DOE OSTI2020
Er3Cu5Tl2S8 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. there are three inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share a cornercorner with one ErS6 octahedra, corners with four equivalent CuS4 tetrahedra, edges with four ErS6 octahedra, and edges with five CuS4 tetrahedra. The corner-sharing octahedral tilt angles are 33°. There are a spread of Er–S bond distances ranging from 2.64–2.77 Å. In the second Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share a cornercorner with one ErS6 octahedra, corners with four equivalent CuS4 tetrahedra, edges with four ErS6 octahedra, and edges with five CuS4 tetrahedra. The corner-sharing octahedral tilt angles are 27°. There are a spread of Er–S bond distances ranging from 2.64–2.77 Å. In the third Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share corners with two ErS6 octahedra, edges with two equivalent ErS6 octahedra, and edges with four CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 27–33°. There are a spread of Er–S bond distances ranging from 2.68–2.80 Å. There are five inequivalent Cu1+ sites. In the first Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share corners with four CuS4 tetrahedra and edges with four ErS6 octahedra. There are three shorter (2.35 Å) and one longer (2.56 Å) Cu–S bond lengths. In the second Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share corners with four CuS4 tetrahedra and edges with four ErS6 octahedra. There are three shorter (2.37 Å) and one longer (2.47 Å) Cu–S bond lengths. In the third Cu1+ site, Cu1+ is bonded in a distorted trigonal planar geometry to one Tl1+ and three S2- atoms. The Cu–Tl bond length is 2.93 Å. There are one shorter (2.26 Å) and two longer (2.31 Å) Cu–S bond lengths. In the fourth Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share corners with four equivalent ErS6 octahedra, corners with four CuS4 tetrahedra, edges with three ErS6 octahedra, and an edgeedge with one CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 13–59°. There are a spread of Cu–S bond distances ranging from 2.33–2.53 Å. In the fifth Cu1+ site, Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share corners with four equivalent ErS6 octahedra, corners with four CuS4 tetrahedra, edges with three ErS6 octahedra, and an edgeedge with one CuS4 tetrahedra. The corner-sharing octahedra tilt angles range from 13–59°. There are a spread of Cu–S bond distances ranging from 2.34–2.51 Å. There are two inequivalent Tl1+ sites. In the first Tl1+ site, Tl1+ is bonded in a 6-coordinate geometry to one Cu1+ and five S2- atoms. There are a spread of Tl–S bond distances ranging from 3.07–3.40 Å. In the second Tl1+ site, Tl1+ is bonded in a 7-coordinate geometry to seven S2- atoms. There are a spread of Tl–S bond distances ranging from 3.16–3.45 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Er3+ and three Cu1+ atoms. In the second S2- site, S2- is bonded in a 6-coordinate geometry to two Er3+, two equivalent Cu1+, and two equivalent Tl1+ atoms. In the third S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Er3+, three Cu1+, and two equivalent Tl1+ atoms. In the fourth S2- site, S2- is bonded in a 4-coordinate geometry to two equivalent Er3+, two Cu1+, and two equivalent Tl1+ atoms. In the fifth S2- site, S2- is bonded in a 6-coordinate geometry to two Er3+, two equivalent Cu1+, and two equivalent Tl1+ atoms. In the sixth S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Er3+, three Cu1+, and two equivalent Tl1+ atoms. In the seventh S2- site, S2- is bonded to three Er3+, two equivalent Cu1+, and one Tl1+ atom to form distorted edge-sharing SEr3TlCu2 octahedra. In the eighth S2- site, S2- is bonded to three Er3+, two equivalent Cu1+, and one Tl1+ atom to form distorted edge-sharing SEr3TlCu2 octahedra.