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1

Rietveld refinement, electrical properties and magnetic characteristics of Ca-Sr substituted barium hexaferrites  

Microsoft Academic Search

M–type Ca-Sr substituted barium hexaferrites having compositions BaFe12O19, Ba0.5Ca0.5Fe12O19 and Ba0.5Ca0.25Sr0.25Fe12O19 have been synthesized by commercial solid state reaction method. The effects of doping on structural, dielectric and magnetic properties were systematically investigated. The Rietveld refinement of X-ray powder diffraction data revealed that the samples possess single hexagonal phase with space group P63\\/mmc, with two molecules in the unit cell

Ashima Hooda; Sujata Sanghi; Ashish Agarwal; Reetu Dahiya

2

Influence of Ca substitution on the microstructure and magnetic properties of SrLaCo ferrite  

NASA Astrophysics Data System (ADS)

M-type ferrites Sr(0.55-x)CaxLa0.45Fe11.65Co0.35O19 (x=0, 0.05, 0.15, 0.25 and 0.35) were prepared by the ceramic process. Phase composition, morphology and sublattice occupation of the material were characterized by X-ray diffraction, scanning electron microscopy and Mössbauer spectroscopy, respectively. Magnetic properties of the materials were tested by a vibrating sample magnetometer. The results show that the samples are all composed of single M-type hexagonal ferrite after the Ca substitution, while the lattice constant c decreases and the lattice constant a does not change basically with increase of the substitution amount. In addition, the intrinsic coercive force increases obviously when the Ca substitution amount x<0.25, while the saturation magnetization does not change after Ca addition, which is attributed to the change of the Fe3+ sublattice occupations suggested by Mössbauer spectroscopy.

Li, Xiao; Yang, Wuguo; Bao, Daxin; Meng, Xiangdong; Lou, Baiyang

2013-03-01

3

Electrical conductivity of cobalt-titanium substituted SrCaM hexaferrites  

NASA Astrophysics Data System (ADS)

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

Eraky, M. R.

2012-03-01

4

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, Mössbauer 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.

González-Angeles, A.; Lipka, J.; Grusková, A.; Sláma, J.; Jan?árik, V.; Sluge?, V.

2010-03-01

5

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

SciTech Connect

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

Yamauchi, Hisao [Laboratory of Inorganic Chemistry, Department of Chemistry, Aalto University, FI-00076 AALTO (Finland); Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Karvonen, Lassi [Laboratory of Inorganic Chemistry, Department of Chemistry, Aalto University, FI-00076 AALTO (Finland); Egashira, Takayuki; Tanaka, Yoshiaki [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Karppinen, Maarit, E-mail: maarit.karppinen@tkk.f [Laboratory of Inorganic Chemistry, Department of Chemistry, Aalto University, FI-00076 AALTO (Finland); Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan)

2011-01-15

6

Computational Insights on Crystal Structures of the Oxygen-Evolving Complex of Photosystem II with Either Ca(2+) or Ca(2+) Substituted by Sr(2+).  

PubMed

The oxygen-evolving complex of photosystem II can function with either Ca(2+) or Sr(2+) as the heterocation, but the reason for different turnover rates remains unresolved despite reported X-ray crystal structures for both forms. Using quantum mechanics/molecular mechanics (QM/MM) calculations, we optimize structures with each cation in both the resting state (S1) and in a series of reduced states (S0, S-1, and S-2). Through comparison with experimental data, we determine that the X-ray crystal structures with either Ca(2+) or Sr(2+) are most consistent with the S-2 state (i.e., Mn4[III,III,III,II] with O4 and O5 protonated). As expected, the QM/MM models show that Ca(2+)/Sr(2+) substitution results in the elongation of the heterocation bonds and the displacement of terminal waters W3 and W4. The optimized structures also show that hydrogen-bonded W5 is displaced in all S states with Sr(2+) as the heterocation, suggesting that this water may play a critical role during water oxidation. PMID:25555204

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

2015-01-27

7

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

8

Substitution of extracellular calcium (Ca2+) by strontium (Sr2+) prolongs inspiratory burst in preBötzinger Complex (preBötC) inspiratory neurons.  

PubMed

The preBötC underlies inspiratory rhythm generation. As a result of network interactions, preBötC neurons burst synchronously to produce rhythmic premotor inspiratory activity. Each inspiratory burst consists of action potentials (AP) on top of a 10-20 mV synchronous depolarization lasting 0.3-0.8 s known as inspiratory drive potential. The mechanisms underlying the initiation and termination of the inspiratory burst are unclear, and the role of Ca(2+) is a matter of intense debate. In order to investigate the role of extracellular Ca(2+) in inspiratory burst initiation and termination, we substituted the extracellular Ca(2+) by Sr(2+). We found for the first time an ionic manipulation that significantly interferes with burst termination. In a rhythmically active slice, we current-clamped preBötC neurons (Vm?-60 mV) while recording integrated hypoglossal nerve (?XIIn) activity as motor output. Substitution of extracellular Ca(2+) by either 1.5 or 2.5 mM Sr(2+) significantly prolonged the duration of inspiratory bursts from 653.4±30.7 ms in control conditions to 981.6±78.5 ms in 1.5 mM Sr(2+) and 2048.2±448.5 ms in 2.5 mM Sr(2+), with a concomitant increase in decay time and area. Substitution of extracellular Ca(2+) by Sr(2+) is a well-established method to desynchronize neurotransmitter release. Our findings suggest that the increase in inspiratory burst duration is determined by a presynaptic mechanism involving desynchronization of glutamate release within the network. PMID:25429120

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

2014-11-26

9

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

PubMed

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

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

2014-10-20

10

Effect of Yb Substitution on Excess Conductivity of (Tl,Pb)(Sr,Yb)2CaCu2O7-? Superconductors  

NASA Astrophysics Data System (ADS)

Superconducting fluctuation behavior has been studied in sintered polycrystalline samples of Yb-substituted Tl0.5Pb0.5Sr2-xYbxCaCu2O7-? (x = 0.1-0.4) by electrical resistivity measurements. Data of ?? was obtained from linear fitting of the normal state resistivity in a suitable temperature region. Analysis of excess conductivity behavior based on Aslamazov-Larkin (AL) theory revealed transition from 2-D to 3-D behavior of the superconducting fluctuation in the mean field region for all samples. This study also suggests that there is a close correlation between the amounts of Yb substitution and the behavior of AL constant (A) both for 2D and 3D fluctuations.

Huda, N.; Yahya, A. K.; Abdullah, W. F.

2008-05-01

11

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

SciTech Connect

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

Seshadri, R.; Maignan, A.; Hervieu, M. [ISMRA et Universite de Caen (France)] [and others] [ISMRA et Universite de Caen (France); and others

1996-11-15

12

Substitution of transition metals for Cu in Bi2(SrCa)n+2Cun+1Oy whisker crystals: Fe and Pd  

NASA Astrophysics Data System (ADS)

We have measured the resistive superconducting transition temperature of single-crystal whiskers of Bi2(SrCa)n+2(Cu1- xMx)n+1Oy in which M represents the transition metals Fe and Pd that have been partially substituted for Cu. Combining these measurements with our earlier results for Co, Ni, and Zn substitutes, we derive a general relationship for the rate at which TC is depressed by substitution of transition metals: dTC/dx~-780 K for all these elements and both the 2212 (n=1) and 2223 (n=2) phases. Further, the normalized residual resistance is also a universal function of x. This is contrary to what others find for YBa2Cu3O7-? (YBCO), in which Zn and Ni substitutions act quite differently on dTC/dx. The explanation of this effect in YBCO apparently does not involve the general behavior of the Cu-O planes. The magnitude of dTC/dx is about half that predicted by the Abrikosov-Gorkov relation, as seen in other Cu-O superconductors.

Kuo, Y. K.; Schneider, C. W.; Nevitt, M. V.; Skove, M. J.; Tessema, G. X.

2001-05-01

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

Two-Phase Microstructures Generating Efficient Pinning Centers in the Heavily Pb-Substituted Bi 2Sr 2CaCu 2O 8+ ?Single Crystals  

NASA Astrophysics Data System (ADS)

Bi 2Sr 2CaCu 2O 8+ ?(Bi-2212) single crystals with a large amount of Pb substituted for Bi were grown by the floating zone method, and their magnetic properties and microstructures have been studied by means of SQUID magnetometory and electron microscopy. Critical current density ( Jc) increases dramatically beyond a critical Pb content of ˜0.4 per formula unit, where characteristic two-phase microstructures are revealed by electron microscopy. The "single" crystals consist of alternating thin (several tens of nanometers) lamellar plates of two phases with the (010) interface, one with lower Pb content (˜0.4) and a modulated structure and the other with higher Pb content (˜0.6) and a modulation-free structure. The relative volume fraction of the latter phase increases systematically with increasing starting Pb content. At higher Pb content, lamellas with irregularly stepped interfaces and bubbles of the latter phase embedded in the matrix of the former phase are also observed. The growth mechanism is discussed in terms of unidirectional solidification of eutectic or eutectoid.

Hiroi, Z.; Chong, I.; Takano, M.

1998-06-01

15

Hall effect and substitution effect in Pb 2Sr 2Y 1-xCa xCu 3O 8+?  

NASA Astrophysics Data System (ADS)

The Hall effect of ceramic samples of Pb 2Sr 2Y 1-xCa xCu 3O 8 has been investigated for 0 ? x ? 0.5. The Hall coefficient R H is positive and decreases with increasing x, which is explained within the doped Mott-Hubbard model. For x < 0.1, R H increases with decreasing temperature like a conventional semiconductor. For x= 0.1, R H is almost constant. For 0.2 ? x ? 0.5, where T c appears, R H increases with decreasing temperature again, and 1/R He is expressed as ?T + ? (? > 0, ? > 0). The temperature coefficient ? increases with increasing T c. These temperature dependences of R H are common to high-T c oxides. Effects of the partial substitution of Fe, Co, Ni, Zn, Ga for Cu on T c have been also studied for x = 0.5. The decrease in T c is marked in order of Ga, Co, Zn, Ni, Fe. This is discussed in relation to experimental results on YBa 2Cu 3O 7.

Sunagawa, Hiromu; Kaiwa, Nasahiro; Koike, Yoji; Noji, Takashi; Saito, Yoshitami

1991-12-01

16

Effect of La3+ substitution for Sr2+ on the phase formation, structure and properties of (Tl0.5Pb0.5 )Sr2Ca2Cu3Oy compounds  

Microsoft Academic Search

Optimization of the hole concentration in (Tl0.5Pb0.5)Sr2Ca2Cu3 Oy (Tl-1223) was attempted though partial replacement of Sr2+ by La3+. Nine samples with nominal composition (Tl0.5Pb0.5)Sr2-xLax Ca2Cu3Oy were prepared, with x varies from 0 to 2. Magnetization measurements as a function of temperature showed that the transition temperature increased with increasing La content. These measurements also showed an increase of the diamagnetic

N. M. Hamdan; H. El-Ghanem; J. Schwartz

2000-01-01

17

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

18

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

SciTech Connect

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

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

2013-11-27

19

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

20

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

21

Dimensional crossover in underdoped BiSrCaCuO  

NASA Astrophysics Data System (ADS)

BiSrCaCuO high quality crystals with x=0.2 were grown. The crystals were characterized by X-ray diffraction and DC susceptibility measurements confirming Bi2223 to be the major phase. The results are compared with those of Bi2223 with x=0.1, revealing that the Bi/Sr substitution ratio does not affect Tc. The doping dependences of the anisotropic normal state susceptibilities ?c(T)(H?c) and ?ab(T)(H?c) show that dimensionality of Bi2223 decreases in underdoped regime.

Iye, Tetsuya; Nagatochi, Takenori; Matsuda, Azusa

2010-12-01

22

Dimensional crossover in underdoped BiSrCaCuO  

NASA Astrophysics Data System (ADS)

BiSrCaCuO high quality crystals with x=0.2 were grown. The crystals were characterized by X-ray diffraction and DC susceptibility measurements confirming Bi2223 to be the major phase. The results are compared with those of Bi2223 with x=0.1, revealing that the Bi/Sr substitution ratio does not affect Tc. The doping dependences of the anisotropic normal state susceptibilities ?c(T) (H ? c) and ?ab(T) (H?c) show that dimensionality of Bi2223 decreases in underdoped regime.

Iye, Tetsuya; Nagatochi, Takenori; Matsuda, Azusa

23

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

NASA Technical Reports Server (NTRS)

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

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

1967-01-01

24

The structure and activation of substrate water molecules in Sr(2+)-substituted photosystem II.  

PubMed

The mechanism of solar water oxidation by photosystem II (PSII) is of fundamental interest and it is the object of extensive studies both in the past and present. The solar water oxidation reaction of PSII occurs in the oxygen-evolving complex (OEC). The OEC consists of a tetranuclear manganese calcium-oxo (Mn4Ca-oxo) cluster that is surrounded by amino acid residues and inorganic cofactors. The role of the Ca(2+) ion in the water oxidation reaction is one of the most interesting questions that is yet to be answered. In this study, we probe the structural and functional differences induced by metal ion substitution in the Mn4Ca-oxo cluster by substituting the Ca(2+) ion in the OEC by a Sr(2+) ion. We apply two-dimensional (2D) hyperfine sublevel correlation (HYSCORE) spectroscopy to detect weak magnetic interactions between the paramagnetic Mn4Sr-oxo cluster and the surrounding protons in the S2 state of the OEC of Sr(2+)-substituted PSII. We identify three groups of protons that are magnetically interacting with the Mn4Sr-oxo cluster. Using the recently reported 1.9 Å resolution X-ray structure of the OEC in the S1 state [Umena et al.] and the high-resolution 2D HYSCORE spectroscopy studies of the S2 state of the OEC of Ca(2+)-containing PSII [Milikisiyants et al., Energy Environ. Sci., 2012, 5, 7747], we discuss the assignments of the three groups of protons that are magnetically coupled to the Mn4Sr-oxo cluster. Since hyperfine interactions are highly sensitive to small perturbations in the electronic and geometric structure of paramagnetic centers, a comparison of the 2D HYSCORE spectra of Sr(2+)-substituted and Ca(2+)-containing PSII allows us to draw important conclusions with respect to the structure of the substrate water molecules in the OEC and the role of the Ca(2+) ion in the water oxidation reaction. In addition, for the first time, we determine the experimental value of the spin projection factor for the Mn(III) ion of the Mn4Ca-oxo cluster as ?1 = ±1.7 from the assignment of the hyperfine interaction of the paramagnetic cluster with the protons of the D1-His332 residue of PSII. PMID:25167223

Chatterjee, Ruchira; Milikisiyants, Sergey; Coates, Christopher S; Koua, Faisal H M; Shen, Jian-Ren; Lakshmi, K V

2014-10-14

25

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

PubMed

To examine regional variation in strontium (Sr), which at high concentrations may reduce eggshell quality, increase egg breakage and reproductive failure, we analyzed Sr, and calcium (Ca) concentrations and Sr/Ca ratios in eggshells from 20 avian species from California, Texas, Idaho, Kansas, and Michigan. In addition, we included data previously reported from Arizona to expand the regional comparisons and to better establish patterns of Sr, and Sr/Ca ratios in bird species across the United States. We found Sr concentrations varied significantly among regions, among species, and among foraging guilds; this variability is strongly influenced by the Sr/Ca ratios in surface water from locations close to the region where the eggshells were collected. Sr concentrations and Sr/Ca ratios were significantly higher in bird eggshells from the Volta wildlife region in the San Joaquin Valley, California and in various locales from Arizona. Sr concentrations and Sr/Ca ratios in bird eggshells from other locations in the USA were lower than those detected in these two regions. Among foraging guilds, invertivores had the highest Sr concentrations and Sr/Ca ratios and carnivores had the lowest. In general, the Sr/Ca ratio increased strongly with increasing Sr concentrations (R(2) = 0.99, P < 0.0001). There was a significant correlation (R(2) = 0.58, P < 0.0001) between Sr/Ca ratios in water and the average Sr/Ca ratios in eggshells suggesting that these values could be determined from Sr/Ca ratios in water. Eggshell thickness was poorly correlated with Sr (R(2) = 0.03) but had a significant and positive correlation with Ca and was more properly correlated by a quadratic equation (R(2) = 0.50, Thickness = 2.13 - 0.02Ca - 3.07 * 10(-5)Ca(2)). Our study provides further evidence that Sr accumulates significantly in the avian eggshell, in some regions at concentrations which could be of concern for potential negative effects on reproduction. We suggest that when assessing the effects of metals on avian reproduction in regions with high Sr deposits in rock and soil, Sr concentrations in the eggshell also should be measured to evaluate additional effects on thickness and reproduction. PMID:21660600

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

2011-08-01

26

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

27

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

28

Injectability of brushite-forming Mg-substituted and Sr-substituted ?-TCP bone cements  

Microsoft Academic Search

The influence of magnesium- and strontium-substitutions on injectability and mechanical performance of brushite-forming ?-TCP\\u000a cements has been evaluated in the present work. The effects of Mg- and Sr-substitutions on crystalline phase composition and\\u000a lattice parameters were determined through quantitative X-ray phase analysis and structural Rietveld refinement of the starting\\u000a calcium phosphate powders and of the hardened cements. A noticeable dependence

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

2010-01-01

29

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

NASA Astrophysics Data System (ADS)

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

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

2006-07-01

30

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. PMID:23243207

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

2013-01-01

31

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

32

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

NASA Astrophysics Data System (ADS)

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

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

1981-03-01

33

Heteronuclear Mn-Ca/Sr Complexes, and Ca/Sr EXAFS SpectralComparisons with the Oxygen-Evolving Complex of Photosystem II  

SciTech Connect

HeterometallicMn Ca and Mn Sr complexes have been preparedand employed as model complexes for Ca and Sr EXAFS spectral comparisonswith the Oxygen-Evolving Complex (OEC) of Photosystem II (PS II); thesehave revealed similarities that support the presence of at least one Oatom bridge between the Mn and Ca/Sr in the OEC.

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

2007-12-19

34

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

35

‘Eventless’ InsP3-dependent SR-Ca2+ release affecting atrial Ca2+ sparks  

PubMed Central

Augmented inositol 1,4,5-trisphosphate receptor (InsP3R) function has been linked to a variety of cardiac pathologies, including cardiac arrhythmia. The contribution of inositol 1,4,5-trisphosphate-induced Ca2+ release (IP3ICR) in excitation-contraction coupling (ECC) under physiological conditions, as well as under cellular remodelling, remains controversial. Here we test the hypothesis that local IP3ICR directly affects ryanodine receptor (RyR) function and subsequent Ca2+-induced Ca2+ release in atrial myocytes. IP3ICR was evoked by UV-flash photolysis of caged InsP3 under whole-cell configuration of the voltage-clamp technique in atrial myocytes isolated from C57/BL6 mice. Photolytic release of InsP3 was accompanied by a significant increase in the Ca2+ release event frequency (4.14 ± 0.72 vs. 6.20 ± 0.76 events (100 ?m)?1 s?1). These individual photolytically triggered Ca2+ release events were identified as Ca2+ sparks, which originated from RyR openings. This was verified by Ca2+ spark analysis and pharmacological separation between RyR and InsP3R-dependent sarcoplasmic reticulum (SR)-Ca2+ release (2-aminoethoxydiphenyl borate, xestospongin C, tetracaine). Significant SR-Ca2+ flux but eventless SR-Ca2+ release through InsP3R were characterized using SR-Ca2+ leak/SR-Ca2+ load measurements. These results strongly support the idea that IP3ICR can effectively modulate RyR openings and Ca2+ spark probability. We conclude that eventless and highly efficient InsP3-dependent SR-Ca2+ flux is the main mechanism of functional cross-talk between InsP3Rs and RyRs, which may be an important factor in the modulation of ECC sensitivity. PMID:23381902

Horn, Tamara; Ullrich, Nina D; Egger, Marcel

2013-01-01

36

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

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

2013-09-01

37

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

SciTech Connect

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

Allancon, C.; Odier, P.; Loup, J.P. [Centre de Recherches sur la Physique des Hautes Temperatures, Orleans (France)] [Centre de Recherches sur la Physique des Hautes Temperatures, Orleans (France); Bassat, J.M. [Institut de Chimie de la Matiere Condensee de Bordeaux, Pessac (France)] [Institut de Chimie de la Matiere Condensee de Bordeaux, Pessac (France)

1997-06-01

38

Synthesis of BiPbSrCaCuO superconductor  

DOEpatents

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

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

1994-04-05

39

Synthesis of BiPbSrCaCuO superconductor  

DOEpatents

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

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

1994-01-01

40

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

41

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

42

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

43

Effects of internal structural parameters on the properties of Ba-substituted La0.5Sr0.5MnO3  

NASA Astrophysics Data System (ADS)

Barium substituted La0.5Sr0.5-xBaxMnO3 materials have been synthesized and investigated using neutron powder diffraction. We show that Ba substitution suppresses the low temperature orbital-ordering previously observed in La0.5Sr0.5MnO3, and demonstrate the evolution of the magnetic and nuclear structures as a function of increasing Ba content. All samples exhibit paramagnetic and ferromagnetic properties near room temperature. The effects of A-site ionic size, size variance, and strains in the lattice on the ferromagnetic ordering temperature, TC, are discussed and compared with other members of the general La0.5(Ca,Sr,Ba)0.5MnO3 series. Depending on the substitution path, the relationship between TC and is either nearly constant or looks like an inverted parabola.

Chmaissem, Omar; Dabrowski, Bogdan; Kolesnik, Stanislaw; Suescun, Leopoldo; Mais, James; Maxwell, Timothy; Jorgensen, James D.

2007-03-01

44

New Fourier transform infrared emission spectra of CaH and SrH: combined isotopomer analyses with CaD and SrD  

NASA Astrophysics Data System (ADS)

In a search for the infrared spectra of gaseous CaH 2 and SrH 2, we obtained new Fourier transform infrared emission spectra of CaH and SrH, but no evidence of the metal dihydrides. The vibration-rotation bands from v=1?0 to v=4?3 of 40CaH and 88SrH, and the v=1?0 band of 87SrH and 86SrH were observed in the X2?+ ground electronic states. The new data were combined with the previous ground state data, obtained from diode laser infrared and pure rotational spectra, and the spectroscopic constants for v=0 to 4 of 40CaH and 88SrH were determined. In addition, the Dunham constants and the Born-Oppenheimer breakdown correction parameters were obtained using the previous ground state data for CaD and SrD in combined isotopomer fits. The equilibrium vibrational constants ( ?e) for CaH and SrH were found to be 1298.400(1) and 1207.035(1) cm -1, respectively, while the equilibrium rotational constants ( Be) are 4.277043(4) and 3.673495(4) cm -1. The equilibrium bond distances ( re) were determined to be 2.0023603(9) Å for CaH and 2.1460574(10) Å for SrH.

Shayesteh, Alireza; Walker, Kaley A.; Gordon, Iouli; Appadoo, Dominique R. T.; Bernath, Peter F.

2004-06-01

45

Raman Spectra of CaWO4, SrWO4, CaMoO4, and SrMoO4  

Microsoft Academic Search

The first-order Raman spectra of CaWO4, CaMoO4, SrWO4, and SrMoO4 have been obtained. All theoretically predicted vibrations have been observed, and assignment has been given for the internal vibrations of the tungstate and molybdate ions as well as for the external vibrations involving the rest of the lattice.

S. P. Porto; J. F. Scott

1967-01-01

46

Probing the links between structure and magnetism in Sr(2-x)Ca(x)FeOsO? double perovskites.  

PubMed

The synthesis, structure, and properties of the ordered double perovskites Sr2FeOsO6, Ca2FeOsO6, and SrCaFeOsO6 are reported. The latter two compounds have monoclinic P2?/n symmetry and a(-)a(-)b(+) tilting of the octahedra, while Sr2FeOsO6 is tetragonal with I4/m symmetry and a(0)a(0)c(-) tilting. Magnetic measurements indicate and neutron powder diffraction studies confirm that Ca2FeOsO6 is a ferrimagnet with a Curie temperature of 350 K. The ferrimagnetism is retained if half of the Ca(2+) ions are replaced with larger Sr(2+) ions to form SrCaFeOsO6 (T(C) = 210 K). This substitution reduces the degree of octahedral tilting, but unlike most perovskites, the magnetic ordering temperature decreases as the Fe-O-Os bond angles approach a linear geometry. In contrast, Sr2FeOsO6 orders antiferromagnetically, as previously reported. X-ray absorption spectroscopy confirms the assignment of Fe(III) and Os(V) oxidation states for all three compounds. In these insulating double perovskites, the magnetic ground state is governed by a competition between the four-bond Fe-O-Os-O-Fe antiferromagnetic superexchange coupling of Fe(III) ions and the two-bond Fe-O-Os antiferromagnetic superexchange coupling between neighboring Fe(III) and Os(V) ions. When the Fe-O-Os bonds are linear, as they are in the c direction in Sr2FeOsO6, the four-bond coupling between Fe(III) ions prevails. The competition shifts in favor of antiferromagnetic coupling of Fe(III) and Os(V) as the Fe-O-Os bond angles bend in response to chemical pressure. PMID:25025612

Morrow, Ryan; Freeland, John W; Woodward, Patrick M

2014-08-01

47

A study of the magnetic properties of hydrothermally synthesised Sr hexaferrite with Sm substitution  

NASA Astrophysics Data System (ADS)

Sm doped Sr hexaferrite particles were synthesised hydrothermally. Post-synthesised calcination with the aim of improving the magnetic properties of as-synthesised particles was conducted at temperatures ranging from 900°C to 1150°C for 2 h in air. The effects of the Sm/Sr ratio and the calcination temperature on the crystallography, particle morphology and magnetic properties of Sm doped Sr hexaferrite were investigated by an X-ray diffractometer, scanning electron microscope and vibrating sample magnetometer. It was found that, unlike transition metal element substitution, Sm substitution does not decrease the hexaferrite particle size. The intrinsic coercivities of Sm doped Sr hexaferrite are significantly higher than those of Sr hexaferrite. It has been observed that Sm substitution can increase the intrinsic coercivity of Sr hexaferrite without causing any deterioration of the saturation magnetisation and remanence. In the Sm/Sr range 1/8-1/2 inclusively, there is little change in the coercivity but a slight fall in both the magnetisation and the remanence.

Wang, J. F.; Ponton, C. B.; Harris, I. R.

2001-09-01

48

High Precision Determination of Sr\\/Ca and Mg\\/Ca Elemental Ratios in Massive Coral Skeletons  

Microsoft Academic Search

Summary The Thermo Scientific ELEMENT 2, a single collector double focusing sector field ICP-MS, was used for the determination of Sr\\/Ca and Mg\\/Ca elemental ratios in microgram samples taken from seasonal growth bands in a coral skeleton (Diploria strigosa). Variations in ?18O values were found to be in good agreement with the results for Sr\\/Ca and Mg\\/Ca elemental ratio deter-

Henning Kuhnert; Julian D. Wills; Meike Hamester; Thermo Fisher; Charles B. Douthitt; S. Raven Ridge

49

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

NASA Astrophysics Data System (ADS)

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

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

2005-08-01

50

Ca Sparks Do Not Explain all Ryanodine Receptor-Mediated SR Ca Leak in Mouse Ventricular Myocytes  

PubMed Central

Abstract Diastolic Ca leak from the sarcoplasmic reticulum (SR) of ventricular myocytes reduces the SR Ca content, stabilizing the activity of the SR Ca release channel ryanodine receptor for the next beat. SR Ca leak has been visualized globally using whole-cell fluorescence, or locally using confocal microscopy, but never both ways. When using confocal microscopy, leak is imaged as “Ca sparks,” which are fluorescent objects generated by the local reaction-diffusion of released Ca and cytosolic indicator. Here, we used confocal microscopy and simultaneously measured the global ryanodine-receptor-mediated leak rate (Jleak) and Ca sparks in intact mouse ventricular myocytes. We found that spark frequency and Jleak are correlated, as expected if both are manifestations of a common phenomenon. However, we also found that sparks explain approximately half of Jleak. Our strategy unmasks the presence of a subresolution (i.e., nonspark) release of potential physiological relevance. PMID:20483318

Santiago, Demetrio J.; Curran, Jerald W.; Bers, Donald M.; Lederer, W.J.; Stern, Michael D.; Ríos, Eduardo; Shannon, Thomas R.

2010-01-01

51

Sr/Ca ratios of modern and fossil Favia corals from the Korea Strait; implications for application of coral Sr/Ca thermometry in a middle latitude region  

NASA Astrophysics Data System (ADS)

Favia, a hermatypic reef building coral, is widely distributed from equator to northern latitudinal limit of coral distribution. An 150-mm-long living, grown for 21 years, and 50-mm-long fossil (2600 cal yr BP) Favia specimens, grown for 13 years, were collected from the Iki Island, Japan (34°48'N, 129°39'E) and analyzed for Sr/Ca ratios, in order to test for a high-resolution paleo-SST proxy. The modern and fossil Favia samples reveal clear annual seasonality in density bands and the measured Sr/Ca ratios. In the modern coral, however, the large inter-annual variability of winter Sr/Ca indicates smoothing of environmental signals during cold season due to very slow growth or frequent growth cessations. An SST - Sr/Ca equation, Sr/Ca (mmol/mol) = 10.428 - 0.049 × SST (°C), constructed under the assumption of growth stopping below 14°C, predicts the observed annual summer maximums within an error range of ± 1.2°C. Large inter-annual variability of Sr/Ca is also observed in the fossil coral, but even in the warm season, indicating more frequent coral growth disturbances due to colder condition at 2600 cal yr BP. With an assumption that growth disturbance had the least effect on the lowest Sr/Ca, the equation predicts summer maximum temperature of 24.6°C, ~ 2°C lower than the present. The SST - Sr/Ca equation established in this study successfully reconstructs SSTs of a subtropical region from reported literature values, suggesting the applicability of Sr/Ca thermometry of Favia in a wide range of climate settings.

Seo, I.; Lee, Y.; Watanabe, T.; Shimamura, M.; Yamano, H.; Yoo, C.; Hyeong, K.

2011-12-01

52

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

PubMed Central

Background The calcium sensing receptor (CaSR) regulates serum calcium by suppressing secretion of parathyroid hormone; it also regulates renal tubular calcium excretion. Inactivating mutations of CaSR raise serum calcium and reduce urine calcium excretion. Thyroid C-cells (which make calcitonin) express CaSR and may, therefore, be regulated by it. Since calcium stimulates release of calcitonin, the higher blood calcium caused by inactivation of CaSR should increase serum calcitonin, unless CaSR mutations alter the responsiveness of calcitonin to calcium. To demonstrate regulatory effects of CaSR on calcitonin release, we studied calcitonin responsiveness to calcium in normal and CaSR heterozygous-ablated (Casr+/-) mice. Casr+/- mice have hypercalcemia and hypocalciuria, and live normal life spans. Each mouse received either 500 ?l of normal saline or one of two doses of elemental calcium (500 ?mol/kg or 5 mmol/kg) by intraperitoneal injection. Ionized calcium was measured at baseline and 10 minutes, and serum calcitonin was measured on the 10 minute sample. Results At baseline, Casr+/- mice had a higher blood calcium, and in response to the two doses of elemental calcium, had greater increments and peak levels of ionized calcium than their wild type littermates. Despite significantly higher ionized calcium levels, the calcitonin levels of Casr+/- mice were consistently lower than wild type at any ionized calcium level, indicating that the dose-response curve of calcitonin to increases in ionized calcium had been significantly blunted or shifted to the right in Casr+/- mice. Conclusions These results confirm that the CaSR is a physiological regulator of calcitonin; therefore, in response to increases in ionized calcium, the CaSR inhibits parathyroid hormone secretion and stimulates calcitonin secretion. PMID:15099400

Fudge, Neva J; Kovacs, Christopher S

2004-01-01

53

Seawater strontium and Sr/Ca variability in the Atlantic and Pacific oceans  

NASA Astrophysics Data System (ADS)

Seawater Sr and Sr/Ca exhibit spatial gradients of 2-3% globally, with the deep ocean more enriched relative to the surface. In latitudinal transects, the highest surface values are found at high latitudes and associated with areas of upwelling. A pronounced upper ocean vertical Sr gradient is attributable to the production of celestite skeletons by surface-dwelling acantharia, coupled to a shallow dissolution cycle. The upper ocean residence time of Sr with respect to celestite cycling is much shorter than its global oceanic residence time. Although the magnitude of seawater Sr/Ca variability is relatively small, it is significant with respect to high-precision paleoceanographic applications. Sr/Ca gradients in the contemporary ocean also complicates evaluating Quaternary changes in seawater Sr/Ca that may have resulted from other processes, such as aragonite recrystallization during sea-level low stands.

de Villiers, Stephanie

1999-09-01

54

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

SciTech Connect

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

de Villiers, S.; Shen, G.T.; Nelson, B.K. (Univ. of Washington, Seattle, WA (United States))

1994-01-01

55

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

NASA Astrophysics Data System (ADS)

SummaryA comparative study of Sr and Ca isotopes was conducted to assess solute sources and effects of biogeochemical processes on surface water and groundwater in four small tropical catchments located at La Selva Biological Station, Costa Rica. Variable concentrations of dissolved Sr2+ and Ca2+ in the catchments are related to mixing of waters from different origin. Three catchments are influenced by high-solute bedrock groundwater, while another catchment is primarily supplied by local recharge. 87Sr/86Sr ratios were employed to discriminate contributions from mineral weathering and atmospheric sources. Solutes in bedrock groundwater have a predominant geogenic origin, whereas local recharge is characterized by low-solute inputs from rainwater and minor in situ weathering releases from nutrient-depleted soils. Bedrock groundwater contributes more than 60% of dissolved Sr2+ to surface discharge in the Salto, Saltito, and Arboleda catchments, whereas the Taconazo catchment receives more than 95% of dissolved Sr2+ from rainwater. ?44/40Ca values of dissolved Ca2+ vary greatly in the catchments, mainly as a result of heterogeneous Ca isotope compositions of the contributing sources. Based on differences in ?44/40Ca values, two distinct bedrock groundwaters discharging at the Salto and the Arboleda catchments are suggested. Effects of biological processes in the plant-soil system on solute generation in the catchments are indicated by variable Ca/Sr ratios. However, these effects cannot clearly be assessed by Ca isotopes due to the strong heterogeneity of ?44/40Ca values of Ca2+ sources and high Ca2+ concentrations in bedrock groundwater.

Wiegand, B. A.; Schwendenmann, L.

2013-04-01

56

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

57

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

SciTech Connect

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

Matsuda, M.; Katsumata, K. [Inst. of Physical and Chemical Research, Wako, Saitama (Japan); Shapiro, S.M.; Shirane, G. [Brookhaven National Lab., Upton, NY (United States). Physics Dept.

