Materials Data on CaAl2(SiO5)2 by Materials Project

Abstract

CaAl2(SiO5)2 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Ca is bonded in a 4-coordinate geometry to four O atoms. There are a spread of Ca–O bond distances ranging from 2.24–2.38 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded to six O atoms to form AlO6 octahedra that share corners with four equivalent SiO5 trigonal bipyramids and edges with two equivalent AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.82–2.12 Å. In the second Al site, Al is bonded to six O atoms to form distorted AlO6 octahedra that share edges with two equivalent AlO6 octahedra and edges with two equivalent SiO5 trigonal bipyramids. There is two shorter (1.86 Å) and four longer (1.97 Å) Al–O bond length. Si is bonded to five O atoms to form SiO5 trigonal bipyramids that share corners with two equivalent AlO6 octahedra, an edgeedge with one AlO6 octahedra, and an edgeedge with one SiO5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 35–42°. There are a spread of Si–O bond distances ranging from 1.68–1.84 Å. There are six inequivalent O sites. In the first O site, O is bonded in a distorted trigonal non-coplanar geometry to one Ca and two equivalent Si atoms. In the second O site, O is bonded in a distorted water-like geometry to one Al and one Si atom. In the third O site, O is bonded in a distorted trigonal planar geometry to one Ca, one Al, and one Si atom. In the fourth O site, O is bonded in a 3-coordinate geometry to two Al and one O atom. The O–O bond length is 1.41 Å. In the fifth O site, O is bonded in a T-shaped geometry to two Al and one Si atom. In the sixth O site, O is bonded in a 3-coordinate geometry to one Ca and two equivalent Si atoms.