Oxygen nonstoichiometry of Ce1-ySmyO2-0.5y-x (y = 0.1, 0.2)

Dependence of oxygen nonstoichiometry of Ce(1-y)Sm(y)O(2-5,5-x) (y = 0.1, 0.2) on temperature, T, and oxygen partial pressure, P(O2), was investigated by thermogravimetry. Based on the experimental data, partial molar enthalpy, Delta (H) over bar(O), and entropy, Delta (S) over bar(O), of oxygen were calculated and the defect model was discussed. In the region where oxygen deficiency, x, was below 0.02 of Ce(0.9)Sm(0.1)O(1.95-x), Delta (H) over bar o was independent of x, indicating that an ideal solution model was applicable for the distribution of oxygen vacancies. Linear relationship between Delta (H) over bar(O) and x observed in the region 0.02 less than or equal to x less than or equal to 0.05 of Ce(0.9)Sm(0.1)O(1.95-x) indicated that the regular solution model was applicable in this range. Experimentally obtained Delta (S) over bar(O), of Ce(0.9)Sm(0.1)O(1.95-x) with x less than or equal to 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 Delta (H) over bar(O) and Delta (S) over bar(O) on x, it was revealed that an ideal solution model for the distribution of oxygen vacancies was applicable in Ce(0.8)Sm(0.2)O(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, Delta (H) over bar(O) and Delta (S) over bar(O) of Sm-doped CeO(2) were compared with those of Gd-doped CeO(2). (C) 1999 Elsevier Science B.V. All rights reserved.