K3AlO3 crystallizes in the monoclinic C2/m space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 5-coordinate geometry to one O(2) and four equivalent O(1) atoms. In the second K site, K(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. In the third K site, K(3) is bonded to four equivalent O(1) atoms to form distorted KO4 tetrahedra that share corners with four equivalent Al(1)O4 tetrahedra and edges with two equivalent K(3)O4 tetrahedra. Al(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form AlO4 tetrahedra that share corners with four equivalent K(3)O4 tetrahedra and  an edgeedge with one Al(1)O4 tetrahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 7-coordinate geometry to two equivalent K(1), two equivalent K(2), two equivalent K(3), and one Al(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), two equivalent K(2), and two equivalent Al(1) atoms.
K3AlO3 crystallizes in the monoclinic C2/m space group. There are three inequivalent K sites. In the first K site, K(1) is bonded in a 5-coordinate geometry to one O(2) and four equivalent O(1) atoms. The K(1)-O(2) bond length is 2.55 Å. There are two shorter (2.76 Å) and two longer (2.82 Å) K(1)-O(1) bond lengths. In the second K site, K(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(1) atoms. Both K(2)-O(2) bond lengths are 3.12 Å. There are two shorter (2.69 Å) and two longer (2.84 Å) K(2)-O(1) bond lengths. In the third K site, K(3) is bonded to four equivalent O(1) atoms to form distorted KO4 tetrahedra that share corners with four equivalent Al(1)O4 tetrahedra and edges with two equivalent K(3)O4 tetrahedra. There are two shorter (2.73 Å) and two longer (2.76 Å) K(3)-O(1) bond lengths. Al(1) is bonded to two equivalent O(1) and two equivalent O(2) atoms to form AlO4 tetrahedra that share corners with four equivalent K(3)O4 tetrahedra and  an edgeedge with one Al(1)O4 tetrahedra. Both Al(1)-O(1) bond lengths are 1.75 Å. Both Al(1)-O(2) bond lengths are 1.83 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 7-coordinate geometry to two equivalent K(1), two equivalent K(2), two equivalent K(3), and one Al(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one K(1), two equivalent K(2), and two equivalent Al(1) atoms.