On the symmetry and structure of the double perovskites Ba2LnRuO6 (Ln=La, Pr and Nd)

The structures of the double perovskites Ba2LnRuO6 (Ln=La, Pr and Nd) at room temperature were re-investigated by profile analysis of X-ray diffraction data. It has been shown that neither the triclinic P1¯/I1¯ nor the monoclinic P21/n space group correctly describes their structures. Ba2LaRuO6 is actually rhombohedral, space group R3¯, cell parameters a=6.03196(10) Å and α=60.298(2)°. On the other hand, both Ba2PrRuO6 and Ba2NdRuO6 are found to be cubic, space group Fm3¯m, with the cell parameters a=8.48416(6) and 8.47061(5) Å, respectively.