Orientationally degenerate (OH)- centers in perovskite-type proton-conducting oxides: Low-temperature thermodynamics and H/D isotope effects
A. Ya. Fishman, V. Ya. Mitrofanov, V. I. Tsidilkovski*
Institute of Metallurgy RAS, 620016 Ekaterinburg, Russia
*Institute of High-Temperature Electrochemistry, RAS, 620219 Ekaterinburg, Russia
PACS: 61.72.Bb
Abstract
It is shown
that proton-associated dipole centers (OH) can
provide significant, glass-like, contributions to the low temperature
properties of perovskite-type proton conducting oxides, such as
ABO3-y doped with cations of lower valence. These contributions
result from the splitting of the orientationally degenerated states of dipole
centers by random crystal fields and protons tunneling. It is demonstrated
that H/D (or H/T) substitution leads to large and abnormal isotope effects
for the properties caused by (OH) degenerated states.