3C.

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

1996-01-01

185

Incommensurate structure in the Bi-Sr-Ca-Cu-O 80-K superconductor  

SciTech Connect

We report on the structure and characterization of the major phase in the Bi-Sr-Ca-Cu-O system that becomes superconducting below 80 K. A superlattice modulation in the structure that is incommensurate with a tetragonal perovskite-based subcell is observed using electron diffraction. High-resolution imaging indicates that the modulation occurs primarily in bismuth-rich layers in the structure.

Shaw, T.M.; Shivashankar, S.A.; La Placa, S.J.; Cuomo, J.J.; McGuire, T.R.; Roy, R.A.; Kelleher, K.H.; Yee, D.S.

1988-06-01

186

Excitonic emission of scheelite tungstates AWO 4 (A=Pb, Ca, Ba, Sr)  

Microsoft Academic Search

Self-trapped exciton emission spectra of four scheelite tungstate single crystals AWO4 (A=Pb, Ca, Sr, Ba) were measured in a wide temperature range and their structure is discussed. We present decay kinetics of PbWO4 in 0.35300K range and a mathematical model, which successfully approximates temperature dependencies of the decay time and intensity with a unique set of parameters. Besides the usual

M. Nikl; P. Bohacek; E. Mihokova; M. Kobayashi; M. Ishii; Y. Usuki; V. Babin; A. Stolovich; S. Zazubovich; M. Bacci

2000-01-01

187

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

NASA Astrophysics Data System (ADS)

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

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

1991-09-01

188

Structures of the chain metaphosphates NaM(PO3)3 (M = Ca or Sr).  

PubMed

Solid-state (23)Na and (31)P magic-angle spinning nuclear magnetic resonance spectroscopy and X-ray crystallography have been used to study the structures of the chain metaphosphates NaCa(PO(3))(3) and NaSr(PO(3))(3). The compounds are isostructural and crystallise in space group P(-1) with the following parameters: NaCa(PO(3))(3), a = 6.711 A, b = 6.934 A, c = 7.619 A, alpha = 83.44 degrees , beta = 81.41 degrees , gamma = 82.80 degrees ; NaSr(PO(3))(3)a = 6.805 A, b = 7.133 A, c = 7.720 A and alpha = 83.71 degrees , beta = 80.48 degrees , gamma = 82.87 degrees . Both structures contain anionic metaphosphate chains of (PO(3))(n) (n) with ionic contacts to Na(+) ions in distorted octahedral sites and Ca(2+) (or Sr(2+)) in distorted dodecahedral sites. (31)P and (23)Na NMR are entirely consistent with the crystallographic data and an empirical method for assigning (31)P resonances to particular crystallographically unique P atoms is described. PMID:18306173

Abrahams, I; Hawkes, G E; Ahmed, A; Di Cristina, T; Demetriou, D Z; Ivanova, G I

2008-04-01

189

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

DOEpatents

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.

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

190

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

DOEpatents

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.

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

1992-12-22

191

cAMP/PKA-Dependent Increases in Ca Sparks, Oscillations and SR Ca Stores in Retinal Arteriolar Myocytes after Exposure to Vasopressin  

PubMed Central

Purpose. To investigate the effects of arginine vasopressin (AVP) on Ca2+ sparks and oscillations and on sarcoplasmic reticulum (SR) Ca2+ content in retinal arteriolar myocytes. Methods. Fluo-4-loaded smooth muscle in intact segments of freshly isolated porcine retinal arteriole was imaged by confocal laser microscopy. SR Ca2+ store content was assessed by recording caffeine-induced Ca2+ transients with microfluorimetry and fura-2. Results. The frequencies of Ca2+ sparks and oscillations were increased both during exposure to, and 10 minutes after washout of AVP (10 nM). Caffeine transients were increased in amplitude 10 and 90 minutes after a 3-minute application of AVP. Both AVP-induced Ca2+ transients and the enhancement of caffeine responses after AVP washout were inhibited by SR 49059, a V1a receptor blocker. Forskolin, an activator of adenylyl cyclase, also persistently enhanced caffeine transients. Rp-8-HA-cAMPS, a membrane-permeant PKA inhibitor, prevented enhancement of caffeine transients by both AVP and forskolin. Forskolin, but not AVP, produced a reversible, Rp-8-HA-cAMPS insensitive reduction in basal [Ca2+]i. Conclusions. AVP activates a cAMP/PKA-dependent pathway via V1a receptors in retinal arteriolar smooth muscle. This effect persistently increases SR Ca2+ loading, upregulating Ca2+ sparks and oscillations, and may favor prolonged agonist activity despite receptor desensitization.

Jeffries, Owen; McGahon, Mary K.; Bankhead, Peter; Lozano, Maria Manfredi; Scholfield, C. Norman; Curtis, Tim M.

2010-01-01

192

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

USGS Publications Warehouse

A 4-year study in a central Texas cave quantifies multiple mechanisms that control dripwater composition and how these mechanisms vary at different drip sites. We monitored cave-air compositions, in situ calcite growth, dripwater composition and drip rate every 4-6weeks. Three groups of drip sites are delineated (Groups 1-3) based on geochemical variations in dripwater composition. Quantitative modeling of mineral-solution reactions within the host carbonate rock and cave environments is used to identify mechanisms that can account for variations in dripwater compositions. The covariation of Mg/Ca (and Sr/Ca) and Sr isotopes is key in delineating whether Mg/Ca and Sr/Ca variations are dictated by water-rock interaction (i.e., calcite or dolomite recrystallization) or prior calcite precipitation (PCP). Group 1 dripwater compositions reflects a narrow range of the extent of water-rock interaction followed by varying amounts of prior calcite precipitation (PCP). Group 2 dripwater compositions are controlled by varying amounts of water-rock interaction with little to no PCP influence. Group 3 dripwater compositions are dictated by variable extents of both water-rock interaction and PCP. Group 1 drip sites show seasonal variations in dripwater Mg/Ca and Sr/Ca, whereas the other drip sites do not. In contrast to the findings of most previous dripwater Mg/Ca-Sr/Ca studies, these seasonal variations (at Group 1 drip sites) are independent of changes in water flux (i.e., rainfall and/or drip rate), and instead significantly correlate with changes in cave-air CO2 concentrations. These results are consistent with lower cave-air CO2, related to cool season ventilation of the cave atmosphere, enhancing calcite precipitation and leading to dripwater geochemical evolution via PCP. Group 1 dripwater Mg/Ca and Sr/Ca seasonality and evidence for PCP as a mechanism that can account for that seasonality, have two implications for many other regions where seasonal ventilation of caves is likely: (1) speleothem trace-element records may provide seasonal signals, and (2) such records may be biased toward recording climate conditions during the season when calcite is depositing. Additionally, we use our results to construct a forward model that illustrates the types of speleothem Mg/Ca and Sr/Ca variations that would result from varying controls on dripwater compositions. The model provides a basis for interpreting paleo-dripwater controls from high frequency Mg/Ca and Sr/Ca variations for speleothems from caves at which long term monitoring studies are not feasible. ?? 2011 Elsevier Ltd.

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

2011-01-01

193

Melting of Bi 2 Sr 2 CaCu 2 O 8 + x Ceramics under Uniform Compression  

Microsoft Academic Search

The effect of quasi-hydrostatic pressure (10 MPa) on the melting point of Bi-2212 ceramics and their phase composition after melting is studied. The results demonstrate that compressive stress increases the melting point of Bi-2212 by about 60C. Melting at normal pressure leads to the precipitation of the Cu-poor phase (Sr,Ca)CuO2, whereas under quasi-hydrostatic pressure the Cu-rich phase (Sr,Ca)14Cu24O41 is formed.

M. F. Imayev; R. R. Daminov; V. A. Popov; O. A. Kaibyshev

2005-01-01

194

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

NASA Astrophysics Data System (ADS)

Measuring the strontium to calcium ratio in coral skeletons reveals information on seawater temperatures during skeletal deposition, but studies have shown additional variables may affect the ratio. Here we measured Sr/Ca in the reef coral Montipora capitata grown in six mesocosms continuously supplied with seawater from the adjacent reef flat. Three mesocosms were ambient controls, and three had seawater chemistry simulating "ocean acidification" (OA). We found that Sr/Ca was not affected by the OA treatment and neither was coral calcification for these small colonies (larger colonies did show an OA effect). The lack of OA effects allowed us to test the hypothesis that coral growth rate can affect Sr/Ca using the natural range in calcification rates of the corals grown at the same temperature. We found that Sr/Ca was inversely related to calcification rate (Sr/Ca = 9.385 - 0.0040 (calcification rate)). Using a previously published calibration curve for this species, a 22 mg d-1 colony-1increase in calcification rate introduced a 1C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9C, with mean 26.6 0.9C standard deviation. Our results lend support to hypotheses invoking kinetic processes and growth rate to explain vital effects on Sr/Ca. However, uncertainty in the slope of the regression of Sr/Ca on calcification and a low R-squared value lead us to conclude that Sr/Ca could still be a useful proxy in this species given sufficient replication or by including growth rate in the calibration.

Kuffner, Ilsa B.; Jokiel, Paul L.; Rodgers, Ku'ulei S.; Andersson, Andreas J.; MacKenzie, Fred T.

2012-08-01

195

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

Microsoft Academic Search

The modulated structure of the Bi2Sr2CaFe2O y compound isomorphous with the Bi2Sr2CaCu2O y phase was refined by the method of the full profile analysis on the basis of the powder X-ray diffraction data. The analysis was carried out in the superspace group of N: Abmm: 1 11 using the parameters of the unit cell of the basic structure a =

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

1996-01-01

196

A multicoral calibration method to approximate a universal equation relating Sr\\/Ca and growth rate to sea surface temperature  

Microsoft Academic Search

(1) Combining strontium-to-calcium ratios (Sr\\/Ca) with mean annual growth rates in Bermuda Diploria labyrinthiformis (brain corals) is shown to improve sea surface temperature (SST) calibrations relative to instrumental data. Growth-corrected Sr\\/Ca-SST calibrations based on single-coral colonies over the same calibration interval, however, are found to be poorly suited for application to data from different coral colonies. This raises concerns about

Nathalie F. Goodkin; Konrad A. Hughen; Anne L. Cohen

2007-01-01

197

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

USGS Publications Warehouse

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 1C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9, with mean 26.6 0.9C 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.

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

2012-01-01

198

Electronic Structure, Chemical Bonding, and Solid-State NMR Spectroscopy of the Digallides of Ca, Sr, and Ba  

Microsoft Academic Search

Combined application of 69,71 Ga NMR spectroscopy and quan- tum mechanical calculations reveals the chemical bonding in the digallides of Ca, Sr, and Ba. An analysis of the electron localization function (ELF) shows honeycomb-like 63 nets of the Ga atoms as the most prominent struc- tural features in SrGa2 and BaGa2 .F or CaGa2 a description of a 3+1-coordi- nated

Frank Haarmann; Katrin Koch; Daniel Grner; Walter Schnelle; Oliver Pecher; Raul Cardoso-Gil; Horst Borrmann; Helge Rosner; Yuri Grin

2009-01-01

199

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

SciTech Connect

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

Lawson, J.K.; Lee, H.W.H.; Payne, S.A. (Lawrence Livermore National Lab., CA (United States)); Boatner, L.A. (Oak Ridge National Lab., TN (United States))

1991-04-01

200

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

NASA Astrophysics Data System (ADS)

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.

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

2004-12-01

201

Ordered substitution of iron for copper in the tetragonal perovskite La{sub 6.4}Sr{sub 1.6}CuO  

Microsoft Academic Search

Two series of iron-substituted cuprates with the tetragonal La{sub 6.4}Sr{sub 1.6}CuO oxygen deficient perovskite structure have been isolated: La{sub 6.4}Sr{sub 1.6}Cu{sub 8-x}FeO (0 x 1.20) and La{sub 6.4-x}Sr{sub 1.6+x}Cu{sub 8-x}FeO (0 x 2). The XRD and Moessbauer studies show that they correspond to a preferential substitution of Fe(III) for copper in the octahedral sites of the

R. Genouel; C. Michel; N. Nguyen; M. Hervieu; B. Raveau

1995-01-01

202

Ordered Substitution of Iron for Copper in the Tetragonal Perovskite La 6.4Sr 1.6Cu 8O 20  

Microsoft Academic Search

Two series of iron-substituted cuprates with the tetragonal La6.4Sr1.6Cu8O20 oxygen deficient perovskite structure have been isolated: La6.4Sr1.6Cu8-xFexO20 (0 ? x ? 1.20) and La6.4-xSr1.6+x Cu8-xFexO20 (0 ? x ? 2). The XRD and Mssbauer studies show that they correspond to a preferential substitution of Fe(III) for copper in the octahedral sites of the structure. In fact the ideal structure can

R. Genouel; C. Michel; N. Nguyen; M. Hervieu; B. Raveau

1995-01-01

203

Muon-spin-relaxation studies of flux pinning in Bi2Sr2CaCu2O8 and Pb0.7Bi1.3Sr2CaCu2O8  

Microsoft Academic Search

We have studied flux-depinning phenomena in the Bi2Sr2CaCu2O8 (Bi 2:2:1:2) and Pb-doped Pb0.7Bi1.3Sr2CaCu2O8 (Pb-Bi 2:2:1:2) systems using the transverse-field muon-spin-relaxation (muSR) technique. Comparison of field-cooled (FC) and zero-field-cooled (ZFC) results with external fields applied along the c axis of single-crystal specimens defines an irreversibility temperature (depinning temperature) Tirr: the FC and ZFC relaxation rates are essentially identical above Tirr, while

W. D. Wu; A. Keren; L. P. Le; B. J. Sternlieb; G. M. Luke; Y. J. Uemura; P. Dosanjh; T. M. Riseman

1993-01-01

204

The ZnR/GPR39 interacts with the CaSR to enhance signaling in prostate and salivary epithelia.  

PubMed

Zinc signaling is mediated by the zinc sensing receptor, ZnR, recently suggested to be the same receptor as G-protein coupled receptor 39, GPR39. However, it is unknown if GPR39 is mediating Zn(2+) -dependent signaling in prostate and salivary tissue where changes in zinc concentrations are frequent and of physiological significance. Here, we show that GPR39 is mediating Zn(2+) -dependent Ca(2+) responses and is regulating activity of MAP and PI3 pathways in prostate cancer cells, PC3, and ductal salivary gland cells, HSY. We next ask whether ZnR/GPR39 interacts with other GPCR family members. We find that endogenous ZnR/GPR39 activity is regulated by the expression and activity of another cation sensing GPCR, the Ca(2+) -sensing receptor (CaSR). Although CaSR is not activated by Zn(2+), co-expression of CaSR and ZnR/GPR39 synergistically enhances Ca(2+) responses in PC3 and HSY cells. Silencing of the CaSR using siRNA or a dominant negative construct reduces the Zn(2+) -dependent signaling. Importantly, overexpression of GPR39 in HEK293 cells is sufficient to trigger Zn(2+) -dependent responses. Nevertheless, application of the CaSR agonist spermine, at concentration below its threshold, enhanced Zn(2+) -dependent Ca(2+) response. Our results suggest that the CaSR interacts with ZnR/GPR39 and thereby regulates its activity. Finally, we show that in PC3 cells ZnR/GPR39 is required for mediating the Zn(2+) -dependent activation of MAPK and PI3K, pathways leading to enhanced cell growth. Importantly, Zn(2+) -dependent activation of ZnR/GPR39 also enhances the expression of the Ca(2+) -binding protein S100A4 that is linked to invasion of prostate cancer cells. PMID:24264723

Asraf, Hila; Salomon, Shimrit; Nevo, Andrey; Sekler, Israel; Mayer, Doris; Hershfinkel, Michal

2014-07-01

205

Accelerated formation of the three Cu-O layered Tl-(Pb,Bi)-Sr-Ca-Cu-O compound  

NASA Astrophysics Data System (ADS)

The preparation of bulk samples containing a nearly single phase of three Cu-O layered compound in the Tl-Pb(Bi)-Sr-Ca-Cu-O system is described. To determine the effect of Ca/Sr ratio on the formation of the three Cu-O layered compound, samples of nominal compositions Tl(0.5)Pb(0.5)Sr2Ca2Cu3O(y) and Tl(0.5)Pb(0.5)Sr(1.6Ca(2.4)Cu3O(y) were synthesized by a solid-state reaction, by first heating SrCO3, CaCO3, and CuO at 920 C. Before the final heat treatment, Tl2O3, PbO, and/or Bi2O3 were added to the pulverized precursor mixture to the desired composition. It was found that, by changing the Ca/Sr ratio to 2.4/1.6, a significant increase of the desired single phase was obtained, as evidenced by XRD and magnetization measurement.

Huang, Y. T.; Wu, S. F.; Chiang, C. K.; Lee, W. H.

1990-11-01

206

High-pressure synthesis and physical properties of perovskite and post-perovskite Ca{sub 1-x}Sr{x}lrO{sub 3}.  

SciTech Connect

The post-perovskite (pPv) is the high-pressure phase of some highly distorted perovskites. The pPv phase of MgSiO{sub 3} stabilized under 125 GPa and 2000 K cannot be quenched to ambient pressure. In contrast, the pPv CaIrO{sub 3} can be synthesized under a modest pressure or even at ambient pressure. However, the pPv CaIrO{sub 3} has not been fully characterized. We report here systematic structural studies, measurements of transport and magnetic properties including critical phenomena, specific heat, and thermal conductivity in a series of samples Ca{sub 1-x}Sr{sub x}IrO{sub 3} synthesized under high pressure. The Ca{sub 1-x}Sr{sub x}IrO{sub 3} samples exhibit an evolution from the pPv phase to the perovskite phase. We have also prepared the perovskite (Pv phase) CaIrO{sub 3} with the wet chemical method. Rietveld refinements of the pPv and Pv phase CaIrO{sub 3} have been made based on high-resolution synchrotron diffraction. In comparison with effects of the chemical substitution on the crystal structure and physical properties, we have studied the structure and magnetic properties of the pPv CaIrO{sub 3} under hydrostatic pressure. Results have been discussed in the context of orbital ordering biased on the intrinsic structural distortion and the strong spin-orbit coupling that is much enhanced in these 5d oxides with the pPv structure.

Cheng, J.-G.; Zhou, J.-S.; Goodenough, J. B.; Sui, Y.; Ren, Y.; Suchomel, M. R. (X-Ray Science Division); (Univ. of Texas at Austin); (Harbin Inst. of Tech.)

2011-02-09

207

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

PubMed

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

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

2010-01-01

208

Strain relaxation in buried SrRuO3 layer in (Ca1-xSrx)(Zr1-xRux)O3/SrRuO3/SrTiO3 system  

NASA Astrophysics Data System (ADS)

A novel relaxation phenomenon occurs in buried SrRuO3 layers in strained (Ca1-xSrx)(Zr1-xRux)O3/SrRuO3/SrTiO3 (001) thin film system. The lightly strained SrRuO3 buried layer is initially clamped by the SrTiO3 substrate. After a heavily strained (Ca1-xSrx)(Zr1-xRux)O3 overlayer is deposited, localized strain relaxation develops in the buried layer. This is manifested by a crosshatch pattern of <100> corrugations on the surface, due to the slip of <110> {110} threading dislocations. The phenomenon can be controlled by tuning the growth kinetics and strain energy of the overlayer.

Kim, Soo Gil; Wang, Yudi; Chen, I.-Wei

2006-07-01

209

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

NASA Astrophysics Data System (ADS)

Vascular plant growth builds soils and ecosystem nutrient capital by sequestering and partitioning atmospheric CO2 into organic matter and continental runoff and driving terrestrial water and energy balances. Plant root-system functions, e.g. nutrient mobilization and uptake, are altered by environmental stress. However, the stress-response relationships are poorly understood. Chemical tracers have potential for assessing contributions of nutrients from various nutrient pools. Our objective is to quantitatively study how varying degrees of nutrient limitation (and corresponding needs to extract base cations from mineral sources) influence Ca and K uptake functions in a plant-root-mineral system. We are studying plant-driven mineral weathering in column experiments with red pine (Pinus resinosa) seedlings. The columns contain quartz sand amended with anorthite and biotite that constitute the sole mineral sources of Ca and K. These minerals also contain known amounts of Sr and Rb, which exhibit chemical behavior similar to Ca and K, respectively. The solution source of Ca and K was varied by adding 0% (no dissolved Ca and K), 10%, 30%, or 100% of a full strength Ca and K nutrient solution through irrigation water in which both Sr and Rb concentrations were negligible. Selected columns were destructively sampled at 3, 6 and 9 months to harvest biomass and measure plant uptake of cations. We used Ca/Sr and K/Rb ratio results to estimate the contributions of Ca and K from mineral and solution sources. For the 0% nutrient treatment, the Ca/Sr and K/Rb ratios in total biomass at 3 months, compared with those in the mineral phases, suggested preferential uptake of Ca and K over Sr and Rb, respectively, and allowed us to determine uptake discrimination factors for both cations. The K/Rb ratios in total biomass increased with greater K availability in the solution source, as expected, but Ca/Sr ratios did not show any dependence on Ca availability in the solution source. Using a tracer mass balance model, we computed the fraction of K from the mineral source in the total biomass, which decreased with longer growth time and more K supply from the solution source. For Ca, the model results suggested that the mineral was the major source of Ca in the plants throughout the experiment. Comparison of results for above- and below-ground biomass showed significantly higher Ca/Sr and K/Rb ratios above ground, indicating strong fractionation of Ca and K during transport within the tree. Our results highlight the potential importance of species-specific and temporal variations in cation uptake that may require consideration as we work to understand water and nutrient cycles in aggrading forest ecosystems.

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

2012-12-01

210

Precise Analysis of Bi2Sr2Can-1CunOy Superconducting Whiskers by SR-XPS and HR-TEM  

NASA Astrophysics Data System (ADS)

We grew Bi-based superconducting whiskers with various substitution ratios of Ca2+ ions for Sr2+ sites (:Ca/Sr substitution ratios) by an Al2O3-seeded glassy quenched platelet method. We found that the critical current density (Jc) of the Bi-based superconducting whiskers is widely controllable by just changing Ca/Sr substitution ratios. The Jc increases by a factor of 200. The Bi-based superconducting whisker with the Ca/Sr substitution ratio of about 25 % shows a high Jc of 2105A/cm2 at 40 K in self-field. From the analysis by X-ray photoemission spectroscopy using synchrotron radiation and high-resolution transmission electron microscopy, we found that the whisker has a strong pinning center. The pinning center consists of a structural distorted two-dimensional nanoplane defect which is introduced by controlling a strain in a Sr-O layer.

Tanaka, H.; Yoshikawa, H.; Tsuruta, C.; Matsui, Y.; Kishida, S.

2011-02-01

211

Broadband microwave study of SrRuO3 and CaRuO3 thin films  

NASA Astrophysics Data System (ADS)

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.

