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Now showing items 145 - 160 of 6688

  • Electron-phonon interaction in ternary silicides MGaSi (M = Ca, Sr and Ba)

    Huang, GQ   Chen, LF  

    The electron-phonon (EP) interaction in ternary silicides MGaSi with M = Ca, Sr and Ba are calculated using the full potential, density-functional-based method. A striking feature of the phonon spectra is the existence of very soft "B-1g" mode, which is strong anharmonic and plays an important role in superconductivity of the MGaSi compounds. The superconducting transition temperatures T-c in these compounds have been evaluated. It is found that the variation trend in T-c can be explained from the strength of the electron-phonon coupling.
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  • Spectral analysis of Eu(3+):B(2)O(3)-Al(2)O(3)-MF(2) (M = Zn, Ca, Pb) glasses

    Azeem, P. Abdul   Kalidasan, M.   Gopal, K. Rama   Reddy, R. R.  

    The influence of glass composition on the optical properties of Eu(3+)-doped borate glasses modified with Zn(2+), Ca(2+) and Pb(2+) cations has been investigated. These glasses have been prepared by melt quenching technique and characterized through optical absorption, photoluminescence and decay times. An intense red luminescence is observed from the (5)D(0) emitting level of Eu(3+) ions in these glasses. The relative luminescence intensity ratio of (5)D(0) -> (7)F(2) to (5)D(0) -> (7)F(1) transitions has been evaluated to estimate the local site symmetry around the Eu(3+) ions. Judd-Ofelt parameters have been evaluated from the absorption spectra. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross-sections for the (5)D(0) -> (7)F(1) (J = 0, 1, 2, 3 and 4) transitions. Decay curves of the (5)D(0) level of Eu(3+) ions in these three glass systems have been measured by monitoring the (5)D(0) -> (7)F(2) transition at room temperature. (C) 2008 Elsevier B.V. All rights reserved.
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  • M2Ba2Sn6 (M =Yb, Ca): Metallic zintl phases with a novel tin chain substructure

    Ge, Ming-Hui   Corbett, John D.  

    The compounds M2Ba2Sn6 (M = Yb, Ca) have been synthesized by solid-state reactions in welded Ta tubes at high temperature. Their structures were determined by single-crystal X-ray diffraction studies to be orthorhombic; space group Cmca (No. 64); Z = 8; a = 15.871(3), 15.912 (3) angstrom; b = 9.387(2), 9.497(2) angstrom; c = 17.212(3), 17.184(3) angstrom; and V = 2564.3(9), 2597.0(9) A(3), respectively. These contain infinite tin chains along constructed from butterflylike 3-bonded Sn tetramers interconnected by pairs of 2-bonded Sn. The chains are further interconnected into corrugated layers by somewhat longer Sn-Sn bonds along . The compounds with the chains alone would be Zintl phases, but the interchain bonding makes them formally one-electron rich per formula unit. The electronic structures calculated by extended HUckel and TB-LMTO-ASA methods indicate that these compounds are metallic but with a deep pseudogap at the Fermi level. States that bind the extra electrons lie just below E-F and involve important Yb(Ca)-Sn contributions. The origin of metallic Zintl phases is briefly discussed.
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  • Dy3+-activated NaM4 (VO4)3 (M = Ca, Ba, Sr) phosphor for near-UV solid-state lighting

    Roshani Singh   S. J. Dhoble  

    ABSTRACT We report the photoluminescence characterization of Dy3+-activated NaM4(VO4)3 (M = Ca, Ba, Sr) phosphors prepared by a solid-state method. The synthesis was confirmed by X-ray diffraction (XRD) characterization and photoluminescence (PL) emission results showed sharp blue and yellow bands for NaM4(VO4)3 (M = Ca, Ba, Sr):Dy3+ phosphors at the excitation wavelength of 323 nm, which is near-UV excitation. Thus, these phosphors could be applicable for near-UV excited solid-state lighting devices. Copyright © 2011 John Wiley & Sons, Ltd.
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  • ChemInform Abstract: The Periodate-Based Double Perovskites M2NaIO6 (M: Ca, Sr, and Ba).

    Frank Kubel   Nicole Wandl   Mariana Pantazi   Vincenza D'Anna and Hans Hagemann  

    The title compounds are prepared from mixtures of MF2 (M: Ca, Sr, Ba) and NaI (Pt crucible, 650 °C, 18 h, yield given in g).
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  • Potential high-energy pentazolides: HB(N5)3M1~2(N5)3BH (M = Be, Mg, Ca, Zn, and Cd)

    Yu Xu   Fengjuan Zhao   Yan Zhang   Yulong Gu   Tongxiang Liu   Jian Cui  

    HB(N 5) 3M 1~2(N 5) 3BH (M = Be, Mg, Ca, Zn, and Cd) have been investigated as potential high-energy density materials in this article by means of density functional theory. They are all of high-energy content and show kinetic stability as to the breakup of N 5 ring, especially HB(N 5) 3Mg(N 5) 3BH. The M-N bondings in the mononuclear compounds are stronger than those in the corresponding dinuclear ones, except in the Be analogues. Furthermore, except HB(N 5) 3Zn 2(N 5) 3BH, all the dinuclear compounds are shown to be energetically stable with respect to disproportionation. copy 2009 Wiley Periodicals, Inc.
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  • Ferroelectric properties of MBi4Ti4O15 (M=Sr, Pb, Ca) thin films

