Cs4HfO4 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 6-coordinate geometry to one O(3), two equivalent O(2), and three equivalent O(1) atoms. In the second Cs site, Cs(2) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), and two equivalent O(1) atoms. In the third Cs site, Cs(3) is bonded to one O(2), one O(3), and two equivalent O(4) atoms to form distorted CsO4 tetrahedra that share corners with four equivalent Hf(1)O4 tetrahedra and  an edgeedge with one Cs(3)O4 tetrahedra. In the fourth Cs site, Cs(4) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(3), and two equivalent O(4) atoms. Hf(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form HfO4 tetrahedra that share corners with four equivalent Cs(3)O4 tetrahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to two equivalent Cs(2), three equivalent Cs(1), and one Hf(1) atom. In the second O site, O(2) is bonded in a 1-coordinate geometry to one Cs(2), one Cs(3), one Cs(4), two equivalent Cs(1), and one Hf(1) atom. In the third O site, O(3) is bonded in a 1-coordinate geometry to one Cs(1), one Cs(2), one Cs(3), two equivalent Cs(4), and one Hf(1) atom. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to one Cs(2), two equivalent Cs(3), two equivalent Cs(4), and one Hf(1) atom.
Cs4HfO4 crystallizes in the monoclinic P2_1/c space group. There are four inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 6-coordinate geometry to one O(3), two equivalent O(2), and three equivalent O(1) atoms. The Cs(1)-O(3) bond length is 3.32 Å. There is one shorter (3.20 Å) and one longer (3.70 Å) Cs(1)-O(2) bond length. There are a spread of Cs(1)-O(1) bond distances ranging from 2.95-3.44 Å. In the second Cs site, Cs(2) is bonded in a 5-coordinate geometry to one O(2), one O(3), one O(4), and two equivalent O(1) atoms. The Cs(2)-O(2) bond length is 2.94 Å. The Cs(2)-O(3) bond length is 3.09 Å. The Cs(2)-O(4) bond length is 3.57 Å. There is one shorter (2.91 Å) and one longer (3.08 Å) Cs(2)-O(1) bond length. In the third Cs site, Cs(3) is bonded to one O(2), one O(3), and two equivalent O(4) atoms to form distorted CsO4 tetrahedra that share corners with four equivalent Hf(1)O4 tetrahedra and  an edgeedge with one Cs(3)O4 tetrahedra. The Cs(3)-O(2) bond length is 2.94 Å. The Cs(3)-O(3) bond length is 2.96 Å. There is one shorter (2.89 Å) and one longer (2.97 Å) Cs(3)-O(4) bond length. In the fourth Cs site, Cs(4) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(3), and two equivalent O(4) atoms. The Cs(4)-O(2) bond length is 3.06 Å. There is one shorter (3.15 Å) and one longer (3.21 Å) Cs(4)-O(3) bond length. There is one shorter (3.12 Å) and one longer (3.15 Å) Cs(4)-O(4) bond length. Hf(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form HfO4 tetrahedra that share corners with four equivalent Cs(3)O4 tetrahedra. The Hf(1)-O(1) bond length is 1.95 Å. The Hf(1)-O(2) bond length is 1.96 Å. The Hf(1)-O(3) bond length is 1.96 Å. The Hf(1)-O(4) bond length is 1.96 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 1-coordinate geometry to two equivalent Cs(2), three equivalent Cs(1), and one Hf(1) atom. In the second O site, O(2) is bonded in a 1-coordinate geometry to one Cs(2), one Cs(3), one Cs(4), two equivalent Cs(1), and one Hf(1) atom. In the third O site, O(3) is bonded in a 1-coordinate geometry to one Cs(1), one Cs(2), one Cs(3), two equivalent Cs(4), and one Hf(1) atom. In the fourth O site, O(4) is bonded in a 1-coordinate geometry to one Cs(2), two equivalent Cs(3), two equivalent Cs(4), and one Hf(1) atom.