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

2012-12-01

212

Ovariectomy enhances SR Ca 2+ release and increases Ca 2+ spark amplitudes in isolated ventricular myocytes  

Microsoft Academic Search

This study compared Ca2+ homeostasis in ventricular myocytes from 8-month-old female C57BL\\/6J mice that had either a bilateral ovariectomy (OVX) or a sham surgery at 3weeks of age. Cells were loaded with fura-2 and field-stimulated or voltage-clamped with steps to membrane potentials between ?40 and +80mV (37C). Peak Ca2+ transients increased by two-fold in OVX myocytes when compared to sham,

Elias Fares; Randi J. Parks; Jennifer K. MacDonald; Jeanne M. S. Egar; Susan E. Howlett

213

Effect of dysprosium substitution on the electrical properties of SrBi4Ti4O15 ceramics  

NASA Astrophysics Data System (ADS)

The four-layer Aurivillius compound SrBi4-xDyxTi4O15 (x = 0.02 - 0.1) was synthesized by using a solid state sintering method. X-ray diffraction (XRD) analysis revealed that the dysprosium-substituted SrBi4Ti4O15 ceramics have a pure four-layer Aurivillius-type structure. The lattice parameters and densities were calculated with XRD studies. The experimental densities obtained were about 95% that of theoretical values. The effects of dysprosium oxide on the microstructure, ferroelectric, dielectric and piezoelectric properties of the ceramics were investigated. The dielectric constant of Dy-doped samples was found to decrease with increasing Dy content. At x = 0.06, the piezoelectric charge coefficient (d33) and the electromechanical coupling factor (kp) were found to be maximum.

Mamatha, B.; Ashok, K.; James, A. R.; Sarah, P.

2012-06-01

214

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

Microsoft Academic Search

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 750C. 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

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

2001-01-01

215

Crystal and magnetic structures of new layered oxides A2GaMnO5+y (A=Ca, Sr)  

NASA Astrophysics Data System (ADS)

Crystal and magnetic structures of new complex manganese oxides A2GaMnO5+y (A=Ca,Sr) were studied by neutron diffraction. Being perovskite-type derivatives, their crystal structures belong to a brownmillerite type and consist of alternating (CaO), (MnO2), (CaO) and (GaO) or (GaO1+x) layers. At temperatures between (100-200)K, these compounds undergo transitions into antiferromagnetic states. The magnetic ordering type depends on the compositions. The Mn magnetic moments are aligned in opposite directions within the MnO2 layer, and the coupling between magnetic moments lying in the adjacent MnO2 layers is, for example, antiferromagnetic for the reduced, and ferromagnetic for the oxidized Sr-containing compound Sr2GaMnO5 and Sr2GaMnO5.52 compositions, respectively.

Sheptyakov, D. V.; Abakumov, A. M.; Antipov, E. V.; Balagurov, A. M.; Billinge, S. J. L.; Fischer, P.; Keller, L.; Lobanov, M. V.; Pavlyuk, B. Ph.; Pomjakushin, V. Yu.; Rozova, M. G.

216

Surface and electronic structure of Bi-Ca-Sr-Cu-O superconductors studied by LEED, UPS and XPS  

NASA Astrophysics Data System (ADS)

Single crystal and polycrystalline samples of Bi2CaSr2Cu2O8 have been studied by various surface sensitive techniques, including low energy electron diffraction (LEED), ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS). The surface structure of the single crystals was characterized by LEED to be consistent with that of the bulk structure. Our data suggest that Bi2CaSr2Cu2O8 single crystals are very stable in the ultrahigh vacuu. No change of XPS spectra with temperature was observed. We have also studied the electronic structure of Bi2Sr2CuO6, which has a lower superconducting transition temperature Tc. Comparing the electronic structure of the two Bi-Ca-Sr-Cu-O superconductors, an important difference in the density of states near EF was observed which seems to be related to the difference in Tc.

Shen, Z.-X.; Lindberg, P. A. P.; Wells, B. O.; Lindau, I.; Spicer, W. E.; Mitzi, D. B.; Eom, C. B.; Kapitulnik, A.; Geballe, T. H.; Soukiassian, P.

1989-02-01

217

Textured thick films of Bi2Sr2Ca1Cu2O(x)  

NASA Astrophysics Data System (ADS)

Thick-textured films of Bi2Sr2Ca1Cu2O(x) are obtained by partially melting and slow cooling doctor-blade-processed tapes. Heat treatment between 890 and 870 C produces aligned microstructures on substrates of either Ag or Ag coated MgO. During heat treatment dissolution of Ag into the liquid oxide occurs. Because silver lowers the melting point of the oxide, the processing temperatures must be increased by about 10 C when an MgO substrate is used. The resulting films show that the oxide surface plays an important role in grain alignment. The Bi2Sr2Cu1O(x) phase, stable for temperatures greater than about 870 C, always transforms to the desired Bi2Sr2Ca1Cu2O(x) phase regardless of the heat treatment history. The texture of the microstructure, however, is dependent upon the heat-treatment path, with a higher texture obtained with slower cooling.

Dietderich, Daniel R.; Kumakura, Hiroaki; Ullmann, Bernd; Freyhardt, Herbert C.; Kase, Junichiro

1990-07-01

218

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

SciTech Connect

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

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

2008-01-11

219

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

SciTech Connect

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

Szecsody, J.E.; Fruchter, J.S.; Burns, C.A.; Rockhold, M.L.; Oostrom, M.; Williams, M.D.; Vermeul, V.R. [Pacific Northwest National Laboratory, Richland, WA (United States)

2008-07-01

220

Percolation behaviour in intergrowth BiSrCaCuO structures grown by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

BiSrCaCuO thin films and specially Bi-2212 compounds were grown on (100) SrTiO 3 substrates by molecular beam epitaxy (MBE). The growth mechanism was controlled in real time by monitoring the RHEED intensity. The deposition sequence of the elements was also varied in order to induce intergrowth structures at nanometer scale. The resulting high density of stacking faults is in contrast with a very low roughness (in the range of 1 nm as measured by atomic force microscopy), a strong c-axis texturation, and a full epitaxy within the ab-plane as confirmed by four circle X-ray diffraction. The local structure of the films was examined by high resolution transmission electron microscopy (HRTEM) in correlation with the superconducting properties. Both structural and transport properties seem to be deeply affected by the percolation of 2212 domains as their concentration in the film is changed.

Moussy, J. B.; Laval, J. Y.; Xu, X. Z.; Beuran, F. C.; Deville Cavellin, C.; Lagus, M.

221

Cluster glass behaviour in Co-substituted double perovskite Ca{sub 2}FeMoO{sub 6}  

SciTech Connect

Research highlights: {yields} We have presented the crystallographic, electrical transport and dc and ac magnetic measurements on double perovskite Ca{sub 2}Fe{sub 1-x}Co{sub x}MoO{sub 6} (0.1 {<=} x {<=} 0.4) system. {yields} Co exists in divalent state in these compounds. {yields} The substituted system exhibits cluster-glass like behaviour, close to that observed earlier in Sr{sub 2}Fe{sub 1-x}Co{sub x}MoO{sub 6} compatible with an electronic phase segregation scenario (Phys. Rev. B 73 (2006) 104417). -- Abstract: The transport and magnetic properties of the double perovskite compounds Ca{sub 2}Fe{sub 1-x}Co{sub x}MoO{sub 6} (0.1 {<=} x {<=} 0.4) have been explored through resistivity [{rho}(T)], dc magnetisation [M(H, T)] and ac susceptibility [{chi}(T, f)] measurements. Introduction of Co increases the lattice volume implying the divalent nature of cobalt in this system. For all the samples, {rho}(T) behaviour over the temperature range (25-273 K) can be adequately described by considering possible disorder-enhanced electron-electron interaction effect as well as spin-wave contribution. Our results reveal that with the increase of Co concentration, the ferromagnetic Curie temperatures (T{sub C}) gradually reduced due to the incorporation of antiferromagnetic Co{sup 2+}-Mo{sup 6+} pairs replacing ferromagnetic Fe{sup 3+}-Mo{sup 5+} pairs. A cluster-glass like behaviour is also observed in the system due to the presence of highly spin-disordered regions.

Poddar, Asok; Mazumdar, Chandan, E-mail: chandan.mazumdar@saha.ac.in

2011-05-15

222

Metal (Ca, Ba, Sr, Pb) heptafluorotantalates(V): Synthesis, Raman spectra and crystal structures  

NASA Astrophysics Data System (ADS)

MTaF 7 (M = Ca, Sr, Ba, Pb) were prepared by the reaction of MF 2 + Ta + F 2 (Ca, Sr, Ba) or MF 2 + TaF 5 in anhydrous HF. CaTaF 7 crystallizes in a monoclinic P2 1/ a space group, a = 9.793(3) , b = 11.608(3) , c = 13.359(4) , ? = 90.539(13), V = 1518.5(7) 3. All Ta atoms possess distorted pentagonal-bipyramidal environment with Ta-F distances of 1.878(14)-2.044(13) . Three crystallographically independent Ca atoms have coordination number 8. Ca-F distances lie in the range of 2.239(16)-2.836(17) . Each Ca 2+ and TaF 72- moiety is bonded to 6 counter-ions. BaTaF 7 crystallizes in a cubic system, space group Pa3,a = 9.9009(3), V = 970.56(5) 3. Coordination sphere around Ta atom is mono-capped trigonal prism with a Ta-F distance of 1.916(5)-2.004(5) . Two crystallographically independent barium atoms have different coordination numbers: for Ba1 C.N. is 12 with Ba1-F distances of 6 2.761(5) and 6 2.858(5) , for Ba2 C.N. is 14 with Ba2-F bond lengths 6 2.718(5), 2 2.814(8) and 6 3.236(5) . Ba 2+ and TaF 72- moieties are bonded to 8 neighbors. Isostructural PbTaF 7 and SrTaF 7 appear to be monoclinic, space group P2 1/ m, a = 4.8657(11) , b = 7.2298(16) , c = 6.7370(16) , ? = 93.932(13), V = 236.44(9) 3 for PbTaF 7, and a = 4.875(3) , b = 7.196(4) , c = 6.7218(13) , ? = 94.265(10), V = 235.2(2) for SrTaF 7. Tantalum coordination polyhedron may be described as a distorted mono-capped trigonal prism with the capping atom located on one of the rectangular faces with Ta-F distances of 1.868(3)-1.982(3) (PbTaF 7) and 1.908(16)-2.019(12) (SrTaF 7). Lead (or strontium) atoms are 9-coordinated and may be viewed as strongly distorted tri-capped trigonal prism, Pb-F 2.438(4)-2.669(3) , Sr-F 2.501(19)-2.860(19) . Each cation is connected to 8 anions.

Buni?, Tina; Tramek, Melita; Goreshnik, Evgeny; emva, Boris

2007-01-01

223

A Homozygous CaSR Mutation Causing a FHH Phenotype Completely Masked by Vitamin D Deficiency Presenting as Rickets.  

PubMed

Context: Heterozygous inactivating calcium-sensing receptor (CaSR) mutations lead to familial hypocalciuric hypercalcemia (FHH), whereas homozygous mutations usually cause neonatal severe hyperparathyroidism. Objective: The objective of the study was to investigate the pathophysiological mechanisms of a homozygous inactivating CaSR mutation identified in a 16-year-old female. Design: Clinical, biochemical, and genetic analyses of the index patient and her family were performed. Functional capacity of CaSRQ459R and CaSR mutants causing FHH (Q27R, P39A, S417C) or neonatal severe hyperparathyroidism (W718X) was assessed. Activation of the cytosolic calcium pathway and inhibition of PTH-induced cAMP signaling were measured. Results: A 16-year-old girl presented with adolescent rickets, vitamin D deficiency, and secondary hyperparathyroidism. Vitamin D treatment unmasked features resembling FHH, and genetic testing revealed a homozygous CaSRQ459R mutation. Two apparently healthy siblings were homozygous for CaSRQ459R and had asymptomatic hypercalcemia and hypocalciuria. The CaSRQ459R mutation leads to mild functional inactivation in vitro, which explains the FHH-like phenotype in homozygous family members and the grossly exaggerated PTH response to vitamin D deficiency in the index case. The patient's parents and two other siblings were heterozygous, had normal serum calcium and PTH, but had marked hypocalciuria, which appeared to be associated with impaired in vitro activation of the calcium signaling pathway by CaSRQ459R. The Q459R mutation responded well to calcimimetic treatment in vitro. Conclusion: CaSR mutations causing mild functional impairment can lead to FHH, even in homozygous patients. The skeletal deformities in the index case were mainly due to severe vitamin D deficiency, and the CaSR mutation did not appear to have played a major independent role in the skeletal phenotype. PMID:24517148

Szczawinska, Dorothea; Schnabel, Dirk; Letz, Saskia; Schfl, Christof

2014-06-01

224

Anisotropic thermal expansion in LiCaAlF6 and LiSrAlF6  

NASA Astrophysics Data System (ADS)

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.

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

2004-08-01

225

Hyperfine structures of Ca+ and Sr+ ions: Summary of trends in hyperfine interactions in the alkaline-earth-metal ions and corresponding series with similar electronic structures  

Microsoft Academic Search

The hyperfine interactions in the alkaline-earth-metal ions, Ca+ and Sr+, have been investigated using the relativistic linked-cluster many-body perturbation theory (RLCMBPT). The calculated theoretical hyperfine fields are found to be 135.3 and 266.3 T for Ca+ and Sr+, respectively, in good agreement with the experimentally obtained values of 139.0 T for Ca+ and 267.2 T for Sr+. The contributions from

Xing Yuan; S. N. Panigrahy; R. W. Dougherty; T. P. Das; J. Andriessen

1995-01-01

226

Kinetics of Luminal Proton Binding to the SR Ca-ATPase  

PubMed Central

An open membrane preparation containing SR Ca-ATPase was prepared from sarcoplasmic-reticulum vesicles to study the ion binding kinetics in the P-E2 conformation. Because Ca2+ and H+ binding are electrogenic reactions, fluorescent styryl dyes could be used to determine changes in the binding site occupation in equilibrium titration experiments and time-resolved relaxation processes triggered by a pH jump. By photo release from caged proton the pH of the electrolyte could be decreased in a step of 0.1 pH units by a single ultraviolet-laser flash. Analysis of the pH-jump induced relaxation process in the P-E2 conformation showed that three Ca-ATPase-specific processes could be identified, fast H+ binding (?<100?s) and pH-insensitive conformational relaxations after the release of the Ca2+ ion (? ?160ms), and a slow process (? ?3.4s) whose origin could not be unambiguously revealed. The Ca2+-binding affinity in the P-E2 conformation was reduced with increasing pH, a behavior that can be explained by a reversible transition of the empty P-E2 state to an inactivated state of the ion pump. All findings are interpreted in the framework of the Post-Albers pump cycle introduced previously, supplemented by an additional transition to an inhibited state of the ion pump.

Fibich, Andreas; Apell, Hans-Jurgen

2011-01-01

227

Alkaline-earth metal mercury intermetallics A11-xHg54+x (A = Ca, Sr).  

PubMed

Re-examination of the mercury-rich regions of the Ca-Hg and Sr-Hg phase diagrams has shown that the phases previously identified as "AHg 3.6" should be reformulated as A(11-x) Hg(54+x) (A = Ca, Sr). The crystal structures for representative members of these A 11- x Hg 54+ x phases were determined from single-crystal X-ray diffraction data (Pearson symbol hP65, space group P6; a = 13.389(1) A, c = 9.615(1) A for Ca(10.92(2))Hg(54.08) (x = 0.08(2)); a = 13.602(2) A, c = 9.818(1) A for Sr(10.48(4))Hg(54.52) ( x = 0.52(4))) and confirmed by powder Rietveld refinements ( R B = 0.020 for Ca(10.7(2))Hg(54.3) and 0.014 for Sr(10.7(3))Hg(54.3)). Diverse coordination polyhedra surround the A (CN14-16, multiply capped pentagonal or hexagonal prisms as well as Friauf polyhedra) and Hg atoms (CN11-13, pentacapped trigonal prisms and icosahedra). Partial disorder of Hg into one of the A sites accounts for the nonstoichiometry in the A(11-x)Hg(54+ x) phases. If this disordered A site is completely occupied by Hg atoms, the composition is constrained to a maximum of x = 2 in A(11-x)Hg(54+ x), corresponding to a small homogeneity range of "A(0.14-0.17)Hg(0.86-0.83)"; the true homogeneity range is likely narrower. The structure can be regarded as being built up from a stacking of triangular nets with hexagonal voids that are filled with single atoms or various clusters. In particular, the presence of triangular Hg 3 clusters in ordered orientations distinguishes this structure from that of the related Gd 14Ag 51-type structure, in which triangular Ag 3 clusters are in disordered orientations. Band structure calculations reveal a small degree of electron transfer from the A to Hg atoms, supporting the presence of a partially anionic mercuride substructure. PMID:18205301

Tkachuk, Andriy V; Mar, Arthur

2008-02-18

228

Anisotropic microwave absorption of Bi-Sr-Ca-Cu-O single crystals  

SciTech Connect

We have measured the microwave absorption of Bi/sub 2.1/Sr/sub 1.6/CaCu/sub 2/O/sub x/ single crystals as a function of the temperature T and the dc magnetic field H. A huge anisotropy, greater than 1000:1, is observed in the absorption, depending on the orientation of the microwave electric field relative to the c axis of the crystal. This result is consistent with the view that superconductivity in this compound may be quasi-two-dimensional. There is an additional, but much smaller, dependence on the orientation of an applied dc magnetic field.

Pakulis, E.J.; Chandrashekhar, G.V.

1988-12-01

229

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

DOEpatents

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.

Shi, Donglu (Chicago, IL) [Chicago, IL

1992-01-01

230

Preparation of Superconducting Bi-Pb-Sr-Ca-Cu-O Films by DC Magnetron Sputtering Method  

Microsoft Academic Search

Superconducting Bi-Pb-Sr-Ca-Cu-O thin films of zero resistivity temperature 108 K and critical current density of 1000 A\\/cm2 (at 77 K) were deposited on MgO(100) single-crystal substrates by DC magnetron sputtering. After depositing at 350-400C and post annealing at 837.5C for 1-5 hours in air, with different cooling rate we got highly c-axis oriented thin films which show zero resistivity at

Y. H. Wang; Y. Z. Zhang; Y. Y. Zhao; X. G. Qiu; P. Xu; L. Lin

1990-01-01

231

Preliminary T-T-T curve of Bi-Pb-Sr-Ca-Cu-O thin films  

NASA Astrophysics Data System (ADS)

Films of Bi-Pb-Sr-Ca-Cu-O with desired 2201, 2212, and 2223 phases have been successfully prepared by means of dc magnetron sputtering and precise control of the postannealing process. A preliminary temperature-time-transformation (T-T-T) diagram is proposed from the observation. Pb-loss control is found to be crucial to the high-T(c)(2223) phase obtained by the postannealing process, a higher PbO content in the films is observed to extend the temperature region of availability of the high-T(c) phase and vice versa.

Lin, W. J.; Wang, L. C.; Lu, H. B.; Lin, I. N.; Young, C. C.

1990-05-01

232

Crystallization of glass-ceramic Bi3Sr2Ca2Cu3Oy superconducting system  

NASA Astrophysics Data System (ADS)

In this study, the nucleation and the crystallization of the material with nominal composition of Bi3Sr2Ca2Cu3O? have been investigated, depending on the heat treatment conditions. It was found that 4 and 8-fold branched nuclei on the samples occurred with increasing the heat treatment temperature. Finally, crystallization occurred with further increase of the temperature. The needle-like crystals (whiskers) perpendicular to the sample surface was formed above 800 C, which consisted of the Bi-2212 phase. The results clearly showed that the anisotropy of surface tension is the most important parameter in determining the shape of the nucleus.

Kizilaslan, O.; Aksan, M. A.

2013-10-01

233

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

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

234

Flux creep in Bi2Sr2Ca1Cu2O(8+x) single crystals  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

235

Effects of lithium additions on processing of Bi-Sr-Ca-Cu-O superconducting tapes  

SciTech Connect

Lithium additions to the high-temperature superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} (2212) increased superconducting transition temperatures and improved resistance to effects of magnetic fields. In addition, these additions lowered the melting point of 2212 and increased reaction kinetics. Ag-clad tapes fabricated from 2212 with and without Li exhibited profound differences. For heating to temperatures less than or equal to 840{degrees}C, grain growth and sintering were much more substantial in the tapes containing Li.

Goretta, K.C.; Li, Y.F.; Poeppel, R.B. [Argonne National Lab., IL (United States); Wu, S.; Guo, J. [Illinois Univ., Urbana, IL (United States). Dept. of Nuclear Engineering; Schwartz, J. [Florida State Univ., Tallahassee, FL (United States). National High Magnetic Field Laboratory

1994-01-01

236

Ion implantation and annealing of SrTiO3 and CaTiO3  

SciTech Connect

Ion implantation damage and thermal annealing results are presented for single crystals of SrTiO3 and CaTiO3. The near-surface region of both of these materials can be made amorphous by low doses (approx.10 V/cmS) of heavy ions (Pb at 540 keV). During annealing, the amorphous implanted region crystallizes epitaxially on the underlying single-crystal substrate. The kinetics of this solid-phase epitaxial recrystallization process have been measured by employing ion channeling techniques.

White, C.W.; Boatner, L.A.; Rankin, J.; Aziz, M.J.

1987-01-01

237

Magnetic, electronic, dielectric and optical properties of Pr(Ca:Sr)MnO 3  

Microsoft Academic Search

: The charge-ordered perovskite Pr0.65Ca0.28Sr0.07MnO3 was investigated by means of magnetic susceptibility, specific heat, dielectric and optical spectroscopy and electron-spin\\u000a resonance techniques. Under moderate magnetic fields, the charge order melts yielding colossal magnetoresistance effects with\\u000a changes of the resistivity over eleven orders of magnitude. The optical conductivity is studied from audio frequencies far\\u000a into the visible spectral regime. Below the

J. Sichelschmidt; M. Paraskevopoulos; M. Brando; R. Wehn; D. Ivannikov; F. Mayr; K. Pucher; J. Hemberger; A. Pimenov; H.-A. Krug von Nidda; P. Lunkenheimer; V. Yu. Ivanov; A. A. Mukhin; A. M. Balbashov; A. Loidl

2001-01-01

238

Calcium Sensing Receptor (CaSR) activation elevates proinflammatory factor expression in human adipose cells and adipose tissue  

PubMed Central

We have previously established that human adipose cells and the human adipose cell line LS14 express the calcium sensing receptor (CaSR) and that its expression is elevated upon exposure to inflammatory cytokines that are typically elevated in obese humans. Research in recent years has established that an important part of the adverse metabolic and cardiovascular consequences of obesity derive from a dysfunction of the tissue, one of the mechanisms being a disordered secretion pattern leading to an excess of proinflammatory cytokines and chemokines. Given the reported association of the CaSR to inflammatory processes in other tissues, we sought to evaluate its role elevating the adipose expression of inflammatory factors. We exposed adipose tissue and in-vitro cultured LS14 preadipocytes and differentiated adipocytes to the calcimimetic cinacalcet and evaluated the expression or production of the proinflammatory cytokines IL6, IL1? and TNF? as well as the chemoattractant factor CCL2. CaSR activation elicited an elevation in the expression of the inflammatory factors, which was in part reverted by SN50, an inhibitor of the inflammatory mediator NF?B. Our observations suggest that CaSR activation elevates cytokine and chemokine production through a signaling pathway involving activation of NF?B nuclear translocation. These findings confirm the relevance of the CaSR in the pathophysiology of obesity-induced adipose tissue dysfunction, with an interesting potential for pharmacological manipulation in the fight against obesity- associated diseases.

