Materials Data on CaAl2O4 by Materials Project

Abstract

CaAl2O4 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.35–2.51 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 24°. There are a spread of Al–O bond distances ranging from 1.90–2.01 Å. In the second Al3+ site, Al3+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing AlO6 octahedra. The corner-sharing octahedral tilt angles are 16°. There are a spread of Al–O bond distances ranging from 1.89–1.92 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to three equivalent Ca2+ and two Al3+ atoms to form distorted OCa3Al2 trigonal bipyramids that share corners with eleven OCa3Al2 trigonal bipyramids, corners with two equivalent OAl4 trigonal pyramids, edges with five OCa3Al2 trigonal bipyramids, an edgeedge with one OAl4 trigonal pyramid, and a faceface with one OCa3Al2 trigonal bipyramid. In the second O2- site, O2- is bonded to four Al3+ atoms to form OAl4 trigonal pyramids that share corners with eight OCa3Al2 trigonal bipyramids, corners with two equivalent OAl4 trigonal pyramids, edges with three OCaAl4 trigonal bipyramids, and edges with two equivalent OAl4 trigonal pyramids. In the third O2- site, O2- is bonded to three equivalent Ca2+ and two Al3+ atoms to form distorted OCa3Al2 trigonal bipyramids that share corners with nine OCa3Al2 trigonal bipyramids, corners with four equivalent OAl4 trigonal pyramids, edges with six OCa3Al2 trigonal bipyramids, and a faceface with one OCa3Al2 trigonal bipyramid. In the fourth O2- site, O2- is bonded to one Ca2+ and four Al3+ atoms to form distorted OCaAl4 trigonal bipyramids that share corners with six OCa3Al2 trigonal bipyramids, corners with two equivalent OAl4 trigonal pyramids, edges with seven OCa3Al2 trigonal bipyramids, and edges with two equivalent OAl4 trigonal pyramids.