Synthesis, structures and temperature-induced phase transitions of the Sr2Cd1−xCaxWO6 (0 ⩽ x ⩽ 1) double perovskite tungsten oxides

The solid solution with double perovskite structure and general chemical formula Sr2Cd1−xCaxWO6 (0 ⩽ x ⩽ 1) has been synthesized by the co-precipitation method. The Cd2+ cation substitution by Ca2+ in the Sr2CdWO6 double perovskite led to a continuous solid solution in the whole (0 ⩽ x ⩽ 1) fraction range. The crystal structures were determined from the Rietveld refinements of laboratory X-ray powder diffraction data. All members of the solid solution crystallize at room temperature in the P21/n   space group. The high-temperature study has revealed the following two phase-transition sequence for all the members of the solid solution: P21/n→I4/m→Fm3¯m. The phase-transition temperatures of both successive phase-transitions showed a linear behavior in the whole (0 ⩽ x ⩽ 1) fraction range. Finally, following the results reported for Sr2CdWO6 and Sr2CaWO6, and comparing those temperatures with others of the Sr2MWO6 family reported previously, it was observed that the transition temperatures are higher in compounds with low tolerance factors.