Synthesis, phase transition and thermal expansion studies on M2MgWO6 (M = 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)Angstrom and V=538.26(2)Angstrom(3), Z=4). The later compound crystallizes in tetragonal symmetry with space group 14/m (a=5.5876(l) and c=7.9490(3)Angstrom; V=248.18(l)Angstrom(3), Z=2). HT-XRD studies on these compounds were carried out in the temperature range of 25-1200degreesC at each 100degreesC interval in the static air atmosphere. Ba2MgWO6 is found to expand linearly in the studied temperature range. At and above 300degreesC, a cubic elpasolite-type phase is observed for Sr2MgWO6. Within the tetragonal lattice, this compound shows anisotropic expansion. In the temperature range of 25-1200degreesC, the typical volume thermal expansion coefficients of Ba2MgWO6 and Sr2MgWO6 are 35.6 x 10(-6) and 39.6 x 10(-6)/degreesC, respectively. The details of the phase transition and thermal expansion are explained in this manuscript. (C) 2004 Elsevier B.V. All rights reserved.