DOE OSTI2020
Yb(ErSe2)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Yb2+ is bonded to seven Se2- atoms to form distorted YbSe7 pentagonal bipyramids that share corners with eight ErSe6 octahedra, edges with five ErSe6 octahedra, edges with two equivalent YbSe7 pentagonal bipyramids, and faces with two equivalent YbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 13–66°. There are a spread of Yb–Se bond distances ranging from 2.97–3.13 Å. There are two 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 four equivalent YbSe7 pentagonal bipyramids, edges with six ErSe6 octahedra, and an edgeedge with one YbSe7 pentagonal bipyramid. The corner-sharing octahedra tilt angles range from 52–59°. There are a spread of Er–Se bond distances ranging from 2.82–2.92 Å. In the second Er3+ site, Er3+ is bonded to six Se2- atoms to form ErSe6 octahedra that share corners with three equivalent ErSe6 octahedra, corners with four equivalent YbSe7 pentagonal bipyramids, edges with four ErSe6 octahedra, and edges with four equivalent YbSe7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 52–59°. There are a spread of Er–Se bond distances ranging from 2.82–2.88 Å. There are four inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to two equivalent Yb2+ and three Er3+ atoms to form a mixture of distorted edge and corner-sharing SeYb2Er3 trigonal bipyramids. In the second Se2- site, Se2- is bonded to two equivalent Yb2+ and three Er3+ atoms to form SeYb2Er3 square pyramids that share corners with two equivalent SeYb3Er2 square pyramids, corners with two equivalent SeYb2Er3 trigonal bipyramids, edges with five SeYb2Er3 square pyramids, and edges with three equivalent SeYb2Er3 trigonal bipyramids. In the third Se2- site, Se2- is bonded to three equivalent Yb2+ and two equivalent Er3+ atoms to form a mixture of edge and corner-sharing SeYb3Er2 square pyramids. In the fourth Se2- site, Se2- is bonded in a rectangular see-saw-like geometry to four Er3+ atoms.