Rapid Preparation And Properties Of CaCu₃Ti₄O₁₂ Ceramics

In recent years,with the development of electronic device in the direction of miniaturization,high dielectric constant materials have attracted more and more concern.Because of the giant dielectric constant which keep stable over a wide temperature range and has good varistor sensitive features,the CaCu3Ti4O12(CCTO)with perovskite-like type structure has received widespread attention.However,relatively high dielectric loss of CCTO material and its sensitive to the preparation limit its application in a certain extent.Therefore,this paper tries to adopt short-term heat preservation method,reaction sintering method and low temperature sintering method to prepare CCTO ceramics to explore and optimize its preparation condition,not only expects to receive good performance CCTO dielectric materials,but also for further explore the mechanism of its giant dielectric.Firstly,the influence of different sintering temperature and heating process on the density,microstructure and dielectric properties of CCTO ceramics prepared by rapid preparation of short-term heat preservation method through solid state reaction were studied.The results show that:within a certain range,the density and dielectric constant of CCTO ceramics increased with the sintering temperature.The CCTO ceramics without heating stage just heat preservation for only 30min at 1130? obtain a high dielectric constant(1kHz,??8500)and a reasonably low dielectric loss(100kHz,tan??0.15),and the dielectric constant of the samples which heat up along with the tube furnace then heat preservation for 30min at 1130? is as high as 12500.Varistor sensitive performance tests show that the CCTO ceramics has a certain nonlinear characteristics.These suggest that the CCTO ceramics with giant dielectric constant and low dielectric loss can be prepared by short-term heat preservation rapid sintering.Then the CCTO ceramics were prepared by the reaction sintering method directly without presintering process.Studied the influence of different sintering temperature and holding time on the density,microstructure and dielectric properties of CCTO ceramics.The results show that the increasing of sintering temperature and extension of holding time contribute to the densification of CCTO ceramics in a certain extent.When the sintering temperature is 1115,the shrinkage rate of CCTO ceramics which heat preservation for 0.5h and 3h are 13.9%and15.3%,respectively.The samples without heating stage only heat preservation for 0.5h at 1115? obtained good performance:??7000 at 1 kHz and tan??0.11 at 100kHz.Moreover,the dielectric constant of samples which heat preservation for 3h is as high as 9400.Finally,in order to prepared CCTO rapidly at lower temperature,the low melting point BaO-B2O3-SiO2(BBS)glass was adding as low temperature sintering additives,combined with the CCTO ceramics powder calcined at 950?.The effect of BBS additives on the sintering charater,microstructure and dielectric properties of CCTO ceramics were investigated.The experimental results show that the BBS glass can lower the sintering temperature?improve the sintering charater and dielectric properties of CCTO ceramics effectively.The sintering temperature of CCTO ceramics decreased to about 950?,meanwhile,when the sintering temperature is 1000 ? and the BBS glass content is 20%,the shrinkage rate of CCTO ceramics can reached 9.3%,in addition,the dielectric loss decreased obviously(tan??0.05),and still had a high dielectric constant.