Grain Boundary Modification And Dielectric Properties Of Nb-Doped CaCu₃Ti₄O₁₂ Dielectric Ceramics

With the development of electronic equipment towards miniaturization,integrated circuits need to achieve higher integration within a limited area,which requires the size of electronic components to be reduced while ensuring higher performance.CaCu₃Ti₄O₁₂（CCTO）giant dielectric ceramics have a large dielectric constant and excellent dielectric properties at high frequencies,which makes them have great potential in electronic device applications.However,the large dielectric loss limits the application of CCTO,so further research is needed to improve the dielectric properties of CCTO.In this thesis,CCTO dielectric ceramics were prepared by traditional solid phase reaction method.The effects of these experiments on the microstructure and dielectric properties of CCTO were investigated by single element doping experiment,grain boundary modification experiment and different cooling process experiment.The experimental contents and results are as follows:（1）CaCu₃Ti_（4-x）Nb_xO₁₂（x=0.00,0.02,0.05,0.08,0.10）（CCTNO）ceramics were prepared by solid-state reaction method.The dielectric constant of CCTO ceramics was significantly increased by Nb⁵⁺doping.When the doping concentration is less than 0.05,the dielectric constant of the ceramic sample increases gradually with the increase of the doping concentration.When the doping concentration is greater than0.05,the dielectric constant of the ceramic sample begins to decrease again.Therefore,when the doping concentration is 0.05,the maximum dielectric constant of 6.7×10⁴（room temperature,1 k Hz）is obtained,which is 6 times higher than that of the undoped CCTO ceramic sample.The dielectric loss is 1.07（room temperature,1 k Hz）.Impedance analysis shows that Nb⁵⁺doping will reduce the grain resistance of CCTO ceramics and increase the conductivity,thus increasing the dielectric constant of ceramics.However,Nb⁵⁺doping also reduces the grain boundary resistance of the ceramics,so the dielectric loss is increased compared with the undoped CCTO ceramics.（2）The first part of the experiment shows that when the Nb doping concentration reaches 0.05,the ceramic sample with the best dielectric properties is obtained.On this basis,different concentrations of tetraethoxysilane（TEOS）hydrolysis solution were added to modify the ceramic grain boundaries.At room temperature and 1 k Hz frequency,the dielectric constant of the ceramic sample with 1.2 m L TEOS dosage is5168 and the dielectric loss is 0.10.The dielectric loss is significantly lower than that of the CCTNO ceramic sample modified for grain boundary,but the dielectric constant is also decreased.When the dose of TEOS is greater than 1.2 m L,the dielectric loss and dielectric constant of the ceramic samples gradually increase.The analysis shows that after adding TEOS hydrolysis solution,Si O₂ will be produced during the sintering process of CaCu₃Ti_3.95Nb_0.05O₁₂ ceramics,which is distributed at the grain boundary of the ceramics.To a certain extent,it will enhance the insulation of the grain boundary and increase the grain boundary resistance,which can effectively reduce the dielectric loss of the ceramics.（3）The heat treatment process of cooling in air was used to further reduce the dielectric loss of ceramics and shorten the preparation time.The CaCu₃Ti_3.95Nb_0.05O₁₂ceramics modified by different concentrations of TEOS hydrolysis solution were directly cooled in air after sintering.Compared with furnace cooling,the dielectric loss of ceramic samples cooled in air is significantly reduced,and the maximum dielectric loss is below 0.5.As the concentration of TEOS hydrolysis solution increases,the dielectric loss of air-cooled ceramic samples also increases gradually.The air-cooled sample with 2.2 m L TEOS has the best comprehensive dielectric properties.At room temperature and 1 k Hz frequency,the dielectric loss is 0.09 and the dielectric constant is 5950.Impedance analysis shows that compared with the ceramic samples cooled in the furnace,the grain boundary resistance of the ceramic samples cooled in air increases,which is beneficial to reduce the dielectric loss.With the increase of the concentration of TEOS hydrolysis solution,the grain boundary resistance of the ceramic sample cooled in air decreases,which makes the dielectric loss increase slowly.