| The rapid growth of the electronic industry needs the miniaturization of the component in mixed-signal integrated circuits, which is restricted to the development of new materials with high dielectric constant. One of the new-high-dielectric material CaCu3Ti4O12(CCTO), which exhibits a high dielectric constant (105) with good temperature stability, has attracted much attention. It is known that the dielectric properties are sensitive to processing and the origin of high dielectric constant is not fully understood. On the other hand, the main problems for the application of CCTO are its high dielectric loss, low breakdown voltage and compatively small I-V nonlinear coefficient. Considering the current research situation, the effects of the calcination and sintering temperatures on the microstructure and dielectric properties of CCTO ceramics have been investigated systematically. Moreover, we have tried to control the microstructure by designing CCTO-based composite to facilitate its practical application in capacitors and varistors.CCTO ceramics were fabricated by a conventional solid-state reaction at various calcination and sintering temperatures. Depending on the relative dielectric constant (εr) at 1 kHz, the specimens can be categorized into three types: type A (ε<5×104), type B (5×104＜εr＜105) and type C (εr＞105). The value ofεr is closely related to the microstructure:type-A specimens show a morphology with large grains embedded in a small-grained matrix, type-B specimens present a network structure and type-C specimens display a core-shell structure. Different dielectric loss variation tendencies are observed in the type-A specimens, which can be well explained by the impedance spectroscopy analysis and further confirmed by the EDX results. Also, the proper calcination and sintering temperature ranges needed to achieve good comprehensive properties are given.The Ca1-xLaxCu3Ti3.8Al0.2O12(x=0,0.1.0.2,0.3) ceramics have been prepared by a solid-state reaction method. The influences of La and Al co-doping on the phase structure, microstructure dielectric properties and current-voltage nonlinear behavior of CCTO ceramics have been studied. It is found that the dielectric loss of both the low and the high frequency range has shown a decrease by La and Al co-doping. Besides, the breakdown voltage has been increased from 28 V/mm of pure CCTO to 740 V/mm. The optimized properties of La and Al co-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 CaCu3Ti4O12-xMgTiO3(x=0,0.25,0.5,1.0) ceramics have been prepared by a solid-state reaction method. The effects of MgTiO3 doping on the phase structure, microstructure, dielectric properties and current-voltage nonlinear behavior of CCTO ceramics have been investigated. The results indicate that MgTiO3 doping has not only reduced the dielectric loss of low frequency range and raised the breakdown voltage but also significantly improved the I-V nonlinear coefficient. The optimized properties of MgTiO3 doped CaCu3Ti4O12 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. Among the specimens in this work, as MgTiO3 doping concentration is 0.5, the CaCu3Ti4O12-0.5MgTiO3 specimen has achieved the best comprehensive properties, which include a dielectric constant (εr) of 53958, dielectric loss (tanδ) of 0.06 at 1 kHz, breakdown voltage (Eb) of 295 V/mm and a large nonlinear coefficient of 66.3. |
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