Dependence of oxygen nonstoichiometry of Ce1-ySmyO2-5,5-x (y = 0.1, 0.2) on
temperature, T, and oxygen partial pressure, P-O2, was investigated by the
rmogravimetry. Based on the experimental data, partial molar enthalpy, Delt
a (H) over bar(O), and entropy, Delta (S) over bar(O), of oxygen were calcu
lated and the defect model was discussed. In the region where oxygen defici
ency, x, was below 0.02 of Ce0.9Sm0.1O1.95-x, Delta (H) over bar o was inde
pendent of x, indicating that an ideal solution model was applicable for th
e distribution of oxygen vacancies. Linear relationship between Delta (H) o
ver bar(O) and x observed in the region 0.02 less than or equal to x less t
han or equal to 0.05 of Ce0.9Sm0.1O1.95-x indicated that the regular soluti
on model was applicable in this range. Experimentally obtained Delta (S) ov
er bar(O), of Ce0.9Sm0.1O1.95-x with x less than or equal to 0.05 also agre
ed with a theoretical calculated ones based on an ideal solution or a regul
ar solution model, in which random distribution of oxygen vacancies was ass
umed. 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 di
stribution of oxygen vacancies was applicable in Ce0.8Sm0.2O1.9-x with x ra
nge below 0.05. With the increase of x larger than 0.05, deviation from ide
al or regular solution model was observed for the both specimens, which cou
ld be attributed to the association among oxygen vacancies. The oxygen nons
toichiometry, Delta (H) over bar(O) and Delta (S) over bar(O) of Sm-doped C
eO2 were compared with those of Gd-doped CeO2. (C) 1999 Elsevier Science B.
V. All rights reserved.