NONSTOICHIOMETRY IN BAFEO3-Y (0.35 LESS-THAN Y LESS-THAN 0.50)

BaFeO3-y compositions (0.35 < y < 0.50) annealed in the temperature range 980 to 1050°C have been investigated by means of electron diffraction and microscopy to resolve contradictory results from previous X-ray diffraction data. For 0.46 < y < 0.50, the nonstoichiometry is accommodated through the formation of microdomains. Each of these domains shows a superstructure of the cubic perovskite structure with either a monoclinic symmetry (as observed in Ba2Fe2O5) or an orthorhombic symmetry which is typical of a phase of composition 0.44 < y ≤ 0.46. With increase in the amount of Fe4+ (0.35 < y ≤ 0.44), BaFeO3-y consists of a two-phase mixture of a 6H hexagonal phase and of the above orthorhombic phase. The limit of pure cubic stacking seems to be y {reversed tilde equals} 0.46. © 1990.