Cifuentes, Mariana; Fuentes, Cecilia; Acevedo, Ingrid; Villalobos, Elisa; Hugo, Eric; Ben Jonathan, Nira; Reyes, Marcela

2013-01-01

239

Generation of Sr2Ca(n-1)CunOy phases (n = 5-7) by high pressure synthesis  

NASA Astrophysics Data System (ADS)

We prepared Sr2Ca(n-1)CunOy (n = 3-7) phases using a high-pressure apparatus. In the Sr-Ca-Cu-O system, the n = 5-7 members of a homologous series, Sr2Ca(n-1)CunOy, were prepared as mixed phases for the first time. The c-axis length increases linearly with increasing n; c = 6.46(n-1) + 14.3 . Half of this slope gives reasonable value of 3.2 as the thickness of a Ca and CuO2 plane. It is likely that a 0(Sr)2(n-1)n phase is formed from a 0(Sr)2(n-2)(n-1) phase to intercalate CaCuO2 into its infinite layer because the number of CuO2 planes increases with increasing sintering temperature and synthetic time. Too high temperature and too long synthesis time result in the formation of the infinite layer phase.

Aoba, Tomoya; Kato, Takahito; Suzuki, Tsuneo; Nakayama, Tadachika; Suematsu, Hisayuki; Niihara, Koichi

2013-11-01

240

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

NASA Astrophysics Data System (ADS)

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.

Bagard, Marie-Laure; Schmitt, Anne-Dsire; Chabaux, Franois; Pokrovsky, Oleg S.; Viers, Jrme; Stille, Peter; Labolle, Franois; Prokushkin, Anatoly S.

2013-08-01

241

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

NASA Astrophysics Data System (ADS)

Our previous work on CaFe2As2 single crystals grown out of FeAs flux has shown that a process of annealing and quenching can be used as an additional control parameter which can tune the ground state of CaFe2As2 systematically, in a manner similar to applied pressure. With combined effect of annealing/quenching and transition metal substitution, CaFe2As2 system offers ready access to the salient low-temperature states associated with Fe-based superconductors: antiferromagnetic/orthorhombic, superconducting, and nonmagnetic/collapsed tetragonal. In this talk we will present systematic studies of the combined effects of annealing/quenching and chemical substitution with various transition metals (Co, Ni, Rh) on the physical properties of CaFe2As2 and construct phase diagrams for different substitution levels and different annealing/quenching temperatures.

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

2013-03-01

242

Temperature and [CO3 ] Effects on Mg/Ca and Sr/Ca in the Benthic Foraminifera Species of Hoeglundina Elegans and Cibicidoides  

NASA Astrophysics Data System (ADS)

Current core-top calibrations suggest that the temperature sensitivity of Mg/Ca in Cibicidoides sp. tests is essentially identical with the 10% increase in Mg/Ca per 1C observed in many planktonic species. However, there is also evidence suggesting that non temperature-related effects may exert additional control on Mg/Ca in foraminiferal calcite. Here we use core-top samples from Atlantic (Little Bahama Banks, LBB; Arctic) and Pacific (Hawaii, and Indonesia) depth transects to assess the influence of bottom water temperature (BWT) and carbonate saturation levels on metal/Ca ratios in the aragonitic benthic foraminifer Hoeglundina elegans and calcitic Cibicidoides sp. We find that in situ CO3 ion concentrations play an important role in determining the Mg/Ca ratios in Cibicidoides sp. and Mg/Ca and Sr/Ca in H. elegans. The CO3 ion effect is limited, however, only to relatively low saturation levels, whereas at over-saturated levels, temperature exert the dominant effect on these metal ratios. Because we find no significant difference between results obtained on ``live'' and ``dead'' specimens, we propose that these differences are due to primary effects on metal uptake during test formations and not because of dissolution. Based on the new results we reappraise the Mg/Ca-temperature relationship of Cibicidoides sp. and propose a new calibration. We also propose that Sr/Ca and Mg/Ca in H. elegans tests can be used to reconstruct thermocline temperatures. Sr/Ca-thermometry in H. elegans may be especially useful in cases where the use of Mg/Ca thermometry in calcitic foraminfera has been compromised by contamination issues. In both cases, temperature estimates in low carbonate saturation levels may be grossly inaccurate.

Lear, C. H.; Rosenthal, Y.; Oppo, D. W.; Linsley, B. K.

2005-12-01

243

Evolution of bulk superconductivity in SrFe2As2 with Ni substitution  

Microsoft Academic Search

Single crystals of the Ni-doped FeAs-based superconductor SrFe2-xNixAs2 were\\u000agrown using a self-flux solution method and characterized via x-ray\\u000ameasurements and low temperature transport, magnetization, and specific heat\\u000astudies. A doping phase diagram has been established where the\\u000aantiferromagnetic order associated with the magnetostructural transition of the\\u000aparent compound SrFe2As2 is gradually suppressed with increasing Ni\\u000aconcentration, giving way to

S. R. Saha; N. P. Butch; K. Kirshenbaum; Johnpierre Paglione

2009-01-01

244

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

SciTech Connect

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.

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

245

Crystalline phases during the melting of Bi sub 2 Sr sub 2 CaCu sub 2 O sub x  

Microsoft Academic Search

The melting of BiSrCaCuO material has been studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in order to study the phases that formed in the high temperature regions. Two distinct phases of (Sr{sub 1-x}Ca)CuO and (Sr{sub 1-x}Ca)CuO have been observed in the Bi-rich matrix depending upon quenching temperatures. Crystallization from the melt by fast cooling usually produce

Ming Xu; J. Polonka; A. I. Goldman; D. K. Finnemore; Qiang Li; F. C. Laabs

1991-01-01

246

MBE growth of compounds on the copper rich side of the (Sr,Ca)CuO system  

Microsoft Academic Search

Thins films belonging to the copper rich family in the (Sr,Ca)?Cu?O system have been synthesized using Molecular Beam Epitaxy (MBE) deposition. The growth conditions have been optimized on two different substrates, MgO (100) and SrTiO3 (100). We discuss in this paper the variations of the electron diffraction pattern (RHEED) during the growth. The films obtained present a single orientation with

B. Eustache; F. C. Beuran; C. Deville Cavellin; C. J. Hatterer; V. Mairet; C. Partiot; X. Z. Xu; P. Germain; M. Lagus

1997-01-01

247

Thermodynamics of the B-Ca, B-Sr, and B-Ba systems: Applications for the fabrications of CaB6, SrB6, and BaB6 thin films  

NASA Astrophysics Data System (ADS)

Using the thermodynamic descriptions previously modeled in the boron-alkaline earth metal systems, B-Ca, B-Sr, and B-Ba, the pressure-temperature phase diagrams of these systems have been obtained in the present work, which provide insights into appropriate processing conditions for depositions of the divalent alkaline-earth metal hexaborides, CaB6, SrB6, and BaB6. The present work indicates that the lower the growth pressures, the wider the growth temperature ranges and, in turn, the more favorite control of the growth of thin films for the ferromagnetic hexaborides.

Shang, Shunli; Liu, Zi-Kui

2007-02-01

248

Measure of the magnitude of Young's modulus in whisker-like samples of the Bi-based high-Tc materials Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox  

Microsoft Academic Search

We have measured Young's modulus in ribbon-like whisker samples of the high-Tc materials: Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox. This is the first direct measurement of Young's modulus for whiskers of any of the high Tc materials. We used a stress-strain probe that applies an axial force (uniaxial stress) to the whisker-like sample and simultaneously measures the corresponding sample elongation. The slope of

T. M. Tritt; M. Marone; Xin-Fen Chen; M. J. Skove; A. C. Ehrlich; G. X. Tessema; D. J. Gillespie; J. P. Franck; J. Jung

1991-01-01

249

Syntheses of Eu-Activated Alkaline Earth Fluoride MF2 (M=Ca, Sr) Nanoparticles  

NASA Astrophysics Data System (ADS)

The Eu2+ ion-activated CaF2 and SrF2 nanoparticles were prepared by the sol-gel technique assisted with the trifluoro-acetic acid (TFA), and were evaluated by X-ray diffraction (XRD), photoluminescence (PL), photoluminescence excitation (PLE) measurements and atomic force microscopy (AFM) observation. A modified reducing method based on the thermal-carbon reducing atmosphere (TCRA) treatment using activated carbon was proposed to realize the effective reduction from Eu3+ to Eu2+ ions, in which the nanoparticles showed a strong and broad luminescence due to the parity allowed 4f7-4f65d1 transition. From the XRD results, it was found that the average particle size proportionally increased in the range of 15 to 120 nm and 10 to 100 nm for CaF2 and SrF2, respectively, with increasing sintering temperatures 300-700 C. The surface images of nanoparticles obtained by the AFM revealed that the grains with high uniformity grew with increasing TCRA temperatures. It was confirmed that the reduced Eu2+ ions were homogeneously dispersed with the critical distance 16-17 in the fluoride nanoparticles from the concentration quenching results.

Hong, Byung-Chul; Kawano, Katsuyasu

2007-09-01

250

Quasiparticle tunneling in Bi-Sr-Ca-Cu-O thin films  

SciTech Connect

Tunnel junctions were formed by depositing a thin layer of Al{sub 2}O{sub 3}(20 A) and Al counter electrodes onto sputtered and annealed Bi-Sr-Ca-Cu-O films. Differential conductance spectra displayed low conductivity at low bias, and two pairs of peaks, symmetric with respect to zero bias, which correlate in energy and relative magnitude with the two superconducting Bi-Sr-Ca-Cu-O phases present in the film (110 and 85 K). The measured values of the peak positions and the reduced gap parameter are {Delta}{sub 1}=18--21 meV(85-K phase), {Delta}{sub 2}=25--28 meV (110-K phase), 2{Delta}/{ital k}{sub {ital B}}T{sub c}=5.5{plus minus}0.6 for both phases. The shape of the conductance curves at higher bias is parabolic. This effect can be explained by the presence of a composite barrier. Such a barrier is likely to be the result of insulating or semiconducting grain surfaces in addition to the artificial barrier.

Kussmaul, A.; Moodera, J.S.; Roesler, G.M. Jr.; Tedrow, P.M. (Francis Bitter National Magnet Laboratory, Massachusetts Institute of (US))

1990-01-01

251

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

NASA Astrophysics Data System (ADS)

Metal tungstates (MeWO 4, Me = Ba, Sr and Ca) were successfully prepared using the corresponding Me(NO 3) 22H 2O and Na 2WO 42H 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.

Thongtem, Titipun; Phuruangrat, Anukorn; Thongtem, Somchai

2008-09-01

252

Effect of La3+ substitution with Gd3+ on the resistive switching properties of La0.7Sr0.3MnO3 thin films  

NASA Astrophysics Data System (ADS)

This study demonstrated that the resistive switching voltage of perovskite manganite material could be controlled by A-site cation substitution in "A" MnO3 perovskite manganite structure. A partial substitution of La3+ in La0.7Sr0.3MnO3 with smaller cation Gd3+ induced A-site vacancy of the largest Sr2+ cation with surface segregation of SrOy due to ionic size mismatch, and the induced vacancies reduced migration energy barrier. The operating voltage decreased from 3.5 V to 2.5 V due to a favorable condition for electrochemical migration and redox of oxygen ions. Moreover, surface-segregated SrOy was enhanced with Gd-substitution and the SrOy reduced Schottky-like barrier height and resistive switching ratio from the potential drop and screening effect. The relationship between A-site vacancy generation resulting in surface segregation of SrOy and resistive switching behavior was also investigated by energy resolved x-ray photoelectron spectroscopy, O 1s near edge x-ray absorption spectroscopy, and current voltage measurement.

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

2014-05-01

253

Room Temperature Epitaxial Stabilization of a Tetragonal Phase in AruO(3) (A=Ca And Sr) Thin Films  

SciTech Connect

We demonstrate that SrRuO{sub 3} and CaRuO{sub 3} thin films undergo a room temperature structural phase transition driven by the substrate imposed epitaxial biaxial strain. As tensile strain increases, ARuO{sub 3} (A=Ca and Sr) films transform from the orthorhombic phase which is usually observed in bulk SrRuO{sub 3} and CaRuO{sub 3} at room temperature into a tetragonal phase which in bulk samples is only stable at higher temperatures. More importantly, we show that the observed phenomenon strongly affects the electronic and magnetic properties of ARuO{sub 3} thin films that are grown on different single crystal substrates which, in turn, offers the possibility to tune these properties.

Vailionis, A.; Siemons, W.; Koster, G.

2009-05-26

254

Electronic structure of Ca_1.5Sr_0.5RuO4 from ARPES  

NASA Astrophysics Data System (ADS)

We report ARPES results on electronic structure and Fermi surface of Ca_2-xSr_xRuO_4, with a focus to x=0.5, which is believed to be a quantum critical point in the phase diagram. By comparing to Sr_2RuO_4, which is believed to be a p-wave superconductor, we find that in Ca_1.5Sr_0.5RuO_4, both, ?, ? (d_yz,zx) bands are clearly observed and remain mostly intact, while ? (d_xy) band is less observabl. While there is a local maxima at x=0.5, there is also a general trend of reduction in coherent spectral weight as adding more Ca, The spectrum shows a two component structure with incoherent part displays a reverse dispersion, suggesting a partial localization effect in single electron spectral function.

Wang, Shancai; Yang, Hongbo; Sekharan, A. K. P.; Ding, Hong; Souma, H.; Matsui, H.; Sato, T.; Takahashi, T.; Lu, Chenxi; Zhang, Jiandi; Jin, R. Y.; Mandrus, D.; Plummer, E. W.

2004-03-01

255

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

NASA Astrophysics Data System (ADS)

One of the basic data to understand global change and past global changes is the measurement and the reconstruction of temperature of marine water masses. E.g. seawater temperature controls the density of seawater and in combination with salinity is the major driving force for the oceans circulation system. Geochemical investigations on cold-water corals Lophelia pertusa and Desmophyllum cristagalli indicated the potential of these organisms as high-resolution archives of environmental parameters from intermediate and deeper water masses (Adkins and Boyle 1997). Some studies tried to use cold-water corals as a high-resolution archive of temperature and salinity (Smith et al. 2000, 2002; Blamart et al. 2005; Lutringer et al. 2005). However, the fractionation of stable isotopes (delta18O and delta13C) and element ratios (Sr/Ca, Mg/Ca, U/Ca) are strongly influenced by vital effects (Shirai et al. 2005; Cohen et al. 2006), and difficult to interpret. Nevertheless, ongoing studies indicate the potential of a predominant temperature dependent fractionation of distinct isotopes and elements (e.g. Li/Ca, Montagna et al. 2008; U/Ca, Mg/Ca, delta18O, Lpez Correa et al. 2008; delta88/86Sr, Rggeberg et al. 2008). Within the frame of DFG-Project TRISTAN and Palo-TRISTAN (Du 129/37-2 and 37-3) we investigated live-collected specimens of cold-water coral L. pertusa from all along the European continental margin (Northern and mid Norwegian shelves, Skagerrak, Rockall and Porcupine Bank, Galicia Bank, Gulf of Cadiz, Mediterranean Sea). These coral samples grew in waters characterized by temperatures between 6C and 14C. Electron Microprobe investigations along the growth direction of individual coral polyps were applied to determine the relationship between the incorporation of distinct elements (Sr, Ca, Mg, S). Cohen et al. (2006) showed for L. pertusa from the Kosterfjord, Skagerrak, that ~25% of the coral's Sr/Ca ratio is related to temperature, while 75% are influenced by the calcification rate of the organism. However, the Sr/Ca-temperature relation of our L. pertusa specimens suggest, that mean values are more reliable for temperature reconstruction along a larger temperature range than local high-resolution investigations. Additionally, our results plot on same line of Sr/Ca-temperature relationship like tropical corals indicating a similar behaviour of element incorporation during calcification. References: Adkins JF, Boyle EA (1997) Changing atmospheric ?14C and the record of deep water paleoventilation ages. Paleoceanography 12:337-344 Blamart D, Rollion-Bard C, Cuif J-P, Juillet-Leclerc A, Lutringer A, Weering Tv, Henriet J-P (2005) C and O isotopes in a deep-sea coral (Lophelia pertusa) related to skeletal microstructure. In: Freiwald A, Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Berlin Heidelberg, p 1005-1020 Cohen AL, Gaetani GA, Lundlv T, Corliss BH, George RY (2006) Compositional variability in a cold-water scleractinian, Lophelia pertusa: New insights into vital effects. Geochemistry, Geophysics, Geosystems 7:Q12004, doi:12010.11029/12006GC001354 Lpez Correa M, Montagna P, Rggeberg A, McCulloch M, Taviani M, Freiwald A (2008) Trace elements and stable isotopes in recent North Atlantic Lophelia pertusa along a latitudal gradient and from fossil Mediterranean sites. ASLO 2008 Summer Meeting, St. John's, Newfoundland & Labrador, Canada, 08.06.-13.06.2008, p. 47 Lutringer A, Blamart D, Frank N, Labeyrie L (2005) Paleotemperatures from deep-sea corals: scale effects. In: Freiwald A, Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Berlin, Heidelberg, p 1081-1096 Montagna P, Lpez-Correa M, Rggeberg A, McCulloch M, Rodolfo-Metalpa R, Dullo W-C, Ferrier-Pags C, Freiwald A, Henderson G, Mazzoli C, Russo S, Silenzi S, Taviani M (2008) Coral Li/Ca in micro-structural domains as a temperature proxy. Goldschmidt Conference, Vancouver, British Columbia, Canada Rggeberg A, Fietzke J, Liebetrau V, Eisenhauer A, Dullo W-C, Freiwald A (2008) Stable strontium isot

Rggeberg, Andres; Riethdorf, Jan-Rainer; Raddatz, Jacek; Lpez Correa, Matthias; Montagna, Paolo; Dullo, Wolf-Christian; Freiwald, Andr

2010-05-01

256

Ab initio study of the structural phase transitions of the double perovskites Sr2MWO6 (M=Zn, Ca, Mg)  

NASA Astrophysics Data System (ADS)

We study the interplay of structural distortions in double perovskites Sr2MWO6 (M = Zn, Ca, Mg) by means of first-principles calculations and group theoretical analysis. Structure relaxations of the cubic, tetragonal, and monoclinic phases show that the ground states of the three compounds are monoclinic, although the energy difference between the monoclinic and tetragonal structures is very small in the case of Sr2MgWO6. The symmetry analysis of the distortions involved in the experimental and calculated low-temperature structures shows that the amplitude of two primary distortions associated to rigid rotations of the MX6 and WO6 octahedra are dominant, although the amplitude of a third mode related to deformations of the MX6 groups can not be neglected. The energy maps of the space spanned by the three relevant modes are calculated, and the couplings among the modes are evaluated, showing that the role of a hard secondary mode (in the Landau sense) coupled trilinearly to the two primary instabilities is crucial to stabilize the monoclinic ground state. Results suggest that the key role of the trilinear coupling among three modes could be rather common. A phenomenological theory including the effects of the chemical pressure is also developed. We find that the evolution of the stiffness constants in terms of the atomic substitution follows an accurate linear dependence and that the influence of quantum saturation of the order parameters could stabilize the tetragonal phase of Sr2MgWO6.

Petralanda, U.; Etxebarria, I.

2014-02-01

257

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

258

Evidence of rainfall variations in Southern Brazil from trace element ratios (Mg\\/Ca and Sr\\/Ca) in a Late Pleistocene stalagmite  

Microsoft Academic Search

Trace element ratios in the Bt2 stalagmite from Botuver cave, Southern Brazil, are explored as a proxy for changes in the local rainfall recharge during the last 116ky. BP Mg\\/Ca and Sr\\/Ca ratios, measured with an electron microprobe, are significantly positively correlated with one another throughout the entire record, and vary in a way that is very consistent with variations

Francisco W. Cruz; Stephen J. Burns; Michael Jercinovic; Ivo Karmann; Warren D. Sharp; Mathias Vuille

2007-01-01

259

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

260

Introduction of artificial pinning centres in Bi2Sr2CaCu2O8 ceramics  

NASA Astrophysics Data System (ADS)

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.

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

1995-04-01

261

Introduction of artificial pinning centres in Bi2Sr2CaCu2O8 ceramics  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

262

X-ray diffraction analysis of the modulated structure of Bi 2 Sr 2 CaFe 2 O y  

Microsoft Academic Search

The modulated structure of the Bi2Sr2CaFe2Oy compound isomorphous with the Bi2Sr2CaCu2Oy phase was refined by the method of the full profile analysis on the basis of the powder X-ray diffraction data. The analysis was carried out in the superspace group of N: Abmm: 1⪟ using the parameters of the unit cell of the basic structure a=5.466(3), b=5.446(5) and c=31.25(9)q+ and

B. Z. Narymbetov; V. S. Shekhtman; A. V. Dubovitskii; V. Sedykh; I. S. Smirnova

1996-01-01

263

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

Microsoft Academic Search

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

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

1990-01-01

264

Phase diagram in the (Bi,Pb)?Sr?Ca?Cu?O system: influence of partial constraint oxygen pressure  

NASA Astrophysics Data System (ADS)

DTA-DTG, X ray diffraction and metallographic measurements at different temperatures and partial oxygen pressure in the isoplethic cut (Bi,Pb) 2Sr 2CuO x?CaCuO 2, were carried out to analyze the influence of partial constraint oxygen pressure on phase transformations. An isobaric invariant equilibrium has been found in the P o2 range 0.5-1. Supplementary phase appearing at invariant equilibrium is (Sr,Ca) 3Cu 5O y. That phase fixes oxygen and then the weight loss is stopped.

Mansori, M.; Satre, P.; Roubin, M.; Vacquier, G.; Strobel, P.; Sebaoun, A.

