Cheng Peng-Fei

Physical meaning of conductivity spectra for ZnO ceramics

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

Dielectric response of CaCu 3 Ti 4 O 12 materials

The dielectric properties and its variation of CaCu3Ti4O12 (CCTO) materials induced by the process conditions are reviewed in this paper. On the basis of heterogeneous microstructure in ceramics and single crystal, the extrinsic Maxwell-Wagner polarization mechanism of internal barrier layer capacitance (IBLC) model is discussed adequately. According to the especial crystal structure and atomic structure, possible grain semiconducting mechanism is proposed. At the end of the paper, theoretical problems in CCTO material, Maxwell-Wagner polarization and dielectric spectroscopy analysis are analyzed.