Steady-state de-mixing of the cations in yttria-stabilized zirconia in an electric field was analyzed for diffusion via independent vacancies, by vacancy pairs and by vacancy triplets. Two conditions were analyzed. One was an open system in which the vacancies were everywhere close to an internal surface and the Schottky defect reaction was allowed to equilibrate the vacancy concentrations. The other was closed system in which such equilibration was possible only at the external surface. For diffusion via independent vacancies and vacancy pairs, critical values of the ratio of the Y to Zr vacancy exchange frequencies causing Y enrichment at the cathode were determined. It was also shown that diffusion via the vacancy-triplet mechanism always led to Y enrichment at the anode end. Using Monte Carlo simulations, it was also possible to verify the analysis of the situation where de-mixing occurred by independent cation vacancies in a closed system.

Analysis of the De-Mixing of Yttria-Stabilized Zirconia in an Electric Field for Different Diffusion Mechanisms. I.V.Belova, D.Samuelis, M.Martin, G.E.Murch: Philosophical Magazine, 2007, 87[10], 1447-63