Strontium tantalates with perovskite-related structure

The perovskite-related solid solution Sr6−2xTa2+2xO11+3x with oxygen structural vacancies has been studied by ac-conductivity measurements and thermogravimetry experiments in atmospheres of various water activities. It is found that Sr6−2xTa2+2xO11+3x with high oxygen vacancy concentrations is a high-temperature mixed oxygen–hydrogen ion conductor the conductivity of which is very sensitive to the presence of water vapour up to 900°C. The TG study indicates that overall water weight loss increased with increasing the concentration of oxygen vacancies, but this relationship is not linear. The deviation of observed water uptake from theoretical value is relatively low only for Sr6Ta2O11. In accordance with the observed two-stage water removal the corresponding mechanism of the dehydration process has been proposed, involving deliberation of water molecules coordinated to metal atoms during the first stage followed by OH groups leaving the framework at the second. The possibility of the formation of oxyhydrate, intercalate or intergrown phases was discussed.