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Now showing items 49 - 64 of 6688

  • Crystal Structute of Complex Oxides in the Nd2O3-MO-Fe2O3 (M =3D Ca,Sr) Systems

    Urusova, A. S.   Vakhromeeva, A. E.   Aksenova, T. V.   Bryuzgina, A. V.   Cherepanov, V. A.  

    The boundaries of homogeneity ranges and structure of solid solutions formed in the quasi-ternary Nd2O3-MO-Fe2O3 (M =3D Ca, Sr) systems at 1373 K in air were determined by the homogenizing annealing and X-ray powder diffraction methods. It was found that two types of solid solutions have formed in the Nd-Ca-Fe-O system: Nd1- xCaxFeO3 - delta (0 <=3D x < 0.35 and 0.95 <=3D x < 1.00) and Ca2- yNdyFeO4 - delta (0.90 <=3D y <=3D 0.95), but four solid solutions in the Nd-Sr-Fe-O system: Nd1- xSrxFeO3 - delta (0 < x <=3D 0.6 and 0.7 <=3D x <=3D 0.9), Sr2 -yNdyFeO4 - delta (0.7 <=3D y <=3D 0.9), Sr3- zNdzFe2O7 - delta (0 < z <=3D 0.4 and 1.8 <=3D z <=3D 1.9) and(.) Sr4 -uNduFe3O10 - delta (0.7 <=3D u <=3D 0.9). The structural parameters of the solid oxides were refined by the full-profile Rietveld analysis. The unit cell parameters versus composition of solid solutions were plotted.
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  • CO2 Adsorption in M-IRMOF-10 (M =3D Mg,Ca,Fe,Cu,Zn,Ge,Sr,Cd,Sn,Ba)

    Borycz, Joshua   Tiana, Davide   Haldoupis, Emmanuel   Sung, Jeffrey C.   Farha, Omar K.   Siepmann, J. Ilja   Gagliardi, Laura  

    Metal organic frameworks (MOFs) have been studied extensively for application in flue gas separation because of their tunability, structural stability, and large surface area. M-IRMOF-10 (M =3D transition metal or main-group atom) is a well-studied series of structures and is composed of saturated tetrahedral Zn4O nodes and dicarboxylate linkers that form a cubit unit cell. We report the results of a computational study on the effects that changing the metal atoms within IRMOF-10 has on the affinity of the material towards CO2 Force fields were parametrized using quantum mechanical calculations to systematically compare the effects of different metal centers on CO2 adsorption at high and low pressure. Two different methods for the determination of partial charges (DDEC and CM5) and force field pararneter sets (TraPPE and UFF) were employed. TraPPE parameters with fitted metal CO2 interactions and CM5 charges resulted in isotherms that were closer to experiment than pure UFF. The results indicate that exchanging the Zn2+ ions in the IRMOF-10 series with metals that have larger ionic radii (Sn2+ and Ba2+ can lead to an increase in CO2 affinity due to the increased exposure of the positive metal charge to the oxygen atoms of CO2 and the increased interaction from the more diffuse electrons.
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  • Blue-emitting phosphor M(2)B(5)O(9)Cl Eu(2+) (M=Sr, Ca) for white LEDs

    Guo, Chongfeng   Xu, Yan   Ding, Xu   Li, Ming   Yu, Jie   Ren, Zhaoyu   Bai, Jintao  

    Eu(2+) doped M(2)B(5)O(9)Cl(M=Ca Sr) phosphors were prepared by a solid-state reaction method Luminescent properties of as-synthesized phosphors were investigated under the excitation of near-ultraviolet (n-UV) light Photoluminescence (PL) spectra revealed a blue emission band and the emission band shifted to a longer wavelength region as Ca(2+) substituted Sr(2+) The photoluminescence excitation (PLE) spectra of M(2)B(5)O(9)Cl Eu(2+) (M=Ca Sr) showed broadband absorptions in the n-UV region Moreover the as-prepared phosphors were also compared with commercial BaMgAl(10)O(17) Eu(2+) (BAM) blue phosphor The present phosphors showed a narrower full width at half-maximum and higher PL intensity than the reference BAM under the n-UV light excitation (C) 2010 Elsevier B V All rights reserved
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  • J. Ca?adell, M. San-Julian: Paediatric bone sarcomas

    Robert U. Ashford  

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  • Photoluminescence property of vanadates M(2)V(2)O(7) (M: Ba, Sr and Ca)

    Nakajima, T.   Isobe, M.   Tsuchiya, T.   Ueda, Y.   Manabe, T.  

