DOE OSTI2020
Tb3Sc2S7 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Tb3+ sites. In the first Tb3+ site, Tb3+ is bonded to seven S2- atoms to form distorted TbS7 pentagonal bipyramids that share corners with two equivalent TbS6 octahedra, corners with six equivalent ScS6 octahedra, an edgeedge with one ScS6 octahedra, edges with three equivalent TbS6 octahedra, edges with two equivalent TbS7 pentagonal bipyramids, and faces with two equivalent TbS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 23–72°. There are a spread of Tb–S bond distances ranging from 2.74–3.04 Å. In the second Tb3+ site, Tb3+ is bonded to six S2- atoms to form TbS6 octahedra that share corners with two equivalent ScS6 octahedra, corners with four equivalent TbS7 pentagonal bipyramids, edges with two equivalent TbS6 octahedra, and edges with six equivalent TbS7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 51°. There are two shorter (2.69 Å) and four longer (2.72 Å) Tb–S bond lengths. Sc+2.50+ is bonded to six S2- atoms to form ScS6 octahedra that share a cornercorner with one TbS6 octahedra, corners with two equivalent ScS6 octahedra, corners with six equivalent TbS7 pentagonal bipyramids, edges with five equivalent ScS6 octahedra, and an edgeedge with one TbS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 0–51°. There are a spread of Sc–S bond distances ranging from 2.55–2.68 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to two equivalent Tb3+ and three equivalent Sc+2.50+ atoms to form distorted STb2Sc3 trigonal bipyramids that share corners with five equivalent STb3Sc tetrahedra, corners with four equivalent STb5 trigonal bipyramids, an edgeedge with one STb3Sc tetrahedra, and edges with five STb2Sc3 trigonal bipyramids. In the second S2- site, S2- is bonded to five Tb3+ atoms to form distorted STb5 trigonal bipyramids that share corners with four equivalent STb3Sc tetrahedra, corners with six STb2Sc3 trigonal bipyramids, edges with three equivalent STb3Sc tetrahedra, and edges with six STb2Sc3 trigonal bipyramids. In the third S2- site, S2- is bonded to three Tb3+ and one Sc+2.50+ atom to form distorted STb3Sc tetrahedra that share corners with three equivalent STb3Sc tetrahedra, corners with nine STb2Sc3 trigonal bipyramids, and edges with four STb2Sc3 trigonal bipyramids. In the fourth S2- site, S2- is bonded in a square co-planar geometry to four equivalent Sc+2.50+ atoms.