Oxycarbides were produced by pyrolysis of polysiloxanes with different contents of methyl/phenyl groups at 1000 degreesC under nitrogen atmosphere. The structure of the three silicon oxycarbides was studied by elemental analysis, spectroscopy, and X-ray diffraction. The free carbon phase was concentrated by treatment with hydrofluoric acid. The sp(2) graphene planes merged in sp(3) structures form the free carbon phase. Its content and location in the SiOC network and its structural pattern reflects the sp(2)/sp(3) ratio of the source polysiloxanes. (C) 2004 Elsevier B.V. All rights reserved.