Materials Data on Mg2Al2SiO9 by Materials Project

Mg2Al2SiO9 crystallizes in the triclinic P1 space group. The structure is two-dimensional and consists of two Mg2Al2SiO9 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form distorted MgO6 octahedra that share a cornercorner with one AlO4 tetrahedra, a cornercorner with one SiO4 tetrahedra, edges with three equivalent MgO6 octahedra, and edges with three equivalent AlO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.05–2.20 Å. In the second Mg site, Mg is bonded to six O atoms to form distorted MgO6 octahedra that share a cornercorner with one AlO4 tetrahedra, a cornercorner with one SiO4 tetrahedra, edges with three equivalent MgO6 octahedra, and edges with three equivalent AlO6 octahedra. There are a spread of Mg–O bond distances ranging from 2.04–2.25 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 a cornercorner with one AlO6 octahedra, corners with two MgO6 octahedra, and corners with three equivalent SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–63°. There are a spread of Al–O bond distances ranging from 1.74–1.81 Å. In the second Al site, Al is bonded to six O atoms to form AlO6 octahedra that share a cornercorner with one AlO4 tetrahedra, a cornercorner with one SiO4 tetrahedra, and edges with six MgO6 octahedra. There are a spread of Al–O bond distances ranging from 1.85–1.98 Å. Si is bonded to four O atoms to form SiO4 tetrahedra that share a cornercorner with one AlO6 octahedra, corners with two MgO6 octahedra, and corners with three equivalent AlO4 tetrahedra. The corner-sharing octahedra tilt angles range from 53–61°. There is three shorter (1.62 Å) and one longer (1.69 Å) Si–O bond length. There are nine 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 trigonal non-coplanar geometry to two Mg and one Al atom. In the third O site, O is bonded in a trigonal non-coplanar geometry to two Mg and one Al atom. In the fourth O site, O is bonded in a distorted rectangular see-saw-like geometry to two Mg and two Al atoms. In the fifth O site, O is bonded in a trigonal non-coplanar geometry to two Mg and one Al atom. In the sixth O site, O is bonded in a bent 120 degrees geometry to one Al and one Si atom. In the seventh O site, O is bonded in a rectangular see-saw-like geometry to two Mg, 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 trigonal non-coplanar geometry to two Mg and one Al atom.