Phase equilibria in the CeO and CeFeO systems

Phase equilibria in the Ce-O system at 1000, 1100, 1153, 1200, 1249, 1310, and 1330°C and those in the Ce-Fe-O system at 1000, 1100, and 1200°C were established. The former system has CeO2 with a fluorite type, Ce3O5 with a C-type rare-earth oxide, and Ce2O3 with a A-type rare-earth oxide. CeO2 and Ce3O5 have nonstoichiometric compositions, but the stoichiometry of Ce2O3 was confirmed at 1200, 1249, and 1310°C. In the latter system, only the one ternary compound CeFeO3 was confirmed under present experimental conditions. On the basis of the established phase diagrams, the standard Gibbs energies of the reactions: (1) 3/2 Ce2O3 + 1/4 O2 = Ce3O5, (2) 1/3 Ce3O5 + 1/6 O2 = CeO2, (3) 1/3 Fe3O4 + CeO2 = CeFeO3 + 1/6 O2, and (4) Fe + CeO2 + 1/2 O2 = CeFeO3, were determined at various temperatures. Also relationships between ΔG° and the temperatures of the same reactions were determined within the experimental temperature range.