The Study On Structure Control And Energy Storage Properties Of Lead-free Relaxor Ferroelectric Ceramics

With the rapid development of integration and miniaturization of electronic industry systems,there is an urgent need for energy storage components applied in the fields of pulse power and hybrid electric vehicle to obtain excellent performance such as hig h power density,fast charge and discharge and high energy storage density.Dielectric ceramics have become a research hotspot due to the advantages of high power density and good temperature stability.However,the low energy storage density limits the applications of dielectric ceramics in the field of energy storage.In this paper,three typical ferroelectric ceramics BaTiO ₃?BT?,Na_0.5Bi_0.5TiO₃?NBT?and Ba_1-x-x Sr_x TiO₃?BST?were selected as the research objects.The effects of external ions doping on the phase structure,micro-morphology,dielectric,ferroelectric and energy storage properties of ferroelectric ceramics were studied systematically.By using ions doping to form solid solution,three typical ferroelectric ceramics were transformed into relax or ferroelectric ceramics,which can reduce the remanent polarization and coercive field,improve the dielectric breakdown strength of the ceramics,then effectively enhance the relaxor characteristics,and finally obtain higher energy storage density and efficiency.The?1-x?BaTiO₃-xCaSnO₃?x=0.05,0.10,0.15,0.20?lead-free ceramics were prepared by traditional solid-state reaction.The effect of CaSnO₃doping on BaTiO₃ of ferroelectric ceramics were studied.The results show that Ca²⁺and Sn⁴⁺occupy A and B sites respectively,and with the increase of CaSnO₃ content,the phase structure of the samples changes from tetragonal phase to cubic phase.The microstructure of the ceramic sample is very dense,and the relative density is as high as 99%at x=0.15,and the average grain size of the sample is reduced by doping CaSnO ₃.CaSnO₃ can obviously expand the dielectric peak and shift the peak to low temperature,which significantly enhances the relaxor properties of ceramics.Moreover,CaSnO₃ can reduce the remanent polarization and dielectric loss,thus improving the energy storage efficiency.The maximum breakdown strength reaches 230 kV/cm at x=0.15,and a maximum recoverable energy density of 1.57 J/cm³ at room temperature is obtained.The ceramics show good temperature,frequency stabilities and fatigue resistance.0.5Na_0.5Bi_0.5TiO₃-0.5SrTiO₃-xCuO?x=0,0.01,0.015,0.02?lead-free ceramics were prepared by solid-state method.The effects of CuO on the structure and electrical properties of NBT-ST were studied.The results show that CuO is successfully dissolved into NBT-ST and the ceramics have a typical perovskite structure.All the samples are dense,and the grain distribution is relatively uniform.The addition of CuO can effectively restrain the average grain size.With the addition of CuO,the remanent polarization of the ceramics decreases,and the breakdown strength increases obviously,and all the components show strong relaxor characteristics.When x=0.01,the breakdown field strength of the ceramics reaches the maximum?240 kV/cm?,and the high energy storage density of 2.01 J/cm³ is obtained.For the ceramics d oped with 0.01 CuO,the energy storage density can be maintained around 1.1 J/cm³ in a certain temperature?30¹50??or frequency?0.2²00 Hz?range,indicating that it has good temperature and frequency stability.In addition,the component also shows good pulse power performance.Lead-free?1-x?Ba_0.95Sr_0.05TiO₃-xBi(Mg_2/3Nb_1/3)O₃?x=0,0.15,0.20,0.25?ceramics were prepared by solid state method.The structure,dielectric,ferroelectric and energy storage properties of BST-x BMN ceramics were studied.The results show that the pure BST ceramics are tetragonal phase,and the ceramics are transformed into pseudo-cubic phase after BMN is added.With the addition of BMN,the remanent polarization decreases,and the breakdown strength increases significantly.The ceramic changes from ferroelectrics to relaxor ferroelectrics,which enhances the relaxor characteristics and is beneficial to the improvement of energy storage.When x=0.15,the breakdown strength increases to 210 kV/cm,and the energy storage density is 1.46 J/cm³.In the range of variable temperature measurement?40¹20??,the energy storage density of 0.01 ceramics is stable,and the efficiency is about 80%.In summary,three typical ferroelectrics are transformed into relaxor ferroelectrics by ion doping,which can effectively improve the relaxation properties of dielectric ceramics,thus significantly improving the energy storage properties of lead-free ferroelectric ceramics.