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 (ACa, 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.

Variation of the reduced lattice parameters and volumes with the average A cation radius for the series A2−xSrxCoWO6. The reduced lattice parameters are, for P21/n  a′=2ap, b′=2bp, c′=2cpc′=2cp for I4/m  , a′=2ap, c'=2cpc'=2cp and for Fm3¯m  a′=2apa′=2ap.Figure optionsDownload as PowerPoint slide