Symmetry-mode analysis of the phase transitions in SrLaZnRuO6 and SrLaMgRuO6 ordered double perovskites

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→R 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.