CaYAl3O7 crystallizes in the monoclinic P2_1 space group. Ca(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(6), one O(7), two equivalent O(1), and two equivalent O(4) atoms. Y(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(6), one O(7), two equivalent O(2), and two equivalent O(5) atoms. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(4), and one O(7) atom to form corner-sharing AlO4 tetrahedra. In the second Al site, Al(2) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form corner-sharing AlO4 tetrahedra. In the third Al site, Al(3) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing AlO4 tetrahedra. There are seven inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ca(1), one Y(1), and one Al(1) atom to form distorted OCa2YAl tetrahedra that share corners with two equivalent O(1)Ca2YAl tetrahedra, corners with two equivalent O(3)CaYAl2 tetrahedra, and  an edgeedge with one O(3)CaYAl2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Y(1), and one Al(2) atom. In the third O site, O(3) is bonded to one Ca(1), one Y(1), one Al(1), and one Al(2) atom to form a mixture of distorted corner and edge-sharing OCaYAl2 tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Al(1), and one Al(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Y(1), one Al(2), and one Al(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1), one Y(1), one Al(2), and one Al(3) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Ca(1), one Y(1), one Al(1), and one Al(3) atom.
CaYAl3O7 crystallizes in the monoclinic P2_1 space group. Ca(1) is bonded in a 8-coordinate geometry to one O(2), one O(3), one O(6), one O(7), two equivalent O(1), and two equivalent O(4) atoms. The Ca(1)-O(2) bond length is 2.72 Å. The Ca(1)-O(3) bond length is 2.45 Å. The Ca(1)-O(6) bond length is 3.05 Å. The Ca(1)-O(7) bond length is 2.41 Å. There is one shorter (2.50 Å) and one longer (2.55 Å) Ca(1)-O(1) bond length. There is one shorter (2.41 Å) and one longer (2.94 Å) Ca(1)-O(4) bond length. Y(1) is bonded in a 8-coordinate geometry to one O(1), one O(3), one O(6), one O(7), two equivalent O(2), and two equivalent O(5) atoms. The Y(1)-O(1) bond length is 2.35 Å. The Y(1)-O(3) bond length is 2.38 Å. The Y(1)-O(6) bond length is 2.35 Å. The Y(1)-O(7) bond length is 2.79 Å. There is one shorter (2.40 Å) and one longer (2.50 Å) Y(1)-O(2) bond length. There is one shorter (2.36 Å) and one longer (2.91 Å) Y(1)-O(5) bond length. There are three inequivalent Al sites. In the first Al site, Al(1) is bonded to one O(1), one O(3), one O(4), and one O(7) atom to form corner-sharing AlO4 tetrahedra. The Al(1)-O(1) bond length is 1.75 Å. The Al(1)-O(3) bond length is 1.77 Å. The Al(1)-O(4) bond length is 1.76 Å. The Al(1)-O(7) bond length is 1.78 Å. In the second Al site, Al(2) is bonded to one O(2), one O(3), one O(5), and one O(6) atom to form corner-sharing AlO4 tetrahedra. The Al(2)-O(2) bond length is 1.75 Å. The Al(2)-O(3) bond length is 1.76 Å. The Al(2)-O(5) bond length is 1.78 Å. The Al(2)-O(6) bond length is 1.77 Å. In the third Al site, Al(3) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form corner-sharing AlO4 tetrahedra. The Al(3)-O(4) bond length is 1.76 Å. The Al(3)-O(5) bond length is 1.77 Å. The Al(3)-O(6) bond length is 1.77 Å. The Al(3)-O(7) bond length is 1.76 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ca(1), one Y(1), and one Al(1) atom to form distorted OCa2YAl tetrahedra that share corners with two equivalent O(1)Ca2YAl tetrahedra, corners with two equivalent O(3)CaYAl2 tetrahedra, and  an edgeedge with one O(3)CaYAl2 tetrahedra. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Ca(1), two equivalent Y(1), and one Al(2) atom. In the third O site, O(3) is bonded to one Ca(1), one Y(1), one Al(1), and one Al(2) atom to form a mixture of distorted corner and edge-sharing OCaYAl2 tetrahedra. In the fourth O site, O(4) is bonded in a 4-coordinate geometry to two equivalent Ca(1), one Al(1), and one Al(3) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Y(1), one Al(2), and one Al(3) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to one Ca(1), one Y(1), one Al(2), and one Al(3) atom. In the seventh O site, O(7) is bonded in a 4-coordinate geometry to one Ca(1), one Y(1), one Al(1), and one Al(3) atom.