DOE OSTI2020
CaCoGeO4 is Spinel-derived structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with four equivalent CaO6 octahedra, corners with four equivalent CoO6 octahedra, corners with four equivalent GeO4 tetrahedra, edges with two equivalent CoO6 octahedra, and an edgeedge with one GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–59°. There are a spread of Ca–O bond distances ranging from 2.30–2.46 Å. Co2+ is bonded to six O2- atoms to form CoO6 octahedra that share corners with four equivalent CaO6 octahedra, corners with two equivalent GeO4 tetrahedra, edges with two equivalent CaO6 octahedra, edges with two equivalent CoO6 octahedra, and edges with two equivalent GeO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–59°. There are a spread of Co–O bond distances ranging from 2.15–2.20 Å. Ge4+ is bonded to four O2- atoms to form GeO4 tetrahedra that share corners with two equivalent CoO6 octahedra, corners with four equivalent CaO6 octahedra, an edgeedge with one CaO6 octahedra, and edges with two equivalent CoO6 octahedra. The corner-sharing octahedra tilt angles range from 55–64°. There are a spread of Ge–O bond distances ranging from 1.77–1.80 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to one Ca2+, two equivalent Co2+, and one Ge4+ atom to form distorted corner-sharing OCaCo2Ge tetrahedra. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to two equivalent Ca2+, one Co2+, and one Ge4+ atom. In the third O2- site, O2- is bonded in a rectangular see-saw-like geometry to one Ca2+, two equivalent Co2+, and one Ge4+ atom.