LiErO2 crystallizes in the monoclinic P2_1/c space group. Li(1) is bonded in a T-shaped geometry to one O(1) and two equivalent O(2) atoms. Er(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form a mixture of corner and edge-sharing ErO6 octahedra. The corner-sharing octahedral tilt angles range from 16-30°. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Li(1) and three equivalent Er(1) atoms to form distorted OLiEr3 tetrahedra that share corners with seven equivalent O(2)Li2Er3 square pyramids, corners with four equivalent O(1)LiEr3 tetrahedra, edges with two equivalent O(2)Li2Er3 square pyramids, and  an edgeedge with one O(1)LiEr3 tetrahedra. In the second O site, O(2) is bonded to two equivalent Li(1) and three equivalent Er(1) atoms to form OLi2Er3 square pyramids that share corners with two equivalent O(2)Li2Er3 square pyramids, corners with seven equivalent O(1)LiEr3 tetrahedra, edges with three equivalent O(2)Li2Er3 square pyramids, and edges with two equivalent O(1)LiEr3 tetrahedra.
LiErO2 crystallizes in the monoclinic P2_1/c space group. Li(1) is bonded in a T-shaped geometry to one O(1) and two equivalent O(2) atoms. The Li(1)-O(1) bond length is 1.92 Å. There is one shorter (2.01 Å) and one longer (2.03 Å) Li(1)-O(2) bond length. Er(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form a mixture of corner and edge-sharing ErO6 octahedra. The corner-sharing octahedral tilt angles range from 16-30°. There are a spread of Er(1)-O(1) bond distances ranging from 2.18-2.25 Å. There are a spread of Er(1)-O(2) bond distances ranging from 2.25-2.30 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to one Li(1) and three equivalent Er(1) atoms to form distorted OLiEr3 tetrahedra that share corners with seven equivalent O(2)Li2Er3 square pyramids, corners with four equivalent O(1)LiEr3 tetrahedra, edges with two equivalent O(2)Li2Er3 square pyramids, and  an edgeedge with one O(1)LiEr3 tetrahedra. In the second O site, O(2) is bonded to two equivalent Li(1) and three equivalent Er(1) atoms to form OLi2Er3 square pyramids that share corners with two equivalent O(2)Li2Er3 square pyramids, corners with seven equivalent O(1)LiEr3 tetrahedra, edges with three equivalent O(2)Li2Er3 square pyramids, and edges with two equivalent O(1)LiEr3 tetrahedra.