Structure And Performance Regulation Of NBT-based Relaxor Ferroelectric Ceramics With Low Electric Field And High Energy Storage Density

In recent years,the use of oil,natural gas and other fuels has caused serious pollution to the environment.The development and utilization of a kind of green and clean energy has become the focus of people’s attention.Dielectric ceramic capacitors have been widely used in aerospace,military,automobile and other industries because of their advantages such as fast charging and discharging speed,good corrosion resistance and stable working at high temperature.At present,the ceramic capacitors that can be put into practical application are mainly lead-based ceramics.In order to avoid the damage of lead-based ceramics to the environment and human health,it is very important to develop a new type of lead-free energy storage ceramics with excellent energy storage performance.This topic is devoted to improving the low comprehensive energy storage performance of lead-free energy storage ceramics,and combined with a variety of characterization methods to conduct comprehensive research and analysis of the related properties of samples.The(1-x)(Na0.5Bi0.5)0.94Ba0.06(Ti0.96Zr0.04)O3-xBi(Ni0.5Sn0.5)O3(abbreviated as(1-x)NBBTZ-xBNS)lead-free energy storage ceramics have been prepared.The introduction of Zr4+ inhibits the residual polarization and leakage current to obtain higher energy density.Meanwhile,the bismuthbased compound BNS disrupts the original long-range ordered ferroelectric properties and enhances the relaxation properties of the ceramics.The results show that the 0.85NBBTZ-0.15BNS ceramic exhibits high energy storage(Wrec=4.0 J·cm-3)density and energy storage efficiency(η=19%)under the electric field of 290 kV·cm-1.The 0.85NBBTZ-0.15BNS ceramics also show ultra-fast discharge time of 88.4 ns,power density of 3.05 MW·cm-3,and excellent temperature stability between 20 and 120℃ in charge-discharge tests.In order to improve the energy storage efficiency of NBT-based ceramics,(1-x)(Na0.5Bi0.5)0.94Ba0.06(Ti0.96Zr0.04)O3-xBi(Mg0.5Ta0.4)O3((1x)NBBTZ-xBMT)lead-free energy storage ceramics were prepared with Mg2+and Ta5+.The introduction of BMT significantly reduced the average grain size of the ceramics,increased the breakdown field strength and inhibited the residual polarization strength,and gradually transformed the materials into relaxation ferroelectric ceramics.When x=0.2(0.8NBBTZ0.2BMT),the best performance is obtained,that is,the effective energy Storage density is 4.45J cm-3,and the energy storage efficiency is 85.6%.The 0.8NBBTZ-0.2BMT ceramics also show ultra-fast discharge time of 69.9 ns,power density of 2.81 MW·cm-3,and excellent temperature stability between 20 and 120℃ in charge-discharge tests.However,Pmax was inhibited while Pr was decreased.The(1-x)(0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3)-xK0.5Na0.5NbO3(abbreviated as(1-x)(NBT-KBT)-xKNN)lead-free energy storage ceramics were prepared in order to maintain the advantages of large Pmax of NBT ceramics.The results show that KNN can be well dissolved into NBT-based ceramics within the doping range,forming a stable solid solution.The structure of all samples is compact without obvious porosity.The temperature stability of ceramics increases with the increase of KNN content.The 0.8(0.8NBT0.2KBT)-0.2KNN ceramics can obtain high energy storage performance(3.38 J·cm-3)and energy storage efficiency(89.3%)under relatively low electric field(255 kV·cm-1).The 0.8(0.8NBT-0.2KBT)-0.2KNN ceramics also show ultra-fast discharge time of 56.6 ns,power density of 23.43 MW·cm-3,and excellent temperature stability between 20 and 120 ℃ in charge-discharge tests.But the overall energy storage performance of ceramics is low.In order to further improve the energy storage performance of the ceramic,the(1-x)(0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3)-xSr0.35La0.1TaO3((1x)(NBT-KBT)-xSLT)lead-free energy storage ceramics was prepared.The introduction of SLT effectively enhances the breakdown field strength of ceramics,thus improving the energy storage performance.The results show that 0.85(0.8NTB-0.2KBT)-0.15SLT at 530 kV·cm-1 can obtain an ultra-high effective energy storage density of 5.81 J·cm-3 and an energy storage efficiency of 85.9%at x=0.15.The 0.85(0.8NTB-0.2KBT)0.15SLT ceramics also show ultra-fast discharge time of 61.8 ns,power density of 2.65 MW·cm-3,and excellent temperature stability between 20 and 120℃ in charge-discharge tests.