DOE OSTI2020
CaCuO2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Ca2+ sites. In the first Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two equivalent CaO6 octahedra, a cornercorner with one CuO5 square pyramid, and edges with seven CaO6 octahedra. The corner-sharing octahedral tilt angles are 13°. There are a spread of Ca–O bond distances ranging from 2.26–2.51 Å. In the second Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two equivalent CaO6 octahedra, edges with seven CaO6 octahedra, and edges with two equivalent CuO5 square pyramids. The corner-sharing octahedral tilt angles are 13°. There are a spread of Ca–O bond distances ranging from 2.26–2.51 Å. In the third Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two equivalent CaO6 octahedra, edges with seven CaO6 octahedra, and edges with two equivalent CuO5 square pyramids. The corner-sharing octahedral tilt angles are 13°. There are a spread of Ca–O bond distances ranging from 2.26–2.47 Å. In the fourth Ca2+ site, Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with two equivalent CaO6 octahedra, corners with two equivalent CuO5 square pyramids, edges with seven CaO6 octahedra, and an edgeedge with one CuO5 square pyramid. The corner-sharing octahedral tilt angles are 13°. There are a spread of Ca–O bond distances ranging from 2.26–2.47 Å. There are four inequivalent Cu2+ sites. In the first Cu2+ site, Cu2+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Cu–O bond distances ranging from 1.97–2.04 Å. In the second Cu2+ site, Cu2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Cu–O bond distances ranging from 1.94–2.78 Å. In the third Cu2+ site, Cu2+ is bonded to five O2- atoms to form distorted CuO5 square pyramids that share corners with three CaO6 octahedra, edges with five CaO6 octahedra, and edges with two equivalent CuO5 square pyramids. The corner-sharing octahedra tilt angles range from 2–15°. There are a spread of Cu–O bond distances ranging from 1.94–2.77 Å. In the fourth Cu2+ site, Cu2+ is bonded in a square co-planar geometry to four O2- atoms. There are a spread of Cu–O bond distances ranging from 1.97–2.04 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to one Ca2+ and four Cu2+ atoms to form OCaCu4 square pyramids that share corners with seven OCa3Cu2 square pyramids and edges with four OCaCu4 square pyramids. In the second O2- site, O2- is bonded to three Ca2+ and two equivalent Cu2+ atoms to form a mixture of edge and corner-sharing OCa3Cu2 square pyramids. In the third O2- site, O2- is bonded to three Ca2+ and two equivalent Cu2+ atoms to form OCa3Cu2 square pyramids that share corners with five OCaCu4 square pyramids and edges with seven OCa3Cu2 square pyramids. In the fourth O2- site, O2- is bonded to one Ca2+ and four Cu2+ atoms to form a mixture of edge and corner-sharing OCaCu4 square pyramids. In the fifth O2- site, O2- is bonded to three Ca2+ and two equivalent Cu2+ atoms to form a mixture of edge and corner-sharing OCa3Cu2 square pyramids. In the sixth O2- site, O2- is bonded to five Ca2+ and one Cu2+ atom to form distorted OCa5Cu square pyramids that share corners with five OCaCu4 square pyramids and edges with ten OCa3Cu2 square pyramids. In the seventh O2- site, O2- is bonded to three Ca2+ and two equivalent Cu2+ atoms to form a mixture of edge and corner-sharing OCa3Cu2 square pyramids. In the eighth O2- site, O2- is bonded in a 5-coordinate geometry to five Ca2+ and one Cu2+ atom.