Protonic conduction in Sr-1-y(Zr1-xDyx)O-3-delta ceramics

Ceramic materials derived from strontium zirconate were prepared by high-temperature solid-state reaction starting from oxides and carbonates. Distorted ABO(3)-type perovskite structures, indexed to the orthorhombic system, were obtained for A-site substoichiometric and/or B-site Dy-doped materials. The conductivity of Sr(Zr1-xDyx)O-3-delta is slightly lower than found for Y-doped strontium zirconate with identical trivalent dopant content, and increases with water vapour pressure, as expected for proton-conducting materials. For Dy-free perovskites with slight A-site substoichiometry (Sr1-yZrO3-delta, with y less than or equal to 0.02), the conductivity drops a few orders of magnitude and is nearly independent of water vapour pressure. The corresponding B-site doped materials [Sr-1-y(Zr1-xDyx) O-3-delta] have the highest conductivities, again dependent on water vapour pressure. This indicates that B-site doping is essential to obtain significant proton conductivity. The behaviour of these materials can be understood based on a classical defect chemistry type of approach, if one assumes that electron hole mobilities at low temperature (approximate to 300 degrees C) are smaller than for protons. This trend is reversed at higher temperatures (>500 degrees C). For highly substoichiometric perovskites (y greater than or equal to 0.05), even when B-site doped, the conductivity is minimal and independent of water vapour pressure. A blocking intergrain phase is believed to control the electrical transport properties of these materials. Copyright (C) 1996 Elsevier Science Ltd