Preparation And Electrical Properties Of Bi-based Composites Doped NaNbO₃ Lead-free Dielectric Ceramics

Dielectric capacitors are widely used in civil（new energy vehicles,smart grids）and military（laser weapons,electromagnetic guns）applications due to their high power density,fast charging and discharging capability and stable operation over a wide temperature range.In recent years,with the rapid develepment of the electronic products and components for miniaturization,light weight and integration,higher requirements have been placed on the energy storage density(W_rec),energy storage efficiency（η）and stability of energy storage performance（temperature and frequency stability）of dielectric capacitors.In this paper,NaNbO₃,an antiferroelectric material with a wide band gap and high dielectric constant,is selected as the object of study to explore two doping ideas that can further optimize the NaNbO₃-Bi Me O₃(Me is a composite ion,e.g.(Mg_0.5Zr_0.5)³⁺,(Mg_0.5Ti_0.5)³⁺)ceramic system.The effects and laws of Bi-based composite doping on the phase structure,dielectric properties,energy storage characteristics and impedance characteristics of NN ceramics are investigated in depth.（1）The 0.93NaNbO₃-0.07Bi(Mg_0.5Zr_0.5)O₃ ceramic with low energy storage density,energy storage efficiency and breakdown strength（E_b）was chosen as the object of study,and（1-x）(0.93NaNbO₃-0.07Bi(Mg_0.5Zr_0.5)O₃)-x(Bi_0.5Na_0.5)_0.7Sr_0.3Ti O₃ceramics were designed and prepared.The introduction of(Bi_0.5Na_0.5)_0.7Sr_0.3Ti O₃further breaks the ferroelectric long-range ordered structure of the ceramic samples and reduces the residual polarisation intensity（P_r）.At the same time,(Bi_0.5Na_0.5)_0.7Sr_0.3Ti O₃ lowers the ceramic sintering temperature,which allows the material to obtain smaller grains,resulting in an enhanced E_b.As x=0.20,the ceramic samples obtained high W_rec（3.35 J/cm³）andη（90.41%）at a field strength of 335k V/cm,achieving the goals of maintaining a high P_max,low P_r and large E_b.（2）The introduction of Ca Ti O₃,a linear dielectric material with low P_r and high intrinsic E_b,was investigated using 0.93NaNbO₃-0.07Bi(Mg_0.5Zr_0.5)O₃,and it was demonstrated that the introduction of Ca Ti O₃ stabilized the room temperature antiferroelectric phase of the samples,and Ca²⁺and Ti⁴⁺could replace Na⁺and Nb⁵⁺in the A and B positions,disrupting the polarization direction inside the crystal and transforming the macro-domains into fine domains,which results in a smaller P_r.At the same time,the introduction of Ca Ti O₃ could effectively improve the microstructure of the ceramic samples and enhance the denseness of the ceramic samples,resulting in high E_b.Finally,the x=0.20 component ceramic achieves excellent energy storage performance at a field strength of 580 k V/cm(W_rec=4.45J/cm³,η=85.75%).（3）In order to further study the effects of(Bi_0.5Na_0.5)_0.7Sr_0.3Ti O₃ and Ca Ti O₃doping on the phase structure and energy storage properties of NaNbO₃-Bi Me O₃ceramics,0.92NaNbO₃-0.08Bi(Mg_0.5Ti_0.5)O₃ ceramics were selected as the research object.（1-x）(0.92NaNbO₃-0.08Bi(Mg_0.5Ti_0.5)O₃)-x(Bi_0.5Na_0.5)_0.7Sr_0.3Ti O₃ and（1-x）(0.92NaNbO₃-0.08Bi(Mg_0.5Ti_0.5)O₃)-x Ca Ti O₃ were designed and prepared.The experimental results show that both doping make the samples have higher P_max,smaller P_r and higher E_b.Finally,0.85(0.92NaNbO₃-0.08Bi(Mg_0.5Ti_0.5)O₃)-0.15(Bi_0.5Na_0.5)_0.7Sr_0.3Ti O₃ ceramics obtained excellent W_rec（6.49J/cm³）andη（79.29%）.0.80(0.92NaNbO₃-0.08Bi(Mg_0.5Ti_0.5)O₃)-0.20Ca Ti O₃ ceramics achieved high W_rec（5.71J/cm³）andη（85%）.