Si 29 magic-angle-spinning nuclear-magnetic-resonance study of spinel-type Si3N4

Abstract

${}^{\mathrm{29}}\mathrm{Si}$ magic-angle-spinning nuclear-magnetic resonance has been measured on spinel-type cubic silicon nitride $\mathrm{(c-}{\mathrm{Si}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}}\mathrm{).}$ $\mathrm{c-}{\mathrm{Si}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}}$ shows two ${}^{\mathrm{29}}\mathrm{Si}$ resonances at $\text{−50.0±0.2}$ and $\text{−225.0±0.2\hspace{0.05em}}\mathrm{ppm},$ corresponding to the tetrahedron ${\mathrm{SN}}_{\mathrm{4}}$ and the octahedron ${\mathrm{SiN}}_{\mathrm{6}},$ respectively. Integration of the spectrum gives ${\mathrm{SN}}_{\mathrm{4}}{\mathrm{/SiN}}_{\mathrm{6}}$ about one half that of the spinel structure. Ab initio self-consistent field Hartree–Fock molecular orbital calculations also indicate that the chemical shift for octahedral Si is more negative in nitride than in oxides.