Preparation Of Copper Bismuth Titanate - Based Ceramics By Sol - Gel Method And Its Performance Regulation

In the last decade, materials with high dielectric constant, which have a potential value in large-capacity capacitor, electronic components miniaturization and integration, are one of the hot research topics. CaCu3Ti4O12 (CCTO) has attracted a significant amount of attentions because of its high permittivity, insignificant temperature dependence on permittivity over the wide temperature range from 100 K to 600 K, at the same time, the dielectric loss of CCTO ceramics is too high to meet the requirements for practical applications. Therefore, many efforts were devoted to decrease the dielectric loss by ion doping. However, limited literatures reported the BCTO ceramics prepared by the solid-state reaction, and the dielectric constant of the ceramics is relatively low for practical applications. Consequently, the work aimed to optimize the coagulating conditions of BCTO powders, explored the best sintering conditions of BCTO ceramics. And then, we study the effects on the dielectric properties of BCTO ceramics with the deviation of Cu and Ti. Lastly, we studied the sintering conditions of Na0.5Bi0.5Cu3Ti4O12 ceramics, furthermore we studied the effect of the Na+ contents on the phase structure, microstructure and dielectric properties of NaxBi<2-X)/3Cu3Ti4O12 ceramics.1. BCTO ceramics were prepared by the sol-gel method and conventional solid-state reaction, respectively. Firstly, we studied the effect on phase structure and dielectric properties of the Ti concentration, the reaction temperature and the aging time of the sol, thereby the optimization coagulating conditions of BCTO powders:the Ti concentration was 0.62 mol/L, the reaction temperature was 40℃ and the aging time of the sol was 16 h. Secondly, we explored the sintering conditions, and obtained the best sintering conditions:The calcining temperature was 800℃ and the sintering temperature was 1000℃. The dielectric constant of BCTO ceramics prepared by the sol-gel method was-1.2×104 measured at 1 kHz and dielectric constant of the ceramics with same composition prepared by the solid-state reaction was～0.30×104 at 1 kHz. The complex impedance spectroscopy verified that Bi2/3Cu3Ti4O12 ceramics irrespective preparation method were electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries. A set of broad dielectric relaxation peaks with the same physical nature were observed at～200℃ in the temperature dependence of dielectric constant, which was due to the Maxwell-Wagner relaxation. Whereas an additional dielectric relaxation Ⅱ was observed at～300℃ only for the sample prepared by the sol-gel method, which was ascribed to the distribution state transition for oxygen vacancies.2. Sintering conditions of Na0.5Bi0.5Cu3Ti4O12 ceramics were investigated. We changed the content of Na+ under the optimal sintering conditions, the effect of the Na+ contents on the phase structure, microstructure and dielectric properties of ceramics was studied. The result showed that the dielectric loss of decreased drastically, the minimum dielectric loss was around 0.038 at 1 kHz. We also investigated the complex impedance spectroscopy, electric modulus and conductivity of NaxBi(2-x)/3Cu3Ti4O12 with different Na+ contents. And the grain boundary resistance was calculated to explain the reason that the dielectric loss decreased.3. The effects on the phase structure, microstructure and dielectric properties of BCTO ceramics with the deviation of Cu and Ti were studied. The result showed the dielectric constant of the Cu-deficient samples significantly increased, when the content of Cu-deficient was 0.2, the dielectric constant increased to 2.2×104. The dielectric constant of the Cu-excessive samples decreased drastically. Accordingly, the dielectric constant of the Ti-excessive samples significantly increased, when the content of Ti-excessive was 0.2, the dielectric constant increased to 2.4×104 The dielectric constant of the Ti-deficient samples decreased drastically. The complex impedance spectroscopy investigated the IBLC mode was weakened when the Cu-excessive and Ti-deficient, this was the reason that the dielectric constant decreased.