Study On Preparation And Properties Of Bi_0.5Na_0.5TiO₃-SrTiO₃ Ceramic For Energy-storage Application

Energy-storage ceramics capacitors with excellent performance are needed to meet the development of pulse power system.Most of BNT-based ferroelectric relaxors reported perform high polarization but low breakdown voltage.ST paraelectrics show excellent voltage-standing property but small permittivity.BNT-ST solid solution was prepared to obtain ferroelectric relaxor with slim P-E loop.BNT was expected to improve P_max and the second member ST to enhance E_maxax to obtain higher energy storage density.?1-x?Bi_0.5Na_0.5TiO₃-xSrTiO₃?0.25?x?0.75??BNST100x,for short?were prepared by solid state method.Pure cubic perovskite structure are confirmed by XRD.But Raman result showed that the local structure is not perfectly cubic,indicating polar nanoregions?PNRs?exist in a broad temperature range.Temperature dependent dielectric constant exhibited distinct relaxor feature with broad peak and frequency dispersion.T_m decrease from 120°C to-80°C with increasing ST content and lie around room-temperature in BNST45.BNT-based BNT-ST obtain higher Pmax,and E_max improved with increasing ST content as expected,but P_max,P_r,E_i are depressed at the same time.The most optimal energy storage property is got from BNST45(?_r=4500,E_max=120kV/cm,P_max=34?C/cm²,J=1.12J/cm³,?=80%)and BNST70(?_r=2800,E_max=140kV/cm,P_max=23.4?C/cm²,J=1.17J/cm³,?=82%).To further discuss influence of Bi vacancy and oxygen vacancy on energy storage property of BNT-ST,Bi nonstoichiometric BNST45 were fabricate and BNST45 annealed at O2 and N2 were studied.Polarization is improved and grain sizes decreased with more Bi content.Small grains could depress P_r and E_c to some degree leading to improved energy storage density.However Bi reduce more pore in ceramics resulting in deteriorative Emax.The best energy storage property is obtained in Bi2 with density of 1.34J/cm³ and efficiency of 82%.Thermal treated BNST45 got smaller and more uniform grain and less pore.Resistivity and conductivity activation energy increased in BNST45 with high concentration of oxygen vacancy.And ferroelectricity is depressed in N₂ annealed BNST45.Energy storage density of all samples improve to more than 1.2J/cm³.The most optimal energy storage property is obtained in N₂-9h ceramic which possess more uniform and dense grain and higher resistivity.The energy storage density is1.6J/cm³ at 135kV/cm.