1998-08-20

58

Cenozoic pelagic Sr/Ca records: Exploring a link to paleoproductivity  

NASA Astrophysics Data System (ADS)

Recent studies have revealed that Sr/Ca ratios of coccolithophores may be affected by productivity. Here we compile published Sr/Ca data from bulk carbonate, fine fraction sediment, and planktonic foraminiferal Sr/Ca records that span the past 60 Myr and attempt to place these records into a paleoceanographic framework. We account for changes in seawater Sr/Ca ratios using the curve of [2003] and discuss our observations with respect to changes in the partitioning coefficient of Sr through time. We discuss limitations associated with postburial processes, temporal changes in the coccolith/planktonic foraminiferal rain ratio, and the coccolith species composition of the sediment. Despite these caveats, we are able to show that in the bulk and fine fraction carbonate records there are two broad periods of enhanced partitioning of Sr relative to today, the Oligocene, and the middle to late Miocene/early Pliocene. Because these are two intervals for which we can cite evidence for a relatively productive ocean on the regional or global scale, we believe that the Sr/Ca ratios of bulk carbonate can be explained, at least in part, by the effects of oceanic nutrient levels on Sr uptake during calcification of coccoliths, which make up the vast majority of these sediments. Within the limits of the inferred seawater Sr/Ca record the results of this study contribute a geologic perspective to recent laboratory and field studies that have raised the possibility that Sr incorporation into biogenic calcite is controlled by biogeochemical processes.

Billups, K.; Rickaby, R. E. M.; Schrag, D. P.

2004-09-01

59

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

PubMed Central

This study examined the effects of SR33805, a fantofarone derivative with reported strong Ca2+ -antagonistic properties, on the contractile properties of intact and skinned rat ventricular myocytes. On intact cells loaded with the Ca2+-fluorescent indicator Indo-1, the application of low concentrations of SR33805 enhanced the amplitude of unloaded cell shortening and decreased the duration of cell shortening. Amplitude of the Ca2+ transient was also decreased. These effects were accompanied with a shortening of the action potential and a dose-dependent blockade of L-type calcium current (IC50=2.4 × 10?8 M). On skinned cardiac cells, the application of a low SR33805 concentration (10?8 M) induced a significant increase in maximal Ca2+-activated force at the two-tested sarcomere lengths (SLs), 1.9 and 2.3 ?m. The application of a larger dose of SR33805 (10?6–10?5 M) induced a significant leftward shift of the tension–pCa relation that accounts for Ca2+-sensitization of the myofilaments, particularly at 2.3 ?m SL. In conclusion, despite its strong Ca2+-antagonistic properties SR33805 increases cardiac cell contractile activity as a consequence of its Ca2+-sensitizing effects. These effects are attributable to both an increase in the maximal Ca2+-activated force and a length-dependent Ca2+-sensitization. PMID:12746228

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

2003-01-01

60

Sr 2+ uptake and leachability study on cured aluminum-substituted tobermorite–OPC 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

61

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

E-print Network

G22048 Strong kinetic effects on Sr/Ca ratios in the calcitic bivalve Pecten maximus Anne Lorrain Although Sr/Ca ratios in abiogenic calcite are strongly controlled by precipitation rates, such a kinetic effect has never been demonstrated in calcitic bivalve shells. Therefore, we report 1 hal-00452403

Brest, Université de

62

Development of CaZn based glassy alloys as potential biodegradable bone graft substitute  

E-print Network

Development of CaZn based glassy alloys as potential biodegradable bone graft substitute W. Jiao, which make it be potential as biodegradable bone graft substitute. Compared to commonly investigated be used as coronary stent and bone graft substitute [1­3]. Up to now, magnesium alloys [4­9] and iron

Zheng, Yufeng

63

Transcription Factor CREB is Involved in CaSR-mediated Cytoskeleton Gene Expression.  

PubMed

Our previous studies illustrated that a steady increase of intracellular calcium concentration ([Ca(2+) ]i) was important for maintaining microtubules (MTs) rearrangement in apoptotic cells. However, little is known about the effect of calcium sensing receptor (CaSR)-mediated increase in [Ca(2+) ]i on cytoskeleton gene expression. We examined the impact of taxol or CaSR agonist/antagonist on the regulation of [Ca(2+) ]i concentration, cytoskeleton arrangement, phosphorylated CREB and cytoskeleton gene expressions in HeLa cells with dominant negative plasmid of CREB (PM). This study demonstrated that Gdcl3 (a specific CaSR agonist) evoked a rapid increase of [Ca(2+) ]i, formed a rigid bundle of MTs which surrounded the nucleus and decreased the cytoskeleton gene expressions in HeLa cells. These effects were rescued by addition of NPS2390 (a specific CaSR antagonist). Moreover, CaSR activity affected cytoskeleton gene expression through transcription factor CREB. Histoscores of pCREB immunoreactivity in tissues of cervical adenocarcinoma, renal clear cell carcinoma, and diffuse large B-cell lymphoma were markedly increased compared with non malignant tissue. These data demonstrate, for the first time, that CaSR-mediated increase in [Ca(2+) ]i probably modulate cytoskeleton organization and gene expression via transcription factor CREB. Anat Rec, 298:501-512, 2015. © 2014 Wiley Periodicals, Inc. PMID:25382680

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

2015-03-01

64

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

65

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

66

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 (6°N, 162°W; Cobb et al., 2003; Nurhati et al., 2011), we measure mm- and ?m-scale Sr/Ca in four overlapping modern Porites cores. Conventional mm-scale Sr/Ca records from these modern cores are well correlated with each other (R = 0.65 to 0.68) and with SST (R = -0.73 to -0.85), but the absolute Sr/Ca values of these records exhibit baseline offsets of ×0.11mmol/mol (1?). Secondary ion mass spectrometry (SIMS) is used to generate 2-3 year long, weekly-resolved, Sr/Ca records from 3 overlapping modern coral segments. While the SIMS Sr/Ca analyses from each core exhibit relatively large point-to-point variations of ~0.17mmol/mol (1?), compared to ~0.06mmol/mol (1?) in mm-scale Sr/Ca, their monthly-scale variability resolves the annual SST cycles observed at Palmyra reasonably well (R = -0.46 to -0.64). Furthermore, the intercolony offsets observed in mm-scale Sr/Ca records are reproduced in the SIMS Sr/Ca records. These large offsets imply that paleo-SST estimates derived from a single fossil coral Sr/Ca dataset would be associated with uncertainties of ×1.4°C (1?). We build a coral Sr/Ca 'stack' for Palmyra Island using Sr/Ca records from the 4 modern cores. This composite Sr/Ca record is more strongly correlated with SST (R=-0.86), as intercolony variability is averaged out. In ongoing work, we apply this composite calibration to fossil coral Sr/Ca stacks, generated from multiple overlapping cores, from Palmyra Island to provide robust SST estimates for select intervals of the last millennium. References: Cobb, K. M., et al., Nature 424, 271-276 (2003). Nurhati, I. S., et al., Journal of Climate 24, 3294-3308 (2011).

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

2013-12-01

67

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

SciTech Connect

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

Deis, T.A.; Eror, N.G.; Krishnaraj, P.; Prorok, B.C.; Lelovic, M. [Univ. of Pittsburgh, PA (United States). Dept. of Materials Science and Engineering; Balachandran, U. [Argonne National Lab., IL (United States). Energy Technology Div.

1995-07-01

68

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

SciTech Connect

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

Sun, B.Z.; Zhou, S.L.; Wang, H.; Fei, Z.Y.; Lu, X.M.; Wang, T.L. [College of Science, Northeastern University, Shenyang 110819 (China); Qi, Y., E-mail: qiyang@imp.neu.edu.cn [College of Science, Northeastern University, Shenyang 110819 (China); Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China)

2014-01-15

69

Hysteresis analysis of CoTi substituted M-type BaSr hexagonal ferrite Charanjeet Singh a,  

E-print Network

Hysteresis analysis of Co­Ti substituted M-type Ba­Sr hexagonal ferrite Charanjeet Singh a, , S.5Sr0.5CoxTixFe(12 - 2x)O19 ferrite have been investigated by XRD, SEM and VSM. XRD and SEM confirm M ferrites are known for their strong uniaxial magne- tocrystalline anisotropy with ease of magnetization

Koledintseva, Marina Y.

70

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

PubMed Central

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

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

2014-01-01

71

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

SciTech Connect

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

Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B. [Argonne National Lab., IL (United States); Nash, A.S. [Marquette Univ., Milwaukee, WI (United States)

1992-05-01

72

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

SciTech Connect

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

Goretta, K.C.; Lanagan, M.T.; Kaufman, D.Y.; Biondo, A.C.; Wu, C.T.; Loomans, M.E.; Cheesman, M.R.; Poeppel, R.B. (Argonne National Lab., IL (United States)); Nash, A.S. (Marquette Univ., Milwaukee, WI (United States))

1992-05-01

73

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

SciTech Connect

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

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

2010-03-11

74

Sr/Ca as a Potential Proxy of Sub-surface Temperature Variability in C. secundum  

NASA Astrophysics Data System (ADS)

There is increasing interest in the development of proxy records of oceanographic variability from intermediate and deep-water environments using deep-sea corals. Recent work has focused on isotopic and elemental ratios as proxies for temperature with limited success. Here we explore the potential uses of Mg/Ca and Sr/Ca in the same Corallium secundum sample using LA-ICP-MS. C. secundum samples where collected from the Makapuu deep-sea coral off the coast of Hawaii at 400 m water depth. Both inter and intra sample reproducibility of several trace elements, including Mg, Sr, Cd, and Ba and any correlation to instrumental time series is explored. The most promising results are presented. Two ~70 year Sr/Ca time-series were developed using a laser ablation ICP-MS (LA-ICP-MS) system in continuous scanning mode with a 20x200 micron slit on C. secundum specimens collected at the same deep-sea coral bed. Both specimens have age models based on radiocarbon measurements. The time-series was compared to a ~35 year monthly averaged temperature record (WOD98 and GSTPP) from 400 meters. The LA-ICP-MS Sr/Ca data show a remarkable degree of correspondent variability over the most recent 35 years respectively to the sub surface temperature record at slightly greater than annual resolution. Water temperatures vary from 8.5 to 10°C while the Sr/Ca varies from 3.3 to 3.0 mmol/mol. Sub decadal variability of the temperature appears to match Sr/Ca variability reasonably well even when assuming a linear growth rate (170 µm/yr). Longer term (~25 year) cycles are evident in the 70 year LA-ICP-MS Sr/Ca time-series. These results suggest Sr/Ca measurements in C. secundum specimens may be a viable proxy of sub-surface temperature variability.

Roark, E.; Fallon, S. J.; Guilderson, T. P.; Dunbar, R. B.; McCulloch, M. T.

2009-12-01

75

Effects of internal structural parameters on the properties of Ba-substituted La0.5Sr0.5MnO3  

NASA Astrophysics Data System (ADS)

A series of barium substituted La0.5Sr0.5-xBaxMnO3 materials has been synthesized and investigated using neutron powder diffraction. We show that Ba substitution suppresses the low-temperature orbital ordering that has been previously observed in La0.5Sr0.5MnO3 , and demonstrate the evolution of the magnetic and nuclear structures as a function of increasing Ba content. All our samples exhibit paramagnetic and ferromagnetic properties near room temperature with the ferromagnetic structures described as I4/mc'm' and P4/mm'm' for x=0 , 0.1, and 0.2 and x=0.3 , 0.4, and 0.5, respectively. The Mn magnetic moments align ferromagnetically in the direction of the c axis with no evidence for any spin canting. The effects of A-site ionic size, size variance, and strains in the lattice on the ferromagnetic ordering temperature, TC , are discussed and compared with other members of the general La0.5(Ca,Sr,Ba)0.5MnO3 series. Depending on the substitution path, the relationship between TC and ?rA? is either near constant or looks like an inverted parabola. Finally, details of the magnetic, resistive, structural, and interatomic properties are presented.

Chmaissem, O.; Dabrowski, B.; Kolesnik, S.; Mais, J.; Suescun, L.; Jorgensen, J. D.

2006-10-01

76

Composition, structure, and electrical properties of Bi2Sr2Ca1-yYyCu2O8: A single-crystal study  

Microsoft Academic Search

A systematic study of yttrium substitution for calcium in the high-temperature superconductor Bi2Sr2CaCu2O8 has been performed. Single crystals were grown, cleaved, and characterized with use of x-ray fluorescence, electron microprobe, and electron- and x-ray-diffraction techniques. The dc resistivity, diamagnetic shielding, and Hall coefficient of the samples were also measured as functions of the temperature from 4 to 300 K for

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

1992-01-01

77

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

78

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

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

79

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 0.51×0.18‰to 1.09×0.14‰, 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 0.215×0.004‰ to 0.333×0.004‰, with a mean ?88/86Sr of rainwater is 0.296×0.01‰. 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

80

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

SciTech Connect

This report summarizes laboratory scale studies investigating the remediation of Sr-90 by Ca-citrate-PO4 solution injection/infiltration to support field injection activities in the Hanford 100N area. This study is focused on experimentally testing whether this remediation technology can be effective under field scale conditions to mitigate Sr-90 migration 100N area sediments into the Columbia River. Sr-90 is found primarily adsorbed to sediments by ion exchange (99% adsorbed, < 1% in groundwater) in the upper portion of the unconfined aquifer and lower vadose zone. Although primarily adsorbed, Sr-90 is still considered a high mobility risk as it is mobilized by seasonal river stage increases and by plumes of higher ionic strength relative to groundwater. This remediation technology relies upon the Ca-citrate-PO4 solution forming apatite precipitate [Ca6(PO4)10(OH)2], which incorporates some Sr-90 during initial precipitation and additionally slowly incorporates Sr-90 by solid phase substitution for Ca. Sr substitution occurs because Sr-apatite is thermodynamically more stable than Ca-apatite. Once the Sr-90 is in the apatite structure, Sr-90 will decay to Y-90 (29.1 y half-life) then Zr-90 (64.1 h half-life) without the potential for migration into the Columbia River. For this technology to be effective, sufficient apatite needs to be emplaced in sediments to incorporate Sr and Sr-90 for 300 years (~10 half-lives of Sr-90), and the rate of incorporation needs to exceed the natural groundwater flux rate of Sr in the 100N area. A primary objective of this study is to supply an injection sequence to deliver sufficient apatite into subsurface sediments that minimizes initial mobility of Sr-90, which occurs because the injection solution has a higher ionic strength compared to groundwater. This can be accomplished by sequential injections of low, then high concentration injection of Ca-citrate-PO4 solutions. Assessment of low concentration Ca-citrate-PO4, citrate-PO4, and PO4 solutions show greater Sr and Sr-90 incorporation during initial precipitation and less initial mobilization with solutions with low Ca2+ concentration. While all solutions showed nearly the same Sr uptake into apatite (14 to 17% by 2 weeks, 21% to 30% by 5 weeks), the incorporation efficiency (i.e., mM Sr incorporated per mM PO4 injected) was higher for solutions containing citrate. The Sr incorporation rate into apatite during initial precipitation (by 1 month) averaged 4.64 ± 1.9 x 10-4 h-1 (half-life 1500 ± 430 h, 8.85 x 10-7 mg Sr/day/mg apatite). The injection solution used in field injections #3 to #18 (10 mM PO4, 1 mM Ca, 2.5 mM citrate), which is deficient in Ca (a total of 16.7 mM needed to form apatite with 10 mM of PO4), resulted in the initial Sr and Ca peak (24 h) at 4.7x groundwater. By 30 days, the aqueous Sr concentration was 0.28x groundwater and Ca 0.43x groundwater, as both Sr and Ca are used to form initial apatite precipitates. Reactive transport simulation of the complex ion exchange, biodegradation, and precipitation processes showed that the initial Sr groundwater increase mobilized only 1.5% of the Sr mass in sediments. Citrate biodegradation, a necessary step in Ca-citrate-PO4 solutions forming apatite, had an average half-life of 50 h (at aquifer sediment/water ratio and temperature), and decreased an order of magnitude with sediment depth as the microbial biomass decreased five orders of magnitude. The rate of citrate biodegradation was relatively invariant with biomass and water saturation (50% to 100%, for vadose zone infiltration) possibly due to significant microbial injection using river water and subsurface microbial mobilization.

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

2007-10-01

81

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

82

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 (˜33°48'N), Japan, one of the highest latitude coral reefs known to exist at present, where winter monthly mean sea surface temperature (SST) drops to 13°C. 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 ±1.1°C (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

83

Changes in Soybean Fruit Ca2+ (Sr2+) and K+ (Rb+) Transport Ability during Development.  

PubMed

Mineral uptake by soybean (Glycine max [L.] Merrill) seeds during development can significantly affect seed quality and value. Little is known about seed mineral transport mechanisms and control processes, although it is clear that each mineral displays a characteristic accumulation pattern. Ion-specific accumulation patterns could result from changes in source availability, in transport kinetics through the seed pod and seed coat, or in the mineral uptake capability of the embryo. Ca2+ and K+ have negligible and high phloem mobilities, respectively. Ca2+ accumulation lags behind dry matter (C and N) and K+ accumulation in soybean embryos. To eliminate source availability influences, the Ca2+ and K+ uptake ability of isolated embryos and of seeds in pod culture was examined during seed development. Sr2+ and Rb+ were used as transport analogs of Ca2+ and K+, respectively. Sr2+ and Rb+ uptake rates by isolated embryos increased with seed fresh weight, indicating that the embryo was not limiting Ca2+ accumulation. However, the pod-cultured embryo Sr2+ and Rb+ uptake rate trends differed: Rb+ uptake increased with seed fresh weight, whereas Sr2+ uptake rates remained constant or decreased slightly. Ovule Sr2+ influx data suggest that the pod and seed coat impose a transport barrier that could account for the relative decline in embryo Ca2+ content during development. PMID:12232138

Laszlo, J. A.

1994-03-01

84

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

NASA Astrophysics Data System (ADS)

Solid solutions of alkaline earth hexaborides were synthesized and densified by spark plasma sintering at 100 MPa. The high-temperature thermoelectric properties (Seebeck coefficients, electrical and thermal diffusivities, heat capacities) were measured between room temperature and 1073 K. CaB6, SrB6, BaB6 and the ternary hexaborides CaxSr1-xB6, CaxBa1-xB6, SrxBa1-xB6 (x = 0.25, 0.5, 0.75) are n-type conducting compounds over the whole compositional and thermal ranges. The values of the figure of merit ZT for CaB6 (ca. 0.3 at 1073 K) were found to be significantly increased compared to earlier investigations which is attributed to the densification process.

Gürsoy, M.; Takeda, M.; Albert, B.

2015-01-01

85

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

86

The Extracellular Calcium-Sensing Receptor (CaSR) Is a Critical Modulator of Skeletal Development  

PubMed Central

The extracellular Ca2+-sensing receptor (CaSR) plays a nonredundant role in the functions of the parathyroid gland (PTG) and the kidney. Severe hyperparathyroidism, premature death, and incomplete gene excision in Casr?/? mice have precluded the assessment of CaSR function in other tissues. We generated mice with tissue-specific deletion of Casr in the PTG, bone, or cartilage. Deletion of Casr in the PTG or bone resulted in profound bone defects, whereas deletion of Casr in chondrocytes (cartilage-producing cells) resulted in death before embryonic day 13 (E13). Mice in which chondrocyte-specific deletion of Casr was induced between E16 and E18 were viable but showed delayed growth plate development. Our data show a critical role for the CaSR in early embryogenesis and skeletal development. PMID:18765830

Chang, Wenhan; Tu, Chialing; Chen, Tsui-Hua; Bikle, Daniel; Shoback, Dolores

2012-01-01

87

Superconducting properties of Ca3Ir4Sn13: a ?SR study  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

88

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 298±2 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.

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

2013-04-01

89

Control of mean ionic radius at Ca site by Sr co-doping for Ce doped LiCaAlF6 single crystals and the effects on optical and scintillation properties  

NASA Astrophysics Data System (ADS)

Sr co-doped Ce:LiCaAlF6 [Ce:Li(Ca,Sr)AlF6] crystals with various Ca/Sr ratios were grown by a micro-pulling-down (?-PD) method and effects of Sr co-doping on crystal structure, chemical composition, optical and scintillation properties for Ce:LiCaAlF6 crystals were investigated as a neutron scintillator. High transparent Ce2%:Li(Ca,Sr)AlF6 crystals with 2% and 5% Sr contents were obtained while Ce2%:Li(Ca,Sr)AlF6 crystals with 10% and 20% Sr contents included milky parts in the crystals. a- and c-axis lengths of Ce:Li(Ca,Sr)AlF6 phase systematically increased with an increase of Sr content. In addition to the emission at 284 and 308 nm from Ce3+ ion, emission peaks at 367 nm appeared by Sr co-doping.

Yokota, Yuui; Yamaji, Akihiro; Kurosawa, Shunsuke; Kamada, Kei; Yoshikawa, Akira

2014-10-01

90

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

91

Standard enthalpies of formation of member oxides in the Bi-Sr-Ca-Cu-O system  

Microsoft Academic Search

The standard enthalpies of formation of member oxides in the Bi-Sr-Ca-Cu-O system have been determined by the solution calorimetric method. On the basis of enthalpy, the chemical stability of member oxides was discussed. It was found that the chemical stability increases in the order of 2223 < 2212 < 2201. The complex oxides formed from SrO were found to be

Yasushi Idemoto; Kenji Shizuka; Youka Yasuda; Kazuo Fueki

1993-01-01

92

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

93

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

94

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

95

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

96

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

97

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

98

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

NASA Astrophysics Data System (ADS)

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

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

99

Sr / Ca ratios as indicators of varying modes of pelagic carbonate diagenesis in the ooze, chalk and limestone realms  

NASA Astrophysics Data System (ADS)

There has been an interest in the application of Sr / Ca ratios in pelagic carbonates to reconstruct paleoceanographic conditions such as changes in the oceanic Ca and Sr budgets or calcareous nannoplankton productivity, but the effect of burial diagenesis on primary Sr / Ca records has not been sufficiently understood. In order to clearly document Sr / Ca records of pelagic carbonates relative to original paleoceanography or secondary diagenetic processes, Sr / Ca analyses were performed on bulk sediments from an 822.5 m-thick ooze-chalk-limestone sequence at the Mid-Pacific Mountains, Deep Sea Drilling Project Site 463. The Sr / Ca ratios exponentially decrease from ˜2.3 to ˜1.1 mmol/mol with increasing burial depth in the ooze-chalk interval (0-452.0 m below seafloor (mbsf)). The Sr / Ca ratios further decline to as low as ˜0.4 mmol/mol in the limestone interval (> 452.0 mbsf), with relatively high values of > 1.1 mmol/mol at carbonate-poor lithology around 620 mbsf. The stratigraphic Sr / Ca trends appear to be consistent with porosity profile, and similar Sr / Ca—porosity covariation in association with diagnetic changes in lithologies is also common in Ontong Java Plateau sections. By adopting a recent diagenetic model from backscattered electron image analysis of Ontong Java Plateau sections, it is postulated for Site 463 that exponential Sr / Ca decrease in the ooze-chalk interval is due to the release of Sr into interstitial water via recrystallization (i.e., purification effect), and that further decrease in Sr / Ca ratios in the limestone interval is most likely due to acquisition of Sr-depleted calcite cement at the 'chalk-limestone transition' (newly proposed as the dilution effect). Specifically, Sr / Ca ratios of deeply buried pelagic limestones are sensitive to the amount of calcite cement that is acquired in proportion to CaCO 3 content; i.e., carbonate-rich lithology facilitates precipitation of secondary calcite at the chalk-limestone transition. Therefore, paleoceanographic interpretation by means of Sr / Ca ratios in pelagic carbonates will become valid only when these diagenetic effects are appropriately constrained.

Ando, Atsushi; Kawahata, Hodaka; Kakegawa, Takeshi

2006-09-01

100

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

PubMed Central

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

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

2012-01-01

101

New alkaline earth aluminium fluorides with the formula (M, M?)AlF 5 (M, M? = Ca, Sr, Ba)  

Microsoft Academic Search

Two new modifications, ??-SrAlF5 and ?-BaAlF5, as well as two solid solutions, Ca0.08Sr0.92AlF5 and Ca0.33Sr0.67AlF5, have been synthesized in the system (M, M?)F2\\/AlF3 with M, M? = Ca, Sr, Ba. The preparation of single crystals has been performed under hydrothermal conditions and solid state reactions, respectively. All crystal structures have been refined from single crystal diffractometer data. A common feature

Matthias Weil; Erich Zobetz; Franz Werner; Frank Kubel

2001-01-01

102

Photoluminescent improvement of SrMoO 4 by the electrochemical formation of Ca 2+-doped solid solutions  

Microsoft Academic Search

Pure SrMoO4 and CaMoO4, and SrMoO4 solid solution crystallites were successfully prepared by a simple electrochemical process. The photoluminescence (PL) of SrMoO4 can be greatly improved by incorporating Ca2+ into its matrix to form solid solutions, and their emission bands slightly red-shift from 500nm to 509nm due to the local structure relaxation. Doping Ca2+ would inhibit the growth of SrMoO4

Yong Sun; Junfeng Ma; Jingrui Fang; Chang Gao; Zhensen Liu

2011-01-01

103

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

104

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

PubMed

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

Saparov, Bayrammurad; Sefat, Athena S

2014-10-28

105

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

DOEpatents

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

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

1992-01-01

106

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

NASA Astrophysics Data System (ADS)

The volcano-hydrothermal system of El Chichón volcano, Chiapas, Mexico, is characterized by numerous thermal manifestations including an acid lake, steam vents and boiling springs in the crater and acid and neutral hot springs and steaming ground on the flanks. Previous research on major element chemistry reveals that thermal waters of El Chichón can be divided in two groups: (1) neutral waters discharging in the crater and southern slopes of the volcano with chloride content ranging from 1500 to 2200 mg/l and (2) acid-to-neutral waters with Cl up to 12,000 mg/l discharging at the western slopes. Our work supports the concept that each group of waters is derived from a separate aquifer (Aq. 1 and Aq. 2). In this study we apply Sr isotopes, Ca/Sr ratios and REE abundances along with the major and trace element water chemistry in order to discriminate and characterize these two aquifers. Waters derived from Aq. 1 are characterized by 87Sr/ 86Sr ratios ranging from 0.70407 to 0.70419, while Sr concentrations range from 0.1 to 4 mg/l and Ca/Sr weight ratios from 90 to 180, close to average values for the erupted rocks. Waters derived from Aq. 2 have 87Sr/ 86Sr between 0.70531 and 0.70542, high Sr concentrations up to 80 mg/l, and Ca/Sr ratio of 17-28. Aquifer 1 is most probably shallow, composed of volcanic rocks and situated beneath the crater, within the volcano edifice. Aquifer 2 may be situated at greater depth in sedimentary rocks and by some way connected to the regional oil-gas field brines. The relative water output (l/s) from both aquifers can be estimated as Aq. 1/Aq. 2-30. Both aquifers are not distinguishable by their REE patterns. The total concentration of REE, however, strongly depends on the acidity. All neutral waters including high-salinity waters from Aq. 2 have very low total REE concentrations (< 0.6 ?g/l) and are characterized by a depletion in LREE relative to El Chichón volcanic rock, while acid waters from the crater lake (Aq. 1) and acid AS springs (Aq. 2) have parallel profile with total REE concentration from 9 to 98 ?g/l. The highest REE concentration (207 ?g/l) is observed in slightly acid shallow cold Ca-SO 4 ground waters draining fresh and old pyroclastic deposits rich in magmatic anhydrite. It is suggested that the main mechanism controlling the concentration of REE in waters of El Chichón is the acidity. As low pH results from the shallow oxidation of H 2S contained in hydrothermal vapors, REE distribution in thermal waters reflects the dissolution of volcanic rocks close to the surface or lake sediments as is the case for the crater lake.

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

2011-08-01

107

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

SciTech Connect

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

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

2004-10-19

108

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 ( Pm3¯m, 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

109

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

SciTech Connect

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

Hinton, T.G.

1989-01-01

110

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

SciTech Connect

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

Dabrowski, B.; Wang, Z. [Northern Illinois Univ., De Kalb, IL (United States). Dept. of Physics; Jorgensen, J.D.; Hitterman, R.L.; Wagner, J.L.; Hunter, B.A.; Radaelli, P.G.; Hinks, D.G. [Argonne National Lab., IL (United States)

1994-05-01

111

Luminescence and absorbance of highly crystalline CaMoO 4, SrMoO 4, CaWO 4 and SrWO 4 nanoparticles synthesized by co-precipitation method at room temperature  

Microsoft Academic Search

Highly crystalline CaMoO4, SrMoO4, CaWO4 and SrWO4 nanoparticles were successfully synthesized by the co-precipitation of mixtures of Ca(NO3)24H2O or Sr(NO3)2, and Na2MoO42H2O or Na2WO42H2O dissolved in ethylene glycol at room temperature (30°C). Phases, morphologies, atomic vibrations and optical properties were analyzed by X-ray diffraction, transmission electron microscopy, Fourier transform infrared and Raman spectrophotometry, and ultraviolet–visible and photoluminescent spectroscopy. All products

Titipun Thongtem; Sukjit Kungwankunakorn; Budsabong Kuntalue; Anukorn Phuruangrat; Somchai Thongtem

2010-01-01

112

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

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

113

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

114

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-SchöNberg, Dieter; Brummer, Geert-Jan A.

2013-04-01

115

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

PubMed

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

Lu, Jin-Ping; Ren, Jiang-Hua; Chen, Ling; Li, Xia; Chen, Hui-Li

2015-02-01

116

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 10°N 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° - 17.7°C). 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, ~ 6°C); a C. phaseoliformis? (Aleutian trench, 4922 m, 1.5°C); and paired C. pacifica and C. kilmeri (Monterey Canyon, 904 m, 4.2°C). 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: T°C = 18160*(Sr/Ca) - 12.2). The C. kilmeri spent most of its early life at 9-12°C, 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 20°C 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 ~ 10°N 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 3-4°C range, but large periods of their lives are spent in the 10°-20°C range, with short spikes to ~ 40°C 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

117

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

118

STM of quasiparticle scattering resonances in Bi 2Sr 2CaCu 2O 8+ ?  

NASA Astrophysics Data System (ADS)

High-resolution, low-temperature scanning tunneling microscopy and spectroscopy on Bi 2Sr 2CaCu 2O 8+ ? reveal the existence of large numbers of scattering centers in this material. The spatial and spectroscopic characteristics of these features are consistent with theories of quasiparticle scattering from atomic scale impurities in a d-wave superconductor. These characteristics include breaking of local particle-hole symmetry and an inverse square dependence of their local density-of-states (LDOS) on distance from the scattering center. Furthermore, these observations identify a source for the anomalously high levels of low-energy excitations in Bi 2Sr 2CaCu 2O 8+ ? at low-temperatures.

Hudson, E. W.; Pan1, S. H.; Lang, K. M.; Gupta, A. K.; Ng, K.-W.; Davis, J. C.

2000-07-01

119

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

120

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

121

Synthesis and luminescent characteristics of Ca 2? x Sr x SiO 4:Eu 2+ as a potential green-emitting phosphor for near UV-white LED applications  

Microsoft Academic Search

The photoluminescence properties of enhanced green-emitting Ca2?xSrxSiO4:Eu2+ were optimized for applications to near ultraviolet light emitting diodes (LEDs). The optimal firing conditions for Ca2?xSrxSiO4:Eu2+ prepared by solid-state reaction synthesis were found to be 1300°C for 6h. Ca2?xSrxSiO4:Eu2+ showed strong green emission peak at approximately 520nm under excitation by near UV light of 390nm. The effects of Sr2+ substitution into the

W. J. Park; Y. H. Song; D. H. Yoon

2010-01-01

122

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

Microsoft Academic Search

Rapid accumulation of CaCO 3 is occurring in Littlefield Lake, a marl lake located in central Michigan. The sediment, which is 95% CaCO 3 , primarily consists of eight different genetic groups of carbonate allochems. These include calcite muds, sands, algal oncoids and Chara encrustations, as well as the dominant aragonitic gastropods Valvota tricarinota . Gyraulus deflectus and Amnicola integra

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

1981-01-01

123

Nuclear Quadrupole Resonance of Cu in High-Tc Bi-Pb-Sr-Ca-Cu-O  

Microsoft Academic Search

Nuclear quadrupole resonance (NQR) signals of Cu have been discovered in the high-Tc superconducting oxide Bi-Pb-Sr-Ca-Cu-O with Tc{=}109 K. It has been observed that there are two Cu sites with a different quadrupole coupling. The temperature dependence of the nuclear relaxation rate, 1\\/T1, was similar to that of the CuO2 plane in YBa2Cu3O7. It is found that the 1\\/T1 for

Kenji Fujiwara; Yoshio Kitaoka; Kunisuke Asayama; Hiroyuki Sasakura; Sinnosuke Minamigawa; Kiyotaka Nakahigashi; Shigemitsu Nakanishi; Mineo Kogachi; Nobuo Fukuoka; Akira Yanase

1989-01-01

124

Structural relationships and a phase diagram for (Ca,Sr)TiO3 perovskites  

Microsoft Academic Search

Sets of lattice parameter data have been obtained from high resolution neutron and synchrotron x-ray powder diffraction patterns collected in situ as a function of temperature for perovskites in the (Ca,Sr)TiO3 solid solution. An updated phase diagram is proposed in which there is a stability field for the I4\\/mcm structure at all compositions across the solid solution. The Pm\\\\bar {3}m\\\\leftrightarrow

M. A. Carpenter; C. J. Howard; K. S. Knight; Z. Zhang

2006-01-01

125

Structural relationships and a phase diagram for (Ca,Sr)TiO3 perovskites  

Microsoft Academic Search

Sets of lattice parameter data have been obtained from high resolution neutron and synchrotron x-ray powder diffraction patterns collected insitu as a function of temperature for perovskites in the (Ca,Sr)TiO3 solid solution. An updated phase diagram is proposed in which there is a stability field for the I4\\/mcm structure at all compositions across the solid solution. The transition is close

M A Carpenter; C J Howard; K S Knight; Z Zhang

2006-01-01

126

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

127

Magnetic Properties of Pb-Doped Bi-Sr-Ca-Cu-O Superconductors  

Microsoft Academic Search

The D.C. magnetization of Bi-Sr-Ca-Cu-O compound was significantly increased by Pb-doping. However, the hysteresis \\\\varDelta M in magnetization curves rapidly decreased with increasing magnetic field, and became almost zero above 0.5 T. This small hysteresis may be related to the thin layers of superconducting phases. Low-temperature tails in superconducting resistive transition curves measured in magnetic fields were drastically decreased by

Hiroaki Kumakura; Kazumasa Togano; Mitsuru Uehara; Hiroshi Maeda; Kazuhiko Takahashi; Eiji Yanagisawa

1988-01-01

128

Crystal growth and superconducting phase formation from Bi-Ca-Sr-Cu-O liquids  

Microsoft Academic Search

Both crystal growth and solidification of dense, high-Tc superconducting composites were carried out from liquids formed by heating a mixture of the oxide powders Bi2O3, SrO, CaO, and CuO to 1150 C. Material that exhibits two distinct transition temperatures with onsets at Tc 112 K and Tc about 87 K or material with a single 90 K transition could be

T. F. Ciszek; J. P. Goral; C. D. Evans; H. Katayama-Yoshida

1988-01-01

129

Store-operated Ca²? entry and depolarization explain the anomalous behaviour of myometrial SR: effects of SERCA inhibition on electrical activity, Ca²? and force.  

