DOI: 10.17188/1203008
title: Materials Data on Sr4Nb2O9 by Materials Project

description: Sr4Nb2O9 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are five inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to six O2- atoms to form distorted SrO6 pentagonal pyramids that share corners with three equivalent SrO6 octahedra, corners with three equivalent NbO6 octahedra, edges with three equivalent NbO6 octahedra, and a faceface with one SrO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 21–70°. There are a spread of Sr–O bond distances ranging from 2.47–2.65 Å. In the second Sr2+ site, Sr2+ is bonded to six O2- atoms to form distorted SrO6 pentagonal pyramids that share corners with three equivalent SrO6 octahedra, corners with three equivalent NbO6 octahedra, edges with three equivalent NbO6 octahedra, and a faceface with one SrO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 21–69°. There are a spread of Sr–O bond distances ranging from 2.48–2.62 Å. In the third Sr2+ site, Sr2+ is bonded in a 3-coordinate geometry to nine O2- atoms. There are a spread of Sr–O bond distances ranging from 2.54–3.08 Å. In the fourth Sr2+ site, Sr2+ is bonded to six O2- atoms to form SrO6 octahedra that share corners with six equivalent NbO6 octahedra and corners with six equivalent SrO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 33–35°. There are two shorter (2.49 Å) and four longer (2.50 Å) Sr–O bond lengths. In the fifth Sr2+ site, Sr2+ is bonded to six O2- atoms to form SrO6 octahedra that share corners with six equivalent NbO6 octahedra and corners with six equivalent SrO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 34°. All Sr–O bond lengths are 2.52 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with three equivalent SrO6 octahedra, corners with three equivalent SrO6 pentagonal pyramids, edges with three equivalent SrO6 pentagonal pyramids, and a faceface with one NbO6 octahedra. The corner-sharing octahedral tilt angles are 34°. There are a spread of Nb–O bond distances ranging from 1.91–2.21 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with three equivalent SrO6 octahedra, corners with three equivalent SrO6 pentagonal pyramids, edges with three equivalent SrO6 pentagonal pyramids, and a faceface with one NbO6 octahedra. The corner-sharing octahedra tilt angles range from 33–35°. There are a spread of Nb–O bond distances ranging from 1.91–2.21 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Nb5+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Nb5+ atom. In the third O2- site, O2- is bonded to three Sr2+ and two Nb5+ atoms to form a mixture of distorted corner and edge-sharing OSr3Nb2 square pyramids. In the fourth O2- site, O2- is bonded to three Sr2+ and two Nb5+ atoms to form a mixture of distorted corner and edge-sharing OSr3Nb2 square pyramids. In the fifth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Nb5+ atom. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Nb5+ atom. In the seventh O2- site, O2- is bonded to three Sr2+ and two Nb5+ atoms to form a mixture of distorted corner and edge-sharing OSr3Nb2 square pyramids. In the eighth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Nb5+ atom. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Nb5+ atom.