Silicon-29 Solid State MAS NMR Investigation of Silicon Carbide Powders Prepared with a Precursor Method.

Abstract

This report represents results of 29Si MAS NMR, investigation of the silicon carbide powders synthesized with a precursor method. The variety in particle morphology is controllable in the precursor method, and the synthesized powders show characteristic NMR spectra. Most of the powders show overlapping three broad signals at peak positions of -16, -21 and -25ppm in the NMR spectra, which indicate variation in second neighbors in coordination of individual silicon atoms. Such variety in the coordination is known to have close relationship to the stacking faults in the quite small and spherical SiC grains.As an exceptional case, the powder synthesized from the SiO2-2.1C precursor (C/SiO2=2.1) at 1973K shows a large broad signal at -19ppm with a spike at -16ppm. This powder contains no residual carbon, and consists of large SiC crystallites of 100-200nm. The fluctuation in chemical shift in type A silicon, which is dominant coordination in β-SiC (3C) structure, should originate the broad signal at -19ppm.