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 3m 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 P2 1 /n-I 4/m phase transitions and Sr 2 CuWO 6 presents a phase transition of the type I 4/mmm-Fm 3m. 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.

In the present work we report x-ray powder diffraction measurements of Sr2CaWO6 and Sr2MgWO6, at different temperatures. The crystal structures at room temperature of both compounds are determined; and results showing the existence of phase transitions in them are presented. For the structure at room temperature of the Ca containing compound, the space group P 21/n is obtained, which is different from that previously suggested. The evolution with temperature of the structure of this compound shows the presence of two phase transitions, a discontinuous one at 1130 K and a continuous one at 1250 K, with the following phase transition sequence: . The crystal structure of the Mg containing compound at room temperature has the I4/m space group. The temperature evolution of the structure has revealed a continuous phase transition at 570 K, changing the symmetry from tetragonal (I4/m) to cubic ().

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