DOE OSTI2020
Cr8Fe3CuS16 is Spinel-derived structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are four inequivalent Cr3+ sites. In the first Cr3+ site, Cr3+ is bonded to six S2- atoms to form CrS6 octahedra that share corners with two equivalent CuS4 tetrahedra, corners with four FeS4 tetrahedra, and edges with six CrS6 octahedra. There are a spread of Cr–S bond distances ranging from 2.36–2.42 Å. In the second Cr3+ site, Cr3+ is bonded to six S2- atoms to form CrS6 octahedra that share a cornercorner with one CuS4 tetrahedra, corners with five FeS4 tetrahedra, and edges with six CrS6 octahedra. There are a spread of Cr–S bond distances ranging from 2.37–2.42 Å. In the third Cr3+ site, Cr3+ is bonded to six S2- atoms to form CrS6 octahedra that share corners with three equivalent FeS4 tetrahedra, corners with three equivalent CuS4 tetrahedra, and edges with six CrS6 octahedra. There are three shorter (2.37 Å) and three longer (2.41 Å) Cr–S bond lengths. In the fourth Cr3+ site, Cr3+ is bonded to six S2- atoms to form CrS6 octahedra that share corners with six FeS4 tetrahedra and edges with six CrS6 octahedra. There are three shorter (2.39 Å) and three longer (2.41 Å) Cr–S bond lengths. There are three inequivalent Fe+2.33+ sites. In the first Fe+2.33+ site, Fe+2.33+ is bonded to four S2- atoms to form FeS4 tetrahedra that share corners with twelve CrS6 octahedra. The corner-sharing octahedra tilt angles range from 55–56°. All Fe–S bond lengths are 2.15 Å. In the second Fe+2.33+ site, Fe+2.33+ is bonded to four S2- atoms to form FeS4 tetrahedra that share corners with twelve CrS6 octahedra. The corner-sharing octahedra tilt angles range from 55–56°. All Fe–S bond lengths are 2.16 Å. In the third Fe+2.33+ site, Fe+2.33+ is bonded to four S2- atoms to form FeS4 tetrahedra that share corners with twelve CrS6 octahedra. The corner-sharing octahedra tilt angles range from 55–56°. All Fe–S bond lengths are 2.16 Å. Cu1+ is bonded to four S2- atoms to form CuS4 tetrahedra that share corners with twelve CrS6 octahedra. The corner-sharing octahedra tilt angles range from 57–58°. There are three shorter (2.24 Å) and one longer (2.25 Å) Cu–S bond lengths. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three Cr3+ and one Fe+2.33+ atom. In the second S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three Cr3+ and one Fe+2.33+ atom. In the third S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three equivalent Cr3+ and one Fe+2.33+ atom. In the fourth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three equivalent Cr3+ and one Fe+2.33+ atom. In the fifth S2- site, S2- is bonded to three Cr3+ and one Cu1+ atom to form a mixture of distorted edge and corner-sharing SCr3Cu trigonal pyramids. In the sixth S2- site, S2- is bonded in a rectangular see-saw-like geometry to three Cr3+ and one Fe+2.33+ atom. In the seventh S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to three equivalent Cr3+ and one Fe+2.33+ atom. In the eighth S2- site, S2- is bonded to three equivalent Cr3+ and one Cu1+ atom to form distorted corner-sharing SCr3Cu trigonal pyramids.