Er2Nb2O7 crystallizes in the cubic Fd-3m space group. Er(1) is bonded in a body-centered cubic geometry to two equivalent O(2) and six equivalent O(1) atoms. Nb(1) is bonded to six equivalent O(1) atoms to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles are 58°. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Er(1) and two equivalent Nb(1) atoms to form OEr2Nb2 tetrahedra that share corners with two equivalent O(2)Er4 tetrahedra, corners with twelve equivalent O(1)Er2Nb2 tetrahedra,  an edgeedge with one O(2)Er4 tetrahedra, and edges with four equivalent O(1)Er2Nb2 tetrahedra. In the second O site, O(2) is bonded to four equivalent Er(1) atoms to form OEr4 tetrahedra that share corners with four equivalent O(2)Er4 tetrahedra, corners with twelve equivalent O(1)Er2Nb2 tetrahedra, and edges with six equivalent O(1)Er2Nb2 tetrahedra.
Er2Nb2O7 crystallizes in the cubic Fd-3m space group. Er(1) is bonded in a body-centered cubic geometry to two equivalent O(2) and six equivalent O(1) atoms. Both Er(1)-O(2) bond lengths are 2.23 Å. All Er(1)-O(1) bond lengths are 2.41 Å. Nb(1) is bonded to six equivalent O(1) atoms to form distorted corner-sharing NbO6 octahedra. The corner-sharing octahedral tilt angles are 58°. All Nb(1)-O(1) bond lengths are 2.08 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Er(1) and two equivalent Nb(1) atoms to form OEr2Nb2 tetrahedra that share corners with two equivalent O(2)Er4 tetrahedra, corners with twelve equivalent O(1)Er2Nb2 tetrahedra,  an edgeedge with one O(2)Er4 tetrahedra, and edges with four equivalent O(1)Er2Nb2 tetrahedra. In the second O site, O(2) is bonded to four equivalent Er(1) atoms to form OEr4 tetrahedra that share corners with four equivalent O(2)Er4 tetrahedra, corners with twelve equivalent O(1)Er2Nb2 tetrahedra, and edges with six equivalent O(1)Er2Nb2 tetrahedra.