Oxygen nonstoichiometry of Ce 1− ySm yO 2−0.5 y− x ( y=0.1, 0.2)

Abstract

Dependence of oxygen nonstoichiometry of Ce 1− y Sm y O 2−0,5 y− x ( y=0.1, 0.2) on temperature, T, and oxygen partial pressure, P O 2 , was investigated by thermogravimetry. Based on the experimental data, partial molar enthalpy, Δ H O, and entropy, Δ S O, of oxygen were calculated and the defect model was discussed. In the region where oxygen deficiency, x, was below 0.02 of Ce 0.9Sm 0.1O 1.95− x , Δ H o was independent of x, indicating that an ideal solution model was applicable for the distribution of oxygen vacancies. Linear relationship between Δ H O and x observed in the region 0 02≦ x≦0.05 of Ce 0.9Sm 0.1O 1.95− x indicated that the regular solution model was applicable in this range. Experimentally obtained Δ S O of Ce 0.9Sm 0.1O 1.95.− x with x≦0 05 also agreed with a theoretical calculated ones based on an ideal solution or a regular solution model, in which random distribution of oxygen vacancies was assumed. From the analysis of dependence of Δ H O and Δ S O on x, it was revealed that an ideal solution model for the distribution of oxygen vacancies was applicable in Ce 0.8Sm 0.2O 1.9− x with x range below 0.05. With the increase of x larger than 0.05, deviation from ideal or regular solution model was observed for the both specimens, which could be attributed to the association among oxygen vacancies. The oxygen nonstoichiometry, Δ H O and Δ S O of Sm-doped CeO 2 were compared with those of Gd-doped CeO 2.