DOI: 10.17188/1676675
title: Materials Data on CaAl2(Si2O7)2 by Materials Project

description: CaAl2(Si2O7)2 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. Ca is bonded to six O atoms to form CaO6 octahedra that share corners with four SiO4 tetrahedra and edges with two AlO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.38–2.52 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded to four O atoms to form AlO4 tetrahedra that share corners with four SiO4 tetrahedra and an edgeedge with one CaO6 octahedra. There are a spread of Al–O bond distances ranging from 1.72–1.79 Å. In the second Al site, Al is bonded to four O atoms to form AlO4 tetrahedra that share corners with four SiO4 tetrahedra and an edgeedge with one CaO6 octahedra. There are a spread of Al–O bond distances ranging from 1.73–1.80 Å. There are four inequivalent Si sites. In the first Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share a cornercorner with one CaO6 octahedra, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. There are a spread of Si–O bond distances ranging from 1.60–1.65 Å. In the second Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share a cornercorner with one CaO6 octahedra, corners with two equivalent AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 67°. There are a spread of Si–O bond distances ranging from 1.60–1.65 Å. In the third Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share a cornercorner with one CaO6 octahedra, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 48°. There are a spread of Si–O bond distances ranging from 1.60–1.65 Å. In the fourth Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share a cornercorner with one CaO6 octahedra, corners with two equivalent AlO4 tetrahedra, and corners with two SiO4 tetrahedra. The corner-sharing octahedral tilt angles are 51°. There are a spread of Si–O bond distances ranging from 1.59–1.65 Å. There are fourteen inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to one Al and one Si atom. In the second O site, O is bonded in a single-bond geometry to one Ca 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 bent 150 degrees geometry to two Si atoms. In the fifth O site, O is bonded in a single-bond geometry to one Ca atom. In the sixth O site, O is bonded in a 3-coordinate geometry to one Ca, one Al, and one Si atom. In the seventh O site, O is bonded in a bent 150 degrees geometry to one Al and one Si atom. In the eighth O site, O is bonded in a bent 150 degrees geometry to one Al and one Si atom. In the ninth O site, O is bonded in a distorted trigonal planar geometry to one Ca, one Al, and one Si atom. In the tenth O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the eleventh O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the twelfth O site, O is bonded in a bent 150 degrees geometry to one Al and one Si atom. In the thirteenth O site, O is bonded in a distorted bent 120 degrees geometry to two Si atoms. In the fourteenth O site, O is bonded in a distorted trigonal planar geometry to one Ca, one Al, and one Si atom.