Structural and Magnetic Properties of BaFeO_2.667 Synthesized by Oxidizing BaFeO_2.5 Obtained via Nebulized Spray...

A vacancy-ordered perovskite-type compound Ba₃Fe₃O₈ (BaFeO_2.667) was prepared by oxidizing BaFeO_2.5 (P2₁/c) with the latter compound obtained by a spray pyrolysis technique. The structure of Ba₃Fe₃O₈ was found to be isotypic to Ba₃Fe₃O₇F (P2₁/m) and can be written as Ba₃Fe³⁺₂Fe⁴⁺₁O₈. Mössbauer spectroscopy and ab initio calculations were used to confirm mixed iron oxidation states, showing allocation of the tetravalent iron species on the tetrahedral site, and octahedral as well as square pyramidal coordination for the trivalent species within a G-type antiferromagnetic ordering. The uptake and release of oxygen were investigated over a broad temperature range from room temperature to 1100 °C under pure oxygen and ambient atmosphere via a combination of DTA/TG and variable temperature diffraction measurements. The compound exhibited a strong lattice enthalpy driven reduction to monoclinic and cubic BaFeO_2.5 at elevated temperatures.