NiAl2O4 is Spinel structured and crystallizes in the orthorhombic Pmn2_1 space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form NiO4 tetrahedra that share corners with three equivalent Al(2)O6 octahedra, corners with three equivalent Al(3)O6 octahedra, and corners with six equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-64°. In the second Ni site, Ni(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form NiO4 tetrahedra that share corners with three equivalent Al(2)O6 octahedra, corners with three equivalent Al(3)O6 octahedra, and corners with six equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-64°. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to two O(1,1); two O(2,2); and two O(3,3) atoms to form AlO6 octahedra that share corners with six Ni(1,1)O4 tetrahedra; edges with two equivalent Al(1)O6 octahedra; edges with two equivalent Al(2)O6 octahedra; and edges with two equivalent Al(3)O6 octahedra. In the second Al site, Al(2) is bonded to two O(2,2) and four O(3,3) atoms to form AlO6 octahedra that share corners with six Ni(1,1)O4 tetrahedra; edges with two equivalent Al(3)O6 octahedra; and edges with four equivalent Al(1)O6 octahedra. In the third Al site, Al(3) is bonded to two O(1,1) and four O(3,3) atoms to form AlO6 octahedra that share corners with six Ni(1,1)O4 tetrahedra; edges with two equivalent Al(2)O6 octahedra; and edges with four equivalent Al(1)O6 octahedra. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ni(1), one Al(3), and two equivalent Al(1) atoms. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Ni(1), one Al(2), and two equivalent Al(1) atoms. In the third O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Ni(1), one Al(2), and two equivalent Al(1) atoms. In the fourth O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ni(1), one Al(3), and two equivalent Al(1) atoms. In the fifth O site, O(3) is bonded to one Ni(1), one Al(1), one Al(2), and one Al(3) atom to form a mixture of distorted edge and corner-sharing OAl3Ni trigonal pyramids. In the sixth O site, O(3) is bonded to one Ni(1), one Al(1), one Al(2), and one Al(3) atom to form a mixture of distorted edge and corner-sharing OAl3Ni trigonal pyramids.
NiAl2O4 is Spinel structured and crystallizes in the orthorhombic Pmn2_1 space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form NiO4 tetrahedra that share corners with three equivalent Al(2)O6 octahedra, corners with three equivalent Al(3)O6 octahedra, and corners with six equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-64°. The Ni(1)-O(1) bond length is 1.98 Å. The Ni(1)-O(2) bond length is 1.97 Å. Both Ni(1)-O(3) bond lengths are 1.97 Å. In the second Ni site, Ni(1) is bonded to one O(1), one O(2), and two equivalent O(3) atoms to form NiO4 tetrahedra that share corners with three equivalent Al(2)O6 octahedra, corners with three equivalent Al(3)O6 octahedra, and corners with six equivalent Al(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-64°. The Ni(1)-O(1) bond length is 1.98 Å. The Ni(1)-O(2) bond length is 1.98 Å. Both Ni(1)-O(3) bond lengths are 1.97 Å. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to two O(1,1); two O(2,2); and two O(3,3) atoms to form AlO6 octahedra that share corners with six Ni(1,1)O4 tetrahedra; edges with two equivalent Al(1)O6 octahedra; edges with two equivalent Al(2)O6 octahedra; and edges with two equivalent Al(3)O6 octahedra. Both Al(1)-O(1,1) bond lengths are 1.92 Å. Both Al(1)-O(2,2) bond lengths are 1.92 Å. Both Al(1)-O(3,3) bond lengths are 1.93 Å. In the second Al site, Al(2) is bonded to two O(2,2) and four O(3,3) atoms to form AlO6 octahedra that share corners with six Ni(1,1)O4 tetrahedra; edges with two equivalent Al(3)O6 octahedra; and edges with four equivalent Al(1)O6 octahedra. There is one shorter (1.92 Å) and one longer (1.93 Å) Al(2)-O(2,2) bond length. All Al(2)-O(3,3) bond lengths are 1.95 Å. In the third Al site, Al(3) is bonded to two O(1,1) and four O(3,3) atoms to form AlO6 octahedra that share corners with six Ni(1,1)O4 tetrahedra; edges with two equivalent Al(2)O6 octahedra; and edges with four equivalent Al(1)O6 octahedra. There is one shorter (1.92 Å) and one longer (1.93 Å) Al(3)-O(1,1) bond length. All Al(3)-O(3,3) bond lengths are 1.95 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ni(1), one Al(3), and two equivalent Al(1) atoms. In the second O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Ni(1), one Al(2), and two equivalent Al(1) atoms. In the third O site, O(2) is bonded in a distorted rectangular see-saw-like geometry to one Ni(1), one Al(2), and two equivalent Al(1) atoms. In the fourth O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ni(1), one Al(3), and two equivalent Al(1) atoms. In the fifth O site, O(3) is bonded to one Ni(1), one Al(1), one Al(2), and one Al(3) atom to form a mixture of distorted edge and corner-sharing OAl3Ni trigonal pyramids. In the sixth O site, O(3) is bonded to one Ni(1), one Al(1), one Al(2), and one Al(3) atom to form a mixture of distorted edge and corner-sharing OAl3Ni trigonal pyramids.