DOE OSTI2020
La2Ce2O7 crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. there are four inequivalent Ce4+ sites. In the first Ce4+ site, Ce4+ is bonded to six O2- atoms to form CeO6 octahedra that share corners with four CeO6 octahedra, a cornercorner with one LaO6 pentagonal pyramid, and an edgeedge with one LaO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 39–48°. There are a spread of Ce–O bond distances ranging from 2.17–2.33 Å. In the second Ce4+ site, Ce4+ is bonded to six O2- atoms to form corner-sharing CeO6 octahedra. The corner-sharing octahedra tilt angles range from 34–48°. There are a spread of Ce–O bond distances ranging from 2.16–2.41 Å. In the third Ce4+ site, Ce4+ is bonded to six O2- atoms to form CeO6 octahedra that share corners with four CeO6 octahedra, corners with two equivalent LaO6 pentagonal pyramids, and an edgeedge with one LaO6 pentagonal pyramid. The corner-sharing octahedra tilt angles range from 38–51°. There are a spread of Ce–O bond distances ranging from 2.16–2.38 Å. In the fourth Ce4+ site, Ce4+ is bonded to six O2- atoms to form distorted corner-sharing CeO6 octahedra. The corner-sharing octahedra tilt angles range from 31–51°. There are a spread of Ce–O bond distances ranging from 2.17–2.50 Å. There are four inequivalent La3+ sites. In the first La3+ site, La3+ is bonded in a 4-coordinate geometry to six O2- atoms. There are a spread of La–O bond distances ranging from 2.37–2.77 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 2.44–2.68 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 2.45–2.77 Å. In the fourth La3+ site, La3+ is bonded to six O2- atoms to form distorted LaO6 pentagonal pyramids that share corners with three CeO6 octahedra, corners with two equivalent LaO6 pentagonal pyramids, and edges with two CeO6 octahedra. The corner-sharing octahedra tilt angles range from 62–76°. There are a spread of La–O bond distances ranging from 2.35–2.77 Å. There are fourteen inequivalent O2- sites. In the first O2- site, O2- is bonded to two Ce4+ and two La3+ atoms to form distorted OLa2Ce2 tetrahedra that share corners with five OLa3Ce tetrahedra and an edgeedge with one OLa2Ce2 tetrahedra. In the second O2- site, O2- is bonded to one Ce4+ and three La3+ atoms to form distorted OLa3Ce tetrahedra that share corners with five OLa2Ce2 tetrahedra and edges with four OLa3Ce tetrahedra. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ce4+ and one La3+ atom. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to two Ce4+ and one La3+ atom. In the fifth O2- site, O2- is bonded to one Ce4+ and three La3+ atoms to form distorted OLa3Ce tetrahedra that share corners with seven OLa2Ce2 tetrahedra and edges with three equivalent OLa3Ce tetrahedra. In the sixth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ce4+ and two La3+ atoms. In the seventh O2- site, O2- is bonded in a 3-coordinate geometry to two Ce4+ and one La3+ atom. In the eighth O2- site, O2- is bonded in a distorted trigonal planar geometry to one Ce4+ and two La3+ atoms. In the ninth O2- site, O2- is bonded to two Ce4+ and two La3+ atoms to form a mixture of distorted corner and edge-sharing OLa2Ce2 tetrahedra. In the tenth O2- site, O2- is bonded in a distorted see-saw-like geometry to two Ce4+ and two La3+ atoms. In the eleventh O2- site, O2- is bonded to two Ce4+ and two La3+ atoms to form a mixture of distorted corner and edge-sharing OLa2Ce2 tetrahedra. In the twelfth O2- site, O2- is bonded to one Ce4+ and three La3+ atoms to form a mixture of distorted corner and edge-sharing OLa3Ce tetrahedra. In the thirteenth O2- site, O2- is bonded in a 4-coordinate geometry to two equivalent Ce4+ and two La3+ atoms. In the fourteenth O2- site, O2- is bonded in a distorted T-shaped geometry to two Ce4+ and one La3+ atom.