PROTONIC CONDUCTION IN SR-1-Y(ZR1-XDYX)O-3-DELTA CERAMICS

Ceramic materials derived from strontium zirconate were prepared by hi gh-temperature solid-state reaction starting from oxides and carbonate s. Distorted ABO(3)-type perovskite structures, indexed to the orthorh ombic system, were obtained for A-site substoichiometric and/or B-site Dy-doped materials. The conductivity of Sr(Zr1-xDyx)O-3-delta is slig htly lower than found for Y-doped strontium zirconate with identical t rivalent 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 i s nearly independent of water vapour pressure. The corresponding B-sit e doped materials [Sr-1-y(Zr1-xDyx) O-3-delta] have the highest conduc tivities, again dependent on water vapour pressure. This indicates tha t B-site doping is essential to obtain significant proton conductivity . The behaviour of these materials can be understood based on a classi cal defect chemistry type of approach, if one assumes that electron ho le mobilities at low temperature (approximate to 300 degrees C) are sm aller 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 mi nimal and independent of water vapour pressure. A blocking intergrain phase is believed to control the electrical transport properties of th ese materials. Copyright (C) 1996 Elsevier Science Ltd