Cobaltous Oxide in an Oxygen Potential Gradient: Morphological Stability of the Phase Boundaries

If the binary transition metal oxide Co1‐δO is exposed to an oxygen potential gradient, a steady state flux of cation vacancies from the high to the low potential and a corresponding flux of cobalt cations in the opposite direction are induced. Thereby, the crystal as a whole moves to the side of the higher oxygen activity. By solving the diffusion equation for the vacancy transport, the following results are obtained: At the reducing side, the Co1‐δO‐surface is morphologically unstable. At the oxidizing side, the surface is morphologically stable. In addition, the influence of surface tension, surface diffusion, phase boundary reaction and concentration dependence of the chemical diffusion coefficient on the movement of the crystal and the morphological stability of the gas/solid interfaces is analysed. The theoretical results are verified experimentally by exposing Co1‐δ O‐discs to oxygen potential gradients in various gas mixtures.