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The dielectric properties and its variation of CaCu 3 Ti 4 O 12 (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.

In this paper, the dielectric property of CaCu3Ti4O12 ceramic is measured by Novocontrol wide band dielectric spectrometer in a temperature range of -100-100 ℃ and frequency range of 0.1 Hz-10 MHz, and the corresponding dielectric relaxation mechanism is discussed. Firstly, on the basis of quantitative analysis of macroscopic shell-core structure, the possibility of colossal dielectric constant (CDC) originating from the surface insulated layer effect is rejected. Secondly, after the analysis of the nature of classical Maxwell-Wagner sandwich polarization and its activation energy, classical Maxwell-Wagner mechanism is also abandoned. Finally, a new model of trapped electron relaxation at the boundary of Schottky barrier is proposed. The new mechanism correctly reflects the essential connection between intrinsic point defects, conductivity and dielectric constant of CaCu3Ti4O12material.

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.

The electrical and dielectric properties of a commercial ZnO-based varistor ceramics were measured in the process of 8/20 μs impulse current degradation up to 5000 times of impulses. The characteristics of U-I in the region of low current and the loss tangent were mainly investigated. It was found that the varistor voltage U1mA will first increase rapidly with impulse times increasing, and then remain stable and finally decrease sharply. Furthermore, a new loss peak emerges at -100℃ in the dielectric spectra after 600 times of impulse degradation, which suggests a new trapping behavior introduced in the degradation process. Activation energy of the new peak first decreases, then becomes independent on impulse times. It was also found that the non-linear coefficient was more sensitive to the degradation process than varistor voltage U1mA. These phenomena have not been reported before, which revealed that the variation of the neutral Fermi level between positive bias Schottky barrier region and reverse bias Schottky barrier region is the origin which leads to the degradation of electrical properties.

Dielectric frequency spectra of ZnO-Bi2O3 based varistor ceramics were measured in the frequency range of 10-2Hz—106Hz from -100℃ to 20℃ by Novocontrol broadband dielectric spectrometer. The intrinsic defect structure of ZnO was calculated according to the theory which assumes that characteristics dielectric loss peaks of ZnO varistor ceramics origin from electronic relaxation process of intrinsic defects in depletion layer. At the same time the micro-electric parameters of grainboundary and the single grainboundary breakdown voltage Vb were obtained. The accordance of theory with experiment in Vb value indicates that the method to calculate grainboundary electronic structure by dielectric spectroscopy proposed in this paper is resonable.

In this paper， the dielectric spectra of ZnO varistor ceramic were measured by Novocontrol wide band dielectric spectrometer in the temperature range of -100 ℃—20 ℃ and frequency range of 10-2—106 Hz. It is found that the activation energy is 0.26 and 0.36 eV， respectively. After careful analysis of the measurement conditions， quantitative calculation results and other phenomena， three relaxations of cathode electron injection， dipole polarization and interface polarization are discarded. Thermally stimulated current（TSC） has three peaks， of which the higher temperature peak comes from thermionic polarization introduced by TSC itself， and other two peaks correspond to the characteristic loss peaks in dielectric spectra. Therefore， it is concluded that the characteristic loss peaks of ZnO ceramics originate from electronic relaxation of intrinsic defects.