Materials Data on Ba4Nb2O9 by Materials Project

Ba4Nb2O9 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. there are three inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded in a 6-coordinate geometry to six equivalent O2- atoms. All Ba–O bond lengths are 2.64 Å. In the second Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with six equivalent BaO12 cuboctahedra and faces with six equivalent NbO6 octahedra. There are six shorter (2.96 Å) and six longer (3.02 Å) Ba–O bond lengths. In the third Ba2+ site, Ba2+ is bonded in a distorted q6 geometry to nine O2- atoms. There are three shorter (2.71 Å) and six longer (3.03 Å) Ba–O bond lengths. Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with three equivalent NbO6 octahedra and faces with three equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are three shorter (1.91 Å) and three longer (2.23 Å) Nb–O bond lengths. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to four Ba2+ and one Nb5+ atom. In the second O2- site, O2- is bonded to four Ba2+ and two equivalent Nb5+ atoms to form a mixture of distorted corner and face-sharing OBa4Nb2 octahedra. The corner-sharing octahedra tilt angles range from 0–60°.