Er2O3 crystallizes in the trigonal R3m space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(2), and three equivalent O(3) atoms to form corner-sharing ErO5 trigonal bipyramids. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(3), three equivalent O(1), and three equivalent O(2) atoms. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Er(1) and three equivalent Er(2) atoms to form a mixture of edge and corner-sharing OEr4 tetrahedra. In the second O site, O(2) is bonded to one Er(1) and three equivalent Er(2) atoms to form a mixture of distorted edge and corner-sharing OEr4 tetrahedra. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Er(2) and three equivalent Er(1) atoms.
Er2O3 crystallizes in the trigonal R3m space group. There are two inequivalent Er sites. In the first Er site, Er(1) is bonded to one O(1), one O(2), and three equivalent O(3) atoms to form corner-sharing ErO5 trigonal bipyramids. The Er(1)-O(1) bond length is 2.26 Å. The Er(1)-O(2) bond length is 2.19 Å. All Er(1)-O(3) bond lengths are 2.14 Å. In the second Er site, Er(2) is bonded in a 7-coordinate geometry to one O(3), three equivalent O(1), and three equivalent O(2) atoms. The Er(2)-O(3) bond length is 2.74 Å. All Er(2)-O(1) bond lengths are 2.27 Å. All Er(2)-O(2) bond lengths are 2.43 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to one Er(1) and three equivalent Er(2) atoms to form a mixture of edge and corner-sharing OEr4 tetrahedra. In the second O site, O(2) is bonded to one Er(1) and three equivalent Er(2) atoms to form a mixture of distorted edge and corner-sharing OEr4 tetrahedra. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Er(2) and three equivalent Er(1) atoms.