Phase transitions in heated Sr2MgTeO6 double perovskite oxide probed by X-ray diffraction and Raman spectroscopy.

Double-perovskite oxide Sr2MgTeO6 has been synthetized, and its crystal structure was probed by the technique of X-ray diffraction at room temperature. The structure is monoclinic, space group I2/m. Temperature-induced phase transitions in this compound were investigated by Raman spectroscopy up to 550 °C. Two low-wavenumber modes corresponding to external lattice vibrations merge at temperature of around 100 °C, indicating a phase transition from the monoclinic (I2/m) to the tetragonal (I4/m) structure. At 300 °C, changes in the slopes of temperature dependencies of external and O-Te-O bending modes are detected and interpreted as a second phase transition from the tetragonal (I4/m) to the cubic (Fm-3m) structure. [ABSTRACT FROM AUTHOR]