| For microelectronics revolution, electronic devices require miniaturization and monolithic, the development of new materials focusing on looking for high dielectric constant materials. One of the new-high-dielectric material CaCu3Ti4O12(CCTO), which exhibits a high dielectric constant (105) with good temperature stability, has attracted much attention. Owing to these remarkable properties, CaCu3Ti4O12 is being considered as a very promising material for application in the fields of high density energy storage, thin film device and high dielectric constant capacitors. However, the dielectric loss of the material is relatively too high, which is undesirable for practical applications, and the breakdown voltage lower limited its use at higher electric field. In this thesis, we have tried to control the microstructures of CCTO by designing CCTO-based composites to facilitate its practical application in capacitors and varistors.The CaCu3Ti4O12 ceramics doped with various Al2O3 (0,0.15,0.30,0.40) constant were fabricated by a solid-state reaction method. The effects of Al2O3 doping on the phase structure, microstructure, dielectric properties and current-voltage nonlinear behavior of CCTO ceramics have been investigated. The results showed that, Al2O3 additive has not only reduced the dielectric loss of low frequency range but also significantly raised the breakdown voltage. As Al2O3 doping concentration x was 0.30, the specimen has achieved the best comprehensive electrical properties, including the dielectric constant of 2000, dielectric loss of 0.04, breakdown voltage of 1084 V/mm and a nonlinear coefficient of 4.6. The optimized properties of Al2O3 doped CCTO is related to the enhanced proportion of the insulting grain boundaries, which is caused by the decrease of the average grain size. This study will help to design CCTO-based materials and promote their application as capacitors.The CaCu3-xLaxTi3.8Al0.2O12 (x=0,0.1,0.2,0.4) ceramics have been prepared by a solid-state reaction method. The results showed that, the dielectric loss of both at low (<104 Hz) and high frequency range (> 105 Hz) has shown a decrease by Al and La co-doping, and significantly improved theⅠ-Ⅴnonlinear coefficient. As x= 0.1, the specimen has achieved the best comprehensive electrical properties, including the dielectric constant of 41 022, dielectric loss of 0.06, breakdown voltage of 320 V/mm and a nonlinear coefficient of 59.4. The optimized properties of CaCu3-xLaxTi3.8Al0.2O12 can be well explained by the uniformity of the grains, the reduction of the average grain boundary thinkness and the enhancement of the grain boundary resistance. In the final part of this thesis, the nonlinear behavior was summaried based on six group typical experimental data of our laboratory in recent two years. It showed that breakdown voltage was in relation to the grain boundary resistance,that is, the raise of breakdown voltage was mainly attributed to the increaseof grain boundary resistance leading to the increase of double Schottky potential barriers. The nonlinear coefficient reflected the variation of current corresponding to that of voltage.The increase of grain size was a primary reason for increase of nonlinear coefficient. |
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