DOE OSTI2020
Pm2O3 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are three inequivalent Pm3+ sites. In the first Pm3+ site, Pm3+ is bonded to six O2- atoms to form a mixture of distorted edge and corner-sharing PmO6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are a spread of Pm–O bond distances ranging from 2.29–2.58 Å. In the second Pm3+ site, Pm3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Pm–O bond distances ranging from 2.32–2.76 Å. In the third Pm3+ site, Pm3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Pm–O bond distances ranging from 2.32–2.84 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to five Pm3+ atoms to form distorted OPm5 square pyramids that share corners with seven OPm4 tetrahedra, corners with two equivalent OPm4 trigonal pyramids, edges with two equivalent OPm6 octahedra, edges with two equivalent OPm5 square pyramids, edges with three OPm4 tetrahedra, and edges with three equivalent OPm4 trigonal pyramids. In the second O2- site, O2- is bonded to four Pm3+ atoms to form OPm4 tetrahedra that share corners with two equivalent OPm6 octahedra, corners with two equivalent OPm5 square pyramids, corners with four OPm4 tetrahedra, corners with six equivalent OPm4 trigonal pyramids, an edgeedge with one OPm6 octahedra, edges with two equivalent OPm5 square pyramids, and an edgeedge with one OPm4 tetrahedra. The corner-sharing octahedral tilt angles are 14°. In the third O2- site, O2- is bonded to four Pm3+ atoms to form distorted OPm4 trigonal pyramids that share a cornercorner with one OPm6 octahedra, corners with two equivalent OPm5 square pyramids, corners with nine OPm4 tetrahedra, corners with two equivalent OPm4 trigonal pyramids, edges with three equivalent OPm5 square pyramids, and edges with two equivalent OPm4 trigonal pyramids. The corner-sharing octahedral tilt angles are 35°. In the fourth O2- site, O2- is bonded to six Pm3+ atoms to form OPm6 octahedra that share corners with six OPm4 tetrahedra, corners with two equivalent OPm4 trigonal pyramids, edges with two equivalent OPm6 octahedra, edges with four equivalent OPm5 square pyramids, and edges with six OPm4 tetrahedra. In the fifth O2- site, O2- is bonded to four Pm3+ atoms to form OPm4 tetrahedra that share a cornercorner with one OPm6 octahedra, corners with five equivalent OPm5 square pyramids, corners with four OPm4 tetrahedra, corners with three equivalent OPm4 trigonal pyramids, edges with two equivalent OPm6 octahedra, an edgeedge with one OPm5 square pyramid, and edges with two equivalent OPm4 tetrahedra. The corner-sharing octahedral tilt angles are 51°.