Synthesis and structural analysis of epsilon-Fe2O3

Powder material of epsilon-Fe2O3 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 epsilon-Fe2O3 were grown as precipitates by internal oxidation of a Pd96Fe4 alloy Analysis of the precipitate crystals by electron diffraction yields an orthorhombic crystal system and space group Pna2(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. epsilon-Fe2O3 is isostructural with kappa-Al2O3, AlFeO3, and GaFeO3 having an anion stacking sequence /ABAC/, and 1/4 of the cations in tetra-hedral co-ordination. Some strongly distorted FeO6 octahedrons with one large Fe-O distance, which may be considered as a 5+1 co-ordination, appear to be characteristic for epsilon-Fe2O3. The structure shows elements known from silicates and oxyhydroxides of iron, respectively.