CaCr2O4 is Spinel-like structured and crystallizes in the trigonal P3m1 space group. There are six inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(9) and three equivalent O(1) atoms to form CaO4 tetrahedra that share corners with three equivalent Ca(5)O6 octahedra, corners with three equivalent Cr(5)O6 octahedra, and corners with six equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 57-68°. In the second Ca site, Ca(2) is bonded to one O(2) and three equivalent O(3) atoms to form CaO4 tetrahedra that share corners with three equivalent Ca(3)O6 octahedra, corners with three equivalent Cr(1)O6 octahedra, and corners with six equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-69°. In the third Ca site, Ca(3) is bonded to three equivalent O(3) and three equivalent O(4) atoms to form CaO6 octahedra that share corners with three equivalent Ca(2)O4 tetrahedra, corners with three equivalent Cr(4)O4 tetrahedra, edges with three equivalent Cr(1)O6 octahedra, and edges with three equivalent Cr(2)O6 octahedra. In the fourth Ca site, Ca(4) is bonded to one O(5) and three equivalent O(7) atoms to form CaO4 tetrahedra that share corners with three equivalent Cr(2)O6 octahedra, corners with three equivalent Cr(3)O6 octahedra, and corners with six equivalent Cr(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 60-62°. In the fifth Ca site, Ca(5) is bonded to three equivalent O(1) and three equivalent O(11) atoms to form CaO6 octahedra that share corners with three equivalent Ca(1)O4 tetrahedra, corners with three equivalent Cr(6)O4 tetrahedra, edges with three equivalent Cr(1)O6 octahedra, and edges with three equivalent Cr(5)O6 octahedra. In the sixth Ca site, Ca(6) is bonded to one O(12) and three equivalent O(8) atoms to form CaO4 tetrahedra that share corners with three equivalent Cr(3)O6 octahedra, corners with three equivalent Cr(5)O6 octahedra, and corners with six equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-63°. There are six inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(2), one O(6), two equivalent O(1), and two equivalent O(4) atoms to form CrO6 octahedra that share  a cornercorner with one Ca(2)O4 tetrahedra,  a cornercorner with one Cr(6)O4 tetrahedra, corners with two equivalent Ca(1)O4 tetrahedra, corners with two equivalent Cr(4)O4 tetrahedra,  an edgeedge with one Ca(3)O6 octahedra,  an edgeedge with one Ca(5)O6 octahedra, and edges with four equivalent Cr(1)O6 octahedra. In the second Cr site, Cr(2) is bonded to one O(10), one O(5), two equivalent O(3), and two equivalent O(8) atoms to form CrO6 octahedra that share  a cornercorner with one Ca(4)O4 tetrahedra,  a cornercorner with one Cr(4)O4 tetrahedra, corners with two equivalent Ca(2)O4 tetrahedra, corners with two equivalent Ca(6)O4 tetrahedra,  an edgeedge with one Ca(3)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, and edges with four equivalent Cr(2)O6 octahedra. In the third Cr site, Cr(3) is bonded to three equivalent O(7) and three equivalent O(8) atoms to form CrO6 octahedra that share corners with three equivalent Ca(4)O4 tetrahedra, corners with three equivalent Ca(6)O4 tetrahedra, edges with three equivalent Cr(2)O6 octahedra, and edges with three equivalent Cr(5)O6 octahedra. In the fourth Cr site, Cr(4) is bonded to one O(10) and three equivalent O(4) atoms to form CrO4 tetrahedra that share corners with three equivalent Ca(3)O6 octahedra, corners with three equivalent Cr(2)O6 octahedra, and corners with six equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-62°. In the fifth Cr site, Cr(5) is bonded to one O(12), one O(9), two equivalent O(11), and two equivalent O(7) atoms to form CrO6 octahedra that share  a cornercorner with one Ca(1)O4 tetrahedra,  a cornercorner with one Ca(6)O4 tetrahedra, corners with two equivalent Ca(4)O4 tetrahedra, corners with two equivalent Cr(6)O4 tetrahedra,  an edgeedge with one Ca(5)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, and edges with four equivalent Cr(5)O6 octahedra. In the sixth