Two silicon oxycarbide glasses with different compositions (O/Si ratio 1.2
and 1.8) were prepared by pyrolysis at moderate temperature (900 °C) of
polysiloxane precursors. Their structure was investigated using quantitative
29Si solid-state NMR and X-ray photoelectron spectroscopy
(XPS). The environment of the silicon atoms in the oxycarbide phase
corresponded to a purely random distribution of Si-O and Si-C bonds
depending on the O/Si ratio of the glass only and not on the structure of
the precursors. At the light of the NMR results, the Si2p XPS spectra of the
glasses may be interpreted using the contribution of the five possible
SiOxC4-x tetrahedra. The Cls
spectra of these glasses indicated the presence of oxycarbide carbon in
CSi4 tetrahedra, similar to carbide
carbon, and graphitic-like excess carbon.