Al2O3 crystallizes in the monoclinic C2/m space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form AlO4 tetrahedra that share corners with seven equivalent Al(2)O6 octahedra and corners with two equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-63°. In the second Al site, Al(2) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form AlO6 octahedra that share corners with seven equivalent Al(1)O4 tetrahedra and edges with four equivalent Al(2)O6 octahedra. There are three inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Al(1) and two equivalent Al(2) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Al(2) and two equivalent Al(1) atoms. In the third O site, O(3) is bonded to one Al(1) and three equivalent Al(2) atoms to form a mixture of distorted edge and corner-sharing OAl4 tetrahedra.
Al2O3 crystallizes in the monoclinic C2/m space group. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form AlO4 tetrahedra that share corners with seven equivalent Al(2)O6 octahedra and corners with two equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 56-63°. The Al(1)-O(1) bond length is 1.75 Å. The Al(1)-O(3) bond length is 1.79 Å. Both Al(1)-O(2) bond lengths are 1.75 Å. In the second Al site, Al(2) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form AlO6 octahedra that share corners with seven equivalent Al(1)O4 tetrahedra and edges with four equivalent Al(2)O6 octahedra. The Al(2)-O(2) bond length is 1.87 Å. Both Al(2)-O(1) bond lengths are 1.87 Å. There is one shorter (1.93 Å) and two longer (2.00 Å) Al(2)-O(3) bond lengths. There are three inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Al(1) and two equivalent Al(2) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Al(2) and two equivalent Al(1) atoms. In the third O site, O(3) is bonded to one Al(1) and three equivalent Al(2) atoms to form a mixture of distorted edge and corner-sharing OAl4 tetrahedra.