    Xianyu, WX   Won, TY   Lee, WI  

    Among the ferroelectric bismuth layered perovskites belonging to Aurivillius family, the MBi4Ti4O15 (MBT15, M = Sr, Ca, Pb) thin films have been fabricated by a chemical solution deposition technique, and their structures and ferroelectric properties were investigated in this work. The SrBi4Ti4O15 (SBT15) film fabricated on IrO2 presented the highest remanent polarization (P-r) among the films in this series. It demonstrated a saturated hysteresis loop at 5 V with P-r of 19 muC/cm(2) and coercive field (P-s) of 116 kV/cm. The PbBi4Ti4O15 (PBT15) thin films were selectively controlled in c-axis and off-c-axis orientation on Pt layer by adjusting the annealing condition. The off-c-axis oriented PbBi4Ti4O15 film demonstrated considerably higher P-r (8.7 muC/cm(2)) than that of c-axis oriented film (3.7 muC/cm(2)). Regardless of grain orientation, however, PBT15 films were not fatigued up to 10(10) cycles under 9V application. The CaBi4Ti4O15 (CBT15) thin films were also produced on Pt and IrO2 electrode, respectively, by controlling the annealing condition. The CBT15 film on IrO2 presented higher P-r (similar to10.8 muC/cm(2)) than that of film (similar to6.7 muC/cm(2)) on Pt.
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  • Tilting structures in inverse perovskites,M(3)TtO (M =3D Ca,Sr,Ba,Eu; Tt =3D Si,Ge,Sn,Pb)

    Nuss, Juergen   Muehle, Claus   Hayama, Kyouhei   Abdolazimi, Vahideh   Takagi, Hidenori  

    Single-crystal X-ray diffraction experiments were performed for a series of inverse perovskites, M3TtO (M =3D Ca, Sr, Ba, Eu; Tt =3D tetrel element: Si, Ge, Sn, Pb) in the temperature range 500-50 K. For Tt =3D Sn, Pb, they crystallize as an 'ideal' perovskite-type structure (Pm (3) over barm, cP5); however, all of them show distinct anisotropies of the displacement ellipsoids of the M atoms at room temperature. This behavior vanishes on cooling for M =3D Ca, Sr, Eu, and the structures can be regarded as 'ideal' cubic perovskites at 50 K. The anisotropies of the displacement ellipsoids are much more enhanced in the case of the Ba compounds. Finally, their structures undergo a phase transition at similar to 150 K. They change from cubic to orthorhombic (Ibmm, oI20) upon cooling, with slightly tilted OBa6 octahedra, and bonding angles O-Ba-O similar or equal to 174 degrees (100 K). For the larger Ba2+ cations, the structural changes are in agreement with smaller tolerance factors (t) as defined by Goldschmidt. Similar structural behavior is observed for Ca(3)TtO. Smaller Tt(4-) anions (Si, Ge) introduce reduced tolerance factors. Both compounds Ca3SiO and Ca3GeO with cubic structures at 500 K, change into orthorhombic (Ibmm) at room temperature. Whereby, Ca3SiO is the only representative within the M(3)TtO family where three polymorphs can be found within the temperature range 500-50 K: Pm (3) over barm-Ibmm-Pbnm. They show tiny differences in the tilting of the OCa6 octahedra, expressed by O-Ca-O bond angles of 180 degrees (500 K), similar to 174 degrees (295 K) and 170 degrees (100 K). For larger M (Sr, Eu, Ba), together with smaller Tt (Si, Ge) atoms, pronounced tilting of the OM6 octahedra, and bonding angles of O-M-O similar or equal to 160 degrees (295 K) are observed. They crystallize in the anti-GdFeO3 type of structure (Pbnm, oP20), and no phase transitions occur between 500 and 50 K. The observed phase transitions are all accompanied by multiple twinning, in terms of pseudo-merohedry or reticular pseudo-merohedry.
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  • Physicochemical properties of La(Ba,M)CuFeO5+δ(M = Sr, Ca, Mg) solid solutions

    A. I. Klyndyuk   E. A. Chizhova  

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  • Polymer-MTiO3 (M =3D Ca,Sr,Ba) composites as facile and scalable supercapacitor separators

    Alvarez-Sanchez, Christian O.   Lasalde-Ramirez, Jose A.   Ortiz-Quiles, Edwin O.   Masso-Ferret, Roberto   Nicolau, Eduardo  

