Materials Data on CaAl2O4 by Materials Project

Abstract

CaAl2O4 crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded in a 3-coordinate geometry to three equivalent O2- atoms. All Ca–O bond lengths are 2.33 Å. In the second Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with twelve AlO4 tetrahedra. There are three shorter (2.38 Å) and three longer (2.54 Å) Ca–O bond lengths. In the third Ca2+ site, Ca2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are three shorter (2.30 Å) and three longer (2.52 Å) Ca–O bond lengths. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two equivalent CaO6 octahedra and corners with four equivalent AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 51–72°. There is one shorter (1.77 Å) and three longer (1.78 Å) Al–O bond length. In the second Al3+ site, Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with two equivalent CaO6 octahedra and corners with four equivalent AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 61–65°. There are a spread of Al–O bond distances ranging from 1.77–1.79 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to one Ca2+ and two Al3+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two Ca2+ and two Al3+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+ and two Al3+ atoms. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+ and two Al3+ atoms.