Synthesis of Barium Ferrates in Oxygen

Phase relations in the system BaO-Fe₂O₃-"FeO₂" at 1 atm (1 atm = 1.013 × 10⁵ N/m²) oxygen and between 800 to 1050 °C are shown in the vicinity (high Ba portion) of the 1:1 cation-cation ratio composition. A hexagonal BaTiO₃-like phase, BaFeO_3- (a = 5.676Å, c = 13.934Å), exists below 960 °C. A perovskite-like phase BaFeO_3- occurs between 960 and 1050 °C. Single-phase tetragonal perovskite can be obtained at room temperature by quenching compositions with Ba-Fe ratios of 67:66 (a = 3.985 Å, c = 4.005 Å, 1000 °C) and 27:26 (a = 3.988 Å, c = 4.003 Å, 1000 °C) from above 960 °C. At the 17:16 ratio, single phase cubic perovskite (a = 3.994 Å, 1000 °C), can be synthesized. Influence of temperature, additions of barium, and use of Pt-containers on phase relations are discussed.