Fine Structure And Electric Performance Of Lead-based Perovskite Antiferroelectric

Lead-based antiferroelectric materials have potential applications in areas such as electrostriction and energy harvesting due to the excellent electrical properties they exhibit when driven by external fields.Revealing the structural mechanism is the backbone for designing new high-performance materials.Currently,the research on antiferroelectric materials mainly focuses on the regulation of their properties,but little on the research of their fine crystal structure.This is mainly due to the complex modulation structure caused by the dope of guest ions in the Pbbased antiferroelectric.This low symmetry structure is a great challenge in characterization.By combining synchrotron radiation technology,neutron powder diffraction,three-dimensional electron diffraction,and spherical aberration correction electron microscopy,the complex modulation structure of Pb-based antiferroelectric materials has been studied in detail in this dissertation.Three different polarization configurations were revealed and the structure-property correlation of antiferroelectric materials is established by comparing the differences in polarization configurations.The main contents and conclusions of the research are as follows.(1)The classical Pb(Zr,Sn,Ti,Nb)O3 was taken as an example,in which,a cycloidal-like polarization configuration was unveiled through joint refinement on high-resolution synchrotron radiation and high-resolution neutron powder diffraction.This polarization configuration differs from the conventional strict antiparallel and fully compensated configuration of PbZrO3.The magnitude and direction of the dipoles in this new configuration oscillate continuously in the ap-by plane,and in the[110]P direction it has not-fully compensated polarization.It was named the mixed type Ising and Neel polarization configuration.(2)Pb1-1.5xLax(Zr,Sn,Ti)O3 are able to exhibit a slim and almost closed hysteresis loop by increasing the amount of La doping.Through the threedimensional electron diffraction and joint refinement on synchrotron radiation and neutron diffraction,it was found to have a commensurate structure and its electric dipole have a spatial canting arrangement along the[001]P direction.Through in situ electric field synchrotron radiation technology,it is found that the dipole rotate continuously to the[001]P direction driven by the electric field.Phase-filed simulation method was also adoped and simulate a hysteresis loop which is consistent with the macroscopic property.This result confirmed that this canting dipole configuration and continuous dipole rotation process were the main cause of the slim hysteresis loops.(3)Near the triple-phase point in the Zr-rich region,the Pb1-1.5xLax(Zr,Sn,Ti)O3 antiferroelectric system has a unique antiferroelectric that exhibits a triplehysteresis loop.In this dissertation,the crystal structure of this antiferroelectric was ab initio resolved using three-dimensional electron diffraction in combination with the Chargeflipping method,and then refined by neutron powder diffraction.It is found that the polarization configuration of this kind of antiferroelectric is threedimensional,and it has not only a sinusoidal polarization component in the ap-bp plane but also a sinusoidal polarization component outside the ap-bp plane.Spherical aberration electron microscopy was also used to reveal the polarization configuration in real space,and it was found that the polarization configuration shows a sinusoidal arrangement in the ap-bp plane,which is similar to that of the neutron diffraction results.This similarity corroborates the neutron diffraction results.(4)The critical electric field is one of the important characteristic parameters of antiferroelectrics,which is of great significance for the design of highperformance materials.In this dissertation,multiple antiferroelectric compositions were selected to investigate the correlation between the incommensurate structure and the critical electric field.Through in situ electric field experiment,the polarization "jump" phenomenon was observed.By comparing the polarization configurations of these antiferroelectrics with different critical electric fields,it is found that the critical electric field is strongly correlated with the rotation angle of this "jump" process.Confirmed by the DFT theoretical calculation,the rotation angle corresponds to the change in free energy,and it is confirmed that the rotation angle is the main factor determining the critical electric field.In this dissertation,the fine structures of several antiferroelectrics were determined through various characterisation methods.Three novel polarization configurations have been uncoverd,which deepen the understanding of the complex structure of antiferroelectrics,enrich the antiferroelectric polarisation configurations,and provide an important complement to the similarity between electric polarization and magnetic physics.At the same time,the establishment of the correlation between the microstructure and macroscopic properties will provide a theoretical basis for the design of high-performance antiferroelectric materials.