DOI: 10.17188/1710956
title: Materials Data on CaNb4O8 by Materials Project

description: CaNb4O8 crystallizes in the monoclinic Cm 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 NbO6 octahedra. There are a spread of Ca–O bond distances ranging from 2.37–2.59 Å. In the second 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 2.29–2.60 Å. In the third Ca2+ site, Ca2+ is bonded to eight O2- atoms to form distorted CaO8 hexagonal bipyramids that share an edgeedge with one CaO8 hexagonal bipyramid, edges with six NbO6 octahedra, and edges with two equivalent NbO6 pentagonal pyramids. There are a spread of Ca–O bond distances ranging from 2.35–2.59 Å. There are eight inequivalent Nb+3.50+ sites. In the first Nb+3.50+ site, Nb+3.50+ is bonded in a distorted square co-planar geometry to four O2- atoms. There are two shorter (2.03 Å) and two longer (2.07 Å) Nb–O bond lengths. In the second Nb+3.50+ site, Nb+3.50+ is bonded in a distorted square co-planar geometry to four O2- atoms. There are two shorter (2.03 Å) and two longer (2.07 Å) Nb–O bond lengths. In the third Nb+3.50+ site, Nb+3.50+ is bonded in a distorted square co-planar geometry to four O2- atoms. There are two shorter (2.05 Å) and two longer (2.06 Å) Nb–O bond lengths. In the fourth Nb+3.50+ site, Nb+3.50+ is bonded in a distorted square co-planar geometry to four O2- atoms. All Nb–O bond lengths are 2.06 Å. In the fifth Nb+3.50+ site, Nb+3.50+ is bonded to six O2- atoms to form distorted NbO6 pentagonal pyramids that share corners with two NbO6 octahedra, an edgeedge with one CaO8 hexagonal bipyramid, and edges with two NbO6 octahedra. The corner-sharing octahedra tilt angles range from 31–69°. There are a spread of Nb–O bond distances ranging from 2.01–2.22 Å. In the sixth Nb+3.50+ site, Nb+3.50+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with two NbO6 octahedra, edges with three CaO8 hexagonal bipyramids, and edges with two NbO6 octahedra. The corner-sharing octahedra tilt angles range from 36–72°. There are a spread of Nb–O bond distances ranging from 2.03–2.22 Å. In the seventh Nb+3.50+ site, Nb+3.50+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share a cornercorner with one NbO6 octahedra, a cornercorner with one NbO6 pentagonal pyramid, an edgeedge with one CaO8 hexagonal bipyramid, an edgeedge with one NbO6 octahedra, and an edgeedge with one NbO6 pentagonal pyramid. The corner-sharing octahedral tilt angles are 36°. There are a spread of Nb–O bond distances ranging from 1.98–2.23 Å. In the eighth Nb+3.50+ site, Nb+3.50+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share a cornercorner with one NbO6 octahedra, a cornercorner with one NbO6 pentagonal pyramid, edges with three CaO8 hexagonal bipyramids, an edgeedge with one NbO6 octahedra, and an edgeedge with one NbO6 pentagonal pyramid. The corner-sharing octahedral tilt angles are 72°. There are a spread of Nb–O bond distances ranging from 2.00–2.25 Å. There are twelve inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three 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 in a 4-coordinate geometry to one Ca2+ and three Nb+3.50+ atoms. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+ and three Nb+3.50+ atoms. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to one Ca2+ and three Nb+3.50+ atoms. 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 4-coordinate geometry to one Ca2+ and three Nb+3.50+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Nb+3.50+ atoms. In the ninth O2- site, O2- is bonded in a distorted T-shaped geometry to one Ca2+ and two Nb+3.50+ atoms. In the tenth O2- site, O2- is bonded to two Ca2+ and two Nb+3.50+ atoms to form a mixture of distorted corner and edge-sharing OCa2Nb2 trigonal pyramids. In the eleventh O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to one Ca2+ and two Nb+3.50+ atoms. In the twelfth O2- site, O2- is bonded to two Ca2+ and two Nb+3.50+ atoms to form a mixture of distorted corner and edge-sharing OCa2Nb2 tetrahedra.