Study on the Origin of Giant Dielectric Constant of Cacu3ti4o12 Ceramics

CaCu3Ti4O12 ceramic (CCTO) were prepared by traditional solid phase sintering methods at 1100 degrees C for 20h. In order to learn the influence of atmosphere on point defects and dielectric properties, the samples sintered were heat treated in oxygen-rich or nitrogen-rich atmosphere at 900 degrees C for 9h. The phase structure and dielectric properties are measured by X-ray diffraction (XRD) and Novocontrol wide band dielectric spectroscopy. It is found that grain resistance and especially grain-boundary resistance increase after oxygen-rich atmosphere treatment. The increase of grain-boundary resistance directly results in the drop of low frequency loss. The increase of grain resistance significantly restrains high frequency giant dielectric constant and dielectric loss. However, the effect of nitrogen-rich atmosphere treatment is quite contrary. It is believed that heat treatment in oxygen-rich or nitrogen-rich atmosphere changes the concentration of oxygen vacancy in CCTO. Different oxygen vacancy concentrations cause huge change of electric performance of grain and grain-boundary, which in turn influences dielectric properties of CCTO ceramics. In addition, the origin of medium and high frequency relaxation peak was done by testing dielectric temperature spectrum of CCTO ceramic, finding that CCTO high frequency relaxation process stems from relaxation polarization caused by monovalent oxygen vacancy, and medium frequency relaxation process stems from relaxation polarization caused by bivalent oxygen vacancy. And the activation energies of the two relaxation processes do not change at all with atmosphere treatment, implying the intrinsic nature of the two intrinsic defects.