Phase Relationship, Structure and Cationic Distribution of Oxides in the Mn₃O₄-Fe₂O₃ System Synthesized at 1200 ℃

Abstract

A series of oxides in the Mn3O4-Fe2O3 system have been synthesized at 1200°C in air, followed by quenching to room temperature. Three solid solutions, Mn3-3xFe3xO4 (0.00£x£0.278), Mn3-3xFe3xO4(0.291£ x£0.667), and Mn2-2xFe2xO3 (0.89£x£1.00), have been identified by powder X-ray diffraction (XRD). Rietveld refinement of the XRD data show that the solids belong to the hausmannite phase with the space group I41/ amd, the spinel phase with the space group Fd3m, and the hematite phase with the space group R3c, respectively. Between these are two-phase regions. 57 Fe Mössbauer spectra indicate that the valence state of Fe in the three solid solutions is +3; in addition, there are two crystallographically independent Fe 3 + ions in the unit cells of the hausmannite and spinel phases, and one Fe 3+ in the hematite phase. Analyses of 57 Fe Mössbauer spectra and X-ray photoelectron spectra (XPS) revealed that a formula of Mn 2+ 1-xFex 3+ [Mnx 2+ Fe 3+ x Mn 3+ 2-3x] O4 describes the cation distribution of both the hausmannite and spinel phases, but that for the hematite [Article] www.whxb.pku.edu.cn