Preparation And Dielectric Properties Of Bismuth Sodium Titanate Based MLCC Dielectric Materials

In order to meet the demand for high temperature capacitor dielectric materials and leadfree requirements in automotive electronics,aerospace,petroleum exploration and high temperature resistant wide band gap semiconductor electronic devices and other cutting-edge technology fields,it is urgent to research and develop lead-free dielectric ceramics in wide temperature zone(-55℃ to more than 300℃).Bismuth sodium titanate(Bi0.5Na0.5TiO3,BNT)based ceramics are a kind of dielectric materials with wide temperature range which are expected to be applied in high temperature field,but they have low dielectric constant and narrow temperature range of dielectric constant and loss stability.In this paper,BNT-based dielectric ceramics with high dielectric and wide temperature region were obtained by adding strontium sodium niobate(Sr0.8Na0.4Nb2O5,SNN)and sodium niobate(NaNbO3,NN)to BNT matrix to improve the relaxation of ceramic materials.Then,the sintering temperature of ceramic was reduced by adding the sintering aid,and the pure Ag paste was used as the internal electrode instead of Ag/Pd paste.The low-cost multilayer ceramic capacitor with excellent dielectric stability was successfully prepared.In this paper,the main research work is as follows:(1)0.99((1-x)Bi0.5Na0.5TiO3-xNaNbO3)-0.01Sr0.8Na0.4Nb2O5(where x=0.15,0.20,0.25 and 0.30)ceramics were prepared by solid phase reaction method.XRD results show that all components of the ceramics are pure perovskite structure,and SEM results show that the ceramics have dense grain structure.When x=0.25,ceramics in-65～360℃ dielectric constant over wide temperature zone meets |ε’-ε’25℃|/ε’25℃≤ 15%and the dielectric loss meets tanδ≤0.02.The dielectric constant value is 1250 at 1kHz and 25℃.It has good dielectric temperature stability,(2)A small amount of Bi2O3,CuO,Li2CO3,ZnO and B2O3 were added as sintering additives to successfully reduce the sintering temperature of ceramics.0.99((1-x)Bi0.5Na0.5TiO3xNaNbO3)-0.01SrO.8Na0.4Nb2O5(where x=0.25 and 0.30)ceramics were prepared by solid phase reaction method.XRD and SEM were used to test the structure of the ceramics.The ceramics were all pure perovskite structure with dense grain structure.When x=0.25,the addition of sintering additives reduces the sintering temperature from 1150℃ to 920℃,and the dielectric constant meets |ε’-ε’25℃|/ε’25℃≤ 15%and the dielectric loss meets tanδ≤0.02 in the temperature range from-65℃ to 358℃.Multilayer ceramic capacitors(x=0.25)were prepared by using pure Ag as internal electrode.The dielectric constant |ε’-ε’25℃|/ε’25℃≤ 15%and the dielectric loss tanδ≤0.02 in the temperature range from-89℃ to 375℃ were obtained.The multilayer capacitor further broadens the dielectric temperature range and provides a new way to reduce the cost of multilayer ceramic capacitor preparation.