Research On Synthesis And Properties Of Dielectric Material CaCu₃Ti₄O₁₂

With the trait of high dielectric constant (above 104 at room temperature and 1 KHz) and good stability at low temperature, the material CaCu₃Ti₄O₁₂ (CCTO) is very desirable for the application in electronic devices, such as capacitor and memory. In this thesis, with high purity raw material, the single-phase CCTO powder was directly prepared in lower temperature (870℃, persevered for 24 hours) via the conventional solid-state reaction technique. The ceramic samples were sintered at 800℃～1000℃, and the temperature was persevered for 8h～24h. After the dielectric property and its temperature dependence were measured, it was found that, at the sintering temperature of 1060℃with preservation for 24 hours, the sample has most shrinkage and best dielectric property that the loss is 0.042 and the dielectric constant can reach above 13000, and they begin to rise rapidly at 80℃. The samples were also observed with SEM, to analyze how the microstructures affect the dielectric property.In addition, the CCTO was doped with Al₂O₃, Y₂O₃ and SiO₂, to study how sintering temperature, preservation time and doping concentration affect the dielectric property and its temperature dependence.In material CaCu₃Ti₄(1-x)Al_4xO₁₂, doping Al3+ can improve the dielectric property that the loss decreases to 0.025, and the dielectric constant also can be above 19000. The temperature dependence is better too, with the dielectric constant and loss increasing rapidly at 100℃.In material Ca(1-x)YxCu3Ti4O12, doping Y3+ results in rise of both dielectric constant and loss, and they fluctuate obviously with the change of doping concentration. Although the dielectric constant can reach above 70000, the loss can only descend to 0.15 with the biggest one is above 1.0. Moreover, they climb with the increase of test temperature.In the CCTO material doped with SiO₂, the dielectric property has little change compared with pure CCTO material. The dielectric constant range from 10000 to 30000 and loss can mostly reach under 0.1. With the increase of sintering temperature, both dielectric constant and loss have downward trend that the lowest loss is 0.027 and dielectric constant can keep over 15000. The dose of SiO₂ has little effect on the temperature-dependent curve. The loss begins to climb when temperature rises to around 60℃, and dielectric constant at around 80℃. Furthermore, the CCTO material has nonlinear current-voltage characteristic. Increasing sintering temperature and prolonging preservation time can improve the nonlinear coefficient. After the current density reaches a certain value, nonlinear coefficient begins to rise with its increase. Doping Al₂O₃ makes the nonlinear coefficient increase, but decrease with the dopant of Y₂O₃. After doped with SiO₂, nonlinear coefficient rise remarkably when increase the sintering temperature.