DOE OSTI2020
Lu3Cu5Tl2Se8 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are three inequivalent Lu3+ sites. In the first Lu3+ site, Lu3+ is bonded to six Se2- atoms to form LuSe6 octahedra that share a cornercorner with one LuSe6 octahedra, corners with four equivalent CuSe4 tetrahedra, edges with four LuSe6 octahedra, and edges with five CuSe4 tetrahedra. The corner-sharing octahedral tilt angles are 40°. There are a spread of Lu–Se bond distances ranging from 2.80–2.86 Å. In the second Lu3+ site, Lu3+ is bonded to six Se2- atoms to form LuSe6 octahedra that share a cornercorner with one LuSe6 octahedra, corners with four equivalent CuSe4 tetrahedra, edges with four LuSe6 octahedra, and edges with five CuSe4 tetrahedra. The corner-sharing octahedral tilt angles are 34°. There are a spread of Lu–Se bond distances ranging from 2.76–2.87 Å. In the third Lu3+ site, Lu3+ is bonded to six Se2- atoms to form LuSe6 octahedra that share corners with two LuSe6 octahedra, edges with two equivalent LuSe6 octahedra, and edges with four CuSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 34–40°. There are a spread of Lu–Se bond distances ranging from 2.77–2.90 Å. There are five inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with four CuSe4 tetrahedra and edges with four LuSe6 octahedra. There are three shorter (2.47 Å) and one longer (2.61 Å) Cu–Se bond lengths. In the second Cu1+ site, Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with four CuSe4 tetrahedra and edges with four LuSe6 octahedra. There are a spread of Cu–Se bond distances ranging from 2.48–2.58 Å. In the third Cu1+ site, Cu1+ is bonded in a 4-coordinate geometry to one Tl1+ and four Se2- atoms. The Cu–Tl bond length is 3.28 Å. There are a spread of Cu–Se bond distances ranging from 2.42–2.81 Å. In the fourth Cu1+ site, Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with four equivalent LuSe6 octahedra, corners with four CuSe4 tetrahedra, edges with three LuSe6 octahedra, and an edgeedge with one CuSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 15–61°. There are two shorter (2.47 Å) and two longer (2.52 Å) Cu–Se bond lengths. In the fifth Cu1+ site, Cu1+ is bonded to four Se2- atoms to form CuSe4 tetrahedra that share corners with four equivalent LuSe6 octahedra, corners with four CuSe4 tetrahedra, edges with three LuSe6 octahedra, and an edgeedge with one CuSe4 tetrahedra. The corner-sharing octahedra tilt angles range from 15–61°. There are a spread of Cu–Se bond distances ranging from 2.46–2.52 Å. There are two inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded in a 7-coordinate geometry to one Cu1+ and eight Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.28–3.76 Å. In the second Tl1+ site, Tl1+ is bonded in a 7-coordinate geometry to seven Se2- atoms. There are a spread of Tl–Se bond distances ranging from 3.21–3.43 Å. There are eight inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 7-coordinate geometry to two equivalent Lu3+, three Cu1+, and two equivalent Tl1+ atoms. In the second Se2- site, Se2- is bonded in a 6-coordinate geometry to two Lu3+, two equivalent Cu1+, and two equivalent Tl1+ atoms. In the third Se2- site, Se2- is bonded in a 7-coordinate geometry to two equivalent Lu3+, three Cu1+, and two equivalent Tl1+ atoms. In the fourth Se2- site, Se2- is bonded in a 4-coordinate geometry to two equivalent Lu3+, two Cu1+, and three Tl1+ atoms. In the fifth Se2- site, Se2- is bonded in a 7-coordinate geometry to two Lu3+, three Cu1+, and two equivalent Tl1+ atoms. In the sixth Se2- site, Se2- is bonded in a 7-coordinate geometry to two equivalent Lu3+, three Cu1+, and two equivalent Tl1+ atoms. In the seventh Se2- site, Se2- is bonded to three Lu3+, two equivalent Cu1+, and one Tl1+ atom to form distorted edge-sharing SeLu3TlCu2 octahedra. In the eighth Se2- site, Se2- is bonded to three Lu3+, two equivalent Cu1+, and one Tl1+ atom to form distorted edge-sharing SeLu3TlCu2 octahedra.