Synthesis and Structural Analysis of ϵ‐Fe 2 O 3

Powder material of ϵ‐Fe 2 O 3 was obtained by thermal decomposition of the clay mineral nontronite and subsequent isolation of the ferric oxide by leaching the silicate phases. Additionally, crystals of ϵ‐Fe 2 O 3 were grown as precipitates by internal oxidation of a Pd 96 Fe 4 alloy. Analysis of the precipitate crystals by electron diffraction yields an orthorhombic crystal system and space group Pna 2 1 ab initio . X‐ray diffraction data of the powder containing small amounts of Al substituting Fe were refined by the Rietveld method. The refinement yields lattice parameters a = 507.15 pm, b = 873.59 pm and c = 941.78 pm, and atom positions. ϵ‐Fe 2 O 3 is isostructural with κ‐Al 2 O 3 , AlFeO 3 , and GaFeO 3 having an anion stacking sequence /ABAC/, and 1/4 of the cations in tetrahedral co‐ordination. Some strongly distorted FeO 6 octahedrons with one large Fe‐O distance, which may be considered as a 5+1 co‐ordination, appear to be characteristic for ϵ‐Fe 2 O 3 . The structure shows elements known from silicates and oxyhydroxides of iron, respectively.