X-ray powder diffraction results for the phase transitions in Sr2MWO6(M Ni, Zn, Co, Cu) double perovskite oxides

As a result of a pseudosymmetry search, the double perovskite compounds Sr 2 MWO 6 (M = Ni, Zn, Co, Cu) were identified as good candidates for presenting Landau-type phase transitions at high temperatures. In the present work, the phases observed at different temperatures are reported and the phase transitions are discussed. The Sr 2 MWO 6 (M = Ni, Zn, Co) compounds present I 4/ m – Fm m phase transitions, while Sr 2 CuWO 6 shows an I 4/ m – I 4/ mmm phase transition. All these transitions are second order and are consistent with the pseudosymmetry concept. Sr 2 ZnWO 6 and Sr 2 CoWO 6 also show P 2 1 / n – I 4/ m phase transitions and Sr 2 CuWO 6 presents a phase transition of the type I 4/ mmm – Fm m . These transitions are first order. Alongside the experimental results a discussion of some aspects of the study of phase transitions in double perovskite materials is presented.