Polycrystalline CeO2 with a relative density in excess of 97% was prepared. The specimens contained a lower concentration of impurities than usual. Oxygen diffusion experiments were performed at 800 to 1300C, in an oxygen partial pressure of 6.6 x 103Pa. The concentration profile of 18O in the specimens following diffusion annealing was measured using secondary ion mass spectroscopy. In the high-temperature region (intrinsic region above 1000C), the present oxygen self-diffusion coefficient agreed reasonably with that obtained by gas phase analysis in a previous study, but the activation energy was slightly smaller. The present results,

D(m2/s) = 3.16 x 10-4exp[-226(kJ/mol)/RT]

at 1100 to 1300C were thought to represent the intrinsic behavior of undoped CeO2. In the low-temperature region (extrinsic region less than 1000), the activation energy was smaller than that in the high-temperature region. Comparison with literature data for CeO2 doped with Y and Gd suggested that the low-temperature oxygen diffusion region was 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:

k(m2/s) = 1.93 x 10-3exp[-136(kJ/mol)/RT]

at 800 to 1300C. The data were also in good agreement with the surface exchange coefficient in ThO2; suggesting that the oxygen surface exchange reaction was insensitive to the cation species.

Intrinsic and Extrinsic Oxygen Diffusion and Surface Exchange Reaction in Cerium Oxide. M.Kamiya, E.Shimada, Y.Ikuma, M.Komatsu, H.Haneda: Journal of the Electrochemical Society, 2000, 147[3], 1222-7