    We investigated the photoluminescent properties including the internal quantum efficiency (eta) for the M(2)V(2)O(7) (M: Ba, Sr, and Ca) as a new vanadate phosphor system. In the M(2)V(2)O(7), the broad band emission spectra from 400 to 800 nm derived from the charge transfer transition in the VO(4) tetrahedra were observed. The emission band of these compounds consisted of two maxima Em(1) and Em(2) corresponding to (3)T(1)-(1)A(1) and (3)T(2)-(1)A(1) transitions, respectively. These two maxima red-shifted with the decreasing ionic radius of M-site, as a result, the luminescent colour was varied from green (M: Ba) to yellowish orange (M: Ca). The eta for the Ba(2)V(2)O(7), Sr(2)V(2)O(7) and Ca(2)V(2)O(7) were 25%, 8% and 0.9%, respectively. This enhancement of eta in the M(2)V(2)O(7) could be due to following structural features: the stronger V-V and weaker V-M correlations. (C) 2010 Elsevier B.V. All rights reserved.
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  • Theoretical studies of the paramagnetic perovskites MTaO3 (M =3D Ca,Sr and Ba)

    Ali, Zahid   Khan, Imad   Ahmad, Iftikhar   Khan, M. Salman   Asadabadi, S. Jalali  

    In the present density functional studies, structural, mechanical and magneto-electronic properties of CaTaO3, SrTaO3 and BaTaO3 perovskites have been investigated. The calculated structural parameters by OFF and analytical methods are found consistent with the experiments. The analytically calculated tolerance factors of these compounds as well as their mechanical properties show that they are stable in the cubic phase. Furthermore elastic properties show that these materials are ductile in nature and confirm that BaTaO3 is harder than the rest compounds. The calculated spin dependent magneto-electronic properties reveal the paramagnetic metallic nature of these compounds. The electrical conductivity curve demonstrates significant conductivity above room temperature. On the basis of the presented properties it is expected that these compounds could be efficient electrode materials and need experimental investigations. (C) 2015 Elsevier B.V. All rights reserved.
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  • The GW electronic structure of cubic RbMF3perovskites (M = Be, Mg, Ca, Sr, Ba)

    Syrotyuk, Stepan V.   Shved, Vira M.  

    The electronic energy band spectra of cubic RbMF3 perovskites (M = Be, Mg, Ca, Sr, Ba) have been evaluated within the projector augmented waves (PAW) approach by means of the ABINIT code. The Kohn-Sham single-particle states have been found in the LDA framework. Our parameters of the electron energy bands obtained in the LDA are in good agreement with the published results of other authors. The calculated GW band gaps and dielectric constants are well compared with the available experimental data. The quasiparticle energies and density of states of electrons as well as the dielectric constants were obtained in the approximation GW for the first time.
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  • Stick-like titania precursor route to MTiO3 (M = Sr, Ba, and Ca) polyhedra

    Yang, Jie   Geng, Baoyou   Ye, Yixing   Yu, Xue  

    In this paper, MTiO3 (M = Sr, Ba, and Ca) perovskite polyhedra have been successfully synthesized through a facile hydrothermal route, in which appropriate amounts of metal salts and sodium hydroxide are mixed with the stick-like titania powders to fabricate the products. Cubic SrTiO3, dodecahedral BaTiO3, and cross-shaped CaTiO3 perovskites are finally obtained. The experimental conditions have also been investigated in detail and a feasible growth mechanism is proposed to illustrate the formation of MTiO3 perovskites. Furthermore, we demonstrate the possibility of the method, in which titania nanorods act as the precursor, to produce titanate compounds with a unique morphology. This work not only enriches the synthesis methods of MTiO3 perovskites, but also facilitates the study of potential applications of titanate perovskite compounds.
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  • Luminescent properties of MMgP2O7:Eu3+ (M=Ca, Sr, Ba) phosphor

    Rongfang WANG   Liya ZHOU   Yilin WANG  

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  • Chemistry of the M (M=Fe, Ca, Ba)-Se-H2O Systems at 25 °C

    Nishimura, Tadahisa   Hata, Ryosuke   Hasegawa, Fumihiko  

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  • Endohedral metalloborofullerenes M@B44(M = Ca, Sr, Ba): a computational investigation

    Yang, Le   Jin, Peng   Hou, Qinghua   Li, Lanlan  

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  • Luminescence properties of Eu2+ in M2MgSi2O7 (M = Ca, Sr, and Ba) phosphors

    Kim, T.   Kim, Y.   Kang, S.  

    The photoluminescence properties of alkali-earth magnesium silicates (M2MgSi2O7, M = Ca, Sr, and Ba) doped with Eu2+ were investigated. Solid solutions of BaxSr2-xSi2O7, Ca2MgSi2O7, and Sr2MgSi2O7 were prepared. BaxSr2-xSi2O7 retained a tetragonal crystal structure similar to the structure of the other compounds up to a stoichiometry of x = 1.6, which enabled a systematic study of the common structure. Monoclinic Ba2MgSi2O7 was prepared, and the luminescence properties were compared with those of other samples. The emission and excitation spectra of tetragonal M2MgSi2O7 (M = Ca, Sr, and Ba) changed as a function of the covalency, site symmetry, and crystal field strength. The luminescence properties showed excellent agreement with theoretical predictions based on these factors. The Stokes shift differentiated the emission behaviors of the tetragonal and monoclinic structures.
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  • New self-activated eulytite-type compounds of M7Zr(PO4)6 (M = Ca, Sr, Ba)

