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 Sr2MWO6 (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 Sr2MWO6 (M = Ni, Zn, Co) compounds present I4/m-Fm (3) over barm phase transitions, while Sr2CuWO6 shows an I4/m-I4/mmm phase transition. All these transitions are second order and are consistent with the pseudosymmetry concept. Sr2ZnWO6 and Sr2CoWO6 also show P2(1)/n-I4/m phase transitions and Sr2CuWO6 presents a phase transition of the type I4/mmm-Fm (3) over barm. 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.