Al2O3 crystallizes in the monoclinic P2_1/m space group. There are six inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(4), two equivalent O(1), and three equivalent O(3) atoms to form a mixture of corner and edge-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 19°. In the second Al site, Al(2) is bonded in a 4-coordinate geometry to one O(4), two equivalent O(2), and three equivalent O(1) atoms. In the third Al site, Al(3) is bonded to one O(3), one O(7), two equivalent O(4), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles range from 19-52°. In the fourth Al site, Al(4) is bonded in a 6-coordinate geometry to one O(2), one O(8), two equivalent O(5), and two equivalent O(6) atoms. In the fifth Al site, Al(5) is bonded to one O(5), two equivalent O(7), and three equivalent O(9) atoms to form a mixture of corner and edge-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 52°. In the sixth Al site, Al(6) is bonded in a 6-coordinate geometry to one O(6), one O(9), two equivalent O(7), and two equivalent O(8) atoms. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Al(1) and three equivalent Al(2) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Al(4) and two equivalent Al(2) atoms. In the third O site, O(3) is bonded to one Al(3) and three equivalent Al(1) atoms to form a mixture of corner and edge-sharing OAl4 trigonal pyramids. In the fourth O site, O(4) is bonded to one Al(1), one Al(2), and two equivalent Al(3) atoms to form a mixture of corner and edge-sharing OAl4 trigonal pyramids. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Al(5) and two equivalent Al(4) atoms. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Al(6), two equivalent Al(3), and two equivalent Al(4) atoms. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Al(3), two equivalent Al(5), and two equivalent Al(6) atoms. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one Al(4) and two equivalent Al(6) atoms. In the ninth O site, O(9) is bonded to one Al(6) and three equivalent Al(5) atoms to form a mixture of corner and edge-sharing OAl4 trigonal pyramids.
Al2O3 crystallizes in the monoclinic P2_1/m space group. There are six inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(4), two equivalent O(1), and three equivalent O(3) atoms to form a mixture of corner and edge-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 19°. The Al(1)-O(4) bond length is 1.93 Å. Both Al(1)-O(1) bond lengths are 1.97 Å. There is one shorter (1.86 Å) and two longer (1.94 Å) Al(1)-O(3) bond lengths. In the second Al site, Al(2) is bonded in a 4-coordinate geometry to one O(4), two equivalent O(2), and three equivalent O(1) atoms. The Al(2)-O(4) bond length is 1.89 Å. Both Al(2)-O(2) bond lengths are 1.78 Å. There is one shorter (1.87 Å) and two longer (2.42 Å) Al(2)-O(1) bond lengths. In the third Al site, Al(3) is bonded to one O(3), one O(7), two equivalent O(4), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles range from 19-52°. The Al(3)-O(3) bond length is 1.95 Å. The Al(3)-O(7) bond length is 1.93 Å. Both Al(3)-O(4) bond lengths are 1.97 Å. Both Al(3)-O(6) bond lengths are 1.95 Å. In the fourth Al site, Al(4) is bonded in a 6-coordinate geometry to one O(2), one O(8), two equivalent O(5), and two equivalent O(6) atoms. The Al(4)-O(2) bond length is 1.82 Å. The Al(4)-O(8) bond length is 1.83 Å. Both Al(4)-O(5) bond lengths are 1.79 Å. Both Al(4)-O(6) bond lengths are 2.41 Å. In the fifth Al site, Al(5) is bonded to one O(5), two equivalent O(7), and three equivalent O(9) atoms to form a mixture of corner and edge-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 52°. The Al(5)-O(5) bond length is 1.79 Å. Both Al(5)-O(7) bond lengths are 2.01 Å. There are two shorter (1.92 Å) and one longer (2.00 Å) Al(5)-O(9) bond length. In the sixth Al site, Al(6) is bonded in a 6-coordinate geometry to one O(6), one O(9), two equivalent O(7), and two equivalent O(8) atoms. The Al(6)-O(6) bond length is 1.92 Å. The Al(6)-O(9) bond length is 1.82 Å. Both Al(6)-O(7) bond lengths are 2.30 Å. Both Al(6)-O(8) bond lengths are 1.78 Å. There are nine inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to two equivalent Al(1) and three equivalent Al(2) atoms. In the second O site, O(2) is bonded in a trigonal planar geometry to one Al(4) and two equivalent Al(2) atoms. In the third O site, O(3) is bonded to one Al(3) and three equivalent Al(1) atoms to form a mixture of corner and edge-sharing OAl4 trigonal pyramids. In the fourth O site, O(4) is bonded to one Al(1), one Al(2), and two equivalent Al(3) atoms to form a mixture of corner and edge-sharing OAl4 trigonal pyramids. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Al(5) and two equivalent Al(4) atoms. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to one Al(6), two equivalent Al(3), and two equivalent Al(4) atoms. In the seventh O site, O(7) is bonded in a 5-coordinate geometry to one Al(3), two equivalent Al(5), and two equivalent Al(6) atoms. In the eighth O site, O(8) is bonded in a trigonal non-coplanar geometry to one Al(4) and two equivalent Al(6) atoms. In the ninth O site, O(9) is bonded to one Al(6) and three equivalent Al(5) atoms to form a mixture of corner and edge-sharing OAl4 trigonal pyramids.