Materials Data on CaAl12O19 by Materials Project

Abstract

CaAl12O19 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Ca2+ is bonded to twelve O2- atoms to form CaO12 cuboctahedra that share corners with six equivalent CaO12 cuboctahedra, edges with six equivalent AlO6 octahedra, edges with three equivalent AlO5 trigonal bipyramids, and faces with six equivalent AlO6 octahedra. There are six shorter (2.72 Å) and six longer (2.81 Å) Ca–O bond lengths. There are five inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to five O2- atoms to form AlO5 trigonal bipyramids that share corners with twelve AlO6 octahedra and edges with three equivalent CaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 41–61°. There is three shorter (1.77 Å) and two longer (2.21 Å) Al–O bond length. In the second Al3+ site, Al3+ is bonded to six equivalent O2- atoms to form AlO6 octahedra that share corners with six equivalent AlO4 tetrahedra and edges with six equivalent AlO6 octahedra. All Al–O bond lengths are 1.90 Å. In the third Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with six equivalent AlO6 octahedra, corners with three equivalent AlO5 trigonal bipyramids, faces with three equivalent CaO12 cuboctahedra, and a faceface with one AlO6 octahedra. The corner-sharing octahedral tilt angles are 52°. There is three shorter (1.89 Å) and three longer (1.97 Å) Al–O bond length. In the fourth Al3+ site, Al3+ is bonded to four O2- atoms to form corner-sharing AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 53–59°. There is three shorter (1.81 Å) and one longer (1.83 Å) Al–O bond length. In the fifth Al3+ site, Al3+ is bonded to six O2- atoms to form AlO6 octahedra that share corners with two equivalent AlO6 octahedra, corners with three equivalent AlO4 tetrahedra, a cornercorner with one AlO5 trigonal bipyramid, an edgeedge with one CaO12 cuboctahedra, and edges with five AlO6 octahedra. The corner-sharing octahedral tilt angles are 52°. There are a spread of Al–O bond distances ranging from 1.82–2.02 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to four Al3+ atoms to form distorted corner-sharing OAl4 tetrahedra. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+ and three Al3+ atoms. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to four Al3+ atoms. In the fifth O2- site, O2- is bonded in a 5-coordinate geometry to two equivalent Ca2+ and three Al3+ atoms.