Ca3Ta2O8 crystallizes in the orthorhombic Cmce space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CaO6 octahedra that share corners with six equivalent Ta(1)O4 tetrahedra, edges with two equivalent Ca(1)O6 octahedra, and edges with two equivalent Ca(2)O6 octahedra. In the second Ca site, Ca(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CaO6 octahedra that share corners with six equivalent Ta(1)O4 tetrahedra and edges with four equivalent Ca(1)O6 octahedra. Ta(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form TaO4 tetrahedra that share corners with three equivalent Ca(2)O6 octahedra and corners with six equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-56°. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one Ta(1) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ca(2), two equivalent Ca(1), and one Ta(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one Ta(1) atom.
Ca3Ta2O8 crystallizes in the orthorhombic Cmce space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form CaO6 octahedra that share corners with six equivalent Ta(1)O4 tetrahedra, edges with two equivalent Ca(1)O6 octahedra, and edges with two equivalent Ca(2)O6 octahedra. Both Ca(1)-O(1) bond lengths are 2.38 Å. Both Ca(1)-O(2) bond lengths are 2.47 Å. Both Ca(1)-O(3) bond lengths are 2.28 Å. In the second Ca site, Ca(2) is bonded to two equivalent O(2) and four equivalent O(1) atoms to form CaO6 octahedra that share corners with six equivalent Ta(1)O4 tetrahedra and edges with four equivalent Ca(1)O6 octahedra. Both Ca(2)-O(2) bond lengths are 2.34 Å. All Ca(2)-O(1) bond lengths are 2.41 Å. Ta(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form TaO4 tetrahedra that share corners with three equivalent Ca(2)O6 octahedra and corners with six equivalent Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 49-56°. The Ta(1)-O(2) bond length is 1.92 Å. The Ta(1)-O(3) bond length is 1.87 Å. Both Ta(1)-O(1) bond lengths are 1.86 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Ca(1), one Ca(2), and one Ta(1) atom. In the second O site, O(2) is bonded in a rectangular see-saw-like geometry to one Ca(2), two equivalent Ca(1), and one Ta(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to two equivalent Ca(1) and one Ta(1) atom.