Synthesis, phase transition and thermal expansion studies on M 2MgWO 6 (M = Ba 2+ and Sr 2+) double perovskites

Abstract

The high-temperature behavior of Ba 2MgWO 6 and Sr 2MgWO 6 double perovskite compounds is studied by high-temperature XRD (HT-XRD) and dilatometer. At ambient temperature, Ba 2MgWO 6 crystallizes in cubic symmetry with space group Fm-3 m ( a = 8.1345(2) Å and V = 538.26(2) Å 3, 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) Å 3, 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. Ba 2MgWO 6 is found to expand linearly in the studied temperature range. At and above 300 °C, a cubic elpasolite-type phase is observed for Sr 2MgWO 6. Within the tetragonal lattice, this compound shows anisotropic expansion. In the temperature range of 25–1200 °C, the typical volume thermal expansion coefficients of Ba 2MgWO 6 and Sr 2MgWO 6 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.