DOE OSTI2020
Na4Zn3Se5 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are four inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded to five Se2- atoms to form distorted NaSe5 trigonal bipyramids that share corners with two equivalent NaSe6 octahedra, corners with two equivalent NaSe5 square pyramids, corners with three ZnSe4 tetrahedra, corners with four equivalent NaSe5 trigonal bipyramids, an edgeedge with one NaSe6 octahedra, edges with four ZnSe4 tetrahedra, and edges with four NaSe5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 33°. There are a spread of Na–Se bond distances ranging from 2.83–2.94 Å. In the second Na1+ site, Na1+ is bonded to five Se2- atoms to form NaSe5 square pyramids that share corners with three equivalent NaSe6 octahedra, corners with four ZnSe4 tetrahedra, corners with five NaSe5 trigonal bipyramids, edges with four equivalent NaSe5 square pyramids, and edges with four ZnSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 34–54°. There are three shorter (3.08 Å) and two longer (3.13 Å) Na–Se bond lengths. In the third Na1+ site, Na1+ is bonded to six Se2- atoms to form NaSe6 octahedra that share corners with three equivalent NaSe5 square pyramids, corners with five ZnSe4 tetrahedra, corners with four NaSe5 trigonal bipyramids, edges with four equivalent NaSe6 octahedra, edges with five ZnSe4 tetrahedra, an edgeedge with one NaSe5 trigonal bipyramid, and a faceface with one NaSe5 trigonal bipyramid. There are a spread of Na–Se bond distances ranging from 2.99–3.25 Å. In the fourth Na1+ site, Na1+ is bonded to five Se2- atoms to form distorted NaSe5 trigonal bipyramids that share corners with two equivalent NaSe6 octahedra, corners with three equivalent NaSe5 square pyramids, corners with six ZnSe4 tetrahedra, corners with four equivalent NaSe5 trigonal bipyramids, edges with two equivalent ZnSe4 tetrahedra, edges with four NaSe5 trigonal bipyramids, and a faceface with one NaSe6 octahedra. The corner-sharing octahedral tilt angles are 60°. There are a spread of Na–Se bond distances ranging from 2.89–3.07 Å. There are three inequivalent Zn2+ sites. In the first Zn2+ site, Zn2+ is bonded to four Se2- atoms to form ZnSe4 tetrahedra that share a cornercorner with one NaSe6 octahedra, corners with two equivalent NaSe5 square pyramids, corners with six ZnSe4 tetrahedra, corners with three NaSe5 trigonal bipyramids, edges with two equivalent NaSe6 octahedra, and edges with three equivalent NaSe5 square pyramids. The corner-sharing octahedral tilt angles are 15°. There are two shorter (2.52 Å) and two longer (2.53 Å) Zn–Se bond lengths. In the second Zn2+ site, Zn2+ is bonded to four Se2- atoms to form ZnSe4 tetrahedra that share corners with two equivalent NaSe6 octahedra, corners with two equivalent NaSe5 square pyramids, corners with six ZnSe4 tetrahedra, corners with two equivalent NaSe5 trigonal bipyramids, an edgeedge with one NaSe5 square pyramid, and edges with four NaSe5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 48°. There are a spread of Zn–Se bond distances ranging from 2.45–2.61 Å. In the third Zn2+ site, Zn2+ is bonded to four Se2- atoms to form ZnSe4 tetrahedra that share corners with two equivalent NaSe6 octahedra, corners with six ZnSe4 tetrahedra, corners with four equivalent NaSe5 trigonal bipyramids, edges with three equivalent NaSe6 octahedra, and edges with two equivalent NaSe5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 18°. There are a spread of Zn–Se bond distances ranging from 2.48–2.60 Å. There are five inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 6-coordinate geometry to four Na1+ and two Zn2+ atoms. In the second Se2- site, Se2- is bonded in a 7-coordinate geometry to five Na1+ and two equivalent Zn2+ atoms. In the third Se2- site, Se2- is bonded in a 8-coordinate geometry to six Na1+ and two Zn2+ atoms. In the fourth Se2- site, Se2- is bonded to three equivalent Na1+ and three Zn2+ atoms to form a mixture of distorted edge and corner-sharing SeNa3Zn3 octahedra. The corner-sharing octahedral tilt angles are 73°. In the fifth Se2- site, Se2- is bonded to three Na1+ and three Zn2+ atoms to form a mixture of distorted edge and corner-sharing SeNa3Zn3 octahedra. The corner-sharing octahedral tilt angles are 73°.