DOE OSTI2020
Sr3(Co0.5Nb0.5)2O7 is (La,Ba)CuO4-derived structured and crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. there are three inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded in a 1-coordinate geometry to nine O2- atoms. There are a spread of Sr–O bond distances ranging from 2.33–2.82 Å. In the second Sr2+ site, Sr2+ is bonded in a 9-coordinate geometry to nine O2- atoms. There are five shorter (2.65 Å) and four longer (2.84 Å) Sr–O bond lengths. In the third Sr2+ site, Sr2+ is bonded in a 12-coordinate geometry to twelve O2- atoms. There are a spread of Sr–O bond distances ranging from 2.58–3.13 Å. Nb5+ is bonded to six O2- atoms to form NbO6 octahedra that share a cornercorner with one CoO6 octahedra and corners with four equivalent NbO6 octahedra. The corner-sharing octahedra tilt angles range from 0–5°. There are a spread of Nb–O bond distances ranging from 1.93–2.07 Å. Co3+ is bonded to six O2- atoms to form CoO6 octahedra that share a cornercorner with one NbO6 octahedra and corners with four equivalent CoO6 octahedra. The corner-sharing octahedra tilt angles range from 0–6°. There are a spread of Co–O bond distances ranging from 1.99–2.13 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded to four Sr2+ and two equivalent Co3+ atoms to form a mixture of distorted face, edge, and corner-sharing OSr4Co2 octahedra. The corner-sharing octahedra tilt angles range from 6–52°. In the second O2- site, O2- is bonded in a distorted linear geometry to four Sr2+ and two equivalent Nb5+ atoms. In the third O2- site, O2- is bonded in a distorted linear geometry to four equivalent Sr2+, one Nb5+, and one Co3+ atom. In the fourth O2- site, O2- is bonded to five Sr2+ and one Co3+ atom to form distorted OSr5Co octahedra that share corners with twelve OSr4Co2 octahedra, edges with eight OSr5Nb octahedra, and faces with four equivalent OSr4Co2 octahedra. The corner-sharing octahedra tilt angles range from 14–52°. In the fifth O2- site, O2- is bonded to five Sr2+ and one Nb5+ atom to form a mixture of distorted edge and corner-sharing OSr5Nb octahedra. The corner-sharing octahedra tilt angles range from 1–49°.