Ca3(CaTa2)O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to six equivalent O(2) atoms to form distorted CaO6 octahedra that share corners with six equivalent Ta(1)O6 octahedra, corners with three equivalent Ca(2)O6 pentagonal pyramids, edges with three equivalent Ca(1)O6 octahedra, and  a faceface with one Ca(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 40-59°. In the second Ca site, Ca(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted CaO6 pentagonal pyramids that share corners with three equivalent Ca(1)O6 octahedra, corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ca(2)O6 pentagonal pyramids, edges with three equivalent Ta(1)O6 octahedra, and  a faceface with one Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-59°. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with six equivalent Ca(1)O6 octahedra, corners with three equivalent Ca(2)O6 pentagonal pyramids, edges with three equivalent Ca(2)O6 pentagonal pyramids, and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 40-59°. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ca(2) and two equivalent Ta(1) atoms to form a mixture of distorted corner and edge-sharing OCa2Ta2 trigonal pyramids. In the second O site, O(2) is bonded in a distorted see-saw-like geometry to one Ca(2), two equivalent Ca(1), and one Ta(1) atom.
Ca3(CaTa2)O9 is Ilmenite-like structured and crystallizes in the trigonal P-3c1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to six equivalent O(2) atoms to form distorted CaO6 octahedra that share corners with six equivalent Ta(1)O6 octahedra, corners with three equivalent Ca(2)O6 pentagonal pyramids, edges with three equivalent Ca(1)O6 octahedra, and  a faceface with one Ca(2)O6 pentagonal pyramid. The corner-sharing octahedral tilt angles range from 40-59°. There are three shorter (2.34 Å) and three longer (2.46 Å) Ca(1)-O(2) bond lengths. In the second Ca site, Ca(2) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted CaO6 pentagonal pyramids that share corners with three equivalent Ca(1)O6 octahedra, corners with three equivalent Ta(1)O6 octahedra, corners with three equivalent Ca(2)O6 pentagonal pyramids, edges with three equivalent Ta(1)O6 octahedra, and  a faceface with one Ca(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 48-59°. All Ca(2)-O(1) bond lengths are 2.26 Å. All Ca(2)-O(2) bond lengths are 2.39 Å. Ta(1) is bonded to three equivalent O(1) and three equivalent O(2) atoms to form distorted TaO6 octahedra that share corners with six equivalent Ca(1)O6 octahedra, corners with three equivalent Ca(2)O6 pentagonal pyramids, edges with three equivalent Ca(2)O6 pentagonal pyramids, and  a faceface with one Ta(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 40-59°. All Ta(1)-O(1) bond lengths are 2.12 Å. All Ta(1)-O(2) bond lengths are 1.92 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ca(2) and two equivalent Ta(1) atoms to form a mixture of distorted corner and edge-sharing OCa2Ta2 trigonal pyramids. In the second O site, O(2) is bonded in a distorted see-saw-like geometry to one Ca(2), two equivalent Ca(1), and one Ta(1) atom.