DOI: 10.17188/1263436
title: Materials Data on CaNb4O8 by Materials Project

description: CaNb4O8 crystallizes in the orthorhombic Pmmn space group. The structure is three-dimensional. there are three inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share an edgeedge with one CaO8 hexagonal bipyramid and edges with eight equivalent NbO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.35–2.57 Å. In the second Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share an edgeedge with one CaO8 hexagonal bipyramid and edges with eight NbO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.38–2.57 Å. In the third Ca2+ site, Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.27–2.59 Å. There are six inequivalent Nb+3.50+ sites. In the first Nb+3.50+ site, Nb+3.50+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with two equivalent NbO6 octahedra, edges with three CaO8 hexagonal bipyramids, and edges with two NbO6 octahedra. The corner-sharing octahedra tilt angles range from 31–72°. There are a spread of Nb–O bond distances ranging from 2.01–2.25 Å. In the second Nb+3.50+ site, Nb+3.50+ is bonded in a rectangular see-saw-like geometry to four equivalent O2- atoms. All Nb–O bond lengths are 2.05 Å. In the third Nb+3.50+ site, Nb+3.50+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with two equivalent NbO6 octahedra, an edgeedge with one CaO8 hexagonal bipyramid, and edges with two NbO6 octahedra. The corner-sharing octahedra tilt angles range from 37–71°. There are a spread of Nb–O bond distances ranging from 1.98–2.23 Å. In the fourth Nb+3.50+ site, Nb+3.50+ is bonded in a distorted square co-planar geometry to four equivalent O2- atoms. All Nb–O bond lengths are 2.05 Å. In the fifth Nb+3.50+ site, Nb+3.50+ is bonded in a distorted square co-planar geometry to four equivalent O2- atoms. All Nb–O bond lengths are 2.05 Å. In the sixth Nb+3.50+ site, Nb+3.50+ is bonded in a distorted square co-planar geometry to four equivalent O2- atoms. All Nb–O bond lengths are 2.05 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted T-shaped geometry to one Ca2+ and two equivalent Nb+3.50+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+ and three Nb+3.50+ atoms. In the third O2- site, O2- is bonded to two Ca2+ and two equivalent Nb+3.50+ atoms to form a mixture of distorted edge and corner-sharing OCa2Nb2 tetrahedra. In the fourth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Nb+3.50+ atoms. In the fifth O2- site, O2- is bonded to two Ca2+ and two equivalent Nb+3.50+ atoms to form a mixture of distorted edge and corner-sharing OCa2Nb2 trigonal pyramids. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+ and three Nb+3.50+ atoms. In the seventh O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Ca2+ and two equivalent Nb+3.50+ atoms. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+ and three Nb+3.50+ atoms.