1994-12-01

265

High-pressure structural study of the scheelite tungstates CaWO4 and SrWO4  

Microsoft Academic Search

Angle-dispersive x-ray-diffraction and x-ray-absorption near-edge structure measurements have been performed on CaWO4 and SrWO4 up to pressures of approximately 20 GPa. Both materials display similar behavior in the range of pressures investigated in our experiments. As in the previously reported case of CaWO4 , under hydrostatic conditions SrWO4 undergoes a pressure-induced scheelite-to-fergusonite transition around 10 GPa. Our experimental results are

D. Errandonea; J. Pellicer-Porres; F. J. Manjn; A. Segura; Ch. Ferrer-Roca; R. S. Kumar; O. Tschauner; P. Rodrguez-Hernndez; J. Lpez-Solano; S. Radescu; A. Mujica; A. Muoz; G. Aquilanti

2005-01-01

266

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

267

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

NASA Astrophysics Data System (ADS)

Paleotemperature estimates based on coral Sr/Ca have not been widely accepted because the reconstructed glacial-Holocene shift in tropical sea-surface temperature (4-6C) is larger than that indicated by foraminiferal Mg/Ca (2-4C). 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 (-7C to +2C 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.

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

2012-03-01

268

Growth and Characterization of High-Quality Single Crystals of Ni- and Zn-Doped Bi2Sr2Ca(Cu2-xMx)O8+? (M = Ni or Zn) High-Temperature Superconductors  

NASA Astrophysics Data System (ADS)

High-quality large single crystals of Ni- and Zn-doped Bi2Sr2Ca(Cu2-xMx)O8+? (M = Ni or Zn) have been successfully grown by the traveling solvent floating zone technique. The single crystals are characterized by compositional and structural analyses and their physical properties are investigated by magnetic susceptibility and resistivity measurements. A record high critical temperature with a Tc = 97.5 K has been achieved in the annealed pristine Bi2212 single crystal. Substitution of Cu by Ni or Zn reduces the superconducting transition temperature when compared with pristine Bi2Sr2CaCu2O8+? (Bi2212) grown under similar conditions. The successful growth of such pristine Ni- and Zn-doped Bi2212 single crystals will facilitate studies of the relationship between the magnetism and superconductivity in high-temperature cuprate superconductors.

Liu, Shan-Yu; Zhang, Wen-Tao; Zhao, Lin; Liu, Hai-Yun; Wu, Yue; Liu, Guo-Dong; Dong, Xiao-Li; Zhou, Xing-Jiang

2012-08-01

269

Structural and electrical changes in NdSrNiO 4? ? by substitute nickel with copper  

Microsoft Academic Search

A novel series of the formula NdSrNi1?xCuxO4?? were synthesized for various values of x ranging from 0 to 1 in 1atm of O2 gas flow using conventional solid-state methods and were characterized by powder X-ray diffraction and electrical resistivity measurements. The compounds have been shown to adopt the K2NiF4-type structure. The oxygen stoichiometry of the compounds was determined from thermo-gravimetric

Hann Chaker; T. Roisnel; M. Potel; R. Ben Hassen

2004-01-01

270

Effect of La-Substitution on the Electrical Conductivity of Sr1-x La x MoO4+? (x = 0-0.3) Compounds  

NASA Astrophysics Data System (ADS)

Various compositions of Sr1-x La x MoO4+? (x = 0.05, 0.1, 0.2, and 0.3) compounds were prepared by solid state reaction route. The samples were characterized by powder-XRD, TG-DTA, and SEM-EDAX techniques. Formation of single crystalline phases of Sr1-x La x MoO4+? was confirmed from powder-XRD patterns. The thermal stability of La-doped SrMoO4 compounds was investigated by TG-DTA. Uniform grain distribution was observed in the SEM image of 10-20 mol.% La-substituted compositions. Needle-shaped structures were observed in the SEM image of Sr0.3La0.1MoO4+? and were confirmed to be La2Mo2O9 by XRD examination. The electrical conductivity of these compounds was measured by AC-impedance technique in the temperature range of 373-1073 K in air ambience and compared with that of pristine SrMoO4. The electrical conductivity was found to decrease for La-substituted SrMoO4 compared to pristine SrMoO4. The diffusion coefficient calculated from the electrical conductivity was found to be in the range of 1.94 0.02 10-13 to 1.15 0.01 10-11 cm2/S at 873-1173 K for substituted composition and 3.47 0.02 10-13 to 2.48 0.01 10-10 cm2/S for pristine SrMoO4 at 673-1073 K temperature range.

Maji, Binoy Kumar; Jena, Hrudananda; Govindan Kutty, K. V.

2014-06-01

271

Synthesis and Characterization of Alkaline-Earth Metal (Ca, Sr, and Ba) Doped Nanodimensional LaMnO3 Rare-Earth Manganites  

NASA Astrophysics Data System (ADS)

The substitution of divalent cations of alkaline-earth elements in nanodimensional structures of rare-earth manganites produces advanced materials with potential electrical and magnetic functionalities. A systematic investigation of La0.65A0.35MnO3 (A = Ca, Sr, Ba) materials synthesized with a modified citrate route adopting ethanol dehydration has been undertaken. The structural and morphological analyses are carried out by using x-ray diffraction and scanning electron microscopy, respectively. Resistivity measurements are performed in variation with temperature to study the electrical transport properties which are found to vary with the size of the A-site cationic radius. Room temperature magnetic measurements are carried out to investigate the type of magnetic phase present in materials. The stability of the magnetic phase and coercivity are found to be dependent on the size of nanocrystallites.

Asma, Khalid; Saadat, Anwar Siddiqi; Affia, Aslam

2013-07-01

272

Effect of Nd Substitution on PrOs4Sb12 Investigated by ?SR Experiments  

NASA Astrophysics Data System (ADS)

The pseudo ternary system Pr1-xNdxOs4Sb12 has been used as a model system to investigate the effect of ferromagnetism (FM) on the unconventional superconductivity (SC) and quantum critical behavior of PrOs4Sb12 [1]. SC in this system disappears near a critical concentration xcr,10.58 and FM appears above xcr,20.33 [1,2]. The new ?SR measurements have been performed on samples with x = 0.25, 0.75, and 1. For x = 1 and 0.75, the estimated frozen moments agree with the Nd^3+ CEF ground state moment. For x = 0.25, neither time reversal symmetry breaking nor evidence of freezing of Nd^3+ spins was observed in zero-field ?SR measurements, the behavior of which is very different than what is observed for x = 0.45-0.55 [2]. In the SC state, an unexpected linear T dependence of the Gaussian relaxation rate was also found in the transverse field ?SR data for x = 0.25, which is different than the plateau in PrOs4Sb12 below 1.3K [3]. [1] Ho, et al., PRB 83, 024511 (2011).[2] Ho, et al., 2010 APS March Meeting, A38.00005 (2010). [3] MacLaughlin et al., PRL 105, 019701 (2010).

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

2013-03-01

273

Photoemission Study of CaF2- and SrF2-GaAs(110) Interfaces Formed at Room Temperature.  

National Technical Information Service (NTIS)

Group-II cubic fluorides such as Calcium Fluoride CaF2 and Strontium Fluoride SrF2 are very promising for growing epitaxial insulator-on-semiconductor and semiconductor-on-insulator structures. Interfaces formed by evaporating CaF2 or SrF2 on room-tempera...

A. Kahn

1989-01-01

274

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

NASA Astrophysics Data System (ADS)

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.

Misra, Sunasira

2012-07-01

275

Crystal growth of high Tc superconductors YBa 2Cu 3O x, Bi 3Sr 3CaCu 2.5O x and Pb 0.6Bi 3Sr 2CaCu 3O x  

NASA Astrophysics Data System (ADS)

Single crystals of YBa 2Cu 3O x, Bi 3Sr 3CaCu 2.5O x and Pb 0.6Bi 3Sr 2CaCu 3O x have been grown by the flux method. The crystals obtained have sizes varying from 2.5 x 2.0 x 0.1 mm 3 to 10 x 4 x 3 mm 3. These crystals have an orthorhombic structure with cell parameters a = 3.838(1) , b = 3.871(1) and c=11.738(4) (YBa 2Cu 3Ox); a = 5.39 X, b = 5.37 and c = 31.01 (Bi 3Sr 3CaCu 2.5Ox); and a = 5.38 , b = 5.34 , c= 30.55 (Pb 0.6Bi 3Sr 2CaCu 3Ox). Measurements of resistivity and AC susceptibility confirmed that these crystals are bulk superconductors with T c (zero) of 91.4, 90 and 82 K, respectively. Differential thermal analysis (DTA) measurements were made to study the crystal growth process and thermal properties of these crystals.

Hong, Wang; Shuxia, Shang; Zhaohe, Yang; Zhuo, Wang; Xiaonong, Shen; Huansui, Zhao; Minhua, Jiang; Huanchu, Chen

1990-01-01

276

ELECTRON PARAMAGNETIC RESONANCE OF Gd$sup 3+$ IN CaF, SrF, AND BaF  

Microsoft Academic Search

Electron paramagnetic resonance (EPR) measurements at room temperature ; were made on trivalent gadolinium ions in single crystals of CaF, SrF\\/sub ; 2\\/, and BaF and also in natural fluorites. The effects of heat treatments ; and of hydrolysis at high temperature on the EPR spectra were studied. In CaF\\/; sub 2\\/ there are four sets of spectra, the first

Sierro

1963-01-01

277

Chemical bond characteristics, thermal expansion property and compressibility of AR 2O 4 (A = Ca, Sr, Ba; R = rare earths)  

Microsoft Academic Search

Theoretical researches were performed on the CaFe2O4-type binary rare earth oxides AR2O4 (A=Ca, Sr, Ba; R=rare earths) by using chemical bond theory of dielectric description. The chemical bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations

Huaiyong Li; Siyuan Zhang; Shihong Zhou; Xueqiang Cao

2009-01-01

278

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

279

Osteopenic bone cell response to strontium-substituted hydroxyapatite  

Microsoft Academic Search

Ionic substitution is a powerful tool to improve the biological performance of calcium phosphate based materials. In this\\u000a work, we investigated the response of primary cultures of rat osteoblasts derived from osteopenic (O-OB) bone to strontium\\u000a substituted hydroxyapatite (SrHA), and to hydroxyapatite (HA) as reference material, compared to normal (N-OB) bone cells.\\u000a Strontium (Sr) and calcium (Ca) cumulative releases in

E. Boanini; P. Torricelli; M. Fini; A. Bigi

280

Thermodynamic properties of Sr-doped LaMnO{sub 3} perovskite in the La-Sr-Mn-O system  

SciTech Connect

Thermodynamic properties of Sr-doped perovskite-type lanthanum manganites (LSM) were generated by measuring the electromotive force (EMF) of test materials, using the solid galvanic cell technique. The cell consisted of an anode (SrO/SrF{sub 2}), an electrolyte (CaF{sub 2} or SrF{sub 2}) and a cathode (LSM/SrF{sub 2}). Two types of cells were tested in which type 1 used a CaF{sub 2} electrolyte and type 2 used a SrF{sub 2} electrolyte. The activity of SrO substituting into various LSM compositions was calculated using the measured EMF. The Sr content was varied from 0.16 to 0.6 mol, and the temperature of interest varied from 700 to 1000 C. It was found that the SrO activity decreased with increasing temperature (at fixed composition) and increased with increasing Sr content (at fixed temperature).

Zheng, F.; Pederson, L.R.

1999-08-01

281

Spin tunneling in Co/Au/I/BiSrCaCuO tunnel junctions  

NASA Astrophysics Data System (ADS)

Conductance spectra of Co/Au/I/Bi2Sr2CaCu2Ox+8(BSCCO) tunnel junctions have been measured to investigate the tunneling of spin polarized quasiparticles. BSCCO thin films prepared by molecular beam epitaxy are used for the Co/Au/I/BSCCO tunnel junctions because those have flat surface without any large steps as observed on the cleaved surface of single crystals. The superconducting gap is clearly observed in the conductance spectra at the temperature below the critical temperature Tc. In addition, a splitting of the zero bias conductance peak and the imbalance of the peak heights are observed. This feature is induced by the spin polarization of quasiparticles injected into the superconductors.

Ishibashi, Takayuki; Sato, Kazushige; Yonemitsu, Koutarou; Sato, Katsuaki

2001-06-01

282

Bipolar resistive switchings in Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

283

Nanosecond and femtosecond laser deposition of BiSrCaCuO on MgO  

NASA Astrophysics Data System (ADS)

Pulsed laser deposition of BiSrCaCuO on MgO (100) using Q-switched Nd:YAG nanosecond laser operating at ?= 1064 nm (ns-PLD) and mode-locked Ti:Sa femtosecond laser at ?= 785 nm (fs-PLD) were performed. Rough surface with spheriodal morphology is the general microstructure of the deposited material from both nanosecond and femtosecond laser ablation. Femtosecond PLD resulted to granular morphology containing both BSCCO phase and rod-like Cu2O grains. Unlike ns-PLD, fs-PLD produced polycrystalline films even without heat treatment. These results indicate that two distinct ablation characteristic for ns-PLD and fs-PLD of BSCCO.

Vitug, Jaziel; Lampa, Krizia Isabel; Olaya, Cherrie May; De Vero, Jeffrey; Santos, Gil Nonato; Sarmago, Roland; Garcia, Wilson

2013-06-01

284

Vortex fluctuations in underdoped Bi(2)Sr(2)CaCu(2)O(8+delta) crystals.  

PubMed

Vortex thermal fluctuations in heavily underdoped Bi(2)Sr(2)CaCu(2)O(8+delta) (T(c)=69.4 K) are studied using Josephson plasma resonance. From the zero-field data, we obtain the c-axis penetration depth lambda(L,c)(0)=230+/-10 micrometer and the anisotropy ratio gamma(T). The low plasma frequency allows us to study phase correlations over the whole vortex solid state and to extract a wandering length r(w) of vortex pancakes. The temperature dependence of r(w) as well as its increase with dc magnetic field is explained by the renormalization of the vortex line tension by the fluctuations, suggesting that this softening is responsible for the dissociation of the vortices at the first order transition. PMID:12689317

Colson, Sylvain; Konczykowski, Marcin; Gaifullin, Marat B; Matsuda, Yuji; Gier?owski, Piotr; Li, Ming; Kes, Peter H; Van Der Beek, Cornelis J

2003-04-01

285

Energy gaps in Bi(2)Sr(2)CaCu(2)O(8+?) cuprate superconductors.  

PubMed

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 Bi(2)Sr(2)CaCu(2)O(8+?) intrinsic Josephson junctions, which provides a clear evidence that ?(s) closes at a temperature T(c) (0) well above the superconducting transition temperature T(c) 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 T(c) (0), 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 T(c) 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

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

286

(Ca, Sr)F 2 surface roughness effect on angle resolved XPS measurements  

NASA Astrophysics Data System (ADS)

Nanometric scale surface morphology of layers on substrates can be investigated using angle dependent X-ray photoemission spectroscopy. Experimentally we differentiate the two typical surface forms of (Ca, Sr)F 2 for the (100) and the (111) orientations by means of angular photoemission intensity profiles. The surfaces of these fluorides are known to be terminated by facets in the case of the (100) orientation and to be flat in the case of the (111) orientation. We calculate the influence of an idealized triangular surface roughness of layers on photoemission intensity. The calculation is compatible with the measurements. We show that within certain conditions the intensity ratio ( {I layer}/{I substrate}) can be used as a measure of the substrate coverage.

Olive, Gino

1993-11-01

287

Energy gaps in Bi2Sr2CaCu2O8+? cuprate superconductors  

PubMed Central

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.

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

288

Fabrication of Bi?Pb?Sr?Ca?Cu?O superconducting composite wires with copper core  

NASA Astrophysics Data System (ADS)

By passing a flexible copper wire through the molten Bi?Pb?Sr?Ca?Cu?O system at a high constant speed, long lengths of composite wires were prepared. Depending on the pulling speed and the temperature of the melt, a coating with different microstructure and thickness from less than ten to several tens of microns can be obtained. The short samples cut out of the composite wires thus obtained were annealed in air in a preheated furnace. After relatively short-time annealing at 800C, both resistivity and d.c. magnetization versus temperature measurements show indications of onset of superconductivity in the 110-115 K region; zero resistance was achieved in the range 65-70 K.

Grozav, A. D.; Konopko, L. A.; Leporda, N. I.; Onu, M. I.; Panaitov, G. I.

1990-11-01

289

Electronic Magnetic and Structural Properties of A2VM0O6 Perovskites (A = Ca, Sr)  

SciTech Connect

The perovskites Sr{sub 2}VMoO{sub 6} and Ca{sub 2}VMoO{sub 6} have been synthesized by liquid-mix technique in citrate melts, and their electronic, magnetic and structural properties have been investigated. No signs of V/Mo ordering are seen by synchrotron X-ray powder diffraction, but despite the chemical disorder both oxides are highly conductive and Pauli paramagnetic. Electrical conductivities of these solid solutions are comparable or higher than those reported for polycrystalline AMoO{sub 3} end members. It is suggested that the delocalized metallic conductivity of these compounds with two different transition-metal atoms implies valence equilibrium between the degenerate oxidation-state couples V{sup 4+}Mo{sup 4+} and V{sup 3+}Mo{sup 5+}.

Karen,P.; Moodenbaugh, A.; Goldberger, J.; Santhosh, P.; Woodward, P.

2006-01-01

290

Bastadins relate ryanodine-sensitive and -insensitive Ca2+ efflux pathways in skeletal SR and BC3H1 cells.  

PubMed

Bastadins potently interact with the FK-506-binding protein of 12 kDa (FKBP12)-ryanodine receptor (Ry1R) complex in skeletal muscle to enhance a high-affinity ryanodine binding conformation (M. M. Mack, T. F. Molinski, E. D. Buck, and I. N. Pessah. J. Biol. Chem. 269: 23236-23249, 1994). Bastadins are used to examine the relationship between ryanodine-sensitive and ryanodine-insensitive Ca2+ efflux pathways that coexist in junctional sarcoplasmic reticulum (SR) vesicles from rabbit skeletal muscle and differentiated BC3H1 cells. Complete block of caffeine-sensitive Ca2+ channels with micromolar ryanodine or ruthenium red does not alter the steady-state loading capacity of SR. Inhibition of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) pumps with thapsigargin unmasks a ryanodine- and ruthenium red-insensitive Ca2+ efflux pathway. Bastadin 5 alone does not inhibit Ca2+ efflux unmasked by inhibition of SERCA pumps, but, in combination with blocking concentrations of ryanodine or ruthenium red, it eliminates the ryanodine-insensitive Ca2+ "leak" and enhances steady-state loading capacity of SR vesicles approximately 2.5-fold. These actions of bastadins occur in the same concentration range that enhances the number of high-affinity binding sites for [3H]ryanodine (50% effective concentration of approximately 2 microM). Similar effects on SR Ca2+ transport are found with FK-506 and ryanodine in combination. Block of Ry1R in intact BC3H1 cells with ryanodine does not eliminate the prominent Ca2+ leak unmasked by thapsigargin. A membrane-permeant mixture of bastadins in combination with ryanodine nearly eliminates the Ca2+ leak unmasked by thapsigargin, even though the Ca2+ stores are replete. The requirement of both a known Ry1R blocker and bastadins in combination provides a pharmacological link between ryanodine-sensitive Ca2+ channels and ryanodine-insensitive leak pathways in isolated junctional SR and BC3H1 cells. Together, these results strongly suggest that bastadins, through their modulatory actions on the FKBP12-Ry1R complex, convert ryanodine-insensitive leak states into ryanodine-sensitive channels that recognize [3H]ryanodine with high affinity. PMID:9124304

Pessah, I N; Molinski, T F; Meloy, T D; Wong, P; Buck, E D; Allen, P D; Mohr, F C; Mack, M M

1997-02-01

291

Single-crystal growth of superconducting Bi2Sr2CaCu2O8 using rotary crucibles  

NASA Astrophysics Data System (ADS)

Superconducting Bi2Sr2CaCu2O8 crystals were grown from mixtures of analytical grade Bi2O3, Sr(OH)2-8H2O, CaCO3, and CuO in stoichiometric amounts, using gold rotary crucibles. The effects of the composition of the melt, the cooling rate, and the kind of crucible employed on the growth of good 2212 single crystals were investigated using results of XRD and SEM. Forty percent of crystals as grown showed a superconducting transition at 90 K. The crystals were found to contain traces of Bi2Sr2CuO6, which could be eliminated by recrystallization.

Campa, J. A.; Gutierrez-Puebla, E.; Monge, M. A.; Rasines, I.; Ruiz-Valero, C.

1992-11-01

292

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

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) .

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

293

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

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 . 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) . PMID:22239480

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

2012-02-15

294

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

PubMed

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

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

2008-05-29

295

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

NASA Astrophysics Data System (ADS)

Electronic open-shell ground-state properties of selected alkali-metal-alkaline-earth-metal polar molecules are investigated. We determine potential energy curves of the 2?+ ground state at the coupled-cluster singles and doubles with partial triples (CCSD(T)) level of electron correlation. Calculated spectroscopic constants for the isotopes (23Na, 39K, 85Rb)-(40Ca, 88Sr) are compared with available theoretical and experimental results. The variation of the permanent dipole moment (PDM), average dipole polarizability, and polarizability anisotropy with internuclear distance is determined using finite-field perturbation theory at the CCSD(T) level. Owing to moderate PDM (KCa: 1.67 D, RbCa: 1.75 D, KSr: 1.27 D, RbSr: 1.41 D) and large polarizability anisotropy (KCa: 566 a.u., RbCa: 604 a.u., KSr: 574 a.u., RbSr: 615 a.u.), KCa, RbCa, KSr, and RbSr are potential candidates for alignment and orientation in combined intense laser and external static electric fields.

Gopakumar, Geetha; Abe, Minori; Hada, Masahiko; Kajita, Masatoshi

2014-06-01

296

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

PubMed

Electronic open-shell ground-state properties of selected alkali-metal-alkaline-earth-metal polar molecules are investigated. We determine potential energy curves of the (2)?(+) ground state at the coupled-cluster singles and doubles with partial triples (CCSD(T)) level of electron correlation. Calculated spectroscopic constants for the isotopes ((23)Na, (39)K, (85)Rb)-((40)Ca, (88)Sr) are compared with available theoretical and experimental results. The variation of the permanent dipole moment (PDM), average dipole polarizability, and polarizability anisotropy with internuclear distance is determined using finite-field perturbation theory at the CCSD(T) level. Owing to moderate PDM (KCa: 1.67 D, RbCa: 1.75 D, KSr: 1.27 D, RbSr: 1.41 D) and large polarizability anisotropy (KCa: 566 a.u., RbCa: 604 a.u., KSr: 574 a.u., RbSr: 615 a.u.), KCa, RbCa, KSr, and RbSr are potential candidates for alignment and orientation in combined intense laser and external static electric fields. PMID:24929384

Gopakumar, Geetha; Abe, Minori; Hada, Masahiko; Kajita, Masatoshi

2014-06-14

297

Copper-oxygen hybridization in Bi-Sr-Ca-Cu-O measured by magnetic-susceptibility anisotropy  

SciTech Connect

Anisotropic-magnetic-susceptibility measurements on single crystals of the high-temperature superconductor Bi-Sr-Ca-Cu-O (2:2:1:2) with {ital T}{sub {ital c}}{congruent}80 K are reported. The anisotropy is a measure of the degree of hybridization of the copper and oxygen orbitals.

