X-ray and neutron powder diffraction study of the double perovskites Ba2LnSbO6 (Ln=La, Pr, Nd and Sm)

The crystal structures of Ba2LnSbO6 (Ln=La, Pr, Nd and Sm) at room temperature have been investigated by profile analysis of the Rietveld method using either combined X-ray and neutron powder diffraction data or X-ray powder diffraction data. It has been shown that the structure of Ba2LnSbO6 with Ln =La, Pr and Nd are neither monoclinic nor cubic as were previously reported. They are rhombohedral with the space group image. The distortion from cubic symmetry is due to the rotation of the LnO6/SbO6 octahedra about the primitive cubic [111]p-axis. On the other hand, the structure of Ba2SmSbO6 is found to be cubic. All compounds contain an ordered arrangement of LnO6 and SbO6 octahedra.