It was shown that proton-associated dipole centers (OH)− could provide significant, glasslike contributions to the low-temperature properties of perovskite-type proton conducting oxides, such as ABO3−y, doped with cations of lower valence. These contributions resulted from the splitting of the orientationally degenerate states of dipole centers by random crystal fields and proton tunneling. It was demonstrated that H/D (or H/T) substitution led to large and abnormal isotope effects for the properties caused by (OH)− degenerate states.

Orientationally Degenerate (OH)− Centers in Perovskite-Type Proton-Conducting Oxides - Low-Temperature Thermodynamics and H/D Isotope Effects. A.Y.Fishman, V.Y.Mitrofanov, V.I.Tsidilkovski: Journal of Experimental and Theoretical Physics Letters, 2006, 83[3], 103-8