PubMed

In the myometrium SR Ca(2+) depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca(2+) sparks-STOCs coupling mechanism to explain this. Given the importance of the control of contractility for successful parturition, we have examined, in pregnant rat myometrium, the effects of SR Ca(2+)-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca(2+) transients and force. Simultaneous recording of electrical activity, calcium and force showed that SERCA inhibition, by cyclopiazonic acid (CPA 20 ?M), caused time-dependent changes in excitability, most noticeably depolarization and elevations of baseline [Ca(2+)]i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca(2+) spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca(2+) and depolarization continued a point was reached when electrical and Ca(2+) spikes and phasic contractions ceased, and a maintained, tonic force and Ca(2+) was produced. Lanthanum, a non-selective blocker of store-operated Ca(2+) entry, but not the L-type Ca(2+) channel blocker nifedipine (1-10 ?M), could abolish the maintained force and calcium. Application of the agonist, carbachol, produced similar effects to CPA, i.e. depolarization, elevation of force and calcium. A brief, high concentration of carbachol, to cause SR Ca(2+) depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca(2+) release is coupled to marked Ca(2+) entry, via store operated Ca(2+) channels, leading to depolarization and enhanced electrical and mechanical activity. PMID:25084623

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

2014-09-01

130

Store-operated Ca2+ entry and depolarization explain the anomalous behaviour of myometrial SR: Effects of SERCA inhibition on electrical activity, Ca2+ and force  

PubMed Central

In the myometrium SR Ca2+ depletion promotes an increase in force but unlike several other smooth muscles, there is no Ca2+ sparks-STOCs coupling mechanism to explain this. Given the importance of the control of contractility for successful parturition, we have examined, in pregnant rat myometrium, the effects of SR Ca2+-ATPase (SERCA) inhibition on the temporal relationship between action potentials, Ca2+ transients and force. Simultaneous recording of electrical activity, calcium and force showed that SERCA inhibition, by cyclopiazonic acid (CPA 20 ?M), caused time-dependent changes in excitability, most noticeably depolarization and elevations of baseline [Ca2+]i and force. At the onset of these changes there was a prolongation of the bursts of action potentials and a corresponding series of Ca2+ spikes, which increased the amplitude and duration of contractions. As the rise of baseline Ca2+ and depolarization continued a point was reached when electrical and Ca2+ spikes and phasic contractions ceased, and a maintained, tonic force and Ca2+ was produced. Lanthanum, a non-selective blocker of store-operated Ca2+ entry, but not the L-type Ca2+ channel blocker nifedipine (1–10 ?M), could abolish the maintained force and calcium. Application of the agonist, carbachol, produced similar effects to CPA, i.e. depolarization, elevation of force and calcium. A brief, high concentration of carbachol, to cause SR Ca2+ depletion without eliciting receptor-operated channel opening, also produced these results. The data obtained suggest that in pregnant rats SR Ca2+ release is coupled to marked Ca2+ entry, via store operated Ca2+ channels, leading to depolarization and enhanced electrical and mechanical activity. PMID:25084623

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

2014-01-01

131

Structural relationships and a phase diagram for (Ca,Sr)TiO3 perovskites  

NASA Astrophysics Data System (ADS)

Sets of lattice parameter data have been obtained from high resolution neutron and synchrotron x-ray powder diffraction patterns collected in situ as a function of temperature for perovskites in the (Ca,Sr)TiO3 solid solution. An updated phase diagram is proposed in which there is a stability field for the I4/mcm structure at all compositions across the solid solution. The Pm\\bar {3}m\\leftrightarrow I4/mcm transition is close to tricritical in the composition range 0-70% SrTiO3 component and then evolves towards second order character (Landau 246 solution) in the range 85-100% SrTiO3. Transition temperatures as a function of composition for I4/mcm\\leftrightarrow Pnma and I4/mcm\\leftrightarrow Pbcm transitions at lower temperatures show a break in slope at ~60% SrTiO3. Variations of octahedral tilt angles and spontaneous strains are much the same for Pbcm structures as they are for Pnma structures. Nearly cubic lattice geometry of orthorhombic structures at intermediate compositions is ascribed to only weak coupling between octahedral tilting and the shear strain e4. The phase diagram topology and variations in structural evolution at different compositions indicate that there is a distinct change in the behaviour of the solid solution at ~85% SrTiO3.

Carpenter, M. A.; Howard, C. J.; Knight, K. S.; Zhang, Z.

2006-12-01

132

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

133

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

134

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

NASA Astrophysics Data System (ADS)

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

Marshall, John F.; McCulloch, Malcolm T.

2002-09-01

135

Crystal chemistry of the noncentrosymmetric eulytites: A(3)Bi(XO(4))(3) (X = V, A = Pb; X = P, A = Ca, Cd, Sr, Pb).  

PubMed

Eulytite compounds, A(3)Bi(XO(4))(3) (X = P, A = Ca, Cd, Sr, Pb), belong to the noncentrosymmetric space group I4?3d (No. 220) as determined by single-crystal X-ray diffraction studies. The crystals were grown from the melt-cool technique with considerable difficulty as the compounds melt incongruently at their melting temperature, except for the compound Pb(3)Bi(PO(4))(3). The unit cell parameter a is 9.984(5), 9.8611(3), 10.2035(3), and 10.3722(2) Å for Ca(3)Bi(PO(4))(3), Cd(3)Bi(PO(4))(3), Sr(3)Bi(PO(4))(3), and Pb(3)Bi(PO(4))(3) respectively, and there are four formula units in the unit cell. The structure of Pb(3)Bi(VO(4))(3), a unique eulytite with vanadium substitution, is compared with all these phosphorus substituted eulytites. The A(2+) and Bi(3+) cations occupy the special position (16c) while the O anions occupy the general Wyckoff position (48e) in the crystal structure. Only one O position has been identified for Pb(3)Bi(PO(4))(3) and Pb(3)Bi(VO(4))(3), whereas two O atom sites were identified for Ca(3)Bi(PO(4))(3), Cd(3)Bi(PO(4))(3), and Sr(3)Bi(PO(4))(3). The UV-vis diffuse reflectance spectra indicate large band gaps for all the phosphate eulytites while a lower band gap is observed for the vanadate eulytite. The feasibility of the use of these compounds in optoelectronic devices has been tested by measuring the second-harmonic generation (SHG) values which have been found to be of a magnitude equivalent to the commercially used KDP (KH(2)PO(4)). PMID:20873768

Sahoo, Prangya Parimita; Guru Row, T N

2010-11-01

136

Preparation of Bi1.5SrCaCu2Ox Glass Fibers Using Melt-Quenched Glasses  

NASA Astrophysics Data System (ADS)

Bi1.5SrCaCu2Ox glass preforms were prepared by the melt-quenching method, and their thermal characteristics and viscosity were investigated to determine the possibility of drawing them into glass fibers. Furthermore, Bi1.5SrCaCu2Ox glass fibers were drawn from glass preforms by the method that is ordinarily applied to optical fiber fabrication. The drawn fibers were very flexible, and the maximum length was 1200 mm.

Onishi, Masashi; Kohgo, Takashi; Chigusa, Yoshiki; Kyoto, Michihisa; Watanabe, Minoru

1989-12-01

137

Study of the optical conductivity of Bi 2Sr 2CaCu 2O 8+ ? material  

NASA Astrophysics Data System (ADS)

We studied the optical conductivity of the Bi 2Sr 2CaCu 2O 8+ ? materials in the normal state as well as in the superconducting state as a function of temperature and doping within the rotating antiferromagnetism theory (RAFT) using the Marginal Fermi Liquid (MFL) ansatz for self-energy. The optical conductivity is calculated using Nambu formalism and Kubo’s formula. Experimental data for Bi 2Sr 2CaCu 2O 8+ ? are discussed.

Bhuiyan, E. H.; Presenza-Pitman, G.; Azzouz, M.

2012-02-01

138

K\\/Rb, Ca\\/Sr und K\\/Ti-Verhältnisse in basaltoiden Gesteinen der Ostalpen und benachbarter Gebiete  

Microsoft Academic Search

Zusammenfassung Es wurden 69 basaltische Gesteine aus dem ostalpinen und westkarpatischen Orogen sowie aus dem pannonischen Zwischengebirge röntgenfluoreszenzspektrometrisch auf K, Ca, Rb, Sr und Ti analysiert. Eine Auswertung der Korrelationsdiagramme K\\/Rb, Ca\\/Sr und K\\/Ti ergibt für verwandte Gesteine definierte Konzentrationsfelder. Die Alkaliolivinbasalte zeichnen sich, soweit sie nicht durch sekundäre Prozesse Veränderungen erfahren haben, durch relativ enge Konzentrationsfelder aus. Als Mittelwerte

G. Agiorgitis; E. Schroll; Erika Stepán

1970-01-01

139

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 1°C warmer temperature estimate, with the 27 corals reporting "temperatures" ranging from 24.9 to 28.9°C, with mean 26.6 ± 0.9°C standard deviation. Our results lend support to hypotheses invoking kinetic processes and growth rate to explain vital effects on Sr/Ca. However, uncertainty in the slope of the regression of Sr/Ca on calcification and a low R-squared value lead us to conclude that Sr/Ca could still be a useful proxy in this species given sufficient replication or by including growth rate in the calibration.

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

2012-08-01

140

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

NASA Astrophysics Data System (ADS)

Coccolithophore CaCO 3 production can account for 20-80% of biogenic carbonate exported from the photic zone, and coccoliths are a dominant biogenic carbonate in many deep-sea sediments. A new method for picking individual coccoliths from sediment traps and sediments for analysis using Secondary Ion Mass Spectrometry (ion probe) allows us to make precise Sr/Ca and Mg/Ca determinations on coccoliths from single species even in samples where material is limited. There are large biological effects in Sr/Ca partitioning in coccoliths that have been related to variations in coccolithophore productivity. In sediment traps from the Sargasso Sea at Bermuda and Arabian Sea in the Somali Basin, we can identify Sr/Ca variations in several species that are consistent with inferred seasonal variations in coccolithophore productivity in surface waters. In the Arabian Sea, coccolith Sr/Ca ratios in Calcidiscus leptoporus and Helicosphaera carteri are lowest during the nonproductive intermonsoon. They are highest during the upwelling of southwest monsoon and during the nutrient entrainment from strong winds of the northeast monsoon. These Sr/Ca variations match seasonal trends in coccolith export flux. Furthermore, Sr/Ca variations in C. leptoporus are larger, and this species also has the greater variation in export flux between southwest monsoon and intermonsoon seasons. At Bermuda, a 1996 fall bloom, driven by passage of a warm mode water eddy, induced a large increase in Sr/Ca of C. leptoporus coincident with an increase of C. leptoporus export. Over an annual series for 2004, highest Sr/Ca ratios of C. leptoporus in the summer months match the typical summer peak in surface standing stock of this species and the stimulation of its productivity by mesoscale cyclonic eddies and eddy-eddy interactions. High Sr/Ca did not coincide with the highest export of C. leptoporus coccoliths, likely because cyclonic eddies, unlike mode-water eddies, are dominated by small phytoplankton with low export efficiency. These data confirm a relationship between coccolith Sr/Ca ratios and productivity. Sr/Ca ratios of the smaller and more slowly sinking Emiliania huxleyi at Bermuda show very small (<4%) seasonal Sr/Ca variations. In contrast, nutrient-limited culture experiments for this species reveal significant (>35%) increases in Sr/Ca with nitrate-stimulated growth rates. The high dominance of E. huxleyi production during bloom events, coupled with suspension of small E. huxleyi coccoliths below the photic zone with very long transport times, appears to attenuate significantly the amplitude of Sr/Ca variations in trap material. Coccoliths from these traps possess low Mg/Ca ratios characteristic of low-Mg calcite, so that higher Mg ratios obtained in some extant coccoliths in cultures are not representative of typical open-ocean coccoliths recovered in sediment trap samples. A significant correlation of Mg/Ca with sea-surface temperature is observed only for H. carteri coccoliths in the Arabian Sea, and not in C. leptoporus in either site.

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

2007-03-01

141

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

NASA Astrophysics Data System (ADS)

Chemical and isotope data (?40Ca, ?44/42Ca, 87Sr/86Sr, ?18O) of river water samples were collected twice daily for 28 days in 2009 from the outlet river of Leverett Glacier, West Greenland. The water chemistry data was combined with detailed geochemical analysis and petrography of bulk rock, mineral separates and sediment samples in order to constrain the mineral weathering sources to the river. The average isotopic compositions measured in the river, with 2SD of all the values measured, were ?40Ca = +4.0 ± 1.4, ?44/42Ca = +0.60 ± 0.10‰ and 87Sr/86Sr = 0.74243 ± 0.00327. Based on changes in bulk meltwater discharge, the hydrochemical data was divided into three hydrological periods. The first period was marked by the tail-end of an outburst event and was characterised by water with decreasing suspended sediment concentrations (SSC), ion concentrations and pH. During the second hydrological period, discharge increased whilst 87Sr/86Sr decreased from 0.74550 to 0.74164. Based on binary mixing diagrams using 87Sr/86Sr with Na/Sr, Ca/Sr and ?40Ca, this is interpreted to reflect an increase in reactive mineral weathering, in particular epidote, as the water residence time decreases. The decrease in water residence time is a result of the evolution from a distributed (long water residence time) to a channelised (short water residence time) subglacial drainage network. The third hydrological period was defined as the period when overall discharge was decreasing. This hydrological period was marked by prominent diurnal cycles in discharge. During this period, significant correlations between ?44/42Ca and SSC and ?18O were observed which are suggestive of fractionation during adsorption. This study demonstrates the potential of radiogenic Ca to both identify temporally changing mineral sources in conjunction with 87Sr/86Sr values and to separate source and fractionation effects in ?44/42Ca values.

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

2014-11-01

142

Crystal Structure Refinement of SrMoO4, SrWO4 CaMoO4, and BaWO4 by Neutron Diffraction  

Microsoft Academic Search

The crystal structures of CaMoO4, SrMoO4, SrWO4, and BaWO4 have been refined from neutron diffraction data taken in the (h0l) and (hhl) zones. Oxygen position refinement is started from the parameters proposed by Sille´n and Nylander and results in an improvement of over an order of magnitude in the oxygen coordinates. A comparison of coordinates for the different compounds shows

Erdogan Gürmen Eugene Daniels; J. S. King

1971-01-01

143

Involvement of palmitate/Ca(2+)(Sr(2+))-induced pore in the cycling of ions across the mitochondrial membrane.  

PubMed

The palmitate/Ca(2+)-induced (Pal/Ca(2+)) pore, which is formed due to the unique feature of long-chain saturated fatty acids to bind Ca(2+) with high affinity, has been shown to play an important role in the physiology of mitochondria. The present study demonstrates that the efflux of Ca(2+) from rat liver mitochondria induced by ruthenium red, an inhibitor of the energy-dependent Ca(2+) influx, seems to be partly due to the opening of Pal/Ca(2+) pores. Exogenous Pal stimulates the efflux. Measurements of pH showed that the Ca(2+)-induced alkalization of the mitochondrial matrix increased in the presence of Pal. The influx of Ca(2+) (Sr(2+)) also induced an outflow of K(+) followed by the reuptake of the ion by mitochondria. The outflow was not affected by a K(+)/H(+) exchange blocker, and the reuptake was prevented by an ATP-dependent K(+) channel inhibitor. It was also shown that the addition of Sr(2+) to mitochondria under hypotonic conditions was accompanied by reversible cyclic changes in the membrane potential, the concentrations of Sr(2+) and K(+) and the respiratory rate. The cyclic changes were effectively suppressed by the inhibitors of Ca(2+)-dependent phospholipase A2, and a new Sr(2+) cycle could only be initiated after the previous cycle was finished, indicating a refractory period in the mitochondrial sensitivity to Sr(2+). All of the Ca(2+)- and Sr(2+)-induced effects were observed in the presence of cyclosporin A. This paper discusses a possible role of Pal/Ca(2+) pores in the maintenance of cell ion homeostasis. PMID:25450352

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

2015-02-01

144

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

145

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

146

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

147

A study of the magnetic properties of hydrothermally synthesised Sr hexaferrite with Sm substitution  

Microsoft Academic Search

Sm doped Sr hexaferrite particles were synthesised hydrothermally. Post-synthesised calcination with the aim of improving the magnetic properties of as-synthesised particles was conducted at temperatures ranging from 900°C to 1150°C for 2h in air. The effects of the Sm\\/Sr ratio and the calcination temperature on the crystallography, particle morphology and magnetic properties of Sm doped Sr hexaferrite were investigated by

J. F. Wang; C. B. Ponton; I. R. Harris

2001-01-01

148

Comparison of the Sr substitution effect on Nd(Ba 1- xSr x) 2Cu 3O 6+ ? and Pr(Ba 1- xSr x) 2Cu 3O 6+ ? prepared under reducing atmosphere  

NASA Astrophysics Data System (ADS)

We report on the results of systematic studies of Sr substitution effect for R(Ba 1- xSr x) 2Cu 3O 6+ ? (where R = Nd, Pr) with 0 ? x ? 0.5, prepared under reducing atmosphere. Single phases were obtained for a wide range of x for both systems of Nd(Ba 1- xSr x) 2Cu 3O 6+ ? and Pr(Ba 1- xSr x) 2Cu 3O 6+ ? by means of synthesis at high-temperature under reducing atmosphere (Ar:O 2 = 100:0.1). In particular, solubility as high as x = 0.5 was successfully achieved for the first time in the Pr(Ba 1- xSr x) 2Cu 3O 6+ ?. For R = Nd, the superconducting transition temperature, Tc, decreases from 95 to 50 K as x increases from 0 to 0.5. From the Rietveld refinement of powder X-ray diffraction (XRD) data, occupancy of Sr at the Nd site is found, gSr/Nd (=2 × gNd/Ba), and the value of gSr/Nd increases with x from 0 ( x = 0) to 0.11 ( x = 0.5). Occupancy of O(4), gO(4), decreases and O(5), gO(5), increases with x. It is demonstrated that the depression of Tc with x is caused by the replacement of Ba 2+ by Sr 2+ and Nd 3+ and also by the replacement of Nd 3+ by Sr 2+. Disorder in the BaO plane induce the disorder in the CuO plane, which results in the decrease of the orthorhombicity. For R = Pr, both of the electrical resistivity and antiferromagnetic ordering temperature, TN, increase with x until x = 0.3, then decreases with x. Refinement results do not show intermixing of Sr and Pr; Sr ions occupy only the Ba site and Pr ions does not occupy the Ba site. The dependence of the orthorhombicity on x is quite different from that of Nd-system. The crystal becomes tetragonal at x = 0.4, which is smaller than that of Nd-system. The hybridization between the Pr 4f and the O 2p orbitals which prefers the tetragonal symmetry is considered to advances the transition to the tetragonal structure.

Wuernisha, Tuerxun; Sano, Fumihiko; Takahashi, Yumiko; Kamiyama, Takashi; Takano, Yoshiki; Sekizawa, Kazuko

2006-02-01

149

Arrhythmogenic effects of ?2-adrenergic stimulation in the failing heart are due to enhanced SR Ca load  

PubMed Central

Ventricular tachycardia (VT) in heart failure (HF) can initiate by nonreentrant mechanisms such as delayed afterdepolarizations. In an arrhythmogenic rabbit model of HF, we have shown that isoproterenol induces VT in vivo, and aftercontractions and transient inward currents in HF myocytes. To determine whether ?2-adrenergic receptor (?2-AR) stimulation contributes, we performed in vivo drug infusion, in vitro myocyte and biochemical studies. Intravenous zinterol (2.5 ?g/kg) led to ventricular arrhythmias including VT up to 13 beats long in 4 of 6 HF rabbits (vs 0 of 5 controls, p<0.01), an effect blocked by ?2-AR antagonist ICI 118,551 (ICI, 0.2 mg/kg). In field stimulated myocytes (0.5?4 Hz, 37°C) ?2-AR stimulation (1?M zinterol + 300 nM ?1-AR antagonist CGP-29712A, CGP) induced aftercontractions and after-Ca-transients in 88% of HF vs 0% of control myocytes (p<0.01). ?2-AR stimulation in HF (but not control) myocytes increased Ca transient amplitude (by 29%), SR Ca load (by 28%), the rate of [Ca]i decline (by 28%; n=12, all p<0.05), and PLB phosphorylation at Ser-16, but Ca current was unchanged. All of these effects in HF myocytes were blocked by ICI (100 nM). While total ?-AR expression was reduced by 47% in HF rabbit LV, ?2-AR number was unchanged, indicating more potent ?2-AR-dependent SR Ca uptake and arrhythmogenesis in HF. Human HF myocytes showed similar ?2-AR-induced aftercontractions, aftertransients, and enhanced Ca transient amplitude, SR Ca load and twitch [Ca]i decline rate. Thus, ?2-AR stimulation is arrhythmogenic in HF, mediated by SR Ca overload-induced spontaneous SR Ca release and aftercontractions. PMID:18467626

DeSantiago, Jaime; Ai, Xun; Islam, Mohammed; Acuna, Georgia; Ziolo, Mark T.; Bers, Donald M.; Pogwizd, Steven M.

2008-01-01

150

Surface magnetism of Al-substituted Sr-M-type hexagonal ferrites  

Microsoft Academic Search

The surface and bulk magnetic structures of Sr-M-type single-crystal hexagonal ferrites (with the chemical formula SrFe12?x\\u000a AlxO19) have been directly compared by simultaneous gamma, x-ray, and electron Mssbauer spectroscopy. It was found, that when the\\u000a magnetic lattice of Sr-M hexagonal ferrites is slightly diluted by diamagnetic Al ions, namely, for x=1.8 (SrFe10.2Al1.8O19), a ?300-nm thick macroscopic anisotropic layer forms on

A. S. Kamzin; L. P. Ol’khovik

1999-01-01

151

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

SciTech Connect

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

Cheng Jihong [Thermochemistry Facility and NEAT ORU, University of California at Davis, One Shields Avenue, Davis, CA 95616 (United States); Navrotsky, Alexandra [Thermochemistry Facility and NEAT ORU, University of California at Davis, One Shields Avenue, Davis, CA 95616 (United States)]. E-mail: anavrotsky@ucdavis.edu

2005-01-15

152

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

153

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

154

Experimental electronic structure of Bi2CaSr2Cu2O8+?  

NASA Astrophysics Data System (ADS)

Highly oriented polycrystalline Bi2CaSr2Cu2O8+? has been studied by x-ray photoemission spectroscopy (XPS) to determine the oxidation states of its constituents and the valence electronic structure. Core-level shifts indicate 3+ and 2+ as main oxidation states for Bi and Cu, respectively. The Ca and Sr core levels exhibit pronounced shifts to lower binding energy compared to the metals. The Ca lines show two main components, indicating either inequivalent sites or the presence of a different phase. The XPS and ultraviolet photoemission spectroscopy valence-band spectra show weak but reproducible metallic emission at the Fermi level (EF) which we ascribe to states originating in the Bi-O planes. The main Cu d-O p band is between 2 and 8 eV below EF; this is about 1 eV lower than predicted by band-structure calculations. We argue that this is due to electronic correlations tending to increase the anisotropy in the ground-state charge distribution compared to that obtained in local-density-approximation calculations.

Hillebrecht, F. U.; Fraxedas, J.; Ley, L.; Trodahl, H. J.; Zaanen, J.; Braun, W.; Mast, M.; Petersen, H.; Schaible, M.; Bourne, L. C.; Pinsukanjana, P.; Zettl, A.

1989-01-01

155

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

156

Oxygen Surface Exchange Kinetics on Sr-Substituted Lanthanum Manganite and Ferrite Thin-Film Microelectrodes  

E-print Network

The surface oxygen exchange kinetics occurring on dense La0.8Sr0.2MnO3 (65nm thick) and La0.8Sr0.2FeO3 (110nm thick) thin films were investigated by electrochemical impedance spectroscopy (EIS). Rutherford backscattering ...

la O', Gerardo Jose

157

Paraconductivity analysis for superconducting Bi-Sr-Ca-Cu-O whiskers  

NASA Astrophysics Data System (ADS)

By means of the paraconductivity analysis, we characterize superconducting Bi 2Sr 2CaCu 2O 8+ d whiskers which show a sharp resistive transition corresponding to the 2223 phase while identified to be mostly in the 2212 phase (99% or more) from XRD and SQUID measurements. The paraconductivity along the a-axis follows the behavior of the Aslamazov-Larkin theory, showing a dimensional crossover from 0D to 1D near TC. This implies that small islands of the 2223 phase distributed randomly in the 2212 phase could form quasi-1D dimensional percolation structure just above TC.

Enomoto, Hiroyuki; Mori, Natsuki; Matsubara, Ichiro; Ozaki, Hajime

2000-07-01

158

Spectroscopy of LiCa and RbSr Molecules on Helium Nanodroplets  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

159

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

160

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

NASA Astrophysics Data System (ADS)

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

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

2005-02-01

161

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

SciTech Connect

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

Matsuda, M.; Murayama, Y.; Kiryu, S.; Kasai, N.; Kashiwaya, S.; Koyanagi, M.; Endo, T. (Electrotechnical Lab., 1-1-4 Umezono, Tsukuba, Ibaraki 305 (JP)); Kuriki, S. (Hokkaido Univ., Sapporo (Japan). Research Inst. of Applied Electricity)

1991-03-01

162

Microstructure of Bi 2(Sr,Ca) 3Cu 2O x thinfilm on vicinal SrTiO 3 substrates  

NASA Astrophysics Data System (ADS)

The microstructure of epitaxial Bi 2(Sr,Ca) 3Cu 2O x films prepared on vicinal SrTiO 3 substrates was studied by cross-sectional high-resolution transmission electron microscopy. The films were prepared in situ by ion beam sputtering on the vicinal SrTiO 3 substrates oriented off[001] by about 4° toward [111] with Bi 2Sr 2CuO x buffer layers. The films grew without 90° misorientation defects (“twinning”). The surface of the substrates consisted of [001] terraces and ledges. The b-axis was aligned with the step direction of the substrate. The c-axis was oriented normal to the [001] terrace surface, not to the macroscopic substrate surface. As a result, the a, b-plane tilted 4° from the substrate surface. While many anti-phase defects were found in the film near the substrate surface, there were relatively few defects in most regions.

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

1992-02-01

163

Seasonal Isotopic Ca, B, O, C and Sr Fractionation in Late Oligocene Oysters (C. Gigantissima)  

NASA Astrophysics Data System (ADS)

Stable isotope compositions preserved in shell calcite may record various aspects of the environment at the time of calcification. Data from natural samples of C. gigantissima from the Belgrade Formation, North Carolina 27+-1 Ma), suggest that Ca and B isotope fractionation is temperature dependent and is also a function of water composition. Also, Ca and B isotope fractionation seems to be highly species dependent and for paleotemperature reconstruction it is important to study each species in order to elucidate their response to both temperature and paleo environment. These relationships make seasonal variations in shells extremely useful for interpreting the paleoecology of fossil organisms, as isotope fractionation is different in seawater and brackish water (as seen with oxygen isotopes). In this study, Ca, B, C and O isotopic values were measured along a profile perpendicular to skeletal growth increments, known as stable isotope sclerochronology. This method enables to resolve intra-annual differences in stable isotopes. High resolution O and C isotopic profiles show that C. Gigantissima formed skeletal growth increments annually at seasonally varying growth rates, with convex and concave bands forming during summer and winter, respectively (Kirby, 2000). Assuming shell growth ceased at 10C, the estimated paleotemperature derived from oxygen isotopes gives a seasonal range of temperature of ca. 15C, with summer temperatures reaching ca. 25C. Samples from winter and summer bands show a small range of total variation in 44Ca/40Ca of 0.5 permil. The Ca isotope fractionation is positively correlated to temperature with more positive ? 44Ca of ca. -1.43+-0.1 permil in the summer and more negative Ca isotopic compositions of ca. 1.93+- 0.1 permil in the winter. The data imply a temperature dependence that is ca. 0.03 permil per C. This is significantly less than the 0.24 permil per C reported by Naegler et al (2000) for cultured Globigerina sacculifer. However, aragonite precipitated in the laboratory at temperatures of 10 and 40C appears to show an even smaller temperature dependence of approximately 0.01 permil per C (Deyhle et al., 2002) to 0.015 permil per C (Gussone et al., 2003). Additional data gained on O, C and B isotopes further confirm that skeletal growth increments in C. Gigantissima show an annual variation, with average seasonal changes of 3.2+- 0.4 permil, 1.1+- 0.4 permil and 4.3+- 0.5 permil, respectively. Interestingly, B isotopes which were previously used as paleo-pH proxy, clearly show an intra-annual temperature dependent fractionation of almost 0.3 permil per C, suggesting that B may be a useful paleo-temperature proxy. Likewise ? 13C, B isotopes may also be influenced by the amount of respired CO2 reaching the site of calcification. 87Sr/86Sr isotopic ratios of 0.70809 +- 0.000018 are the same within our analytical uncertainty and thus suggest fully marine conditions with no change in any freshwater input summer to winter. In summary, stable isotope analysis show significant intra-annual changes which are influenced by temperature and possibly other factors. Further studies need to be conducted on Ca and B isotopes to better understand whether temperature is the main fractionation mechanism on a seasonal time scale or if parameters like shell growth rate and other vital effects play also a critical role in isotopic variations.

Deyhle, A.; MacDougall, D.; Kirby, M. X.

2003-12-01

164

?SR investigation of the intercalated graphite superconductor CaC6  

NASA Astrophysics Data System (ADS)

The superconducting properties of the graphite intercalation compound CaC6, available as high-quality c-axis-oriented polycrystals, were investigated through muon-spin spectroscopy measurements. An unconventional TF-?SR procedure, applicable to superconductors characterized by close-lying critical fields, was successfully adopted for measuring the muon-spin relaxation rates. Field-dependent measurements provide a value ?ab(0)=62(4) nm for the in-plane magnetic field penetration depth, ?=1.4(2) for the GL parameter, and hint at the presence of a slight gap anisotropy in the ab plane. The dependence of relaxation on temperature confirms the s-wave character of CaC6 superconductivity, with an average zero-temperature superconducting gap of 2.1(1) meV.

Shiroka, T.; Lamura, G.; De Renzi, R.; Belli, M.; Emery, N.; Rida, H.; Cahen, S.; Marêché, J.-F.; Lagrange, P.; Hérold, C.

2011-01-01

165

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. PMID:22449852

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

2013-01-01

166

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-Désirée; Chabaux, François; Pokrovsky, Oleg S.; Viers, Jérôme; Stille, Peter; Labolle, François; Prokushkin, Anatoly S.

2013-08-01

167

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

168

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, Lòpez Correa et al. 2008; delta88/86Sr, Rüggeberg et al. 2008). Within the frame of DFG-Project TRISTAN and Paläo-TRISTAN (Du 129/37-2 and 37-3) we investigated live-collected specimens of cold-water coral L. pertusa from all along the European continental margin (Northern and mid Norwegian shelves, Skagerrak, Rockall and Porcupine Bank, Galicia Bank, Gulf of Cadiz, Mediterranean Sea). These coral samples grew in waters characterized by temperatures between 6°C and 14°C. Electron Microprobe investigations along the growth direction of individual coral polyps were applied to determine the relationship between the incorporation of distinct elements (Sr, Ca, Mg, S). Cohen et al. (2006) showed for L. pertusa from the Kosterfjord, Skagerrak, that ~25% of the coral's Sr/Ca ratio is related to temperature, while 75% are influenced by the calcification rate of the organism. However, the Sr/Ca-temperature relation of our L. pertusa specimens suggest, that mean values are more reliable for temperature reconstruction along a larger temperature range than local high-resolution investigations. Additionally, our results plot on same line of Sr/Ca-temperature relationship like tropical corals indicating a similar behaviour of element incorporation during calcification. References: Adkins JF, Boyle EA (1997) Changing atmospheric ?14C and the record of deep water paleoventilation ages. Paleoceanography 12:337-344 Blamart D, Rollion-Bard C, Cuif J-P, Juillet-Leclerc A, Lutringer A, Weering Tv, Henriet J-P (2005) C and O isotopes in a deep-sea coral (Lophelia pertusa) related to skeletal microstructure. In: Freiwald A, Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Berlin Heidelberg, p 1005-1020 Cohen AL, Gaetani GA, Lundälv T, Corliss BH, George RY (2006) Compositional variability in a cold-water scleractinian, Lophelia pertusa: New insights into vital effects. Geochemistry, Geophysics, Geosystems 7:Q12004, doi:12010.11029/12006GC001354 López Correa M, Montagna P, Rüggeberg A, McCulloch M, Taviani M, Freiwald A (2008) Trace elements and stable isotopes in recent North Atlantic Lophelia pertusa along a latitudal gradient and from fossil Mediterranean sites. ASLO 2008 Summer Meeting, St. John's, Newfoundland & Labrador, Canada, 08.06.-13.06.2008, p. 47 Lutringer A, Blamart D, Frank N, Labeyrie L (2005) Paleotemperatures from deep-sea corals: scale effects. In: Freiwald A, Roberts JM (eds) Cold-water Corals and Ecosystems. Springer-Verlag, Berlin, Heidelberg, p 1081-1096 Montagna P, López-Correa M, Rüggeberg A, McCulloch M, Rodolfo-Metalpa R, Dullo W-C, Ferrier-Pagès C, Freiwald A, Henderson G, Mazzoli C, Russo S, Silenzi S, Taviani M (2008) Coral Li/Ca in micro-structural domains as a temperature proxy. Goldschmidt Conference, Vancouver, British Columbia, Canada Rüggeberg A, Fietzke J, Liebetrau V, Eisenhauer A, Dullo W-C, Freiwald A (2008) Stable strontium isot

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

2010-05-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

170

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

171

Trace elements in buried human bones: intra-population variability of Sr/Ca and Ba/Ca ratios - diet or diagenesis?  

NASA Astrophysics Data System (ADS)

A comparative analysis of trace element data of human skeletal material from four archaeological sites is presented. We show that the state of histomorphological preservation of bone, which is a measurement for the degree of its diagenetic alteration, closely corresponds to the Sr/Ca and Ba/Ca ratios at an intra-population level. This study challenges the validity of dietary studies that are based on the presently used procedures for sample preparation and subsequent evaluation of strontium and barium concentrations.

