Materials Data on AlCr2O4 by Materials Project
Cr2AlO4 is Spinel structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Cr+2.50+ sites. In the first Cr+2.50+ site, Cr+2.50+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six equivalent AlO4 tetrahedra and edges with six CrO6 octahedra. There are four shorter (2.10 Å) and two longer (2.15 Å) Cr–O bond lengths. In the second Cr+2.50+ site, Cr+2.50+ is bonded to six equivalent O2- atoms to form CrO6 octahedra that share corners with six equivalent AlO4 tetrahedra and edges with six equivalent CrO6 octahedra. All Cr–O bond lengths are 2.10 Å. Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with twelve CrO6 octahedra. The corner-sharing octahedra tilt angles range from 53–55°. There is one shorter (1.80 Å) and three longer (1.85 Å) Al–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to three Cr+2.50+ and one Al3+ atom. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to three equivalent Cr+2.50+ and one Al3+ atom.