Materials Data on Na6Ge2Se7 by Materials Project

Abstract

Na6Ge2Se7 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are four 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 two equivalent GeSe4 tetrahedra, edges with four equivalent NaSe6 octahedra, and edges with two equivalent GeSe4 tetrahedra. The corner-sharing octahedral tilt angles are 5°. There are a spread of Na–Se bond distances ranging from 2.91–3.24 Å. In the second Na1+ site, Na1+ is bonded to six Se2- atoms to form distorted NaSe6 octahedra that share corners with two NaSe6 octahedra, a cornercorner with one GeSe4 tetrahedra, edges with four NaSe6 octahedra, and edges with three equivalent GeSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 5–40°. There are a spread of Na–Se bond distances ranging from 3.02–3.53 Å. In the third Na1+ site, Na1+ is bonded in a 4-coordinate geometry to four Se2- atoms. There are two shorter (2.87 Å) and two longer (2.94 Å) Na–Se bond lengths. In the fourth Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of Na–Se bond distances ranging from 2.99–3.60 Å. Ge4+ is bonded to four Se2- atoms to form GeSe4 tetrahedra that share corners with two NaSe6 octahedra, a cornercorner with one GeSe4 tetrahedra, and edges with four NaSe6 octahedra. The corner-sharing octahedra tilt angles range from 20–59°. There are a spread of Ge–Se bond distances ranging from 2.36–2.44 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to five Na1+ and one Ge4+ atom. In the second Se2- site, Se2- is bonded to five Na1+ and one Ge4+ atom to form a mixture of edge and corner-sharing SeNa5Ge octahedra. The corner-sharing octahedra tilt angles range from 0–4°. In the third Se2- site, Se2- is bonded to five Na1+ and one Ge4+ atom to form a mixture of distorted edge and corner-sharing SeNa5Ge octahedra. The corner-sharing octahedra tilt angles range from 0–76°. In the fourth Se2- site, Se2- is bonded in a 2-coordinate geometry to four Na1+ and two equivalent Ge4+ atoms.