DOE OSTI2020
CeNb3O9 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Ce3+ sites. In the first Ce3+ site, Ce3+ is bonded to twelve O2- atoms to form CeO12 cuboctahedra that share faces with four CeO12 cuboctahedra and faces with eight NbO6 octahedra. There are a spread of Ce–O bond distances ranging from 2.60–2.72 Å. In the second Ce3+ site, Ce3+ is bonded to twelve O2- atoms to form CeO12 cuboctahedra that share corners with four equivalent CeO12 cuboctahedra, faces with two equivalent CeO12 cuboctahedra, and faces with eight NbO6 octahedra. There are a spread of Ce–O bond distances ranging from 2.66–2.77 Å. In the third Ce3+ site, Ce3+ is bonded to twelve O2- atoms to form CeO12 cuboctahedra that share corners with four CeO12 cuboctahedra, a faceface with one CeO12 cuboctahedra, and faces with eight NbO6 octahedra. There are a spread of Ce–O bond distances ranging from 2.62–2.90 Å. There are three inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra and faces with two equivalent CeO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–14°. There are a spread of Nb–O bond distances ranging from 1.97–2.03 Å. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra and faces with three CeO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–20°. There are a spread of Nb–O bond distances ranging from 1.94–2.09 Å. In the third Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with six NbO6 octahedra and faces with three CeO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 2–22°. There are a spread of Nb–O bond distances ranging from 1.92–2.13 Å. There are thirteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a linear geometry to two Nb5+ atoms. In the second O2- site, O2- is bonded in a linear geometry to two equivalent Nb5+ atoms. In the third O2- site, O2- is bonded in a 2-coordinate geometry to three Ce3+ and two Nb5+ atoms. In the fourth O2- site, O2- is bonded in a distorted linear geometry to two equivalent Ce3+ and two equivalent Nb5+ atoms. In the fifth O2- site, O2- is bonded in a distorted T-shaped geometry to one Ce3+ and two equivalent Nb5+ atoms. In the sixth O2- site, O2- is bonded in a 3-coordinate geometry to one Ce3+ and two equivalent Nb5+ atoms. In the seventh O2- site, O2- is bonded in a 2-coordinate geometry to two Ce3+ and two equivalent Nb5+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to one Ce3+ and two equivalent Nb5+ atoms. In the ninth O2- site, O2- is bonded in a distorted T-shaped geometry to one Ce3+ and two equivalent Nb5+ atoms. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to two Ce3+ and two equivalent Nb5+ atoms. In the eleventh O2- site, O2- is bonded in a 4-coordinate geometry to two Ce3+ and two Nb5+ atoms. In the twelfth O2- site, O2- is bonded in a distorted T-shaped geometry to one Ce3+ and two Nb5+ atoms. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to one Ce3+ and two Nb5+ atoms.