DOE OSTI2020
Sr4Pr3CeNb2(CuO5)4 crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are four inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form distorted SrO12 cuboctahedra that share corners with eight SrO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with four NbO6 octahedra, and faces with four equivalent CuO5 square pyramids. There are a spread of Sr–O bond distances ranging from 2.82–3.08 Å. In the second Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form distorted SrO12 cuboctahedra that share corners with eight SrO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with four NbO6 octahedra, and faces with four equivalent CuO5 square pyramids. There are a spread of Sr–O bond distances ranging from 2.74–3.12 Å. In the third Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form distorted SrO12 cuboctahedra that share corners with eight SrO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with four NbO6 octahedra, and faces with four CuO5 square pyramids. There are a spread of Sr–O bond distances ranging from 2.75–3.11 Å. In the fourth Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form distorted SrO12 cuboctahedra that share corners with eight SrO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with four NbO6 octahedra, and faces with four CuO5 square pyramids. There are a spread of Sr–O bond distances ranging from 2.75–3.11 Å. There are three inequivalent Pr+3.33+ sites. In the first Pr+3.33+ site, Pr+3.33+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.41 Å) and four longer (2.61 Å) Pr–O bond lengths. In the second Pr+3.33+ site, Pr+3.33+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.40 Å) and four longer (2.63 Å) Pr–O bond lengths. In the third Pr+3.33+ site, Pr+3.33+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.40 Å) and four longer (2.63 Å) Pr–O bond lengths. Ce4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are four shorter (2.26 Å) and four longer (2.63 Å) Ce–O bond lengths. 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 four equivalent NbO6 octahedra, corners with two CuO5 square pyramids, and faces with eight SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There is four shorter (1.98 Å) and two longer (2.00 Å) Nb–O bond length. In the second Nb5+ site, Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share corners with four equivalent NbO6 octahedra, corners with two CuO5 square pyramids, and faces with eight SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There is four shorter (1.99 Å) and two longer (2.00 Å) Nb–O bond length. There are three inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded to five O2- atoms to form CuO5 square pyramids that share a cornercorner with one NbO6 octahedra, corners with four equivalent CuO5 square pyramids, and faces with four SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (1.99 Å) and one longer (2.17 Å) Cu–O bond lengths. In the second Cu2+ site, Cu2+ is bonded to five O2- atoms to form CuO5 square pyramids that share a cornercorner with one NbO6 octahedra, corners with four equivalent CuO5 square pyramids, and faces with four SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (1.99 Å) and one longer (2.16 Å) Cu–O bond lengths. In the third Cu2+ site, Cu2+ is bonded to five O2- atoms to form CuO5 square pyramids that share a cornercorner with one NbO6 octahedra, corners with four equivalent CuO5 square pyramids, and faces with four SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (1.99 Å) and one longer (2.16 Å) Cu–O bond lengths. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded to two Sr2+, one Pr+3.33+, one Ce4+, and two equivalent Cu2+ atoms to form distorted OSr2CePrCu2 octahedra that share corners with two equivalent OSr2CePrCu2 octahedra, corners with six equivalent OCePr3 tetrahedra, edges with two equivalent OSr2CePrCu2 octahedra, an edgeedge with one OCePr3 tetrahedra, and faces with four equivalent OSr2CePrCu2 octahedra. The corner-sharing octahedral tilt angles are 9°. In the second O2- site, O2- is bonded to two Sr2+, two Pr+3.33+, and two Cu2+ atoms to form distorted OSr2Pr2Cu2 octahedra that share corners with two equivalent OSr2Pr2Cu2 octahedra, corners with six equivalent OCePr3 tetrahedra, edges with two equivalent OSr2Pr2Cu2 octahedra, an edgeedge with one OCePr3 tetrahedra, and faces with four equivalent OSr2Pr2Cu2 octahedra. The corner-sharing octahedral tilt angles are 8°. In the third O2- site, O2- is bonded in a 2-coordinate geometry to four Sr2+, one Nb5+, and one Cu2+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to four Sr2+, one Nb5+, and one Cu2+ atom. In the fifth O2- site, O2- is bonded in a 2-coordinate geometry to four Sr2+, one Nb5+, and one Cu2+ atom. In the sixth O2- site, O2- is bonded in a linear geometry to four Sr2+ and two Nb5+ atoms. In the seventh O2- site, O2- is bonded to three Pr+3.33+ and one Ce4+ atom to form OCePr3 tetrahedra that share corners with twelve OSr2CePrCu2 octahedra, corners with four equivalent OCePr3 tetrahedra, edges with two OSr2CePrCu2 octahedra, and edges with four equivalent OCePr3 tetrahedra. The corner-sharing octahedra tilt angles range from 7–70°.