Cr site, Cr(6) is bonded to one O(6) and three equivalent O(11) atoms to form CrO4 tetrahedra that share corners with three equivalent Ca(5)O6 octahedra, corners with three equivalent Cr(1)O6 octahedra, and corners with six equivalent Cr(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-63°. There are twelve inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ca(5), and two equivalent Cr(1) atoms to form distorted OCa2Cr2 trigonal pyramids that share  a cornercorner with one O(9)CaCr3 trigonal pyramid, corners with two equivalent O(1)Ca2Cr2 trigonal pyramids, corners with two equivalent O(6)Cr4 trigonal pyramids,  an edgeedge with one O(2)CaCr3 trigonal pyramid, and edges with two equivalent O(1)Ca2Cr2 trigonal pyramids. In the second O site, O(2) is bonded to one Ca(2) and three equivalent Cr(1) atoms to form distorted OCaCr3 trigonal pyramids that share corners with three equivalent O(3)Ca2Cr2 trigonal pyramids, corners with three equivalent O(6)Cr4 trigonal pyramids, and edges with three equivalent O(1)Ca2Cr2 trigonal pyramids. In the third O site, O(3) is bonded to one Ca(2), one Ca(3), and two equivalent Cr(2) atoms to form OCa2Cr2 trigonal pyramids that share corners with four equivalent O(8)CaCr3 tetrahedra,  a cornercorner with one O(2)CaCr3 trigonal pyramid, corners with two equivalent O(3)Ca2Cr2 trigonal pyramids,  an edgeedge with one O(5)CaCr3 tetrahedra, and edges with two equivalent O(3)Ca2Cr2 trigonal pyramids. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Ca(3), one Cr(4), and two equivalent Cr(1) atoms. In the fifth O site, O(5) is bonded to one Ca(4) and three equivalent Cr(2) atoms to form distorted OCaCr3 tetrahedra that share corners with three equivalent O(7)CaCr3 tetrahedra, corners with six equivalent O(8)CaCr3 tetrahedra, and edges with three equivalent O(3)Ca2Cr2 trigonal pyramids. In the sixth O site, O(6) is bonded to one Cr(6) and three equivalent Cr(1) atoms to form distorted OCr4 trigonal pyramids that share corners with three equivalent O(2)CaCr3 trigonal pyramids and corners with six equivalent O(1)Ca2Cr2 trigonal pyramids. In the seventh O site, O(7) is bonded to one Ca(4), one Cr(3), and two equivalent Cr(5) atoms to form a mixture of edge and corner-sharing OCaCr3 tetrahedra. In the eighth O site, O(8) is bonded to one Ca(6), one Cr(3), and two equivalent Cr(2) atoms to form OCaCr3 tetrahedra that share  a cornercorner with one O(12)CaCr3 tetrahedra, corners with two equivalent O(5)CaCr3 tetrahedra, corners with two equivalent O(8)CaCr3 tetrahedra, corners with three equivalent O(7)CaCr3 tetrahedra, corners with four equivalent O(3)Ca2Cr2 trigonal pyramids, and edges with two equivalent O(8)CaCr3 tetrahedra. In the ninth O site, O(9) is bonded to one Ca(1) and three equivalent Cr(5) atoms to form distorted OCaCr3 trigonal pyramids that share corners with three equivalent O(12)CaCr3 tetrahedra, corners with three equivalent O(1)Ca2Cr2 trigonal pyramids, and edges with three equivalent O(7)CaCr3 tetrahedra. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to one Cr(4) and three equivalent Cr(2) atoms. In the eleventh O site, O(11) is bonded in a rectangular see-saw-like geometry to one Ca(5), one Cr(6), and two equivalent Cr(5) atoms. In the twelfth O site, O(12) is bonded to one Ca(6) and three equivalent Cr(5) atoms to form corner-sharing OCaCr3 tetrahedra.
CaCr2O4 is Spinel-like structured and crystallizes in the trigonal P3m1 space group. There are six inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to one O(9) and three equivalent O(1) atoms to form CaO4 tetrahedra that share corners with three equivalent Ca(5)O6 octahedra, corners with three equivalent Cr(5)O6 octahedra, and corners with six equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 57-68°. The Ca(1)-O(9) bond length is 2.31 Å. All Ca(1)-O(1) bond lengths are 2.16 Å. In the second Ca site, Ca(2) is bonded to one O(2) and three equivalent O(3) atoms to form CaO4 tetrahedra that share corners with three equivalent Ca(3)O6 octahedra, corners