DOI: 10.17188/1298691
title: Materials Data on Sr4Ta2O9 by Materials Project

description: Sr4Ta2O9 is Krennerite-derived structured and 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 in a 3-coordinate geometry to nine O2- atoms. There are a spread of Sr–O bond distances ranging from 2.54–3.24 Å. In the second Sr2+ site, Sr2+ is bonded to six O2- atoms to form SrO6 octahedra that share corners with six equivalent TaO6 octahedra and corners with six equivalent SrO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 33–34°. There are four shorter (2.53 Å) and two longer (2.54 Å) Sr–O bond lengths. In the third Sr2+ site, Sr2+ is bonded to six O2- atoms to form SrO6 octahedra that share corners with six equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 34–36°. All Sr–O bond lengths are 2.47 Å. In the fourth 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 TaO6 octahedra, and edges with three equivalent TaO6 octahedra. The corner-sharing octahedra tilt angles range from 21–70°. There are a spread of Sr–O bond distances ranging from 2.49–2.65 Å. In the fifth Sr2+ site, Sr2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Sr–O bond distances ranging from 2.44–2.70 Å. There are two inequivalent Ta5+ sites. In the first Ta5+ site, Ta5+ is bonded to six O2- atoms to form distorted TaO6 octahedra that share corners with three equivalent SrO6 octahedra, corners with three equivalent SrO6 pentagonal pyramids, and a faceface with one TaO6 octahedra. The corner-sharing octahedra tilt angles range from 34–36°. There are a spread of Ta–O bond distances ranging from 1.90–2.19 Å. In the second Ta5+ site, Ta5+ is bonded to six O2- atoms to form distorted TaO6 octahedra that share corners with three equivalent SrO6 octahedra, edges with three equivalent SrO6 pentagonal pyramids, and a faceface with one TaO6 octahedra. The corner-sharing octahedra tilt angles range from 33–34°. There are a spread of Ta–O bond distances ranging from 1.92–2.17 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded to three Sr2+ and two Ta5+ atoms to form a mixture of distorted edge and corner-sharing OSr3Ta2 trigonal bipyramids. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Ta5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to three Sr2+ and one Ta5+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Ta5+ atom. In the fifth O2- site, O2- is bonded in a 1-coordinate geometry to three Sr2+ and one Ta5+ atom. In the sixth O2- site, O2- is bonded to three Sr2+ and two Ta5+ atoms to form a mixture of distorted edge and corner-sharing OSr3Ta2 trigonal bipyramids. In the seventh O2- site, O2- is bonded to three Sr2+ and two Ta5+ atoms to form a mixture of distorted edge and corner-sharing OSr3Ta2 trigonal bipyramids. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to three Sr2+ and one Ta5+ atom. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to three Sr2+ and one Ta5+ atom.