Study On The Structure Design And Doping Effect Of Lead Zirconate-based Antiferroelectric Thin Films For Energy Storage

Dielectric capacitors are widely used in national defense,high-tech,civilian and other fields due to their fast charging-and-discharging capabilities.Although dielectric capacitors possess extremely high output power density,the energy storage density is relatively low in comparison with other energy storage devices such as batteries and electrochemical capacitors.Therefore,improving the energy storage density of dielectric capacitors has become a research hotspot.Among all dielectric materials,antiferroelectric materials are considered to be the most potential energy storage materials due to their unique antiferroelectric-ferroelectric phase transition behavior and high energy storage performance.Lead zirconate-based materials with perovskite structures are the most typical antiferroelectric materials.Regarding the common problems of low energy storage density and low breakdown strength in current antiferroelectric materials,optimizing the energy storage performance of lead zirconate-based antiferroelectric materials has become an urgent problem to be solved.Compared with traditional bulk materials,thin films are more meeting the requirements of device integration and miniaturization.Besides,the breakdown strength of the thin film is relatively higher.Therefore,this thesis selected lead zirconate-based antiferroelectric thin films as the research object,optimizing films’energy storage properties by designing multilayer structures and doping effects.The main contents are as follows:（1）Structure design on the energy storage properties of（PbZrO₃/PbTiO₃）_nmultilayer thin film.Multilayer structure films of（PbZrO₃/PbTiO₃）_n（（PZO/PTO）_n,n=1,2,3,6,9）were designed.The effects of interfacial density in heterostructures on the microstructure and electrical properties of lead zirconate-based antiferroelectric composite films were specifically explored.It is found that the existence of PTO ferroelectric layer enhances the overall saturation polarization of the thin film.In terms of dielectric properties,the dielectric constant of thin films with low interfacial density（n=1,2）exhibits an asymmetry phenomenon under a biased electric field,which is caused by the asymmetry of the built-in electric field and the difference in the dielectric properties of the two materials.Based on Weibull distribution analysis,the multilayer thin film with n=3 has the highest breakdown strength up to 2.9 MV/cm and the highest energy storage density up to 36.4 J/cm³.Meanwhile,this multilayer film possesses good fatigue properties and thermal stability.Although the breakdown strength raises in the multilayer structure films,the film with n=3 possesses the maximum breakdown strength.This result indicates that the existence of interfaces can hinder the development of the electrical tree and increase the breakdown strength of the multilayer thin film.However,there is no monotonic increase in the relationship between the breakdown strength and the interfacial density.It indicates that the interface has both positive and negative effects on the breakdown strength.In order to further explore the effect of interfaces on the breakdown strength of thin films,the interface structure of n=3 multilayer thin film was performed through Aberration Corrected Transmission Electron Microscope.It is found that Zr/Ti ions diffuse at the interface,with a range of2-3 nm.Besides,there are some regular interfacial dislocations at the interface due to the lattice mismatch between PZO and PTO.Dislocations can behave as a fast diffusion path like channel diffusion.Therefore,in multilayer films with high interfacial density,the negative effect of dislocations on the breakdown strength is prominent.This study provides a scientific reference for designing layered composite films with high energy storage characteristics.（2）A-site co-doping effects on the energy storage properties of PZO thin films.Element doping is a common method to improve energy storage properties.According to the tolerance factor law,antiferroelectric thin films of Pb_0.94-xLa_0.04Sr_xZr O₃（PLSZ,x=0,0.03,0.06,0.09,0.12）co-doped with La³⁺and Sr²⁺at the A-site were designed.It is found that with the increase of Sr content,the X-ray diffraction peaks shift to a higher angle as the Sr²⁺ion radius（1.44?）is smaller than the Pb²⁺ion radius（1.49?）,indicating that Sr²⁺successfully entered the lattice.The saturation polarization tends to decrease with the increase of Sr²⁺content,which is related to the decrease in the relative displacement of B-site ions caused by the decrease in the cell volume.According to the tolerance factor law,the more Sr²⁺doped,the more stable the antiferroelectric phase of the thin film is,which increases the switching field of phase transition.It is found that the breakdown strength of A-site co-doped PLSZ thin films has been improved,and the breakdown strength is around 1.5 MV/cm.The thin film of x=0.03 possesses the highest energy storage density,reaching 31.7 J/cm³,which is due to the high breakdown field strength and the high saturation polarization of the sample.All thin films have high energy storage efficiency,even up to 75%.This study provides a new idea for designing antiferroelectric films with high energy storage properties through doping modification.