Impedance Spectroscopy Study on the Two-phase to Three-phase Transformation in Polymer Derived SiC Pyrolyzed at High Temperature

摘要

The electrical behavior and evolution of free carbon phase and ceramic phase in pristine polymer derived (PDC) SiC matrix with high pyrolysis temperature were studied by complex impedance spectroscopy. The results from low pyrolysis temperature (1300-1500°C) showed that the contact resistance at the free carbon and amorphous PDC SiC interphase decreases with increasing pyrolysis temperature. At this temperature range, the dielectric response of the system is not sensitive to the increased ordering of non-ferromagnetic carbon clusters. At higher pyrolysis temperature (1600-1800°C), transformation of free carbon from nanocrystalline carbon to turbostratic phase occurs. This phenomenon leads to the Introduction of inductance in the equivalent circuit. The percolative network of turbostratic carbon acts as a conductive helical winding in the PDC system. The study demonstrated that when an alternate current of certain frequency made to flow through the PDC system, it behaves as an inductor. Also, carbon cluster- turbostratic carbon transition observed with microstructural investigation is correlated with the equivalent circuit model.