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The complex impedance spectra of polymer-derived amorphous silicon oxycarbides synthesized at different temperatures are reported. Analysis of the spectra using equivalent circuit models showed that the conduction of current is dominantly through the matrix and free carbon in series, instead of through the matrix or free carbon only. We found that the conductivity of both matrix and free-carbon phase increases with increasing synthesis temperature, whereas the relaxation time of the matrix is much shorter than that of the free carbon. The results are correlated with the structures of the materials.

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We studied the electric conductivity and structure of polymerderived carbon-rich amorphous SiC pyrolyzed at different temperatures. The conductivity of the material increased drastically with pyrolysis temperature followed an Arrhenius relationship with the activation energy of~3.4 eV. Raman and X-ray photoelectron spectroscopy analysis revealed that the order of free carbon phase increased with pyrolysis temperature, accompanied by sp 3 ?sp 2 transition. The activation energy for such a structure change was 3.1-3.8 eV, which is close to that for the conductivity change. We thus believe that the increase in the conductivity was mainly due to the increase in conductivity of the free carbon phase.R. Riedel-contributing editor Manuscript No. 34335.

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