DOE OSTI2020
Nb4As3 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. there are five inequivalent Nb+2.25+ sites. In the first Nb+2.25+ site, Nb+2.25+ is bonded to six As3- atoms to form NbAs6 octahedra that share corners with six NbAs6 octahedra, corners with five equivalent NbAs5 square pyramids, corners with two equivalent NbAs5 trigonal bipyramids, edges with two equivalent NbAs6 octahedra, edges with three equivalent NbAs5 trigonal bipyramids, faces with two NbAs6 octahedra, and a faceface with one NbAs5 square pyramid. The corner-sharing octahedra tilt angles range from 43–53°. There are a spread of Nb–As bond distances ranging from 2.57–2.79 Å. In the second Nb+2.25+ site, Nb+2.25+ is bonded to five As3- atoms to form NbAs5 square pyramids that share corners with five equivalent NbAs6 octahedra, a cornercorner with one NbAs5 square pyramid, corners with six equivalent NbAs5 trigonal bipyramids, edges with two equivalent NbAs6 octahedra, edges with two equivalent NbAs5 square pyramids, edges with two equivalent NbAs5 trigonal bipyramids, and a faceface with one NbAs6 octahedra. The corner-sharing octahedra tilt angles range from 35–56°. There are a spread of Nb–As bond distances ranging from 2.60–2.67 Å. In the third Nb+2.25+ site, Nb+2.25+ is bonded to five As3- atoms to form distorted NbAs5 trigonal bipyramids that share corners with four NbAs6 octahedra, corners with six equivalent NbAs5 square pyramids, edges with three equivalent NbAs6 octahedra, edges with two equivalent NbAs5 square pyramids, and edges with four equivalent NbAs5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 30–44°. There are a spread of Nb–As bond distances ranging from 2.66–2.73 Å. In the fourth Nb+2.25+ site, Nb+2.25+ is bonded in a square co-planar geometry to four As3- atoms. There are two shorter (2.67 Å) and two longer (2.76 Å) Nb–As bond lengths. In the fifth Nb+2.25+ site, Nb+2.25+ is bonded to six As3- atoms to form NbAs6 octahedra that share corners with eight equivalent NbAs6 octahedra, corners with four equivalent NbAs5 trigonal bipyramids, edges with two equivalent NbAs6 octahedra, edges with four equivalent NbAs5 square pyramids, and faces with two equivalent NbAs6 octahedra. The corner-sharing octahedra tilt angles range from 43–53°. There are a spread of Nb–As bond distances ranging from 2.59–2.73 Å. There are four inequivalent As3- sites. In the first As3- site, As3- is bonded in a 7-coordinate geometry to seven Nb+2.25+ atoms. In the second As3- site, As3- is bonded in a 8-coordinate geometry to eight Nb+2.25+ atoms. In the third As3- site, As3- is bonded to six Nb+2.25+ atoms to form distorted face-sharing AsNb6 pentagonal pyramids. In the fourth As3- site, As3- is bonded in a 6-coordinate geometry to six Nb+2.25+ atoms.