The material described by Cr2AlO4 is Spinel structured and crystallizes in the trigonal R-3m space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with four equivalent Cr(1)O6 octahedra. In the second Cr site, Cr(2) is bonded to six equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra and edges with six equivalent Cr(1)O6 octahedra. Al(1) is bonded to one O(2) and three equivalent O(1) atoms to form AlO4 tetrahedra that share corners with three equivalent Cr(2)O6 octahedra and corners with nine equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-55°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Cr(2), two equivalent Cr(1), and one Al(1) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to three equivalent Cr(1) and one Al(1) atom. is represented by the CIF card [CIF]
data_AlCr2O4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.997
_cell_length_b   5.997
_cell_length_c   5.997
_cell_angle_alpha   59.650
_cell_angle_beta   59.650
_cell_angle_gamma   59.650
_symmetry_Int_Tables_number   1
_cell_volume   151.293
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Al  Al0  1  0.624  0.624  0.624  1.0
  Al  Al1  1  0.376  0.376  0.376  1.0
  Cr  Cr2  1  0.500  0.000  0.000  1.0
  Cr  Cr3  1  0.000  0.000  0.000  1.0
  Cr  Cr4  1  0.000  0.500  0.000  1.0
  Cr  Cr5  1  0.000  0.000  0.500  1.0
  O  O6  1  0.751  0.245  0.751  1.0
  O  O7  1  0.249  0.249  0.755  1.0
  O  O8  1  0.755  0.249  0.249  1.0
  O  O9  1  0.254  0.254  0.254  1.0
  O  O10  1  0.751  0.751  0.245  1.0
  O  O11  1  0.249  0.755  0.249  1.0
  O  O12  1  0.245  0.751  0.751  1.0
  O  O13  1  0.746  0.746  0.746  1.0
[/CIF]
.
The material described by Cr2AlO4 is Spinel structured and crystallizes in the trigonal R-3m space group. There are two inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra, edges with two equivalent Cr(2)O6 octahedra, and edges with four equivalent Cr(1)O6 octahedra. In the second Cr site, Cr(2) is bonded to six equivalent O(1) atoms to form CrO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra and edges with six equivalent Cr(1)O6 octahedra. Al(1) is bonded to one O(2) and three equivalent O(1) atoms to form AlO4 tetrahedra that share corners with three equivalent Cr(2)O6 octahedra and corners with nine equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 53-55°. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Cr(2), two equivalent Cr(1), and one Al(1) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to three equivalent Cr(1) and one Al(1) atom. is represented by the CIF card [CIF]
data_AlCr2O4
_symmetry_space_group_name_H-M   'P 1'
_cell_length_a   5.997
_cell_length_b   5.997
_cell_length_c   5.997
_cell_angle_alpha   59.650
_cell_angle_beta   59.650
_cell_angle_gamma   59.650
_symmetry_Int_Tables_number   1
_cell_volume   151.293
_cell_formula_units_Z   2
loop_
 _symmetry_equiv_pos_site_id
 _symmetry_equiv_pos_as_xyz
  1  'x, y, z'
loop_
 _atom_site_type_symbol
 _atom_site_label
 _atom_site_symmetry_multiplicity
 _atom_site_fract_x
 _atom_site_fract_y
 _atom_site_fract_z
 _atom_site_occupancy
  Al  Al0  1  0.624  0.624  0.624  1.0
  Al  Al1  1  0.376  0.376  0.376  1.0
  Cr  Cr2  1  0.500  0.000  0.000  1.0
  Cr  Cr3  1  0.000  0.000  0.000  1.0
  Cr  Cr4  1  0.000  0.500  0.000  1.0
  Cr  Cr5  1  0.000  0.000  0.500  1.0
  O  O6  1  0.751  0.245  0.751  1.0
  O  O7  1  0.249  0.249  0.755  1.0
  O  O8  1  0.755  0.249  0.249  1.0
  O  O9  1  0.254  0.254  0.254  1.0
  O  O10  1  0.751  0.751  0.245  1.0
  O  O11  1  0.249  0.755  0.249  1.0
  O  O12  1  0.245  0.751  0.751  1.0
  O  O13  1  0.746  0.746  0.746  1.0
[/CIF]
.