Preparation And Energy Storage Properties Of Barium Strontium Titanate Based Ceramic Materials

With the intensification of energy consumption and environmental pollution issues,the development of green energy such as hydropower,wind power,nuclear power and other new clean energy has been paid attention.Among many energy storage devices,pulse energy storage capacitors have excellent temperature stability,mechanical properties,high power density and ultra-high impulse discharge rate.As the core material of pulse energy storage capacitor,energy storage medium has been widely studied.With the trend of miniaturization and integration of devices,higher demands have been seek for the energy storage property and stability of energy storage dielectric.As a typical lead-free ceramic,Ba_0.4Sr_0.6Ti O₃ ceramics own medium dielectric constant（～1000）and low dielectric loss,which are benefit to energy storage.However,relatively low breakdown strength field and high residual polarization（P_r）limit its prospect.In this thesis,the energy storage performance of BST-based energy storage ceramics is enhanced by introducing relaxation through formula design and process adjustment.The main contents and experimental results are depicted as below:1.Bi(Zn_0.5Sn_0.5)O₃ was introduced into BST matrix.Through doping with different radii and valence ions,lattice distortion and local random field are induced,and long-range order is destroyed,and finally relaxation performance is induced.At the same time,Bi³⁺ions can enhance the polarization ability of ceramics.Bi₂O₃ and Zn O can be used as sintering aids,which can reduce the sintering temperature of ceramics and play a role in refining the grain.At the same time,lower sintering temperature is conducive to inhibiting the price change of titanium ions,reducing the concentration and loss of oxygen vacancies,and improving the material resistance.Substitution of Ti⁴⁺with Sn⁴⁺at B site can effectively inhibit grain growth and reduce the valence variation of titanium ions,thus obtaining higher breakdown strength.Finally,0.86BST-0.14BZS ceramics have excellent energy storage performance and pulse discharge performance,as well as good temperature stability and fatigue resistance.Wherein,W_rec is 2.2 J/cm³,E_b is 35.86k V/mm,and P_max is 15.2μC/cm²,ηis 82.8%.High power density（P_D=164.4 MW/cm³）,current density（C_D=939.5 A/cm²）and discharge energy density（W_d=1.99 J/cm³）are obtained at 35 k V/mm field strength,and have a fast charge-discharge rate,t_0.9 is about40 ns.2.Some studies have shown that rare earth La³⁺can improve the resistivity of energy storage ceramic materials and reduce the dielectric loss.At the same time,La₂O₃ has a large band gap（E_g=5.5 e V）.In order to obtain higher E_b andη,La³⁺ion is introduced at A-site,and design the component（1-x）BST-x(Bi_0.5La_0.5)(Zn_0.5Sn_0.5)O₃（BST-BLZS）.With ascending of La³⁺ion doping concentration,the average grain size of ceramics firstly declines and then increases.When x=0.12,the grain size is 0.73μm.E_b is significantly increased to 48 k V/mm,corresponding to a P_max value of 13.4μC/cm²,ceramics obtain high energy storage density（2.76 J/cm³）and efficiency（92%）.At the same time,0.88BST-0.12BLZS ceramics have excellent frequency reliability and temperature stability.In addition,0.88BST-0.12BLZS shows good pulse performance,t_0.9 is about 200ns,P_D is more than 48.4 MW/cm³ at 25 k V/mm,and C_D is 386.8 A/cm².3.In order to obtain high polarization strength and breakdown strength simultaneously,a formula of 0.86BST-0.14(Bi_1-xLa_x)(Zn_0.5Sn_0.5)O₃（BST-BLx ZS）was designed based on the above two experiments.It is expected that by adjusting the concentration of La³⁺ions at A-site,together with a certain proportion of Bi³⁺ions will ensure a higher P_max while increasing E_b.When x=0.2,BST-BL_0.2ZS obtains excellent energy storage performance,E_b reaches 39 k V/mm,and the corresponding P_max value is17.13μC/cm²,the maximum energy storage density（2.73 J/cm³）and excellent energy storage efficiency（87.6%）are finally obtained.At the same time,it has good energy storage performance and frequency stability.As for pulse discharge performance,huge current density（1035.03 A/cm²）and enormous power density（175.96 MW/cm³）are acquired at 34 k V/mm.Besides,it has good temperature stability and fatigue resistance.At 33 k V/mm,W_d reaches 2.05 J/cm³ and has a fast discharge rate,t_0.9 is about 46 ns.