Materials Data on Al2Cr2O7 by Materials Project
Cr2Al2O7 crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Cr4+ is bonded to six equivalent O2- atoms to form distorted corner-sharing CrO6 octahedra. The corner-sharing octahedral tilt angles are 61°. All Cr–O bond lengths are 1.95 Å. Al3+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are two shorter (2.06 Å) and six longer (2.18 Å) Al–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded to four equivalent Al3+ atoms to form OAl4 tetrahedra that share corners with sixteen OAl4 tetrahedra and edges with six equivalent OAl2Cr2 tetrahedra. In the second O2- site, O2- is bonded to two equivalent Cr4+ and two equivalent Al3+ atoms to form a mixture of corner and edge-sharing OAl2Cr2 tetrahedra.