Effect Of Doping Modification On Dielectric Properties And Breakdown Strength Of Bi_0.5Na_0.5TiO₃-based Energy Storage Ceramics

Recently,there has been an increasing demand for energy in human society.Therefore,there is a need for improved diversified energy storage strategies.Among these strategies,dielectric capacitors have been found to possess unique characteristics,such as tiny volume,ultra-low order of charge-discharge time and power density.These characteristics make them suitable for a large number of electric power equipment,electronic integrated devices,and new energy vehicles,establishing them as an indispensable core component of new energy storage devices.Bi_0.5Na_0.5Ti O₃（abbreviated as BNT）is a new lead-free energy storage ceramic.The BNT matrix has large spontaneous polarization and high Curie temperature,making it a very promising energy storage material.However,its large remanent polarization and poor electric breakdown limit its further development.The current strategy for modifying BNT involves improving the preparation technology,component doping,and element replacement,making it a stable relaxor at room temperature.In this research,a binary ceramic of Bi_0.48Na_0.48Ba_0.04Ti O₃（BNBT）was prepared using traditional solid-state sintering method,and different modification strategies were investigated to explore their effects on the dielectric properties and breakdown strength of energy storage ceramics.The specific work is as follows:（1）A small ionic radius Ca²⁺was introduced into the A-site to form the ternary（1-x）Bi_0.48Na_0.48Ba_0.04Ti O₃-x Ca Ti O₃ system.This reduced the grain size and achieved a new disorder state at A-site,resulting in a shifting of the dielectric transition peak towards room temperature.This successful activation and evolution of the polar nanoscale regions at room temperature improved the relaxation property of the material.Ceramics achieved a recoverable energy storage density of 5.86 J cm^-3 and an energy conversion efficiency of 79.4%under an electric field of 350 k V cm^-1.Moreover,the pulse overdamped charge-discharge test conducted under the same electric field resulted in a discharge energy density of 5.53 J cm^-3 and a super-fast discharge rate of 3.58μs.The material also demonstrated good stability in the frequency range of 0.1-130 Hz and the temperature range of 20-170℃.（2）In the first work,the energy storage properties obtained in the medium electric field were not ideal,and there was still significant energy loss.In the second work,modified BNBT energy storage ceramics were successfully prepared by introducing the same element A-site complex ion(Na_0.97Bi_0.01)⁺and B-site cation Ta⁵⁺.These modifications resulted in stable relaxation properties under low electric fields.Combined with strategies such as grain refinement,band gap regulation,the coexistence of two phases,and activation of polar nanoscale regions,the ceramics achieved a recoverable energy storage density of 6.2 J cm^-3at 280 k V cm^-1,with a high energy efficiency of 84.2%.Furthermore,the pulse overdamped charge-discharge test conducted on the ceramics resulted in a super-fast discharge rate of 2.896μs and a similar energy density.The modified BNBT energy storage ceramics also demonstrated good stability in the frequency range of 0.5-130 Hz and the temperature range of 20-180℃..（3）Combining the experience gained from the previous work,Bi(Mg_2/3Ta_1/3)O₃（BMT）components were doped into the BNBT matrix to aid in maintaining high saturation polarization under high electric fields,thus achieving superior energy storage density.With the cooperative efforts of B-site disorder,a strongly tetragonal phase at room temperature,and high resistivity,the energy storage ceramics obtained a recoverable energy density of 10.73 J cm^-3 and an energy conversion efficiency of 80.5%at a high electric field of 540 k V cm^-1,as well as excellent charge-discharge performance,excellent frequency and temperature stability.Additionally,the components of Bi(Mg_2/3Ta_1/3)O₃,Bi_2/3(Mg_1/3Ta_2/3)O₃,and Bi_1/2(Mg_1/6Ta_5/6)O₃ were explored for their effects on dielectric and ferroelectric properties,including A-site vacancies and regulation of the Mg/Ta ratio.