Mehran, F.; McGuire, T.R.; Chandrashekhar, G.V. (IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (US))

1990-06-01

298

Effect of cooling rate on the transition temperature in Bi-Pb-Sr-Ca-Cu-O system.  

National Technical Information Service (NTIS)

The resistance and a.c. susceptibility measurement show that cooling rate of the cast-annealing samples in heat treatment process has some effect on the 110K superconducting phase in Bi-Pb-Sr-Ca-Cu-O system. Rapid quenching of the sample in air from 845 d...

Y. Wang J. Wang N. Wang X. Jiao G. Han

1989-01-01

299

Forming process of 110 K high-Tc phase in Bi-Pb-Sr-Ca-Cu-O system.  

National Technical Information Service (NTIS)

The effect of heat treatment on the forming process of the high-T(sub c) phase in the cast-annealing samples has been discussed. Experiments show that the high-T(sub c) phase is formed based on the low-T(sub c) phase. Adding Pb to Bi-Sr-Ca-Cu-O system can...

Y. Wang N. Wang X. Jiao J. Wang G. Han Guchang

1989-01-01

300

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

NASA Technical Reports Server (NTRS)

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.

Kaesche, Stefanie; Majewski, Peter; Aldinger, Fritz

1995-01-01

301

Hole doping by pressure on the 1111 pnictides CaFeAsF and SrFeAsF.  

PubMed

We determine the pressure phase diagram of the 1111 compounds CaFeAsF and SrFeAsF, up to 20?GPa and down to 4?K by electrical resistivity measurements and the change of structure up to 40?GPa at room temperature. The antiferromagnetic transition temperature, as determined by the derivative peak, shows a minimum at ~5?GPa (10?GPa) for the Ca (Sr) compound. For CaFeAsF, superconductivity appears at this minimum, coincident with the development of a previously reported monoclinic phase. For SrFeAsF, where the orthorhombic and the monoclinic phase were reported to coexist, superconductivity exists above P?1?GPa. Both phase diagrams can be scaled by a shift of ~10?GPa pressure at which the volume of SrFeAsF and that of CaFeAsF at ambient pressure coincide. The difference of our phase diagram with that of electron-doped 1111 samples is accounted for by hole doping under pressure, which we verified through electron band structure calculations. PMID:24675791

Freitas, Daniele C; Garbarino, Gastn; Weht, Ruben; Sow, Amadou; Zhu, Xiyu; Han, Fei; Cheng, Peng; Ju, Jing; Wen, Hai Hu; Nez-Regueiro, Manuel

2014-04-16

302

Hole doping by pressure on the 1111 pnictides CaFeAsF and SrFeAsF  

NASA Astrophysics Data System (ADS)

We determine the pressure phase diagram of the 1111 compounds CaFeAsF and SrFeAsF, up to 20?GPa and down to 4?K by electrical resistivity measurements and the change of structure up to 40?GPa at room temperature. The antiferromagnetic transition temperature, as determined by the derivative peak, shows a minimum at ~5?GPa (10?GPa) for the Ca (Sr) compound. For CaFeAsF, superconductivity appears at this minimum, coincident with the development of a previously reported monoclinic phase. For SrFeAsF, where the orthorhombic and the monoclinic phase were reported to coexist, superconductivity exists above P?1?GPa. Both phase diagrams can be scaled by a shift of ~10?GPa pressure at which the volume of SrFeAsF and that of CaFeAsF at ambient pressure coincide. The difference of our phase diagram with that of electron-doped 1111 samples is accounted for by hole doping under pressure, which we verified through electron band structure calculations.

Freitas, Daniele C.; Garbarino, Gastn; Weht, Ruben; Sow, Amadou; Zhu, Xiyu; Han, Fei; Cheng, Peng; Ju, Jing; Wen, Hai Hu; Nez-Regueiro, Manuel

2014-04-01

303

Composite Superconducting Wires Obtained by High-Rate Tinning in Molten Bi-Pb-Sr-Ca-Cu-O System.  

National Technical Information Service (NTIS)

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 fi...

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

1990-01-01

304

Relation Between Ca and Sr Transport Rates, as Determined Simultaneously in Isolated Segments of Vetch, Barley, and Pine Roots.  

National Technical Information Service (NTIS)

Root segments of vetch, barley, and pine were exposed to nutrient containing 85Sr and 45Ca tracers. Transport in both vetch and barley usually declined before an elapsed time of 24 hours unlike corn, which maintains its steady state beyond 24 hours. Pine ...

M. E. Hutchin B. E. Vaughan

1968-01-01

305

Superstructure of the Superconductor Bi2 Sr2 CaCu2 O8 by High Resolution Electron Microscopy.  

National Technical Information Service (NTIS)

The superstructure of the high Tc superconducting oxide Bi/sub 2/Sr/sub 2/CaCu/sub 2/0/sub 8/ has been studied by high resolution electron microscopy. Waves of distortion along the b-axis give an incommensurate superlattice slightly larger or smaller than...

E. A. Hewat J. J. Capponi C. Chaillout J. L. Hodeau M. Marezio

1988-01-01

306

Occurrence of a strontium hexaferrite field in the CaO-SrO-Fe2O3 system  

Microsoft Academic Search

The phase relations at 1100oC in the system CaO Fe2O3-7 SrO Fe2O3-Fe2o3 were determined by X-ray diffraction analysis and microscopical observation of polished sections of air quenched specimens. In particular, the boundaries of a homogeneous strontium hexaferrite field were determined by metallographic methods.

E. Lucchini; G. Slokar

1980-01-01

307

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

Microsoft Academic Search

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

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

1999-01-01

308

STM Studies of Near-Optimal Doped Bi_2Sr_2CaCu_2O_8 delta  

SciTech Connect

In this paper we summarize our STM studies of the density of electronic states in nearly optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8 + {delta}} in zero field. We report on the inhomogeneity of the gap structure, density of states modulations with four-lattice constant period, and coherence peak modulation.

Kapitulnik, Aharon

2010-04-05

309

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

PubMed

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

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

2012-03-12

310

Structural and electrical changes in NdSrNiO 4-? by substitute nickel with copper  

NASA Astrophysics Data System (ADS)

A novel series of the formula NdSrNi 1-xCu xO 4-? were synthesized for various values of x ranging from 0 to 1 in 1 atm of O 2 gas flow using conventional solid-state methods and were characterized by powder X-ray diffraction and electrical resistivity measurements. The compounds have been shown to adopt the K 2NiF 4-type structure. The oxygen stoichiometry of the compounds was determined from thermo-gravimetric analysis (TGA). An analysis of the micro-structure of the neodymium strontium nickel copper oxide is described. All the samples were semi-conducting from room temperature down to 77 K. The effect of Cu 2+ incorporation on the structural and electrical properties of NdSrNi 1-xCu xO 4-?, 0?x?1, are discussed in terms of Jahn-Teller distortion of the (Ni/Cu)O 6 octahedra and mixed valence character of copper.

Chaker, Hann; Roisnel, T.; Potel, M.; Hassen, R. Ben

2004-11-01

311

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

SciTech Connect

A variety of experimental techniques were utilized to examine the high temperature phase equilibria in the Bi-Sr-Ca-Cu-O-Ag system. Quenching studies were used to determine the liquid solubility of Ag in the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO{sub 2}). A liquid immiscibility region between oxide and Ag liquids in the 8--98 at% range was found above 900 C. Two eutectics were found in the Bi2212-Ag pseudobinary. On the oxide rich side, a eutectic exists at approximately 4 at% Ag. On the Ag rich side, a eutectic exists at approximately 98 at% Ag at a temperature of 15 C below the melting point of pure Ag. Six distinct solid phases were found to be in equilibrium with the partial melt within the Ag content and PO{sub 2} range studied. The stability of these solid phases were found to be highly sensitive to PO{sub 2}, and to a much lesser extent Ag content. High temperature x-ray diffraction (HTXRD) studies of this system are in conflict with these results. It is suggested that these discrepancies are due to experimental artifacts caused by the significant thermal gradients and lack of full bulk sampling which is inherent in conventional HTXRD designs. In part 2, a new furnace design compatible with synchrotron radiation sources is introduced to address these problems. This design allows for full bulk sampling in a low thermal gradient environment using Debye-Scherrer transmission geometry. Sample spinning is also introduced in the design to eliminate preferred orientation and incomplete powder averaging and allow for quantitative phase analysis and structural refinement. Studies on model systems are presented to demonstrate the capabilities for high resolution structural studies (Al{sub 2}O{sub 3}) and time resolved phase transformation studies (SrCO{sub 3}). Finally, the Bi2212 system is examined to confirm the quenching results of part 1, and to demonstrate the degree to which this new HTXRD design solves the problems associated with conventional designs.

Margulies, Lawrence

1999-11-08

312

The Expression of SR Calcium Transport ATPase and the Na +\\/Ca 2+Exchanger are Antithetically Regulated During Mouse Cardiac Development and in Hypo\\/hyperthyroidism  

Microsoft Academic Search

The mouse has been used extensively for generating transgenic animal models to study cardiovascular disease. Recently, a number of transgenic mouse models have been created to investigate the importance of sarcoplasmic reticulum (SR) Ca2+transport proteins in cardiac pathophysiology. However, the expression and regulation of cardiac SR Ca2+ATPase and other Ca2+transport proteins have not been studied in detail in the mouse.

Thomas D Reed; Gopal J Babu; Yong Ji; Alla Zilberman; Mark Ver Heyen; Frank Wuytack; Muthu Periasamy

2000-01-01

313

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

PubMed Central

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.

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

2011-01-01

314

Ca-Sr-Ga-Nb mixed oxide system for high temperature superconductor substrate applications  

NASA Astrophysics Data System (ADS)

Twin-free crystals with relatively low melting temperatures are desirable as substrates for high temperature superconductor (HTSC) oxide substrate materials. In the selection of new oxide substrate compositions, special requirements (e.g. suitable dielectric properties for microwave application and perovskite structure with good lattice matching with YBa2Cu3O(7 - delta) were considered. In this study the calcium-strontium gallate-niobate (CSGN) system has been investigated in both ceramic and single crystal samples, focusing on their crystal growth. The CSGN compositions were formed by mixing orthorhombic calcium gallate-niobate (CGN) and cubic strontium gallate-niobate (SGN) complex perovskites. CGN-excess mixtures do not create a single phase, as opposed to SGN-excess compositions, where single phase solid solutions are formed. The SGN-excess compositions can produce twin-free CSGN single crystals, which have excellent room temperature dielectric loss (tan delta less thanEQ 3 x 10(exp - 4)) and reasonably low dielectric constant (K = 41) values at 100 kHz. The growth temperature for a 50 mol% SGN starting composition (CSGN1) was about 1600deg C, but for a 65 mol% SGN concentration (CSGN2) it increased to 1750deg C. A lattice parameter a = 3.939 angstrom was obtained for the CSGN1 crystal increasing with SGN concentration. A significant drawback was observed for the Ca-Sr-Ga-Nb oxide system: the effective distribution coefficient of Ca(sup 2 + ) is very small (k(sub eff)(Ca(sup 2 + )) approximately = 0.4). This can cause crystal growth difficulties due to constitutional supercooling phenomena.

Erdei, S.; Cross, L. E.; Ainger, F. W.; Bhalla, A.

1994-05-01

315

Ordered Substitution of Iron for Copper in the Tetragonal Perovskite La 6.4Sr 1.6Cu 8O 20  

NASA Astrophysics Data System (ADS)

Two series of iron-substituted cuprates with the tetragonal La 6.4Sr 1.6Cu 8O 20 oxygen deficient perovskite structure have been isolated: La 6.4Sr 1.6Cu 8- xFe xO 20 (0 ? x ? 1.20) and La 6.4- xSr 1.6+ x Cu 8- xFe xO 20 (0 ? x ? 2). The XRD and Mssbauer studies show that they correspond to a preferential substitution of Fe(III) for copper in the octahedral sites of the structure. In fact the ideal structure can be described as 90-oriented "123" copper ribbons interconnected with [FeO 3] ? rows of FeO 6 octahedra. The transport properties of these phases show a transition from a metallic to a semiconducting state. The difference in behavior between the La 6.4Sr 1.6Cu 8- xFe xO 20 series and the La 6.4- xSr 1.6+ xCU 8- xFe xO 20 series is interpreted on the basis of hole carrier density introduced by Cu(III) and of the trapping of carriers by Fe(III) species. The possibility of anisotropic transport properties with a metallic conductivity along c is discussed.

Genouel, R.; Michel, C.; Nguyen, N.; Hervieu, M.; Raveau, B.

1995-03-01

316

First principles calculations of hyperfine parameters on the Ca manganite with substitutional Cd-modeling of a PAC experiment  

NASA Astrophysics Data System (ADS)

The APW+lo (augmented plane waves+local orbitals) method of density functional theory, as implemented in the Wien2k code, is applied to calculate the electric field gradient of manganites. We report the first principles calculations on CaMnO3, and modeling of a perturbed angular correlation experiment with implanted Cd111m isotope. To model the experiment we additionally calculate in CaCdxMnO3, where we substitute Cd at the Ca site. Increasing Cd dilution is done with the use of supercells. We find that the experimental CaMnO3 low-temperature value Vzz?610-21 V/m2 is reproduced, when optimizing internal parameters. The analysis of the EFG tensor at the Ca atoms, with different electric field gradients at inequivalent positions, reveals that the convergence of the calculations is obtained.

Gonalves, J. N.; Haas, H.; Lopes, A. M. L.; Amaral, V. S.; Correia, J. G.

2010-05-01

317

Local work function measurement on Bi 2Sr 2CaCu 2O y single crystal with STM  

NASA Astrophysics Data System (ADS)

Bi 2Sr 2CaCu 2O y was studied by the local work function measurement with STM. The modulation with the same periodicity as the superstructure on BiO plane was observed on the work function images. The protrude lines in STM image have lower work function, which supports the model that part of the Bi sites are replaced by Sr atoms in the Bi-deficient bands. This work also suggests that the local work function measurement with STM can provide some information for studying the distribution of charges in high- Tc superconducting oxides.

Jia, J. F.; Hasegawa, Y.; Sakurai, T.; Zhang, H.

1998-02-01

318

Effects of antimony substitution on bismuth based superconductors  

NASA Technical Reports Server (NTRS)

The effect of Sb substitution and simultaneous substitution of Pb and Sb on the superconducting transition temperatures in the BiSrCaCuO system is investigated. The 2:2:2:3 phase is of particular interest since any small increase in the transition temperature could be of great interest. More that 90 different samples were prepared based on 2:2:2:3 stoichiometry in the BiSrCaCuO system. After this preliminary attempt, four different families of samples were investigated. In the first family of samples, Bi was substituted by Sb to form Bi(1.9)Sb(0.1)Sr2Ca2Cu3O(y). The second group of samples were prepared by simultaneous addition of Pb and Sb with nominal composition Bi(1.8)Pb(0.1)Sb(0.1)Sr2Ca2Cu3O(y). The third and fourth groups were prepared to determine the effect created when the Pb concentration is increased with the nominal compositions being Bi(1.7)Pb(0.1)Sr2Ca2Cu3O(y) and Bi(1.6)Sb(0.1)Sr2Ca2Cu3O(y). The results of these investigations are presented with a discussion.

Barrientos, Alfonso

1990-01-01

319

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

PubMed Central

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 CaSRHEK 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.

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

2010-01-01

320

Resistive transitions under high magnetic fields in Bi2Sr2CaCu2Oy/Bi2Sr2CuOx multilayer thin films  

NASA Astrophysics Data System (ADS)

This paper is a report on the results of a study done on the superconductive transitions of Bi2Sr2CaCu2Oy/Bi2Sr2CuOx (BSCCO/BSCO) multilayer thin films in magnetic fields parallel or perpendicular to the films, which were prepared using a multitarget rf magnetron sputtering technique. In the multilayers with BSCCO (a superconductor) of constant nominal layer thickness of 47 , the resistive transition showed broadening and reduction of Tc with an increase of the BSCO (a nonsuperconductor) layer thickness from 36 to 144 . The resistive transition showed a slight broadening, even under the aligned magnetic field parallel to the Cu-O planes. This result suggests that the superconductive layers are coupled through BSCO layers, and that the interlayer coupling was induced by the proximity effect.

Odagawa, A.; Setsune, K.; Matsushima, T.; Fujita, T.

1993-11-01

321

Site symmetry and crystal field splittings of Ce3+ in LiLuF4 and LiSr0.8Ca0.2AlF6  

NASA Astrophysics Data System (ADS)

Electron paramagnetic resonance (EPR) spectra of Ce3+ in LiLuF 4 (LLF) and LiSr0.8Ca0.2AlF6 (LSCAF) observed at low temperatures (<20 K) show that the Ce3+ centers have tetragonal and pseudo-trigonal symmetry with (g(parallel to) , g(perpendicular to) )=(2.751, 1.467) and (2.14, 0.80), respectively. The EPR lines of Ce3+ in LSCAF are inhomogeneously broadened by different Ce3+ configurations which correspond to the random occupation of the second nearest neighbor cation sites by Ca2+ and Sr2+ and/or charge compensators. These EPR results indicate that the Ce3+ centers in LLF and LSCAF are associated with substitution of Ce3+ for Lu3+ with eight-fold coordination and Sr2+/Ca2+ with six-fold coordination, respectively. Fourier transform infrared absorption has been used to measure transitions between the F-2(5/2) ground state and the F-2(7/2) multiplet of Ce3+ in LLF at 10 K. The optical absorption and luminescence of Ce3+ :LLF and Ce3+ :LSCAF in the UV range are strongly polarized. The energy levels and polarization dependence of the optical transitions can be accounted for in terms of the crystal field potential experienced by the Ce3+ ions under the action of the different point group symmetries.

Yamaga, M.; Inoue, T.; Yabashi, S.; Honda, M.; Wells, J. P. R.; Shimamura, K.; Fukuda, T.

322

The incongruent melting and melt textured solidification process of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}  

SciTech Connect

The melting and solidification was studied using in-situ high temperature XRD from melting point to 900{degree}C in 0.2, 0.1, 0.02 atm O{sub 2} and pure N{sub 2}. The incongruent melting point of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} was lowered by decreasing the partial O{sub 2} pressure from 870C (in .2 atm O{sub 2}) to 830C (in pure N{sub 2} atmosphere). As temperature was increased the incongruent melting of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} followed a phase sequence in which (Ca, Sr)CuO{sub 2} {r_arrow} (Ca, Sr)CuO{sub 2} {r_arrow} (Ca,Sr)O occur in presence of Bi-rich liquid. At 900C, the only crystalline phase present in the melt was (Ca,Sr)O. This phase sequence remained the same for all four different partial O{sub 2} pressures. During the solidification of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}, from 10C below the melting point to 760C, the major phases that form depend on the partial O{sub 2} pressure. As partial O{sub 2} pressures was lowered from 0.2 to 0 atm, the major second phase formation out of the melt follows the sequence of (Ca, Sr)CuO{sub 2} {r_arrow} (Ca, Sr)CuO{sub 2} {r_arrow} (Ca,Sr)O respectively. At 0.1 Atm partial O{sub 2} pressure and below, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} solidified out of the melt; at 0.2 atm of O{sub 2} Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 6} forms instead.

Polonka, J.

1993-09-01

323

Efficient red phosphor double-perovskite Ca3WO6 with A-site substitution of Eu3+.  

PubMed

Luminescent properties of Eu(3+) activated double perovskite structure Ca3WO6 were investigated. It emits an ideal red color centered at the wavelength of 618 nm with suitable excitation from f-f transitions of Eu(3+) ions (360-550 nm) matching the near ultraviolet and blue LEDs. Charge compensation effect of Li(+), Na(+), and K(+) was investigated, and K(+) proved to be the best. The co-doping ion K(+) has a great effect on the lattice distortion of the host matrix Ca3WO6, which facilitates the red emission of Eu(3+). The substitution site for Ca in Ca3WO6 was analyzed in detail by Raman spectra and calculation results. A-site substitution is responsible for the red emission of Eu(3+) activated Ca3WO6. The integrated emission intensity of optimal Ca3WO6:K(+),Eu(3+) excited at 395 nm is about 3.5 times greater than that of Y2O2S:Eu(3+) commercial phosphors, which makes it a promising red phosphor for white LEDs. PMID:23897245

Zhao, Xin; Wang, Jiajia; Fan, Li; Ding, Yufeng; Li, Zhaosheng; Yu, Tao; Zou, Zhigang

2013-10-01

324

Structural and Superconducting Properties of Bi4Sr3Ca3CuyOw and Bi4Sr3Ca3Cu4-xMxOz (M=Fe, cr and Mn) Glass Ceramics  

NASA Astrophysics Data System (ADS)

The synthesis of glass ceramic superconductors of Bi4Sr3Ca3CuyOw (3?y?6) and Bi4Sr3Ca3Cu4-xMxOz (M=Fe, Cr, Mn and 0?x?0.2) compositions is reported. The 4334 sample is found to be the optimum composition to obtain Bi-2212 superconducting phase. X ray diffraction studies indicate that the solid solubility of 3d metal ions in the 4334 system is limited to x=0.05 in the case of Fe and Cr and x=0.1 in the case of Mn. A systematic decrease in Tc with increasing dopant concentration is observed from resistivity as well as AC susceptibility measurements. Tc depression rates, however, are found to differ for different dopants. XRD studies indicate the decrease in c lattice parameter with increase in dopant content. The systematics of the superconducting transition is discussed in view of Tc depression rates.

Zacharias, E.; Singh, R.

325

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

326

Structural and dielectric behavior of pulsed laser ablated Sr 0.6Ca 0.4TiO 3 thin film and asymmetric multilayer of SrTiO 3 and CaTiO 3  

NASA Astrophysics Data System (ADS)

Homogeneous thin films of Sr 0.6Ca 0.4TiO 3 (SCT40) and asymmetric multilayer of SrTiO 3 (STO) and CaTiO 3 (CTO) were fabricated on Pt/Ti/SiO 2/Si substrates by using pulsed laser deposition technique. The electrical behavior of films was observed within a temperature range of 153 K-373 K. A feeble dielectric peak of SCT40 thin film at 273 K is justified as paraelectric to antiferroelectric phase transition. Moreover, the Curie-Weiss temperature, determined from the ?'( T) data above the transition temperature is found to be negative. Using Landau theory, the negative Curie-Weiss temperature is interpreted in terms of an antiferroelectric transition. The asymmetric multilayer exhibits a broad dielectric peak at 273 K, and is attributed to interdiffusion at several interfaces of multilayer. The average dielectric constants for homogeneous Sr 0.6Ca 0.4TiO 3 films (650) and asymmetric multilayered films (350) at room temperature are recognized as a consequence of grain size effect. Small frequency dispersion in the real part of the dielectric constants and relatively low dielectric losses for both cases ensure high quality of the films applicable for next generation integrated devices.

