The Construction And Properties Of High Temperature Ceramic Capacitor Materials Based On NBT-KBT

Capacitor is one of the most important passive electronic components,which is widely used in the circuits of various electronic equipment.Multilayer ceramic capacitors have the characteristics of small size,low cost,long service life and low heating,which have become the mainstream of the capacitor market.With the rapid development of technology,the working environment of electronic equipment is becoming more and more demanding.For example,the actual operating temperature of car engines and rockets can exceed 200 ℃ or even 300 ℃.This requires the ceramic capacitor to work stably over a wide temperature range,thus better matching the circuits in the electronic equipment.However,the highest operating temperature of the most commonly usedΙΙtype commercial ceramic capacitors is no more than 200 ℃,which cannot meet the application of the high-temperature field.Therefore,researchers are trying to find ceramic capacitor materials which can be used in high temperature environment.In this study,the relaxor ferroelectrics 0.8Na_0.5Bi_0.5TiO₃-0.2K_0.5Bi_0.5TiO₃（0.8NBT-0.2KBT）were modified,by the means of modulating of the content of two different polar nanoregion.The material with high dielectric constant,low dielectric loss and good temperature stability was successfully built up at the temperature range of 100 ℃ to 440 ℃.At the same time,the multilayer ceramic capacitor was made.These works provide a reliable solution and experience for the application of next generation high temperature ceramic capacitor.Firstly,the system（1-x）(0.8Na_0.5Bi_0.5TiO₃-0.2K_0.5Bi_0.5TiO₃)-xBi(Zn_2/3Nb_1/3)O₃（NBT-KBT-x BZN）was designed to study the influence of the introduction of BZN on the microstructure and electrical properties of the matrix.The results showed that the introduction of BZN reduced the content of the rhombohedral phase polar nanoregion and the macroscopic polarization ability of the material.Finally,materials with good temperature stability and high dielectric constant are obtained in the high temperature section.Then,in view of the high dielectric loss and poor insulation performance of the above systems at high temperature,another component Bi(Mg_2/3Nb_1/3)O₃was introduced into the matrix,and the following material system（1-x）(0.8Na_0.5Bi_0.5TiO₃-0.2K_0.5Bi_0.5TiO₃)-xBi(Mg_2/3Nb_1/3)O₃（NBT-KBT-x BMN）was designed,mainly to explore the influence of the introduction of BMN on the temperature stability,dielectric loss and insulation resistivity of the materials.The results show that with the introduction of BMN,the content of the strongly polar rhombohedral phase polar nanoregion decreases,the content of the weakly polar tetragonal phase polar nanoregion increases,and the temperature stability,dielectric loss and insulation resistance characteristics of the material are optimized.The optimal composition of NBT-KBT-0.2BMN samples obtain excellent temperature stability(ε_r150℃=1860±15%,1k Hz)over the temperature range of 106 ℃ to 492 ℃,and the dielectric loss is less than 0.025 in the temperature range of 112 ℃ to 410 ℃.The insulation resistance is more than 10¹³Ω·cm at room temperature,can meet the demand of practical application of ceramic capacitor.Finally,based on the excellent electrical performance of the optimal component NBT-KBT-0.2BMN,the green sheet with uniform and no coarse particles was successfully obtained by exploring the tape casting process.Then the MLCC was successfully constructed by electrode printing,stacking,laminating,and sintering.By observing and analyzing the microstructure of MLCC,the differences of dielectric properties between MLCC and bulk samples were discussed.The results show that the dielectric properties of MLCC are similar to that of bulk samples,which proves that the NBT-KBT-0.2BMN material has excellent device portability.MLCC can reach the excellent electrical performance of maintainingε_r150℃=1800±15%and tanδ≤0.025in the temperature range of 100 ℃ to 440 ℃.At the same time,the temperature stability of energy storage density of MLCC is in a relatively optimal levels from 25℃ to 150 ℃.Therefore,the NBT-KBT-0.2BMN material is expected to be applied in high-temperature ceramic capacitors and provides a reliable solution and reference for the next generation of high-temperature ceramic capacitors.