CaTm2O4 crystallizes in the orthorhombic Cmcm space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. Tm(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form a mixture of corner and edge-sharing TmO6 octahedra. The corner-sharing octahedral tilt angles range from 0-58°. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ca(1) and four equivalent Tm(1) atoms to form distorted OCa2Tm4 octahedra that share corners with two equivalent O(1)Ca2Tm4 octahedra, corners with eight equivalent O(3)Ca2Tm3 trigonal bipyramids, edges with two equivalent O(1)Ca2Tm4 octahedra, edges with four equivalent O(2)Ca2Tm2 tetrahedra, and edges with six equivalent O(3)Ca2Tm3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 48°. In the second O site, O(2) is bonded to two equivalent Ca(1) and two equivalent Tm(1) atoms to form OCa2Tm2 tetrahedra that share corners with two equivalent O(2)Ca2Tm2 tetrahedra, corners with ten equivalent O(3)Ca2Tm3 trigonal bipyramids, edges with four equivalent O(1)Ca2Tm4 octahedra, and edges with two equivalent O(3)Ca2Tm3 trigonal bipyramids. In the third O site, O(3) is bonded to two equivalent Ca(1) and three equivalent Tm(1) atoms to form distorted OCa2Tm3 trigonal bipyramids that share corners with four equivalent O(1)Ca2Tm4 octahedra, corners with five equivalent O(2)Ca2Tm2 tetrahedra, corners with two equivalent O(3)Ca2Tm3 trigonal bipyramids, edges with three equivalent O(1)Ca2Tm4 octahedra,  an edgeedge with one O(2)Ca2Tm2 tetrahedra, and edges with five equivalent O(3)Ca2Tm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 9-42°.
CaTm2O4 crystallizes in the orthorhombic Cmcm space group. Ca(1) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), and four equivalent O(3) atoms. Both Ca(1)-O(1) bond lengths are 2.97 Å. Both Ca(1)-O(2) bond lengths are 2.30 Å. All Ca(1)-O(3) bond lengths are 2.59 Å. Tm(1) is bonded to one O(2), two equivalent O(1), and three equivalent O(3) atoms to form a mixture of corner and edge-sharing TmO6 octahedra. The corner-sharing octahedral tilt angles range from 0-58°. The Tm(1)-O(2) bond length is 2.18 Å. Both Tm(1)-O(1) bond lengths are 2.33 Å. There are two shorter (2.22 Å) and one longer (2.30 Å) Tm(1)-O(3) bond length. There are three inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ca(1) and four equivalent Tm(1) atoms to form distorted OCa2Tm4 octahedra that share corners with two equivalent O(1)Ca2Tm4 octahedra, corners with eight equivalent O(3)Ca2Tm3 trigonal bipyramids, edges with two equivalent O(1)Ca2Tm4 octahedra, edges with four equivalent O(2)Ca2Tm2 tetrahedra, and edges with six equivalent O(3)Ca2Tm3 trigonal bipyramids. The corner-sharing octahedral tilt angles are 48°. In the second O site, O(2) is bonded to two equivalent Ca(1) and two equivalent Tm(1) atoms to form OCa2Tm2 tetrahedra that share corners with two equivalent O(2)Ca2Tm2 tetrahedra, corners with ten equivalent O(3)Ca2Tm3 trigonal bipyramids, edges with four equivalent O(1)Ca2Tm4 octahedra, and edges with two equivalent O(3)Ca2Tm3 trigonal bipyramids. In the third O site, O(3) is bonded to two equivalent Ca(1) and three equivalent Tm(1) atoms to form distorted OCa2Tm3 trigonal bipyramids that share corners with four equivalent O(1)Ca2Tm4 octahedra, corners with five equivalent O(2)Ca2Tm2 tetrahedra, corners with two equivalent O(3)Ca2Tm3 trigonal bipyramids, edges with three equivalent O(1)Ca2Tm4 octahedra,  an edgeedge with one O(2)Ca2Tm2 tetrahedra, and edges with five equivalent O(3)Ca2Tm3 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 9-42°.