NONSTOICHIOMETRY OF CE0.9GD0.1O1.95-X

Oxygen nonstoichiometry of Ce0.9Gd0.1O1.95-x, as a function of tempera ture 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 par tial molar enthalpy, Delta (H) over bar(o) and entropy, Delta (S) over bar(o) of oxygen were calculated. At temperatures higher than 800 deg rees C, oxygen nonstoichiometry, x, is proportional to the -1/4 power of P-o2. showing that oxygen vacancies are doubly charged. At 700 degr ees C, however, x is proportional to the -1/4.6 power of P-o2. For sma ll x, Delta (H) over bar(o) is independent of x, and Delta (S) over ba r(o) is in agreement with a theoretical calculation based on random di stribution of defects. When x becomes larger, Delta (H) over bar(o) in creases and Delta (S) over bar(o) deviates from the theoretical calcul ation.