DOE OSTI2020
NaCu3O4 crystallizes in the tetragonal P4_122 space group. The structure is three-dimensional. Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with six CuO6 octahedra, edges with two equivalent NaO6 octahedra, and edges with ten CuO6 octahedra. The corner-sharing octahedra tilt angles range from 10–15°. There are four shorter (2.35 Å) and two longer (2.41 Å) Na–O bond lengths. There are three inequivalent Cu+2.33+ sites. In the first Cu+2.33+ site, Cu+2.33+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with six CuO6 octahedra, edges with four equivalent NaO6 octahedra, and edges with eight CuO6 octahedra. The corner-sharing octahedra tilt angles range from 10–19°. There are a spread of Cu–O bond distances ranging from 1.92–2.19 Å. In the second Cu+2.33+ site, Cu+2.33+ is bonded to six O2- atoms to form distorted CuO6 octahedra that share corners with two equivalent CuO6 octahedra, corners with four equivalent NaO6 octahedra, edges with two equivalent NaO6 octahedra, and edges with ten CuO6 octahedra. The corner-sharing octahedra tilt angles range from 10–15°. There are four shorter (1.95 Å) and two longer (2.49 Å) Cu–O bond lengths. In the third Cu+2.33+ site, Cu+2.33+ is bonded to six O2- atoms to form CuO6 octahedra that share corners with two equivalent NaO6 octahedra, corners with four equivalent CuO6 octahedra, edges with four equivalent NaO6 octahedra, and edges with eight CuO6 octahedra. The corner-sharing octahedra tilt angles range from 10–19°. There are a spread of Cu–O bond distances ranging from 2.01–2.15 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 6-coordinate geometry to one Na1+ and five Cu+2.33+ atoms. In the second O2- site, O2- is bonded to two equivalent Na1+ and four Cu+2.33+ atoms to form a mixture of corner and edge-sharing ONa2Cu4 octahedra. The corner-sharing octahedra tilt angles range from 6–7°.