Synthesis of mixed-valent α- and β-NaFe2O3 polymorphs under controlled partial oxygen pressure

Synthesis of mixed valent compounds, especially when multiple polymorphs exist, requires careful control of the preparation conditions. α- and β-NaFe2O3 polymorphs were synthesized under controlled partial oxygen pressure (pO2). pO2 regions of stability at 850 °C were determined for both phases for the first time. A modified oxygen buffer method was developed for the facile preparation of mixed valent oxides under controlled pO2. β-NaFe2O3 is the only known n=2 member of the AMnOn+1 (A=alkali metal, M=3d metal) rock-salt related homolog series with layered cation ordering. The possibility of new members of the homolog series with other 3d metals is considered.