Intrinsic and Extrinsic Oxygen Diffusion and Surface Exchange Reaction in Cerium Oxide

Abstract

Polycrystalline with a relative density in excess of 97% was prepared. The specimens contained a lower concentration of impurities than those examined previously. Oxygen diffusion experiments were performed for the temperature range from 800 to 1300°C, in an oxygen partial pressure of . The concentration profile of in the specimens following diffusion annealing was measured by secondary ion mass spectroscopy (SIMS). In the high‐temperature region (intrinsic region, above 1000°C), the oxygen self‐diffusion coefficient obtained using SIMS was observed to agree reasonably with that obtained by gas phase analysis in a previous study, but the activation energy was found to be slightly smaller. The present result, , is thought to represent the intrinsic behavior of undoped . In contrast, in the low temperature region (extrinsic region, less than 1000°C), the activation energy was smaller than that in the high temperature region. Comparison with data reported in the literature for doped with Y and Gd, suggests that the low‐temperature oxygen diffusion region is controlled by a trivalent impurity. The surface exchange coefficients obtained from gas phase analysis and SIMS agreed very well with each other and were represented by . The data were also in good agreement with the surface exchange coefficient in , suggesting that the oxygen surface exchange reaction is insensitive to cation species. © 2000 The Electrochemical Society. All rights reserved.