DOI: 10.17188/1665754
title: Materials Data on CaAl2(Si2O7)2 by Materials Project

description: CaAl2(Si2O7)2 crystallizes in the monoclinic C2 space group. The structure is three-dimensional. Ca is bonded to six O atoms to form distorted CaO6 pentagonal pyramids that share corners with four SiO4 tetrahedra and edges with two AlO4 tetrahedra. There are a spread of Ca–O bond distances ranging from 2.32–2.51 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 pentagonal pyramid. There are a spread of Al–O bond distances ranging from 1.73–1.80 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 pentagonal pyramid. There is two shorter (1.73 Å) and two longer (1.80 Å) Al–O bond length. 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 pentagonal pyramid, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.61–1.65 Å. In the second Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share a cornercorner with one CaO6 pentagonal pyramid, corners with two equivalent AlO4 tetrahedra, and corners with two SiO4 tetrahedra. 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 pentagonal pyramid, corners with two equivalent AlO4 tetrahedra, and corners with two SiO4 tetrahedra. 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 pentagonal pyramid, corners with two AlO4 tetrahedra, and corners with two SiO4 tetrahedra. There are a spread of Si–O bond distances ranging from 1.61–1.65 Å. There are fourteen inequivalent O sites. In the first O site, O is bonded in a bent 150 degrees geometry to two Si atoms. In the second O site, O is bonded in a distorted trigonal planar geometry to one Ca, 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 one Ca, one Al, and one Si atom. In the fifth O site, O is bonded in a 3-coordinate geometry to one Ca, one Al, and one Si atom. In the sixth O site, O is bonded in a bent 150 degrees geometry to 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 two Si atoms. In the ninth O site, O is bonded in a bent 150 degrees geometry to two Si atoms. 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 one Al and one Si atom. 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 single-bond geometry to one Ca atom. In the fourteenth O site, O is bonded in a single-bond geometry to one Ca atom.