DOI: 10.17188/1748008
title: Materials Data on Ba4TiNb9O18 by Materials Project

description: Ba4TiNb9O18 crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are two inequivalent Ba2+ sites. In the first Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with eight equivalent BaO12 cuboctahedra, faces with five equivalent BaO12 cuboctahedra, faces with four equivalent NbO6 octahedra, and faces with four equivalent NbO5 square pyramids. There are a spread of Ba–O bond distances ranging from 2.89–2.98 Å. In the second Ba2+ site, Ba2+ is bonded to twelve O2- atoms to form BaO12 cuboctahedra that share corners with eight equivalent BaO12 cuboctahedra, faces with five equivalent BaO12 cuboctahedra, faces with four equivalent TiO6 octahedra, and faces with four equivalent NbO5 square pyramids. There are a spread of Ba–O bond distances ranging from 2.85–3.00 Å. Ti4+ is bonded to six O2- atoms to form TiO6 octahedra that share corners with four equivalent TiO6 octahedra, corners with two equivalent NbO5 square pyramids, and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (1.97 Å) and four longer (2.10 Å) Ti–O bond lengths. There are four inequivalent Nb+2.67+ sites. In the first Nb+2.67+ site, Nb+2.67+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Nb–O bond distances ranging from 2.11–2.16 Å. In the second Nb+2.67+ site, Nb+2.67+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with four equivalent NbO6 octahedra, corners with two equivalent NbO5 square pyramids, and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.01 Å) and four longer (2.10 Å) Nb–O bond lengths. In the third Nb+2.67+ site, Nb+2.67+ is bonded to five O2- atoms to form NbO5 square pyramids that share a cornercorner with one NbO6 octahedra, corners with four equivalent NbO5 square pyramids, and faces with four equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.11 Å) and one longer (2.17 Å) Nb–O bond lengths. In the fourth Nb+2.67+ site, Nb+2.67+ is bonded to five O2- atoms to form NbO5 square pyramids that share a cornercorner with one TiO6 octahedra, corners with four equivalent NbO5 square pyramids, and faces with four equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.11 Å) and one longer (2.14 Å) Nb–O bond lengths. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded to two equivalent Ba2+ and three Nb+2.67+ atoms to form a mixture of distorted edge and corner-sharing OBa2Nb3 trigonal bipyramids. In the second O2- site, O2- is bonded in a distorted T-shaped geometry to two equivalent Ba2+ and three Nb+2.67+ atoms. In the third O2- site, O2- is bonded to four equivalent Ba2+ and two equivalent Ti4+ atoms to form a mixture of distorted edge, corner, and face-sharing OBa4Ti2 octahedra. The corner-sharing octahedral tilt angles are 0°. In the fourth O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ba2+ and two equivalent Nb+2.67+ atoms. In the fifth O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ba2+ and two Nb+2.67+ atoms. In the sixth O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ba2+, one Ti4+, and one Nb+2.67+ atom. In the seventh O2- site, O2- is bonded in a rectangular see-saw-like geometry to four equivalent Nb+2.67+ atoms.