Fabig, Alexander; Herrmann, Bernd

2002-03-01

172

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

173

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

NASA Astrophysics Data System (ADS)

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

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

1990-06-01

174

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

175

Characterization of MMoO 4 (M = Ba, Sr and Ca) with different morphologies prepared using a cyclic microwave radiation  

Microsoft Academic Search

Scheelite molybdates (MMoO4, M=Ba, Sr and Ca) were successfully prepared by the reactions of M(NO3)2·2H2O and Na2MoO4·2H2O in propylene glycol and NaOH using a microwave radiation. The phases were detected using XRD and SAED. TEM analysis revealed the presence of micro-sized bi-pyramids with a square base, nano-sized particles in clusters, and dispersed nano-sized particles for BaMoO4, SrMoO4 and CaMoO4, respectively.

Titipun Thongtem; Anukorn Phuruangrat; Somchai Thongtem

2008-01-01

176

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

SciTech Connect

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

Wang, Xia [Superconducting Properties Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba Ibaraki 305-0044 (Japan); Department of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Guo, Yanfeng, E-mail: Yangfeng.Guo@physics.ox.ac.uk [Superconducting Properties Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba Ibaraki 305-0044 (Japan); Sun, Ying [International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science, 1-1 Namiki, Tsukuba Ibaraki 305-0044 (Japan); Tsujimoto, Yoshihiro [Materials Processing Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba Ibaraki 305-0047 (Japan); Matsushita, Yoshitaka [Materials Analysis Station, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba Ibaraki 305-0047 (Japan); Yamaura, Kazunari, E-mail: yamaura.kazunari@nims.go.jp [Superconducting Properties Unit, National Institute for Materials Science, 1-1 Namiki, Tsukuba Ibaraki 305-0044 (Japan); Department of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan)

2013-08-15

177

Mean-Field Critical Behavior in the Sr1-x(Ca0.5Ba0.5)xRuO3 (0 <= x <= 0.35)  

NASA Astrophysics Data System (ADS)

Orthorhombic SrRuO3 is a metallic ferromagnet with Tc 160 K where mean-field (MF) critical behavior has been observed. [1] Recently, we have shown that cubic BaRuO3 belongs to the 3D Heisenberg universality class with short-range exchange interactions. [2] The partial chemical substitution by either smaller Ca^2+ or larger Ba^2+ in Sr1-xAxRuO3 which changes the bond angle and introduces an A-cation size variance ?^2 ? - ^2 , causes a clear deviation from the MF behavior. In order to distinguish effects of versus ?^2, we have synthesized Sr1-x(Ca0.5Ba0.5)xRuO3 (0 <= x <= 0.35) under 1000 C and 10 GPa in a Walker-type multianvil; these samples have the same average as that of SrRuO3, but a different ?^2. All samples exhibit perfect MF critical behaviors, which indicates that the peculiar bond angle 163 plays an essential role in determining the MF critical behavior of SrRuO3.[0pt] [1] D. Kim, et al., Phys. Rev. B 67, 100406 (2003).[0pt] [2] J.-S. Zhou, et al., Phys. Rev. Lett. 101, 077206 (2008).

Cheng, Jinguang; Zhou, Jianshi; Goodenough, John

2009-03-01

178

Electric Quadrupole Moments of Metastable States of Ca^+, Sr^+, and Ba^+  

NASA Astrophysics Data System (ADS)

Electric quadrupole moments of the metastable nd3/2 and nd5/2 states of Ca^+, Sr^+, and Ba^+ are calculated using the relativistic all-order method including all single, double, and partial triple excitations of the Dirac-Hartree-Fock wave function to provide recommended values for the cases where no experimental data are available. The contributions of all non-linear single and double terms are also calculated for the case of Ca^+ for comparison of our approach with the CCSD(T) results. The third- order many body perturbation theory is used to evaluate contributions of high partial waves and the Breit interaction. The remaining omitted correlation corrections are estimated as well. Extensive study of the uncertainty of our calculations is carried out to establish accuracy of our recommended values to be 0.5% - 1% depending on the particular ion. Comprehensive comparison of our results with other theoretical values and experiment is carried out. Our result for the quadrupole moment of the 3d5/2 state of Ca^+ ion, 1.849(17) ea0^2, is in agreement with the most precise recent measurement 1.83(1) ea0^2 by Roos et al. [Nature 443, 316 (2006)].

Jiang, Dansha; Arora, Bindiya; Safronova, Marianna

2009-05-01

179

Electric quadrupole moments of metastable states of Ca+ , Sr+ , and Ba+  

NASA Astrophysics Data System (ADS)

The electric quadrupole moments of the metastable nd3/2 and nd5/2 states of Ca+ , Sr+ , and Ba+ are calculated using the relativistic all-order method including all single, double, and partial triple excitations of the Dirac-Hartree-Fock wave function to provide recommended values for the cases where no experimental data are available. The contributions of all nonlinear single and double terms are also calculated for the case of Ca+ for comparison of our approach with results of the coupled-cluster method with singles, doubles, and perturbative triples. Third-order many-body perturbation theory is used to evaluate the contributions of high partial waves and the Breit interaction. The remaining omitted correlation corrections are estimated as well. An extensive study of the uncertainty of our calculations is carried out to establish the accuracy of our recommended values as 0.5 1 % depending on the particular ion. A comprehensive comparison of our results with other theoretical values and experimental results is carried out. Our result for the quadrupole moment of the 3d5/2 state of the Ca+ ion, 1.849(17)ea02 , is in agreement with the most precise recent measurement 1.83(1)ea02 by Roos [Nature (London) 443, 316 (2006)].

Jiang, Dansha; Arora, Bindiya; Safronova, M. S.

2008-08-01

180

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

SciTech Connect

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

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

1996-08-01

181

Vortex matter in Bi2Sr2CaCu2O8 with pointlike disorder  

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

182

Anisotropic compressibility of the orthorhombic phase Bi 2Sr 2Ca 1Cu 2O 8  

NASA Astrophysics Data System (ADS)

The anisotropic compressibility factors of the superconducting phase Bi 2Sr 2Ca 1Cu 2O 8 (2212) are measured at 300 K by means of powder neutron diffraction under pressure up to 10 kbar. The values (in Pa -1) ?a=(4.9±1.0)×10 -12, ?b=(2.0±0.4)×10 -12 and ?c=(9.8±2.0)×10 -12 have been found. The resulting volumic coefficients is ?v=17×10 -12Pa-1. This result is to be compared with the results concerning Y 1Ba 2Cu 3O 7: ?v=5.3×10 -12Pa-1. A comparison between the Grüneisen parameters of the superconductors is made.

Gavarri, Jean-Raymond; Monnereau, Odile; Vacquier, Gilbert; Carel, Claude; Vettier, Christian

1990-12-01

183

Interaction Between Neuronal NOS Signaling and Temperature Influences SR Ca2+ Leak: Role of Nitroso-Redox Balance.  

PubMed

Rationale: While nitric oxide (NO) signaling modulates cardiac function and excitation-contraction coupling, opposing results due to inconsistent experimental conditions, particularly with respect to temperature, confound the ability to elucidate NO signaling pathways. Here we show that temperature significantly modulates NO effects. Objective: Test the hypothesis that temperature profoundly impacts nitroso-redox equilibrium, thereby affecting sarcomeric reticulum (SR) Ca(2+) leak. Methods and Results: We measured SR Ca(2+) leak in cardiomyocytes from wild-type (WT), NO/redox imbalance (NOS1(-?-)), and hyper S-nitrosylation (GSNOR(-?-)) mice. In WT cardiomyocytes, SR Ca(2+) leak increased as temperature decreased from 37°C to 23°C, whereas, in NOS1(?/?) cells, the leak suddenly increased when the temperature surpassed 30ºC. GSNOR(?/?) cardiomyocytes exhibited low leak throughout the temperature range. Exogenously added NO had a biphasic effect on NOS1(?/?) cardiomyocytes; reducing leak at 37ºC but increasing it at sub-physiologic temperatures. Oxypurinol and Tempol diminished the leak in NOS1(-?-) cardiomyocytes. Cooling from 37° to 23°C increased ROS generation in WT but decreased it in NOS1(-?-) cardiomyocytes. Oxypurinol further reduced ROS generation. At 23°C in WT cells, leak was decreased by tetrahydrobiopterin, an essential NOS cofactor. Cooling significantly increased SR Ca(2+) content in NOS1(-?-) cells but had no effect in WT or GSNOR(-?-). Conclusions: Ca(2+) leak and temperature are normally inversely proportional, whereas NOS1 deficiency reverses this effect, increasing leak and elevating ROS production as temperature increases. Reduced denitrosylation (GSNOR deficiency) eliminates the temperature dependence of leak. Thus, temperature regulates the balance between NO and ROS which in turn has a major impact on SR Ca(2+). PMID:25326127

Dulce, Raul; Mayo, Vera; Rangel, Erika B; Balkan, Wayne; Hare, Joshua M

2014-10-17

184

Superconducting and normal-state properties of APd2As2 (A = Ca, Sr, Ba) single crystals  

NASA Astrophysics Data System (ADS)

The synthesis and crystallography, magnetic susceptibility ?, magnetization M, specific heat Cp, in-plane electrical resistivity ?, and in-plane magnetic penetration depth measurements are reported for single crystals of APd2As2 (A = Ca, Sr, Ba) versus temperature T and magnetic field H. The crystals were grown using PdAs self-flux. CaPd2As2 and SrPd2As2 crystallize in a collapsed body-centered tetragonal ThCr2Si2-type structure (I4/mmm), whereas BaPd2As2 crystallizes in the primitive tetragonal CeMg2Si2-type structure (P4/mmm), in agreement with literature data. The ?(T) data exhibit metallic behavior for all three compounds. Bulk superconductivity is reported for CaPd2As2 and SrPd2As2 below Tc=1.27 and 0.92 K, respectively, whereas only a trace of superconductivity is found in BaPd2As2. No other phase transitions were observed. The ?(T) and M(H) data reveal anisotropic diamagnetism in the normal state, with ?c>?ab for CaPd2As2 and BaPd2As2, and ?cSrPd2As2. The normal and superconducting state data indicate that CaPd2As2 and SrPd2As2 are conventional type-II nodeless s-wave electron-phonon superconductors. The electronic superconducting state heat capacity data for CaPd2As2, which has an extremely sharp heat capacity jump at Tc, are analyzed using our recent elaboration of the ?-model of the BCS theory of superconductivity, which indicates that the s-wave gap in this compound is anisotropic in momentum space.

Anand, V. K.; Kim, H.; Tanatar, M. A.; Prozorov, R.; Johnston, D. C.

2013-06-01

185

Oxyhydrides of (Ca,Sr,Ba)TiO3 perovskite solid solutions.  

PubMed

The oxyhydride solid solutions (Ca,Sr)TiO(3-x)H(x) and (Sr,Ba)TiO(3-x)H(x) have been prepared by reducing the corresponding ATiO(3) oxides with calcium hydride. Under the reaction conditions examined, a hydride content of x = 0.1-0.3 was obtained for all compositions. Compared to our previous result with BaTiO(3-x)H(x), the larger particle size in this study (20-30 ?m vs 170 nm) resulted in a somewhat lower hydride amount despite prolonged reaction times. We examined changes in cell volume, octahedral tilt angle, and site occupancy of different anion sites after conversion to oxyhydrides; it appears that these oxyhydrides fit the geometrical descriptions typical for regular ABO(3) perovskites quite well. The hydrogen release temperature, previously shown to be indicative of the hydride exchange temperature, however, does not scale linearly with the A-site composition, indicating a potential effect of chemical randomness. PMID:23082857

Sakaguchi, Tatsunori; Kobayashi, Yoji; Yajima, Takeshi; Ohkura, Masatoshi; Tassel, Cédric; Takeiri, Fumitaka; Mitsuoka, Shingo; Ohkubo, Hiroshi; Yamamoto, Takafumi; Kim, Jung eun; Tsuji, Naruki; Fujihara, Akihiko; Matsushita, Yoshitaka; Hester, James; Avdeev, Maxim; Ohoyama, Kenji; Kageyama, Hiroshi

2012-11-01

186

Accumulation of nitrotyrosine on the SERCA2a isoform of SR Ca-ATPase of rat skeletal muscle during aging: a peroxynitrite-mediated process?  

Microsoft Academic Search

The SR Ca-ATPase in skeletal muscle SR vesicles isolated from young adult (5 months) and aged (28 months) rats was analyzed for nitrotyrosine. Only the SERCA2a isoform contained significant amounts with approximately one and four nitrotyrosine residues per young and old Ca-ATPase, respectively. The in vitro exposure of SR vesicles of young rats to peroxynitrite yielded selective nitration of the

Rosa I. Viner; Deborah A. Ferrington; Andreas F. R. Hühmer; Diana J. Bigelow; Christian Schöneich

1996-01-01

187

Alkaline-earth metal carboxylates characterized by 43Ca and 87Sr solid-state NMR: impact of metal-amine bonding.  

PubMed

A series of calcium and strontium complexes featuring aryl carboxylate ligands has been prepared and characterized by alkaline-earth ((43)Ca and (87)Sr) solid-state NMR experiments in a magnetic field of 21.1 T. In the 11 compounds studied as part of this work, a range of coordination motifs are observed including nitrogen atom binding to Ca(2+) and Sr(2+), a binding mode which has not been investigated previously by (43)Ca or (87)Sr solid-state NMR. (43)Ca isotopic enrichment has enabled the full characterization of the (43)Ca electric field gradient (EFG) and chemical shift tensors of the two calcium sites in calcium p-aminosalicylate (Ca(pams)), where both NMR interactions are affected by the presence of a nitrogen atom in the first coordination sphere of one of the metal sites. The (43)Ca isotropic chemical shift is sensitive to the Ca-N distance as exemplified by the NMR parameters of a second form of Ca(pams) and density functional theory (DFT) calculations. Studies of the strontium analogue, Sr(pams), confirm a similar sensitivity of the (87)Sr EFG tensor to the presence or absence of nitrogen in the first coordination sphere. To our knowledge, this is the first systematic (87)Sr NMR study of strontium complexes featuring organic ligands. The |CQ((87)Sr)| values are found to be sensitive to the coordination number about Sr(2+). In general, this work has also established a larger data set of reliable experimental |CQ((43)Ca)| values which correlate well with those obtained using gauge-including projector-augmented-wave (GIPAW) DFT calculations. It is found that the use of a recently recommended quadrupole moment for (43)Ca, -44.4 mbarn, improves the agreement with experimental values. This contribution lays the groundwork for the interpretation of (43)Ca and (87)Sr NMR spectra of more challenging systems, particularly where nitrogen-alkaline earth metal bonding is occurring. PMID:24359541

Burgess, Kevin M N; Xu, Yang; Leclerc, Matthew C; Bryce, David L

2014-01-01

188

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

189

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

NASA Astrophysics Data System (ADS)

The phase relations of equilibrium compounds in the pseudoternary system Bi2O3-(Ca,Sr)O-CuO at 850 and 900 C were studied. The ratio of Ca:Sr was fixed at 1:2. Starting materials of Bi2O3, CaCO3, SrCO3, and CuO with various ratios were mixed, pressed into pellets, and heated at or above and then brought back to 850 or 900 C for different durations to ensure that equilibrium had been reached. The products were cooled in air or quenched in liquid nitrogen and then identified by X-ray powder diffraction. At 850 C, only the superconducting phase, Bi2CaSr2Cu2Ox (2122), was observed inside the triangle. The other stable phases were all positioned on the boundary lines. At 900 C, the above-boundary line phases remained stable, but the 2122 phase was not observed. The tie lines among the stable phases in the two isotherms were established.

Lee, C.-L.; Chen, J.-J.; Wen, W.-J.; Perng, T.-P.; Wu, J. M.

1990-07-01

190

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

191

The amounts Fe, Ba, Sr, K, Ca and Ti in some lichens growing in Erzurum province (Turkey)  

Microsoft Academic Search

The amounts of Fe, Ba, Sr, K, Ca and Ti were determined qualitatively and quantitatively by using energy-dispersive X-ray fluorescence in eight lichen species, Pinus sylvestris, rock and soil in district of Erzurum province (Turkey). Lichen species were Cetraria pinastri (Scop.) Gray, Dermatocarpon miniatum (L.) W. Mann, Lecanora muralis (Schreb.) Rabenh., Pseudevernia furfuracea (L.) Zopf., Ramalina capitata (Ach.) Nyl., Rhizoplaca

Ali Aslan; Gökhan Budak; Abdulhalik Karabulut

2004-01-01

192

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

193

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, Gastón; Weht, Ruben; Sow, Amadou; Zhu, Xiyu; Han, Fei; Cheng, Peng; Ju, Jing; Wen, Hai Hu; Núñez-Regueiro, Manuel

2014-04-16

194

Effect of vibrational excitation on the molecular beam reactions of Ca and Sr with HF and OF  

E-print Network

of this technique to Ca and Sr. For the latter reagents, un- like Ba, the reaction with HF (v =0) is endothermic, while the reaction with HF (v =1) is exothermic. This has the advantage that the reaction rate for HF (v that reagent vibration is necessary to promote endothermic reactions. 4 While the present investigation only

Zare, Richard N.

195

Seasonal d18O and Sr\\/Ca Records from Submerged Pleistocene Fossil Corals in the Western Equatorial Pacific  

Microsoft Academic Search

We have monthly d18O and Sr\\/Ca records from three submerged fossil Porites corals from the Huon Gulf, Papua New Guinea and from two modern Porites corals from New Britain and Sanaroa Island, which have been used for calibration. The fossil corals grew on the lower plate of an active convergent margin in the Huon Gulf and formed a series of

L. M. Gruhn; C. D. Gallup; A. C. Ravelo; K. Riker-Coleman; F. W. Taylor; J. M. Webster; E. A. Silver; D. C. Potts

2005-01-01

196

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

NASA Astrophysics Data System (ADS)

3 d metal K-shell X-ray absorption spectra of perovskites with the composition La 1- xCa xCoO 3- ? ( x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La 1- xSr xCoO 3- ? ( x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La 1- xSr xFeO 3- ? ( x=0, 0.2, 0.4, 0.5, 0.6, 0.8) are compared on the basis of pre-edges, white line features and extended fine structures. The measurements were performed at 300 K and for La 1- xCa xCoO 3- ? also at temperatures as low as 10-20 K. Going to low-temperature the measurements indicate an increase in t2g* and a decrease in eg* orbital occupancy, which is most accentuated in the LaCoO 3 sample. Virtually no Co K-edge shift was observed for the La 1- xCa xCoO 3- ? and La 1- xSr xCoO 3- ? compounds and the Co-O distances are also not significantly reduced when La 3+ is partially substituted by Ca 2+ or Sr 2+. From the pre-edge features of these perovskites we are tended to conclude that the t2g* orbitals are less, and the eg* orbitals are more occupied with increasing x in the Ca and Sr substituted compounds, whereas the total d-electron density is not changing. These results indicate that cobalt prefers a valence state of 3 + in these Co perovskites. This could also be confirmed with iodometric titrations. The Fe perovskites behave differently. In contrast to the Co perovskites, for La 1- xSr xFeO 3- ? perovskites the Fe K-edge is shifted, the pre-edge features intensity is increasing and the Fe-O bond length is decreasing with increasing x. The valence states of the iron in the La 1- xSr xFeO 3- ? perovskites in fact increase as much as x increases.

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

2011-12-01

197

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

198

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

199

Thermoelectric power studies of La–Co substituted Sr M-type hexagonal ferrites  

Microsoft Academic Search

Thermoelectric power studies of Sr–La–Co hexagonal ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The values of the charge carrier concentration have been computed from the observed values of the Seebeck coefficient.

D Ravinder; P Shalini; P Mahesh; A Morel; P Tenaud

2004-01-01

200

Synthesis and magnetic properties of La-substituted M-type Sr hexaferrites  

NASA Astrophysics Data System (ADS)

Single-phase M-type hexagonal ferrites Sr 1-xLa xFe 12O 19 (0? x?1) were prepared by a ceramic route. The stability limits of the ferrite phases were determined with a combination of various microscopy techniques, electron-probe micro-analysis, powder X-ray diffraction and thermal analysis. SrFe 12O 19 ( x=0) is stable up to 1420 °C, whereas LaFe 12O 19 ( x=1) exists between 1360 and 1400 °C only. The lattice parameters of Sr 1-xLa xFe 12O 19 exhibit a linear variation with x, i.e. a0 slightly increases and c0 decreases with x, leading to a decrease of the unit cell volume with x. The saturation magnetization at T=5 K decreases with increasing La concentration. Room temperature Mössbauer analysis shows that the Fe 3+/Fe 2+ valence change occurs in the 2a sites for the whole composition range.

Seifert, D.; Töpfer, J.; Langenhorst, F.; Le Breton, J.-M.; Chiron, H.; Lechevallier, L.

2009-12-01

201

High oxygen pressure single crystal growth of highly Ca-doped spin ladder compound Sr 14- xCa xCu 24O 41 ( x>12)  

NASA Astrophysics Data System (ADS)

Large size high-quality Ca-doped Sr 14- xCa xCu 24O 41 ( x=12.2, 12.6 and 13) spin ladder superconducting single crystals were grown using a modified mirror floating zone furnace with oxygen pressure up to 35 bar. The qualities of the as-grown single crystals were confirmed by polarized optical microscopy, neutron diffraction and X-ray diffraction methods. The sample compositions and homogeneity were measured using micro-X-ray fluorescence spectroscopy. The lattice parameters of each sample have been refined using the Rietveld method. The oxygen stoichiometry measurements which were performed by hydrogen reduction/thermogravimetry method show that all the three samples are slightly oxygen deficient even though high oxygen pressure was applied during growth. The high oxygen pressure is indispensible for growing highly Ca-doped Sr 14- xCa xCu 24O 41 single crystals. The susceptibility was measured along c-axis for all three compositions, fitting well with the one dimensional dimer model, consistent with the reported values of undoped Sr 14Cu 24O 41 parent compounds.

Deng, Guochu; Radheep, D. Mohan; Thiyagarajan, R.; Pomjakushina, Ekaterina; Wang, Shuang; Nikseresht, Neda; Arumugam, S.; Conder, Kazimierz

2011-07-01

202

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

NASA Astrophysics Data System (ADS)

We present a temperature-dependent resonant elastic soft x-ray scattering (REXS) study of the metal-insulator transition in Sr3(Ru1-xMnx)2O7, performed at both Ru and Mn L-edges. Resonant magnetic superstructure reflections together with ab-initio density functional theory calculations identify the ground state as a spin checkerboard with blocks of 4 spins up and 4 spins down. Based on modelling of the REXS intensity from randomly distributed Mn impurities, we establish the inhomogeneous nature of the metal-insulator transition, with an effective percolation threshold corresponding to an anomalously low x˜0.05 Mn substitution. Perhaps more important, our results suggest that the same checkerboard instability might be present already in the parent compound Sr3Ru2O7. In collaboration with: A.G. Cruz Gonzalez, J.D. Denlinger (Berkeley) I. Zegkinoglou, M.W. Haverkort (MPI) J. Geck, D.G. Hawthorn (UBC) R. Mathieu, Y. Tokura, S. Satow, H. Takagi (Tokyo) H.-H. Wu and C. Schussler-Langeheine (Cologne).

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

2011-03-01

203

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

NASA Technical Reports Server (NTRS)

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

Duncan, R. C., Jr.

1972-01-01

204

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

205

The deposition of strontium-substituted hydroxyapatite coatings.  

PubMed

Strontium substituted hydroxyapatite (SrHA) coatings have received a lot of interest recently as strontium (Sr) has been shown to have the dual benefit of promoting bone formation and reducing bone resorption, in vivo. In this work, SrHA coatings were deposited onto polycrystalline titanium surfaces using radio frequency (RF) magnetron co-sputtering and compared to those deposited from HA alone. In particular, the influence of different levels of Sr-substitution of the sputtering targets (5 and 13 % Sr-substituted HA targets) on the properties of the deposited coatings produced at a low discharge power level (150 W) were investigated using FTIR, XPS, XRD, ToFSIMS and AFM techniques (both before and after annealing at 500 °C). The results show that Sr could be successfully incorporated into the HA lattice to form SrHA coatings and that they contained no other impurities. However, the coating produced from the 13 % Sr-substituted target had a higher Ca + Sr/P ratio (1.95 ± 0.14) and Sr content when compared to the coating produced from the 5 % Sr-substituted target (1.58 ± 0.20). The deposition rate also decreased with increasing Sr content of the sputtering targets. Furthermore, as the Sr content of the coatings increased, so did the preferred 002 orientation of the coating along with increased surface roughness and heterogeneity of the surface features. Therefore, this study has shown that RF magnetron sputtering offers a means to control attendant properties of Sr-substituted HA, such as the crystallinity, stoichiometry, phase purity and surface topography. PMID:25631262

Boyd, Adrian R; Rutledge, L; Randolph, L D; Mutreja, I; Meenan, B J

2015-02-01

206

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

PubMed

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

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

2011-03-01

207

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

208

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

SciTech Connect

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

Takano, Yoshihiko; Noro, Sumiko; Yamadaya, Tokio [Yokohama City Univ. (Japan). Dept. of Physics] [Yokohama City Univ. (Japan). Dept. of Physics; Isobe, Masaaki; Ami, Takaaki; Suzuki, Masayuki; Tanaka, Masahiro [Sony Corp. Research Center, Yokohama (Japan)] [Sony Corp. Research Center, Yokohama (Japan)

1995-02-01

209

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

210

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

DOEpatents

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

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

1996-05-14

211

Different roles of anisotropy and disorder on the vortex matter of Bi 2Sr 2CaCu 2O 8+ ? single crystal  

NASA Astrophysics Data System (ADS)

The oxygen doped and Pb-substituted single crystalline Bi 2Sr 2CaCu 2O 8+ ? samples having Tc,on and anisotropy ( ?2) ranging respectively from 65 to 93 K and from 773 to 49,715 have been studied in the basis of magneto-resistance and magnetization data. It is found that the lowering of anisotropy due to higher oxygen content or Pb substitution is responsible for the reduction of magnetic field-induced transitional broadening and a shift of Hirr( T) and Hg( T) to higher temperatures and magnetic field. Meanwhile, the increasing disorder manifested by decreasing Tc also leads to the extended range of appearance for the second magnetization peak (SMP) and enlarged critical glassy region. It is shown that decreasing anisotropy does not necessarily lead to the lowering of Tc in contrast to the monotonic dependence of Tc on the disorder measured in the temperature range of SMP effect. Additionally, a remarkable monotonic correlation between Tc and the glassy exponent s has been established.

Darminto, D.; Diantoro, M.; Sutjahja, I. M.; Nugroho, A. A.; Loeksmanto, W.; Tjia, M. O.

2002-10-01

212

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

213

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

PubMed

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

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

2013-11-01

214

X-ray absorption investigation of the valence state and electronic structure of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} in comparison with La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}  

SciTech Connect

3d metal K-shell X-ray absorption spectra of perovskites with the composition La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8), La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (x=0, 0.1, 0.2, 0.3, 0.4, 0.5) and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} (x=0, 0.2, 0.4, 0.5, 0.6, 0.8) are compared on the basis of pre-edges, white line features and extended fine structures. The measurements were performed at 300 K and for La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} also at temperatures as low as 10-20 K. Going to low-temperature the measurements indicate an increase in t{sub 2g}{sup Low-Asterisk} and a decrease in e{sub g}{sup Low-Asterisk} orbital occupancy, which is most accentuated in the LaCoO{sub 3} sample. Virtually no Co K-edge shift was observed for the La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} compounds and the Co-O distances are also not significantly reduced when La{sup 3+} is partially substituted by Ca{sup 2+} or Sr{sup 2+}. From the pre-edge features of these perovskites we are tended to conclude that the t{sub 2g}{sup Low-Asterisk} orbitals are less, and the e{sub g}{sup Low-Asterisk} orbitals are more occupied with increasing x in the Ca and Sr substituted compounds, whereas the total d-electron density is not changing. These results indicate that cobalt prefers a valence state of 3{sup +} in these Co perovskites. This could also be confirmed with iodometric titrations. The Fe perovskites behave differently. In contrast to the Co perovskites, for La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites the Fe K-edge is shifted, the pre-edge features intensity is increasing and the Fe-O bond length is decreasing with increasing x. The valence states of the iron in the La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites in fact increase as much as x increases. - Graphical abstract: Co K and Fe K pre-edge of La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} perovskites one of the evidences in favor of {delta}=x/2 for the Co-perovskites and {delta}=0 for the Fe-perovskites. Highlights: Black-Right-Pointing-Pointer XAS a valuable tool to evaluate the valence states of Co and Fe perovskites. Black-Right-Pointing-Pointer For La{sub 1-x}Ca{sub x}CoO{sub 3-{delta}} and La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} perovskites {delta} is close to x/2. Black-Right-Pointing-Pointer For La{sub 1-x}Sr{sub x}FeO{sub 3-{delta}} series {delta} is close to 0. Black-Right-Pointing-Pointer Discussion of the x dependency of the pre-edge bands.

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

2011-12-15

215

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

SciTech Connect

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

Samal, Saroj L. [Ames Laboratory; Gulo, Fakhili [Ames Laboratory; Corbett, John D. [Ames Laboratory

2013-02-18

216

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

PubMed

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

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

2012-01-01

217

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

PubMed Central

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

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

2012-01-01

218

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 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.

2013-01-01

219

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

220

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

221

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

NASA Astrophysics Data System (ADS)

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

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

2004-02-01

222

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

223

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

SciTech Connect

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

Parker, David S [ORNL; Singh, David J [ORNL

2013-01-01

224

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

PubMed

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

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

2012-05-30

225

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

PubMed

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

Delmotte, Philippe; Sieck, Gary C

2015-02-01

226

Direct measurements of SR free Ca reveal the mechanism underlying the transient effects of RyR potentiation under physiological conditions  

PubMed Central

Aims Most of the calcium that activates contraction is released from the sarcoplasmic reticulum (SR) through the ryanodine receptor (RyR). It is controversial whether activators of the RyR produce a maintained increase in the amplitude of the systolic Ca transient. We therefore aimed to examine the effects of activation of the RyR in large animals under conditions designed to be as physiological as possible while simultaneously measuring SR and cytoplasmic Ca. Methods and results Experiments were performed on ventricular myocytes from canine and ovine hearts. Cytoplasmic Ca was measured with fluo-3 and SR Ca with mag-fura-2. Application of caffeine resulted in a brief increase in the amplitude of the systolic Ca transient accompanied by an increase of action potential duration. These effects disappeared with a rate constant of ?3 s?1. Similar effects were seen in cells taken from sheep in which heart failure had been induced by rapid pacing. The decrease of Ca transient amplitude was accompanied by a decrease of SR Ca content. During this phase, the maximum (end-diastolic) SR Ca content fell while the minimum systolic increased. Conclusions This study shows that, under conditions designed to be as physiological as possible, potentiation of RyR opening has no maintained effect on the systolic Ca transient. This result makes it unlikely that potentiation of the RyR has a maintained role in positive inotropy. PMID:24947416

Greensmith, David J.; Galli, Gina L.J.; Trafford, Andrew W.; Eisner, David A.

2014-01-01

227

Structure and photoluminescence properties of Ce 3+-doped novel silicon-oxynitride Ba 4- zMzSi 8O 20-3 xN 2 x ( M=Mg, Ca, Sr)  

NASA Astrophysics Data System (ADS)

Structural and photoluminescence properties of undoped and Ce 3+-doped novel silicon-oxynitride phosphors of Ba 4- zMzSi 8O 20-3 xN 2 x ( M=Mg, Sr, Ca) are reported. Single-phase solid solutions of Ba 4- zMzSi 8O 20-3 xN 2 x oxynitride were synthesized by partial substitutions of 3O 2-?2N 3- and Ba? M ( M=Mg, Ca, Sr) in orthorhombic Ba 2Si 4O 10. The influences of the type of alkaline earth ions of M, the Ce 3+ concentration on the photoluminescence properties and thermal quenching behaviors of Ba 3MSi 8O 20-3 xN 2 x ( M=Mg, Ca, Sr, x=0.5) were investigated. Under excitation at about 330 nm, Ba 3MSi 8O 20-3 xN 2 x:Ce 3+ ( x=0.5) exhibits efficient blue emission centered at 400-450 nm in the range of 350-650 nm owing to the 5 d?4 f transition of Ce 3+. The emission band of Ce 3+ shifts to long wavelength by increasing the ionic size of M due to the modification of the crystal field, as well as the Ce 3+ concentrations due to the Stokes shift and energy transfer or reabsorption of Ce 3+ ions. Among the silicon-oxynitride phosphors of Ba 3MSi 8O 18.5N:Ce 3+, M=Sr 0.6Ca 0.4 possesses the best thermal stability probably related to its high onset of the absorption edge of Ce 3+.

Fang, Y.; Li, Y. Q.; Xie, R. J.; Hirosaki, N.; Takade, T.; Li, X. Y.; Qiu, T.

2011-06-01

228

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

SciTech Connect

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

Liu, Mingquan [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Shen, Xiangqian, E-mail: shenxq@ujs.edu.c [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Song, Fuzhan; Xiang, Jun; Meng, Xianfeng [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China)

2011-04-15

229

Fluctuation conductivity of Bi2Sr2CaCu2O8 + ? in a two-band superconductivity model  

NASA Astrophysics Data System (ADS)

A modified analytical Aslamazov-Larkin formula for the temperature dependence of the fluctuation conductivity near the critical temperature T c is obtained for two-band superconducting compounds on the basis of linearized equations of the two-band Ginzburg-Landau theory. The results are compared to experimental data for the high- T c superconductor compound Bi2Sr2CaCu2O8 + ?.

Askerzade, I. N.; Ragimov, S. S.

