Research On Energy Storage Properties Of Sodium Niobate Lead-free Ceramics

Dielectric capacitors have become one of the most important components in pulse power supply equipment because of their high charge and discharge rate and high power density.In many dielectric capacitor energy storage materials,ceramic capacitors have the advantages of medium breakdown field strength,low dielectric loss and excellent temperature stability,so they have a broad application prospect in aerospace,oil drilling and electromagnetic pulse weapons.Therefore,it is very important to design and prepare ceramic capacitors with excellent comprehensive performance.Sodium niobate（NaNbO₃）is one of the research hotspots in the field of lead-free dielectric energy storage due to its low raw material cost and no extra protective atmosphere during sintering.As an antiferroelectric material with ABO₃ perovskite structure,NaNbO₃ exhibits very complex phase transition with temperature change.At room temperature,NaNbO₃ is an antiferroelectric phase,but its free energy of the antiferroelectric phase is very close to that of the ferroelectric phase,so its antiferroelectric phase at room temperature is very unstable.When the conventional synthesized NaNbO₃ is tested with external electric field,the hysteresis loop is usually single loop,which leads to its low energy storage density and efficiency.At present,the hysteresis of electric hysteresis loop can be reduced by introducing heterovalent ions into NaNbO₃ to improve the relaxation characteristics of the system,so as to improve its energy storage performance.In this paper,NaNbO₃ is taken as the main research object,and the disordered material Ba(Mg_1/3Nb_2/3)O₃ is selected to form a solid solution with NaNbO₃.On the one hand,the long range order of NaNbO₃ system can be destroyed by heterovalent doping,and the relaxation characteristics of the system can be improved.On the other hand,it can improve the breakdown resistance of the system.By adjusting the concentration of Ba(Mg_1/3Nb_2/3)O₃ in the solid solution and optimizing the preparation process（including sintering temperature,discharge conditions and sealing degree of ceramic sintering,etc.）,the（1-x）NaNbO₃-x Ba(Mg_1/3Nb_2/3)O₃ ceramics with both high energy storage density and high energy storage efficiency were finally obtained.When the concentration of Ba(Mg_1/3Nb_2/3)O₃ is 25%,0.75 NaNbO₃-0.25 Ba(Mg_1/3Nb_2/3)O₃ ceramics obtain 2.43 J/cm³ energy storage density and 52.25%energy storage efficiency under 262.64 k V/cm electric field.According to the analysis of dielectric constant and dielectric loss,the relaxation property of the system is the strongest when the concentration of Ba(Mg_1/3Nb_2/3)O₃is 25%.Finally,the dielectric breakdown field strength of ceramics is analyzed by Weibull distribution,and the maximum breakdown field strength is 290.45 k V/cm when the concentration of Ba(Mg_1/3Nb_2/3)O₃ is 30%.In order to further improve the energy storage density and efficiency of 0.75NaNbO₃-0.25Ba(Mg_1/3Nb_2/3)O₃ ceramics,this paper explored six different uniaxial pressures during the pressing of ceramic embryos.Experimental results show that under 1.5mpa pressure,0.75NaNbO₃-0.25Ba(Mg_1/3Nb_2/3)O₃ ceramics have the highest energy storage density and efficiency.By analyzing the intrinsic dielectric breakdown field strength of ceramics through Weibull distribution,the maximum breakdown field strength of ceramics obtained at 2 MPa pressure is 262.66 k V/cm.