Frequency-dependent conductive behavior of polymer-derived amorphous silicon carbonitride

The AC conductive behavior of a polymer-derived amorphous silicon carbonitride ceramic was systemically studied. The conductivity exhibited a frequency-dependent switch: at low frequencies, the conductivity is constant and independent of frequency; while at high frequencies, the conductivity increases with frequency, showing a strong relaxation process. Both the frequency-independent conductivity and the characteristic frequency for the relaxation follow the Arrhenius relation with respect to the annealing temperature and follow a band-tail hopping process with respect to the testing temperature. XPS analysis revealed that a sp³-sp² transition took place in the free-carbon phase of the material with increasing annealing temperature. The activation energy of the transition is similar to those for the Arrhenius relations. The following conductive mechanisms were proposed to account for the observed behaviors: the frequency-independent conductivity in the low frequency region is dominated by a long-distance transport of charge carriers via matrix-free carbon path, enhanced by an electric-field concentration effect; while the frequency-dependent conductivity in the high frequency region is dominated by a interfacial polarization process governed by charge carrier relaxation within the free-carbon phase.