CaAl2O4 crystallizes in the hexagonal P6_3 space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 3-coordinate geometry to three equivalent O(4) atoms. In the second Ca site, Ca(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form CaO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra and corners with six equivalent Al(2)O4 tetrahedra. In the third Ca site, Ca(3) is bonded in a 6-coordinate geometry to three equivalent O(2) and three equivalent O(3) atoms. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AlO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra and corners with four equivalent Al(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-72°. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AlO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra and corners with four equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 61-65°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ca(2), one Al(1), and one Al(2) atom. In the second O site, O(2) is bonded to one Ca(2), one Ca(3), one Al(1), and one Al(2) atom to form distorted edge-sharing OCa2Al2 trigonal pyramids. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(3), one Al(1), and one Al(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Al(2) atom.
CaAl2O4 crystallizes in the hexagonal P6_3 space group. There are three inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 3-coordinate geometry to three equivalent O(4) atoms. All Ca(1)-O(4) bond lengths are 2.33 Å. In the second Ca site, Ca(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form CaO6 octahedra that share corners with six equivalent Al(1)O4 tetrahedra and corners with six equivalent Al(2)O4 tetrahedra. All Ca(2)-O(1) bond lengths are 2.38 Å. All Ca(2)-O(2) bond lengths are 2.54 Å. In the third Ca site, Ca(3) is bonded in a 6-coordinate geometry to three equivalent O(2) and three equivalent O(3) atoms. All Ca(3)-O(2) bond lengths are 2.52 Å. All Ca(3)-O(3) bond lengths are 2.30 Å. There are two inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AlO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra and corners with four equivalent Al(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 51-72°. The Al(1)-O(1) bond length is 1.78 Å. The Al(1)-O(2) bond length is 1.78 Å. The Al(1)-O(3) bond length is 1.77 Å. The Al(1)-O(4) bond length is 1.78 Å. In the second Al site, Al(2) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form AlO4 tetrahedra that share corners with two equivalent Ca(2)O6 octahedra and corners with four equivalent Al(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 61-65°. The Al(2)-O(1) bond length is 1.77 Å. The Al(2)-O(2) bond length is 1.79 Å. The Al(2)-O(3) bond length is 1.78 Å. The Al(2)-O(4) bond length is 1.77 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ca(2), one Al(1), and one Al(2) atom. In the second O site, O(2) is bonded to one Ca(2), one Ca(3), one Al(1), and one Al(2) atom to form distorted edge-sharing OCa2Al2 trigonal pyramids. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(3), one Al(1), and one Al(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to one Ca(1), one Al(1), and one Al(2) atom.