Chakraborty, Pradip; Choudhury, Palash Roy; Krupanidhi, S. B.

2011-12-01

327

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

NASA Astrophysics Data System (ADS)

The decay of 40K to 40Ar forms the basis of the potassium-argon dating method, although only one out of every 10 parent atoms decays to daughter 40Ar. The other 90% decay to 40Ca giving, in principle, the 40K-40Ca decay system great potential for dating samples with high K/Ca. This method, however, has not been utilized as an ion-microprobe-based geochronometer, largely because these isotopes require a very high mass resolving power (MRP) of ~25k for full separation. We found that limiting secondary ion transmission in our ims1270 ion microprobe to ~20% permits sufficient separation of 40K from 40Ca (MRP? 20k) to permit isotope ratio analysis, albeit with 40Ca+ on the shoulder of the more intense 40K+ peak. A pegmatitic muscovite from Jack Hills (K-Ca age = 2.54 Ga; Fletcher et al., Chem. Geol. 138, 289) yields ~104 cps of both 40K+ and 40Ca+ with a 15 ?m primary spot size and O- beam current of 10 nA. The 40Ca+ signal is >90% radiogenic and reflects a common Ca content of ? 100 ppm. However, application of the relative sensitivity factor (RSF) calculated from the Jack Hills muscovite to unknowns yields relatively high age dispersion, perhaps related to the incompletely separated mass interferences. Theorizing that the noble gas electronic structure of K+ would likely resist further electron loss, we investigated an alternative approach involving analysis of Ca++/K++. The double-plus method provides an important advantage in that K++ species are suppressed by a factor of ~103 relative to K+, thereby effectively removing 40K++ from the spectrum at m/e? 20 and leaving 40Ca++ free from any significant interferences at an MRP? 4k. Measurement of the much more abundant 39K++ then permits 40Ca++/40K++ to be calculated from the known 39K/40K ratio. We applied this approach to Precambrian muscovite samples obtaining ages similar to, but generally younger than, their associated 40Ar/39Ar ages. This could reflect a minor matrix effect or a lower intrinsic retentivity of 40Ca* relative to 40Ar* in white micas. This approach offers the potential to develop a branched-decay thermochronometer (K-Ca-Ar) permitting simultaneous solution of temperature-time history from ?m-scale isotopic variations. A further advantage is that even low resolution SIMS instruments (e.g., ims7f) can utilize the double-plus method. Initial investigations using the same double-plus approach for Rb-Sr dating show promise. While resolving 87Rb+ from 87Sr+ requires an MRP of ~290k, unattainable using any current SIMS instrument, 87Rb++ is so strongly suppressed that determination of 87Sr++ is possible with minor peak stripping. 87Rb/86Sr can be determined either from 85Rb+/88Sr+ at MRP? 8k or by the use of energy filtering. In addition to micas, these approaches may be applicable to any mineral systems enriched in alkali metals relative to alkaline earths, such as alkali feldspars, feldspathoids, and alkaline halides.

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

2009-12-01

328

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)

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.

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

2013-12-01

329

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

USGS Publications Warehouse

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 150180 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.

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

2013-01-01

330

Luminescence and energy transfer in Eu2+, Mn2+ co-doped Ca2SrNaLa(PO4)3F  

NASA Astrophysics Data System (ADS)

A new compound Ca2SrNaLa(PO4)3F, isotypic with hexagonal Ca(Sr,Na,Ca)(Ca,Sr,Ce)3(PO4)3F, is reported. Its cell parameters have been determined from X-ray powder diffraction data. Crystallization occurs in the hexagonal space group P63 (No. 173) with a = 9.515(1) , c = 7.028(1) , and Z = 2. Eu2+ and Mn2+ activated Ca2SrNaLa(PO4)3F phosphors have been prepared. The energy transfer of Eu2+ ? Mn2+ has been investigated. The resonant type energy transfer from Eu2+ to Mn2+ has been demonstrated, and the energy transfer efficiency has also been calculated according to their PL decay curves. A color-tunable emission in Ca2SrNaLa(PO4)3F phosphors can be realized by Eu2+ ? Mn2+ energy transfer. White light can be achieved in a single-phased Ca2SrNaLa(PO4)3F host by co-doping Eu2+ and Mn2+ with CIE (0.32, 0.31). Our results demonstrate that the potential application of these phosphors in solid-state lighting and (or) other areas.

Shanshan, Hu; Wanjun, Tang

2013-12-01

331

Oxygen nonstoichiometry and the thermodynamic properties of manganites Ca1 - x - y Sr x La y MnO3 - ?  

NASA Astrophysics Data System (ADS)

The content of oxygen in Ca0.6 - y Sr0.4La y MnO3 - ?, where y = 0 and 0.05, was determined by coulometric titration over the temperature range 650-950C at oxygen partial pressure in the gas phase varied from 10-4 to 1 atm. The results were used to calculate the partial molar enthalpy, ? bar H O(?), and entropy, ? bar S O(?), of oxygen in manganites. Changes in the ? bar H O(?) and ? bar S O(?) dependences caused by the introduction of lanthanum are evidence of the formation of local clusters of the double perovskite type in the Ca0.6Sr0.4MnO3 - ? matrix.

Leonidova, E. I.; Markov, A. A.; Patrakeev, M. V.; Leonidov, I. A.; Kozhevnikov, V. L.

2011-03-01

332

Evolution of the thermoelectric performance in low Ca-doped layered cobaltite Bi2Sr2Co2Oy  

NASA Astrophysics Data System (ADS)

We have synthesized a series of layered cobaltite Bi2Sr2-xCaxCo2Oy (0?x?0.3). Reduced resistivity was observed with x?0.2 due to the possible chemical pressure induced charge transfer between the Bi2Sr2O4 layer and CoO2 layer. Enhanced thermoelectric power S was also observed in the Ca-doped samples with the largest S as for x=0.2. The variation of S(T) could reflect the change of electronic correlation or the modification of local density of states and band structure near the Fermi energy. In addition, magnetic measurements show that the samples with x=0.0 exhibit abnormal and abrupt changes, revealing a possible thermally excited spin-state transition. It is found that the thermoelectric performance is obviously enhanced by the low Ca-doping.

Yin, L. H.; Ang, R.; Zhao, B. C.; Huang, Y. N.; Liu, Y.; Tan, S. G.; Song, W. H.; Sun, Y. P.

2013-03-01

333

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

NASA Astrophysics Data System (ADS)

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.

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

2008-04-01

334

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

NASA Astrophysics Data System (ADS)

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.

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

2012-06-01

335

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

NASA Astrophysics Data System (ADS)

Tropical sea surface temperature (SST) has been implicated as a driver of climate changes during the Medieval Climate Anomaly (MCA, 950-1300 A.D.) but little data exists from the tropical oceans during this time period. We collected three modern and seven sub-fossil Diploria strigosa coral colonies from an overwash deposit on Anegada, British Virgin Islands (18.73 N, 63.33 W) in order to reconstruct climate in the northeastern Caribbean and Tropical North Atlantic during the MCA. The first step in our reconstruction was to verify the climate signal from this species at this site. We sub-sampled the modern corals along thecal walls with an average sampling resolution of 11-13 samples per year. Sr/Ca ratios measured in the sub-samples were calibrated to temperature using three different calibration techniques (ordinary least squares, reduced major axis, and weighted least squares (WLS)) on the monthly data that includes the seasonal cycles and on the monthly anomaly data. WLS regression accounts for unequal errors in the x and y terms, so we consider it the most robust technique. The WLS regression slope between gridded SST and coral Sr/Ca is similar to the previous two calibrations of this species. Mean Sr/Ca for each of the three modern corals is 8.993 0.004 mmol/mol, 9.127 0.003 mmol/mol, and 8.960 0.007 mmol/mol. These straddle the mean Diploria strigosa Sr/Ca found by Giry et al., (2010), 9.080 mmol/mol, at a site with nearly the same mean SST as Anegada (27.4 C vs. 27.5 C). The climatological seasonal cycles for SST derived from the modern corals are statistically indistinguishable from the seasonal cycles in the instrumental SST data. The coral-based seasonal cycles have ranges of 2.70 0.31 C, 2.65 0.08 C and 2.71 0.53 C. These results indicate that this calibration can be applied to our sub-fossil coral data. We applied the WLS calibration to monthly-resolution Sr/Ca data from multiple sub-fossil corals dating to the medieval period with initial U-series dates near the top of the cores ranging from 1277 5 A.D. to 1327 5 A.D. Initial Sr/Ca results from the first sub-fossil coral have a seasonal range of 2.65 0.27 C when converted to temperature units with our modern calibration, indicating no significant change from modern times. However, the mean Sr/Ca for this coral is very high (9.388 mmol/mol) compared to the modern corals. We explore the potential causes for this discrepancy in our study. Because reconstructing the mean SST during the Medieval Climate Anomaly may be difficult without temporal overlap with modern corals, our focus is on interannual variability. The coral Sr/Ca based monthly SST anomalies for both modern and sub-fossil corals have larger interannual variances than the instrumental record. One explanation for this is that the SSTs derived from sub-fossil corals are local data for which one expects larger variances than the instrumental data averaged over a 2 x 2 grid. This species shows great promise for future paleoclimate reconstructions.

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

2013-12-01

336

Magnetic transition in 122 pnictides XFe2As2 (X=Ca, Sr) probed by hyperfine interaction of 66Ga  

NASA Astrophysics Data System (ADS)

Employing the time differential perturbed angular distribution (TDPAD) method we have studied the temperature dependence of the magnetic hyperfine field, Bhf for 66Ga in 122 type pnictides, XFe2As2 (X = Ca and Sr). The saturation hyperfine field, Bhf (0) of Ga in Ca(Sr)Fe2As2 have been observed to be 16.2 kG and 22 kG respectively. Scaled by the hyperfine field of 66Ga in ferromagnetic elements Fe, Co and Ni, our Bhf (0) data indicate small local moments on Fe, consistent with itinerant type magnetism of these materials. The observed temperature dependence of the hyperfine field data suggests second order type magnetic phase transition with a critical exponent ??0.22(3) indicating quasi-two dimensional magnetic ordering, possibly due to canting of Fe moments out of the ab plane.

Mishra, S. N.; Mohanta, S. K.; Davane, S. M.; Kumar, Neeraj; Thamizhavel, A.

2014-01-01

337

Phase coherence and Josephson plasma in Bi 2Sr 2CaCu 2O 8+?  

NASA Astrophysics Data System (ADS)

The recently discovered Josephson plasma phenomena in layered high- Tc superconductors have opened possibilities for testing fundamental ideas of physics of high- Tc superconductivity as well as for the device applications at high frequencies above 100 GHz. The observation of Josephson plasma resonance manifests the existence of a series stack of equivalent weak Josephson junctions between CuO 2 layers in Bi 2Sr 2CaCu 2O 8+?, through which a Cooper pair can tunnel with phase coherence. This unique situation brings the superconducting plasma frequency into a microwave frequency region, simply because the number of Cooper pairs participating in plasma phenomena is greatly reduced by the restricted tunneling probability of Cooper pairs. It is known that two collective excitation modes, longitudinal and transverse modes, can exist in this case. Using a different dispersion relation between two modes we were able to separate two modes experimentally for the first time. Since the plasma resonance is the consequence of phase coherence between superconducting layers, the dynamical nature of the vortex state can in principle be studied by this technique. The results of the vortex correlation observed by the Josephson plasma resonance with and without correlated disorder is discussed.

Kazuo Kadowaki; Itsuhiro Kakeya; Koichi Kindo; Saburo Takahashi; Tomio Koyama; Masashi Tachiki

1997-12-01

338

EPR study of doped (Sr,Ca) 10Cu 17O 29-type single crystals  

NASA Astrophysics Data System (ADS)

We report on electron paramagnetic resonance (EPR) measurements on the S= {1}/{2} quasi-one-dimensional system (Sr,Ca) 10Cu 17O 29, doped with Y, Bi, Pb and Al, which has simple chains and two-leg ladder chains of copper ions. A very broad absorption line, coming from the ladder chains, dominates near room temperature. The EPR signals observed below room temperature mainly come from the simple (dimerized) chains. A detailed analysis of the temperature dependencies of the resonance field, line width and intensity of EPR signal is presented. EPR spectra of Cu 2+ ions located in chains are described in terms of Wannier excitons. It is also found that at low temperatures the EPR line experiences a sharp broadening and shifts to the lower field region. These findings are discussed by taking into account two different mechanisms: the magnetic dipole interactions among short-range ordered Cu 2+ spins in the chains and the exchange interaction between Cu 2+ ions located in chains and holes (bottleneck effect).

Mosiniewicz-Szablewska, E.; Szymczak, H.; Baran, M.; Szymczak, R.; ?wi ?tek, K.; Leonyuk, L.; Babonas, G. J.

2001-01-01

339

Characterization of Bi2Sr2Ca1Cu2O8  

NASA Astrophysics Data System (ADS)

The electronic structure of the high temperature superconductor Bi2Sr2Ca1Cu2O8+x is determined from single crystal samples using photoelectron spectroscopy and polarization dependent near edge absorption spectroscopy. The valence band exhibits at O2p, Cu3d peak at 3.5 eV below the Fermi level EF. The photoemission intensity at EF is higher than in the other high temperature superconductors. Also, the peak at EF-9 eV, previously associated with carbonate, is absent. A resonant Cu3d8 satellite is seen at EF-12.6 eV, giving a hole-hole repulsion U=5.6 eV at the Cu site. The O1s edge exhibits a peak at threshold, h?=528.2 eV, corresponding to O2p holes at EF. This peak is excited only by the component of the electric field vector in the ab-plane. Using a dipole selection rules for the O1s-O2p transition it is concluded that the oxygen holes have px,y character, with x,y in the CuO planes.

Himpsel, F. J.; Chandrashekhar, G. V.; Taleb-Ibrahimi, A.; McLean, A. B.; Shafer, M. W.

1989-02-01

340

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

NASA Technical Reports Server (NTRS)

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

Bansal, Narottam P.

1989-01-01

341

Electronic structure of A2CrSbO6 [A=Sr, Ca]: Ab-initio study  

NASA Astrophysics Data System (ADS)

First principles calculations have been performed to study the electronic structure and magnetic properties of Cr-based double perovskite oxides Sr2CrSbO6 and Ca2CrSbO6 using full potential linearized augmented plane wave method under generalized gradient approximation (GGA) scheme. In our calculation, we have applied onsite Coulomb potential U at Cr site. The density of states (DOS) of Sr2CrSbO6 has been studied in three different crystal structures. Due to the different crystal symmetry of Sr2CrSbO6 at different temperatures, the DOS spectra differ from one another near the Fermi level. The insulating ground states have been obtained from GGA+U calculation for both the materials. It has been observed from DOS spectra that oxygen 2p-derived states hybridize strongly with Cr-d states and this hybridization plays an important role in the magnetic properties. The calculated magnetic moments for Cr are found to be 2.65, 2.60 and 2.72 ?B for monoclinic, tetragonal, cubic phases of Sr2CrSbO6, respectively and 2.68 ?B for Ca2CrSbO6. The obtained magnetic moments suggest the 3+ states of Cr (3d3) in these oxides.

Dutta, Alo; Sinha, T. P.

2013-02-01

342

Mssbauer Study on the Ordered Double Perovskite A2FeReO6 (A = Ca, Sr)  

Microsoft Academic Search

57Fe Mssbauer study on the ordered double perovskite A2FeReO6 (A = Ca, Sr) has been conducted. Fe ions are in 2.5+ states that correspond to the hybridized state of 3d t2g down-spin electrons with Re5+ 5d t2g down-spin electrons. The orbital effect due to this seems to be absent. On the metal-insulator transition of Ca2FeReO6 specimen, slight change of the

Shin Nakamura; Midori Tanaka; Hisato Kato; Yoshinori Tokura

2003-01-01

343

Selective etching of habit faces of ferroelectric Ca 2 Sr(C 2 H 5 CO 2 ) 6 crystals  

Microsoft Academic Search

Crystallographically oriented etch traces produced by selective etchant on (111) and (110) habit faces of dicalcium strontium\\u000a propionate [Ca2Sr(C2H5CO2)6] crystals are attributed to the growth traces nucleated during the superficial growth of crystal. This view is supported\\u000a by the absence of such etch traces on seized habit faces and from the observations of layer structure on the bottom faces.\\u000a Mother

R M Chaudhari; R K Rishnakumar

1988-01-01

344

Excitation of Josephson plasmon in the vortex state of Bi 2Sr 2CaCu 2O 8+?  

NASA Astrophysics Data System (ADS)

Josephson plasma excitation of Bi 2Sr 2CaCu 2O 8+? in parallel magnetic fields is studied by angular alignment with ?0.02 precision. A disappearance of the resonance has been found for angles within ? ? 0.2 (? is an angle between the field and the CuO 2-plane). The origin of the phenomenon is discussed in terms of the Josephson plasma oscillation and Josephson vortex oscillation modes.

Matsuda, Yuji; Gaifullin, Marat B.; Kosugi, Makoto; Kumagai, Ken-ichi; Hirata, Kazuto

1997-12-01

345

Fabrication of spherical CaOSrOZnOSiO 2 particles by solgel processing  

Microsoft Academic Search

This study was concerned with the fabrication of ceramic CaOSrOZnOSiO2 spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from\\u000a these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit\\u000a the calcification of hydroxyapatite in the body. The glass phase of GPCs require

Ill Yong Kim; Mark R. Towler; Anthony Wren; Chikara Ohtsuki

2009-01-01

346

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

SciTech Connect

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

Bhatt, Himal, E-mail: himalphy@gmail.co [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Bahadur, J. [Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Deo, M.N. [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Ramanathan, S. [Materials Processing Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Pandey, K.K. [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Sen, D.; Mazumder, S. [Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India); Sharma, Surinder M. [High Pressure and Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)

2011-01-15

347

Linear and non-linear flux dynamics in multilayered Bi2Sr2CaCu2Ox single crystals  

Microsoft Academic Search

Analytic solutions for excitations in the anisotropic, multilayered high-Tc superconductor of the Bi2Sr2CaCu2Ox-type are discussed. Understanding such excitations is important as a diagnostic tool for the experimental investigation of intrinsic materials properties, as well as being a basis for making devices. The linear plasma resonance is derived theoretically using the inductive coupling model. The eigenmodes of the plasma oscillation are

N. F. Pedersen

2002-01-01

348

Transparency of the ab Planes of Bi2Sr2CaCu2O8+delta to Magnetic Fields  

Microsoft Academic Search

A sample composed of many Bi2Sr2CaCu2O8+delta single crystals was cooled to 2 K in a magnetic field of 100 G at 45 from the c axis. Muon-spin-rotation measurements were made for which the polarization was initially approximately in the ab plane. The time dependent polarization components along this initial direction and along the c axis were obtained. Cosine transforms of

W. J. Kossler; Y. Dai; K. G. Petzinger; A. J. Greer; D. Ll. Williams; E. Koster; D. R. Harshman; D. B. Mitzi

1998-01-01

349

Resistive switching behaviors in Bi2Sr2CaCu2O8+d (Bi2212) stacks  

Microsoft Academic Search

A coupled stacked Josephson junctions (SJJs) with completely perforated holes of 0.2 mum 0.4 mum in high-Tc superconducting Bi2Sr2CaCu2O8+d (Bi-2212) were fabricated using a 3D focused ion beam etching method. We investigated external field angle thetai dependence of junction resistance Rj at various magnetic fields and temperatures. When a constant external magnetic fields He value of 1 T and

Sang-Jae Kim

2011-01-01

350

Enhancement of transport critical current densities in Bi2Sr2Ca2Cu3Ox tapes by fission tracks  

Microsoft Academic Search

Bi2Sr2Ca2Cu3Ox (Bi-2223) tapes were processed by the standard powder-in-tube technique, but small amounts of UO4 were added prior to processing. Both U-doped and undoped tapes were subsequently exposed to a reactor spectrum of neutrons. Whereas the undoped materials show moderate enhancements of the critical current densities Jc due to the pinning action of the fast-neutron-induced collision cascades, Jc in the

G. W. Schulz; C. Klein; H. W. Weber; S. Moss; R. Zeng; S. X. Dou; R. Sawh; Y. Ren; R. Weinstein

1998-01-01

351

Superconducting bi-ca-sr-cu-o fibers grown by the laser-heated pedestal growth method.  

PubMed

Superconducting fibers of several compositions including the nominal composition Bi(2)CaSrCu(2)O(8) have been grown by means of the laser-heated pedestal growth method. The influence of starting composition and growth conditions on structure and superconducting properties is discussed. The a-b planes of the material are parallel to the fiber axis (along the growth direction), providing the ideal condition for conduction along the copper-oxygen planes. PMID:17745220

Feigelson, R S; Gazit, D; Fork, D K; Geballe, T H

1988-06-17

352

Microwave dielectric properties of scheelite (A = Ca, Sr, Ba) and wolframite (A = Mg, Zn, Mn) AMoO 4 compounds  

Microsoft Academic Search

The microwave dielectric properties of scheelite (A=Ca, Sr, Ba) and wolframite (A=Mg, Mn, Zn) AMoO4 compounds and their relations with structure have been examined using a network analyzer and X-ray powder diffraction. The Mo ion polarizability has been also investigated from AMoO4 compounds using a least square refinement technique in conjunction with the ClausiusMosotti equation. It was found that dielectric

Geun-Kyu Choi; Jeong-Ryeol Kim; Sung Hun Yoon; Kug Sun Hong

2007-01-01

353

Eu2+-Activated CaSrSiO4: a New Red-Emitting Oxide Phosphor for White-Light-Emitting Diodes  

NASA Astrophysics Data System (ADS)

Ca1-xSr1-xEu2xSiO4 (CaSrSiO4:Eu2+) phosphors were prepared by a novel aqueous solution technique using propylene glycol-modified silane (PGMS), combined with a freeze-drying process. The precursors were heat-treated under a reducing atmosphere with BaCl2 flux. X-ray diffraction indicated that the obtained phosphors exhibited an ?'-CaSrSiO4 structure. The wavelength at the phosphors' maximum emission was systematically shifted beyond 600 nm as the Eu2+ concentration was increased. The corresponding excitation spectra were extended to the visible light region (400--500 nm) with increasing Eu2+ concentration. These results implied that CaSrSiO4:Eu2+ is a red-emitting phosphor excited by near-UV and blue-light-emitting diodes.

Tezuka, Satoko; Sato, Yasushi; Komukai, Tetsufumi; Takatsuka, Yuji; Kato, Hideki; Kakihana, Masato

2013-07-01

354

Ab initio study of ground and excited states of 6Li40Ca and 6Li88Sr molecules.  

