HOPPING CONDUCTION IN A NANOMETER-SIZE CRYSTALLINE SYSTEM - A SIC FIBER

The effect of nanometer-size inhomogeneities on the electronic transport is not easy to study from an experimental point of view because of the scarcity of candidate materials. SiC fibers, with SiC crystallites and graphitic clusters 2 nm in size embedded in an amorphous matrix, are found to be good candidates for such a study. In the present work, x-ray diffraction, high-resolution electron microscopy, and magic-angle spinning nuclear magnetic resonance are used to characterize the nanostructure and the chemical disorder. Conductivity measurements were performed as a function of temperature (10-300 K) and frequency (0-10 GHz). Electron-spin-resonance experiments are performed to identify the charge carriers and to determine their concentration. Transport is dominated by hopping of charge carriers, as seen from dc- and ac-conductivity measurements. The latter reveals the different scales of disorder present in the material. Noteworthy is the fact that the relaxation due to the nanostructure occurs in the frequency range where hopping is also effective.