The Research On The Dielectric And Energy Storage Properties Of BaTiO₃-based Relaxor Ferroelectric Ceramics

The increasingly serious energy crisis and environmental pollution have prompted countries around the world to commit themselves to the development,collection and utilization of new energy.Capacitors,as a core capacitive component applicable to the field of pulse devices,need to improve their dielectric breakdown strength and energy storage density in order to meet the development needs of corresponding equipment,such as miniaturization,integration,and environmental protection.Barium titanate?BT?has excellent dielectric and ferroelectric properties,and is an important material for the manufacture of green and environmentally friendly dielectric capacitors.Therefore,BT is selected as the starting point in this study.First,BT ferroelectrics are converted into relaxor ferroelectric by means of composition modification.The ferroelectrics were doped with ions of different valences to reduce the residual polarization and improve the dielectric breakdown strength.At the same time,in order to improve the density of the ceramics,we tried the viscous polymer processing in the monovalent ion doped component,and finally obtain the optimized energy storage performance.The details are as follows:A series of BT-xSBT ceramics were prepared by introducing different contents of strontium bismuth titanate?SBT?into pure BT.Sr²⁺and Bi³⁺enter the A site of the ABO₃structure to replace Ba²⁺,destroying the long-range ferroelectric order,which promotes the phase transition peak to widen,decrease,and move to a low temperature direction,thereby significantly improving the relaxation characteristics of the ceramic.At the same time,SBT can refine grains,reduce sintering temperature,and improve dielectric breakdown strength.However,although the low content of SBT can destroy the long-range ferroelectric order of BT,the effect is not obvious;the high content of SBT makes sintering difficult and is not conducive to densification of ceramics.Studies have found that an appropriate amount of SBT?x=0.35?can effectively improve the relaxation of BT and show relatively good room temperature energy storage performance.Therefore,the fourth to seventh chapters of this paper select the component BT-0.35SBT for further doping of different valence ions,in order to obtain further improvement of energy storage performance.Doping studies show that the tetravalent doped ion Sn⁴⁺occupies the B site and has the effect of refining the grains;the BT-SBT-Sn ceramic has obtained an energy storage density of 1.22 J/cm³ at 220 kV/cm.Zr⁴⁺,which is also a tetravalent doped ion,also occupies the B site,but does not have the effect of grain refining;BT-SBT-Zr ceramic achieved an energy storage density of 0.87 J/cm³ at 150 kV/cm.In BT-SBT-Nd and BT-SBT-La ceramics,the trivalent doped ions Nd³⁺and La³⁺both occupy the A site of the perovskite structure,and both have refined grains,shifted peaks toward low temperature direction,and improved relaxation.The two ceramics achieved energy storage densities of 2.01 J/cm³ and 1.61 J/cm³ at 280 kV/cm and 190 kV/cm,respectively,and their pulse performance was good.Divalent ion-doped BT-SBT-Cu and BT-SBT-Zn ceramics have obtained energy storage of 1.28 J/cm³ and 1.10 J/cm³ at dielectric breakdown strengths of 160 kV/cm and 210 kV/cm,respectively.Cu²⁺and Zn²⁺both occupy the B site of the perovskite structure,and both can widen the dielectric peaks and move towards the low temperature direction.Monovalent ion-doped BT-SBT-Na and BT-SBT-Li ceramics both have liquid phase participation in sintering.The dielectric breakdown strength of BT-SBT-Na ceramic was increased to 170 kV/cm,and an energy storage density of 1.38 J/cm³was obtained.BT-SBT-Li ceramics achieved an energy storage density of 2.43 J/cm³ at340 kV/cm.The viscous polymer processing was tried in a monovalent ion-doped BT-SBT-Li component,and BT-SBT-Li-VPP ceramic was obtained.Due to the significant increase in density,BT-SBT-Li-VPP ceramic achieved a high energy storage density of 3.54 J/cm³at 410 kV/cm.At the same time,this ceramic also showed excellent energy storage performance in terms of temperature and frequency stability.In short,compared with B-site doping,BT-SBT-based relaxor ferroelectric ceramics containing A-site substitution ions such as Na⁺,Li⁺,Nd³⁺,and La³⁺show relatively good energy storage performance.Combining VPP technology can effectively improve the density of ceramics,thereby significantly improving the energy storage performance.The composition-controlled phase structure and doping optimization of A-site ions proposed in this paper can provide reference for the preparation of other relaxor ferroelectric ceramics.