DOE OSTI2020
Sm3NbO7 crystallizes in the triclinic P-1 space group. The structure is three-dimensional. there are three inequivalent Sm3+ sites. In the first Sm3+ site, Sm3+ is bonded to seven O2- atoms to form distorted SmO7 pentagonal bipyramids that share corners with two NbO6 octahedra, a cornercorner with one SmO7 pentagonal bipyramid, an edgeedge with one NbO6 octahedra, and edges with four SmO7 pentagonal bipyramids. The corner-sharing octahedra tilt angles range from 45–48°. There are a spread of Sm–O bond distances ranging from 2.35–2.49 Å. In the second Sm3+ site, Sm3+ is bonded in a 7-coordinate geometry to seven O2- atoms. There are a spread of Sm–O bond distances ranging from 2.30–2.87 Å. In the third Sm3+ site, Sm3+ is bonded to seven O2- atoms to form distorted SmO7 pentagonal bipyramids that share corners with two NbO6 octahedra, a cornercorner with one SmO7 pentagonal bipyramid, edges with two NbO6 octahedra, and edges with four SmO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 44°. There are a spread of Sm–O bond distances ranging from 2.26–2.46 Å. There are two inequivalent Nb5+ sites. In the first Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with two equivalent NbO6 octahedra, corners with four SmO7 pentagonal bipyramids, and edges with four SmO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 34°. There are four shorter (2.01 Å) and two longer (2.04 Å) Nb–O bond lengths. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with two equivalent NbO6 octahedra, corners with four SmO7 pentagonal bipyramids, and edges with two equivalent SmO7 pentagonal bipyramids. The corner-sharing octahedral tilt angles are 34°. There are a spread of Nb–O bond distances ranging from 2.00–2.07 Å. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to three Sm3+ and one Nb5+ atom. In the second O2- site, O2- is bonded in a 4-coordinate geometry to three Sm3+ and one Nb5+ atom. In the third O2- site, O2- is bonded in a 4-coordinate geometry to three Sm3+ and one Nb5+ atom. In the fourth O2- site, O2- is bonded in a 4-coordinate geometry to three Sm3+ and one Nb5+ atom. In the fifth O2- site, O2- is bonded in a 3-coordinate geometry to one Sm3+ and two Nb5+ atoms. In the sixth O2- site, O2- is bonded to four Sm3+ atoms to form a mixture of edge and corner-sharing OSm4 tetrahedra. In the seventh O2- site, O2- is bonded to four Sm3+ atoms to form a mixture of edge and corner-sharing OSm4 tetrahedra.