DOE OSTI2020
Er3SmSe6 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are three inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to six Se2- atoms to form ErSe6 octahedra that share corners with three equivalent ErSe6 octahedra, corners with two equivalent ErSe7 pentagonal bipyramids, and edges with four equivalent ErSe6 octahedra. The corner-sharing octahedra tilt angles range from 56–60°. There are a spread of Er–Se bond distances ranging from 2.77–2.88 Å. In the second Er3+ site, Er3+ is bonded to seven Se2- atoms to form distorted ErSe7 pentagonal bipyramids that share corners with three ErSe6 octahedra, edges with two equivalent ErSe6 octahedra, and edges with four equivalent ErSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 36–50°. There are a spread of Er–Se bond distances ranging from 2.81–3.05 Å. In the third Er3+ site, Er3+ is bonded to six Se2- atoms to form ErSe6 octahedra that share corners with three equivalent ErSe6 octahedra, a cornercorner with one ErSe7 pentagonal bipyramid, edges with four equivalent ErSe6 octahedra, and edges with two equivalent ErSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 56–60°. There are a spread of Er–Se bond distances ranging from 2.79–2.88 Å. Sm3+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Sm–Se bond distances ranging from 2.99–3.13 Å. There are six inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to three Er3+ and one Sm3+ atom to form distorted SeSmEr3 trigonal pyramids that share corners with two equivalent SeSm2Er3 square pyramids, corners with four SeSm3Er2 trigonal bipyramids, corners with two equivalent SeSmEr3 trigonal pyramids, edges with three equivalent SeSm2Er3 square pyramids, and edges with two equivalent SeSm3Er2 trigonal bipyramids. In the second Se2- site, Se2- is bonded to three equivalent Er3+ and two equivalent Sm3+ atoms to form distorted SeSm2Er3 square pyramids that share corners with six SeSm2Er3 trigonal bipyramids, corners with two equivalent SeSmEr3 trigonal pyramids, edges with four equivalent SeSm2Er3 square pyramids, edges with two SeSm2Er3 trigonal bipyramids, and edges with three equivalent SeSmEr3 trigonal pyramids. In the third Se2- site, Se2- is bonded to two equivalent Er3+ and three equivalent Sm3+ atoms to form distorted SeSm3Er2 trigonal bipyramids that share corners with four equivalent SeSm2Er3 square pyramids, corners with two equivalent SeSm2Er3 trigonal bipyramids, a cornercorner with one SeSmEr3 trigonal pyramid, an edgeedge with one SeSm2Er3 square pyramid, edges with seven SeSm3Er2 trigonal bipyramids, and edges with two equivalent SeSmEr3 trigonal pyramids. In the fourth Se2- site, Se2- is bonded in a 4-coordinate geometry to four Er3+ atoms. In the fifth Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to four Er3+ atoms. In the sixth Se2- site, Se2- is bonded to three Er3+ and two equivalent Sm3+ atoms to form distorted SeSm2Er3 trigonal bipyramids that share corners with two equivalent SeSm2Er3 square pyramids, corners with two equivalent SeSm3Er2 trigonal bipyramids, corners with three equivalent SeSmEr3 trigonal pyramids, an edgeedge with one SeSm2Er3 square pyramid, and edges with five SeSm3Er2 trigonal bipyramids.