2009-06-01

230

Precise magnetization measurements of single crystalline Bi2Sr2CaCu2O8+delta  

Microsoft Academic Search

Precise dc-magnetization measurements, using a superconducting quantum interference device magnetometer (SQUID), have been performed on single crystalline Bi2Sr2CaCu2O8+delta in magnetic fields both parallel to the c axis (H||c) and tilted away from the c axis towards the ab plane to investigate the vortex state at various temperatures between 40 K and Tc=83.0 K. The magnetization curves at a fixed temperature

Kazuo Kadowaki; Kazuhiro Kimura

1998-01-01

231

Thermal Expansion of Alkaline-Earth-Metal Disilicides AeSi2 (Ae= Ca, Sr, and Ba)  

Microsoft Academic Search

The thermal expansion of alkaline-earth-metal disilicides AeSi2 (Ae= Ca, Sr, and Ba) has been investigated at temperatures ranging from room temperature to 873 K using powder X-ray diffractometry. The coefficients of linear thermal expansion, alphai's, of AeSi2 range from 9 × 10-6 to 18 × 10-6 K-1, which are larger than those of Si (2.6 × 10-6 K-1 at 298

Motoharu Imai

2011-01-01

232

Gas-phase particle size distributions and lead loss during spray pyrolysis of (Bi,Pb)-Sr-Ca-Cu-O  

Microsoft Academic Search

Gas-phase particle size distributions and lead loss were measured during formation of (Bi,Pb)--Sr--Ca--Cu--O and pure PbO particles by spray pyrolysis at different temperatures. A differential mobility analyzer (DMA) in conjunction with a condensation particle counter (CPC) was used to monitor the gas-phase particle size distributions, and a Berner-type low-pressure impactor was used to obtain mass size distributions and a Berner-type

Abhijit S. Gurav; Toivo T. Kodas; Jorma Joutsensaari; Esko I. Kauppinen; Riita Zilliacus

1995-01-01

233

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

234

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

Microsoft Academic Search

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

K. Tao; E. L. Grossman

2009-01-01

235

Evolution of Crystal Structure and Magnetism in Single-Crystal (Ba,Sr,Ca)Fe2As2 Solid Solutions  

Microsoft Academic Search

Superconductivity in the FeAs-based materials has motivated extensive studies of structural, magnetic and electronic properties of these systems. A common element of the 122 FeAs- based intermetallic series is the occurrence of a simultaneous structural and antiferromagnetic phase transition, which occurs at temperatures ranging between 130 K and 200 K in the Ba, Sr, and Ca-based parent compounds. We present

Johnpierre Paglione; K. Kirshenbaum; S. R. Saha; N. P. Butch; P. Y. Zavalij; B. G. Ueland; J. W. Lynn

2010-01-01

236

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

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

237

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) Å, c = 7.028(1) Å, and Z = 2. Eu2+ and Mn2+ activated Ca2SrNaLa(PO4)3F phosphors have been prepared. The energy transfer of Eu2+ ? Mn2+ has been investigated. The resonant type energy transfer from Eu2+ to Mn2+ has been demonstrated, and the energy transfer efficiency has also been calculated according to their PL decay curves. A color-tunable emission in Ca2SrNaLa(PO4)3F phosphors can be realized by Eu2+ ? Mn2+ energy transfer. White light can be achieved in a single-phased Ca2SrNaLa(PO4)3F host by co-doping Eu2+ and Mn2+ with CIE (0.32, 0.31). Our results demonstrate that the potential application of these phosphors in solid-state lighting and (or) other areas.

Shanshan, Hu; Wanjun, Tang

2013-12-01

238

Hanford 100N Area Apatite Emplacement: Laboratory Results of Ca-Citrate-PO4 Solution Injection and Sr90 Immobilization in 100N Sediments  

Microsoft Academic Search

This report summarizes laboratory scale studies investigating the remediation of Sr-90 by Ca-citrate-PO4 solution injection\\/infiltration to support field injection activities in the Hanford 100N area. This study is focused on experimentally testing whether this remediation technology can be effective under field scale conditions to mitigate Sr-90 migration 100N area sediments into the Columbia River. Sr-90 is found primarily adsorbed to

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

2007-01-01

239

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

240

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

241

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

E-print Network

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

Vodhanel, Mark E

2005-01-01

242

Optical properties of eu doped M-Ga2S4 (M: Zn, Ca, Sr) phosphors for white light emitting diodes.  

PubMed

Eu2+ doped M-thiogallate (MGa2S4, M: Zn, Ca, Sr) phosphors were prepared by solid-state reaction. The dependence of luminescent properties, photoluminescence and cathodoluminescence, on M2+ ions was investigated. ZnGa2S4: Eu2+, CaGa2S4: Eu2+, and SrGa2S4: Eu2+ exhibited a green emission band at 540 nm, 560 nm, and 535 nm, respectively. The red-shift between CaGa2S4: Eu2+ and SrGa2S4: Eu2+ was originated from the radius difference of Ca2+ and Sr2+ ions. However, it did not apply to ZnGa2S4 : Eu2+ despite of smaller radius of Zn2+ ion. The particle size of ZnGa2S4 : Eu2+ was much smaller than those of the other thiogallates, leading to extremely low CL emission. PMID:18047120

Kim, Joo Won; Kim, Young Jin

2007-11-01

243

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.; VanGeen, A.

2004-01-01

244

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

E-print Network

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

Messing, Gary L.

245

Multiple Changes of Order of the Vortex Melting Transition in Bi2Sr2CaCu2O8 with Dilute Columnar Defects  

E-print Network

a first-order vortex lattice melting line in Bi2Sr2CaCu2O8 crystals into alternating segments of firstMultiple Changes of Order of the Vortex Melting Transition in Bi2Sr2CaCu2O8 with Dilute Columnar is the flux quantum, and BmðT� is the melting field. Compared to the pinning energy to CD, the elastic energy

Zeldov, Eli

246

Hydrothermal Synthesis of nanocrystalline powders of alkaline-earth hydroxyapatites, A 10 (PO 4 ) 6 (OH) 2 (A = Ca, Sr and Ba)  

Microsoft Academic Search

In the present work, we report a direct precipitation of nanocrystalline powders of alkaline-earth hydroxyapatites of the\\u000a compositions, A10(PO4)6(OH)2 (A = Ca, Sr or Ba) from aqueous solutions containing Na3PO4 and MCl2 (M = Ca, Sr or Ba) at 150C for 2 days and autogeneous pressure under hydrothermal conditions. The products were characterized\\u000a by X-ray powder diffraction, transmission electron microscopy

P. Parhi; A. Ramanan; A. R. Ray

2006-01-01

247

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

248

Precise magnetization measurements of single crystalline Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

Precise dc-magnetization measurements, using a superconducting quantum interference device magnetometer (SQUID), have been performed on single crystalline Bi2Sr2CaCu2O8+? in magnetic fields both parallel to the c axis (H?c) and tilted away from the c axis towards the ab plane to investigate the vortex state at various temperatures between 40 K and Tc=83.0 K. The magnetization curves at a fixed temperature as a function of magnetic field (H?c) show a clear jump at HM, which corresponds to the flux-line-lattice-melting transition (FLLMT) as observed previously. In the vicinity of Tc=83.0 K, it is shown that the HM(T) line changes its character near T*=79.5 K, below which it can be described well by the FLLMT and above which the change of magnetization, ?M, and the corresponding change of the entropy, ?S, at HM, falls sharply as Tc is approached. A simultaneous decoupling of the Josephson coupling and the melting of the flux-line lattice may be an appropriate picture below T*, whereas above T* an additional degree of freedom makes a contribution to the FLLMT due, perhaps, to vortex-antivortex creation and annihilation processes. In a tilted magnetic field, it is found that the angular dependence of HM, as well as ?M and ?S, obeys a scaling law up to ?<=80°. The deduced anisotropy parameter ?s~=9 is found to be much lower than the value of ?l~=150-200 found in the liquid state. We interpret such a discrepancy as due to the difference of the dimensionality of the vortex pancake state above and below HM. Furthermore, from the scaling behavior of ?S in tilted fields, it is inferred that the FLLMT is predominantly ruled by the number of pancake vortices, n, in the superconducting CuO2 layers and that Josephson vortices do not play an important role for the FLLMT.

Kadowaki, Kazuo; Kimura, Kazuhiro

1998-05-01

249

Thermochemical behavior and transport properties of Pr-substituted SrTiO3 as potential solid oxide fuel cell anode  

NASA Astrophysics Data System (ADS)

Phase composition, structural stability, electrical properties, thermochemical expansion and redox behavior of Pr-substituted SrTiO3 were assessed for potential application in solid oxide fuel cell anodes. XRD analysis confirms formation of single-phase perovskite-like Sr1-xPrxTiO3±? and Sr1-1.5xPrxTiO3±? (x = 0.02-0.30) ceramics under both oxidizing and reducing conditions, although microstructural studies indicate minor precipitation of TiO2 in reduced Sr-deficient ceramics with high Pr content. XPS analysis in combination with XRD suggests that Pr cations substitute into strontium sublattice in mixed 4+/3+ oxidation state and are essentially insoluble in titanium sublattice. Reduction at elevated temperatures results in 2-3 orders of magnitude increase of n-type electronic conductivity with respect to oxidized materials. Thermogravimetric and electrical studies demonstrate however very slow reduction kinetics at temperatures below 1273 K associated with nearly frozen equilibrium in cation sublattice and low oxygen vacancy concentration in oxidized materials. Electrical behavior is discussed in conjunction with defect chemistry of donor-doped strontium titanate. All oxidized and reduced materials exhibit moderate thermal expansion coefficients, compatible with that of common solid electrolytes, and a small contribution of chemical expansion on reduction.

Yaremchenko, A. A.; Patrício, S. G.; Frade, J. R.

2014-01-01

250

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

PubMed Central

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

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

2012-01-01

251

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. PMID:23553082

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

252

An ion probe study of annual cycles of Sr/Ca and other trace elements in corals  

NASA Astrophysics Data System (ADS)

Corals show great promise for preserving century-long records of ocean chemistry and temperature with weekly time resolution. Allison and Tudhope (1992) showed that direct microscale analysis of coral skeletons was possible with ion microprobe techniques. We show here that analysis of B, F, Mg, Sr, and Ba (relative to Ca) can be rapidly achieved on Porites skeleton at 50 ?m (subweekly) spatial scales with precisions of 0.3-3%. The B, F, and Mg concentrations show large well-behaved annual variations of 44-57%, well-correlated with Sr/Ca variations of 12%, in the 1967-1969 bands from a live Porites from Two-Mile Reef, South Africa. The Sr/Ca ratio correlates well with the ? 18O record but shows a larger annual temperature amplitude, with additional numerous sub-weekly temperature spikes. Ba/Ca in recent bands of Porites shows both a large (factor of 5) annual cycle and a large yearly spike in the late summer; the annual variation is not observed in 30-year-old bands, though the annual spikes are still sharp and clear. Barium thus appears to be unstable in Porites during aging and is probably not skeletally-bound. Deep-sea (nonzooxanthellate) corals show uncorrelated variations of these same trace elements, with amplitudes similar to the Porites. These variations are likely biologically-mediated, as the thermal forcing function in the deep sea is nil. This suggests that the annual variations seen in Porites may also be driven by vital effects and not directly by temperature. Ion microprobe techniques are shown to provide rapid, precise, and high-resolution trace-element records in corals. Full exploitation of trace element paleotemperature methods in corals will require a more sophisticated understanding of how corals accrete their skeletal components. Ion probe analysis can contribute significantly to this understanding.

Hart, Stanley R.; Cohen, Anne L.

1996-08-01

253

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

PubMed Central

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

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

2008-01-01

254

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

SciTech Connect

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

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

2011-09-15

255

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

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

2012-01-01

256

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

SciTech Connect

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

Goretta, K.C.; Miller, D.J.; Poeppel, R.B. [Argonne National Lab., IL (United States); Nash, A.S. [Marquette Univ., Milwaukee, WI (United States)

1991-11-01

257

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 ˜2.3×10 -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

258

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

259

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

260

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

261

Structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba)  

NASA Astrophysics Data System (ADS)

The structural, electronic and mechanical properties of alkaline earth metal oxides MO (M=Be, Mg, Ca, Sr, Ba) in the cubic (B1, B2 and B3) phases and in the wurtzite (B4) phase are investigated using density functional theory calculations as implemented in VASP code. The lattice constants, cohesive energy, bulk modulus, band structures and the density of states are computed. The calculated lattice parameters are in good agreement with the experimental and the other available theoretical results. Electronic structure reveals that all the five alkaline earth metal oxides exhibit semiconducting behavior at zero pressure. The estimated band gaps for the stable wurtzite phase of BeO is 7.2 eV and for the stable cubic NaCl phases of MgO, CaO, SrO and BaO are 4.436 eV, 4.166 eV, 4.013 eV, and 2.274 eV respectively. A pressure induced structural phase transition occurs from wurtzite (B4) to NaCl (B1) phase in BeO at 112.1 GPa and from NaCl (B1) to CsCl (B2) phase in MgO at 514.9 GPa, in CaO at 61.3 GPa, in SrO at 42 GPa and in BaO at 14.5 GPa. The elastic constants are computed at zero and elevated pressures for the B4 and B1 phases for BeO and for the B1 and B2 phases in the case of the other oxides in order to investigate their mechanical stability, anisotropy and hardness. The sound velocities and the Debye temperatures are calculated for all the oxides using the computed elastic constants.

Cinthia, A. Jemmy; Priyanga, G. Sudha; Rajeswarapalanichamy, R.; Iyakutti, K.

2015-04-01

262

Fabrication of spherical CaO-SrO-ZnO-SiO? particles by sol-gel processing.  

PubMed

This study was concerned with the fabrication of ceramic CaO-SrO-ZnO-SiO(2) spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol-gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO-SrO-ZnO-SiO(2) particles by sol-gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H(2)O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3-5 mum homogenous spherical particles were obtained at a H(2)O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO(3)):Ca(NO(3))(2):Zn(NO(3))(2):Si(OC(2)H(5))(4) = x:0.12:(0.40 - x):0.48 (0

Kim, Ill Yong; Towler, Mark R; Wren, Anthony; Ohtsuki, Chikara

2009-11-01

263

Imaging the effects of individual zinc impurity atoms on superconductivity in Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

Although the crystal structures of the copper oxide high-temperature superconductors are complex and diverse, they all contain some crystal planes consisting of only copper and oxygen atoms in a square lattice: superconductivity is believed to originate from strongly interacting electrons in these CuO2 planes. Substituting a single impurity atom for a copper atom strongly perturbs the surrounding electronic environment and can therefore be used to probe high-temperature superconductivity at the atomic scale. This has provided the motivation for several experimental and theoretical studies. Scanning tunnelling microscopy (STM) is an ideal technique for the study of such effects at the atomic scale, as it has been used very successfully to probe individual impurity atoms in several other systems. Here we use STM to investigate the effects of individual zinc impurity atoms in the high-temperature superconductor Bi2Sr2CaCu 2O8+?. We find intense quasiparticle scattering resonances at the Zn sites, coincident with strong suppression of superconductivity within ~15 Å of the scattering sites. Imaging of the spatial dependence of the quasiparticle density of states in the vicinity of the impurity atoms reveals the long-sought four-fold symmetric quasiparticle `cloud' aligned with the nodes of the d-wave superconducting gap which is believed to characterize superconductivity in these materials.

Pan, S. H.; Hudson, E. W.; Lang, K. M.; Eisaki, H.; Uchida, S.; Davis, J. C.

2000-02-01

264

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

265

Normal-state dielectric and transport properties of In-doped Bi–Pb–Sr–Ca–Cu–O  

Microsoft Academic Search

The effect of indium doping on the normal-state transport and dielectric properties of the Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06InxOy (0?x?0.15) has been investigated. The dielectric constant, loss tangent, carrier concentration and electrical resistivity were measured at room temperature as a function of indium concentration. The dielectric constant is found to increase with increasing dopant concentration possibly due to increase in polarization. Impurities in any

R. K Nkum; M. O Gyekye; F Boakye

2002-01-01

266

Photoluminescence property of A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] phosphors.  

PubMed

A new efficient phosphor, A9B(VO4)7 [A = Ca, Sr, Ba and B = La, Gd] has been synthesized by the solid-state method at high temperature. X-ray diffraction analysis confirmed the formation of the compound. Photoluminescence excitation measurements show that the phosphor can be efficiently excited by near-ultraviolet light from 300 nm to 400 nm to realize emission covering the 397-647 nm region of visible spectrum. Therefore, newly synthesized novel phosphor may be useful as green-emitting phosphor in solid-state lighting. PMID:22961920

Singh, Roshani; Dhoble, S J

2013-01-01

267

The features of structural transformations in lanthanum manganites La1-xAxMnO3+? (A = Ca, Sr, Ba)  

NASA Astrophysics Data System (ADS)

In this work, the effect of the ionic radius and concentration of a doping element on the features of the structural transformations in polycrystalline lanthanum manganites, La1-xAxMnO3+? (A = Ca, Sr, Ba), has been studied by Mössbauer spectroscopy and X-ray diffraction analysis. For Mössbauer investigations, a small amount of 57Fe (2 at%) Mössbauer isotope was introduced into the samples. It follows from the analysis of the obtained data that both common features of the structural transformations and differences between them exist in lanthanum manganites depending on ionic radius and concentration of a doping element.

Sedykh, Vera D.

2014-10-01

268

STM Studies of the Electronic Structure of Vortex Cores in Bi2Sr2CaCu2O8+?  

NASA Astrophysics Data System (ADS)

We report on low temperature scanning tunneling microscopy (STM) studies of the electronic structure of vortex cores in Bi 2Sr 2CaCu 2O 8+?. At the vortex core center, an enhanced density of states is observed at energies near ? = +/-7 meV. Spectroscopic imaging at these energies reveals an exponential decay of these ``core states'' with a decay length of 22+/-3 Å. The fourfold symmetry sometimes predicted for d-wave vortices is not seen in spectroscopic vortex images. A locally nodeless order parameter induced by the magnetic field may be consistent with these measurements.

Pan, S. H.; Hudson, E. W.; Gupta, A. K.; Ng, K.-W.; Eisaki, H.; Uchida, S.; Davis, J. C.

2000-08-01

269

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

270

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

Microsoft Academic Search

In recent years, SrRuO3 thin films have received considerable interest because of their potential for use as electrodes in oxide-based spintronic applications. SrRuO3 bulk materials are known to exhibit good room temperature thermal and electrical conductivity, a stable perovskite crystal structure, and itinerant ferromagnetic properties at temperatures below 163 K. To the best of our knowledge, attempts to enhance the

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

2010-01-01

271

Structural, electrical, dielectric and magnetic properties of Gd-Sn substituted Sr-hexaferrite synthesized by sol-gel combustion method  

NASA Astrophysics Data System (ADS)

The effect of Gd-Sn substitution on the structural, electrical and magnetic properties of Sr1-xGdx Fe12-ySny O19 (where x=0.00, 0.025, 0.05, 0.075, 0.1) and (y=0.00, 0.25, 0.5, 0.75, 1) prepared by the sol-gel combustion method has been investigated. The XRD analysis shows the presence of Fe2O3 phase at higher substitution. The average crystallite size obtained lies between 19-42 nm which is beneficial in obtaining suitable signal-to-noise ratio in high density recording media. The FTIR spectra of annealed samples of SrFe12O19, Sr0.95Gd0.05 Fe11.5Sn0.5O19 show that strontium hexaferrite nanoparticles have been synthesized successfully. DC electrical resistivity shows metal-to-semiconductor transition with temperature. The value of transition temperature increases with dopant content. Room temperature dc resistivity and energy of activation decreases while drift mobility increases on increasing the dopant concentration. The magnetic properties such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) decreases with increasing the dopant concentration.

Ashiq, Muhammad Naeem; Shakoor, Sajeela; Najam-ul-Haq, Muhammad; Warsi, Muhammad Farooq; Ali, Irshad; Shakir, Imran

2015-01-01

272

Dielectric properties of [(Pb 0.2Ca 0.8) 1? x Sr x ](Ca 1\\/3Nb 2\\/3)O 3 ceramics at microwave frequencies  

Microsoft Academic Search

Microwave dielectric properties of the [(Pb0.2Ca0.8)1?xSrx](Ca1\\/3Nb2\\/3)O3 (PCSCN) have been investigated as a function of Sr2+ content (0.05?x?0.2). A perovskite single phase with the CaTiO3-type structure was obtained throughout the entire composition range. Dielectric constant (K) increased with increase of Sr2+ content, however, the quality factor (Qf) was decreased. The increase of dielectric constant (K) could be attributed to the increase

Eung Soo Kim; Yong Hyun Kim; Jung Hoon Chae; Dong Woon Kim; Ki Hyun Yoon

2003-01-01

273

Correlation between upconversion photoluminescence and dielectric response in Ba-substituted (Sr1-xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30  

NASA Astrophysics Data System (ADS)

The filled tetragonal tungsten bronze (Sr1-xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30 (SBLTNx: Ho-Yb) ceramics with different Ba substitution levels (x) are prepared. The upconversion photoluminescence (UC-PL) and dielectric permittivity are investigated. The substitution of Sr2+ ions at the A2-sites by larger Ba2+ ions results in substantial variation of the UC-PL intensity as a function of substitution level x. Furthermore, the dielectric response to the substitution of Sr2+ by Ba2+ suggests a close correlation between the UC-PL intensity and dielectric permittivity. The origin for this correlation is discussed based on the random stress field (RSF) model.

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

2014-06-01

274

Three monthly coral Sr\\/Ca records from the Chagos Archipelago covering the period of 1950–1995 A.D.: reproducibility and implications for quantitative reconstructions of sea surface temperature variations  

Microsoft Academic Search

In order to assess the fidelity of coral Sr\\/Ca for quantitative reconstructions of sea surface temperature variations, we\\u000a have generated three monthly Sr\\/Ca time series from Porites corals from the lagoon of Peros Banhos (71°E, 5°S, Chagos Archipelago). We find that all three coral Sr\\/Ca time series are\\u000a well correlated with instrumental records of sea surface temperature (SST) and air

Miriam Pfeiffer; Wolf-Christian Dullo; Jens Zinke; Dieter Garbe-Schönberg

2009-01-01

275

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

SciTech Connect

Polycrystalline tungsten-substituted CaMn{sub 1?x}W{sub x}O{sub 3??} (0.00???x???0.05) powders were synthesized from a polymeric precursor, pressed and sintered to high density. The impact of tungsten substitution on the crystal structure, thermal stability, phase transition, electronic and thermal transport properties is assessed. Tungsten acts as an electron donator and strongly affects high-temperature oxygen stoichiometry. Oxygen vacancies form in the high figure-of-merit (ZT)-region starting from about T?=?1000?K and dominate the carrier concentration and electronic transport far more than the tungsten substitution. The analysis of the transport properties yields that in the investigated regime the band filling is sufficiently high to overcome barriers of polaron transport. Therefore, the Cutler-Mott approach describes the electrical transport more accurately than the Mott approach for small polaron transport. The lattice thermal conductivity near room temperature is strongly suppressed with increasing tungsten concentration due to mass-difference impurity scattering. A ZT of 0.25 was found for x?=?0.04 at 1225?K.

Thiel, Philipp; Eilertsen, James; Populoh, Sascha, E-mail: sascha.populoh@empa.ch; Saucke, Gesine; Shkabko, Andrey; Sagarna, Leyre; Karvonen, Lassi [Laboratory for Solid State Chemistry and Catalysis, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf (Switzerland); Döbeli, Max [Ion Beam Physics, Schafmattstrasse 20, ETH Hönggerberg, Swiss Federal Institute of Technology, CH-8093 Zürich (Switzerland); Weidenkaff, Anke [Laboratory for Solid State Chemistry and Catalysis, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf (Switzerland); Materials Chemistry, Institute for Materials Science, University of Stuttgart, Heisenbergstr. 3, DE-70569 Stuttgart (Germany)

2013-12-28

276

Tropical Atlantic SSTS at the Last Glacial Maximum derived from Sr/Ca ratios of fossil coral  

NASA Astrophysics Data System (ADS)

The sensitivity of the tropics to climate change is a particularly controversial issue in paleoclimatology. At the heart of this controversy are disagreements amongst different proxy datasets regarding the amplitude of glacial-interglacial changes in temperature, particularly at the sea surface. Data obtained from the aragonitic skeletons of massive reef corals have contributed in no small measure to the debate, yielding LGM and deglacial SSTs 5-6°C cooler than today (Guilderson et al., 1994; McCulloch et al., 1999; Correge et al., 2004), that imply a high sensitivity of Earth's climate to changes in boundary conditions (Crowley, 2000). We used SIMS ion microprobe to analyze Sr/Ca ratios of small pieces of Montastrea coral retrieved from a Barbados drillcore (Guilderson et al., 2001). U/Th dates place the samples between 22 and 24 kyr BP. Localized areas of dissolution and re-growth of secondary (diagenetic) aragonite crystals were identified at centers of septa. Sr/Ca ratios of these crystals were higher than Sr/Ca ratios of original coral crystals preserved in adjacent fasciculi and yielded relatively cooler derived SSTs. The original coral crystals, recognized by their size and orientation, were selectively targeted for analysis using a 20 micron-diameter sample spot. Our calibration study using modern corals from Bermuda, St Croix (USVI) and Barbados indicates that Montastrea Sr/Ca is strongly correlated with SST and with annual extension (growth) rate (Saenger et al., 2006). Growth rate of the fossil corals was determined from measurement of daily growth bands identified in petrographic thin-sections. Application of a growth-dependent Sr/Ca-T calibration yielded Barbados SSTs that were, on average, 2.5°C cooler than today during the LGM and ~1°C cooler than today during Heinrich Event 2. Our LGM SSTs are consistent with the original CLIMAP estimates (CLIMAP, 1976) and with more recent Mg/Ca-based SSTs derived from calcitic foraminifera in the Caribbean (Schmidt et al., 2004). References: CLIMAP Project members (1976) The surface of the ice-age Earth, Science, 191(4232), 1131-1137. Correge T, Gagan MK, Beck JW, Burr GS, Cabioch G, Le Cornec F (2004) Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dryas event, Nature, (6986) 927-928 Crowley TJ (2000) CLIMAP SSTs re-revisited, Climate Dynamics, 16, 241-255 Guilderson TP, Fairbanks RG, Rubenstone JL (1994) Tropical temperature variations since 20,000 years ago: modulating interhemspheric climate change, Science, 263:663-665. Guilderson TP, Fairbanks RG, Rubenstone JL (2001) Tropical Atoantic coral oxygen isotopes: glacial- interglacial sea surface temperatures and climate change, Marine Geology, 172, 75-89 McCulloch MT, Tudhope AW, Esat TM, Mortimer GE, Chappell J, Pillans B, Chivas, AR, Omura A (1999) Coral record of equatorial sea-surface temperatures during the pen-ultimate deglaciation at Huon Peninsula, Science, 283, 202-204 Saenger CP, Cohen AL, Oppo D, Hubbard D (2006) Tropical North Atlantic Coral-Based Sea Surface Temperature and Salinity Reconstructions From the Little Ice Age and Early Holocene. Abstract, Fall AGU.

Cohen, A. L.; Saenger, C. P.

2006-12-01

277

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

PubMed Central

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

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

2011-01-01

278

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

E-print Network

in the human body [1-3]. For these reasons, apatite and whitlockite have been widely used as biocompatible in the body is confined in bone [1]. The total amount of Sr in human skeleton is small but not insignificant) and Tri Calcium Phosphate (-TCP). Doping with Sr2+ ions has a clear effect on the proportions

Paris-Sud XI, Université de

279

Reactions between oxides and Ag-sheathed Bi2Sr2CaCu2Ox conductors  

NASA Astrophysics Data System (ADS)

We studied reactions between Ag-sheathed Bi2Sr2CaCu2Ox (2212) conductors and a variety of oxides. We identified two intrinsic reactions: solid-state diffusion of a metallic species from the 2212 melt through the Ag sheath to react with an oxide, and direct reaction between Ag and an oxide. The dominant species that diffused through the Ag sheath was Cu because its solubility in Ag and diffusivity through Ag under 2212 melt processing conditions are the highest of the BSCCO metallic species. Al2O3, CeO2, pure SiO2, Y2O3, ZrO2, CaZrO3, and SrZrO3 were identified as non-reactive when heat treated in contact with Ag-sheathed 2212 tape. Fe2O3, MgO, and NiO reacted with Cu that diffused through Ag during the heat treatment. Cr2O3 and SiO2-based Pyrex glass reacted directly with Ag in the sheath during the heat treatment, which can create cracks and pinholes in the Ag sheath through which liquid can flow. Based on thermodynamic estimates, we calculated the Cu concentration in Ag at the 2212/Ag interface at 900 °C and 1 bar O2 to be between 0.15 and 0.22 at.%, which is consistent with 0.19 ± 0.02 at.% deduced from the experimentally measured diffusion flux.

Wesolowski, D. E.; Rikel, M. O.; Jiang, J.; Arsac, S.; Hellstrom, E. E.

2005-07-01

280

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

SciTech Connect

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

Subramanian, M.A. [Dupont Company, Wilmington, DE (United States). Central Research and Development] [Dupont Company, Wilmington, DE (United States). Central Research and Development

1995-03-01

281

Crystal and chemical anisotropy effects in AE2ZnN2, (AE = Ca, Sr, Ba) from ab initio  

NASA Astrophysics Data System (ADS)

In the tetragonal ternary nitrides AE2ZnN2 (AE = Ca, Sr, Ba), Zn has a rare linear coordination with nitrogen (N-Zn-N) along the c axis and N is located in an AE5Zn-like octahedron. Such features lead to original anisotropic crystal and chemical bond effects addressed herein with DFT-GGA based methods accounting for the cohesive energies, the energy volume equations of state EOS, the elastic constants and the properties of chemical bonding. Along AE = Ca, Sr, Ba an increasing overall compressibility under hydrostatic pressure is inferred from the respective EOS's, but the elastic constants Cij exhibit highly anisotropic features with large magnitudes of C33 along the tetragonal c axis versus smaller C11 = C22 along a, b. Decreasing C33-C11 along the title compounds signals decreasing anisotropy. The three ternaries are calculated as small gap insulators in agreement with experimental results of conductivity. The chemical bonding characterizes strong Zn-N bonds versus weaker AE-N thus reflecting the crystal anisotropy.

Matar, Samir F.; Etourneau, Jean; Ouaini, Naïm

2015-01-01

282

Structural and transport properties of A2HoTaO6 [A=Ba, Sr, and Ca  

NASA Astrophysics Data System (ADS)

Double perovskite oxides A2HoTaO6 [A=Ba, Sr, and Ca] are synthesized by a solid state reaction technique. The Rietveld refinement of the X-ray diffraction pattern shows that Ba2HoTaO6 crystalizes in cubic Fm3m symmetry whereas Sr2HoTaO6 and Ca2HoTaO6 adopt the monoclinic P21/n symmetry. The field cooled and zero field cooled magnetic susceptibilities of the materials are measured in the temperature range from 5 K to 300 K. The temperature dependence of inverse magnetic susceptibility shows the antiferromagnetic behavior of these systems. The dielectric relaxation of the samples is investigated by the Cole-Cole model in the frequency range from 50 Hz to 1 MHz and in the temperature range from 303 K to 673 K. The frequency dependent conductivity spectra follow the power law. The scaling behavior of the imaginary part of the impedance spectra suggests that the relaxation shows the same mechanism at various temperatures.

Dutta, Alo; Sinha, T. P.; Das, Dipankar

2014-06-01

283

Disorder promotes ferromagnetism: rounding of the quantum phase transition in Sr(1-x)Ca(x)RuO3.  

PubMed

The subtle interplay of randomness and quantum fluctuations at low temperatures gives rise to a plethora of unconventional phenomena in systems ranging from quantum magnets and correlated electron materials to ultracold atomic gases. Particularly strong disorder effects have been predicted to occur at zero-temperature quantum phase transitions. Here, we demonstrate that the composition-driven ferromagnetic-to-paramagnetic quantum phase transition in Sr(1-x)Ca(x)RuO3 is completely destroyed by the disorder introduced via the different ionic radii of the randomly distributed Sr and Ca ions. Using a magneto-optical technique, we map the magnetic phase diagram in the composition-temperature space. We find that the ferromagnetic phase is significantly extended by the disorder and develops a pronounced tail over a broad range of the composition x. These findings are explained by a microscopic model of smeared quantum phase transitions in itinerant magnets. Moreover, our theoretical study implies that correlated disorder is even more powerful in promoting ferromagnetism than random disorder. PMID:22681090

Demkó, L; Bordács, S; Vojta, T; Nozadze, D; Hrahsheh, F; Svoboda, C; Dóra, B; Yamada, H; Kawasaki, M; Tokura, Y; Kézsmárki, I

2012-05-01

284

Controlled peak wavelength shift of Ca 1-xSr x(S ySe 1-y):Eu 2+ phosphor for LED application  

NASA Astrophysics Data System (ADS)

The highly efficient red-orange-yellow-emitting phosphor (Ca 1-xSr x)(S 1-ySe y):Eu 2+ in combination with commercial green phosphor SrGa 2S 4:Eu 2+ and blue LED are proposed for a three-band white LED. The luminescence mechanism and optimization parameters are discussed on the basis of proposed peak wavelength diagram.

Nazarov, Mihail; Yoon, Chulsoo

2006-08-01

285

Sr-containing hydroxyapatite: morphologies of HA crystals and bioactivity on osteoblast cells.  

PubMed

A series of Sr-substituted hydroxyapatites (HA), of general formula Ca(10-x)Srx(PO4)6(OH)2, where x=2 and 4, were synthesized by solid state methods and characterized extensively. The reactivity of these materials in cell culture medium was evaluated, and the behavior towards MG-63 osteoblast cells (in terms of cytotoxicity and proliferation assays) was studied. Future in vivo studies will give further insights into the behavior of the materials. A paper by Lagergren et al. (1975), concerning Sr-substituted HA prepared by a solid state method, reports that the presence of Sr in the apatite composition strongly influences the apatite diffraction patterns. Zeglinsky et al. (2012) investigated Sr-substituted HA by ab initio methods and Rietveld analyses and reported changes in the HA unit cell volume and shape due to the Sr addition. To further clarify the role played by the addition of Sr on the physico-chemical properties of these materials we prepared Sr-substituted HA compositions by a solid state method, using different reagents, thermal treatments and a multi-technique approach. Our results indicated that the introduction of Sr at the levels considered here does influence the structure of HA. There is also evidence of a decrease in the crystallinity degree of the materials upon Sr addition. The introduction of increasing amounts of Sr into the HA composition causes a decrease in the specific surface area and an enrichment of Sr-apatite phase at the surface of the samples. Bioactivity tests show that the presence of Sr causes changes in particle size and/or morphology during soaking in MEM solution; on the contrary the morphology of pure HA does not change after 14 days of reaction. The presence of Sr, as Sr-substituted HA and SrCl2, in cultures of human MG-63 osteoblasts did not produce any cytotoxic effect. In fact, Sr-substituted HA increased the proliferation of osteoblast cells and enhanced cell differentiation: Sr in HA has a positive effect on MG-63 cells. In contrast, Sr ions alone, at the concentrations released by Sr-HA (1.21-3.24 ppm), influenced neither cell proliferation nor differentiation. Thus the positive effects of Sr in Sr-HA materials are probably due to the co-action of other ions such as Ca and P. PMID:23827552

Aina, Valentina; Bergandi, Loredana; Lusvardi, Gigliola; Malavasi, Gianluca; Imrie, Flora E; Gibson, Iain R; Cerrato, Giuseppina; Ghigo, Dario

2013-04-01

286

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

PubMed Central

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

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

1996-01-01

287

Synthesis and sintering properties of (La 0.8 Ca 0.2? x Sr x )CrO 3 perovskite materials for SOFC interconnect  

Microsoft Academic Search

Synthesis and sintering properties of the (La0.8Ca0.2?x\\u000a Sr\\u000a x\\u000a )CrO3 samples doped by two alkaline earth metals in comparison to the doped only by one alkaline earth metal were evaluated by\\u000a phase analysis, sintering properties, thermal expansion behaviors, and electrical conductivity. The sintered (La0.8Ca0.2?x\\u000a Sr\\u000a x\\u000a )CrO3 (x = 0, 0.05, and 0.1) and (La0.8Ca0.2?x\\u000a Sr\\u000a x\\u000a )CrO3 (x =

Jong-Hee Kim; Dong-Hyun Peck; Rak-Hyun Song; Gil-Young Lee; Dong-Ryul Shin; Sang-Hoon Hyun; Jürgen Wackerl; Klaus Hilpert

2006-01-01

288

Synthesis, structure, and magnetic properties of Sr2NiOsO6 and Ca2NiOsO6: two new osmium-containing double perovskites.  