    The quantum of research in the area of supercapacitors is typically focused on the electrode materials. As such, there are many opportunities for the optimization of the other components, such as the separators, to further increase the power, efficiency, and longevity of supercapacitors. To contribute to this field of research, we present an innovative alternative for the fabrication of separators; using polymer/ceramic composites (PCC) based on polyvinylidene fluoride (PVDF) and polypropylene (PPG) mixed with different alkaline earth metal-based titanates (eg barium, calcium, and strontium). The PCC separators were prepared via phase inversion precipitation technique, a feasible and scalable method for the fabrication of these composites. Different additives were used to modulate the porosity and thus, improve the charge transfer rates. Then, a heating process ensured a uniform organization of the composites. Furthermore, we tested the effect of thermally annealing the ceramics on the separators' performance. The precursor materials and the PCC's were extensively characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical, mechanical, and dielectric properties of the PCC's were measured and compared to common commercial separators used today. Results suggest that thermal treatment improves tensile strength of the separators by at least ca. 60% without compromising the similar electrochemical profile to the commercial separators (44.52 +/- 2.82 omega vs 67.65 +/- 29.01 omega). Lastly, all of the fabricated PCC's showed higher dielectric constants (4.52 in average for the as prepared separators and 2.99 for the heated PCC's) than the polymer based commercial separators (2.2).
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  • Lumineszenz der Eu2+-dotierten Perowskite CsMBr3 (M = Mg, Ca, Sr)

    Patrick Larsen   Claudia Wickleder  

    No abstract is available for this article.
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  • Open-Domain Question Answering from Large Text Collectionby M. Pa?ca

    Review by: Jochen L. Leidner  

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  • Microwave dielectric properties of alkaline earth orthosilicates M2SiO4 (M=Ba, Sr, Ca)

    Tony Joseph   Mailadil Thomas Sebastian  

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  • Metal-Metal and Metal-Ligand Bonds in (eta(5)-C5H5)(2)M-2 (M = Be, Mg, Ca, Ni, Cu, Zn)

    Li, Xiaoyan   Huo, Suhong   Zeng, Yanli   Sun, Zheng   Zheng, Shijun   Meng, Lingpeng  

    The metal-metal and metal-ligand bonds in a series of binuclear metallocenes (eta(5)-C5H5)(2)M-2 (M = Be, Mg, Ca, Ni, Cu, Zn) have been characterized within the framework of the atoms in molecules (AIM) theory, electron localization function (ELF), and molecular formation density difference (MFDD). The calculated results show that the metal-metal bonds in the binuclear main-group-metal metallocenes are different from those in binuclear transition-metal metallocenes. In binuclear main-group-metal metallocenes, the metal-metal bonds are linked by two metal-"non-nuclear attractor (NNA)" bonds, while such NNAs do not exist in the binuclear transition-metal metallocenes. In addition, the transition-metal-transition-metal bonds are more delocalized than those of the main-group-metal-main-group-metal bonds. The main-group-metal-main-group-metal bonds show covalent characteristics while the transition-metal-transition-metal bonds display "closed shell" ionic characteristics. The metal-ligand bonds are mainly ionic. There are both sigma and pi characteristics in the metal-ligand interactions, and the pi interaction is predominant.
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  • Ab initio study of ground state MH2, HMHe+ and MHe22+, M = Mg, Ca RID B-6515-2011

    Page, Alister J.   von Nagy-Felsobuki, Ellak I.  

    The ground states of MH2, HMHe+ and MHe22+ (M = Mg, Ca) have been investigated using relativistically-corrected CCSD(T), IC-MRCI and IC-MRCI+Q, in conjunction with ANO-RCC (Mg, Ca) and aug-cc-pVQZ (H, He) basis sets. The ground states of all magnesium species are predicted to be linear, in agreement with predicted trends. Conversely, HCaHe+ and CaHe22+ were determined to be quasi-linear species, with linear-inversion barriers of ca. 115 and 3 cm(-1), respectively. For CaH2, a stationary point on the molecular potential energy surface corresponding to a non-linear equilibrium structure was not observed. Trends in bonding, dissociative potential well-depths and spectroscopic constants for these species have been considered with regards to isoelectronic and isovalent reasoning. These trends are consistent with helium and hydrogen forming electrostatic and covalent bonds with the metal ion, respectively.
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  • Br? anion-conducting properties in La1?xMxOBr1?x solid (M=Ca, Sr)

    Yasuhiro Kato   Nobuhito Imanaka  

    A new Br - anion-conducting solid electrolyte with a low solubility in water and a high thermal stability at elevated temperatures was developed by selecting lanthanum oxybromide (LaOBr) as a mother solid electrolyte phase. By the partial substitution of La 3+ site in LaOBr with divalent Ca 2+ or Sr 2+ , the bromide anion conductivity was greatly enhanced, and the highest Br - ion conductivity of 1.9times10 -3 and 1.2times10 -4 Smiddotcm -1 was obtained at 873 K for La 0.9Sr 0.1OBr 0.9 and La 0.9 Ca 0.1OBr 0.9, respectively. The Br - anion conduction in La 0.9M 0.1OBr 0.9 (M=Ca, Sr) was directly demonstrated by DC electrolysis
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