Structural phase transitions in the ordered double perovskite Sr₂MnTeO₆

Abstract

The crystal structure of the ordered double perovskite Sr2MnTeO6 has been refined at ambient temperature from high resolution neutron and x-ray powder diffraction data in the monoclinic space group P 121/n 1 with a = 5.7009(1) A, b = 5.6770(1) A, c = 8.0334(1) A and β = 90.085(1)°. This represents a combination of in-phase (+) and out-of-phase (−) rotations of virtually undistorted MnO6 and TeO6 octahedra in the (−−+) sense about the axes of the ideal cubic perovskite. High temperature x-ray powder diffraction shows three structural phase transitions at approximately 250, 550 and 675 °C, each corresponding to the disappearance of rotations about one of these axes. The first transition was analysed by differential scanning calorimetry and showed a thermal hysteresis with an enthalpy of 0.55 J g−1. We propose the () sequence of structural transitions which has not been previously reported for a double perovskite oxide.