DOE OSTI2020
CuCo2O4 is Spinel-like structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are two inequivalent Co3+ sites. In the first Co3+ site, Co3+ is bonded to four O2- atoms to form CoO4 tetrahedra that share corners with three equivalent CuO6 octahedra and corners with nine equivalent CoO6 octahedra. The corner-sharing octahedra tilt angles range from 57–60°. There is three shorter (1.94 Å) and one longer (1.99 Å) Co–O bond length. In the second Co3+ site, Co3+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with three equivalent CoO4 tetrahedra, corners with three equivalent CuO4 tetrahedra, edges with two equivalent CuO6 octahedra, and edges with four equivalent CoO6 octahedra. There are a spread of Co–O bond distances ranging from 1.96–1.99 Å. There are two inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded to four O2- atoms to form CuO4 tetrahedra that share corners with three equivalent CuO6 octahedra and corners with nine equivalent CoO6 octahedra. The corner-sharing octahedra tilt angles range from 57–60°. There is three shorter (1.95 Å) and one longer (2.00 Å) Cu–O bond length. In the second Cu2+ site, Cu2+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with three equivalent CoO4 tetrahedra, corners with three equivalent CuO4 tetrahedra, and edges with six equivalent CoO6 octahedra. There are three shorter (2.02 Å) and three longer (2.03 Å) Cu–O bond lengths. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded to three Co3+ and one Cu2+ atom to form a mixture of distorted edge and corner-sharing OCo3Cu trigonal pyramids. In the second O2- site, O2- is bonded to four Co3+ atoms to form a mixture of distorted edge and corner-sharing OCo4 trigonal pyramids. In the third O2- site, O2- is bonded to three equivalent Co3+ and one Cu2+ atom to form distorted corner-sharing OCo3Cu trigonal pyramids. In the fourth O2- site, O2- is bonded in a rectangular see-saw-like geometry to two equivalent Co3+ and two Cu2+ atoms.