Materials Data on NaCr3O8 by Materials Project
NaCr3O8 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with six equivalent CrO4 tetrahedra and edges with two equivalent CrO6 octahedra. There are two shorter (2.47 Å) and four longer (2.51 Å) Na–O bond lengths. There are two inequivalent Cr5+ sites. In the first Cr5+ site, Cr5+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with three equivalent NaO6 octahedra and corners with three equivalent CrO6 octahedra. The corner-sharing octahedra tilt angles range from 34–63°. There are a spread of Cr–O bond distances ranging from 1.61–1.70 Å. In the second Cr5+ site, Cr5+ is bonded to six O2- atoms to form CrO6 octahedra that share corners with six equivalent CrO4 tetrahedra and edges with two equivalent NaO6 octahedra. There are two shorter (1.99 Å) and four longer (2.01 Å) Cr–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one Na1+ and two Cr5+ atoms. In the second O2- site, O2- is bonded in a bent 150 degrees geometry to two Cr5+ atoms. In the third O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Na1+ and one Cr5+ atom.