Study On Energy Storage Characteristics And Glass Modification Of NBT-ST Based Relaxor Ferroelectric Ceramics

With the wide application and rapid development of ceramic dielectric capacitors,high energy storage density materials are in increasing demand.NBT is an ABO₃ structure,with good ferroelectricity,high polarization strength,and relatively easy to undergo ferroelectric phase/relaxation phase transition.ST is a precursory ferroelectric,which has no ferroelectricity at room temperature,but ST can be combined with NBT With any ratio of solid solution,the phase transition temperature of NBT and the phase region at room temperature can be adjusted.0.75NBT-0.25ST is a quasi-homotype phase.The saturated polarization strength of this component ceramic is very high,but the residual polarization strength is also very high.The small breakdown field strength limits its energy storage applications.In response to these problems,this paper uses doped"ion pairs"and the addition of stable materials that are resistant to breakdown to perform composite modification to reduce the residual polarization strength of NBT-ST ceramics and increase the breakdown field strength to increase the NBT-ST base.The purpose of energy storage performance.Doping Nb₂O₅ in NBT-ST to introduce Nb⁵⁺to replace Ti⁴⁺in the ABO₃ structure,forcing Ti⁴⁺to change to Ti³⁺,constructing a Nb⁵⁺-Ti³⁺ion pair.The formation of the ion pair changes the surrounding electric field and stress field and reduces the residual polarization.In order to achieve the purpose of"thin waist"with electric hysteresis loop.The results show that the doping of Nb⁵⁺reduces the remanent polarization while also reducing the saturation polarization.When the Nb⁵⁺doping content is 2.5 mol.%,the difference between the saturation polarization of the ceramic and the remanent polarization is the largest.On the basis of this doping content,the introduction of the second phase composite modification can maintain a higher effective polarization strength.At this time,the breakdown field strength of the ceramic is 50 k V/cm and the effective energy storage density is 0.367 J/cm³,The energy storage efficiency is 63.2%.Adding SiO₂ composite modification on the basis of doping Nb⁵⁺.SiO₂ is added as a glass phase to the pre-fired powder.The ceramic grains obtained by sintering are smaller,which can act as a sintering aid and improve the structure of the ceramic;The amorphous SiO₂ glass at the boundary can slow down the stress change caused by the dielectric under the action of the electric field,thereby increasing the E_b of the ceramic.The results show that the addition of SiO₂ increases the breakdown field strength of the ceramics,while also reducing the saturated polarization strength.When the SiO₂ content is 1 mol.%,the effective energy storage density is the largest,0.615 J/cm³.The penetration field strength is 75 k V/cm,and the energy storage efficiency is 75.3%.Adding high-entropy oxide compound modification on the basis of doping Nb⁵⁺,the five metal ions of high-entropy oxide form a united lattice,which has high disorder,similar to the glass phase,which hinders the crystal lattice The migration of defects can improve the breakdown while maintaining the high stability of the material.When the high-entropy oxide content is 4 mol.%,the E_b of the ceramic is up to 90 k V/cm,the effective energy storage density is up to 0.885 J/cm³,and the W_rec is up to 86.1%.Therefore,the experimental content of high-entropy oxide composite Nb⁵⁺-doped NBT-based ceramics brings new expectations for exploring greater P_m-P_r,breakdown field strength,effective energy storage density and energy storage efficiency.