Cs2HfO3 crystallizes in the orthorhombic Cmce space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 7-coordinate geometry to two equivalent O(1), two equivalent O(2), and three equivalent O(3) atoms. In the second Cs site, Cs(2) is bonded to two equivalent O(1), two equivalent O(3), and three equivalent O(2) atoms to form distorted CsO7 hexagonal pyramids that share corners with four equivalent Cs(2)O7 hexagonal pyramids,  a cornercorner with one Hf(1)O4 tetrahedra, edges with three equivalent Cs(2)O7 hexagonal pyramids, and edges with four equivalent Hf(1)O4 tetrahedra. Hf(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form HfO4 tetrahedra that share  a cornercorner with one Cs(2)O7 hexagonal pyramid, corners with two equivalent Hf(1)O4 tetrahedra, and edges with four equivalent Cs(2)O7 hexagonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Hf(1) atoms. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Cs(1), three equivalent Cs(2), and one Hf(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to two equivalent Cs(2), three equivalent Cs(1), and one Hf(1) atom.
Cs2HfO3 crystallizes in the orthorhombic Cmce space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 7-coordinate geometry to two equivalent O(1), two equivalent O(2), and three equivalent O(3) atoms. Both Cs(1)-O(1) bond lengths are 3.65 Å. There is one shorter (3.08 Å) and one longer (3.31 Å) Cs(1)-O(2) bond length. There are two shorter (3.31 Å) and one longer (3.40 Å) Cs(1)-O(3) bond length. In the second Cs site, Cs(2) is bonded to two equivalent O(1), two equivalent O(3), and three equivalent O(2) atoms to form distorted CsO7 hexagonal pyramids that share corners with four equivalent Cs(2)O7 hexagonal pyramids,  a cornercorner with one Hf(1)O4 tetrahedra, edges with three equivalent Cs(2)O7 hexagonal pyramids, and edges with four equivalent Hf(1)O4 tetrahedra. Both Cs(2)-O(1) bond lengths are 3.34 Å. There is one shorter (3.04 Å) and one longer (3.17 Å) Cs(2)-O(3) bond length. There is one shorter (3.25 Å) and two longer (3.29 Å) Cs(2)-O(2) bond lengths. Hf(1) is bonded to one O(2), one O(3), and two equivalent O(1) atoms to form HfO4 tetrahedra that share  a cornercorner with one Cs(2)O7 hexagonal pyramid, corners with two equivalent Hf(1)O4 tetrahedra, and edges with four equivalent Cs(2)O7 hexagonal pyramids. The Hf(1)-O(2) bond length is 1.92 Å. The Hf(1)-O(3) bond length is 1.92 Å. Both Hf(1)-O(1) bond lengths are 2.01 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted bent 150 degrees geometry to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Hf(1) atoms. In the second O site, O(2) is bonded in a distorted single-bond geometry to two equivalent Cs(1), three equivalent Cs(2), and one Hf(1) atom. In the third O site, O(3) is bonded in a distorted single-bond geometry to two equivalent Cs(2), three equivalent Cs(1), and one Hf(1) atom.