Materials Data on Ca3Nb4(O6F)2 by Materials Project

Abstract

Ca3Nb4(O6F)2 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Ca2+ is bonded to six O2- and two equivalent F1- atoms to form distorted CaO6F2 hexagonal bipyramids that share edges with four equivalent CaO6F2 hexagonal bipyramids and edges with six NbO6 octahedra. There are two shorter (2.63 Å) and four longer (2.67 Å) Ca–O bond lengths. Both Ca–F bond lengths are 2.23 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six equivalent O2- atoms to form NbO6 octahedra that share corners with six equivalent NbO6 octahedra and edges with six equivalent CaO6F2 hexagonal bipyramids. The corner-sharing octahedral tilt angles are 44°. All Nb–O bond lengths are 2.00 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra and edges with four equivalent CaO6F2 hexagonal bipyramids. The corner-sharing octahedra tilt angles range from 40–44°. All Nb–O bond lengths are 2.01 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Ca2+ and two equivalent Nb5+ atoms. In the second O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ca2+ and two Nb5+ atoms. F1- is bonded in a trigonal planar geometry to three equivalent Ca2+ atoms.