X-ray diffraction and Raman spectroscopy studies of temperature and composition induced phase transitions in Ba2−xSrxMgTeO6 (0 ⩽ x ⩽ 2)

• Synthesis and characterization of new double perovskites Ba2−xSrxMgTeO6 (0 ⩽ x ⩽ 2).
• High temperature studies of Ba2−xSrxMgTeO6 double perovskite using Raman spectroscopy.
• Temperature and compositions induced phase transitions in these materials.
• Structural determination/refinement of these compounds as a function of composition.

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 ∼ 1.5(1), and from the tetragonal to monoclinic structure at x ∼ 1.9(1). Furthermore, upon temperature increase up to 430 °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.