Thermal expansion behaviour in the oxygen deficient perovskites Sr2BSbO5.5 B=Ca, Sr, Ba. Competing effects of water and oxygen ordering

Abstract

Neutron diffractions studies reveal the presence of oxygen disorder in the oxygen deficient perovskites Sr(2)BSbO(5.5) (B=Ca, Sr, Ba). Synchrotron X-ray studies demonstrate that these oxides have a double perovskite:type structure with the cell size increasing as the size of the B cation increases from 8.2114(2) angstrom for B=Ca to 8.4408(1) angstrom for B=Ba. It is postulated that a combination of local clustering of the anions and vacancies together with water-water and water-host hydrogen bonds plays a role in defining the volume of the encapsulated water clusters and that changes in the local structure upon heating result in anomalous thermal expansion observed in variable temperature diffraction measurements. (C) 2011 Elsevier Inc.