Oxygen nonstoichiometry of Ce 0.8 Gd 0.2 O 1.9 − x was gravimetrically measured at temperatures from 700 to 1000°C and oxygen partial pressures between 10 −24 and 1 atm. Based on the experimental data, the relationship between log x and log p O 2 , (where x is the oxygen deficiency and p O 2 the oxygen partial pressure) is discussed and partial molar enthalpy, Δ H¯ O , and entropy, Δ S¯ O , of oxygen are calculated. In the region of x ≦ 0.04, x is proportional to the −1/4 power of p O 2 and Δ H¯ O , and Δ S¯ O , behave as in an ideal solution, showing that oxygen vacancies are doubly charged and defects in Ce 0.8 Gd 0.2 O 1.9 − x are randomly distributed. Thus, the mass action law is satisfied in the area x ≦ 0.04.
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Wang et al. (1997) studied this question.