Crystal structures and high-temperature phase transitions of the new ordered double perovskites Sr2SmSbO6Sr2SmSbO6 and Sr2LaSbO6Sr2LaSbO6

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: P21/n→R3¯→Fm3¯m.

Clinographic projections of the structures of the new ordered double perovskites (a) Sr2SmSbO6 and (b) Sr2LaSbO6, along the [001]p[001]p and [010]p[010]p directions, as indicated, in the upper and in the lower panels, respectively. SmO6 octahedra are shown green, LaO6 in cyan, SbO6 in blue and Sr cations in gray. Sr2LaSbO6 is more distorted than Sr2SmSbO6, as can be appreciated in the upper panel in the projection of the cuboctahedral site occupied by the Sr. The angle of rotation of the octahedra around the simple perovskite cubic axis is greater in the more distorted Sr2LaSbO6 phase.Figure optionsDownload as PowerPoint slide