DOE OSTI2020
Sc2(NbSi)3 crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are three inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to five Si4- atoms to form distorted ScSi5 trigonal bipyramids that share corners with eight equivalent NbSi6 octahedra, corners with eight ScSi5 trigonal bipyramids, edges with two equivalent ScSi5 trigonal bipyramids, edges with four equivalent NbSi5 trigonal bipyramids, and faces with four equivalent NbSi6 octahedra. The corner-sharing octahedra tilt angles range from 42–55°. There are a spread of Sc–Si bond distances ranging from 2.68–2.90 Å. In the second Sc3+ site, Sc3+ is bonded to five Si4- atoms to form distorted ScSi5 trigonal bipyramids that share corners with eight equivalent NbSi6 octahedra, corners with eight ScSi5 trigonal bipyramids, edges with two equivalent ScSi5 trigonal bipyramids, edges with four equivalent NbSi5 trigonal bipyramids, and faces with four equivalent NbSi6 octahedra. The corner-sharing octahedra tilt angles range from 42–55°. There are a spread of Sc–Si bond distances ranging from 2.67–2.90 Å. In the third Sc3+ site, Sc3+ is bonded to five Si4- atoms to form distorted ScSi5 trigonal bipyramids that share corners with eight equivalent NbSi6 octahedra, corners with two equivalent ScSi5 trigonal bipyramids, corners with six equivalent NbSi5 trigonal bipyramids, edges with six ScSi5 trigonal bipyramids, and faces with four equivalent NbSi6 octahedra. The corner-sharing octahedra tilt angles range from 41–56°. There are a spread of Sc–Si bond distances ranging from 2.68–2.91 Å. There are two inequivalent Nb2+ sites. In the first Nb2+ site, Nb2+ is bonded to five Si4- atoms to form distorted NbSi5 trigonal bipyramids that share corners with eight equivalent NbSi6 octahedra, corners with three equivalent ScSi5 trigonal bipyramids, corners with five equivalent NbSi5 trigonal bipyramids, edges with six ScSi5 trigonal bipyramids, and faces with four equivalent NbSi6 octahedra. The corner-sharing octahedra tilt angles range from 39–56°. There are a spread of Nb–Si bond distances ranging from 2.66–2.87 Å. In the second Nb2+ site, Nb2+ is bonded to six Si4- atoms to form distorted NbSi6 octahedra that share corners with six equivalent NbSi6 octahedra, corners with four equivalent NbSi5 trigonal bipyramids, corners with eight ScSi5 trigonal bipyramids, edges with three equivalent NbSi6 octahedra, faces with two equivalent NbSi6 octahedra, faces with two equivalent NbSi5 trigonal bipyramids, and faces with four ScSi5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 34–36°. There are a spread of Nb–Si bond distances ranging from 2.72–2.76 Å. There are four inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 9-coordinate geometry to five Sc3+ and four equivalent Nb2+ atoms. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to three Sc3+ and six Nb2+ atoms. In the third Si4- site, Si4- is bonded in a 9-coordinate geometry to three Sc3+ and six Nb2+ atoms. In the fourth Si4- site, Si4- is bonded in a 9-coordinate geometry to three Sc3+ and six Nb2+ atoms.