Crystal structures and high-temperature phase transitions of the new ordered double perovskites Sr2SmSbO6 and Sr2LaSbO6

Abstract In the present work we report X-ray powder diffraction measurements of Sr 2 SmSbO 6 and Sr 2 LaSbO 6 , at different temperatures. The crystal structures at room temperature of both compounds are determined; and results showing the existence of high-temperature phase transitions in them are presented. Both compounds have double perovskite structure with 1:1 ordered arrangement of the B site cations. At room temperature their symmetries are described with the P 2 1 / n space group, that correspond to the ( a + b - b - ) tilt system. The evolution with temperature of the structure of both compounds shows the presence of two phase transitions: a discontinuous one, at 885 and 945 K, for Sr 2 SmSbO 6 and Sr 2 LaSbO 6 , respectively; and a continuous one, at 1170 and 118 K, for Sr 2 SmSbO 6 and Sr 2 LaSbO 6 , respectively, with the following phase transition sequence: P 2 1 / n → R 3 ¯ → Fm 3 ¯ m .