Study On Dielectric Properties Of Modified CaCu₃Ti₄O₁₂ Ceramics With Giant Dielectric Permittivity And Preparation Of Capacitor

Since CaCu₃Ti₄O₁₂?CCTO?ceramics was discovered in 2000,a lot of research efforts have been devoted to CCTO ceramics due to its high dielectric constant??_r?of approximately 10⁴–10⁵ and phase transition stability in a wide temperature range from 100 to 400 K.CCTO ceramics also exhibits non-ohmic characteristic,which is promising in applications of energy storage capacitors and over-voltage protection devices.However,the relatively high dielectric loss?tan??of CCTO ceramics limits its applications in devices.Despite the origin of the promising properties of CCTO ceramics not yet being well-understood,it is believed that both the giant dielectric constant property and non-ohmic characteristics are attributed to an internal barrier layer capacitor?IBLC?effect originating from extrinsic polarization at the grain boundaries.In this model,bulk grains behave as a semiconductor,and grain boundaries exhibit insulating behavior with high resistance.Generally,high resistance of the grain boundary layer corresponds to the low conductance,which means low tan?.Therefore,the tan?could be reduced by methods which increase the grain boundary resistance.In this article,CCTO powders were prepared by sol-gel method.Then,in order to reduce the loss of CCTO,Sr/Zr elements were used to dope in CCTO ceramic,and the effects on dielectric properties of CCTO were studied.Finally,Ca_0.9Sr_0.1Cu₃Ti_3.96Zr_0.04O₁₂2 ceramic was developed to capacitor.The main findings are as follows:?1?A low-loss CCTO ceramic was prepared using an alkaline conditioner.The effects of various processes during the sol-gel process on the dielectric properties of the final ceramic sample were systematically studied.The results show that the sample prepared by using citric acid as a complexing agent,using ammonia water to adjust the pH of the solution to 4,sintering at 1050°C for 12h,has the best dielectric properties.The dielectric constant of this sample is6120,the dielectric loss is 0.018,the compressive strength was 1060.66 V/cm,and the nonlinear coefficient was 4.30.Although this experiment reduced the dielectric loss by adjusting the pH value by using ammonia,the dielectric constant of the sample also decreased significantly.?2?The effects of Sr,Zr and Sr/Zr co-doping on the dielectric properties of CCTO ceramics have been studied.When only Sr is doped,Ca_0.8Sr_0.2Cu₃Ti₄O₁₂has a dielectric constant of 38000 and a dielectric loss of 0.036.When using Zr doped,the dielectric constant of CaCu₃Ti_3.96yZr_0.04O₁₂ is 4959,and the dielectric loss is 0.024.The co-doped sample Ca_0.9Sr_0.1Cu₃Ti_3.96Zr_0.04O₁₂ has a dielectric constant of 10613 and a dielectric loss of 0.020.The prepared co-doped CCTO ceramic samples not onlt have lower dielectric loss,but also a huge dielectric constant,which is more practical than pure CCTO ceramic samples.?3?Ceramic capacitors were fabricated using Ca_0.9Sr_0.1Cu₃Ti_3.96Zr_0.04O₁₂powders,and the influence of sintering process on the dielectric properties of ceramic capacitors was studied.The results showed that the doped powder prepared with solution p H=4,compacted at P=24 MPa,sintered at 1050°C.,and kept for 12 h has the maximum capacitance.At this time,the prepared ceramic capacitor has larger capacitance,excellent frequency stability and temperature stability.Then we studied the time stability of the Ca_0.9Sr_0.1Cu₃Ti_3.96Zr_0.04O₁₂ceramic capacitors at room temperature and 60°C.Studies have shown that the electrical capacity of the Ca_0.9Sr_0.1Cu₃Ti_3.96Zr_0.04O₁₂ ceramic capacitor changes over two time periods.After 15 days of aging,the electrical properties are basically stable,and the rate of change of its dielectric constant does not exceed10%.At the same time,the prepared Ca_0.9Sr_0.1Cu₃Ti_3.96Zr_0.04O₁₂ ceramic capacitor was subjected to high-temperature impact test and cycling charge and discharge experiments.The results showed that under the two different impact conditions,the capacitance reduction of the capacitor was less than 1%,consistent with the capacitor The determination criteria of electrical properties show that the ceramic capacitors produced in this experiment have good high-temperature impact stability and cycle charge-discharge stability.