| 1. |
- Manoun, B., et al.
(författare)
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High temperature induced phase transitions in Sr2ZnWO6 and Sr2CoWO6 double perovskite oxides : Raman spectroscopy as a tool
- 2012
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 1029, s. 81-85
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report high-temperature (up to 550 °C) Raman spectroscopy of phase transitions in Sr2MWO6 (M = Zn, Co) double perovskite oxides. For Sr2ZnWO6 modes centered at 137 cm−1, 152 cm−1, merge around 80 °C. The same behavior was observed for the 436 cm−1 and 447 cm−1 modes. The mode centered at 854 cm−1 shows a change in the slope at the same temperature, thus indicating a first order phase transition from the monoclinic (P21/n) to tetragonal (I4/m) structure. With increasing temperature, a little change in the slope of the temperature dependence of mode centered at 855 cm−1 is observed around 480 °C which might be a sign of the second phase transition in Sr2ZnWO6 (tetragonal (I4/m) to cubic (Fm-3m)). The temperature dependence of the full width at half maximum (FWHM) of the most intense modes in Sr2ZnWO6 spectra was studied. The width behaves linearly as a function of temperature with a break observed in the slope of the width of the modes at 80 °C; thus, showing the first phase transition occurrence. For Sr2CoWO6 the transition from tetragonal (I4/m) structure to cubic (Fm-3m) phase is accompanied by considerable changes in the temperature dependence of modes centered at 438 cm−1 and 845 cm−1. The transition was observed around 420 °C.
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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-xSrxZnWO6 (0 <= x <= 2) double perovskite oxides
- 2012
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 533, s. 43-52
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction and Raman spectroscopy studies of Sr doped double perovskites compound Ba2-xSrxZnWO6 with (0 <= x <= 2) were investigated. As a function of composition while increasing strontium amount, the samples show two phase transitions from cubic to tetragonal phase and from tetragonal to monoclinic structure. Both Rietveld refinements and Raman studies showed that the first phase transition occurs between x = 1 and 1.2; the second phase transition is observed around x = 2. Furthermore, increasing the temperature for the compositions (1.2 <= x <= 2), manifests the tetragonal to cubic phase transition. For x = 2 two phase transitions were observed as a function of temperature. For this series, the phase transitions are illustrated by considerable changes in the composition and temperature dependence of the modes. All the Raman modes show a linear behavior when the composition or temperature is increased, then the slope change indicating the symmetry change.
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