Preparation Of CaCu₃Ti₄O₁₂by Sol-gel Method And Study On Its Dielectric Properties

As the microelectronics industry continues to develop,small and fast microelectronic devices become the current development trend,it is necessary to find a new generation of the dielectric material with high polarity.CaCu₃Ti₄O₁₂（Later referred to CCTO）Is a kind of new type dielectric material with perovskite structure,has the following properties:1.At room temperature,CCTO dielectric constant can be as high as 104 or more;2.CCTO has a large dielectric constant that can be maintained over a wide temperature band（100-400 K）and frequency band（100 Hz-1 MHz）.This phenomenon is called dielectric flattening effect;3.Solid phase sintering method is easy to get CCTO phase,the process is simple and no pollution.However,since the two main dielectric parameters of the dielectric constant and the dielectric loss are simultaneously increased or decreased,the CCTO has a large dielectric constant and exhibits a higher dielectric loss.Maintaining CCTO high dielectric coefficient while reducing dielectric loss has become one of the main research contents in this field.The polarizability of the dielectric material is an important factor affecting the microstructure.It is closely related to the grain size,distribution and grain boundary of the material.And different preparation process will have a greater impact on the microstructure of the material,which further affect the dielectric properties of the material.In this paper,CCTO was prepared by sol-gel method,and the relationship between the microstructure of CCTO ceramic samples and the corresponding dielectric properties was investigated by adjusting different process parameters.The following experimental results:1 When the CCTO sample was prepared by sol-gel method,the optimized amount of acetic acid,sintering temperature andsintering method were optimized.When the amount of acetic acid was 4 ml and the sintering temperature was 1090 ℃,a better CCTO sample was obtained.It is found that CCTO samples with grain boundary segregation and high dielectric coefficient are obtained when continuous sintering is used.CCTO samples with uniform grain density and higher density can be obtained by using segmented sintering method;2.The results show that the ball milling has a great influence on the dielectric constant of CCTO ceramic samples.With the increase of milling time,the dielectric constant of the sample increased significantly.When the milling time is 4 hours,the constant can reach a value of 106,much higher than that of the untreated sample and it increases with temperatures of the sample.Besides,SEM analysis indicates that the increase of the dielectric constant is related to the microstructure of CCTO,especially the secondary phase of CuO precipitated at grain boundaries can greatly enhance the polarization of CCTO;3.The CCTO samples of the surface-fired silver electrode were polished to varying degrees and the corresponding complex impedance parameters.It is found that with the increase of electrode wear,the complex impedance curve appears to shift to the right.It is presumed that the oxygen space between CCTO and Ag electrode is polarized and the oxygen potential of the internal grain boundary or domain boundary is also ionized to make the complex impedance curve midline and the low frequency semicircle change at the same time;4.Under different temperatures and different voltages,CCTO samples were subjected to voltage cycle impact test to observe the abrupt change of sample resistance.It is found that the relaxation phenomenon of the sample can change more rapidly with the increase of the ambient temperature,and the effect of the voltage change on the I-V curve is not significant.The experimental results show that the microstructure and dielectric properties of CCTO ceramic materials are investigated by changing the process,which can guide the further study of the dielectric properties of CCTO ceramics.