PubMed

Two new double perovskite oxides, Ca(2)NiOsO(6) and Sr(2)NiOsO(6), have been prepared as polycrystalline powders by solid state synthesis. The two oxides were structurally characterized by variable-temperature powder neutron diffraction. Ca(2)NiOsO(6) was found to adopt a monoclinic structure (P2(1)/n), while Sr(2)NiOsO(6) was found to be tetragonal (I4/m). Magnetic susceptibility measurements indicate that Ca(2)NiOsO(6) orders in a canted antiferromagnetic state at about 175 K while Sr(2)NiOsO(6) orders antiferromagnetically at about 50 K. PMID:16363836

Macquart, René; Kim, Seung-Joo; Gemmill, William R; Stalick, Judith K; Lee, Yongjae; Vogt, Tom; zur Loye, Hans-Conrad

2005-12-26

289

X-ray crystal truncation rod scattering from MBE grown (CaF 2-SrF 2)/Si(111) superlattices  

NASA Astrophysics Data System (ADS)

Flouride CaF 2-SrF 2 superlattices (SLs) grown by molecular beam epitaxy have been studied by means of X-ray diffractometry for the first time. The diffraction patterns showed reasonably good crystalline quality of the SLs and a type-B epitaxial relation to the Si(111) substrate. From the analysis of the crystal truncation rod (CTR) profiles, based on the pseudomorphic model, it was obtained that despite the same high temperature (770°C) of formation of the CaF 2/Si(111) interface its structure depended on the growth temperature of the SLs. The shape of the CTR profiles confirmed the existence of the superlattice which consists of one or two monolayer thick SrF 2 layers. Some CaF 2/SrF 2-interface roughness was noticeable.

Harada, J.; Itoh, Y.; Shimura, T.; Takahashi, I.; Alvarez, J. C.; Sokolov, N. S.

1994-01-01

290

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

NASA Astrophysics Data System (ADS)

The most catastrophic extinction event in the history of animal life occurred at the end of the Permian Period, ca. 252 Mya. Ocean acidification and global oceanic euxinia have each been proposed as causes of this biotic crisis, but the magnitude and timing of change in global ocean chemistry remains poorly constrained. Here we use multiple isotope systems - Ca, Sr, Mo and U - measured from well dated Upper Permian- Lower Triassic sedimentary sections to better constrain the magnitude and timing of change in ocean chemistry and the effects of ocean acidification and de-oxygenation through this interval. All the investigated carbonate successions (Turkey, Italy and China) exhibit decreasing ?44/40Ca compositions, from ~-1.4‰ to -2.0‰ in the interval preceding the main extinction. These values remain low during most of the Griesbachian, to finally return to -1.4‰ in the middle Dienerian. The limestone succession from southern Turkey also displays a major decrease in the ?88/86Sr values from 0.45‰ to 0.3‰ before the extinction. These values remain low during the Griesbachian and finally increase to 0.55‰ by the middle Dienerian. The paired negative anomalies on the carbonate ?44/40Ca and ?88/86Sr suggest a decrease in the carbonate precipitation and thus an episode of ocean acidification coincident with the major biotic crisis. The Mo and U isotope records also exhibit significant rapid negative anomalies at the onset of the main extinction interval, suggesting rapid expansion of anoxic and euxinic marine bottom waters during the extinction interval. The rapidity of the isotope excursions in Mo and U suggests substantially reduced residence times of these elements in seawater relative to the modern, consistent with expectations for a time of widespread anoxia. The large C-isotope variability within Lower Triassic rocks, which is similar to that of the Lower-Middle Cambrian, may reflect biologically controlled perturbations of the oceanic carbon cycle. These findings strengthen the evidence for a global ocean acidification event coupled with rapid expansion of anoxic zones as drivers of end-Permian extinction in the oceans.

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

2014-05-01

291

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

Microsoft Academic Search

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

S. R. Hart

2009-01-01

292

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

SciTech Connect

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

Kate, O.M. ten, E-mail: o.m.tenkate@tudelft.nl [Luminescent Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Energy Materials and Devices, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Den Dolech 2, 5600MB Eindhoven (Netherlands); Zhang, Z. [Energy Materials and Devices, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Den Dolech 2, 5600MB Eindhoven (Netherlands); Dorenbos, P. [Luminescent Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Hintzen, H.T. [Energy Materials and Devices, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Den Dolech 2, 5600MB Eindhoven (Netherlands); Kolk, E. van der [Luminescent Materials Research Group, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands)

2013-01-15

293

Crystal structure and magnetic properties of Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy  

SciTech Connect

Bi{sub 0.8}A{sub 0.2}FeO{sub 3} (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A{sup 2+} results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe{sup 4+} ruled out by Mössbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi{sub 0.8}Ba{sub 0.2}FeO{sub 3} sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

Rangi, Manisha; Agarwal, Ashish, E-mail: aagju@yahoo.com; Sanghi, Sujata [Department of Applied Physics, Guru Jambheshwar University of Science and Technology, Hisar-125001 (Haryana) India (India); Singh, Ripandeep; Meena, S. S.; Das, A. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai-400 085 (India)

2014-08-15

294

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

NASA Astrophysics Data System (ADS)

Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics were studied using x-ray, neutron diffraction and magnetization techniques. All the samples crystallized in rhombohedral structure with space group R3c. The compounds exhibit antiferromagnetic (AFM) ordering at 300 K and no evidence of further structural or magnetic transition was observed on lowering of temperature below it. The magnetic structure of these substituted compounds are found to be collinear G-type AFM structure as against the non collinear incommensurate magnetic structure reported in the case of parent compound. The moments on Fe at 6 K are aligned along the a-axis in the case of Ca-doped sample. With increase in the ionic radii of dopant, the moments are found to be aligned in the ac plane and the angle of tilt away from the a-axis increases. The observed change in the magnetic structure with substitution is attributed to the intrinsic structural distortion as evidenced by the change in the bond angle (Fe-O-Fe) and bond distances (Bi-O, Fe-O). It has been found that heterovalent substitution A2+ results in the formation of oxygen vacancies in the parent lattices as the possibility of Fe4+ ruled out by Mössbauer spectra recorded at room temperature. Higher value of remnant magnetization (0.4187 emu/g) and coercivity (4.7554kOe) is observed in Bi0.8Ba0.2FeO3 sample in comparison to other substituted samples revealing a strong correlation between ionic radii and magnetization.

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

2014-08-01

295

Effects of (LiCe) co-substitution on the structural and electrical properties of CaBi2Nb2O9 ceramics  

NASA Astrophysics Data System (ADS)

The piezoelectric, dielectric, and ferroelectric properties of the (LiCe) co-substituted calcium bismuth niobate (CaBi2Nb2O9, CBNO) are investigated. The piezoelectric properties of CBNO ceramics are significantly enhanced and the dielectric loss tan ? decreased. This makes poling using (LiCe) co-substitution easier. The ceramics (where ? represents A-site Ca2+ vacancies, possess a pure layered structure phase and no other phases can be found. The Ca0.88(LiCe)0.04?0.04Bi2Nb2O9 ceramics possess optimal piezoelectric properties, with piezoelectric coefficient (d33) and Curie temperature (TC) found to be 13.3 pC/N and 960 °C, respectively. The dielectric and piezoelectric properties of the (LiCe) co-substituted CBNO ceramics exhibit very stable temperature behaviours. This demonstrates that the CBNO ceramics are a promising candidate for ultrahigh temperature applications.

Tian, Xiao-Xia; Qu, Shao-Bo; Du, Hong-Liang; Li, Ye; Xu, Zhuo

2012-03-01

296

Variations in the Sr/Ca, ?44Ca and ?18O composition of calcite as a function of solution chemistry and crystal growth rate  

NASA Astrophysics Data System (ADS)

The trace element and isotopic composition of calcite can be used to probe the temperatures and rates of mineral formation as well as the degree of post-mineralization alteration. The accuracy with which these effects can be interpreted is limited by our ability to distinguish signatures arising from equilibrium partitioning versus kinetic or mass transport effects. Our focus in this work is on mass transport effects in aqueous environments, and specifically, the growth rate-dependence of trace element and isotopic incorporation into calcite. This requires experiments in which the degree of supersaturation, or the solution chemistry, is held constant and the rate of crystal growth can be determined. In our experiments, N2+CO2 gas mixture is bubbled through a beaker containing 1300 mL of solution (30 mM CaCl2 + 5 mM NH4Cl + 0.1 mM SrCl2). The degree of supersaturation with respect to calcite is controlled by the pCO2 of the gas mixture, which is constantly replenished from a gas source. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls and the pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. During an experiment we control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate. At the same time we monitor the total alkalinity, the pCO2 of the gas outflow, the gas outflow rate, and the amount of NaOH added. The rate of calcite precipitation can be determined in three ways: (1) the change in total alkalinity due to Ca2+ removal, mass balance of C in the system, and (3) post-run measurement of [Ca2+] in aliquots of solution taken during an experiment. We present results from experiments where growth rates are estimated to range from 0.5 to 16 mmol/m2/hr. Our experiments thus far have yielded calcite crystals that are out of calcium and oxygen isotopic equilibrium with the parent solution. Crystals are enriched in the light isotope of Ca by 0.4 to 1.8‰. The light isotope enrichment increases with growth rate and is correlated with Sr/Ca in calcite. These results are in excellent agreement with the results of Tang et al. (2008) for crystals grown at 25°C and suggest that mass discrimination is controlled by mass transport kinetics at the mineral-solution interface. Oxygen isotopes are more complicated because of the addition of CO2 to the bulk solution. For crystals grown from our stock solution, the O composition is highly variable and not correlated with growth rate. We attribute this to relatively slow kinetics of O isotope exchange between gaseous or dissolved CO2 and water. For crystals grown in the presence of 0.01 grams of bovine carbonic anhydrase (CA), an enzyme which catalyzes the interconversion of CO2 and H2O to bicarbonate and protons, the O isotope composition of calcite appears to be independent of growth rate. Hence addition of CA to solution might offer a means of determining the equilibrium fractionation factor for oxygen isotopes in carbonate minerals. We will present results from additional experiments that test how CA and other organic molecules in solution affect the growth rate and mass discrimination during mineral precipitation.

Watkins, J. M.; DePaolo, D. J.; Ryerson, F. J.

2012-12-01

297

A high-resolution Sr/Ca and [delta][sup 18]O coral record from the Great Barrier Reef, Australia, and the 1982-1983 El Nino  

SciTech Connect

A high-resolution (near weekly) Sr/Ca and oxygen isotopic record is presented for a coral from the Pandora Reef in the Great Barrier Reef (GBR) of Australia during the period of 1978 to 1984. The records are well correlated except for periods of high rainfall when river runoff has significantly modified the [delta][sup 18]O value of seawater. Using the Sr/Ca temperature calibration of De Villiers et al., the Sr/Ca records exhibit seasonally controlled cyclical SST (sea surface temperature) variations of from [approximately] 21 to [approximately] 28[degrees]C. During the very strong El Nino of 1982-1983, the Sr/CA systematics indicate a sharp drop in the winter SST to [approximately] 18.5[degrees]C. This represents a temperature anomaly of -3[degrees]C which is approximately twice that given by the [delta][sup 18]O variations, suggesting an [approximately] x2 amplification of the anomaly by the Sr/Ca system, possibly due to the increasing dominance of inorganically controlled aragonite-seawater fractionation. The oxygen isotope systematics show the combined effects of both temperature and changing seawater [delta][sup 18]O values, the latter reflecting the influx of [sup 18]O-depleted runoff during periods of high rainfall. Due to the extremely low ([approximately] 10[sup [minus]3]) Sr and Ca contents of river runoff relative to seawater, it is possible to use the Sr/Ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the [delta][sup 18]O value of seawater. Using this approach it is possible to quantitatively reproduce the volume of runoff from the Burdekin River during the periods of major flooding that occurred in early 1979 and 1981. The results of this study demonstrate that the combined use of high-resolution Sr/Ca and [delta][sup 18]O systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate.

McCulloch, M.T.; Gagan, M.K.; Mortimer, G.E.; Chivas, A.R. (Australian National Univ., Canberra (Australia)); Isdale, P.J. (Australian Institute of Marine Science, Queensland (Australia))

1994-06-01

298

Scanning Tunneling Microscopy Study of Individual Ni Impurities in Bi_2Sr_2Ca(Cu_1­xNi_x)_2O_8+?  

NASA Astrophysics Data System (ADS)

Tunneling spectroscopy was performed on in situ cleaved Bi_2Sr_2Ca(Cu_1-xNi_x)O_8+? single crystals with a very low temperature scanning tunneling microscope. Preliminary results show spectral features more complex than those observed on Zn atoms^1. The energy and spatial structure of the DOS at the resonance sites will be discussed. ^1 S.H. Pan, et. al. Imaging the Effects of Individual Zinc Impurity Atoms on Superconductivity in Bi_2Sr_2CaCu_2O_8+?. cond-mat/9909365.

Lang, K. M.; Hudson, E. W.; Madhavan, Vidya; Pan, S. H.; Eisaki, H.; Uchida, S.; Davis, J. C.

2000-03-01

299

Effect of CaO and SiO2 additives on magnetic properties of SrZn2-W type hexagonal ferrite  

Microsoft Academic Search

An experiment was carried out to investigate the effect of CaO and SiO2 additives on the magnetic and physical properties of Sr-Zn W-type hexagonal ferrite. The specimens were prepared by the conventional manufacturing method without atmosphere control. It was found that the magnetic properties of SrO·2ZnO·8Fe2 O3 are considerably improved on adding 1 wt% CaO and SiO2 together. The optimum

H. Yamamoto; T. Mitsuoka

1994-01-01

300

Effects of A1 site occupation on dielectric and ferroelectric properties of Sr4CaRTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics  

NASA Astrophysics Data System (ADS)

Sr4CaRTi3Nb7O30 (R = Ce, Eu) tungsten bronze ceramics are prepared by a standard solid state reaction method. The effects of A1 site occupation on the dielectric and ferroelectric properties of Sr4CaRTi3Nb7O30 (R = Ce, Eu) tetragonal tungsten bronzes are investigated. The Sr4CaCeTi3Nb7O30 shows a normal transition behavior due to the closer size ion occupation in A1 sites, which could suppress the distortion of B2 octahedra effectively. Sr4CaEuTi3Nb7O30 ceramic exhibits two dielectric anomalies, which might be related to the fact that the large radius difference between Ca2+ and Eu3+ could lead to the uneven distribution of Ca2+ and Eu3+ in A1 sites and form two slightly different kinds of compositions with different transition temperatures in the structure. Our results indicate that the ionic radius difference in A1 sites plays an important role in determining the dielectric and ferroelectric natures of the filled tungsten bronze ceramics. Polarization—electric field (P—E) curves are evaluated at room temperature and both of them show hysteresis loops. Sr4CaCeTi3Nb7O30 shows a fat hysteresis loop, indicating the long-range ferroelectric order in the ceramic. The current density—electric field (J—E) curves are measured at room temperature with a largest leakage current density of ~ 10?6 A/cm2, indicating that their leakage currents are rather low.

Fang, Yu-Jiao; Gong, Gao-Shang; Gebru, Zerihun; Yuan, Song-Liu

2014-12-01

301

Thermoelectric properties and electronic structure of the Zintl phase Sr5In2Sb6 and the Ca5?xSrxIn2Sb6 solid solution  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

302

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

PubMed

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

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

2014-12-28

303

High-temperature transport properties, thermal expansion and cathodic performance of Ni-substituted LaSr{sub 2}Mn{sub 2}O{sub 7-{delta}}  

SciTech Connect

The substitution of manganese with nickel in LaSr{sub 2}Mn{sub 2}O{sub 7-{delta}}, 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{sub 2}Mn{sub 2-y}Ni{sub y}O{sub 7-{delta}} (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)x10{sup -6} K{sup -1} at y=0 up to (12.5-14.4)x10{sup -6} K{sup -1} at y=0.4. The conductivity and Seebeck coefficient of LaSr{sub 2}Mn{sub 1.6}Ni{sub 0.4}O{sub 7-{delta}}, analyzed in the oxygen partial pressure range 10{sup -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 {approx}2.3x10{sup -11} atm at 1223 K. Within the phase stability domain, the electronic transport properties are essentially p(O{sub 2})-independent. The steady-state oxygen permeability of dense LaSr{sub 2}Mn{sub 1.6}Ni{sub 0.4}O{sub 7-{delta}} membranes is higher than that of (La,Sr)MnO{sub 3-{delta}}, but lower if compared to perovskite-like (Sr,Ce)MnO{sub 3-{delta}}. Porous LaSr{sub 2}Mn{sub 1.6}Ni{sub 0.4}O{sub 7-{delta}} cathodes in contact with apatite-type La{sub 10}Si{sub 5}AlO{sub 26.5} solid electrolyte exhibit, however, a relatively poor electrochemical performance, partly associated with strong cation interdiffusion between the materials. - Graphical abstract: The substitution of manganese with nickel in Ruddlesden-Popper-type LaSr{sub 2}Mn{sub 2}O{sub 7-{delta}}, where the solubility limit corresponds to approximately 25% Mn sites, increases phase stability at elevated temperatures and thermal expansion, and decreases unit cell volume and total conductivity. The Seebeck coefficient and conductivity of LaSr{sub 2}Mn{sub 1.6}Ni{sub 0.4}O{sub 7-{delta}}, analyzed in the oxygen partial pressure range 10{sup -15}-0.3 atm at 600-1270 K, display that the electronic transport is n-type and occurs via a small polaron mechanism.

Yaremchenko, A.A. [Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Bannikov, D.O. [Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Department of Chemistry, Ural State University, Lenin av. 51, Ekaterinburg 620083 (Russian Federation); Kovalevsky, A.V. [Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal); Materials Department, Flemish Institute for Technological Research (VITO), 2400 Mol (Belgium); Cherepanov, V.A. [Department of Chemistry, Ural State University, Lenin av. 51, Ekaterinburg 620083 (Russian Federation); Kharton, V.V. [Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro (Portugal)], E-mail: kharton@ua.pt

2008-11-15

304

Combined effects of transition metal (Ni and Rh) substitution and annealing/quenching on the physical properties of CaFe2As2  

SciTech Connect

We performed systematic studies of the combined effects of annealing/quenching temperature (TA/Q) and T=Ni, Rh substitution (x) on the physical properties of Ca(Fe1?xTx)2As2. We constructed two-dimensional, TA/Q-x phase diagrams for the low-temperature states for both substitutions to map out the relations between ground states and compared them with that of Co substitution. Ni substitution, which brings one more extra electron per substituted atom and suppresses the c-lattice parameter at roughly the same rate as Co substitution, leads to a similar parameter range of antiferromagnetic/orthorhombic phase space in the TA/Q-x space as that found for Co substitution, but the parameter range for superconductivity has been shrunk (roughly by a factor of 2). This result is similar to what is found when Co- and Ni-substituted BaFe2As2 are compared. On the other hand, Rh substitution, which brings the same amount of extra electrons as does Co substitution, but suppresses the c-lattice parameter more rapidly, has a different phase diagram. The collapsed tetragonal phase exists much more pervasively, to the exclusion of the normal, paramagnetic, tetragonal phase. The range of antiferromagnetic/orthorhombic phase space is noticeably reduced, and the superconducting region is substantially suppressed, essentially truncated by the collapsed tetragonal phase. In addition, we found that whereas for Co substitution there was no difference between phase diagrams for samples annealed for 1 or 7 days, for Ni and Rh substitutions a second, reversible effect of annealing was revealed by 7-day anneals.

Ran, S [Ames Laboratory; Bud'ko, S L [Ames Laboratory; Straszheim, W E [Ames Laboratory; Canfield, P C [Ames Laboratory

2014-08-01

305

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

SciTech Connect

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

Kung, P.J.; Maley, M.P.; Coulter, J.Y.; Willis, J.O.; Peterson, D.E. [Los Alamos National Lab., NM (United States); McHenry, M.E. [Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Metallurgical Engineering and Materials Science; Wahlbeck, P.G. [Wichita State Univ., KS (United States). Dept. of Chemistry

1992-05-01

306

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

SciTech Connect

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

Kung, P.J.; Maley, M.P.; Coulter, J.Y.; Willis, J.O.; Peterson, D.E. (Los Alamos National Lab., NM (United States)); McHenry, M.E. (Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Metallurgical Engineering and Materials Science); Wahlbeck, P.G. (Wichita State Univ., KS (United States). Dept. of Chemistry)

1992-01-01

307

Magnetic properties and electronic structure of doped multiferroic YxA1-xMnO3(A=Ca, Sr, Ba)  

Microsoft Academic Search

We report the magnetic properties, X-ray absorption spectroscopy (XAS) on a series of doped multiferroic materials YxA1-xMnO3 (A=Ca, Sr, Ba). YMnO3 when doped by alkaline-earth metal with various ionic sizes, display dramatic changes in magnetic properties as compared with the parent compound. For Ca-doped sample, the antiferromagnetic (AFM) phase transition appears to take place at a much lower temperature (30

J. Y. Juang; C. C. Hsieh; T. Y. Cheng; J. M. Lee; J. M. Chen; J.-Y. Lin; K. H. Wu; T. M. Uen; Y. S. Gou

2007-01-01

308

Effects of Ge doping on the fluctuative conductivity in Bi 2Sr 2CaCu 2O 8+ ?  

NASA Astrophysics Data System (ADS)

The fluctuation conductivity in Bi 2- xGe xSr 2CaCu 2O 8+ ? (0? x?0.15) single crystals prepared by the self-flux method was measured in order to investigate the effects of Ge doping on the superconducting properties. In the analysis of the fluctuation conductivity, we adopt the Aslamazov-Larkin and Lawrence-Doniach theories in which the short-wavelength cutoff in the fluctuation spectrum is taken into account, and find good agreement between theory and experiment. From the analysis, we deduce that the main effect of Ge doping is to increase the out-of-plane coherence length ?c and to decrease the in-plane coherence length ?ab, consequently, reducing the anisotropy.

Asaka, Kota; Koizumi, Ken; Bando, Hiroyuki; Mori, Natsuki; Ozaki, Hajime

2000-07-01

309

Excess conductivity of overdoped Bi2Sr2CaCu2O8+x crystals well above Tc  

NASA Astrophysics Data System (ADS)

We have used a multiterminal technique in order to measure the (a,b) plane excess conductivity ?? in several Bi2Sr2CaCu2O8+x single crystals. We find that the experimental ?? does not follow a simple power law ??~?-?, with ?= ln(T/Tc), and that it drops faster than the two-dimensional Aslamazov-Larkin law, ?=1, with increasing temperature. In addition, data for samples with different doping do not scale on a universal curve. We discuss our data in terms of microscopic and Ginzburg-Landau theories, where high-momentum fluctuations are either not excited, or phenomenologically cut off. The experimental ?? drops even faster than the prediction of the extended microscopic theory. However, we can accurately describe all our data up to T~1.3 Tc with the GL theory, assuming a sample-dependent cutoff value. We relate the cutoff parameter to the doping level of our samples.

Silva, E.; Sarti, S.; Fastampa, R.; Giura, M.

2001-10-01

310

Rotational symmetry breaking in Bi2Sr2CaCu2O8+? probed by polarized femtosecond spectroscopy  

NASA Astrophysics Data System (ADS)

The quasiparticle (QP) dynamics with different symmetry is investigated in the superconducting (SC) and normal state of the high-temperature superconductor Bi2Sr2CaCu2O8+? (Bi2212) using optical pump-probe experiments with different light polarizations at different doping levels. The observation of distinct selection rules for SC excitations present in A1g and B1g symmetries, and for the pseudogap (PG) excitations present in A1g and B2g symmetries by the probe, and absence of any dependence on the pump beam polarization leads to the unequivocal conclusion of the existence of a spontaneous spatial symmetry breaking in the PG state not limited to the sample surface.

Toda, Y.; Kawanokami, F.; Kurosawa, T.; Oda, M.; Madan, I.; Mertelj, T.; Kabanov, V. V.; Mihailovic, D.

2014-09-01

311

Bond covalency in perovskite oxynitrides ATaO2N (A = Ca, Sr, Ba) studied by 14N NMR spectroscopy  

NASA Astrophysics Data System (ADS)

Local geometry and bond ionicity around the nitride ions in simple perovskite oxynitrides ATaO2N (A = Ca, Sr, Ba) have been investigated by solid-state magic-angle spinning (MAS) NMR spectroscopy. From all three compounds, fairly sharp 14N NMR peaks were observed, suggestive of the symmetric coordination environment of nitride ions. The 14N chemical shifts of ATaO2N, ? = 269-272 ppm relative to NH4Cl (? = 0 ppm), are correlated to the bond ionicity, based on the N-Ta bond distances and Ta-N-Ta bond angles determined from the Rietveld refinement of neutron diffraction patterns. The 1H NMR measured for BaTaO2N presented a peak corresponding to H2O, implying that the polycrystalline surface of present oxynitride phases is covered by hydroxide terminals.

Kim, Young-Il; Paik, Younkee

2012-05-01

312

High pressure induced spin state crossover in Sr2CaYCo4O10.5  

NASA Astrophysics Data System (ADS)

The layered cobaltite Sr2CaYCo4O10.5 with formal average cobalt oxidation state close to 3+ has been studied as functions of both temperature and pressure up to 4 GPa by neutron powder diffraction (NPD). The crystal structure is shown to have tetragonal symmetry (space group I4/mmm; 2ap × 2ap × 4ap superstructure), and the magnetic structure at ambient pressure is found to be G-type antiferromagnetic with TN close to 310 K. The magnetic moments within the CoO6 octahedral layers and anion-deficient CoO4.5 layers are 1.2?B and 2.8?B, respectively. At 25 K, and applied pressure of 3.5 GPa is sufficient to completely suppress a long-range magnetic order. This result is interpreted in terms of a pressure-induced high-to-low spin state crossover of the Co3+ ions.

Sikolenko, V.; Troyanchuk, I.; Bushinsky, M.; Efimov, V.; Keller, L.; White, J. S.; Schilling, F. R.; Schorr, S.

2015-02-01

313

High pressure induced spin state crossover in Sr2CaYCo4O10.5.  

PubMed

The layered cobaltite Sr2CaYCo4O10.5 with formal average cobalt oxidation state close to 3+ has been studied as functions of both temperature and pressure up to 4 GPa by neutron powder diffraction (NPD). The crystal structure is shown to have tetragonal symmetry (space group I4/mmm; 2ap × 2ap × 4ap superstructure), and the magnetic structure at ambient pressure is found to be G-type antiferromagnetic with TN close to 310 K. The magnetic moments within the CoO6 octahedral layers and anion-deficient CoO4.5 layers are 1.2?B and 2.8?B, respectively. At 25 K, and applied pressure of 3.5 GPa is sufficient to completely suppress a long-range magnetic order. This result is interpreted in terms of a pressure-induced high-to-low spin state crossover of the Co(3+) ions. PMID:25567194

Sikolenko, V; Troyanchuk, I; Bushinsky, M; Efimov, V; Keller, L; White, J S; Schilling, F R; Schorr, S

2015-02-01

314

Diamagnetism above Tc in Underdoped Bi2.2Sr1.8Ca2Cu3O10+?  

NASA Astrophysics Data System (ADS)

Single crystals of Bi2+xSr2-xCa2Cu3O10+? (Bi2223) with x=0.2 were grown by a traveling solvent floating zone method in order to investigate the superconducting properties of highly underdoped Bi2223. Grown crystals were characterized by X-ray diffraction, DC susceptibility and resistivity measurements, confirming Bi2223 to be the main phase. The crystals were annealed under various oxygen partial pressures to adjust their carrier densities from optimally doped to highly underdoped. The fluctuation diamagnetic component above the superconducting transition temperature Tc extracted from the anisotropic normal state susceptibilities ?ab(T) (H\\perp c) and ?c(T) (H\\parallel c) was found to increase with underdoping, suggesting a decrease in the superconducting dimensionality and/or increase in the fluctuating vortex liquid region.

Iye, Tetsuya; Nagatochi, Takenori; Ikeda, Ryusuke; Matsuda, Azusa

2010-11-01

315

Symmetry of the hole states in BiCaSrCuO high-T/sub c/ superconductors  

SciTech Connect

Polarized CuL/sub 3/-edge X-ray absorption spectra (XAS) of oriented film of Bi/sub 2/Sr/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub 2/O/sub y/ have been measured to determine the symmetry of the orbital of the electronic holes. The states with the configuration 3d/sup 9/L (L indicates ligand holes) have been detected. The holes d in superconducting materials are found to be in the antiferromagnetic band with b/sub 1/ symmetry, derived by the Cu 3d/sub chi/sup 2/-y/sup 2// orbital, but also in a second band wit8h a/sub 1/ molecular symmetry, derived by Cu 3d/sub z/sup 2/-r/sup 2// orbital at the Cu site. The results can be rationalized with the formation of both d (b/sub 1/) L and ed(a/sub 1/) L states in the ground state of this high-T/sub c/ superconductor.

Bianconi, A. (Universita degli Studi dell'Aquila, Collemaggio, 67100 L'Aquila (IT)); Castrucci, P.; DeSantis, M.; Fabrizi, A. (CISM-GNSM, Dipartimento di Fisica, Universita degli Studi di Roma La Sapienza , 00185 Roma (IT)); DiCicco, A. (Dipartimento di Matematica e Fisica, Dell' universita di Camerino, 62032 Camerino MC (IT)); Katayama-Yoshida, H.; Kotani, A. (Tohoku Univ., Sendai (Japan). Dept. of Physics); Flank, A.M.; LaGarde, P. (Lure, CNRS-CEA-MEN, Batiment 209 D, Universite Paris Sud. 91405 Orsay (FR))

1988-12-01

316

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

NASA Technical Reports Server (NTRS)

The preparation of high-T(sub c) superconducting long composite wires by short-time tinning of the metal wires in a molten Bi-Pb-Sr-Ca-Cu-O compound is discussed. The application of this method to the high-T(sub c) materials is tested, possibly for the first time. The initial materials used for this experiment were ceramic samples with nominal composition Bi(1.5)Pb(0.5)Sr2Ca2Cu3O(x) and T(sub c) = 80 K prepared by the ordinary solid-state reaction, and industrial copper wires from 100 to 400 microns in diameter and from 0.5 to 1 m long. The continuously moving wires were let through a small molten zone (approximately 100 cubic mm). The Bi-based high-T(sub c) ceramics in a molten state is a viscous liquid and it has a strongly pronounced ability to spread on metal wire surfaces. The maximum draw rate of the Cu-wire, at which a dense covering is still possible, corresponds to the time of direct contact of wire surfaces and liquid ceramics for less than 0.1 s. A high-rate draw of the wire permits a decrease in the reaction of the oxide melt and Cu-wire. This method of manufacture led to the fabrication of wire with a copper core in a dense covering with uniform thickness of about h approximately equal to 5 to 50 microns. Composite wires with h approximately equal to 10 microns (h/d approximately equal to 0.1) sustained bending on a 15 mm radius frame without cracking during flexing.

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

1990-01-01

317

San Francisco Estuary Striped Bass Migration History Determined by Electron-microprobe Analysis of Otolith Sr/Ca Ratio  

SciTech Connect

Habitat use has been shown to be an important factor in the bioaccumulation of contaminants in striped bass. This study examines migration in striped bass as part of a larger study investigating bioaccumulation and maternal transfer of xenobiotics to progeny in the San Francisco Estuary system. Habitat use, residence time and spawning migration over the life of females (n = 23) was studied. Female striped bass were collected between Knights Landing and Colusa on the Sacramento River during the spawning runs of 1999 and 2001. Otoliths were removed, processed and aged via otolith microstructure. Subsequently, otoliths were analyzed for strontium/calcium (Sr/Ca) ratio using an electron-microprobe to measure salinity exposure and to distinguish freshwater, estuary, and marine habitat use. Salinity exposure during the last year before capture was examined more closely for comparison of habitat use by the maternal parent to contaminant burden transferred to progeny. Results were selectively confirmed by ion microprobe analyses for habitat use. The Sr/Ca data demonstrate a wide range of migratory patterns. Age of initial ocean entry differs among individuals before returning to freshwater, presumably to spawn. Some fish reside in freshwater year-round, while others return to more saline habitats and make periodic migrations to freshwater. Frequency of habitat shifts and residence times differs among fish, as well as over the lifetime of individual fish. While at least one fish spent its final year in freshwater, the majority of spawning fish spent their final year in elevated salinity. However, not all fish migrated to freshwater to spawn in the previous year. Results from this investigation concerning migration history in striped bass can be combined with contaminant and histological developmental analyses to better understand the bioaccumulation of contaminants and the subsequent effects they and habitat use have on fish populations in the San Francisco Estuary system.

Ostrach, D J; Phillis, C C; Weber, P K; Ingram, B L; Zinkl, J G

2004-09-17

318

Effect of Ca substitution on some physical properties of nano-structured and bulk Ni-ferrite samples  

NASA Astrophysics Data System (ADS)

Nanoparticles of Ni1-xCaxFe2O4 (x=0.0, 0.02, 0.04, 0.06 and 0.10) were prepared by citrate precursor method. A part of these samples was sintered at 600 °C for 2 h in order to keep the particles within the nano-size while the other part was sintered at 1000 °C to let the particles to grow to the bulk size. The effect of Ca2+ ion substitution in nickel ferrite on some structural, magnetic, electrical and thermal properties was investigated. All samples were characterized by using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). A two probe method was used to measure the dc electrical conductivity whereas the photoacoustic (PA) technique was used to determine the thermal diffusivity of the samples. To interpret different experimental results for nano and bulk samples some cation distributions were assumed based on the VSM and XRD data. These suggested cation distributions give logical explanations for other experimental results such as the observed values of the absorption bands in FTIR spectra and the dc conductivity results. Finally, in the thermal measurements it was found that increasing the Ca2+ ion content causes a decrease in the thermal diffusivity of both nano and bulk samples. The explanation of this behavior is ascribed to the phonon-phonon scattering.