with three equivalent Cr(1)O6 octahedra, and corners with six equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-69°. The Ca(2)-O(2) bond length is 2.27 Å. All Ca(2)-O(3) bond lengths are 2.16 Å. In the third Ca site, Ca(3) is bonded to three equivalent O(3) and three equivalent O(4) atoms to form CaO6 octahedra that share corners with three equivalent Ca(2)O4 tetrahedra, corners with three equivalent Cr(4)O4 tetrahedra, edges with three equivalent Cr(1)O6 octahedra, and edges with three equivalent Cr(2)O6 octahedra. All Ca(3)-O(3) bond lengths are 2.26 Å. All Ca(3)-O(4) bond lengths are 2.35 Å. In the fourth Ca site, Ca(4) is bonded to one O(5) and three equivalent O(7) atoms to form CaO4 tetrahedra that share corners with three equivalent Cr(2)O6 octahedra, corners with three equivalent Cr(3)O6 octahedra, and corners with six equivalent Cr(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 60-62°. The Ca(4)-O(5) bond length is 2.18 Å. All Ca(4)-O(7) bond lengths are 2.18 Å. In the fifth Ca site, Ca(5) is bonded to three equivalent O(1) and three equivalent O(11) atoms to form CaO6 octahedra that share corners with three equivalent Ca(1)O4 tetrahedra, corners with three equivalent Cr(6)O4 tetrahedra, edges with three equivalent Cr(1)O6 octahedra, and edges with three equivalent Cr(5)O6 octahedra. All Ca(5)-O(1) bond lengths are 2.24 Å. All Ca(5)-O(11) bond lengths are 2.35 Å. In the sixth Ca site, Ca(6) is bonded to one O(12) and three equivalent O(8) atoms to form CaO4 tetrahedra that share corners with three equivalent Cr(3)O6 octahedra, corners with three equivalent Cr(5)O6 octahedra, and corners with six equivalent Cr(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 58-63°. The Ca(6)-O(12) bond length is 2.31 Å. All Ca(6)-O(8) bond lengths are 2.17 Å. There are six inequivalent Cr sites. In the first Cr site, Cr(1) is bonded to one O(2), one O(6), two equivalent O(1), and two equivalent O(4) atoms to form CrO6 octahedra that share  a cornercorner with one Ca(2)O4 tetrahedra,  a cornercorner with one Cr(6)O4 tetrahedra, corners with two equivalent Ca(1)O4 tetrahedra, corners with two equivalent Cr(4)O4 tetrahedra,  an edgeedge with one Ca(3)O6 octahedra,  an edgeedge with one Ca(5)O6 octahedra, and edges with four equivalent Cr(1)O6 octahedra. The Cr(1)-O(2) bond length is 2.04 Å. The Cr(1)-O(6) bond length is 2.15 Å. Both Cr(1)-O(1) bond lengths are 1.99 Å. Both Cr(1)-O(4) bond lengths are 2.12 Å. In the second Cr site, Cr(2) is bonded to one O(10), one O(5), two equivalent O(3), and two equivalent O(8) atoms to form CrO6 octahedra that share  a cornercorner with one Ca(4)O4 tetrahedra,  a cornercorner with one Cr(4)O4 tetrahedra, corners with two equivalent Ca(2)O4 tetrahedra, corners with two equivalent Ca(6)O4 tetrahedra,  an edgeedge with one Ca(3)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, and edges with four equivalent Cr(2)O6 octahedra. The Cr(2)-O(10) bond length is 2.17 Å. The Cr(2)-O(5) bond length is 2.07 Å. Both Cr(2)-O(3) bond lengths are 1.99 Å. Both Cr(2)-O(8) bond lengths are 2.05 Å. In the third Cr site, Cr(3) is bonded to three equivalent O(7) and three equivalent O(8) atoms to form CrO6 octahedra that share corners with three equivalent Ca(4)O4 tetrahedra, corners with three equivalent Ca(6)O4 tetrahedra, edges with three equivalent Cr(2)O6 octahedra, and edges with three equivalent Cr(5)O6 octahedra. All Cr(3)-O(7) bond lengths are 2.07 Å. All Cr(3)-O(8) bond lengths are 2.00 Å. In the fourth Cr site, Cr(4) is bonded to one O(10) and three equivalent O(4) atoms to form CrO4 tetrahedra that share corners with three equivalent Ca(3)O6 octahedra, corners with three equivalent Cr(2)O6 octahedra, and corners with six equivalent Cr(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 56-62°. The Cr(4)-O(10) bond length is 2.21 Å. All Cr(4)-O(4) bond lengths are 1.95 Å. In the fifth Cr site, Cr(5) is bonded to one O(12), one O(9), two equivalent O(11), and two equivalent O(7) atoms to form CrO6 octahedra that share  