Materials Data on Si3N4 by Materials Project

Si3N4 is Hausmannite structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are two inequivalent Si4+ sites. In the first Si4+ site, Si4+ is bonded to six equivalent N3- atoms to form SiN6 octahedra that share corners with six equivalent SiN4 tetrahedra and edges with six equivalent SiN6 octahedra. All Si–N bond lengths are 1.89 Å. In the second Si4+ site, Si4+ is bonded to four equivalent N3- atoms to form corner-sharing SiN4 tetrahedra. The corner-sharing octahedral tilt angles are 57°. All Si–N bond lengths are 1.79 Å. N3- is bonded in a distorted rectangular see-saw-like geometry to four Si4+ atoms.