PubMed

We present quantum-chemical calculations for the ground and some low-lying excited states of isolated LiCa and LiSr molecules using multi-state complete active space second-order perturbation theory (MS-CASPT2). The potential energy curves (PECs) and their corresponding spectroscopic constants, obtained at the spin-free (SF) and spin-orbit (SO) levels, agree well with available experimental values. Our SO-MS-CASPT2 calculation at the atomic limit (R = 100 a.u.) with the largest basis set reproduces experimental atomic excitation energies within 3% for both LiCa and LiSr. In addition, permanent dipole moments and transition dipole moments at the SF level are also obtained. Rovibrational calculations of the ground and selected excited states, together with the spontaneous emission rates, demonstrate that the formation of ultracold LiCa and LiSr molecules in low-lying vibrational levels of the electronic ground state may be possible. PMID:23697418

Gopakumar, Geetha; Abe, Minori; Hada, Masahiko; Kajita, Masatoshi

2013-05-21

355

Suppression of the charge-density-wave state in Sr10Ca4Cu24o41 by external pressure  

NASA Astrophysics Data System (ADS)

The influence of external pressure on the charge-density-wave (CDW) ground state of the quasi-one-dimensional two-leg ladder compound Sr10Ca4Cu24o41 has been studied by optical reflectivity measurements as a function of temperature (10-300 K) and pressure P (0.3-4.3 GPa) over the spectral range 580-6000 cm1. With increasing pressure the CDW transition temperature TCDW decreases with the linear pressure coefficient ?-70 K/GPa, and above ?3 GPa the CDW phase is suppressed at all temperatures. This behavior is similar to that in compounds Sr14-xCaxCu24o41 with increasing Ca content x at ambient pressure, with the simple scaling x ?3P(GPa). The size of the CDW gap decreases with increasing pressure, whereas the dimensionality of the high-temperature insulating phase in Sr10Ca4Cu24o41 within the ladder plane is hardly affected by external pressure.

Kuntscher, C. A.; Huber, A.; Hcker, M.

2014-04-01

356

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

SciTech Connect

Divalent metal tungstates, MWO{sub 4}, with wolframite (M=Zn and Mg) and scheelite (M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO{sub 4} and MgWO{sub 4}) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO{sub 4} and SrWO{sub 4}), which was attributed to their enhanced electron transfer resulting from their appropriate band positions. - Graphical abstract: The electronic band structures of divalent metal tungstates are described from the combination of experimental results and theoretical calculations, and their electronic structure-dependent photovoltaic performances are also studied. Highlights: > MWO{sub 4} compounds with wolframite (M=Zn and Mg) and scheelite structure (M=Ca and Sr) were prepared. > Their electronic band structures were investigated by the calculations and the measurements. > Their photovoltaic properties were determined by the crystal and electronic structures.

Kim, Dong Wook, E-mail: dong0414@snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of); Cho, In-Sun [Department of Mechanical Engineering, Stanford University, Stanford, California 94305 (United States); Shin, Seong Sik [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Lee, Sangwook [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of); Noh, Tae Hoon; Kim, Dong Hoe [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Jung, Hyun Suk [School of Advanced Materials Engineering, Kookmin University, Seoul 136-702 (Korea, Republic of); Hong, Kug Sun, E-mail: kshongss@plaza.snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, Seoul 151-744 (Korea, Republic of); Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul 151-744 (Korea, Republic of)

2011-08-15

357

First-principles calculations of structural, elastic, electronic and optical properties of XO (X=Ca, Sr and Ba) compounds under pressure effect  

Microsoft Academic Search

The structural, elastic, electronic and optical properties of XO (X= Ca, Sr and Ba) compounds were investigated by the density functional theory. A good agreement was found between our calculated results and the available theoretical and experimental data of the lattice constants. Young's modulus, Poisson ratio, bulk modulus, elastic constants and their pressure derivatives are also calculated. SrO and BaO

B. Ghebouli; M. A. Ghebouli; M. Fatmi; M. Benkerri

2010-01-01

358

Thermodynamics of the BCa, BSr, and BBa systems: Applications for the fabrications of CaB6, SrB6, and BaB6 thin films  

Microsoft Academic Search

Using the thermodynamic descriptions previously modeled in the boron-alkaline earth metal systems, B-Ca, B-Sr, and B-Ba, the pressure-temperature phase diagrams of these systems have been obtained in the present work, which provide insights into appropriate processing conditions for depositions of the divalent alkaline-earth metal hexaborides, CaB6, SrB6, and BaB6. The present work indicates that the lower the growth pressures, the

Shunli Shang; Zi-Kui Liu

2007-01-01

359

Rheology and microstructure of (Ca0.9,Sr0.1)TiO3 perovskite deformed in compression and torsion  

Microsoft Academic Search

Polycrystalline samples of (Ca0.9,Sr0.1)TiO3 were synthesized from high-purity oxides yielding samples with <1% porosity and grain sizes between 10 and 100 ?m. These samples were used to study the rheological properties of the tetragonal and cubic phases of (Ca,Sr)TiO3. Data from compression experiments performed over a temperature range spanning the tetragonal to cubic phase transition show a change from a

Julian Mecklenburgh; Florian Heidelbach; Elisabetta Mariani; Stephen Mackwell; Friedrich Seifert

2010-01-01

360

Effects of heating temperature and atmosphere on critical current density of Bi2Sr2Ca1Cu2Ag 0.8Oy Ag-sheathed tapes  

Microsoft Academic Search

In partial melt processing of Bi2Sr2Ca1 Cu2Ag0.8Oy silver sheathed tapes, the effects of heating temperature and atmosphere on the critical current density, Jc, were studied. It was found that Jc is higher for the samples treated in pure oxygen than those in air and has the maximum value at a heating temperature of 885C. During partial melting, nonsuperconducting Sr-Ca-Cu-O precipitates

A. Endo; S. Nishikida

1993-01-01

361

Migratory history of the Russian sturgeon Acipenser guldenstadti in the Caspian Sea, as revealed by pectoral fin spine Sr:Ca ratios  

Microsoft Academic Search

Ontogenic patterns of change in pectoral fin spine Sr:Ca ratios were examined in the Russian sturgeon Acipenser guldenstadti from the Caspian Sea. Pectoral fin spine Sr:Ca ratios of the sturgeon fluctuated strongly along the life history transect in accordance with the migration pattern from freshwater to sea (brackish) water habitats, i.e. all specimens exhibited a typical anadromous pattern in the

T. Arai; A. Levin; A. Boltunov; N. Miyazaki

2002-01-01

362

Oxygen reduction at a YSZ interface with cathode materials La{sub 1-x}(Ca or Sr){sub x}MnO{sub 3} or Y{sub 1-x}CaMnO{sub 3}  

SciTech Connect

Impedance spectroscopy combined with an unbonded interface cell (UIC) design, was used to assess oxygen reduction at an yttria-stabilized zirconia electrolyte interface with several substituted yttrium and lanthanum manganite cathode compositions. By analyzing impedance spectra taken using the UIC, effective length of reaction zone at the solid-gas triple phase boundary can be estimated and used to normalize the oxygen reduction reaction rate for each cell, thus effectively removing effect of interface morphology. Intrinsic reaction rates (specific oxygen activities) were determined from spectra as function of temperature and oxygen partial pressure for cathodes La{sub 1-x}(Ca or Sr){sub x}MnO{sub 3} and Y{sub 1-x}Ca{sub x}MnO{sub 3} (LCM, LSM and YCM, respectively) and for Pt. Specific activities in the temperature and P(O{sub 2}) ranges of an operating solid oxide fuel cell (SOFC) cathode, 1173--1273K and 10{sup 5}-10{sup 3} Pa, were highest for LCM intermediate for YCM and lowest for LSM. For LCM and YCM, compositions with x=0.5 gave highest specific activities. Specific activities for all of the tested manganite compositions exceeded the platinum specific activities by at least an order of magnitude. Shapes of impedance spectra for all the manganite systems were similar. Examination of spectra shapes revealed that the overall cathodic polarization process was rather complex and made up of at least two or more fundamental steps.

Youngblood, G.E.; Windisch, C.F. Jr.; Bates, J.L.

1993-09-01

363

Record of Little Ice Age sea surface temperatures at Bermuda using a growth-dependent calibration of coral Sr/Ca  

NASA Astrophysics Data System (ADS)

Strontium to calcium ratios (Sr/Ca) are reported for a massive brain coral Diploria labyrinthiformis collected from the south shore of Bermuda and are strongly correlated with both sea surface temperature (SST) and mean annual skeletal growth rate. High Sr/Ca ratios correspond with cold SSTs and slow skeletal growth rate and vice versa. We provide a quantitative calibration of Sr/Ca to extension rate and SST along the axis of maximum growth and derive a growth-dependent Sr/Ca-SST calibration equation to reconstruct western subtropical North Atlantic SSTs for the past 223 years. When the influence of growth rate is excluded from the calibration, Sr/Ca ratios yield SSTs that are too cold during cool anomalies and too warm during warm anomalies. Toward the end of the Little Ice Age (1850), SST changes derived using a calibration that is not growth-dependent are exaggerated by a factor of 2 relative to those from the growth-corrected model that yields SSTs 1.5C cooler than today. Our results indicate that incorporation of growth rate effects into coral Sr/Ca calibrations may improve the accuracy of SSTs derived from living and fossil corals.

Goodkin, Nathalie F.; Hughen, Konrad A.; Cohen, Anne L.; Smith, Struan R.

2005-12-01

364

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

USGS Publications Warehouse

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.

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

2004-01-01

365

Enhanced red fluorescence in Sr2Si1-xGexO4:Eu3+ phosphors by the substitution of Si by Ge for white light emitting diodes  

NASA Astrophysics Data System (ADS)

Eu3+-doped Sr2Si1-xGexO4 (x=0-1) phosphors have been prepared by the high temperature solid-state reaction method. The luminescent properties of these phosphors were investigated. Red fluorescence of Eu3+ is enhanced gradually in the samples with increasing substitution of Si by Ge upon the excitation of 393 nm light. The intensity is increased by 50% with full substitution of Si by Ge. These results are originated from the structural changes and the phonon energy reduction in the samples due to the substitution of Si by Ge. The CIE chromaticity coordinates of the phosphors vary slightly around (0.62, 0.37) and all are in the red color region. The results indicate that these phosphors could be promising red phosphors for white light emitting diodes.

Huang, Lihui; Xu, Shiqing; Guo, Meiquan; Wang, Chenyue; Hua, Youjie; Zhao, Shilong; Deng, Degang; Wang, Huanping; Jia, Guohua

2012-07-01

366

Isovalent-substitution effect on the Verwey-type transition in the A -site-ordered double perovskite (Ba,Sr) R Fe2 O5  

NASA Astrophysics Data System (ADS)

Two types of chemical-pressure effects on the Verwey-type transition in BaSmFe2O5 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 TV from 232Kto264K , the Sr-for-Ba substitution decreases it from 232Kto180K for x=0.15 in (Ba1-xSrx)SmFe2O5 . Of various structural parameters determined by synchrotron x-ray diffraction above TV , the magnitude of the orthorhombic distortion (=b-a) is found to correlate with TV in a manner that unifies both substitution schemes. It is suggested that when an increase in b-a above TV is achieved by means of the structural substitution, it makes it easier for the dxz Fe2+ orbital ordering to occur below TV .

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

2004-10-01

367

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

NSDL National Science Digital Library

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.

Tepper, Jeff

368

High-temperature transport properties, thermal expansion and cathodic performance of Ni-substituted LaSr 2Mn 2O 7-?  

NASA Astrophysics Data System (ADS)

The substitution of manganese with nickel in LaSr 2Mn 2O 7-?, where the solubility limit corresponds to approximately 25% Mn sites, enhances the Ruddlesden-Popper phase stability at elevated temperatures and atmospheric oxygen pressure. The total conductivity of LaSr 2Mn 2-yNi yO 7-? ( y=0-0.4) decreases with nickel additions, whilst the average thermal expansion coefficients calculated from dilatometric data in the temperature range 300-1370 K increase from (11.4-13.7)10 -6 K -1 at y=0 up to (12.5-14.4)10 -6 K -1 at y=0.4. The conductivity and Seebeck coefficient of LaSr 2Mn 1.6Ni 0.4O 7-?, analyzed in the oxygen partial pressure range 10 -15-0.3 atm at 600-1270 K, display that the electronic transport is n-type and occurs via a small polaron mechanism. Reductive decomposition is observed at the oxygen pressures close to Ni/NiO boundary, namely 2.310 -11 atm at 1223 K. Within the phase stability domain, the electronic transport properties are essentially p(O 2)-independent. The steady-state oxygen permeability of dense LaSr 2Mn 1.6Ni 0.4O 7-? membranes is higher than that of (La,Sr)MnO 3-?, but lower if compared to perovskite-like (Sr,Ce)MnO 3-?. Porous LaSr 2Mn 1.6Ni 0.4O 7-? cathodes in contact with apatite-type La 10Si 5AlO 26.5 solid electrolyte exhibit, however, a relatively poor electrochemical performance, partly associated with strong cation interdiffusion between the materials.

Yaremchenko, A. A.; Bannikov, D. O.; Kovalevsky, A. V.; Cherepanov, V. A.; Kharton, V. V.

2008-11-01

369

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

PubMed Central

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 (SiO2P2O5CaONa2O) with 0100% 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 37C 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 compositionstructureproperty 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.

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

2012-01-01

370

Targeted ablation of the histidine-rich Ca2+-binding protein (HRC) gene is associated with abnormal SR Ca2+-cycling and severe pathology under pressure-overload stress  

PubMed Central

The histidine-rich Ca2+-binding protein (HRC) is located in the lumen of the sarcoplasmic reticulum (SR) and exhibits high capacity Ca2+ binding properties. Overexpression of HRC in the heart resulted in impaired SR Ca2+ uptake and depressed relaxation through its interaction with SERCA2a. However, the functional significance of HRC in overall regulation of calcium cycling and contractility is not currently well defined. To further elucidate the role of HRC in vivo under physiological and pathophysiological conditions, we generated and characterized HRC-knockout (KO) mice. The KO mice were morphologically and histologically normal compared to wild type (WT) mice. At the cellular level, ablation of HRC resulted in significantly enhanced contractility, Ca2+ transients, and maximal SR Ca2+ uptake rates in the heart. However, after-contractions were developed in 50% of HRC-KO cardiomyocytes, compared to 11% in WT mice under stress conditions of high frequency stimulation (5 Hz) and isoproterenol application. A parallel examination of the electrical activity revealed significant increases in the occurrence of Ca2+ spontaneous SR Ca2+ release and delayed after depolarizations (DADs) with ISO in HRC-KO, compared to WT cells. The frequency of Ca2+ sparks was also significantly higher in HRC-KO cells with ISO, consistent with the elevated SR Ca2+ load in the KO cells. Furthermore, HRC-KO cardiomyocytes showed significantly deteriorated cell contractility and Ca2+-cycling caused possibly by depressed SERCA2a expression after transverse-aortic constriction (TAC). Also HRC null mice exhibited severe cardiac hypertrophy, fibrosis, pulmonary edema and decreased survival after TAC. Our results indicate that ablation of HRC is associated with poorly regulated SR Ca2+-cycling, and severe pathology under pressure-overload stress, suggesting an essential role of HRC in maintaining the integrity of cardiac function.

Park, Chang Sik; Chen, Shan; Lee, Hoyong; Cha, Hyeseon; Hong, Sunghee; Han, Peidong; Ginsburg, Kenneth S.; Jin, Sora; Park, Inju; Singh, Vivek P.; Wang, Hong-Sheng; Franzini-Armstrong, Clara; Park, Woo Jin; Bers, Donald M.; Kranias, Evangelia G.; Cho, Chunghee; Kim, Do Han

2014-01-01

371

M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba): Crystal structure, phase transitions and thermal expansion  

SciTech Connect

Three earth alkali-germanium monophosphates M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) were prepared by solid state reaction and their structures, previously unknown, studied by Rietveld analysis. BaGe(PO{sub 4}){sub 2} and high-temperature {beta}-SrGe(PO{sub 4}){sub 2} (space group C2/m, Z=2) are fully isotypic with yavapaiite, whereas CaGe(PO{sub 4}){sub 2} and low-temperature {alpha}-SrGe(PO{sub 4}){sub 2} (C2/c, Z=4) are distorted derivatives. The phase transition between the two forms is observed for the first time. The thermal expansion, resulting from several structural mechanisms, is very anisotropic. - Graphical abstract: The superstructure of SrGe(PO{sub 4}){sub 2} at room temperature ({alpha}) results from the off-centering of cation Sr{sup II}. Highlights: > Crystal structures of yavapaiite-type M{sup II}Ge(PO{sub 4}){sub 2} (M=Ca, Sr, Ba) have been solved. > Distortion and superstructure result from Ca and Sr off-centering. > A global scheme for the polymorphism of yavapaiites is proposed.

Popa, Karin ['Al.I. Cuza' University, Department of Chemistry, 11-Carol I Blvd., 700506 Iasi (Romania); Wallez, Gilles, E-mail: gilles.wallez@upmc.fr [Chimie ParisTech, UPMC Univ. Paris 06, CNRS-UMR 7574, Laboratoire de Chimie de la Matiere Condensee de Paris (LCMCP), 75005 Paris (France); Bregiroux, Damien; Loiseau, Pascal [Chimie ParisTech, UPMC Univ. Paris 06, CNRS-UMR 7574, Laboratoire de Chimie de la Matiere Condensee de Paris (LCMCP), 75005 Paris (France)

2011-10-15

372

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

373

Texture analysis of monofilamentary, Ag-sheathed (Pb,Bi) 2Sr 2Ca 2Cu 3O x tapes by electron backscatter diffraction (EBSD)  

NASA Astrophysics Data System (ADS)

Using automated orientation imaging, the grain orientations and texture of monofilamentary, Ag-sheathed (Pb,Bi) 2Sr 2Ca 2Cu 3O x (Bi-2223) tape is analysed in detail by means of electron backscatter diffraction (EBSD). The achieved high image quality of the Kikuchi patterns enables multi-phase scans including Bi-2223, Bi 2Sr 2CaCu 2O x, Bi 2Sr 2CuO x, (Sr,Ca) 14Cu 24O 41 and Ag to be performed. Two areas are selected for the EBSD analysis, one close to the silver sheath, the other located in the center of the sample. The grain orientation maps are presented for each phase separately allowing a new insight into the microtexture of Ag-sheathed Bi-2223 tapes. Furthermore, the EBSD analysis provides the possibility for a misorientation angle analysis within each individual phase.

Koblischka-Veneva, A.; Koblischka, M. R.; Qu, T.; Han, Z.; Mcklich, F.

2008-02-01

374

Thermodynamic parameters of Bi 2 Sr 2 CaCu 2 O 8+ ? thin film prepared by molecular beam epitaxy  

NASA Astrophysics Data System (ADS)

Bi 2Sr 2CaCu 2O 8+ ? (Bi2212) thin film is an important superconducting material ascribed to its high transition temperatures and low toxicity, but the application of Bi2212 thin films is limited due to the appearances of intergrowth and impurity phases. To achieve high-quality Bi2212 thin film by molecular beam epitaxy (MBE), the oxidizing gas pressure and substrate temperature are the key parameters. Here, the phase formation in Bi-based thin films grown by MBE was studied as a function of oxidizing gas pressure and substrate temperature. Furthermore, the thermodynamic parameters have been investigated through enthalpy change. This study indicates that the substrate temperature was increased with the enhancing of ozone partial pressure when the composition ratio is fixed, Bi2212 single phase can be formed. Moreover, the chemical stability decreases in the order of Bi 2Sr 2CuO 6+ ? > Bi2212 > Bi 2Sr 2Ca 2Cu 3O 10+ ?.

Zhang, Bingsen; Qi, Yang

2011-09-01

375

The Study of Electronic Structure and Unavoidable Impurities in Incipient Ferroelectric SrTiO3 Ceramics Doped by Ba or Ca  

Microsoft Academic Search

ESR investigation of Sr1 ? xBaxTiO3 and Sr1 ? xCaxTiO3 at x = 0.01, 0.02, 0.04 and 0.06 was carried out in 3 cm frequency region at T = 300 K and T = 77 K. The observed spectra were identified as originating from Mn, Cr, Fe substituted for Ti. The investigation of the electronic structure was carried out by

M. D. Glinchuk; I. P. Bykov; T. N. Bondarenko; A. V. Zyrin; L. P. Yurchenko; E. P. Garmash; V. N. Pavlikov

2008-01-01

376

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

SciTech Connect

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.

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

377

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)

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.

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

1989-01-01

378

Preparation and characterization of Bi2Sr2CaCu2O8+? thin films on MgO single crystal substrates by chemical solution deposition  

NASA Astrophysics Data System (ADS)

Bi2Sr2CaCu2O8 thin films have been deposited on MgO single crystal substrates by spin-coating a solution based on 2-ethylhexanoate precursors. Pyrolysis takes place between 200 C and 450 C and is accompanied by the release of 2-ethylhexanoic acid, CO2 and H2O vapour. Highly c-axis oriented Bi2Sr2CaCu2O8 films were obtained after heat treatment at 840 C in air. The highest Tc of 81 K was measured in a 10-layer film. Subsequent post-annealing in Ar and pure O2 did not improve the superconducting properties of the films and resulted in the appearance of Bi2CaCuO5 or Bi2(Sr, Ca)2CuO6 impurities.

Grivel, J.-C.; K?pa, K.; Hlsek, T.; Andersen, N. H.; Rubeov, K.

2013-03-01

379

Effect of (Sr, Ba) substitution in La 3Ga 5SiO 14 and La 3M 0.5Ga 5.5O 14(M=Nb 5+, Ta 5+) crystals on their synthesis, structure and piezoelectricity  

Microsoft Academic Search

Alkali-earth ion (Sr, Ba) substituted La3Ga5SiO14 and La3M0.5G5.5O14 (M=Nb5+,Ta5+) compounds were synthesized by solid state reaction. Sr-substituted La3Ta0.5Ga5.5O14 (Sr-LTG) single crystals were grown by the micro-pulling down and Czochralski techniques. The cation distribution in Sr-LTG has been determined by X-ray structure analysis. Some piezoelectric properties of Sr-LTG crystal are reported and compared with those of pure La3Ta0.5Ga5.5O14.

H. Takeda; T. Kato; V. I. Chani; H. Morikoshi; K. Shimamura; T. Fukuda

1999-01-01

380

Dielectric and ferroelectric characteristics of 0.7PZT 0.3PZN ceramics substituted with Sr  

NASA Astrophysics Data System (ADS)

Lead zirconate titanate-lead zinc niobate (PZT-PZN) ceramics with compositions close to the morphotropic phase boundary were investigated as a function of Sr doping. The powders were prepared using the columbite-(wolframite) precursor method. Dielectric and ferroelectric properties of the as-sintered and annealed samples were measured. The results showed that with increasing Sr concentration dielectric constant versus temperature curves become gradually broader. Sr doping has been shown to produce a linear reduction in the transition temperature (Tm) (294.1-12.7x C) with concentration (x). The maximum value of the dielectric constant decreased and the degree of diffuse phase transition was enhanced with Sr doping. However, the results indicated that the degree of disorder in Sr-modified PZT-PZN was further improved by thermal annealing. After thermal annealing at 900C for 48 h a strong enhancement of dielectric constant (?r) and remanent polarization (Pr) was observed.