    Lin Qina   Donglei Weib   Yanlin Huanga   Sun Il Kimb   Young Moon Yuc   Hyo Jin Seob  

    Eulytite-type orthophosphates M7Zr(PO4)6 (M = Ca, Sr, Ba) were prepared by conventional high temperature solid-state reaction. Sr7Zr(PO4)6 and Ba7Zr(PO4)6 crystallize in the pure eulytite-type phase with cubic space group (). The impurity phase β-Ca3(PO4)2 was inevitably coexisted with the Ca7Zr(PO4)6 phase. The luminescence properties are investigated by UV-VUV excitation and emission spectroscopy and X-ray-excited luminescence (XEL) spectroscopy. The broad excitation and emission bands are observed due to the charge transfer transition from Zr4+ to O2?/sup> in M7Zr(PO4)6 (M = Ca, Sr, Ba) eulytite. The characteristics of the phosphors including the luminescence mechanism are explained by Stokes shift, decay curves, and CIE color coordinates. The Sr7Zr(PO4)3 and Ba7Zr(PO4)3 phosphors exhibit unusual spectral features with the emission bands at 470 and 480 nm, respectively. The weak luminescence centered at 495 nm is observed in the Ca7Zr(PO4)6 eulytite with lifetime of 4.67 μs. The unusual self-activated luminescence is discussed on the base of the crystal structure of eulytite.
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  • Luminescent Afterglow Behavior in the M2Si5N8: Eu Family (M = Ca, Sr, Ba)

    Van den Eeckhout, Koen   Smet, Philippe F.   Poelman, Dirk  

    Persistent luminescent materials are able to emit light for hours after being excited. The majority of persistent phosphors emit in the blue or green region of the visible spectrum. Orange- or red-emitting phosphors, strongly desired for emergency signage and medical imaging, are scarce. We prepared the nitrido-silicates Ca(2)Si(5)N(8):Eu (orange), Sr(2)Si(5)N(8):Eu (reddish), Ba(2)Si(5)N(8):Eu (yellowish orange), and their rare-earth codoped variants (R = Nd, Dy, Sm, Tm) through a solid state reaction, and investigated their luminescence and afterglow properties. In this paper, we describe how the persistent luminescence is affected by the type of codopant and the choice and ratio of the starting products. All the materials exhibit some form of persistent luminescence, but for Sr(2)Si(5)N(8):Eu, R this is very weak. In Ba(2)Si(5)N(8):Eu the afterglow remains visible for about 400 s, and Ca(2)Si(5)N(8):Eu, Tm shows the brightest and longest afterglow, lasting about 2,500 s. For optimal persistent luminescence, the dopant and codopant should be added in their fluoride form, in concentrations below 1 mol%. A Ca(3)N(2) deficiency of about 5% triples the afterglow intensity. Our results show that Ba(2)Si(5)N(8):Eu(,R) and Ca(2)Si(5)N(8):Eu(,R) are promising persistent phosphors for applications requiring orange or red light.
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  • The GW electronic structure of cubic RbMF3 perovskites (M =3D Be,Mg,Ca,Sr,Ba)

    Syrotyuk, Stepan V.   Shved, Vira M.  

    The electronic energy band spectra of cubic RbMF3 perovskites (M =3D Be, Mg, Ca, Sr, Ba) have been evaluated within the projector augmented waves (PAW) approach by means of the ABINIT code. The Kohn-Sham single-particle states have been found in the LDA framework. Our parameters of the electron energy bands obtained in the LDA are in good agreement with the published results of other authors. The calculated GW band gaps and dielectric constants are well compared with the available experimental data. The quasiparticle energies and density of states of electrons as well as the dielectric constants were obtained in the approximation GW for the first time.
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  • Environmental-friendly yellow pigment based on Tb and M (M=Ca or Ba) co-doped Y2O3

    De la Luz, Verónica   Prades, Marta   Beltrán, Héctor   Cordoncillo, Eloisa  

    A yellow inorganic ceramic pigment with general formula Y 1.86-xM xTb 0.14O 3-x/2 (M=Ca and/or Zn) with x=0.06, 0.32 and 0.64 were synthesized by a modified Pechini method. XRD, SEM and HRTEM/EDX analysis showed the formation of solid solution at 1300degC when x=0.06 and 0.32. The best b* yellow coordinates were obtained for Ca and Zn co-doped Y 1.86Tb 0.14O 3 samples. The intensity of the yellow colour in the samples is related to the presence of Tb 4+ ions. Samples with higher concentration of Tb 4+ ions lead to a better yellow colour. The chemical stability of these pigments was determinate in an industrial glaze. The glazing tests indicated that the powder samples with x=0.06 and 0.32 fired at 1300degC were stable in the glaze. These results make it a potential candidate for environmental friendly yellow ceramic pigment to be used in applications such as pigment for glazes or inkjet printers. [All rights reserved Elsevier].
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