OXYGEN-TRANSFER PROPERTIES OF ION-IMPLANTED YTTRIA-STABILIZED ZIRCONIA

The influence of surface modification by ion implantation on oxygen transfer in yttria-stabilized zirconia (YSZ) has been studied. Implantation of 15 keV Fe-56 in YSZ with a maximum dose of 8x 10(16) atoms cm-2 yields reproducible surface layers of approximately 20 nm deep with a maximum Fe cation fraction of 0. 5 at the surface. After annealing these layers are stable up to 700-800-degrees-C. The exchange current densities for the Fe-implanted layers, measured using porous gold electrodes, are a factor of 10-50 larger than observed for hot-implanted YSZ. O-18 isotope exchange experiments show that for Fe-implanted samples the surface oxygen exchange rate is at least a factor 30 larger than for normal YSZ. The electrode kinetics has been studied for normal and implanted YSZ using current-overvoltage measurements and impedance measurements under bias. An electrode reaction model for the transfer of oxygen has been developed. This model is able to explain the low frequency inductive loop in the impedance diagram which is observed at high cathodic and anodic polarizations for implanted as well as normal YSZ.