Microstructure And Energy Storage Properties Of Bi_0.5Na_0.5TiO₃-based Relaxor Ferroelectric Ceramic Thick Films Based On Orientation Control

In the context of"peak carbon dioxide emissions,carbon neutrality",Petroleum and gas is an important bridge from high carbon fossil energy（coal）to low carbon clean energy.In the future,the proportion of energy consumption will continue to increase,and oil and gas resources will remain dominant for long time.In order to reduce the dependence on foreign oil and gas resources and ensure energy security,the state proposed to strengthen the exploration of deep-water oil and gas resources.Electric spark source is widely used in oil and gas exploration because its advantages of safety,environmental protection and rich spectrum.However,due to the influence of environmental factors,such as deep-water exploration and complex terrain,the energy storage capacitor of traditional electric spark source cannot meet the demand.Therefore,it is urgent to develop capacitor materials with excellent energy storage characteristics,high Curie temperature and good frequency and temperature stability.Bi_0.5Na_0.5TiO₃（BNT）is a ferroelectric material with high saturation polarization(P_max>40μC/cm²),high Curie temperature（～320℃）,low dielectric loss,good temperature and frequency stability.However,the residual polarization intensity（P_r>35μC/cm²）of BNT is large and the breakdown field strength（E_b<100 kV/cm）is small,which leads to its low energy storage density(W_rec)and energy storage efficiency（η）,and limits its application in the field of dielectric energy storage.Therefore,in this paper,the microstructure and electrical properties of BNT-based ceramics were optimized by solid solution of other types of perovskite materials（such as BiYbO₃（BYO）in BiMeO₃（Me is a trivalent metal or composite metal cation）,high-gap linear dielectric SrTiO₃（STO））and orientation control of textured ceramics.Finally,the energy storage performance was greatly improved.The main results obtained in this paper are as follows:（1-x）BNT-xBYO（x=0.005-0.040）ceramics were prepared by introducing BiYbO₃（BYO）with low tolerance factor and high Curie temperature into BNT.On the one hand,the crystal structure of BNT ceramics was transformed from rhombohedral phase to pseudo cubic phase.On the other hand,it can significantly refine the grain size（the minimum grain size is only 0.44μm）and enhance the relaxor behavior（the maximum dispersion coefficient is 1.87）,thus greatly improving the energy storage performance of BNT ceramics.Compared with the pure BNT ceramics,when x=0.010,the E_bincreased by 1 times,△P increased by 4 times,W_rec=2.07 J/cm³（10 times increase）,η=31.66%（8 times increase）.Based on the optimized composition 0.99BNT-0.01BYO,the linear dielectric SrTiO₃（STO）with high band gap was introduced into the ceramics.The ternary BNT-BYO-STO ceramics are pseudo-cubic phase,and the ceramic grains were gradually refined from 0.48μm to 0.18μm.The pores at grain boundaries gradually aggregate into larger pores,resulting in a sharp decrease in impedance and E_b at the high STO content.The introduction of STO enhanced the relaxor behavior of the ceramic,and the maximum dispersion coefficient reached 2.11,which significantly reduced P_r（from25.5μC/cm² to 2.2μC/cm²）.The maximum W_rec value of 2.78 J/cm³（34.30%increase）and the maximumηvalue of 80.97%（155.75%increase）were obtained in the range of x=0.2-0.4,and it has good temperature,frequency stability and ferroelectric fatigue resistance.<111>oriented（1-x）（0.99BNT-0.01BYO）-xSTO（x=0.2-0.4）texture ceramics thick-film were prepared by template grain growth method（TGG method）.By studying the influencing factors of two-step molten salt reaction of BTO template,the lamellar structure of BTO template was obtained good phase,orientation and size,so that the prepared textured ceramic<111>orientation was higher than 70%.Compared with the nontextured ceramics,the grain size increases,the relaxor behavior increases,T_Cdecreases（between 80℃ and 150℃）,the impedance increases,P_r effectively decreases,and△P and E_b increase.At x=0.2,W_rec increases from 2.78 J/cm³ to 3.26 J/cm³（17.27%increase）,andηincreases from 58.26%to 76.32%（31.00%increase）,showing excellent frequency and temperature stability.<001>oriented（1-x）（0.99BNT-0.01BYO）-xSTO（x=0.2-0.4）textured ceramic thick-film were prepared by TGG method.By optimizing the preparation conditions of three-step molten salt reaction of BNT template,ultrasonic mixing time,excessive raw material Na₂CO₃ and calcination temperature,etc.The lamellar structure of BNT template with good phase,orientation and size was obtained,and the prepared textured ceramic<001>orientation was higher than 70%.Compared with the nontextured ceramics,the grain size increased,the T_C is above 150℃,the impedance increased,and the P_max increased significantly（x=0.3,from 27.02μC/cm² to 43.06μC/cm²）,and the△P increased（x=0.3,from 23.165μC/cm² to 40.471μC/cm²）.Finally,the energy storage performance of the ceramics was greatly improved(x=0.3,W_rec increases from2.32 J/cm³ to 5.34 J/cm³,130.17%increase;ηincreases from 66.13%to 83.91%,26.89%increase),showing excellent charge-discharge properties,frequency and temperature stability.