Assar, S. T.; Abosheiasha, H. F.

2015-01-01

319

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

SciTech Connect

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

Lee, Hong-Sub; Park, Chang-Sun; Park, Hyung-Ho, E-mail: hhpark@yonsei.ac.kr [Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749 (Korea, Republic of)

2014-05-12

320

Dissolution-induced Changes in Planktic Foraminiferal Mg\\/Ca and Sr\\/Ca Records from the Western Equatorial Pacific: Implications for Phase Relationships Between Temperature and Ice Volume  

Microsoft Academic Search

Downcore Mg\\/Ca and Sr\\/Ca records were constructed at two western equatorial Pacific sites (227 ka record at 2\\\\deg S 157\\\\deg E and 434 ka at 1\\\\deg 45'N 159\\\\deg 27'E) located at 1600 and 2600 m respectively, compared to the present calcite saturation horizon of about 3000 m in this area, and have well-documented carbonate preservation histories. Isotope records are based

S. de Villiers; H. E. Elderfield; N. J. Shackleton

2001-01-01

321

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

E-print Network

Dielectric properties of layered perovskite Sr1Ã?xAxBi2Nb2O9 ferroelectrics ,,AÃ?La,Ca and xÃ?0 in air. X-ray diffraction analysis indicated that single-phase layered perovskite ferroelectrics were of full polarization switching.3 Bismuth layered perovskite materi- als have high fatigue resistance

Cao, Guozhong

322

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

E-print Network

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

Falkowski, Paul G.

323

Sr Ca and 13C 12C ratios in skeletal calcite of Mytilus trossulus: Covariation with metabolic rate, salinity, and carbon isotopic composition of seawater  

Microsoft Academic Search

Minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity. Although molluscan calcite is secreted at or near oxygen isotope equilibrium, the influence of metabolic activity (i.e., vital effects) on skeletal SrCa ratios and ? 13C values is not well known. We present measurements of skeletal chemistry from (a) consecutive

Robert T. Klein; Kyger C. Lohmann; Charles W. Thayer

1996-01-01

324

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

NASA Astrophysics Data System (ADS)

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

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

2006-03-01

325

Measuring the Josephson plasma resonance in Bi2Sr2CaCu2O8 using intense coherent THz synchrotron radiation  

E-print Network

Measuring the Josephson plasma resonance in Bi2Sr2CaCu2O8 using intense coherent THz synchrotron this source for reflectivity measurements we have been able to observe the Josephson plasma resonance JPR are enabled across a diverse array of disciplines: con- densed matter physics, medicine, manufacturing

326

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

E-print Network

Stoichiometry control of magnetron sputtered Bi2Sr2Ca1Ã?xYxCu2Oy (0 6 x 6 0.5) thin film Received 15 April 2005; accepted 3 June 2005 Available online 15 July 2005 Abstract A magnetron sputtering superconductors (high-Tc and insulating parent compound); Composition spread libraries; Magnetron sputtering

Hewitt, Kevin

327

Controlled peak wavelength shift of Ca 1? x Sr x (S y Se 1? y ):Eu 2+ phosphor for LED application  

Microsoft Academic Search

The highly efficient red-orange-yellow-emitting phosphor (Ca1?xSrx)(S1?ySey):Eu2+ in combination with commercial green phosphor SrGa2S4:Eu2+ and blue LED are proposed for a three-band white LED. The luminescence mechanism and optimization parameters are discussed on the basis of proposed peak wavelength diagram.

Mihail Nazarov; Chulsoo Yoon

2006-01-01

328

Pressure Dependence of Flux Dynamics in Bi2Sr2CaCu2O8+ M. P. Raphael, M. E. Reeves, C. Kendziora, and E. F. Skelton  

E-print Network

Pressure Dependence of Flux Dynamics in Bi2Sr2CaCu2O8+ M. P. Raphael, M. E. Reeves, C. Kendziora are presented in this paper which were obtained using a new technique for measuring the pressure dependence of pressure on flux motion. Pressure changes the atomic interplanar spacing, and hence the interplanar

Reeves, Mark E.

329

The critical current and magnetization anisotropy in TmBa 2Cu 3O x and Bi 2Sr 2CaCu 2O y single crystals  

NASA Astrophysics Data System (ADS)

The relations between critical current and magnetisation were derived for anisotropic superconductors The critical current and magnetisation anisotropy for TmBa 2Cu 3O x and Bi 2Sr 2CaCu 2O y single crystals was studied.

Moshchalkov, V. V.; Zhukov, A. A.; Rybachuk, V. A.; Bush, A. A.; Voronkova, V. I.; Yanovsky, V. K.

1991-02-01

330

Ion substitutions and non-stoichiometry of carbonated apatite-(CaOH) synthesised by precipitation and hydrothermal methods  

NASA Astrophysics Data System (ADS)

Apatite-(CaOH), either carbonate-free or with different concentrations of carbonate ions of the predominantly (not less than 60%) B type, was synthesised by precipitation from solutions, by hydrothermal methods from solid compounds and by hydrothermal treatment of calcite. In B type apatite, the concentration of CO32- ions could be up to 20.5 wt.%. The reverse precipitation method and hydrothermal treatment of calcite obtained monophase samples with a maximal concentration of CO32- ions of 10.3-10.5 wt.%. In apatites of a mixed type, the total concentration of CO32- ions did not exceed 8 wt.%. The synthesised apatites could be divided into three groups according to the degree and origin of non-stoichiometry: Apatite of nearly stoichiometric composition. Apatite of this type was synthesised by all methods. Calcium-deficient apatite. The Ca deficit was mainly due to CO32- incorporation. Monophase samples with maximal concentrations of CO32- ions were synthesised by the reverse precipitation method and by hydrothermal treatment of calcite. Calcium-deficient apatite. The Ca deficit was mainly due to a deficit of OH - ions and resulted in the incorporation of water into channels of the crystal structure. This group was synthesised by reverse precipitation and hydrothermal methods. This apatite was a crystal chemical analogue of the apatite formed in the hard tissues of the human body such as teeth, bone and different stones. Apatites formed by the precipitation methods revealed higher variations in composition (including variations in the concentration of CO32- ions), compared to hydrothermally-synthesised samples. The observed effect of aqueous solution composition on the ion substitution and apatite composition was stronger than previously reported.

Frank-Kamenetskaya, Olga; Kol'tsov, Alexander; Kuz'mina, Maria; Zorina, Maina; Poritskaya, Lilya

2011-04-01

331

Synthesis, neutron diffraction study and cation substitutions in Sr n?1 Cu n+1 O 2 n ( n = 3, 5)  

Microsoft Academic Search

The n = 3 and n = 5 members of the homologous series Srn?1Cun+1O2n have been synthesized by a high-pressure, high-temperature technique and characterized by X-ray powder diffraction and electron microscopy as well as EDS microanalysis. The solubility range of Sr4?xNdxCu6O10 solid solution was found to be ? 0.1. The crystal structure of Sr4Cu6O10 was refined from neutron powder diffraction

S. M. Kazakov; S. Pachot; E. M. Kopnin; S. N. Putilin; E. V. Antipov; C. Chaillout; J. J. Capponi; P. G. Radaelli; M. Marezio

1997-01-01

332

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

333

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

Technology Transfer Automated Retrieval System (TEKTRAN)

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

334

Apolipoprotein CIII hyperactivates ? cell CaV1 channels through SR-BI/?1 integrin-dependent coactivation of PKA and Src.  

PubMed

Apolipoprotein CIII (ApoCIII) not only serves as an inhibitor of triglyceride hydrolysis but also participates in diabetes-related pathological events such as hyperactivation of voltage-gated Ca(2+) (CaV) channels in the pancreatic ? cell. However, nothing is known about the molecular mechanisms whereby ApoCIII hyperactivates ? cell CaV channels. We now demonstrate that ApoCIII increased CaV1 channel open probability and density. ApoCIII enhanced whole-cell Ca(2+) currents and the CaV1 channel blocker nimodipine completely abrogated this enhancement. The effect of ApoCIII was not influenced by individual inhibition of PKA, PKC, or Src. However, combined inhibition of PKA, PKC, and Src counteracted the effect of ApoCIII, similar results obtained by coinhibition of PKA and Src. Moreover, knockdown of ?1 integrin or scavenger receptor class B type I (SR-BI) prevented ApoCIII from hyperactivating ? cell CaV channels. These data reveal that ApoCIII hyperactivates ? cell CaV1 channels through SR-BI/?1 integrin-dependent coactivation of PKA and Src. PMID:23949443

Shi, Yue; Yang, Guang; Yu, Jia; Yu, Lina; Westenbroek, Ruth; Catterall, William A; Juntti-Berggren, Lisa; Berggren, Per-Olof; Yang, Shao-Nian

2014-04-01

335

High-order picosecond SRS and self-SRS generation in Nd 3+ -doped CaMoO 4 , SrMoO 4 , and SrWO 4 laser crystals  

Microsoft Academic Search

The results of a stimulated Raman scattering (SRS) spectroscopy study of Nd3+-doped CaMoO4, SrMoO4, and SrWO4 crystals are presented. All the wavelengths of the Stokes and anti-Stokes generation observed in these crystals are identified.\\u000a For the first time, the self-SRS conversion of the emission frequency of activator Nd3+-ions is attained in these lasing molybdates and tungstate with scheelite-type structures.

A. A. Kaminskii; S. N. Bagaev; K. Ueda; K. Takaichi; H. J. Eichler

2002-01-01

336

Rolled-up tubes and cantilevers by releasing SrRuO3-Pr0.7Ca0.3MnO3 nanomembranes  

PubMed Central

Three-dimensional micro-objects are fabricated by the controlled release of inherently strained SrRuO3/Pr0.7Ca0.3MnO3/SrRuO3 nanometer-sized trilayers from SrTiO3(001) substrates. Freestanding cantilevers and rolled-up microtubes with a diameter of 6 to 8 ?m are demonstrated. The etching behavior of the SrRuO3 film is investigated, and a selectivity of 1:9,100 with respect to the SrTiO3 substrate is found. The initial and final strain states of the rolled-up oxide layers are studied by X-ray diffraction on an ensemble of tubes. Relaxation of the sandwiched Pr0.7Ca0.3MnO3 layer towards its bulk lattice parameter is observed as the major driving force for the roll-up of the trilayers. Finally, ?-diffraction experiments reveal that a single object can represent the ensemble proving a good homogeneity of the rolled-up tubes. PACS: 81.07.-b; 68.60.-p; 68.37.Lp; 81.16.Dn. PMID:22151894

2011-01-01

337

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

SciTech Connect

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

Smith, Andrew E. [Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, Oregon 97331-4003 (United States); Calvarese, T.G. [DuPont Central Research and Development, Experimental Station, Wilmington, Delaware 19880-0328 (United States); Sleight, A.W. [Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, Oregon 97331-4003 (United States); Subramanian, M.A. [Department of Chemistry, Oregon State University, 153 Gilbert Hall, Corvallis, Oregon 97331-4003 (United States)], E-mail: mas.subramanian@oregonstate.edu

2009-02-15

338

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

SciTech Connect

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

Dai, Jing-Cao; Corbett, John D.

2007-04-17

339

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

SciTech Connect

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

Ori, D.M. [Centro Informazioni, Studi ed Esperienze Material Division, P.O. Box 12081, 20134 Milano (Italy)] [Centro Informazioni, Studi ed Esperienze Material Division, P.O. Box 12081, 20134 Milano (Italy); Goldoni, A. [Dipartimento di Fisica, Universita di Trieste, Via Valerio 2, 34100 Trieste (Italy)] [Dipartimento di Fisica, Universita di Trieste, Via Valerio 2, 34100 Trieste (Italy); [Laboratorio Tecnologie Avanzate Superfici e Catalisi (TASC)-Istituto Nazionale di Fisica della Materia, Padriciano 99, 34012 Trieste (Italy); del Pennino, U. [Dipartimento di Fisica, Universita di Modena, Via Campi 123/A, 41100 Modena (Italy)] [Dipartimento di Fisica, Universita di Modena, Via Campi 123/A, 41100 Modena (Italy); Parmigiani, F. [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 34, 20133 Milano (Italy)] [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 34, 20133 Milano (Italy)

1995-08-01

340

Role of Zr-Co substitution at iron site on structural, magnetic and electrical properties of Sr-hexaferrites nanomaterials synthesized by the sol-gel combustion method  

NASA Astrophysics Data System (ADS)

The sol-gel auto-combustion technique has been employed to synthesize the M-type Sr-hexaferrites nanomaterials substituted with binary mixture of zirconium and cobalt at the iron site. The phase purity of the samples is confirmed by X-ray diffraction analysis and the crystallite size is found in the range of 31-45 nm. The scanning electron microscopic analysis also confirms that the particles are in nanosize (25-50 nm). The magnetic parameters like saturation magnetization, remanence, squareness ratio and the coercivity are calculated from the hysteresis loops. The values of saturation magnetization and remanence increase with the increase in Zr-Co content up to x=0.4 while the coercivity decreases continuously with the substituents. The squareness ratio is above 0.5 which indicates that the samples are in single magnetic domain. The room temperature DC electrical resistivity is measured by the two point probe method and is found to increase with Zr-Co content up to the substitution level of x=0.6. These materials can be used in microwave devices as these devices require highly resistive materials with low eddy current losses.

Naeem Ashiq, Muhammad; Fahad Ehsan, Muhammad; Javed Iqbal, Muhammad; Najam-ul-Haq, Muhammad

2013-04-01

341

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

PubMed

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

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

2013-06-01

342

Melt processing of the Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] superconductor in oxygen and argon atmospheres  

SciTech Connect

Solidification and subsequent annealing of Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub y] (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O[sub 2] and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutetic structure of Bi[sub 2]Sr[sub 3-x]Ca[sub x]O[sub y] and Cu[sub 2]O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi[sub 2.15]Sr[sub 2]Ca[sub 0.85]Cu[sub 2]O[sub y].

Holesinger, T.G.; Miller, D.J. (Argonne National Lab., IL (United States)); Chumbley, L.S. (Ames Lab., IA (United States))

1992-08-01

343

Melt processing of the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} superconductor in oxygen and argon atmospheres  

SciTech Connect

Solidification and subsequent annealing of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub y} (2212) in oxygen and argon atmospheres were investigated in order to identify alternative processing routes for controlling microstructures and superconducting properties. In addition to 2212, several other phases formed on cooling in O{sub 2} and did not disappear upon subsequent annealing. Crystallization in Ar resulted in a divorced eutetic structure of Bi{sub 2}Sr{sub 3-x}Ca{sub x}O{sub y} and Cu{sub 2}O/CuO. The superconductor was formed on subsequent anneals. Samples melted in Ar and then annealed generally possessed a more uniform microstructure compared with samples that were melted in oxygen and annealed. Compositional measurements of the 2212 phase suggest that CaO segregation in the melt may be minimized with an overall composition such as Bi{sub 2.15}Sr{sub 2}Ca{sub 0.85}Cu{sub 2}O{sub y}.

Holesinger, T.G.; Miller, D.J. [Argonne National Lab., IL (United States); Chumbley, L.S. [Ames Lab., IA (United States)

1992-08-01

344

A ?SR study of the ruthenium perovskites ACu3Ru4O12 with A = Ca, Pr, Nd  

NASA Astrophysics Data System (ADS)

The metallic ruthenium perovskites ACu3Ru4O12 with A = Ca, Pr,Nd were investigated by zero field (ZF) and weak transverse field (TF) muon spin rotation/relaxation (?SR) spectroscopy. The ZF spectra for CaCu3Ru4O12 show pure static Gaussian Kubo-Toyabe relaxation arising from the interaction between the muon spin and the nuclear moments of the Cu ions. This confirms that no atomic magnetic moment exists. A sudden increase of the lattice parameter a when heating above ~150 K had previously been detected by neutron diffraction. The root mean square field at the muon site Brms was found to be 0.15 mT independent of temperature, in particular around 150 K. Also, no change of spectral parameters is seen in the weak TF data in that temperature range. Those findings imply that the structural change around 150 K takes place without noticeably shifting atomic positions. The spectra for PrCu3Ru4O12 and NdCu3Ru4O12 are dominated by the interaction with the dynamic rare earth moments. The analysis requires the use of the electron-nuclear double relaxation formalism. The electronic part shows simple exponential relaxation typical for a paramagnet. It features, with reducing the temperature a steep increase of paramagnetic relaxation rate as is characteristic for an approach to a magnetic spin freezing transition from above. That result suggests that the magnetic ground states of PrCu3Ru4O12 and NdCu3Ru4O12 are spin frozen states, although bulk magnetic data give no direct evidence in that direction.

Kalvius, G. M.; Hartmann, O.; Günther, A.; Krimmel, A.; Loidl, A.; Wäppling, R.; Sedlak, K.; Scheuermann, R.

2014-12-01

345

Symmetry of the hole states in BiCaSrCuO high-T sub c superconductors  

SciTech Connect

This paper reports on polarized CuL{sub 3}-edge X-ray absorption spectra (XAS) of oriented film of Bi{sub 2}Sr{sub 2}Ca{sub 1}Cu{sub 2}O{sub y} that have been measured to determine the symmetry of the orbital of the electronic holes. The states with the configuration of 3d{sup 9}L (L indicates ligand holes) have been detected. The holes d in superconducting materials are found to be in the antiferromagnetic band with b{sub 1} symmetry, derived by the Cu 3d{sub x{sup 2}{minus}y{sup 2}} orbital, but also in a second band with a{sub 1} molecular symmetry, derived by Cu 3d{sub x{sup 2}{minus}r{sup 2}} orbital at the Cu site. The authors' results can be rationalized with the formation of both d(b{sub 1})L and d(a{sub 1}) L states in the ground state of this high-T{sub c} superconductor.

Bianconi, A.; Castrucci, P.; De Santis, M.; Di Cicco, A.; Fabrizi, A. (CISM-GNSM, Dipt. di Fisica, Univ. delgi Studi Roma, 00185 Roma (IT)); Flank, A.M.; Lagarde, P. (LURE, CNRS-CEA-MEN, Batiment 209 D, Univ. Paris Sud, 91405 Orsay (FR)); Katayama-Yoshida, H.; Kotani, A. (Dept. of Physics, Tohoku Univ., Sendai 980 (JP)); Marcelli, A. (Lab. Nazionali di Frascati, INFN, Frascati 00044 (IT)); Zhao, Z.X. (Inst. of Physics, Academica Sinica, Beijing (CN)); Politis, C. (Kernforschungszentrum Karlsruhe, Inst. fur Nukleare Festkorperphysik, Karslruhe (DE))

1988-09-01

346

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

NASA Technical Reports Server (NTRS)

Long lengths of metal superconductor composites were prepared by passing a copper wire through the bismuth based molten oxide system at a constant speed. The key to successful composite preparation is the high pulling speed involved, which permits minimization of the severe interaction between the unbuffered metal surface and the oxide melt. Depending on the temperature of the melt and the pulling speed, a coating with different thickness and microstructure appeared. The nonannealed thick coatings contained a Bi2(Sr,Ca)2Cu1O6 phase as a major component. After relatively short time annealing at 800 C, both resistivity and initial magnetization versus temperature measurements show superconducting transitions beginning in the 110 to 115 K region. The effects of annealing and composition on obtained results are discussed. This method of manufacture led to the fabrication of wire with a copper core in a dense covering with uniform thickness of about h approximately equal to 5 to 50 microns. Composite wires with h approximately equal to 10 microns (h/d approximately equal to 0.1) sustained bending on a 15 mm radius frame without cracking during flexing.

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

1991-01-01

347

Study of macroscopic quantum tunnelling in Bi2Sr2CaCu2O8+? intrinsic Josephson junctions  

NASA Astrophysics Data System (ADS)

We report an experimental observation of the macroscopic quantum tunnelling (MQT) in a d-wave high-temperature superconductor (HTSC) Bi2Sr2CaCu2O8+? intrinsic Josephson junction (IJJs). It is well known that the current-biased Josephson tunnel junction provides an ideal stage for studying a variety of macroscopic quantum phenomena such as MQT. They have been studied and observed in low-temperature superconductor (LTSC) Josephson junctions since the early 1980s and have been established well by now. On the other hand, in the case of HTSC the d-wave pairing symmetry allows for dissipative quasiparticle excitations within the superconducting energy gap, which is expected to severely interfere with an observation of MQT. Contrary to this naive conception, our experimental results have explained that the effects of the nodal quasiparticles are not strong enough to obscure the observation of the MQT. Furthermore, we found that the MQT in IJJs was observed at approximately 1 K, which was ten times higher than that of LTSC Josephson junctions. This higher classical-to-quantum crossover temperature is due to their high plasma frequency. We also discuss the resonant activation of IJJs in the presence of microwave radiation.

Inomata, K.; Sato, S.; Kinjo, M.; Kitabatake, N.; Wang, H. B.; Hatano, T.; Nakajima, Koji

2007-02-01

348

A momentum-dependent perspective on quasiparticleinterference in Bi2Sr2CaCu2O_8+delta  

SciTech Connect

Angle Resolved Photoemission Spectroscopy (ARPES) probes the momentum-space electronic structure of materials, and provides invaluable information about the high-temperature superconducting cuprates. Likewise, cuprates real-space, inhomogeneous electronic structure is elucidated by Scanning Tunneling Spectroscopy (STS). Recently, STS has exploited quasiparticle interference (QPI) - wave-like electrons scattering off impurities to produce periodic interference patterns - to infer properties of the QP in momentum-space. Surprisingly, some interference peaks in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212) are absent beyond the antiferromagnetic (AF) zone boundary, implying the dominance of particular scattering process. Here, we show that ARPES sees no evidence of quasiparticle (QP) extinction: QP-like peaks are measured everywhere on the Fermi surface, evolving smoothly across the AF zone boundary. This apparent contradiction stems from different natures of single-particle (ARPES) and two-particle (STS) processes underlying these probes. Using a simple model, we demonstrate extinction of QPI without implying the loss of QP beyond the AF zone boundary.

Vishik, I. M.

2010-04-29

349

Shielding currents and current-voltage characteristics of Bi 2Sr 2Ca 1Cu 2O 8+? single crystal  

NASA Astrophysics Data System (ADS)

The dependence of the irreversible magnetization on the external magnetic field sweep rate, d He/d t, and its time relaxation are studied in a Bi 2+ xSr 2+ yCa 1+ zCu 2O 8+? ( x=0.11, y=0.12, z=-0.25) single crystal. Two characteristic regions are found with a transition temperature T? between 15 and 20 K depending on d He/d t and relaxation time. Below T? the magnetic field dependence of the shielding currents follows a scaling law Js( He, T)/ Js(0, T)= f[ He/ Js(0,T)] with a universal function f independent of temperature and sweep rate of magnetic field. Voltage-current characteristics are described quite well by a power-like law E/ Ec=( Js/ Jc) n with n?1/ T. Above T? a deviation from the Js( He) scaling behavior and a transition to much steeper voltage-current characteristics are observed. Possible reasons of these different shielding current behaviours are discussed.

Zhukov, A. A.; Kupfer, H.; Rybachuk, V. A.; Ponomarenko, L. A.; Murashov, V. A.; Martynkin, A. Yu.

1994-01-01

350

2D-3D transformation of layered perovskites through metathesis: synthesis of new quadruple perovskites A2La2CuTi3O12 (A = Sr, Ca).  

PubMed

We describe the synthesis of two new quadruple perovskites, Sr(2)La(2)CuTi(3)O(12) (I) and Ca(2)La(2)CuTi(3)O(12) (II), by solid-state metathesis reaction between K(2)La(2)Ti(3)O(10) and A(2)CuO(2)Cl(2) (A = Sr, Ca). I is formed at 920 degrees C/12 h, and II, at 750 degrees C/24 h. Both the oxides crystallize in a tetragonal (P4/mmm) quadruple perovskite structure (a = 3.9098(2) and c = 15.794(1) A for I; a = 3.8729(5) and c = 15.689(2) A for II). We have determined the structures of I and II by Rietveld refinement of powder XRD data. The structure consists of perovskite-like octahedral CuO(4/2)O(2/2) sheets alternating with triple octahedral Ti(3)O(18/2) sheets along the c-direction. The refinement shows La/A disorder but no Cu/Ti disorder in the structure. The new cuprates show low magnetization (0.0065 micro(B) for I and 0.0033 micro(B) for II) suggesting that the Cu(II) spins are in an antiferromagnetically ordered state. Both I and II transform at high temperatures to 3D perovskites where La/Sr and Cu/Ti are disordered, suggesting that I and II are metastable phases having been formed in the low-temperature metathesis reaction. Interestingly, the reaction between K(2)La(2)Ti(3)O(10) and Ca(2)CuO(2)Cl(2) follows a different route at 650 degrees C, K(2)La(2)Ti(3)O(10) + Ca(2)CuO(2)Cl(2) --> CaLa(2)Ti(3)O(10) + CaCuO(2) + 2KCl, revealing multiple reaction pathways for metathesis reactions. PMID:15018504

Sivakumar, T; Ramesha, K; Lofland, S E; Ramanujachary, K V; Subbanna, G N; Gopalakrishnan, J

2004-03-22

351

M 2 Si 5 N 8 :Eu 2+ -based (M = Ca, Sr) red-emitting phosphors fabricated by nitrate reduction process  

NASA Astrophysics Data System (ADS)

M 2Si 5N 8:Eu 2+-based (M = Ca, Sr) red-emitting phosphors were fabricated at relatively low temperature (1200 °C) and atmospheric pressure using a simple solid-state reaction process. Several processing parameters were systematically investigated to optimize the phosphors structural characterization and photoluminescence performance, including the amount of europium and the properties of the precursor and activated materials. The as-prepared M 2Si 5N 8:Eu 2+-based (M = Ca, Sr) phosphors were orange in color and emitted intensively in the red region of 580-670 nm under 465 nm excitation. This simple fabrication technique can be readily used for the optimization of phosphor microstructures and high-performance red-emitting phosphors since it eliminates many air-sensitive precursors.

Chen, Changcheng; Chen, Wanjun; Rainwater, Benjamin; Liu, Lixin; Zhang, Hongliang; Liu, Yanxia; Guo, Xiaosong; Zhou, Jinyuan; Xie, Erqing

2011-09-01

352

Raman spectroscopy study of the interface structure in (CaCuO2)n/(SrTiO3)m superlattices  

NASA Astrophysics Data System (ADS)

Raman spectra of CaCuO2/SrTiO3 superlattices show clear spectroscopic marker of two structures formed in CaCuO2 at the interface with SrTiO3. For non-superconducting superlattices, grown in low oxidizing atmosphere, the 425 cm-1 frequency of oxygen vibration in CuO2 planes is the same as for CCO films with infinite layer structure (planar Cu-O coordination). For superconducting superlattices grown in highly oxidizing atmosphere, a 60 cm-1 frequency shift to lower energy occurs. This is ascribed to a change from planar to pyramidal Cu-O coordination because of oxygen incorporation at the interface. Raman spectroscopy proves to be a powerful tool for interface structure investigation.

Di Castro, D.; Caramazza, S.; Innocenti, D.; Balestrino, G.; Marini, C.; Dore, P.; Postorino, P.

2013-11-01

353

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

SciTech Connect

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

Bernhard, K.; Gritzner, G.; Wang, Xianzhong; Baeuerle, D. (Johannes Kepler Universitaet Linz (Austria))

1990-06-01

354

The dx2 y2-wave superconducting gap in Bi2Sr2CaCu2O8: scanning tunnelling microscope spectroscopy  

Microsoft Academic Search

We have carried out electron tunnelling spectroscopy on Bi2Sr2CaCu2O8 single crystals with the use of a scanning tunnelling microscope at 4.2 K. A conductance peak structure was observed near zero bias voltage for the tunnelling along the Cu-O bonding direction. A clear superconducting gap was observed for the tunnelling along the Cu-Cu direction. Curves along the Cu-O and Cu-Cu directions

Koji Suzuki; Koichi Ichimura; Kazushige Nomura; Shunji Takekawa

355

Vortex dynamics in Bi 2 Sr 2 CaCu 2 O 8 -thin films in the presence of columnar defects  

Microsoft Academic Search

With heavy ion irradiation we create continous amorphous columnar defects in Bi2Sr2CaCu2O8-thin films. With regard to a reliable comparison of irradiation effects three of four identical striplines on the same samples were exposed to different irradiation procedures. We performed irradiations as well parallel as under different angles with respect to the film\\u000a

F. Hillmer; G. Wirth; P. Haibach; U. Frey; Th. Kluge; H. Adrian

1996-01-01

356

Calibration and Natural Variability of Skeletal Stable Isotopes and Sr\\/Ca in two species of Pacific sclerosponges (Acanthocheatetes wellsi and Astroclera welleyana)  

Microsoft Academic Search

Sclerosponges are reef organisms that deposit a calcium carbonate exoskeleton in layers and can live for centuries. Increasingly, the isotopic and elemental compositions of their skeletons are being used to reconstruct tropical paloeceanographic records. Here preliminary data on the in situ calibration of the skeletal stable carbon (delta13C), stable oxygen (delta18O), and strontium to calcium ratios (Sr\\/Ca) in the Pacific

A. G. Grottoli; J. F. Adkins; K. Moots

2005-01-01

357

Ab initio prediction of the structural, electronic, elastic and thermodynamic properties of the tetragonal ternary intermetallics XCu2Si2 (X = Ca, Sr)  

NASA Astrophysics Data System (ADS)

Structural parameters, electronic structure, elastic constants and thermodynamic properties of the tetragonal ternary intermetallics CaCu2Si2 and SrCu2Si2 are investigated theoretically for the first time using the plane-wave ultra-soft pseudopotential method based on the density functional theory. The calculated equilibrium structural parameters agree well with the existing experimental data. Pressure dependence of the structural parameters is also explored. Analysis of the band structure, total and site-projected l-decomposed densities of states and valence charge distributions reveals the conducting character of both considered materials with a mixture of ionic-covalent chemical bonding character. Pressure dependences of the single-crystal elastic constants Cij for CaCu2Si2 and SrCu2Si2 are explored. The elastic wave velocities propagating along the principal crystallographic directions are numerically estimated. The elastic anisotropy is estimated and further illustrated by 3D-direction-dependent of the Young's modulus. A set of some macroscopic elastic moduli, including the bulk, Young's and shear moduli, Poisson's coefficient, average elastic wave velocities and Debye temperature, were calculated for polycrystalline CaCu2Si2 and SrCu2Si2 from the Cij via the Voigt-Reuss-Hill approximations. Through the quasiharmonic Debye model, which takes into account the phonon effects, the temperature and pressure dependencies of the bulk modulus, unit cell volume, volume thermal expansion coefficient, Debye temperature and volume constant and pressure constant heat capacities of CaCu2Si2 and SrCu2Si2 are explored systematically in the ranges of 0-40 GPa and 0-1400 K.

Reffas, Mounir; Bouhemadou, Abdelmadjid; Haddadi, Khelifa; Bin-Omran, Saad; Louail, Layachi

2014-12-01

358

Hydration Energies and Structures of Alkaline Earth Metal Ions, M2+ (H2O)n, n = 5–7, M = Mg, Ca, Sr, and Ba  

PubMed Central

The evaporation of water from hydrated alkaline earth metal ions, produced by electrospray ionization, was studied in a Fourier transform mass spectrometer. Zero-pressure-limit dissociation rate constants for loss of a single water molecule from the hydrated divalent metal ions, M2+(H2O)n (M = Mg, Ca, and Sr for n = 5–7, and M = Ba for n = 4–7), are measured as a function of temperature using blackbody infrared radiative dissociation. From these values, zero-pressure-limit Arrhenius parameters are obtained. By modeling the dissociation kinetics using a master equation formalism, threshold dissociation energies (Eo) are determined. These reactions should have a negligible reverse activation barrier; therefore, Eo values should be approximately equal to the binding energy or hydration enthalpy at 0 K. For the hepta- and hexahydrated ions at low temperature, binding energies follow the trend expected on the basis of ionic radii: Mg > Ca > Sr > Ba. For the hexahydrated ions at high temperature, binding energies follow the order Ca > Mg > Sr > Ba. The same order is observed for the pentahydrated ions. Collisional dissociation experiments on the tetrahydrated species result in relative dissociation rates that directly correlate with the size of the metals. These results indicate the presence of two isomers for hexahydrated magnesium ions: a low-temperature isomer in which the six water molecules are located in the first solvation shell, and a high-temperature isomer with the most likely structure corresponding to four water molecules in the inner shell and two water molecules in the second shell. These results also indicate that the pentahydrated magnesium ions have a structure with four water molecules in the first solvation shell and one in the outer shell. The dissociation kinetics for the hexa- and pentahydrated clusters of Ca2+, Sr2+, and Ba2+ are consistent with structures in which all the water molecules are located in the first solvation shell. PMID:16429612

Rodriguez-Cruz, Sandra E.; Jockusch, Rebecca A.

2005-01-01

359

High-pressure synchrotron-diffraction study of the superconducting spin-ladder compounds (Sr, M)14Cu24O41 (M=Ca, Ba, Nd)  

Microsoft Academic Search

The evolution of the cell parameters as a function of pressure of five samples of the spin-ladder compounds (Sr, M)14Cu24O41, with M=Ca, Ba, Nd has been investigated up to ~10 GPa by high-pressure synchrotron x-ray diffraction on the ID9 beam line of the ESRF. A large anisotropy of compressibility is observed, with a very strong compression along the b axis,

Stéphanie Pachot; Pierre Bordet; Robert J. Cava; Catherine Chaillout; Céline Darie; Michael Hanfland; Massimo Marezio; Hidenori Takagi

1999-01-01

360

AC transport losses under self fields in Ag-sheathed (Bi,Pb) 2Sr 2Ca 2Cu 3O x conductors  

Microsoft Academic Search

The AC transport losses under self fields were investigated at 77 K on the Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox 19-filamentary untwisted and twisted (with a pitch of 13 mm) tapes. The filament twist neither causes notable influence on the loss behavior nor equalizes the current distribution in the filaments, although the main contribution to the losses comes from the hysteresis loss. Using the

T Fukunaga; A Oota

1997-01-01

361

Spatial Variations in the Superconducting Order Parameter of Bi_2Sr_2CaCu_2O_8+? as Revealed by Low Temperature Scanning Tunneling Spectroscopy  

NASA Astrophysics Data System (ADS)

Scanning tunneling spectroscopy was performed on Zn- and Ni-doped Bi_2Sr_2CaCu_2O_8+? single crystals. Reproducible spectroscopy shows atomic scale spatial variations in the energy and magnitude of the superconducting coherence peaks. We report the results of a statistical analysis of this data and discuss the potential ramifications on spatially averaged measurements. We also consider some possible explanations for such rapid gap magnitude variations.

Madhavan, Vidya; Lang, K. M.; Hudson, E. W.; Pan, S. H.; Eisaki, H.; Uchida, S.; Davis, J. C.

