Protonic conduction in Sr 1 − y(Zr 1 − xDy x)O 3 − δ ceramics

Abstract

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 sub-stoichiometric and/or B-site Dy-doped materials. The conductivity of Sr(Zr 1 − x Dy x )O 3 − δ is slightly lower than found for Y-doped strontium zirconate with identical trivalent dopant content, and increases with water vapour pressure, as expected for protonconducting materials. For Dy-free perovskites with slight A-site substoichiometry (Sr 1 − y ZrO 3 − δ, with y ≤ 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 (Zr 1 − x Dy x )O 3 − δ] 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 (≈300 °C) are smaller than for protons. This trend is reversed at higher temperatures (>500 °C). For highly substoichiometric perovskites ( y ≥ 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.