DOE OSTI2020
Er4F2O11Si3 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are four inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to six O2- and one F1- atom to form distorted ErO6F pentagonal bipyramids that share corners with four SiO4 tetrahedra, edges with two equivalent ErO6F pentagonal bipyramids, and an edgeedge with one SiO4 tetrahedra. There are a spread of Er–O bond distances ranging from 2.23–2.39 Å. The Er–F bond length is 2.33 Å. In the second Er3+ site, Er3+ is bonded in a 7-coordinate geometry to five O2- and two F1- atoms. There are a spread of Er–O bond distances ranging from 2.22–2.37 Å. There are one shorter (2.23 Å) and one longer (2.40 Å) Er–F bond lengths. In the third Er3+ site, Er3+ is bonded to six O2- and one F1- atom to form distorted ErO6F pentagonal bipyramids that share corners with four SiO4 tetrahedra, edges with two equivalent ErO6F pentagonal bipyramids, and an edgeedge with one SiO4 tetrahedra. There are a spread of Er–O bond distances ranging from 2.20–2.42 Å. The Er–F bond length is 2.24 Å. In the fourth Er3+ site, Er3+ is bonded in a 8-coordinate geometry to six O2- and two F1- atoms. There are a spread of Er–O bond distances ranging from 2.25–2.84 Å. Both Er–F bond lengths are 2.35 Å. There are three inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent ErO6F pentagonal bipyramids, a cornercorner with one SiO4 tetrahedra, and an edgeedge with one ErO6F pentagonal bipyramid. There are a spread of Si–O bond distances ranging from 1.63–1.67 Å. In the second Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with two ErO6F pentagonal bipyramids and a cornercorner with one SiO4 tetrahedra. There is three shorter (1.64 Å) and one longer (1.67 Å) Si–O bond length. In the third Si4+ site, Si4+ is bonded to four O2- atoms to form SiO4 tetrahedra that share corners with three equivalent ErO6F pentagonal bipyramids and an edgeedge with one ErO6F pentagonal bipyramid. There are a spread of Si–O bond distances ranging from 1.63–1.70 Å. There are eleven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two Er3+ and one Si4+ atom. In the second O2- site, O2- is bonded in a 3-coordinate geometry to two Er3+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to three Er3+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to two Er3+ and one Si4+ atom. In the fifth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Er3+ and one Si4+ atom. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Er3+ and one Si4+ atom. In the seventh O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Er3+ and two Si4+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to two Er3+ and one Si4+ atom. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to two Er3+ and one Si4+ atom. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to three Er3+ and one Si4+ atom. In the eleventh O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Er3+ and one Si4+ atom. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted trigonal planar geometry to three Er3+ atoms. In the second F1- site, F1- is bonded in a 3-coordinate geometry to three Er3+ atoms.