Study of the pyrolysis process of an hybrid CH₃SiO_1.5 gel into a SiCO glass

Silicon oxycarbide samples were prepared by polymer pyrolysis using a methyltriethoxysilane-derived precursor. Transparent crack-free gel samples were obtained from the alkoxide by the sol-gel process. The dried gel samples were pyrolysed at different temperatures in the range between 400 and 1500 °C in Ar atmosphere. The chemical and microstructural evolution during pyrolysis were followed by FT-IR absorption, Raman scattering and photoluminescence (PL). The FT-IR spectra show the change in Si-O-Si asymmetric stretching, C-H_x, Si-CH₃ stretching vibrational bands. The peak position and shape of these bands were found stable up to 600 °C. Above this temperature, a remarkable change in shape and peak position of Si-O-Si related vibration, reduction in C-H_x and Si-CH₃ stretching absorption bands have been observed. Degradation of Si-CH₃ and the simultaneous formation of Si-CH₂-Si via Si-CH₂-CH₂-Si is explicitly observed, experimentally. Annealing the sample at 800 °C starts to show the clear presence of D and G bands, related to the free carbon precipitation and its segregation with the temperature. The broad PL spectra centered at around 670 nm for the samples pyrolysed at 1500 °C shows an important information regarding the presence of crystalline SiC.