DOE OSTI2020
Li6CuF8 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are four inequivalent Li1+ sites. In the first Li1+ site, Li1+ is bonded in a rectangular see-saw-like geometry to four F1- atoms. There are a spread of Li–F bond distances ranging from 1.80–2.02 Å. In the second Li1+ site, Li1+ is bonded to six F1- atoms to form LiF6 octahedra that share edges with two equivalent CuF6 octahedra and edges with six LiF6 octahedra. There are two shorter (1.91 Å) and four longer (2.13 Å) Li–F bond lengths. In the third Li1+ site, Li1+ is bonded to six F1- atoms to form LiF6 octahedra that share corners with six equivalent CuF6 octahedra and edges with six LiF6 octahedra. The corner-sharing octahedra tilt angles range from 0–3°. There are two shorter (1.95 Å) and four longer (2.17 Å) Li–F bond lengths. In the fourth Li1+ site, Li1+ is bonded to six F1- atoms to form LiF6 octahedra that share edges with two equivalent CuF6 octahedra and edges with six LiF6 octahedra. There are a spread of Li–F bond distances ranging from 1.90–2.19 Å. Cu2+ is bonded to six F1- atoms to form CuF6 octahedra that share corners with six equivalent LiF6 octahedra and edges with six LiF6 octahedra. The corner-sharing octahedra tilt angles range from 0–3°. There are four shorter (1.97 Å) and two longer (2.38 Å) Cu–F bond lengths. There are three inequivalent F1- sites. In the first F1- site, F1- is bonded to four Li1+ and one Cu2+ atom to form distorted FLi4Cu square pyramids that share corners with five equivalent FLi4Cu square pyramids, corners with three equivalent FLi4 tetrahedra, a cornercorner with one FLi4Cu trigonal bipyramid, edges with three equivalent FLi4Cu square pyramids, an edgeedge with one FLi4 tetrahedra, and edges with three equivalent FLi4Cu trigonal bipyramids. In the second F1- site, F1- is bonded to four Li1+ atoms to form FLi4 tetrahedra that share corners with six equivalent FLi4Cu square pyramids, corners with three equivalent FLi4 tetrahedra, corners with three equivalent FLi4Cu trigonal bipyramids, edges with two equivalent FLi4Cu square pyramids, and an edgeedge with one FLi4Cu trigonal bipyramid. In the third F1- site, F1- is bonded to four Li1+ and one Cu2+ atom to form distorted FLi4Cu trigonal bipyramids that share corners with two equivalent FLi4Cu square pyramids, corners with three equivalent FLi4 tetrahedra, corners with four equivalent FLi4Cu trigonal bipyramids, edges with six equivalent FLi4Cu square pyramids, and an edgeedge with one FLi4 tetrahedra.