Preparation And Properties Study Of Bismuth Sodium Titanate Based Energy Storage Ceramics

With the development of pulse technology,improving energy storage density to achieve miniaturization of the device is a key issues for dielectric capacitors.To solve this problem,taking Bi₀.5Na₀.5TiO₃ based ceramics as the research object,three different formulas were designed through strengthening breakdown field,increasing maximum polarization and reducing remnant polarization.The phase structure,the micro-morphology,dielectric and ferroelectric energy storage properties have been studied to analyze the relationship between material structure and performance.（1）The Bi₀.5Na₀.5TiO₃-BaTiO3-xSrZrO₃-NaNbO₃ lead-free ferroelectric ceramic samples were prepared by conventional solid state reaction method.XRD Rietveld refinement indicates that R3c and P4bm phases coexist in the sample,while P4bm weakly polar phase accounts for the major.Slim P-E ferroelectric hysteresis loops were obtained due to the long range of ferroelectric order broken by the addition of SrZrO₃ and NaNbO₃ as well as the enhancement of the weakly polar region.The excellent energy storage properties can be obtained for the composition of x=0.08,with high energy storage density of 0.95J/cm3 at 110 kV/cm and small variation（7%）in the temperature range of 25-175℃.（2）In order to enhance the ferroelectricity and increase the maximum polarization of the sample,the ceramic samples of Bi₀.5Na₀.5TiO₃-BaTiO₃-xAgNbO₃ were successfully prepared by the solid state reaction method.XRD Rietveld refinement indicated that R3c and P4bm phases coexist in the sample.With the increase of AgNbO₃ content,the proportion of R3c phase decreased and the proportion of P4bm phase increased.The introduction of AgNbO₃ resulted that permittivity peaks moved toward the low temperature and the permittivity decreased.When x≥0.03,the electric field-induced ferroelectric transition peak（TF-R）from relaxor moved under room temperature.With the increase of AgNbO₃,the hysteresis loop changed from a typical ferroelectric to an anti-ferroelectric-like feature,and it eventually exhibits a slim hysteresis loop.The excellent energy storage properties were obtained at the composition of x=0.10,which has higher energy storage density（1.15J/cm3）and comparable efficiency（68.3%）under the relatively lower electric field（90 kV/cm）compared with other lead-free systems.（3）A new lead-free system of Bi₀.5Na₀.5TiO₃-Sr₀.8Bi₀.1 □ ₀.1TiO₃-xSrTiO₃-ySrZrO₃,in which SrTiO₃ and SrZrO₃ were simultaneously incorporated in BNT-based ceramics,was designed.The effects of SrTiO₃ and SrZrO₃ contents on the lattice parameters,microstructure,dielectric and energy storage properties were investigated.The introduction of SrTiO₃ and SrZrO₃ led to an expansion of cel volume and refinement of grain size.With the increasing of SrTiO₃ and SrZrO₃ contents,permittivity peaks shift to the lower temperature and become more diffused.And a slim P-E ferroelectric hysteresis loops were obtained due to the long range of ferroelectric order broken by the addition of SrTiO₃ and SrZrO₃.More importantly,when SrZrO₃ content was fixed to y=0.06,increasing SrTiO₃ content led to an enhancement of the breakdown strength（BDS）and simultaneously keeping nearly constant Pmax-Pr.The excellent energy storage properties were obtained at the composition of x=0.24,y=0.06,which had higher energy storage density（1.25J/cm3）and comparable efficiency（79%）under the relatively lower electric field（108kV/cm）compared with other lead-free systems.