Hydrated niobates and tantalates of alkaline-earth metals, having a perovskite-related structure, were investigated by using wide-line 1H nuclear magnetic resonance, thermogravimetry, conductivity and infra-red spectroscopic measurements. Thermogravimetric data showed that these phases could incorporate up to about 1mol of water. This corresponded to the theoretical limit of hydration. A wide-line 1H nuclear magnetic resonance study indicated that the proton signal consisted of 3 components because the protons present were in the form of relatively isolated OH groups, paired OH groups bound to the same metal atom and of closely-spaced OH groups which belonged to different octahedra and localized within a defect cluster. The niobates and the tantalates had different ratios of those groups. This was explained by the differing coordination tendencies of Nb and Ta, and, consequently, of different arrangements of O vacancies.

States of H+-Containing Species and Proton Migration Forms in Hydrated Niobates and Tantalates of Alkaline-Earth Metals with a Perovskite-Related Structure. I.Animitsa, T.Denisova, A.Neiman, A.Nepryahin, N.Kochetova, N.Zhuravlev, Colomban: Solid State Ionics, 2003, 162-163, 73-81