Materials Data on Ca2Al2SiO8 by Materials Project
Ca2Al2SiO8 crystallizes in the tetragonal I-42m space group. The structure is three-dimensional. Ca is bonded to six O atoms to form distorted CaO6 octahedra that share corners with two equivalent SiO4 tetrahedra, corners with four equivalent AlO4 tetrahedra, and edges with three equivalent CaO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.33–2.44 Å. Al is bonded to four O atoms to form AlO4 tetrahedra that share corners with four equivalent CaO6 octahedra, corners with two equivalent AlO4 tetrahedra, and corners with two equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 67–69°. There is two shorter (1.75 Å) and two longer (1.79 Å) Al–O bond length. Si is bonded to four equivalent O atoms to form SiO4 tetrahedra that share corners with four equivalent CaO6 octahedra and corners with four equivalent AlO4 tetrahedra. The corner-sharing octahedral tilt angles are 63°. All Si–O bond lengths are 1.64 Å. There are three inequivalent O sites. In the first O site, O is bonded in a trigonal non-coplanar geometry to three equivalent Ca atoms. In the second O site, O is bonded in a distorted trigonal planar geometry to one Ca and two equivalent Al atoms. In the third O site, O is bonded in a distorted trigonal planar geometry to one Ca, one Al, and one Si atom.