Giant Dielectric Material CaCu₃Ti₄O₁₂ And Its Application In Large-capacity Capacitors

In recent years,CaCu₃Ti₄O₁₂（referred to as CCTO）ceramic materials have received extensive attention due to their high dielectric constant and excellent temperature and frequency stability.However,in terms of its practicality,it is also necessary to solve two problems of high dielectric loss and giant dielectric response mechanism.Therefore,it is an important direction of CCTO research to maintain the dielectric constant of CCTO material while reducing its dielectric loss.In this paper,CCTO powders were prepared by sol-gel method,and different CCTO ceramic materials were prepared by changing the process.The microstructure and dielectric properties were studied by XRD,SEM,dielectric spectrum and impedance spectroscopy.Then,the Co and La elements were used to dope the CCTO ceramic materials.The effects of Co doping,La doping,Co and La co-doping on the dielectric properties of CCTO ceramics were investigated,and the mechanism of giant dielectric effect of CCTO ceramics was analyzed.Finally,Ca_0.95La_0.05Cu_2.7Co_0.3Ti₄O₁₂and Ca_0.97La_0.03Cu_2.4Co_0.6Ti₄O₁₂2 ceramic capacitors were prepared.The following conclusions are drawn:1.The effects of different process flows on the dielectric properties of ceramic samples during the preparation of CCTO ceramic materials were systematically studied.The results show that the sol-gel method is used to prepare the powder with citric acid as the complexing agent.PVA was added for granulation in the preparation process of ceramics,and it was pressed and formed under the pressure of 30 MPa.Finally,it was sintered at 1050℃for 12h in an air atmosphere to form porcelain.The obtained ceramic samples had the best dielectric properties,the dielectric constant was 5.5×10⁴ and dielectric loss was 0.034（room temperature,1kHz）.2.The effects of Co doping and La doping on the dielectric properties of CCTO ceramics were investigated.For the single doping of Co element,the dielectric constant of CaCu_2.4Co_0.6Ti₄O₁₂2 ceramic was 1.5×10⁵,and the dielectric loss wad 0.028（room temperature,1kHz）.At this time,the crystal grains of the ceramic sample grew uniformly,and a second phase with high insulating property was formed at the grain boundary.When La element was doped,the grain size of Ca_0.95La_0.05Cu₃Ti₄O₁₂ ceramic was reduced,and the distribution was uniform and dense,its dielectric constant was1.05×10⁵,dielectric loss was 0.081（room temperature,1kHz）,and the reduction in dielectric loss was mainly manifested in the high frequency range..3.Ca_1-xLa_xCu_3-yCo_yTi₄O₁₂（x=0⁰.05;y=0⁰.06）ceramics were prepared,and the effects of La and Co co-doping on the dielectric properties of CCTO ceramics were investigated.In the co-doped samples,the ceramic sample with doping amount of x=0.05 and y=0.3 had a dielectric constant of 9.9×10⁴,a dielectric loss of 0.020（room temperature,1kHz）.The ceramic sample with doping amount of x=0.03 and y=0.6 had the highest dielectric constant of 1.55×10⁵,but the dielectric loss reached 0.074（room temperature,1kHz）.The co-doped ceramic samples had higher dielectric constant and lower dielectric loss than the pure CCTO ceramic sample,and its had more practical value.Ca_0.95La_0.05Cu_2.7Co_0.3Ti₄O₁₂ and Ca_0.97La_0.03Cu_2.4Co_0.6Ti₄O₁₂ ceramic capacitors were prepared respectively.And the time stability and high temperature impact stability of the two ceramic capacitors were tested.It was found that the capacitance retention rate of the two ceramic capacitors remained at 90%or more after being left at room temperature for 30 days,and the loss of the capacitance value was less than 1%after the high temperature impact at 200℃.