DOE OSTI2020
Sc3(NbSi2)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to six Si4- atoms to form distorted ScSi6 octahedra that share corners with four equivalent ScSi6 octahedra, corners with eight equivalent NbSi7 pentagonal bipyramids, and faces with four equivalent NbSi7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 50–58°. There are a spread of Sc–Si bond distances ranging from 2.62–3.01 Å. In the second Sc3+ site, Sc3+ is bonded in a 6-coordinate geometry to six Si4- atoms. There are a spread of Sc–Si bond distances ranging from 2.59–2.77 Å. Nb+3.50+ is bonded to seven Si4- atoms to form distorted NbSi7 pentagonal bipyramids that share corners with four equivalent ScSi6 octahedra, corners with six equivalent NbSi7 pentagonal bipyramids, edges with two equivalent NbSi7 pentagonal bipyramids, faces with two equivalent ScSi6 octahedra, and faces with three equivalent NbSi7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 47–50°. There are a spread of Nb–Si bond distances ranging from 2.74–3.03 Å. There are three inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 9-coordinate geometry to six Sc3+, two equivalent Nb+3.50+, and one Si4- atom. The Si–Si bond length is 2.37 Å. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to four Sc3+, four equivalent Nb+3.50+, and one Si4- atom. In the third Si4- site, Si4- is bonded in a 9-coordinate geometry to four Sc3+, four equivalent Nb+3.50+, and one Si4- atom. The Si–Si bond length is 2.59 Å.