Materials Data on NaCr2O4 by Materials Project
NaCr2O4 crystallizes in the orthorhombic Pmmn space group. The structure is three-dimensional. there are two inequivalent Na1+ sites. In the first Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are two shorter (2.39 Å) and four longer (2.52 Å) Na–O bond lengths. In the second Na1+ site, Na1+ is bonded in a 6-coordinate geometry to six O2- atoms. There are two shorter (2.44 Å) and four longer (2.55 Å) Na–O bond lengths. There are two inequivalent Cr+3.50+ sites. In the first Cr+3.50+ site, Cr+3.50+ is bonded to six O2- atoms to form edge-sharing CrO6 octahedra. There are a spread of Cr–O bond distances ranging from 1.91–2.01 Å. In the second Cr+3.50+ site, Cr+3.50+ is bonded to six O2- atoms to form edge-sharing CrO6 octahedra. There are four shorter (2.00 Å) and two longer (2.02 Å) Cr–O bond lengths. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to two Na1+ and three Cr+3.50+ atoms to form distorted ONa2Cr3 trigonal bipyramids that share corners with five equivalent ONa2Cr3 trigonal bipyramids, corners with two equivalent ONaCr3 trigonal pyramids, edges with four equivalent ONa2Cr3 trigonal bipyramids, and edges with two equivalent ONaCr3 trigonal pyramids. In the second O2- site, O2- is bonded in a distorted rectangular see-saw-like geometry to one Na1+ and three Cr+3.50+ atoms. In the third O2- site, O2- is bonded to one Na1+ and three Cr+3.50+ atoms to form distorted ONaCr3 trigonal pyramids that share corners with four equivalent ONa2Cr3 trigonal bipyramids, corners with three equivalent ONaCr3 trigonal pyramids, and edges with four equivalent ONa2Cr3 trigonal bipyramids.