DOE OSTI2019
Nb2Se3 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are four inequivalent Nb3+ sites. In the first Nb3+ site, Nb3+ is bonded to five Se2- atoms to form distorted NbSe5 trigonal bipyramids that share corners with four equivalent NbSe6 octahedra, corners with two equivalent NbSe7 pentagonal bipyramids, corners with two equivalent NbSe6 pentagonal pyramids, corners with two equivalent NbSe5 trigonal bipyramids, edges with two equivalent NbSe6 pentagonal pyramids, and a faceface with one NbSe7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 40–43°. There are a spread of Nb–Se bond distances ranging from 2.48–2.73 Å. In the second Nb3+ site, Nb3+ is bonded to six Se2- atoms to form distorted NbSe6 pentagonal pyramids that share corners with two equivalent NbSe6 octahedra, corners with two equivalent NbSe7 pentagonal bipyramids, corners with two equivalent NbSe5 trigonal bipyramids, edges with two equivalent NbSe7 pentagonal bipyramids, edges with two equivalent NbSe6 pentagonal pyramids, edges with two equivalent NbSe5 trigonal bipyramids, and a faceface with one NbSe6 octahedra. The corner-sharing octahedral tilt angles are 46°. There are a spread of Nb–Se bond distances ranging from 2.59–2.69 Å. In the third Nb3+ site, Nb3+ is bonded to seven Se2- atoms to form distorted NbSe7 pentagonal bipyramids that share corners with two equivalent NbSe6 octahedra, corners with two equivalent NbSe6 pentagonal pyramids, corners with two equivalent NbSe5 trigonal bipyramids, edges with two equivalent NbSe6 octahedra, edges with two equivalent NbSe6 pentagonal pyramids, faces with two equivalent NbSe7 pentagonal bipyramids, and a faceface with one NbSe5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 41°. There are a spread of Nb–Se bond distances ranging from 2.61–2.82 Å. In the fourth Nb3+ site, Nb3+ is bonded to six Se2- atoms to form NbSe6 octahedra that share corners with two equivalent NbSe7 pentagonal bipyramids, corners with two equivalent NbSe6 pentagonal pyramids, corners with four equivalent NbSe5 trigonal bipyramids, edges with two equivalent NbSe6 octahedra, edges with two equivalent NbSe7 pentagonal bipyramids, and a faceface with one NbSe6 pentagonal pyramid. There are a spread of Nb–Se bond distances ranging from 2.45–2.66 Å. There are six inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 1-coordinate geometry to three Nb3+ atoms. In the second Se2- site, Se2- is bonded to six Nb3+ atoms to form distorted edge-sharing SeNb6 pentagonal pyramids. In the third Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb3+ atoms. In the fourth Se2- site, Se2- is bonded in a 3-coordinate geometry to three Nb3+ atoms. In the fifth Se2- site, Se2- is bonded in a distorted rectangular see-saw-like geometry to four Nb3+ atoms. In the sixth Se2- site, Se2- is bonded in a 5-coordinate geometry to five Nb3+ atoms.