Materials Data on Ca4Nb2O9 by Materials Project

Abstract

Ca4Nb2O9 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are five inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 37–43°. There are four shorter (2.30 Å) and two longer (2.32 Å) Ca–O bond lengths. In the second Ca2+ site, Ca2+ is bonded in a 4-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.32–3.04 Å. In the third 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 2.35–2.81 Å. In the fourth Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six NbO6 octahedra. The corner-sharing octahedra tilt angles range from 37–41°. There are a spread of Ca–O bond distances ranging from 2.28–2.33 Å. In the fifth Ca2+ site, Ca2+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Ca–O bond distances ranging from 2.28–2.95 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with three CaO6 octahedra and corners with three NbO6 octahedra. The corner-sharing octahedra tilt angles range from 29–41°. There are a spread of Nb–O bond distances ranging from 1.94–2.21 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with three CaO6 octahedra and corners with three NbO6 octahedra. The corner-sharing octahedra tilt angles range from 28–43°. There are a spread of Nb–O bond distances ranging from 1.92–2.21 Å. There are nine inequivalent O2- sites. In the first O2- site, O2- is bonded to two Ca2+ and two Nb5+ atoms to form distorted corner-sharing OCa2Nb2 tetrahedra. In the second O2- site, O2- is bonded in a 5-coordinate geometry to four Ca2+ and one Nb5+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to four Ca2+ and one Nb5+ atom. In the fourth O2- site, O2- is bonded in a 5-coordinate geometry to three Ca2+ and two equivalent Nb5+ atoms. In the fifth O2- site, O2- is bonded in a 5-coordinate geometry to three Ca2+ and two equivalent Nb5+ atoms. In the sixth O2- site, O2- is bonded in a 5-coordinate geometry to four Ca2+ and one Nb5+ atom. In the seventh O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Nb5+ atom. In the eighth O2- site, O2- is bonded to three Ca2+ and one Nb5+ atom to form distorted corner-sharing OCa3Nb tetrahedra. In the ninth O2- site, O2- is bonded in a 4-coordinate geometry to three Ca2+ and one Nb5+ atom.