DOE OSTI2020
AlFe2O4 is Spinel structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Fe+2.50+ sites. In the first Fe+2.50+ site, Fe+2.50+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six equivalent AlO4 tetrahedra and edges with six FeO6 octahedra. All Fe–O bond lengths are 2.11 Å. In the second Fe+2.50+ site, Fe+2.50+ is bonded to six equivalent O2- atoms to form FeO6 octahedra that share corners with six equivalent AlO4 tetrahedra and edges with six equivalent FeO6 octahedra. All Fe–O bond lengths are 2.07 Å. Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with twelve FeO6 octahedra. The corner-sharing octahedra tilt angles range from 54–55°. There is one shorter (1.79 Å) and three longer (1.82 Å) Al–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Fe+2.50+ and one Al3+ atom. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to three equivalent Fe+2.50+ and one Al3+ atom.