a cornercorner with one Ca(1)O4 tetrahedra,  a cornercorner with one Ca(6)O4 tetrahedra, corners with two equivalent Ca(4)O4 tetrahedra, corners with two equivalent Cr(6)O4 tetrahedra,  an edgeedge with one Ca(5)O6 octahedra,  an edgeedge with one Cr(3)O6 octahedra, and edges with four equivalent Cr(5)O6 octahedra. The Cr(5)-O(12) bond length is 2.06 Å. The Cr(5)-O(9) bond length is 2.04 Å. Both Cr(5)-O(11) bond lengths are 2.14 Å. Both Cr(5)-O(7) bond lengths are 2.00 Å. In the sixth Cr site, Cr(6) is bonded to one O(6) and three equivalent O(11) atoms to form CrO4 tetrahedra that share corners with three equivalent Ca(5)O6 octahedra, corners with three equivalent Cr(1)O6 octahedra, and corners with six equivalent Cr(5)O6 octahedra. The corner-sharing octahedral tilt angles range from 54-63°. The Cr(6)-O(6) bond length is 2.25 Å. All Cr(6)-O(11) bond lengths are 1.93 Å. There are twelve inequivalent O sites. In the first O site, O(1) is bonded to one Ca(1), one Ca(5), and two equivalent Cr(1) atoms to form distorted OCa2Cr2 trigonal pyramids that share  a cornercorner with one O(9)CaCr3 trigonal pyramid, corners with two equivalent O(1)Ca2Cr2 trigonal pyramids, corners with two equivalent O(6)Cr4 trigonal pyramids,  an edgeedge with one O(2)CaCr3 trigonal pyramid, and edges with two equivalent O(1)Ca2Cr2 trigonal pyramids. In the second O site, O(2) is bonded to one Ca(2) and three equivalent Cr(1) atoms to form distorted OCaCr3 trigonal pyramids that share corners with three equivalent O(3)Ca2Cr2 trigonal pyramids, corners with three equivalent O(6)Cr4 trigonal pyramids, and edges with three equivalent O(1)Ca2Cr2 trigonal pyramids. In the third O site, O(3) is bonded to one Ca(2), one Ca(3), and two equivalent Cr(2) atoms to form OCa2Cr2 trigonal pyramids that share corners with four equivalent O(8)CaCr3 tetrahedra,  a cornercorner with one O(2)CaCr3 trigonal pyramid, corners with two equivalent O(3)Ca2Cr2 trigonal pyramids,  an edgeedge with one O(5)CaCr3 tetrahedra, and edges with two equivalent O(3)Ca2Cr2 trigonal pyramids. In the fourth O site, O(4) is bonded in a rectangular see-saw-like geometry to one Ca(3), one Cr(4), and two equivalent Cr(1) atoms. In the fifth O site, O(5) is bonded to one Ca(4) and three equivalent Cr(2) atoms to form distorted OCaCr3 tetrahedra that share corners with three equivalent O(7)CaCr3 tetrahedra, corners with six equivalent O(8)CaCr3 tetrahedra, and edges with three equivalent O(3)Ca2Cr2 trigonal pyramids. In the sixth O site, O(6) is bonded to one Cr(6) and three equivalent Cr(1) atoms to form distorted OCr4 trigonal pyramids that share corners with three equivalent O(2)CaCr3 trigonal pyramids and corners with six equivalent O(1)Ca2Cr2 trigonal pyramids. In the seventh O site, O(7) is bonded to one Ca(4), one Cr(3), and two equivalent Cr(5) atoms to form a mixture of edge and corner-sharing OCaCr3 tetrahedra. In the eighth O site, O(8) is bonded to one Ca(6), one Cr(3), and two equivalent Cr(2) atoms to form OCaCr3 tetrahedra that share  a cornercorner with one O(12)CaCr3 tetrahedra, corners with two equivalent O(5)CaCr3 tetrahedra, corners with two equivalent O(8)CaCr3 tetrahedra, corners with three equivalent O(7)CaCr3 tetrahedra, corners with four equivalent O(3)Ca2Cr2 trigonal pyramids, and edges with two equivalent O(8)CaCr3 tetrahedra. In the ninth O site, O(9) is bonded to one Ca(1) and three equivalent Cr(5) atoms to form distorted OCaCr3 trigonal pyramids that share corners with three equivalent O(12)CaCr3 tetrahedra, corners with three equivalent O(1)Ca2Cr2 trigonal pyramids, and edges with three equivalent O(7)CaCr3 tetrahedra. In the tenth O site, O(10) is bonded in a rectangular see-saw-like geometry to one Cr(4) and three equivalent Cr(2) atoms. In the eleventh O site, O(11) is bonded in a rectangular see-saw-like geometry to one Ca(5), one Cr(6), and two equivalent Cr(5) atoms. In the twelfth O site, O(12) is bonded to one Ca(6) and three equivalent Cr(5) atoms to form corner-sharing OCaCr3 tetrahedra.