The determination of the oxygen self-diffusion and gas-solid exchange coefficients for stabilized zirconia by SIMS

Abstract

Oxides with high anionic conductivities can be used as electrolytes in electrochemical devices such as fuel cells and oxygen monitors. Two important parameters for any such materials are the oxygen self-diffusion coefficient D ∗ , which determines the rate of mass transport in the material, and the surface exchange coefficient K, which determines the kinetics of the exchange interaction between lattice oxygen and oxygen in the gas phase. SIMS measurements of 18O depth profiles, from samples annealed in oxygen environments enriched in the isotope 18O, yield values of both these parameters. Our measurements have been performed on yttria stabilised zirconia (YSZ) single crystals, known to have a high value of D ∗ but slow surface kinetics at low temperatures (>500° C). In an attempt to prepare surfaces with enhanced exchange kinetics we have subjected single crystal 〈100〉 YSZ surfaces to various treatments, including ion implantation, to introduce high impurity cation concentrations (e.g. Bi and Ce) at the surface. SIMS analysis of 18O profiles have been obtained for treated and untreated surfaces using 10 keV Ar + bombardment. Charge compensation was achieved by flooding the sample surface with 500 eV electron flood gun. Negative secondary ions were monitored to achieve high sensitivity.