SPECTROSCOPIC STUDIES OF THE STRUCTURE OF AMORPHOUS AND MICROCRYSTALLINE SIC PREPARED BY THE POLYMER ROUTE

The structural evolution of amorphous and microcrystalline SiC prepared from polycarbosilane was studied using various spectroscopic methods, C-13 CPMAS NMR (cross-polarization, magic angle spinning nuclear magnetic resonance), ESR (electron spin resonance), FTIR (Fourier transformation infrared spectroscopy), and Raman. These studies indicate that the carbon-rich a-SiC has two major structural defects, C = C double bonds and C-dangling bonds. Both defect concentrations vary with firing conditions. The effect of hydrogen on the defect concentrations was also investigated by heat-treating the sample under hydrogen atmosphere. The mechanisms of the conversion process were discussed and the structural models for both amorphous and microcrystalline SiC were also proposed.