Ho2Hf2O5 crystallizes in the tetragonal P4/mmm space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded in a distorted body-centered cubic geometry to eight equivalent O(1) atoms. In the second Ho site, Ho(2) is bonded to four equivalent O(2) and eight equivalent O(1) atoms to form HoO12 cuboctahedra that share corners with four equivalent Ho(2)O12 cuboctahedra, faces with four equivalent Ho(2)O12 cuboctahedra, and faces with eight equivalent Hf(1)O5 square pyramids. Hf(1) is bonded to one O(2) and four equivalent O(1) atoms to form HfO5 square pyramids that share corners with five equivalent Hf(1)O5 square pyramids and faces with four equivalent Ho(2)O12 cuboctahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ho(1), two equivalent Ho(2), and two equivalent Hf(1) atoms to form a mixture of distorted face, corner, and edge-sharing OHo4Hf2 octahedra. The corner-sharing octahedral tilt angles range from 0-65°. In the second O site, O(2) is bonded in a linear geometry to four equivalent Ho(2) and two equivalent Hf(1) atoms.
Ho2Hf2O5 crystallizes in the tetragonal P4/mmm space group. There are two inequivalent Ho sites. In the first Ho site, Ho(1) is bonded in a distorted body-centered cubic geometry to eight equivalent O(1) atoms. All Ho(1)-O(1) bond lengths are 2.82 Å. In the second Ho site, Ho(2) is bonded to four equivalent O(2) and eight equivalent O(1) atoms to form HoO12 cuboctahedra that share corners with four equivalent Ho(2)O12 cuboctahedra, faces with four equivalent Ho(2)O12 cuboctahedra, and faces with eight equivalent Hf(1)O5 square pyramids. All Ho(2)-O(2) bond lengths are 2.90 Å. All Ho(2)-O(1) bond lengths are 2.71 Å. Hf(1) is bonded to one O(2) and four equivalent O(1) atoms to form HfO5 square pyramids that share corners with five equivalent Hf(1)O5 square pyramids and faces with four equivalent Ho(2)O12 cuboctahedra. The Hf(1)-O(2) bond length is 2.08 Å. All Hf(1)-O(1) bond lengths are 2.07 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded to two equivalent Ho(1), two equivalent Ho(2), and two equivalent Hf(1) atoms to form a mixture of distorted face, corner, and edge-sharing OHo4Hf2 octahedra. The corner-sharing octahedral tilt angles range from 0-65°. In the second O site, O(2) is bonded in a linear geometry to four equivalent Ho(2) and two equivalent Hf(1) atoms.