Nonstoichiometry of Ce0.9Gd0.1O1.95-x

Oxygen nonstoichiometry of Ce0.9Gd0.1O1.95-x, as a function of temperature and P-o2 was gravimetrically measured at temperatures from 700 to 1100 degrees C and oxygen partial pressures between 10(-24) and 1 atm. Based on the experimental data, a defect model was discussed and partial molar enthalpy, Delta (H) over bar(o) and entropy, Delta (S) over bar(o) of oxygen were calculated. At temperatures higher than 800 degrees C, oxygen nonstoichiometry, x, is proportional to the -1/4 power of P-o2. showing that oxygen vacancies are doubly charged. At 700 degrees C, however, x is proportional to the -1/4.6 power of P-o2. For small x, Delta (H) over bar(o) is independent of x, and Delta (S) over bar(o) is in agreement with a theoretical calculation based on random distribution of defects. When x becomes larger, Delta (H) over bar(o) increases and Delta (S) over bar(o) deviates from the theoretical calculation.