• double perovskites;
  • phase transitions;
  • symmetry-mode analysis

The crystal structures of double perovskites SrLaMRuO6 (M = Zn and Mg) have been studied using X-ray and neutron diffraction data. Both compounds have monoclinic structure at room temperature with space group P21/n. A first-order structural phase transition P21/n[RIGHTWARDS ARROW]Rinline image has been observed in SrLaZnRuO6 and SrLaMgRuO6, at about 800 and 500 K, respectively, with the two phases coexisting in a temperature interval of 150 K. The temperature- and tolerance-factor-dependent phase diagram of the SrLnMRuO6 (Ln = La, Nd and Pr; M = Zn, Co, Cu, Mg and Ni) family shows two different phase transition sequences depending on the A-site cation. The structures of the title compounds at room and high temperatures have been analyzed using the symmetry-mode decomposition approach.