2000-03-01

362

Use of microsatellite DNA and otolith Sr:Ca ratios to infer genetic relationships and migration history of four morphotypes of Rhinogobius sp. OR  

Microsoft Academic Search

The genetic diversity and relationship among four morphotypes of Rhinogobius sp. OR, Gobiidae (“T?shoku,” “Shinjiko,” “Gi-t?shoku,” and “Shimahire”) were investigated with seven microsatellite DNA loci,\\u000a and amphidromy of these morphotypes was verified by strontium (Sr) and calcium (Ca) deposition in the otolith. Samples of\\u000a “T?shoku,” “Shinjiko,” “Gi-t?shoku,” and “Shimahire” were collected from, respectively, three, three, two, and four locations\\u000a in

Kenichi Ohara; Momoko Hotta; Daisuke Takahashi; Takashi Asahida; Hitoshi Ida; Tetsuya Umino

2009-01-01

363

Preparation and magnetic properties of the double-perovskite A2FeMoO6 (A=Ca, Sr, Ba) polycrystals with nanometer-scale particles  

Microsoft Academic Search

Polycrystalline double perovskites A2FeMoO6 (A=Ca, Sr, Ba) with nanometer-scale grain size have been synthesized using a sol–gel method. The grain size of the samples is controlled within nanometer scale by sintering at different temperatures. The phase purity and the crystal structure of the samples are analyzed by x-ray powder diffraction measurements. The electrotransport and magnetic properties are also measured in

W. H. Song; J. M. Dai; S. L. Ye; K. Y. Wang; J. J. Du; Y. P. Sun

2001-01-01

364

Preparation and magnetic properties of the double-perovskite A2FeMoO6 (A=Ca, Sr, Ba) polycrystals with nanometer-scale particles  

Microsoft Academic Search

Polycrystalline double perovskites A2FeMoO6 (A=Ca, Sr, Ba) with nanometer-scale grain size have been synthesized using a sol-gel method. The grain size of the samples is controlled within nanometer scale by sintering at different temperatures. The phase purity and the crystal structure of the samples are analyzed by x-ray powder diffraction measurements. The electrotransport and magnetic properties are also measured in

W. H. Song; J. M. Dai; S. L. Ye; K. Y. Wang; J. J. Du; Y. P. Sun

2001-01-01

365

NONLINEAR OPTICAL PHENOMENA: Stimulated Raman scattering of picosecond pulses in SrMoO4 and Ca3(VO4)2 crystals  

Microsoft Academic Search

An express technique is proposed for the study of stimulated Raman scattering (SRS) in crystals excited by long trains of picosecond pulses. SRS was studied in several crystals excited by 15-ps pulses from an Nd3+:CLNGG disordered garnet laser. SRS in SrMoO4 and Ca3(VO4)2 crystals was obtained and investigated for the first time, and compared with SRS in popular SRS-active BaWO4

Petr G. Zverev; Aleksandr Ya Karasik; Tasoltan T. Basiev; Lyudmila I. Ivleva; Vyacheslav V. Osiko

2003-01-01

366

Josephson vortex contribution to c-axis thermopower in Bi2Sr2CaCu2O8+? single crystals  

NASA Astrophysics Data System (ADS)

We report on the temperature and magnetic field dependence of the c-axis thermopower in high-quality Bi2Sr2CaCu2O8+? single crystals. In contrast to the in-plane thermopower the temperature dependence of the c-axis thermopower is nonmonotonic below Tc and we show that this is the result of a significant contribution of Josephson vortices. The magnetic field dependence of the thermopower supports the proposed explanation.

Logvenov, G. Yu.; Waldmann, O.; Kleiner, R.; Müller, Paul

1998-07-01

367

Crystal and magnetic structure of Cr- and Ni-substituted (La0.50Ca0.50)MnO3  

NASA Astrophysics Data System (ADS)

The crystal and magnetic structure of (La0.50Ca0.50)(Mn1-xBx)O3 (x = 0.00, 0.03, 0.08; B = Cr, Ni) has been investigated between 5 and 300 K by means of dc magnetic measurements and neutron powder diffraction followed by Rietveld refinement. In the pristine compound an orthorhombic to monoclinic phase transition is detected on cooling, accompanied by a CE-type antiferromagnetic (AFM) ordering arising. Ni2+ and Cr3+ substitutions have similar effects on the structural and magnetic properties of (La0.50Ca0.50)MnO3, despite the fact that these ions are characterized by different external electronic configurations. After substitution, the orthorhombic to monoclinic phase transition is hindered. As a consequence, charge and orbital orderings are suppressed, as is the superexchange; double exchange takes place inducing ferromagnetic (FM) interactions. No evidence for stable magnetic interaction between Cr3+ or Ni2+ and the neighbouring Mn ions was detected. Nevertheless, in the Ni-substituted samples a detectable quantity of monoclinic phase forms during cooling, inside which AFM interactions take place. The amount of this secondary monoclinic phase decreases on increasing Ni substitution; the global FM magnetic moment decreases as well, due to a spin-cluster glass-type state arising. As a result a FM state is found to coexist with a spin-cluster glass-type state.

Martinelli, A.; Ferretti, M.; Castellano, C.; Cimberle, M. R.; Ritter, C.

2008-04-01

368

Effect of SR load and pH regulatory mechanisms on stretch-dependent Ca(2+) entry during the slow force response.  

PubMed

When cardiac muscle is stretched, there is an initial inotropic response that coincides with the stretch followed by a slower increase in twitch force that develops over several minutes (the "slow force response", or SFR). Unlike the initial response to stretch, the SFR is produced by an increase in Ca(2+) transient amplitude, but the cellular mechanisms that give rise to the increased transients are still debated. We have examined the relationship between the SFR, intracellular [Ca(2+)] and the inotropic state of right ventricular trabeculae from rat hearts at 37°C. The magnitude of the SFR varied with [Ca(2+)]o and stimulation frequency, so that the SFR was greatest for conditions associated with a reduced SR Ca(2+) content. The SFR was not blocked by the AT1 receptor blocker losartan, but was reduced by SN-6, an inhibitor of reverse mode Na(+)/Ca(2+)-exchange (NCX). The Na(+)/H(+)-exchange (NHE) inhibitor HOE642 had no effect in HCO3(-)-buffered solutions, but blocked 50% of the SFR in HCO3(-)-free solution. Inhibition of HCO3(-) transport by DIDS increased the SFR and made it sensitive to HOE642. The addition of cross-bridge cycle inhibitors (20mM BDM or 20?M blebbistatin) to the superfusate reduced the SFR as monitored by changes in Ca(2+). In HCO3(-)-free conditions, the SFR was associated with a slow acidification that was inhibited by BDM, and by stopping electrical stimulation. These results can be explained by stretch increasing metabolic demand and stimulating Na(+) entry via both NHE and the Na(+)/HCO3(-) transporters. This mechanism provides a novel link between inotropic state and stretch, as well as a way for the cell to compensate for increased acid load. The feedback mechanism between force and Ca(2+) transient amplitude that we describe is also limited by the degree of SR Ca(2+) load. PMID:23880608

Shen, Xin; Cannell, Mark B; Ward, Marie-Louise

2013-10-01

369

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

SciTech Connect

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

Cao Qigao [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai 200050 (China); Graduate School of Chinese Academy of Science, Beijing 100080 (China); Zhang Hui; Tang Meibo; Chen Haohong; Yang Xinxin; Zhao Jingtai [Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Sciences, Shanghai Institute of Ceramics, Shanghai 200050 (China); Grin, Yuri [Max-Planck-Institut fuer Chemische Physik fester Stoffe, Noethnitzer Str. 40, 01187 Dresden (Germany)

2010-03-15

370

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

SciTech Connect

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

Zhang, Xinmin, E-mail: zhangxinminam@yahoo.com [College of Materials Science and Engineering, Central South University of Forestry and Technology, Changsha 410004 (China)] [College of Materials Science and Engineering, Central South University of Forestry and Technology, Changsha 410004 (China); Seo, Hyo Jin, E-mail: hjseo@pknu.ac.kr [Department of Physics, Pukyong National University, 599-1, Daeyeon 3-Dong, Nam-Gu,, Busan 608-737 (Korea, Republic of)

2012-08-15

371

Charge-compensation effect of Al on luminescence properties of M2(Si, Al)5N8:Ce3+ (M = Ca, Sr, Ba)  

NASA Astrophysics Data System (ADS)

The charge-compensated materials, M2AlxSi5-xN8:Ce3+ (M = Ca, Sr, Ba), were synthesized from appropriate mixtures of MSi, MAlSi, (MSiHy, MAlSiHy), Si3N4 and CeF3 by a direct nitriding process in a N2 gas and the luminescence properties were characterized. The resultant phosphors showed green emission suitable for LED illumination by optimizing the mixing ratio of metal elements. These phosphors were effectively excited by violet or blue light (400-430 nm) and the emission bands were observed at various wavelength regions for Ca: 489-528 nm, Sr: 511-520 nm, and Ba: 508-514 nm. Although the emission intensity of Ca2(Si, Al)5N8:Ce3+ was decreased with increasing amount of Al, those of Sr- and Ba-analogues were maximized at x = 0.5 of Al content in M2Si5-xAlxN8:Ce3+.

Kuramoto, Daiki; Horikawa, Takashi; Hanzawa, Hiromasa; Machida, Ken-ichi

2013-09-01

372

Endohedral and Exohedral Metalloborospherenes: M@B40 (M=Ca, Sr) and M&B40 (M=Be, Mg).  

PubMed

The recent discovery of the all-boron fullerenes or borospherenes, D2d B40 (-/0) , paves the way for borospherene chemistry. Here we report a density functional theory study on the viability of metalloborospherenes: endohedral M@B40 (M=Ca, Sr) and exohedral M&B40 (M=Be, Mg). Extensive global structural searches indicate that Ca@B40 (1, C2v , (1) A1 ) and Sr@B40 (3, D2d , (1) A1 ) possess almost perfect endohedral borospherene structures with a metal atom at the center, while Be&B40 (5, Cs , (1) A') and Mg&B40 (7, Cs , (1) A') favor exohedral borospherene geometries with a ?(7) -M atom face-capping a heptagon on the waist. Metalloborospherenes provide indirect evidence for the robustness of the borospherene structural motif. The metalloborospherenes are characterized as charge-transfer complexes (M(2+) B40 (2-) ), where an alkaline earth metal atom donates two electrons to the B40 cage. The high stability of endohedral Ca@B40 (1) and Sr@B40 (3) is due to the match in size between the host cage and the dopant. Bonding analyses indicate that all 122 valence electrons in the systems are delocalized as ? or ? bonds, being distributed evenly on the cage surface, akin to the D2d B40 borospherene. PMID:25418022

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

2014-11-21

373

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

PubMed Central

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

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

2014-01-01

374

Li doping effects on the upconversion luminescence of Yb3+/Er3+-doped ABO4 (A = Ca, Sr; B = W, Mo) phosphors  

NASA Astrophysics Data System (ADS)

ABO4 (A = Ca, Sr; B = W, Mo):Er3+/Yb3+/Li+ phosphors tri-doped with different concentrations of Li+ ion ranging from 0 to 22.5 mol% were prepared by using a solid-state reaction method. And their upconversion (UC) luminescence properties were in estimated under a 975 nm laser-diode excitation. The four kinds of phosphors (CaWO4, CaMoO4, SrWO4, and SrMoO4) tri-doped with Er3+, Yb3+ and Li+ ions showed strong green UC emission peaks at 530 nm and 550 nm and weak red UC emission. The intensity of green UC emission of Li+ doped samples was several higher than that of Li+ un-doped samples due to the reduction of lattice constant and the local crystal field distortion around rare-earth ions. The optimum doping concentration of Li+ ions was investigated and the effects of Li+ concentration for UC emission intensity were studied in detail.

Kim, Jung Hwan; Choi, Haeyoung; Kim, Eun Ock; Noh, Hyeon Mi; Moon, Byung Kee; Jeong, Jung Hyun

2014-12-01

375

Measurement of the mass attenuation coefficients and electron densities for BiPbSrCaCuO superconductor at different energies  

NASA Astrophysics Data System (ADS)

The mass attenuation coefficients for Bi, Pb, Sr, Ca, Cu metals, Bi 2O 3, PbO, SrCO 3, CaO, CuO compounds and solid-state forms of Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O 10 superconductor were determined at 57.5, 65.2, 77.1, 87.3, 94.6, 122 and 136 keV energies. The samples were irradiated using a 57Co point source emitted 122 and 136 keV ?-ray energies. The X-ray energies were obtained using secondary targets such as Ta, Bi 2O 3 and (CH 3COO) 2UO 22H 2O. The ?- and X-rays were counted by a Si(Li) detector with a resolution of 0.16 keV at 5.9 keV. The effect of absorption edges on electron density, effective atomic numbers and their variation with photon energy in composite superconductor samples was discussed. Obtained values were compared with theoretical values.

Çevik, U.; Balta?, H.

2007-03-01

376

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

DOEpatents

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

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

2001-01-01

377

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

SciTech Connect

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

Omoto, Kazuki [Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajousui, Setagaya-ku, Tokyo 156-8550 (Japan); Norberg, Stefan T. [Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom); Hull, Steve [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom); Aoto, Akimitsu [Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajousui, Setagaya-ku, Tokyo 156-8550 (Japan); Hashimoto, Takuya, E-mail: takuya@chs.nihon-u.ac.j [Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences, Nihon University, 3-25-40 Sakurajousui, Setagaya-ku, Tokyo 156-8550 (Japan)

2010-02-15

378

Electronic Phase Separation in Pr sub 1 sub x (Ca, Sr) sub x MnO sub 3 subdelta and Tunneling Magnetoresistance in Sr sub 2 FeMoO sub 6  

E-print Network

In this work, we approach two aspects of the physics of magnetic perovskites presenting colossal magnetoresistance (CMR). Firstly, we go deeply into the phase separation (PS) between the ferromagnetic (FM) metallic state and the antiferro-magnetic (AFM) charge ordered (CO) insulating state, in manganites of the type Pr sub 1 sub x (Ca,Sr) sub x MnO sub 3 subdelta. Secondly, and more briefly, we analyze the problem of the influence of the grain boundary insulating barriers on the tunneling magnetoresistance in the Sr sub 2 FeMoO sub 6 double perovskite.The use of different measurement techniques allowed us to make a complete characterization of the PS state in the compounds Pr sub 0.65Ca sub 0 sub . sub 3 sub 5 sub - sub y Sr sub y MnO sub 3 for 0 ) keeping constant the carrier concentration (x = 0.35). This material presents an evolution from a CO insulating phase for small (y =0), towards the FM metallic phase for large (y = 0.20). In t

Niebieskikwiat, D G

2003-01-01

379

Effect of substitution of nitrogen ions to red-emitting Sr 3B 2O 6?3\\/2 x N x :Eu 2+ oxy-nitride phosphor for the application to white LED  

Microsoft Academic Search

The luminescence properties of orange–red-emitting Eu2+ activated Sr3B2O6?3\\/2xNx were optimized for application to blue\\/near UV light-emitting diodes (LEDs). Sr3B2O6?3\\/2xNx:Eu2+ phosphor showed broad orange–red emission peaking at 600–650nm under blue and n-UV excitations of 450 and 360nm, respectively; the emission peak of phosphor was affected by nitrogen ion substitution. Boron nitride raw materials affect luminescence properties of phosphor; a small amount

Sang Hoon Jung; Dong Seok Kang; Duk Young Jeon

2011-01-01

380

Investigating the influence of Na(+) and Sr (2+) on the structure and solubility of SiO 2-TiO 2-CaO-Na 2O/SrO bioactive glass.  

PubMed

This study was conducted to determine the influence that network modifiers, sodium (Na(+)) and strontium (Sr(2+)), have on the solubility of a SiO2-TiO2-CaO-Na2O/SrO bioactive glass. Glass characterization determined each composition had a similar structure, i.e. bridging to non-bridging oxygen ratio determined by X-ray photoelectron spectroscopy. Magic angle spinning nuclear magnetic resonance (MAS-NMR) confirmed structural similarities as each glass presented spectral shifts between -84 and -85 ppm. Differential thermal analysis and hardness testing revealed higher glass transition temperatures (Tg 591-760 °C) and hardness values (2.4-6.1 GPa) for the Sr(2+) containing glasses. Additionally the Sr(2+) (~250 mg/L) containing glasses displayed much lower ion release rates than the Na(+) (~1,200 mg/L) containing glass analogues. With the reduction in ion release there was an associated reduction in solution pH. Cytotoxicity and cell adhesion studies were conducted using MC3T3 Osteoblasts. Each glass did not significantly reduce cell numbers and osteoblasts were found to adhere to each glass surface. PMID:25644099

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

2015-02-01

381

The influence of SrSO 4 additives to Bi 2Sr 2CaCu 2O 8 high temperature superconductors  

NASA Astrophysics Data System (ADS)

For application in electrical engineering BSCCO 2212 high temperature superconductors have been manufactured with an admixture of strontium sulphate (SrSO 4). On three samples with different SrSO 4 content we have measured the specific heat and the thermal expansion behaviour in the temperature region between 4.2 K and 293 K. The admixture increases the specific heat and the contraction, which indicates a decreasing Debye temperature. At both properties anomalies indicate the phase transition point at about 90 K. The temperature dependence of the thermal properties below 20 K is characteristic for amorphous behaviour of solids.

Escher, U.; Samuel, R.; Gladun, A.; Hegenbarth, E.

1996-02-01

382

Suppression of superconductivity with Pr substitution in Nd 1- xPr xBaCaCu 3O 7 system  

NASA Astrophysics Data System (ADS)

The structural, superconducting and magnetic properties of Nd 1- xPr xBaCaCu 3O 7 system with x=0.0, 0.10, 0.25, 0.35, 0.50, 0.75 and 1.0 have been investigated. X-ray diffraction results reveal that Pr substitutes isostructurally in NdBaCaCu 3O 7 (Nd:1113) superconductor with complete solubility. The superconducting transition temperature ( Tc), measured by ac susceptibility technique, decreases with increasing x. However, suppression of Tc with increasing Pr substitution is less in Nd:1113 superconductor compared to that reported for Nd 1- xPr xBa 2Cu 3O 7 system. Interestingly, in the fully Pr substituted compounds of the above series, i.e., in PrBaCaCu 3O 7 and PrBa 2Cu 3O 7, the Pr moments order antiferromagnetically with TN of 10 and 17 K, respectively. The present results along those reported earlier [V.P.S. Awana, J. Horvat, S.X. Dou, A. Sedky, A.V. Narlikar, J. Magn. Magn. Mater., 182 (1998) L280; V.P.S. Awana, S.X. Dou, S.K. Malik, Rajvir Singh, A.V. Narlikar, D.A. Landinez Tellez, J.M. Ferreira, J. Albino Aguiar, S. Uma, E. Gmelin, W.B. Yelon, J. Magn. Magn. Mater., 187 (1998) 192], clearly suggest that there is a correlation between the Tc suppression due to Pr and the magnetic ordering temperature of the fully substituted Pr moments in these systems. The TN may be taken to be a measure of the strength of hybridization between the Pr-4f electrons with Cu-O conduction band, and hence a lower TN may imply a less deleterious effect on superconductivity.

Awana, V. P. S.; Cardoso, Claudio A.; de Lima, O. F.; Singh, Rajvir; Narlikar, A. V.; Yelon, W. B.; Malik, S. K.

1999-05-01

383

Suppression of photovoltaic effect by magnetic field in Pr0.65(Ca0.75Sr0.25)0.35MnO3/Nb:SrTiO3 heterostructure  

NASA Astrophysics Data System (ADS)

The heterostructure composed of Pr0.65(Ca0.75Sr0.25)0.35MnO3 and 0.7 wt. % Nb-doped SrTiO3 was fabricated. The heterostructure exhibits an asymmetric current-voltage relation similar to that of p-n junctions and an obvious photovoltaic effect with its maximum value of about 25.1 mV at T = 140 K. It is interesting that the magnetic field has a strong suppression effect on photovoltaic effect, and the maximum relative change of photovoltage under the magnetic field of 1 T is about 63% with the illumination of 15 mW/mm2 light (532 nm) at T ˜ 140 K. The physical mechanism is explained by the electronic phase separation mechanism.

Luo, C.; Jin, K. X.; Chen, C. L.; Wu, T.

2013-11-01

384

Calcium EXAFS establishes the Mn-Ca cluster in the oxygen-evolving complex of Photosystem II  

SciTech Connect

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

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

2002-08-02

385

Stable isotopes and Mg/Ca and Sr/Ca ratios from benthic foraminifera across the Danian-Selandian boundary (early-middle Paleocene) in the North Sea Basin  

NASA Astrophysics Data System (ADS)

The Danian-Selandian boundary (early to middle Paleocene, ~60 Ma) marks the cessation of 40 million years of carbonate deposition in the North Sea Basin and a shift to siliciclastic deposition. Recent investigations from south Tethys have revealed that the boundary here is also linked to sedimentological shifts. Furthermore, micropaleontological data and excursions in the ?13C values in some Tethyan sections in connection with the boundary have indicated possible abrupt environmental changes suggestive of a precursor event to the Paleocene-Eocene thermal maximum (PETM). In the eastern North Sea, the late Danian deposits consist of bryozoan limestone overlain by a chalk composed mainly of fragments of braarudosphaerids, a calcareous nannofossil generally connected to marginal conditions. This unit is again overlain by a calcareous greensand of Selandian age. We have measured stable isotope values (?13C and ?18O) and Mg/Ca and Sr/Ca ratios on the benthic foraminifera Cibicides howelli, Stensioeina beccariformis and Anomalinoides nobilis in a section comprising a time span of about 3.0 Ma equally distributed on both sides of the boundary. The ?13C values and Sr/Ca ratios show a clear trend with very little scatter in the data. The Mg/Ca data and, in particular, the ?18O values are more variable with considerable scatter, although clear trends are discernable here as well. The changes in the geochemical parameters often coincide with changes in lithology suggesting that the changes could be due to either environmental changes or to different grades of diagenesis. However, the fact that both the Sr/Ca and Mg/Ca ratios exhibit distinct trends crossing several lithological boundaries speaks in favour of environmental factors as the most important cause. The ?13C values are high (~1.5%) in both the bryozoan limestone and in the Selandian greensand and lower in the braarudospahaerid chalk (~1.0%). These variations probably reflect changes in surface productivity, with high productivity during the deposition of the bryozoan limestone and the Selandian greensand and low productivity during the deposition of the braarudosphaerids chalk. This interpretation is consistent with the high abundance of micro- and macrofossils in the bryozoan limestone and Selandian greensand and the almost total lack of macrobenthic fossils in the braarudosphaerid chalk. In the same sequence both the Sr/Ca and Mg/Ca ratios show steadily increasing trends. The Sr/Ca values increase from about 1.15 mmol/mol in the Danian bryozoan limestone to about 1.6 mmol/mol in the Selandian greensand, while Mg/Ca ratios increase from ~9 to ~11 mmol/mol for C. howelli. The trend in the Mg/Ca ratio could indicate a gradual increase in the bottom water temperatures from the late Danian to the early Selandian. However, neither ?13C values nor the other measured parameters show any indications of abrupt changes in relation to the boundary resembling the PETM. We suggest that the geochemical changes across Danian-Selandian boundary in the North Sea basin mainly have local causes.

Thomsen, E.; Clemmensen, A.; Groeneveld, J.

2009-12-01

386

Controlled peak wavelength shift of Ca{sub 1-} {sub x} Sr {sub x} (S {sub y} Se{sub 1-} {sub y} ):Eu{sup 2+} phosphor for LED application  

SciTech Connect

The highly efficient red-orange-yellow-emitting phosphor (Ca{sub 1-} {sub x} Sr {sub x} )(S{sub 1-} {sub y} Se {sub y} ):Eu{sup 2+} in combination with commercial green phosphor SrGa{sub 2}S{sub 4}:Eu{sup 2+} and blue LED are proposed for a three-band white LED. The luminescence mechanism and optimization parameters are discussed on the basis of proposed peak wavelength diagram. - Graphical abstract: 'Peak wavelength diagram for (Ca{sub 1-} {sub x} Sr {sub x} )(S{sub 1-} {sub y} Se {sub y} ):Eu{sup 2+}'.

Nazarov, Mihail [Samsung Electro-Mechanics Co, LTD, Metan 3-Dong, Yeogtong-Gu, Suwon (Korea, Republic of)]. E-mail: nazarov.mihail@samsung.com; Yoon, Chulsoo [Samsung Electro-Mechanics Co, LTD, Metan 3-Dong, Yeogtong-Gu, Suwon (Korea, Republic of)

2006-08-15

387

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

SciTech Connect

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

Li Yuanliang [Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072 (China)], E-mail: lylll2007@yahoo.cn; Qu Yuanfang [Key Laboratory for Advanced Ceramics and Machining Technology of Ministry of Education, Tianjin University, Tianjin 300072 (China)

2009-01-08

388

Electric field gradient measurements on 111Cd in the high- Tc superconductor Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O y  

NASA Astrophysics Data System (ADS)

The electric field gradients (EFGs) in the sites of a 111Cd probe nucleus have been measured by the perturbed angular correlation (PAC) method in the high- Tc superconductor Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O y between 77 and 473 K. The probe atoms sense two defined EFGs with quadrupole coupling constants of 90(3) and 67(1) MHz, and asymmetry parameters of 0.51(3) and 0.30(2) at 300 K which were assigned to Bi- and Ca-sites, respectively. The frequency distribution broadening of the Bi-site has been observed, and this broadening is due to charge inhomogeneity surrounding the Bi-site which is interpreted by Pb-doping and structure modulation of the Bi layer. The frequency distribution broadening in the Ca-site has been also observed.

Li, Dong Ming; Shan, Du Hong; Bin, Du Shu; Hua, Li Jian; Yong, Jiang; Ting, Tong Bo; Can, Che Guang

1997-02-01

389

Transport and photoresponse properties in Pr0.5Ca0.5CoO3/Nb-SrTiO3 heterostructure  

NASA Astrophysics Data System (ADS)

Transport and photoresponse properties of the heterostructure consisting of a Pr0.5Ca0.5CoO3 film and a Nb-SrTiO3 substrate were investigated. The Pr0.5Ca0.5CoO3 film exhibits semiconducting behavior and the resistances are decreased when irradiated by a 532 nm laser. The rectifying behaviors are observed in the heterostructure. The ideality factors and the diffusion voltages monotonically decrease with increasing the temperature. The photovoltatges of the heterostructure under the irradiation approach the saturation at about 8.5 \\text{mW/mm}2 . The minority carrier lifetime of ?p=0.281 \\text{s} is estimated from the time response properties in the falling process of photovoltages. These results reveal that the Pr0.5Ca0.5CoO3 heterostructures have great potentials in photoresponse and photoelectric conversion applications.

Zhao, S. G.; Gu, A.; Yan, X. L.; Hao, L. M.; Xie, Y.; Zhang, T.; Jin, K. X.

2015-01-01

390

Ab initio study of the positronation of the CaO and SrO molecules including calculation of annihilation rates.  

PubMed

Ab initio multireference single- and double-excitation configuration interaction calculations have been performed to compute potential curves for ground and excited states of the CaO and SrO molecules and their positronic complexes, e(+)CaO, and e(+)SrO. The adiabatic dissociation limit for the (2)?(+) lowest states of the latter systems consists of the positive metal ion ground state (M(+)) and the OPs complex (e(+)O(-)), although the lowest energy limit is thought to be e(+)M + O. Good agreement is found between the calculated and experimental spectroscopic constants for the neutral diatomics wherever available. The positron affinity of the closed-shell X (1)?(+) ground states of both systems is found to lie in the 0.16-0.19 eV range, less than half the corresponding values for the lighter members of the alkaline earth monoxide series, BeO and MgO. Annihilation rates (ARs) have been calculated for all four positronated systems for the first time. The variation with bond distance is generally similar to what has been found earlier for the alkali monoxide series of positronic complexes, falling off gradually from the OPs AR value at their respective dissociation limits. The e(+)SrO system shows some exceptional behavior, however, with its AR value reaching a minimum at a relatively large bond distance and then rising to more than twice the OPs value close to its equilibrium distance. PMID:22522712

Buenker, Robert J; Liebermann, Heinz-Peter

2012-07-15

391

Magnetic, Mössbauer and optical spectroscopic properties of the AFe3O(PO4)3 (A = Ca, Sr, Pb) series of powder compounds  

NASA Astrophysics Data System (ADS)

AFe3O(PO4)3 (A = Ca, Sr and Pb) powder compounds were studied by means of X-ray diffraction (XRD), electron-probe microanalysis (EPMA) coupled with wavelength dispersion spectroscopy (WDS), Raman and diffuse reflectance spectroscopies, specific heat and magnetic properties measurements. Magnetization, magnetic susceptibility and specific heat measurements carried out on AFe3O(PO4)3 (A = Sr, Ca and Pb) powders firmly establish a series of three ferromagnetic (FM)-like second order phase transitions spanned over the 32-8 K temperature range. Room temperature Mössbauer spectroscopy and associated DFT calculations confirm the existence of three crystallographically non equivalent Fe3+ sites in the three compounds. Mössbauer spectra recorded as a function of temperature in the PbFe3O(PO4)3 compound also establishes the occurrence of two purely magnetic and reversible phase transitions at 32 and 10 K. Diffuse reflectance measurements reveal two broad absorption bands at 1047 and 837 nm, in both PbFe3O(PO4)3 and SrFe3O(PO4)3 powders, with peak cross sections ?10-20 cm2 typical of spin-forbidden and forced electric dipole intraconfigurational transitions.

El Hafid, Hassan; Velázquez, Matias; El Jazouli, Abdelaziz; Wattiaux, Alain; Carlier, Dany; Decourt, Rodolphe; Couzi, Michel; Goldner, Philippe; Delmas, Claude

2014-10-01

392

Structural distortions in Sr3-xAxMO4F (A=Ca, Ba; M=Al, Ga, In) anti-Perovskites and corresponding changes in photoluminescence  

NASA Astrophysics Data System (ADS)

The ordered oxyfluoride family Sr3-xAxMO4F (A=Ca, Ba and M=Al, Ga) has formed the basis of several new inorganic phosphors, and shows great potential for use in phosphor-conversion LED lamp devices. This study examines the correlation between subtle structural changes and photoluminescent behaviour in some of these materials. In order to ascertain whether cation charge compensation has any influence on structure and subsequent photoluminescent behaviour, a comparison was carried out between phases with the nominal compositions Sr2.975Ce0.025AlO4F and Sr2.95Ce0.025Na0.025AlO4F using structural characterisation based upon high-resolution neutron powder diffraction (NPD) data. Additionally, NPD data has been used to elucidate the role of different M cations in these materials, using Sr2.25Ba0.6Eu0.1M0.95In0.05O4-?F1-? (M=Al, Ga) to determine the effect M cation size has on structure and photoluminescent properties.

Sullivan, Eirin; Avdeev, Maxim; Vogt, Thomas

2012-10-01

393

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

394

Effect of sodium substitution on the structural, magnetic and magnetocaloric properties of La0.5Ca0.5MnO3 perovskite manganites  

NASA Astrophysics Data System (ADS)

The perovskite-type La0.5Ca0.5-xNaxMnO3 (0.05?x?0.2) ceramic samples were prepared using the solid-state reaction at high temperature. The X-ray powder diffraction refinement by means of the Rietveld technique reveals that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Lattice parameters and unit cell volume are found to increase with increasing the average A-site ionic radius < rA > . The substitution of calcium by monovalent element (Na) in La0.5Ca0.5MnO3 drives the system from a charge ordering state to a ferromagnetic behaviors observed near room temperature for all our substituted compounds with a Curie temperature TC slightly decreasing from 297 K for x = 0.05 to 278 K for x = 0.2. Magnetic entropy change | ?SM | , deduced from magnetization measurements versus magnetic applied field at several temperatures, shifts to higher values with increasing Na content and reaches 1.14 J/kg K and 3.1 J/kg K for La0.5Ca0.3Na0.2MnO3 under magnetic applied field of 2 T and 7 T respectively.

Mehri, A.; Cheikh-Rouhou Koubaa, W.; Koubaa, M.; Cheikh-Rouhou, A.

2009-11-01

395

Alkaline-alkaline earth fluoride carbonate crystals ABCO3F (A = K, Rb, Cs; B = Ca, Sr, Ba) as nonlinear optical materials.  

PubMed

A new series of alkaline-alkaline earth fluoride carbonates (KSrCO(3)F, RbSrCO(3)F, KCaCO(3)F, RbCaCO(3)F, CsCaCO(3)F, and Cs(3)Ba(4)(CO(3))(3)F(5)) were synthesized by spontaneous crystallization with molten fluxes. Their crystal structures, except for Cs(3)Ba(4)(CO(3))(3)F(5), exhibit the stacking of [AF](?) (A = K, Rb, Cs) and [B(CO(3))](?) (B = Ca, Sr) layers, and the coplanar alignment of [CO(3)] triangles. The results from the UV-vis diffuse reflectance spectroscopy study of the powder samples indicated that the short-wavelength absorption edges were all below 200 nm, except for Cs(3)Ba(4)(CO(3))(3)F(5), which is about 210 nm. Second-harmonic generation (SHG) on polycrystalline samples was measured using the Kurtz and Perry technique, which indicated that these carbonates are all phase-matchable materials in both visible and the UV region, and their measured SHG coefficients were about 3.33, 3.33, 3.61, 1.11, 1.11, and 1.20 times as large as that of d(36) (KDP), respectively. PMID:22035561

Zou, Guohong; Ye, Ning; Huang, Ling; Lin, Xinsong

2011-12-14

396

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

SciTech Connect

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

Mahboub, M.S., E-mail: mmsad1@yahoo.fr [Departement de Physique, Institut des Sciences et Technologie, Centre Universitaire d'El-Oued, B.P. 789 cite chouhada, El-Oued 39000 (Algeria); Laboratoire de Cristallographie, Departement de Physique, Faculte des Sciences Exactes, Universite Mentouri, Constantine 25000 (Algeria); Zeroual, S. [Departement de Physique, Institut des Sciences et Technologie, Centre Universitaire d'El-Oued, B.P. 789 cite chouhada, El-Oued 39000 (Algeria) [Departement de Physique, Institut des Sciences et Technologie, Centre Universitaire d'El-Oued, B.P. 789 cite chouhada, El-Oued 39000 (Algeria); Laboratoire de Cristallographie, Departement de Physique, Faculte des Sciences Exactes, Universite Mentouri, Constantine 25000 (Algeria); Boudjada, A. [Laboratoire de Cristallographie, Departement de Physique, Faculte des Sciences Exactes, Universite Mentouri, Constantine 25000 (Algeria)] [Laboratoire de Cristallographie, Departement de Physique, Faculte des Sciences Exactes, Universite Mentouri, Constantine 25000 (Algeria)