Optimization Of Energy Storage Performance Of Bismuth Potassium Titanate Based Relaxor Ferroelectric Ceramics

Dielectric capacitors with fast charge/discharge rates and high power densities have been actively used in hybrid electric vehicles,high-speed trains,and power electronics.In recent decades,many dielectric materials have been developed to enhance the energy storage performance of dielectric capacitors.In the early years,most of the reported dielectric materials for high-performance capacitor applications were lead-based materials.The heavy use of Pb in these materials has several undesirable implications for the environment.With increasing awareness of environmental and human health issues,studies have increasingly focused on lead-free energy storage dielectric materials in recent years.Bi_0.5K_0.5TiO₃ lead-free energy storage ceramic exhibits large spontaneous polarisation due to their A-site lone pair effect,suggesting great potential for energy storage.However,the low breakdown strength and large hysteresis greatly restrict the enhancement of the energy storage density and lead to a weak energy efficiency.In addition,Bi_0.5K_0.5TiO₃ ceramic also possesses problems of difficult preparation,low density and low hardness,which also seriously hinder the energy storage application of Bi_0.5K_0.5TiO₃ceramic.In this paper,（1-x）Bi_0.5K_0.5TiO₃-x Ba_0.4Sr_0.6TiO₃composite ceramics were fabricated using the conventional solid-state sintering reaction.The energy storage characteristics of ceramics were further explored and modified in two different ways.The phase structure,dielectric and ferroelectric properties of ceramics were systematically analyzed.The specific research contents are as follows:（1）（1-x）Bi_0.5K_0.5TiO₃-x Ba_0.4Sr_0.6TiO₃ composite ceramics were prepared by compounding Ba_0.4Sr_0.6TiO₃.The results showed that the composite of Ba_0.4Sr_0.6TiO₃optimized the sintering temperature of Bi_0.5K_0.5TiO₃ ceramic and obtained the composite ceramics with high density and fine grain.Meanwhile,with the increase of the content of Ba_0.4Sr_0.6TiO₃,the maximum polarization of ceramics increased first and then decreased.According to the P-E curves of the composite ceramics,the maximum polarization of 0.6Bi_0.5K_0.5TiO₃-0.4Ba_0.4Sr_0.6TiO₃（BKT-BST）is 48.8μC/cm²,showing great energy storage potential.（2）On the basis of the above experiments,in order to further improve the energy storage performance,the ternary composite ceramics were constructed by composite Ca TiO₃,Ca Zr O₃,Ca Sn O₃ linear dielectrics.The results showed that the compositing of linear dielectrics can reduce the remnant polarisation of BKT-BST ceramic,expand the band gap energy,and enhance the breakdown strength.All composite ceramics exhibit extremely high recoverable energy storage densities.Among them,a recoverable energy storage density of 5.78 J/cm³ and an energy storage efficiency of 87.85%were achieved in the BKT-BST-0.3Ca TiO₃ ceramic.A recoverable energy storage density of5.56 J/cm³ and an energy storage efficiency of 91.24%are realised in the BKT-BST-0.125Ca Zr O₃ ceramic.A recoverable energy storage density of 4.86 J/cm³ and a high energy storage efficiency of 90.86%were achieved in BKT-BST-0.1Ca Sn O₃ ceramic.The experimental results further prove the feasibility of composite linear dielectrics.（3）By introducing NaNbO₃ and Ag Nb O₃ antiferroelectrics,the energy storage performance of BKT-BST ceramic was further improved.The experimental results showed that submicron size of ultra-small grains in composite ceramics were obtained by introducing antiferroelectrics.At the same time,the relaxation of BKT-based ceramic was enhanced,and a slender P-E curve was obtained.Finally,a recoverable energy storage density of 4.53 J/cm³ and an energy storage efficiency of 67%were achieved in BKT-BST-0.2NaNbO₃ ceramic.A recoverable energy storage density of4.17 J/cm³ and an energy storage efficiency of 89.61%were achieved in BKT-BST-0.15Ag Nb O₃ ceramic.