Compositional Design And In-depth Research Of Energy Storage Properties In Pb(Yb_1/2Nb_1/2)O₃-based Antiferroelectric Ceramics

Unlike conventional energy storage applications,which last a long-time cycle,such as chemical batteries and supercapacitors,the electronic circuit exhibits growing demands on ultrafast storage and release rate of electrical energy.The research of dielectric energy storage maerials flourishes since they feature fast charge-discharge process,up to micro-seconds level.And dielectric energy storage materials are widely used in extremely fast electrical energy conversion scenarios,such as cardiac defibrillators,laser pulse deposition instruments,traction inverters for electric vehicles,and frequency converters in smart grids.The current dielectric energy storage capacitors are universally fabricated by polymer thin films,however,their volume fraction often accounts for more than 50%,due to their intrinsical low energy density.At the same time,the inferior energy density limits the output current or voltage,so that fails to support the high-power applications.The pursuit of high energy density dielectric materials is imperative in order to meet the demand of device miniaturization and elevate output electrical power.The energy density of the dielectric material corresponds to the electrostatic potential energy on the surface of the electrode,which is determined by the polarization-electric field curve（P-E loop）.Only two polarization patterns have the access to high energy density,one is the relaxor ferroelectric（RFE）pattern,and the other is the antiferroelectric（AFE）pattern.Hence,it is necessary to acquire AFE/RFE patterns by composition design,and the key to effective composition design is to understand what govern the polarization pattern and figure out a clear physical picture behind AFE/RFE polarization process.Unfortunately,existing researches have not involved in such"underlying"topics.With the attempt to dig underlying principle,this paper aims to explore the‘characteristic structures’that profoundly affect the polarization pattern of AFE and RFEs,and to further conclude what strategy of composition design relates to‘characteristic structures’,consequently deduce a logic chain of high energy density dielectric material,from composition to structure,property and performance.Therefore,this paper selected lead ytterbium niobate,chemical formula Pb(Yb_1/2Nb_1/2)O₃,as research target,because it can be constructed to a binary phase zone with both of RFE and AFE phase structure by a binary solid solution Pb(Yb_1/2Nb_1/2)O₃-Pb Ti O₃,which will facilitate the follow-up research about AFE/RFE polarization patterns.Based on the compositions in RFE phase zone,this paper compares the different polarization patterns by PFM and first-order reversible curve（FORC）,answering three critical questions that is related to high energy density for RFE polarization patterns:‘how to obtain reversible polarization’,‘how to delay polarizations to a high electric field’and‘how to reduce the hysteresis during polarization’.The answers given by this work are‘reversible polarization occurs above depolarization temperature T_d（measured in dielectric spectrum）’,‘Higher peak temperature T_m（also obtained in dielectric temperature spectrum）corresponds to flat lattice barrier,consequently delay polarization to high electric field’and‘doping in spontaneous polarization site increases polarization heterogeneity,and lead to weak polarization correlation,which ultimately leads to low polarization hysteresis’.Additionally,‘the current peak in I-E loop corresponds to the collective orientation of the dipole’and‘the flat current peak is a fingerprint of low polarization hysteresis’are also constructive for RFE polarization.Based on the compositions of the antiferroelectric phase zone,this paper uses density functional theory（DFT）calculation to explain the core problem of AFE polarization pattern‘how to enhance the antiferroelectric-ferroelectric phase change electric field E_F’.By DFT calculation results,three existing but unrelated interpretations of E_F are finally connected,and which are"tolerance factor-average difference in electronegativity"principle,octahedral tilting and octahedral distortion observed by XRD refinement and Raman spectroscopy and the LGD free energy phenomenological theory.This work draws a significant conclution that the formation energy of AFE phase structure is determined by the competition beween the energy decrease from electron cloud overlap in[AO₁₂]and the energy increase from[BO₆]distortion.Therefore,incorporating smaller size and lower polarizability A-site ions is the suggested material chemistry solution to enhance E_F.The above conclusion not only reveals the principle behind the"tolerance factor-the average difference of electronegativity",but also quite consistent with the structure observed by XRD refined in Raman spectroscopy.This paper hopes the above results can further contribute to the understanding of the polarization patter,or at least to provide meaningful structural indicators and physical parameters for efficient composition design of high energy density dielectric materials.