| 1. |
- El Hachmi, Abdelhadi, et al.
(författare)
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Synthesis and Rietveld refinements of new ceramics Sr2CaFe2WO9 and Sr2PbFe2TeO9 perovskites
- 2018
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Ingår i: Powder Diffraction. - : J C P D S-INT CENTRE DIFFRACTION DATA. - 0885-7156 .- 1945-7413. ; 33:2, s. 134-140
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Tidskriftsartikel (refereegranskat)abstract
- Ceramics of Sr2CaFe2WO9 and Sr2PbFe2TeO9 double perovskites have been prepared in polycrystalline form by solid-state technique, in the air. The crystalline structure was analyzed using X-ray powder diffraction (XRPD) at room temperature. Rietveld analysis of XRPD) patterns show that both compounds adopt a tetragonal structure with space group I4/m, with unit cell parameters a = 5.5453(1) angstrom, c = 7.8389(1) angstrom for Sr(2)CaFc(2)WO(9), and a = 5.5994(15) angstrom, c = 7.8979(30) angstrom for Sr2PbFe2TeO9. A certain degree of anti-site disordering of W and/or Te and Fe on the B -sites have been detected, indicating the presence of a partial amount of W and/or Te at Fe positions and vice versa.
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| 2. |
- Manoun, Bouchaib, et al.
(författare)
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X-ray diffraction and Raman spectroscopy studies of temperature and composition induced phase transitions in Ba2-xSrxMWO6 (M = Ni, Co and 0 <= x <= 2) double perovskite oxides
- 2013
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 1045, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction and Raman spectroscopy studies of Sr doped double perovskites compound Ba2-xSrxMWO6 with (M = Ni, Co and 0 <= x <= 2) were investigated. The samples show a transition from cubic to tetragonal phase as a function of composition while increasing strontium amount; both Rietveld refinements and Raman studies showed that this transition occurs between x = 1.2 and 1.4. Furthermore, increasing temperature for the tetragonal compositions (1.4 <= x <= 2), manifest the tetragonal to cubic phase transition. For this series, the transition from tetragonal (I4/m)/to cubic (Fm-3m) shows considerable changes in the composition and temperature dependence of the modes: all the Raman modes show a linear behavior when temperature is increased, then the slope change dramatically indicating the symmetry change from tetragonal to cubic. To better view this phase transition, the full width at half maximum (FWHM) temperature dependence of the most intense modes were studied; by this study, we have obtained a sensitive guide to the onset of the phase transition. A large increase of the FWHM with increasing temperature is observed for all modes in the spectrum, clear transitional effects were observed: the width behaves in a linear way as a function of temperature; when the temperature reached the transition temperature, a drop in the width of this mode was observed.
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| 3. |
- Tamraoui, Y., et al.
(författare)
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Temperature and composition induced phase transitions in Sr2-xCa1+xTeO6 (0 <= x <= 2) double perovskite oxides
- 2017
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 1131, s. 103-113
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Tidskriftsartikel (refereegranskat)abstract
- Structures of Sr2-xCa1+xTeO6 double perovskites have been studied by the profile analysis of X-ray diffraction data and Raman spectroscopy at room temperature. This series adopts a monoclinic symmetry for the compositions (0 <= x <= 0.5) with P2(1)/n as space group and a triclinic system with P (1) over bar space group for the compositions (0.5 < x <= 2). These results were confirmed by the observed tolerance factor calculated from the distances obtained from the Rietveld refinements which indicates that the true tilt system for the compositions range (0.5 < x <= 2) is the triclinic tilt system. Clear changes in the Raman modes centered at 600, 610 and 620 cm(-1) and the FWHM of O-Te-O bending vibrations, centered at 738 cm(-1) confirmed that the triclinic symmetry takes place between the compositions x = 0.5 and x = 1. Furthermore, Raman spectroscopy studies at high temperature were done for Ca3TeO6. For this compound, considerable changes in the temperature dependence of the modes were well illustrated.
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| 4. |
- Tamraoui, Y., et al.
(författare)
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X-ray diffraction and Raman spectroscopy studies of temperature and composition induced phase transitions in Ba2-xSrxMgTeO6 (0 <= x <= 2)
- 2014
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 603, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction and Raman spectroscopy studies of Sr-substituted double perovskite compounds Ba2-xSrxMgTeO6 with (0 <= x <= 2) were carried out. At room temperature, both Rietveld refinements and Raman studies showed that two phase transitions occurred as a function of increased strontium content; from cubic to tetragonal structure, at x similar to 1.5(1), and from the tetragonal to monoclinic structure at x similar to 1.9(1). Furthermore, upon temperature increase up to 430 degrees C, the monoclinic and tetragonal perovskites manifest transformations to the tetragonal and cubic symmetries, and to the cubic symmetry, respectively. For this series, the transitions show considerable changes in the compositional and temperature dependencies of the modes, the spectral positions of which exhibit a linear behavior. The symmetry transformations between the encountered three crystal systems is revealed by significant changes of the slopes. (C) 2014 Elsevier B. V. All rights reserved.
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