| In recent years,under the background of "carbon peak" and "carbon neutral",lead-free energy storage ceramics have received more and more attention and applications.Bismuth sodium titanate（Bi0.5Na0.5TiO3,BNT for short）is regarded as one of the most competitive systems to replace lead-based composite ceramics due to its advantages（such as strong ferroelectric property,high Curie temperature and mature preparation process,etc.）.However,the small polarization intensity difference（Pmax-Pr）and the breakdown field strength（Eb）of BNT-based ceramics affect the improvement of their energy storage characteristics.Therefore,in this paper,BNT is used as the matrix material,and the method of solution component and ion doping is used to regulate the microstructure of ceramics,improve the relaxation characteristics of ceramics,make the electric hysteresis curve to thin state transformation,improve the energy storage characteristics greatly of ceramics,and a series of characterization and research on its performance.（1）（1-x）（Bi0.5Na0.5）TiO3-xSr（Mg0.3334Nb0.6666）O3（abbreviated as（1-x）BNT-xSMN）ceramics were prepared by solid state reaction method with Sr（Mg0.3334Nb0.6666）O3 solution of（Bi0.5Na0.5）TiO3.The results show that SMN can form a good solid solution with BNT.The introduction of SMN makes the grain size of ceramic samples decrease gradually,the corresponding residual polarization intensity Pr decreases significantly,and the P-E loops gradually change from "saturated" to "nearly linear".（1-x）BNT-xSMN energy storage ceramics had the best comprehensive performance at x=0.10,（W=3.04 J/cm3,Wrec=1.59 J/cm3,η=52.28%）.At the same time,0.90BNT-0.10SMN ceramic achieved excellent temperature stability（40～160 ℃）and frequency stability（1～200 Hz）under 110 kV/cm.In addition,the 0.90BNT0.10SMN ceramic exhibited excellent power density（PD=1.66 MW/cm3）and faster discharge time（t0.9=0.95 μs）under120 kV/cm.（2）Using BNT as the matrix,a composition design strategy was adopted by promoting PNRs to reduce Pr and inhibiting the growth of grain size to improve the Eb.Sr（Ti0.5Zr0.5）03 was used to modify BNT ceramics,and（1-x）Bio.5Nao.5TiO3-xSrTi0.5Zr0.5O3（abbreviated as（1-x）BNTxSTZ）energy storage ceramics were prepared by solid state reaction method.The analysis results show that（1-x）BNT-xSTZ ceramics have a single pure perovskite structure,without any secondary phase.The introduction of STZ reduces the grain size of the ceramic samples to submicron level,and the corresponding Pr gradually decreases,the saturation polarization intensity Pmax remains at a high level,the P-E loops of the samples becomes "thin",and the relaxation characteristics of the samples are significantly enhanced.When x=0.20,W=3.33J/cm3,Wrec=1.85 J/cm3,and η=65.92%,which is 4.5 times the effective energy storage of pure BNT.In addition,the energy density and energy efficiency of 0.80BNT-0.20STZ ceramic exhibited significant temperature stability（40-160℃）and frequency stability（1-500 Hz）at 100 kV/cm.0.80BNT-0.20STZ ceramic exhibited excellent power density（PD=3.64 MW/cm3）and ultra-fast discharge time（t0.9=0.632 μs）at 160 kV/cm.（3）It is considered that the introduction of Sr2+can disturb the long-range order of ferroelectric cells and generate polar nanocrystals（PNRs）in the matrix,and has the ability to maintain large polarization intensity difference（Pmax-Pr）,（1-x）（Bi0.5Na0.5）0.7Sr0.3TiO3xSr0.85Bi0.1ZrO3（abbreviated as（1-x）BNST-xSBZ）were constructed based on A-site defect engineering.The introduction of SBZ can greatly limit the growth of ceramic grain and effectively improve the breakdown field strength.When x=0.125,（1-x）BNST-xSBZ ceramics show the best energy storage characteristics（W=4.05 J/cm3,Wrec=3.53 J/cm3,η=87.15%）.In addition,the energy density and energy efficiency of 0.875BNST-0.125SBZ ceramic show excellent temperature（40～120℃）and frequency（5～200 Hz）stability at 150 kV/cm.Furthermore,0.875BNST-0.125SBZ ceramic exhibit outstanding power density（PD=7.32 MW/cm3）and short discharge time（t0.9=0.86μs）at 120 kV/cm. |
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