Aging Effect And Energy Storage Properties Of Ferroelectrics

Ferroelectrics（FEs）are the most important dielectric materials,which have been widely applied in many fields due to their high dielectric constants and significant electrostrictive properties.Despite their usefulness,there have been a number of defects in real materials.Among these defects,oxygen vacancy is the mostcommon and typical defect in oxides,strongly influencing the stability and reliability of ferroelectric devices.Many studies have reported the corresponding FE aging phenomena after a long time aging in a certain FE phase.However,there is little work reporting the influence of a long time aging in a certain FE phase on the domain switching and loops in other FE phases and the evolution process of the crystal symmetry and the defect configuration after experiencing a quick FE-FE transition cycle.In the thesis,it is the first time to give the structural and Raman spectra before and after aging.Then,the aging-induced hysteresis loop evolutions under different FE phases and external fields reveal some factors influencing the distribution symmetry of oxygen vacancies,which can only memorize and stabilize the original domain pattern rather than the other phase domain pattern.Typical features of dielectric capacitors are that they intrinsically exhibit a high energy density and a fast charge/discharge performance compared to Li-ion batteries or fuel cells,which makes them promising candidates for energy-storage devices in some specific areas.In order to maximize the charge that a capacitor can hold,the dielectric material needs to have high permittivity and high dielectric-breakdown voltage.Unfortunately,each dielectric has its own limitation.Generally,ceramics exhibit high permittivity but low breakdown strength;while polymers and glass matrixes possess large breakdown strength but low permittivity.In the thesis,Poly（vinylidene fluoride）（PVDF）,containing with small amount of modified graphene oxide or modified BaTiO₃nanoparticles.It is revealed that when the content of ceramic nanoparticles is 20vol%,the energy storage density of the composite film is 4 times as high as that of pure PVDF film.However,the energy storage density of the polymer containing 1vol%modified graphene oxide is 0.8J/cm³,which is nearly 10 times higher than that of pure polymer film.These results were also designed to induce the enhanced energy-storage properties.