Mass transport properties of Ce_0.9Gd_0.1O_2-δ at the surface and in the bulk

The isothermal thermogravimetry was performed on the system of Ce_0.9Gd_0.1O_2-δ (CGO10) to determine the oxygen nonstoichiometry, δ, in the temperature range between 1073 and 1173 K and the oxygen partial pressure range of 10^-22-1 bar. In addition, chemical diffusion coefficients, D_chem, and surface reaction rate constants, k, were obtained in CO-CO₂ and H₂-H₂O atmospheres through the analysis of a weight relaxation process. The values of obtained chemical diffusion coefficients were consistent with those estimated from partial conductivity and oxygen nonstoichiometry through the PO₂ regions from predominant ionic conduction to predominant electronic conduction. Surface reaction rate constants are not directly related with oxygen partial pressure but depend on the gas species and the composition. The isotope exchange depth profiling with secondary ion mass spectrometry (SIMS) was done to examine the relationship between k and surface exchange coefficients, k_s. It was shown that the hydrogen partial pressure dependence of k_s converted from k was the same, although the absolute value was about 1 over 30 of those from SIMS analysis.