Specific heat and phase diagram of nonstoichiometric ceria (CeO2−x)

The phase diagram for nonstoichiometric ceria, CeO_2?x, was determined from specific heat measurements in the temperature range 320–1200 K and composition range CeO₂CeO_1.72. Coexistence temperatures of three phases are found at 722, 736, 766, 913, and 1084 K. There is some indication for the existence of two other coexistence temperatures at 850 and at 880 K. The maximum of the miscibility gap occurs at T = 910 K and 2 ? x = 1.93. The phase diagram exhibits some phases in the homologous series Ce_nO_2n?2 with n = 7, 10, 11, and two phases at 2 ? x = 1.79 and 2 ? x = 1.808 not belonging to this series.