Materials Data on Na6Si2Se7 by Materials Project

Na6Si2Se7 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 in a 4-coordinate geometry to four Se2- atoms. There are two shorter (2.86 Å) and two longer (2.94 Å) Na–Se bond lengths. In the second 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 SiSe4 tetrahedra, edges with four equivalent NaSe6 octahedra, and edges with two equivalent SiSe4 tetrahedra. The corner-sharing octahedral tilt angles are 4°. There are a spread of Na–Se bond distances ranging from 2.90–3.29 Å. In the third 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 SiSe4 tetrahedra, edges with four NaSe6 octahedra, and edges with three equivalent SiSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 4–40°. There are a spread of Na–Se bond distances ranging from 2.99–3.54 Å. 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 2.97–3.60 Å. Si4+ is bonded to four Se2- atoms to form SiSe4 tetrahedra that share corners with two NaSe6 octahedra, a cornercorner with one SiSe4 tetrahedra, and edges with four NaSe6 octahedra. The corner-sharing octahedra tilt angles range from 19–59°. There are a spread of Si–Se bond distances ranging from 2.27–2.35 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a distorted bent 120 degrees geometry to four Na1+ and two equivalent Si4+ atoms. In the second Se2- site, Se2- is bonded to five Na1+ and one Si4+ atom to form a mixture of distorted edge and corner-sharing SeNa5Si octahedra. The corner-sharing octahedra tilt angles range from 0–78°. In the third Se2- site, Se2- is bonded to five Na1+ and one Si4+ atom to form a mixture of edge and corner-sharing SeNa5Si octahedra. The corner-sharing octahedra tilt angles range from 0–3°. In the fourth Se2- site, Se2- is bonded in a 6-coordinate geometry to five Na1+ and one Si4+ atom.