Materials Data on K3NaCr2O8 by Materials Project
K3Na(CrO4)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to six equivalent O2- atoms to form distorted KO6 cuboctahedra that share corners with six equivalent CrO4 tetrahedra and faces with two equivalent NaO6 octahedra. All K–O bond lengths are 2.98 Å. In the second K1+ site, K1+ is bonded in a 1-coordinate geometry to ten O2- atoms. There are a spread of K–O bond distances ranging from 2.62–3.20 Å. Na1+ is bonded to six equivalent O2- atoms to form NaO6 octahedra that share corners with six equivalent CrO4 tetrahedra and faces with two equivalent KO6 cuboctahedra. All Na–O bond lengths are 2.40 Å. Cr6+ is bonded to four O2- atoms to form CrO4 tetrahedra that share corners with three equivalent KO6 cuboctahedra and corners with three equivalent NaO6 octahedra. The corner-sharing octahedral tilt angles are 18°. There is one shorter (1.65 Å) and three longer (1.67 Å) Cr–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to four K1+, one Na1+, and one Cr6+ atom. In the second O2- site, O2- is bonded in a distorted linear geometry to one K1+ and one Cr6+ atom.