DOE OSTI2020
Ca(HoS2)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ca2+ is bonded to seven S2- atoms to form distorted CaS7 pentagonal bipyramids that share corners with eight HoS6 octahedra, edges with five HoS6 octahedra, edges with two equivalent CaS7 pentagonal bipyramids, and faces with two equivalent CaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 14–67°. There are a spread of Ca–S bond distances ranging from 2.89–3.02 Å. There are two inequivalent Ho3+ sites. In the first Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three equivalent HoS6 octahedra, corners with four equivalent CaS7 pentagonal bipyramids, edges with six HoS6 octahedra, and an edgeedge with one CaS7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 52–60°. There are a spread of Ho–S bond distances ranging from 2.70–2.81 Å. In the second Ho3+ site, Ho3+ is bonded to six S2- atoms to form HoS6 octahedra that share corners with three equivalent HoS6 octahedra, corners with four equivalent CaS7 pentagonal bipyramids, edges with four HoS6 octahedra, and edges with four equivalent CaS7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 52–60°. There are a spread of Ho–S bond distances ranging from 2.70–2.78 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to two equivalent Ca2+ and three Ho3+ atoms to form a mixture of distorted edge and corner-sharing SCa2Ho3 trigonal bipyramids. In the second S2- site, S2- is bonded to two equivalent Ca2+ and three Ho3+ atoms to form SCa2Ho3 square pyramids that share corners with two equivalent SCa3Ho2 square pyramids, corners with two equivalent SCa2Ho3 trigonal bipyramids, edges with five SCa2Ho3 square pyramids, and edges with three equivalent SCa2Ho3 trigonal bipyramids. In the third S2- site, S2- is bonded to three equivalent Ca2+ and two equivalent Ho3+ atoms to form a mixture of edge and corner-sharing SCa3Ho2 square pyramids. In the fourth S2- site, S2- is bonded in a rectangular see-saw-like geometry to four Ho3+ atoms.