DOE OSTI2020
Na2SnSe3 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to six Se2- atoms to form NaSe6 octahedra that share corners with two equivalent NaSe6 octahedra, corners with three equivalent SnSe4 tetrahedra, corners with six equivalent NaSe5 trigonal bipyramids, edges with three equivalent NaSe6 octahedra, edges with two equivalent SnSe4 tetrahedra, and edges with two equivalent NaSe5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 19°. There are a spread of Na–Se bond distances ranging from 2.98–3.27 Å. In the second Na1+ site, Na1+ is bonded to five Se2- atoms to form NaSe5 trigonal bipyramids that share corners with six equivalent NaSe6 octahedra, corners with two equivalent SnSe4 tetrahedra, corners with two equivalent NaSe5 trigonal bipyramids, edges with two equivalent NaSe6 octahedra, edges with two equivalent SnSe4 tetrahedra, and edges with two equivalent NaSe5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 16–89°. There are a spread of Na–Se bond distances ranging from 3.02–3.20 Å. Sn4+ is bonded to four Se2- atoms to form SnSe4 tetrahedra that share corners with three equivalent NaSe6 octahedra, corners with two equivalent SnSe4 tetrahedra, corners with two equivalent NaSe5 trigonal bipyramids, edges with two equivalent NaSe6 octahedra, and edges with two equivalent NaSe5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 25–68°. There are a spread of Sn–Se bond distances ranging from 2.52–2.62 Å. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to five Na1+ and one Sn4+ atom to form distorted SeNa5Sn pentagonal pyramids that share corners with two equivalent SeNa5Sn pentagonal pyramids, corners with four equivalent SeNa4Sn trigonal bipyramids, corners with three equivalent SeNa2Sn2 trigonal pyramids, edges with three equivalent SeNa5Sn pentagonal pyramids, edges with three equivalent SeNa4Sn trigonal bipyramids, and edges with two equivalent SeNa2Sn2 trigonal pyramids. In the second Se2- site, Se2- is bonded to four Na1+ and one Sn4+ atom to form distorted SeNa4Sn trigonal bipyramids that share corners with four equivalent SeNa5Sn pentagonal pyramids, corners with two equivalent SeNa4Sn trigonal bipyramids, corners with four equivalent SeNa2Sn2 trigonal pyramids, edges with three equivalent SeNa5Sn pentagonal pyramids, edges with two equivalent SeNa4Sn trigonal bipyramids, and an edgeedge with one SeNa2Sn2 trigonal pyramid. In the third Se2- site, Se2- is bonded to two Na1+ and two equivalent Sn4+ atoms to form distorted SeNa2Sn2 trigonal pyramids that share corners with three equivalent SeNa5Sn pentagonal pyramids, corners with four equivalent SeNa4Sn trigonal bipyramids, corners with two equivalent SeNa2Sn2 trigonal pyramids, edges with two equivalent SeNa5Sn pentagonal pyramids, and an edgeedge with one SeNa4Sn trigonal bipyramid.