Ce0.6La0.4O2-δ (40LDC) is considered as a material for the interlayer between Ni-cermet anodes and LaGaO3 based electrolytes in solid oxide fuel cells. The oxygen nonstoichiometry of 40LDC was measured as a function of oxygen partial pressure P(O2) and temperature by thermogravimetry. The decrease of weight due to the formation of oxygen vacancies was observed under low P(O2) conditions. The weight of 40LDC sample increased under humidified conditions. Using the reaction rate equation of adsorption, the weight change was explained as the adsorption of H2O on the surface of 40LDC. The weight change without the influence of adsorption was calculated. The oxygen nonstoichiometry was derived and successfully simulated using a regular solution model. The standard Gibbs energy change of oxygen vacancy formation and interaction parameters between oxygen vacancy and 40LDC were estimated as fitting parameters.
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