Materials Data on Sr6Nb7O21 by Materials Project

Abstract

Sr6Nb7O21 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with ten equivalent SrO12 cuboctahedra, faces with five equivalent SrO12 cuboctahedra, and faces with eight NbO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.80–2.90 Å. There are two inequivalent Nb+4.29+ sites. In the first Nb+4.29+ site, Nb+4.29+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra and faces with seven equivalent SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–6°. There are a spread of Nb–O bond distances ranging from 2.01–2.06 Å. In the second Nb+4.29+ site, Nb+4.29+ is bonded to six equivalent O2- atoms to form NbO6 octahedra that share corners with six equivalent NbO6 octahedra and faces with six equivalent SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 5°. All Nb–O bond lengths are 2.04 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to three equivalent Sr2+ and two Nb+4.29+ atoms. In the second O2- site, O2- is bonded in a distorted linear geometry to three equivalent Sr2+ and two equivalent Nb+4.29+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+ and two equivalent Nb+4.29+ atoms. In the fourth O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+ and two equivalent Nb+4.29+ atoms.