Composition and temperature dependent phase transitions in Co–W double perovskites, a synchrotron X-ray and neutron powder diffraction study

High-resolution synchrotron and neutron powder diffraction techniques were used to determine precise structures for the series of perovskite oxides A2−xSrxCoWO6 (A6-point double bond; length half of m-dashCa, or Ba, 0⩽x⩽2). The studies demonstrated that the symmetry decreases as the average size of the A-site cation decreases with a sequential introduction of in-phase and out-of-phase tilting of the BO6 octahedra. A cubic structure in Fm3¯m with rock-salt like ordering of the Co and W cations was formed for Ba2−xSrxCoWO6 with x∼<1.4. As the Sr content was increased, the materials became tetragonal in I4/m and ultimately monoclinic in P21/n. A mixture of monoclinic and tetragonal phases occurs in Sr2CoWO6 at room temperature but this was purely monoclinic at 20 K.