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Now showing items 81 - 96 of 6688

  • Electrical Properties of (CeO2)0.9(MO)0.1 (M=Ca or Mg) Solid Electrolyte System

    Montalvo-Lozano, R. A.   Padmasree, K. P.   Fuentes, A. F.   Montemayor, S. M.  

    Electrical conductivity studies of alkaline earth oxides doped ceria Ce0.9M0.1O2-delta, (where M=Ca and Mg) is reported in this work. The samples were prepared at room temperature by mechanical milling. X-ray diffraction patterns confirm the cubic fluorite structure. Scanning electron micrographs of MgO doped sample shows the presence of the segregation of Mg2+ which results a negative effect on the electric properties of the MgO doped sample. Frequency dependence of ac conductivity (sigma(ac)) of these oxide ion conductors showed a remarkably different behavior from that of the cation ones. As temperature increases above 350 degrees C, ac conductivity sigma(ac) in the low frequency range was strongly influenced by space charge polarization at grain boundary and the high frequency plateau agreed with the bulk conductivity of the system. Bulk and grain boundary conductivity studies show that CaO doped ceria exhibit better electrical properties compared to MgO doped sample.
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  • Dy3+emission in M5(PO4)3F (M = Ca, Ba) phosphor

    K. N. Shinde; I. M. Nagpure; S. J. Dhoble; S. V. Godbole; M. K. Bhide  

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  • Reversible Hydrogen Storage in LiBH4?MH2 (M = Ce, Ca) Composites

    Jin, Seon-Ah   Lee, Young-Su   Shim, Jae-Hyeok   Cho, Young Whan  

    Hydrogen desorption and absorption properties of two destabilized systems, 6LiBH 4 + CeH 2 + 0.2TiCl 3 (Ce system) and 6UBH 4 + CaH 2 + 0.2TiCl 3 (Ca system), have been characterized. The theoretical hydrogen capacity is 7.39 and 11.67 wt % for the Ce and Ca systems, respectively. Both systems follow the thermodynamically predicted dehydrogenation reaction path, forming LiH and metal hexaborides (MB 6) as the dehydrogenated products, which is confirmed by X-ray diffraction data. After hydrogenation at 623 K (Ce system) or 673 K (Ca system) under 100 bar H 2 pressure for 20 h, LiH + MB 6 was converted back to the initial reactants, LiBFL, + MH 2. The amount of H 2 released during the first and the second dehydrogenation proves that the first dehydrogenation-hydrogenation cycle is fully reversible. The temperature required to achieve the reversibility is lower in the case of the Ce system, in agreement with our thermodynamic calculation. Our study is the first report of reversible hydrogen storage in 6LiBH 4 + CeH 2; this composite is one of the few destabilized systems shown to be fully reversible at this relatively low temperature range with a reasonably high hydrogen capacity.
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  • Dy3+emission in M5(PO4)3F (M = Ca, Ba) phosphor

    K. N. Shinde   I. M. Nagpure   S. J. Dhoble   S. V. Godbole   M. K. Bhide  

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  • Luminescence properties of MAl12O19:Mn4+ (M = Ca, Sr, Ba) for UV LEDs

    KANG, Hyun Goo   PARK, Joung Kyu   KIM, Chang Hae   CHOI, Seung Chul  

    The luminescence properties of Mn(4+)-aCtivated MAl(12)O(19) (M = Ca, Sr, Ba) were studied. The Mn(4+)-activated MAl(12)O(19) compounds were synthesized in an air atmosphere for oxidation from Mn(2+) to Mn(4+)center dot Mn(4+)-activated CaAl(12)O(19) and SrAl(12)O(19) materials could be excited under the UV region but Mn(4+)-activated BaAl(12)O(19) materials could not be efficiently emitted under the UV region. The luminescence properties of the Ba-containing compounds deviated from the other compounds, which was attributed to different co-ordinations of the activator ions. Mn(4+)-activated CaAl(12)O(19) and SrAl(12)O(19) compounds exhibited a main emission peak at 658 nm because of the (2)E ->(4)A(2) transition of the Mn(4+) ion. The CaAl(12)O(19) and SrAl(12)O(19) phosphors had a hexagonal structure. The highest crystallinity and luminescent intensity of these phosphors were obtained at 1873 K for 3 h. (C) 2009 The Ceramic Society of Japan. All rights reserved.
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  • Luminescence properties of MAl12O19:Mn4+ (M = Ca, Sr, Ba) for UV LEDs

