Materials Data on Al2Si2O9 by Materials Project

Al2Si2O9 crystallizes in the monoclinic Cc space group. The structure is two-dimensional and consists of two Al2Si2O9 sheets oriented in the (0, 0, 1) direction. 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 two SiO4 tetrahedra and edges with three equivalent AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.88–1.99 Å. In the second Al site, Al is bonded to six O atoms to form AlO6 octahedra that share corners with two SiO4 tetrahedra and edges with three equivalent AlO6 octahedra. There are a spread of Al–O bond distances ranging from 1.88–1.99 Å. There are two inequivalent Si sites. In the first Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with two AlO6 octahedra and corners with three equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 51–54°. There is three shorter (1.62 Å) and one longer (1.66 Å) Si–O bond length. In the second Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with two AlO6 octahedra and corners with three equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 51–54°. There are a spread of Si–O bond distances ranging from 1.61–1.66 Å. There are nine inequivalent O sites. In the first O site, O is bonded in a water-like geometry to two Al atoms. In the second O site, O is bonded in a distorted bent 120 degrees geometry to two Si atoms. In the third O site, O is bonded in a distorted bent 120 degrees geometry to two Si atoms. 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 distorted trigonal planar geometry to two Al and one Si atom. In the sixth O site, O is bonded in a distorted trigonal planar geometry to two Al and one Si atom. In the seventh O site, O is bonded in a bent 120 degrees geometry to two Al atoms. In the eighth O site, O is bonded in a water-like geometry to two Al atoms. In the ninth O site, O is bonded in a water-like geometry to two Al atoms.