Materials Data on Mg7(SiO7)2 by Materials Project

Abstract

Mg7(SiO7)2 is beta indium sulfide-derived structured and crystallizes in the hexagonal P6_3 space group. The structure is three-dimensional. there are three inequivalent Mg sites. In the first Mg site, Mg is bonded to six O atoms to form distorted MgO6 octahedra that share corners with five MgO6 octahedra, corners with three SiO4 tetrahedra, and edges with four MgO6 octahedra. The corner-sharing octahedra tilt angles range from 17–63°. There are a spread of Mg–O bond distances ranging from 1.97–2.21 Å. In the second Mg site, Mg is bonded to six O atoms to form MgO6 octahedra that share corners with four equivalent MgO6 octahedra, corners with two SiO4 tetrahedra, edges with four MgO6 octahedra, and an edgeedge with one SiO4 tetrahedra. The corner-sharing octahedra tilt angles range from 17–63°. There are a spread of Mg–O bond distances ranging from 1.98–2.32 Å. In the third Mg site, Mg is bonded to six O atoms to form a mixture of distorted corner and edge-sharing MgO6 octahedra. The corner-sharing octahedral tilt angles are 55°. There are three shorter (1.98 Å) and three longer (2.07 Å) Mg–O bond lengths. 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 nine MgO6 octahedra. The corner-sharing octahedra tilt angles range from 44–58°. All Si–O bond lengths are 1.66 Å. In the second Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share corners with six MgO6 octahedra and edges with three equivalent MgO6 octahedra. The corner-sharing octahedra tilt angles range from 51–57°. There is one shorter (1.65 Å) and three longer (1.66 Å) Si–O bond length. There are six inequivalent O sites. In the first O site, O is bonded in a see-saw-like geometry to four Mg atoms. In the second O site, O is bonded in a distorted trigonal pyramidal geometry to three equivalent Mg and one Si atom. In the third O site, O is bonded in a distorted rectangular see-saw-like geometry to three equivalent Mg and one Si atom. In the fourth O site, O is bonded in a rectangular see-saw-like geometry to three Mg and one Si atom. In the fifth O site, O is bonded in a trigonal planar geometry to three Mg atoms. In the sixth O site, O is bonded in a distorted trigonal planar geometry to two Mg and one Si atom.