DOI: 10.17188/1730815
title: Materials Data on NaCa6Ti(Si2O9)2 by Materials Project

description: NaCa6Ti(Si2O9)2 is Esseneite-derived structured and crystallizes in the triclinic P-1 space group. The structure is three-dimensional. Na is bonded to eight O atoms to form distorted NaO8 hexagonal bipyramids that share edges with two equivalent TiO6 octahedra and edges with four SiO4 tetrahedra. There are a spread of Na–O bond distances ranging from 2.33–2.85 Å. There are three inequivalent Ca sites. In the first Ca site, Ca is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Ca–O bond distances ranging from 2.27–2.69 Å. In the second Ca site, Ca is bonded in a 7-coordinate geometry to seven O atoms. There are a spread of Ca–O bond distances ranging from 2.24–2.94 Å. In the third Ca site, Ca is bonded to six O atoms to form CaO6 octahedra that share a cornercorner with one TiO6 octahedra, corners with five SiO4 tetrahedra, and an edgeedge with one CaO6 octahedra. The corner-sharing octahedral tilt angles are 51°. There are a spread of Ca–O bond distances ranging from 2.35–2.47 Å. Ti is bonded to six O atoms to form TiO6 octahedra that share corners with two equivalent CaO6 octahedra, corners with four SiO4 tetrahedra, and edges with two equivalent NaO8 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 51°. There is two shorter (1.91 Å) and four longer (2.03 Å) Ti–O bond length. There are two 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 TiO6 octahedra, corners with two equivalent CaO6 octahedra, a cornercorner with one SiO4 tetrahedra, and an edgeedge with one NaO8 hexagonal bipyramid. The corner-sharing octahedra tilt angles range from 32–53°. There are a spread of Si–O bond distances ranging from 1.62–1.70 Å. In the second Si site, Si is bonded to four O atoms to form SiO4 tetrahedra that share a cornercorner with one TiO6 octahedra, corners with three equivalent CaO6 octahedra, a cornercorner with one SiO4 tetrahedra, and an edgeedge with one NaO8 hexagonal bipyramid. The corner-sharing octahedra tilt angles range from 33–56°. There are a spread of Si–O bond distances ranging from 1.62–1.70 Å. There are nine inequivalent O sites. In the first O site, O is bonded in a 4-coordinate geometry to one Na, one Ca, one Ti, and one Si atom. In the second O site, O is bonded in a 3-coordinate geometry to three Ca and one Si atom. In the third O site, O is bonded in a 4-coordinate geometry to one Na, one Ca, one Ti, and one Si atom. In the fourth O site, O is bonded in a 4-coordinate geometry to three Ca and one Si atom. In the fifth O site, O is bonded in a 4-coordinate geometry to one Na, two equivalent Ca, and one O atom. The O–O bond length is 1.38 Å. In the sixth O site, O is bonded in a 4-coordinate geometry to one Na, one Ca, and two Si atoms. In the seventh O site, O is bonded to three Ca and one Ti atom to form distorted OCa3Ti tetrahedra that share a cornercorner with one OCa3Ti tetrahedra, corners with two equivalent OCa3Si trigonal pyramids, and an edgeedge with one OCa3Ti tetrahedra. In the eighth O site, O is bonded in a distorted trigonal planar geometry to two Ca and one Si atom. In the ninth O site, O is bonded to three Ca and one Si atom to form distorted OCa3Si trigonal pyramids that share corners with two equivalent OCa3Ti tetrahedra and an edgeedge with one OCa3Si trigonal pyramid.