    KANG, Hyun Goo; PARK, Joung Kyu; KIM, Chang Hae; CHOI, Seung Chul  

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  • Photoluminescence properties of M2MgSi2O7 : Re2+(M = Ba, Sr, Ca)

    He, Dawei   Shi, Yanning   Zhou, Dan   Hou, Tao  

    Excitation spectrum of M2MgSiO7:Eu2+ was composed of two broad bands centered around 3 10 and 395 nm, respectively, in which the latter belonged to 4f -> 5d transitions of Eu2+. It was found that the introduction of Zn2+ into Ba2MgSi2O7:Eu2+ effectively increased its emission intensity without changing the position of emission peak. A further Eu2+ and Ce3+ co-doped pyrosilicate phosphor was found to be an efficient phosphor excited by long UV light and emitted in blue around 438 nm, which was originated from the 5d to 4f transition of Ce3+ ion in MgMgSi2O7:Eu2+, Ce3+. (c) 2006 Elsevier B.V. All rights reserved.
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  • Synthesis and dehydrogenation of M(AlH4)2 (M = Mg, Ca)

    K. Komiya   N. Morisaku   Y. Shinzato   K. Ikeda   S. Orimo   Y. Ohki   K. Tatsumi   H. Yukawa   M. Morinaga  

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  • X-ray diffraction study of ErMFe(2)O(5.5) (M = Ca, Sr, Ba) double ferrites

    Kasenov, B. K.   Mustafin, E. S.   Akubaeva, M. A.   Edil'baeva, S. T.   Sergazina, S. M.   Erkasov, R. Sh.   Zhumadilov, E. K.  

    Double ferrites ErCaFe(2)O(5.5), ErSrFe(2)O(5.5), and ErBaFe(2)O(5.5) were synthesized by solid-state reactions from erbium and iron(III) oxides and calcium, strontium, and barium carbonates. The compounds were found to crystallize in the orthorhombic system. Their unit cell parameters were determined by X-ray powder diffraction; their densities were measured.
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  • Cancer du sein métastatiques : intérêt du CA 15-3

    T. Mahfoud   A. Debbagh   M.R. Khmamouche   Y. Moussaid   R. Aassab   H. Errihani   M. Ichou  

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  • Photoluminescence characteristics of Ce and Eu activated MBPO5 (M= Sr, Ca) phosphors

    Kharabe, V.R.   Oza, Abha H.   Dhoble, S.J.  

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  • Luminescence properties of silicate apatite phosphors M2La8Si6O26:Eu (M = Mg, Ca, Sr)

    Khaidukov, N.M.   Kirm, M.   Feldbach, E.   M?gi, H.   Nagirnyi, V.   T?ldsepp, E.   Vielhauer, S.   Jüstel, T.   Jansen, T.   Makhov, V.N.  

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  • Magnetic behaviour of the MTbF(6) fluoroterbates (M=Cd, Ca, Sr, (alpha/beta)-Ba)

    Josse, M.   El-Ghozzi, M.   Avignant, D.   Andre, G.   Bouree, F.   Isnard, O.  

