Preparation And Energy Storage Properties Of Potassium Sodium Niobate Based Ceramics

The advantages of energy storage dielectric ceramics are high power density and extremely fast charge and discharge speed.In addition,energy storage dielectric ceramics have long service life and good electrical performance in wide temperature and frequency domain.At present,they have become the core components of dielectric capacitors.However,the low energy storage density of dielectric ceramics limits its wider development.Therefore,it is necessary to study and develop energy storage ceramic system with better energy storage performance.Potassium sodium niobate(K_0.5Na_0.5NbO₃)based ceramics have the characteristics of high Curie temperature,high electromechanical coupling coefficient and high breakdown field strength compared with other dielectric ceramics.Different from other ceramics because of its unique light transmittance and good energy storage characteristics,it is considered to be one of the most potential lead-free ceramics.In this paper,KNN is modified by binary solid solution to change the internal grain distribution and size and improve the energy storage performance of ceramics.The microstructure,phase structure,ferroelectricity and temperature stability were evaluated,and the results were analyzed in detail.1.Using Bi Zn_0.5Zr_0.5O₃and K_0.5Na_0.5NbO₃constructed the lead-free ceramic system（1-x）(K_0.5Na_0.5NbO₃)-x(Bi Zn_0.5Zr_0.5O₃)by solid solutio.The results show that,（1-x）KNN-x BZZ is perovskite structure and no impurity phase is formed.The temperature T_mcorresponding to the maximum dielectric constant decreases with the increase of BZZ content,the phase structure changes from orthogonal phase to pseudo cubic phase,the ferroelectric properties of ceramics are weakened and the relaxation is enhanced.When x=10mol%,0.90KNN-0.10BZZ ceramic has the maximum effective energy storage density(W_rec)of 2.6J/cm~3;When x=20mol%,0.80KNN-0.20BZZceramic has the maximum energy storage efficiency（η）96%.The test of temperature and frequency stability shows that 0.90KNN-0.10BZZ ceramic has excellent temperature and frequency stability.The influence of temperature change on energy storage performance is less than 0.6%in the temperature range of 30℃～150℃,and the influence of frequency on energy storage performance is less than 3.6%in the frequency range of 5Hz-500Hz.Through the charge discharge test,it is found that 0.90KNN-0.10BZZ ceramic has a fast charge discharge speed（1.6μs）,reaching the microsecond level.2.Secondly,（1-x）(K_0.5Na_0.5NbO₃)-x(Bi Zr_0.5Sn_0.5O₃)（abbreviated as:（1-x）KNN-x BZS,x=5mol%,10mol%,15mol%,20mol%）lead-free relaxor ferroelectric ceramics were prepared by solid-state reaction method,and various tests were carried out.SEM and XRD analysis of ceramic samples show that,（1-x）KNN-x BZS ceramic is a typical perovskite ceramic with pseudo cubic phase structure and no impurity phase.It shows that the introduced second component Bi Zn_0.5Sn_0.5O₃has a good solid solution with KNN.The SEM test of scanning electron microscope shows that with the continuous addition of BZS,the grain size first decreases and then increases.When x=0.15,the grain size decreases to 0.35μm,and when the field strength is 255kv/cm,the maximum available energy storage density of 1.88J/cm~3is obtained,and the material has good frequency stability.When x=0.2,the energy storage efficiency is as high as 90%.In the frequency range of 5Hz-500Hz,the impact of frequency on energy storage performance is less than 4%,the impact on energy storage efficiency is less than3.3%,and the measured charge discharge time is 1.78μs.3.The （1-x）(K_0.5Na_0.5NbO₃)-x(Bi Mg_2/3Nb_1/3O₃)（where x=8mol%,10mol%,12mol%,14mol%）energy storage ceramics were successfully prepared by solid state reaction method.The internal phase structure,micro grain distribution,dielectric behavior and energy storage characteristics were tested.The test results were analyzed.It was found that by doping Bi Mg_2/3Nb_1/3O₃into KNN matrix,the density of ceramics increased,the porosity decreased and the grain growth was significantly inhibited.The breakdown field strength is significantly increased.The hysteresis loop shows that when x=10mol%,when the critical field strength reaches205kv/cm,0.90KNN-0.10BMN ceramics have the maximum energy storage density,W_recreaches 1.9J/cm~3,and when x=14mol%,0.86KNN-0.14BMN energy storage ceramics have the maximum energy storage efficiency of 90%.The lattice constant increases with the increase of x,indicating that Bi³⁺and(Mg_2/3Nb_1/3)³⁺enter the A and B positions in the KNN matrix lattice respectively.The relaxation factor gradually increases and the value is closer to 2,（1-x）KNN-x BMN ceramics gradually transition from ferroelectrics to relaxor ferroelectrics.BMN modified KNN ceramics have remarkable energy storage performance,and（1-x）KNN-x BMN ceramics have a wide application prospect in the field of energy storage.