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

In the present work we report X-ray powder diffraction measurements of Sr2SmSbO6Sr2SmSbO6 and Sr2LaSbO6Sr2LaSbO6, 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 P21/nP21/n space group, that correspond to the (a+b-b-)(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 Sr2SmSbO6Sr2SmSbO6 and Sr2LaSbO6Sr2LaSbO6, respectively; and a continuous one, at 1170 and 118 K, for Sr2SmSbO6Sr2SmSbO6 and Sr2LaSbO6Sr2LaSbO6, respectively, with the following phase transition sequence: View the MathML sourceP21/n→R3¯→Fm3¯m.