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

Neutron diffractions studies reveal the presence of oxygen disorder in the oxygen deficient perovskites Sr2BSbO5.5 (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) Å for B=Ca to 8.4408(1) Å 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.

The oxides Sr2BSbO5.5 (B=Ca, Sr, Ba) have unusual anion disorder. There is a lag in the contraction in the cell size of Sr2CaSbO5.5nH2O established from X-ray diffraction measurements following the loss of water suggesting changes on the local structure are important.Figure optionsDownload as PowerPoint slideHighlights
► The average structures of the defect perovskites Sr2MSbO5.5 established.
► Anion and cation disorder quantified by neutron and synchrotron X-ray diffraction.
► Anomalous thermal expansion due to local clustering of anions and vacancies observed.