DOE OSTI2020
Sr8Re5Fe5O28 crystallizes in the tetragonal P4/mmm space group. The structure is two-dimensional and consists of one Sr8Re5Fe5O28 sheet oriented in the (0, 0, 1) direction. there are two inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with eight SrO12 cuboctahedra, faces with five SrO12 cuboctahedra, faces with two equivalent ReO6 octahedra, and faces with two equivalent FeO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.75–2.88 Å. In the second Sr2+ site, Sr2+ is bonded to twelve O2- atoms to form SrO12 cuboctahedra that share corners with twelve SrO12 cuboctahedra, faces with six SrO12 cuboctahedra, faces with four ReO6 octahedra, and faces with four FeO6 octahedra. There are a spread of Sr–O bond distances ranging from 2.79–2.82 Å. There are three inequivalent Re5+ sites. In the first Re5+ site, Re5+ is bonded in a single-bond geometry to five O2- atoms. There is one shorter (1.89 Å) and four longer (1.92 Å) Re–O bond length. In the second Re5+ site, Re5+ is bonded to six O2- atoms to form ReO6 octahedra that share corners with five FeO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–1°. There is four shorter (1.95 Å) and two longer (1.96 Å) Re–O bond length. In the third Re5+ site, Re5+ is bonded to six O2- atoms to form ReO6 octahedra that share corners with six FeO6 octahedra and faces with eight equivalent SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There is four shorter (1.95 Å) and two longer (1.97 Å) Re–O bond length. There are three inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded in a single-bond geometry to five O2- atoms. There are one shorter (2.00 Å) and four longer (2.03 Å) Fe–O bond lengths. In the second Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with five ReO6 octahedra and faces with eight SrO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–1°. There are a spread of Fe–O bond distances ranging from 1.99–2.09 Å. In the third Fe3+ site, Fe3+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six ReO6 octahedra and faces with eight equivalent SrO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. There are four shorter (2.00 Å) and two longer (2.05 Å) Fe–O bond lengths. There are seven inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+, one Re5+, and one Fe3+ atom. In the second O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+, one Re5+, and one Fe3+ atom. In the third O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+, one Re5+, and one Fe3+ atom. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two equivalent Sr2+, one Re5+, and one Fe3+ atom. In the fifth O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+, one Re5+, and one Fe3+ atom. In the sixth O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+, one Re5+, and one Fe3+ atom. In the seventh O2- site, O2- is bonded in a distorted linear geometry to four Sr2+, one Re5+, and one Fe3+ atom.