Aspects of the formation and mobility of protonic charge carriers and the stability of perovskite-type oxides

Proton conducting acceptor-doped perovskite-type alkaline earth cerates, zirconates, niobates and titanates have been investigated experimentally and by numerical simulations. For all cubic perovskites the concentration of protonic defects almost reaches the acceptor dopant concentration under appropriate conditions, and the mobility of protonic defects fall into a narrow range. Any symmetry reduction, however, leads to a reduction of the concentration and mobility of protonic defects. For all oxides, dynamical hydrogen bonding is suggested to lead to a local lattice softening, which provides an advantageous environment for high proton-mobility. This effect may explain the very high proton conductivity in covalent acceptor-doped BaZrO3, which has been found experimentally for the first time. Since this oxide also shows good thermodynamic phase stability, it is an interesting candidate as separator material in high-drain electrochemical applications such as fuel-cells. (C) 1999 Elsevier Science B.V. All rights reserved.