DOE OSTI2020
ErAgS2 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are four inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share corners with two equivalent AgS6 octahedra, corners with four equivalent ErS6 octahedra, corners with two equivalent AgS5 trigonal bipyramids, edges with four ErS6 octahedra, and edges with four equivalent AgS6 octahedra. The corner-sharing octahedra tilt angles range from 8–18°. There are a spread of Er–S bond distances ranging from 2.72–2.77 Å. In the second Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share corners with four equivalent ErS6 octahedra, a cornercorner with one AgS5 trigonal bipyramid, edges with four ErS6 octahedra, edges with four AgS6 octahedra, and edges with two equivalent AgS5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 14–19°. There are a spread of Er–S bond distances ranging from 2.73–2.75 Å. In the third Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share corners with four equivalent ErS6 octahedra, edges with four ErS6 octahedra, edges with four AgS6 octahedra, and edges with two equivalent AgS5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 14–19°. There are a spread of Er–S bond distances ranging from 2.71–2.75 Å. In the fourth Er3+ site, Er3+ is bonded to six S2- atoms to form ErS6 octahedra that share corners with two equivalent AgS6 octahedra, corners with four equivalent ErS6 octahedra, edges with four ErS6 octahedra, edges with four equivalent AgS6 octahedra, and edges with two equivalent AgS5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 7–18°. There are a spread of Er–S bond distances ranging from 2.73–2.77 Å. There are four inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Ag–S bond distances ranging from 2.48–3.09 Å. In the second Ag1+ site, Ag1+ is bonded to five S2- atoms to form distorted AgS5 trigonal bipyramids that share corners with two equivalent AgS6 octahedra, corners with three ErS6 octahedra, edges with two equivalent AgS6 octahedra, and edges with six ErS6 octahedra. The corner-sharing octahedra tilt angles range from 8–81°. There are a spread of Ag–S bond distances ranging from 2.48–3.07 Å. In the third Ag1+ site, Ag1+ is bonded to six S2- atoms to form distorted AgS6 octahedra that share corners with two equivalent ErS6 octahedra, corners with four equivalent AgS6 octahedra, corners with two equivalent AgS5 trigonal bipyramids, and edges with eight ErS6 octahedra. The corner-sharing octahedra tilt angles range from 7–15°. There are a spread of Ag–S bond distances ranging from 2.48–3.53 Å. In the fourth Ag1+ site, Ag1+ is bonded to six S2- atoms to form distorted AgS6 octahedra that share corners with two equivalent ErS6 octahedra, corners with four equivalent AgS6 octahedra, edges with eight ErS6 octahedra, and edges with two equivalent AgS5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 8–15°. There are a spread of Ag–S bond distances ranging from 2.55–3.52 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded to three Er3+ and three Ag1+ atoms to form distorted SEr3Ag3 octahedra that share corners with five SEr3Ag2 square pyramids, edges with six SEr3Ag3 octahedra, and edges with two equivalent SEr3Ag2 square pyramids. In the second S2- site, S2- is bonded to three Er3+ and two equivalent Ag1+ atoms to form distorted SEr3Ag2 square pyramids that share corners with seven SEr3Ag3 octahedra, edges with four SEr3Ag3 octahedra, and edges with two equivalent SEr3Ag2 square pyramids. The corner-sharing octahedra tilt angles range from 4–84°. In the third S2- site, S2- is bonded in a 6-coordinate geometry to three Er3+ and three Ag1+ atoms. In the fourth S2- site, S2- is bonded to three Er3+ and three Ag1+ atoms to form distorted SEr3Ag3 octahedra that share corners with two SEr3Ag2 square pyramids, edges with six SEr3Ag3 octahedra, and edges with two SEr3Ag2 square pyramids. In the fifth S2- site, S2- is bonded in a 6-coordinate geometry to three Er3+ and three Ag1+ atoms. In the sixth S2- site, S2- is bonded to three Er3+ and three Ag1+ atoms to form distorted SEr3Ag3 octahedra that share corners with two SEr3Ag2 square pyramids, edges with six SEr3Ag3 octahedra, and edges with two SEr3Ag2 square pyramids. In the seventh S2- site, S2- is bonded to three Er3+ and two equivalent Ag1+ atoms to form SEr3Ag2 square pyramids that share corners with seven SEr3Ag3 octahedra, edges with four SEr3Ag3 octahedra, and edges with two equivalent SEr3Ag2 square pyramids. The corner-sharing octahedra tilt angles range from 4–85°. In the eighth S2- site, S2- is bonded to three Er3+ and three Ag1+ atoms to form distorted SEr3Ag3 octahedra that share corners with five SEr3Ag2 square pyramids, edges with six SEr3Ag3 octahedra, and edges with two equivalent SEr3Ag2 square pyramids.