Synthesis, phase transition and thermal expansion studies on M2MgWO6 (MÂ =Â Ba2+ and Sr2+) double perovskites

The high-temperature behavior of Ba2MgWO6 and Sr2MgWO6 double perovskite compounds is studied by high-temperature XRD (HT-XRD) and dilatometer. At ambient temperature, Ba2MgWO6 crystallizes in cubic symmetry with space group Fm-3m (a = 8.1345(2) Å and V = 538.26(2) Å3, Z = 4). The later compound crystallizes in tetragonal symmetry with space group I4/m (a = 5.5876(1) and c = 7.9490(3) Å; V = 248.18(1) Å3, Z = 2). HT-XRD studies on these compounds were carried out in the temperature range of 25-1200 °C at each 100 °C interval in the static air atmosphere. Ba2MgWO6 is found to expand linearly in the studied temperature range. At and above 300 °C, a cubic elpasolite-type phase is observed for Sr2MgWO6. Within the tetragonal lattice, this compound shows anisotropic expansion. In the temperature range of 25-1200 °C, the typical volume thermal expansion coefficients of Ba2MgWO6 and Sr2MgWO6 are 35.6 × 10−6 and 39.6 × 10−6 /°C, respectively. The details of the phase transition and thermal expansion are explained in this manuscript.