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

摘要

High-resolution synchrotron and neutron powder diffraction techniques were used to determine precise structures for the series of perovskite oxides A(2-x)Sr(x)CoWO(6) (A = Ca, 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 Fm (3) over barm with rock-salt like ordering of the Co and W cations was formed for Ba2-xSrxCoWO6 with x similar to < 1.4. As the Sr content was increased, the materials became tetragonal in I4/m and ultimately monoclinic in P2(1). A mixture of monoclinic and tetragonal phases occurs in Sr2CoWO6 at room temperature but this was purely monoclinic at 20 K. (c) 2006 Elsevier Inc. All rights reserved.