High temperature induced phase transitions in Sr₂ZnWO₆ and Sr₂CoWO₆ double perovskite oxides: Raman spectroscopy as a tool
2012
Manoun, Bouchaib | Igartua, Josu M. | Lazor, Peter | Ezzahi, Amine
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 137cm⁻¹, 152cm⁻¹, merge around 80°C. The same behavior was observed for the 436cm⁻¹ and 447cm⁻¹ modes. The mode centered at 854cm⁻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 855cm⁻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 438cm⁻¹ and 845cm⁻¹. The transition was observed around 420°C.
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