Phase Equilibria in Fe–Fe2O3–Ln2O3 (Ln=Sm and Er) Systems at 1200 °C

Phase equilibria in Fe–Fe2O3–Ln2O3 (Ln=Sm and Er) systems were established at 1200 °C. In the Fe–Fe2O3–Sm2O3 system, perovskite, garnet, magnetite, wustite, and metallic iron were stable, while in the Fe–Fe2O3–Er2O3 system, the ErFe2O4 phase appeared in addition to the other five phases. On the basis of the phase equilibria, the Gibbs free energy for the reaction of LnFeO3, Ln3Fe5O12, and ErFe2O4 from Ln2O3, metallic iron, and oxygen was determined to be as follows: SmFeO3 −64.1±0.1 kcal, Sm3Fe5O12 −298.5±0.5 kcal, ErFe2O4 −100.8±0.1 kcal, ErFeO3 −59.7±0.3 kcal, and Er3Fe5O12 −286.2±0.7 kcal.