Physical meaning of conductivity spectra for ZnO ceramics

With the help of broadband dielectric spectroscopy in a wide temperature and frequency range, conductivity spectra of ZnO polycrystalline ceramics are measured and direct-current-like (DC-like) conductivity and relaxation polarization conductivity are observed successively along the frequency axis. According to classical Debye theory and Cole-Cole equation, the physical meanings of the two conductivities are discussed. It is found that the DC-like conductivity corresponds to electron transportation over Schottky barrier at grainboundary. The relaxation polarization conductivity corresponds to electronic trap relaxation of intrinsic point defects (zinc interstitial and oxygen vacancy). When it is in the high frequency region, relaxation conductivity obeys the universal law with the index n equal to the index α in Cole-Cole equation as an indictor of disorder degree.