This perovskite-related solid solution, Sr6-2xTa2+2xO11+3x, with O structural vacancies was studied by performing alternating-current conductivity and thermogravimetric experiments in atmospheres with various water activities. It was found that samples with high O-vacancy concentrations were high-temperature mixed O-H ion conductors; the conductivity of which was very sensitive to the presence of water vapour at up to 900C. The thermogravimetric data indicated that the overall water weight loss increased with increasing concentration of O vacancies. This relationship was not linear. The deviation of the observed water uptake, from the theoretical value, was relatively low only in the case of Sr6Ta2O11. In accord with the observed 2-stage water removal, a corresponding mechanism for the dehydration process was proposed which involved water molecules being coordinated with metal atoms during the first stage, followed by OH groups leaving the framework in the second. The possible formation of oxyhydrate, intercalated or intergrown phases was considered.

Strontium Tantalates with Perovskite-Related Structure. I.Animitsa, A.Neiman, A.Sharafutdinov, S.Nochrin: Solid State Ionics, 2000, 136-137[1-2], 265-71