    Neutron powder diffraction has been performed on the MTbF(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(6)](2-) chains and only differs by the chains relative orientations. Thus this series represents a valuable opportunity to evaluate the Tb(4+)-Tb(4+) magnetic interactions. All the compounds displayed antiferromagnetic order (T(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(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(6) and beta-BaTbF(6) magnetic structures were determined, together with the metamagnetic behaviour of beta-BaTbF(6) as a function of an external magnetic field. A tentative phase diagram is then given for beta-BaTbF(6). Advantage was taken of the polymorphism of the BaTbF(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(6), and that these interactions may also rule the magnetic behaviour of the other MTbF(6) (M=Ca, Sr, Cd) tetravalent terbium fluorides. (C) 2011 Elsevier Inc. All rights reserved.
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  • Reduction of Eu3+ to Eu2+ in MAl2Si2O8 (M=Ca, Sr, Ba) in air condition

    Cuimiao Zhang   Jun Yang   Cuikun Lin   Chunxia Li   Jun Lin  

    In general, the reduction of Eu 3+ to Eu 2+ in solids needs an annealing process in a reducing atmosphere. In this paper, it is of great interest and importance to find that the reduction of Eu 3+ to Eu 2+ can be realized in a series of alkaline-earth metal aluminum silicates MAl 2Si 2O 8 (M=Ca, Sr, Ba) just in air condition. The Eu 2+-doped MAl 2Si 2O 8 (M=Ca, Sr, Ba) powder samples were prepared in air atmosphere by Pechini-type sol-gel process. It was found that the strong band emissions of 4f 65d 1-4f 7 from Eu 2+ were observed at 417, 404 and 373 nm in air-annealed CaAl 2Si 2O 8, SrAl 2Si 2O 8 and BaAl 2Si 2O 8, respectively, under ultraviolet excitation although the Eu 3+ precursors were employed. In addition, under low-voltage electron beam excitation, Eu 2+-doped MAl 2Si 2O 8 also shows strong blue or ultraviolet emission corresponding to 4f 65d 1-4f 7 transition. The reduction mechanism from Eu 3+ to Eu 2+ in these compounds has been discussed in detail. [All rights reserved Elsevier].
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  • Study on Red Long-Time Luminescent Material Y2O2S:Eu, M (M = Mg, Ca, Sr, Ba)

    Chen Yongjie   Qiu Guanming   Geng Xiujuan   Yang Ying   Shi Shuang   Wang Hui   Zhang Zhongqiu  

    The red long-time luminescent material Y(2)O(2)S:Eu(3+), M (M = Mg, Ca, Sr, Ba) was prepared by high temperature solid-state method. The XRD result of the sample showed that the crystal phase was Y(2)O(2)S, which belong to hexagonal system, and no new crystal phase were by doping different amount of Mg, Ca, Sr, Ba. The excitation spectrum was a broad band within 200 similar to 400 nm region, the characteristic peaks of emission spectrum were located at 583, 595, 597, 617, 627, 707 nm. There was no marked change in excitation spectra, emission spectra and maximum of their wavelengths of the luminescent materials by doping with different ions. The luminescent intensity of the phosphors were stronger when the concentration of doping ions was Mg/Y = 6%, Ca/Y = 4%, Sr/Y = 8%, Ba/Y = 2.5 %, respectively. Its sequence of luminescent intensity from high to low is Sr > Ba > Mg > Ca.
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  • Electronic Structure and Bonding Situation in M2O2 (M =3D Be,Mg,Ca) Rhombic Clusters

    Li, Wan-Lu   Lu, Jun-Bo   Zhao, Lili   Ponec, Robert   Cooper, David L.   Li, Jun   Frenking, Gernot  

    Quantum chemical calculations using ab initio methods at the CCSD(T) level and density functional theory have been carried out for the title molecules. The electronic structures of the molecules were analyzed with a variety of charge and energy decomposition methods. The equilibrium geometries of the M2O2 rhombic clusters exhibit very short distances between the transannular metal atoms M =3D Be, Mg, Ca. The calculated distances are close to standard values between double and triple bonds, but there are no chemical M-M bonds. The metal atoms M carry large positive partial charges, which are even bigger than in diatomic MO. The valence electrons of M are essentially shifted toward oxygen in M2O2, which makes it possible that there is practically no electronic charge in the region between the metal atoms. The bond dissociation energies for fragmentation of M2O2 into two metal oxides MO are very large. The metal-oxide bonds in the rhombic clusters are shorter and stronger than in diatomic MO. A detailed analysis of the electronic structure suggests that there is no significant direct M M interaction in the M2O2 rhombic clusters, albeit weak three-center M-O-M bonding.
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