DOE OSTI2020
La2Hf2O7 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are four inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are a spread of La–O bond distances ranging from 2.38–2.86 Å. In the second La3+ site, La3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of La–O bond distances ranging from 2.39–2.73 Å. In the third La3+ site, La3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of La–O bond distances ranging from 2.47–2.63 Å. In the fourth La3+ site, La3+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of La–O bond distances ranging from 2.42–3.10 Å. There are four inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to six O2- atoms to form corner-sharing HfO6 octahedra. The corner-sharing octahedra tilt angles range from 29–38°. There are a spread of Hf–O bond distances ranging from 2.01–2.19 Å. In the second Hf4+ site, Hf4+ is bonded to six O2- atoms to form corner-sharing HfO6 octahedra. The corner-sharing octahedra tilt angles range from 23–38°. There are a spread of Hf–O bond distances ranging from 2.00–2.23 Å. In the third Hf4+ site, Hf4+ is bonded to six O2- atoms to form corner-sharing HfO6 octahedra. The corner-sharing octahedra tilt angles range from 29–41°. There are a spread of Hf–O bond distances ranging from 1.98–2.24 Å. In the fourth Hf4+ site, Hf4+ is bonded to six O2- atoms to form corner-sharing HfO6 octahedra. The corner-sharing octahedra tilt angles range from 23–41°. There are a spread of Hf–O bond distances ranging from 2.00–2.27 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded to two La3+ and two Hf4+ atoms to form distorted OLa2Hf2 tetrahedra that share corners with five OLa3Hf tetrahedra and an edgeedge with one OLa2Hf2 tetrahedra. In the second O2- site, O2- is bonded to three La3+ and one Hf4+ atom to form distorted OLa3Hf tetrahedra that share corners with five OLa2Hf2 tetrahedra and edges with four OLa3Hf tetrahedra. In the third O2- site, O2- is bonded in a 2-coordinate geometry to two La3+ and two Hf4+ atoms. In the fourth O2- site, O2- is bonded in a distorted T-shaped geometry to one La3+ and two Hf4+ atoms. In the fifth O2- site, O2- is bonded to three La3+ and one Hf4+ atom to form distorted OLa3Hf tetrahedra that share corners with seven OLa2Hf2 tetrahedra and edges with three equivalent OLa3Hf tetrahedra. In the sixth O2- site, O2- is bonded in a 5-coordinate geometry to three La3+ and two equivalent Hf4+ atoms. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to two La3+ and two Hf4+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to two La3+ and one Hf4+ atom. In the ninth O2- site, O2- is bonded to two La3+ and two Hf4+ atoms to form a mixture of distorted corner and edge-sharing OLa2Hf2 tetrahedra. In the tenth O2- site, O2- is bonded in a 4-coordinate geometry to two La3+ and two Hf4+ atoms. In the eleventh O2- site, O2- is bonded to two La3+ and two Hf4+ atoms to form a mixture of distorted corner and edge-sharing OLa2Hf2 tetrahedra. In the twelfth O2- site, O2- is bonded to three La3+ and one Hf4+ atom to form a mixture of distorted corner and edge-sharing OLa3Hf tetrahedra. In the thirteenth O2- site, O2- is bonded in a 5-coordinate geometry to three La3+ and two equivalent Hf4+ atoms. In the fourteenth O2- site, O2- is bonded in a 2-coordinate geometry to two La3+ and two Hf4+ atoms.