DOE OSTI2020
Er2O3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Er3+ sites. In the first Er3+ site, Er3+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing ErO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Er–O bond distances ranging from 2.18–2.45 Å. In the second Er3+ site, Er3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Er–O bond distances ranging from 2.22–2.72 Å. In the third Er3+ site, Er3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Er–O bond distances ranging from 2.22–2.55 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to four Er3+ atoms to form distorted OEr4 trigonal pyramids that share a cornercorner with one OEr6 octahedra, corners with two equivalent OEr5 square pyramids, corners with nine OEr4 tetrahedra, corners with two equivalent OEr4 trigonal pyramids, edges with three equivalent OEr5 square pyramids, and edges with two equivalent OEr4 trigonal pyramids. The corner-sharing octahedral tilt angles are 37°. In the second O2- site, O2- is bonded to four Er3+ atoms to form distorted OEr4 tetrahedra that share corners with two equivalent OEr6 octahedra, corners with two equivalent OEr5 square pyramids, corners with four OEr4 tetrahedra, corners with six equivalent OEr4 trigonal pyramids, an edgeedge with one OEr6 octahedra, edges with two equivalent OEr5 square pyramids, and an edgeedge with one OEr4 tetrahedra. The corner-sharing octahedral tilt angles are 13°. In the third O2- site, O2- is bonded to four Er3+ atoms to form OEr4 tetrahedra that share a cornercorner with one OEr6 octahedra, corners with five equivalent OEr5 square pyramids, corners with four OEr4 tetrahedra, corners with three equivalent OEr4 trigonal pyramids, edges with two equivalent OEr6 octahedra, an edgeedge with one OEr5 square pyramid, and edges with two equivalent OEr4 tetrahedra. The corner-sharing octahedral tilt angles are 49°. In the fourth O2- site, O2- is bonded to six Er3+ atoms to form OEr6 octahedra that share corners with six OEr4 tetrahedra, corners with two equivalent OEr4 trigonal pyramids, edges with two equivalent OEr6 octahedra, edges with four equivalent OEr5 square pyramids, and edges with six OEr4 tetrahedra. In the fifth O2- site, O2- is bonded to five Er3+ atoms to form distorted OEr5 square pyramids that share corners with seven OEr4 tetrahedra, corners with two equivalent OEr4 trigonal pyramids, edges with two equivalent OEr6 octahedra, edges with two equivalent OEr5 square pyramids, edges with three OEr4 tetrahedra, and edges with three equivalent OEr4 trigonal pyramids.