Vittayakorn, Naratip; Uttiya, Sureeporn; Rujijanagul, Gobwute; Cann, David P.

2005-08-01

381

Combustion Synthesis of CaAl2Si2O8:Eu2+, Dy3+ And CaSrAl2SiO7:Eu2+ Long After Glow Phosphors  

NASA Astrophysics Data System (ADS)

CaSrAl2SiO7:Eu2+ and CaAl2Si2O8:Eu2+, Dy3+ are prepared through modified combustion technique. The photoluminescence and long after glow decay characteristics are studied. PL emission spectra of both the phosphors are obtained in blue region.

Talwar, Gurjeet; Joshi, C. P.; Moharil, S. V.; Kondawar, V. K.

2011-10-01

382

A RRKM study and a DFT assessment on gas-phase fragmentation of formamide-M(2+) (M = Ca, Sr).  

PubMed

A kinetic study of the unimolecular reactivity of formamide-M(2+) (M = Ca, Sr) systems was carried out by means of RRKM statistical theory using high-level DFT. The results predict M(2+), [M(NH2)](+) and [HCO](+) as the main products, together with an intermediate that could eventually evolve to produce [M(NH3)](2+) and CO, for high values of internal energy. In this framework, we also evaluated the influence of the external rotational energy on the reaction rate constants. In order to find a method to perform reliable electronic structure calculations for formamide-M(2+) (M = Ca, Sr) at a relatively low computational cost, an assessment of different methods was performed. In the first assessment twenty-one functionals, belonging to different DFT categories, and an MP2 wave function method using a small basis set were evaluated. CCSD(T)/cc-pWCVTZ single point calculations were used as reference. A second assessment has been performed on geometries and energies. We found BLYP/6-31G(d) and G96LYP/6-31+G(d,p) as the best performing methods, for formamide-Ca(2+) and formamide-Sr(2+), respectively. Furthermore, a detailed assessment was done on RRKM reactivity and G96LYP/6-31G(d) provided results in agreement with higher level calculations. The combination of geometrical, energetics and kinetics (RRKM) criteria to evaluate DFT functionals is rather unusual and provides an original assessment procedure. Overall, we suggest using G96LYP as the best performing functional with a small basis set for both systems. PMID:24921953

Martn-Smer, Ana; Gaigeot, Marie-Pierre; Yez, Manuel; Spezia, Riccardo

2014-06-25

383

Metallic and nonmetallic double perovskites: A case study of A2FeReO6 (A=Ca, Sr, Ba)  

Microsoft Academic Search

We have investigated the structure and electronic properties of ferrimagnetic double perovskites, A2FeReO6 (A=Ca, Sr, Ba). The A=Ba phase is cubic (Fm3m) and metallic, while the A=Ca phase is monoclinic (P21\\/n) and nonmetallic. 57Fe Mssbauer spectroscopy shows that iron is present mainly in the high spin (S=52) Fe3+ state in the Ca compound, while it occurs in an intermediate state

J. Gopalakrishnan; A. Chattopadhyay; S. B. Ogale; T. Venkatesan; R. L. Greene; A. J. Millis; K. Ramesha; B. Hannoyer; G. Marest

2000-01-01

384

Uniaxial anisotropic flux trapping in Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O single crystals  

SciTech Connect

Measurements of the angular dependence of the remanent magnetization of Y-Ba-Cu-O and of Bi-Sr-Ca-Cu-O single crystals reveal uniaxial anisotropy for flux trapping; the anisotropy axis is the crystalline {bold c} axis. The amount of trapped flux is determined by the component of the field {bold H} along {bold c}. For flux trapping with {bold H} in the {ital a}-{ital b} plane, we observe unidirectional anisotropy; the anisotropy direction is defined by {bold H} during the cooling process.

Felner, I.; Yaron, U. (Racah Institute for Physics, The Hebrew University of Jerusalem, 91 904, Jerusalem, Israel (IL)); Yeshurun, Y. (Department of Physics, Bar-Ilan University, 52 100 Ramat-Gan, Israel); Chandrashekhar, G.V.; Holtzberg, F. (IBM Thomas J. Watson Laboratories, Yorktown Heights, New York 11598-0218)

1989-09-01

385

Structure in the magnetic-field-dependent microwave absorption of Bi-Sr-Ca-Cu-O single crystals  

SciTech Connect

We have observed structure in the magnetic field dependence of the microwave absorption of Bi/sub 2.1/Sr/sub 1.6/CaCu/sub 2/O/sub x/ single crystals below the superconducting transition temperature. An absorption peak is observed at low fields, and the peak position and width have strong temperature and angular dependences. Two peaks can be resolved in some samples. Hysteresis in the low-field absorption peak indicates extremely anisotropic flux trapping in these crystals for T<25 K. Flux parallel to the c axis of the crystal is almost completely trapped, whereas flux normal to c is only weakly trapped.

Pakulis, E.J.; Chandrashekhar, G.V.

1989-01-01

386

Electronic structure and unusual superconducting properties of of CaAlSi and SrAlSi  

NASA Astrophysics Data System (ADS)

We report full-potential LAPW calculations for CaAlSi and SrAlSi in ordered structures and in the virtual crystal approximation, at normal and elevated pressures. We also estimate the electron-phonon coupling using either frozen-phon calculations at the zone center, or the rigid muffin tin approximation. We conclude that there is no simple way to explain the recently reported qualitative disparity in the superconducting properties of the two compounds. An assumption of an ultrasoft phonon mode, on the other hand, allows to reconcile in a reasonable way the experimental findings with the theory.

Mazin, Igor I.; Papaconstantopoulos, Dimitris

2004-03-01

387

Formation of the 110-K superconducting phase in Pb-doped Bi-Sr-Ca-Cu-O thin films  

SciTech Connect

Investigation of the 110-K Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub {ital x}} phase formation in superconducting thin films of Bi-based cuprates is reported. The films were dc magnetron sputtered from single Bi(Pb)-Sr-Ca-Cu-O targets of various stoichiometries, and subsequently annealed in air at high temperatures. The influence of the initial Pb content, annealing conditions, as well as the substrate material on the growth of the 110-K phase was investigated. We found that the films, fully superconducting above 100 K could be reproducibly fabricated on various dielectric substrates from Pb-rich targets by optimizing annealing conditions for each initial Pb/Bi ratio. Heavy Pb doping considerably accelerated formation of the 110-K phase, reducing the film annealing time to less than 1 h. Films containing, according to the x-ray measurement, more than 90% of the 110-K phase were obtained on MgO substrates, after sputtering from the Bi{sub 2}Pb{sub 2.5}Sr{sub 2}Ca{sub 2.15}Cu{sub 3.3}O{sub {ital x}} target and annealing in air for 1 h at 870 {degree}C. The films were {ital c}-axis oriented, with 4.5-K-wide superconducting transition, and zero resistivity at 106 K. Their critical current density was 2 {times} 10{sup 2} A/cm{sup 2} at 90 K, and above 10{sup 4} A/cm{sup 2} below 60 K. The growth of the 110-K phase on epitaxial substrates, such as CaNdAlO{sub 4} and SrTiO{sub 3}, was considerably deteriorated, and the presence of the 80- and 10-K phases was detected. Nevertheless, the best films deposited on these substrates were fully superconducting at 104 K and exhibited critical current densities above 2 {times} 10{sup 5} A/cm{sup 2} below 60 K{minus}one order of magnitude greater than the films deposited on MgO.

Kula, W.; Sobolewski, R.; Gorecka, J.; Lewandowski, S.J. (Instytut Fizyki, Polska Akademia Nauk, Al. Lotnikow 32/46, PL-02668 Warszawa (Poland))

1991-09-15

388

Preparation of High-Quality Bi-Pb-Sr-Ca-Cu Oxide Precursor by the Citrate Gel Process  

NASA Astrophysics Data System (ADS)

In order to achieve a high-Tc superconducting phase of Bi-Pb-Sr-Ca-Cu oxide, we applied a highly reactive citrate gel process to yield a precursor powder. A citrate-nitrate solution was dehydrated and heated to form the desired compound. We applied a thermogravimetric analysis, scanning electron microscopy and X-ray diffraction to study thermal decomposition during the heat stage. Sintered sample showed good superconducting properties with Tc above 100 K. Chemical analyses revealed negligible loss of metals during the preparation procedure, indicating that the citrate gel process is an excellent and reliable method for this compound.

Aoki, Aiko

1990-02-01

389

Magnetic behaviour of the MTbF{sub 6} fluoroterbates (M=Cd, Ca, Sr, ({alpha}/{beta})-Ba)  

SciTech Connect

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.

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

390

Interpretation of EXAFS in scheelite-type AWO4 (A = Ca, Sr, Ba) compounds using molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

In this work we successfully interpret the W L3-edge EXAFS spectra in scheelite-type AWO4 (A = Ca, Sr, Ba) compounds using a combination of classical NVT molecular dynamics (MD) and ab initio multiple-scattering (MS) theory. The configuration-averaged EXAFS spectra show good agreement with our room temperature experimental data supporting the reliability of the developed force-field models. The contributions from all coordination shells up to 6 are elucidated. The contribution of the MS effects into the total EXAFS signal in AWO4 compounds is small, being around 10%.

Kalinko, Aleksandr; Kuzmin, Alexei

2013-04-01

391

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

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.

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

1993-01-01

392

First-principles calculations of phonon and thermodynamic properties in the boron-alkaline earth metal binary systems: B-Ca, B-Sr, and B-Ba  

NASA Astrophysics Data System (ADS)

The phonon and thermodynamic properties of the divalent alkaline-earth hexaborides, MB6 ( M=Ca , Sr, Ba), and the reference elements ?-B , fcc-Ca, fcc-Sr, and bcc-Ba are investigated on the basis of first-principles projector augmented wave method together with the quasiharmonic phonon calculations. The calculated phonon dispersion relations by using the supercell approach are in good agreements with those obtained by the inelastic neutron scattering, Raman scattering, and infrared absorption. The experimentally revealed anomalous behaviors of phonon dispersions in the alkaline-earth metals are correctly predicted; i.e., for both fcc-Ca and fcc-Sr, the frequency of the lower transverse [??0] branch exhibits slightly positive dispersion, and for bcc-Ba the frequency of the longitudinal branch along the [?00] direction is lower than that of the transverse branch. These anomalous phenomena can be traced back to the effect of d electron. The predicted phonon dispersion relations among CaB6 , SrB6 , and BaB6 show similar features except that the frequencies decrease from CaB6 , SrB6 , to BaB6 due to the influence of mass. It is also found that the low frequency T1u modes of CaB6 , SrB6 , and BaB6 have large LO/TO splitting (greater than 5THz ). To that end, the finite temperature thermodynamic properties (entropy, enthalpy, and Gibbs energy) of MB6 ( M=Ca , Sr, Ba) and elements B, Ca, Sr, and Ba are calculated; herein, both the electronic and phonon contributions are considered. This work indicates that the difference of the enthalpies of formation of CaB6 , SrB6 , and BaB6 is small (less than 4kJ/mol instead of the measured 30kJ/mol ), which agrees with the facts that they possess the similar phonon dispersion relations, melting temperatures, bulk moduli, and Debye temperatures.

Shang, Shunli; Wang, Yi; Liu, Zi-Kui

2007-01-01

393

Processing, microstructure, and critical current density of Silver-sheathed Bi2Sr2CaCu2Ox multifilamentary round wire  

NASA Astrophysics Data System (ADS)

Ag-sheathed multifilamentary Bi2Sr2CaCu2Ox round wire is one of the leading hightemperature superconductors that can generate a magnetic field exceeding the maximum of ~23 T available in present Nb-based low-temperature superconducting magnet technology. However, the magnet fabrication of power-in-tube (PIT) Ag-Bi2Sr2CaCu 2Ox multifilamentary round wire to develop critical current density Jc > 105 A/cm2 in magnetic fields up to 45 T is difficult, due to complicated material processing, as-yet incompletely understood microstructure, and the problem that Jc is sensitive to high-temperature reactions. This thesis analyzed the critical steps of melt processing PIT Bi2Sr2CaCu2Ox multifilamentary wires, systematically investigating the relationships between processing, microstructure, and conductor & magnet performance. The phase transformation and microstructure development during the melt processing of Bi2Sr2CaCu2Ox wires were thoroughly examined using a brine-quench technique that preserves the high-temperature microstructures. On heating to the maximum temperature (~890 C), Bi2Sr2CaCu2Ox powder melts incongruently, producing a mixture of liquid and secondary solid phases. On subsequent cooling, the liquid reacts with the solid phases and Bi 2Sr2CaCu2Ox reforms. The phase reaction to Bi2Sr2CaCu2Ox is often incomplete, leaving remnant nonsuperconducting phases from the melt and the Bi2Sr 2CaCu2Ox phase and intergrowth in the superconducting matrix, all of which become current limiting mechanisms (CLMs) and block current flow. Moreover, the gas between precursor powder grains accumulates into large pores upon melting, which divide the filament into segments. The consequence of having large pores in the melt is that the pore regions may become bottlenecks for current flow in fully reacted wires. The high population of CLMs strongly indicates that the fraction of oxide filament area that is effectively used for carrying current is low and increasing the connectivity is the key to improving Jc of Bi2Sr2CaCu2Ox wires.

Shen, Tengming

394

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

395

The high-temperature thermal expansion of BiPbSrCaCuO superconductor and the oxide components (Bi2O3, PbO, CaO, CuO)  

Microsoft Academic Search

The thermal expansion of superconducting Bi1.6Pb0.4Sr2Ca2Cu3Ox (BiPbSrCaCuO) and its oxide components Bi2O3, PbO, CaO and CuO have been studied by high-temperature dilatometric measurements (30800C). The thermal expansion coefficient for the BiPbSrCaCuO superconductor in the range 150830C is a=6.410-6K-1. The temperature dependences of ?L\\/L of pressed Bi2O3 reveals sharp changes of length on heating (T1=712C), and on cooling (T2=637C and T3=577C),

T. D. Dzhafarov; M. Altunbas; O. Grr

1996-01-01

396

SrZn2Sn2 and Ca2Zn3Sn6 two new Ae-Zn-Sn polar intermetallic compounds (Ae: alkaline earth metal)  

NASA Astrophysics Data System (ADS)

SrZn2Sn2 and Ca2Zn3Sn6, two closely related new polar intermetallic compounds, were obtained by high temperature reactions of the elements. Their crystal structures were determined with single crystal XRD methods, and their electronic structures were analyzed by means of DFT calculations. The Zn-Sn structure part of SrZn2Sn2 comprises (anti-)PbO-like {ZnSn4/4} and {SnZn4/4} layers. Ca2Zn3Sn6 shows similar {ZnSn4/4} layers and {Sn4Zn} slabs constructed of a covalently bonded Sn scaffold capped by Zn atoms. For both phases, the two types of layers are alternatingly stacked and interconnected via Zn-Sn bonds. SrZn2Sn2 adopts the SrPd2Bi2 structure type, and Ca2Zn3Sn6 is isotypic to the R2Zn3Ge6 compounds (R=La, Ce, Pr, Nd). Band structure calculations indicate that both SrZn2Sn2 and Ca2Zn3Sn6 are metallic. Analyses of the chemical bonding with the electron localization function (ELF) show lone pair like basins at Sn atoms and Zn-Sn bonding interactions between the layers for both title phases, and covalent Sn-Sn bonding within the {Sn4Zn} layers of Ca2Zn3Sn6.

Stegmaier, Saskia; Fssler, Thomas F.

2012-08-01

397

CuO as sintering additive to Sr0.4Ca0.6La4Ti5O17 ceramics  

NASA Astrophysics Data System (ADS)

The effects of CuO addition on the sintering behavior and microwave dielectric properties of Sr0.4Ca0.6La4Ti5O17 ceramics were investigated. CuO was selected as a liquid phase sintering aid to lower the sintering temperature of Sr0.4Ca0.6La4Ti5O17 ceramics. With CuO addition, the sintering temperature of Sr0.4Ca0.6La4Ti5O17 ceramics was effectively reduced from 1550 C to 1475 C. The crystalline phase exhibited no phase difference and no second phase was detected at all addition levels. The electric permittivity was not significantly affected by various amounts of CuO addition and ranged from 52 to 54. Small values (<+7 ppm/K) of the temperature coefficient of resonant frequency were obtained for Sr0.4Ca0.6La4Ti5O17 ceramics. However, the unloaded quality factor Q u was strongly dependent upon the CuO concentration. Q u f o 10500 GHz was obtained for Sr0.4Ca0.6La4Ti5O17 ceramics with 0.5 wt.% of CuO addition, sintered at 1475 C.

Manan, A.; Shah, L. A.; Attaullah

2013-01-01

398

Crystal structures and chemistry of double perovskites Ba2M(II)M?(VI)O6 (M=Ca, Sr, M?=Te, W, U)  

NASA Astrophysics Data System (ADS)

Structures of the double perovskites Ba 2M(II) M '(VI)O 6 ( M=Ca, Sr, M'=Te, W, U) at room temperature have been investigated by the Rietveld method using X-ray and neutron powder diffraction data. For double perovskites with M=Sr, the observed space groups are I2/ m ( M' =W) and R3 ( M'=Te), respectively. In the case of M=Ca, the space groups are either monoclinic P2 1/ n ( M'=U) or cubic Fm3m ( M'=W and Te). The tetragonal and orthorhombic symmetry reported earlier for Ba 2SrTeO 6 and Ba 2CaUO 6, respectively, were not observed. In addition, non-ambient X-ray diffraction data were collected and analyzed for Ba 2SrWO 6 and Ba 2CaWO 6 in the temperature range between 80 and 723 K. It was found that the rhombohedral R3 structure exists in Ba 2SrWO 6 above room temperature between the monoclinic and the cubic structure, whereas the cubic Ba 2CaWO 6 undergoes a structural phase transition at low temperature to the tetragonal I4/ m structure.

Fu, W. T.; Au, Y. S.; Akerboom, S.; IJdo, D. J. W.

2008-09-01

399

Systematic study on synthesis and structural, electrical transport and magnetic properties of Pb-substituted BiCaCoO misfit-layer cobaltites  

Microsoft Academic Search

Single-phases of Pb-substituted BiCaCoO misfit-layer cobaltites with various Pb concentrations have been synthesized and the Pb-substitution effects on the structural, electrical and magnetic properties have been systematically investigated. Powder X-ray diffraction analysis showed that the single-phases of Bi1.8?x\\/2PbxCa2Co2Oz were obtained up to x=0.60.7 under the optimized synthesis conditions. The lattice parameters of Bi1.8?x\\/2PbxCa2Co2Oz continuously changed with increasing Pb concentration. The

Yoshiaki Tanaka; Tatsuo Fujii; Makoto Nakanishi; Yoshihiro Kusano; Hideki Hashimoto; Yasunori Ikeda; Jun Takada

2007-01-01

400

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

SciTech Connect

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

Jones, T.E.; Schindler, J.W.; Boss, R.D.; Thibado, P.M.; McGinnis, W.C. (Naval Ocean Systems Center, Code 633, San Diego, California 92152-5000 (USA))

1990-04-01

401

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

NASA Astrophysics Data System (ADS)

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

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

2005-03-01

402

Electrical properties and charge imbalance for Ca,Ge-substituted garnet films grown by liquid-phase epitaxy from PbO-BO fluxed melts  

Microsoft Academic Search

Ca,Ge-substituted garnet films show p-type conduction when grown from melts of Ca\\/Ge molar ratio, R5 parameter?[CaO]\\/([CaO]+[GeO2]) >~0.486. n-type conduction is observed for films grown from R5-parameter ?0.275 melts. Through experiments on Ge and\\/or Ca doping to (Y,Sm)3(Fe,Ga)5O12 garnet films, these dopants are concluded to play important roles in the resistivity, as well as the conduction type. It is inferred that

Taketoshi Hibiya; Yasuharu Hidaka; Kozaburo Suzuki

1978-01-01

403

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

SciTech Connect

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.

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

2007-01-01

404

Ni and Zn doping of Cu sites in superconducting Nd2-zCezCuO4, La2-?Sr?CuO4, Bi2Sr2CaCu2O8, Bi18Pb02Sr2Ca2Cu3O10, YBa2Cu3O7, La06Ca04Ba135La065Cu3Ox and YBa2Cu4O8  

Microsoft Academic Search

A unified Cooper pair-breaking picture is presented for the observed degradation of the superconducting critical temperatures by Cu-site Zn and Ni impurities in Nd2-zCezCuO4, La2-?Sr?CuO4, Bi2Sr2CaCu2O8, Bi18Pb02Sr2Ca2-Cu3O10, Lao.06Ca04.4Ba135La0.65Cu3Ox (with x ? 7), YBa2Cu3O7 and YBa2Cu4O8. Independent of any specific model, the data alone require physics outside the cuprate planes, and hence no two-dimensional cuprate-plane model can consistently explain all the

Howard A. Blackstead; John D. Dow

1996-01-01

405

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

406

Competitive inhibition and selectivity enhancement by Ca in the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, Hf) by carrot (Daucus carota cv. U.S. harumakigosun).  

PubMed

We investigated the uptake of inorganic elements (Be, Na, Mg, K, Ca, Sc, Mn, Co, Zn, Se, Rb, Sr, Y, Zr, Ce, Pm, Gd, and Hf) and the effect of Ca on their uptake in carrots (Daucus carota cv. U.S. harumakigosun) by the radioactive multitracer technique. The experimental results suggested that Na, Mg, K, and Rb competed for the functional groups outside the cells in roots with Ca but not for the transporter-binding sites on the plasma membrane of the root cortex cells. In contrast, Y, Ce, Pm, and Gd competed with Ca for the transporters on the plasma membrane. The selectivity, which was defined as the value obtained by dividing the concentration ratio of an elemental pair, K/Na, Rb/Na, Be/Sr, and Mg/Sr, in the presence of 0.2 and 2 ppm Ca by that of the corresponding elemental pair in the absence of Ca in the solution was estimated. The selectivity of K and Rb in roots was increased in the presence of Ca. The selectivity of Be in roots was not affected, whereas the selectivity of Mg was increased by Ca. These observations suggest that the presence of Ca in the uptake solution enhances the selectivity in the uptake of metabolically important elements against unwanted elements. PMID:15695849

Ozaki, Takuo; Ambe, Shizuko; Abe, Tomoko; Francis, Arokiasamy J

2005-01-01

407

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

NASA Astrophysics Data System (ADS)

The insertion compound LixBi2Sr2CaCu2O8+ y (for lithium contents up to the studied level of x=2) was prepared by electro-chemical insertion of lithium into Bi2Sr2CaCu2O8+ y pellets at room temperature in galvanic cells using 1.4 M LiAsF 6 in 2Me-THF as electrolyte. The reaction proceeds with retention of the host