Raman characterization of oxidation behavior of free carbon in silicon oxycarbide ceramics

Abstract

Tantalum and niobium containing silicon oxycarbide ceramics were prepared from hybrid gels through cohydrolysis with methyltriethoxysilane and pentaethoxyniobium/tantalum, and pyrolysis at 1000°C. To investigate the behavior of free carbon in Si-Nb-C-O and Si-Ta-C-O ceramics, Raman spectroscopy was used. The spectra obtained before oxidation showed a higher shift of the G band at around approximately 1610 cm-1, which means a cumulative band of G and D′. After oxidation, however, a symmetric G band, the shift toward a normal position at 1580 cm-1 and a weaker background were detected. These phenomena were found to strongly correlate with the oxidation of carbon reactive sites, i.e., those of radical and edge carbon specks in tiny graphene layer of free carbon.