Regulation On Flexoelectric Properties Of Crystalline Via Defect Dipoles And The Preliminary Exploration Of The Physical

The flexoelectric effect describes the electromechanical coupling of polarization induced by inhomogeneous strain（e.g.bending）in a material.Compared with the piezoelectric effect,the flexoelectric effect exhibits two unique characteristics:（1）the flexoelectric coefficient is a fourth order tensor,independent of lattice symmetry,and the choice of materials is large;（2）The size effect of the material is significant,and the flexoelectric response can even exceed the piezoelectric response at the micro-nano scale.However,the flexoelectric response of macroscopic materials is very weak,so their practical application is still limited.Hence,exploring the flexoelectric enhancement effect and developing materials with high flexoelectric coefficient is still one of the important research topics.The precise introduction and precise regulation of lattice defects has proved to be an effective means to adjust the physical properties of materials,but the contribution of specific coupling between lattice defects and flexoelectric properties has not been systematically understood.Therefore,it is of great scientific importance to investigate the modulation of flexural electrical properties of crystalline materials by defects and their physical mechanisms from the perspective of flexoelectric enhancement effects.In this paper,based on the study of the flexoelectric properties of ferroelectric ceramic Ba Ti O₃（BTO）,defects are introduced by means of doping modification to regulate the flexoelectric properties,and certain research progress has been made in the flexoelectric enhancement effect.The main research contents and innovations of this article are as follows:1.Using low-valent Fe³⁺as the dopant,Ba Ti_1-xFe_xO₃ and Ba Ti_1-xFe_4x/3O₃ doped ceramics were designed by chemical doping and non-stoichiometric doping.In principle,oxygen vacancy defects and trap charge defects were introduced into BTO ceramics,and the effects of different defect types on the flexoelectric properties of BTO ceramics were systematically investigated.XRD,SEM,and Raman test methods verified the solid solution of Fe³⁺in BTO materials,and showed the small differences caused by Fe³⁺doping on the structure of the materials.Impedance spectroscopy,XPS,EPR,and TSDC characterization methods verified that lattice defects were introduced into the two doped ceramics,and the types of lattice defects brought were different.The characterization of dielectric and ferroelectric properties verified the subtle changes in the electrical properties of materials caused by lattice defects.The significant difference in flexoelectric response,that is,Compared with the nominal BTO ceramic,the flexoelectric coefficient of the stoichiometric Fe-BTO ceramic at room temperature is increased by 5 times（from9.5μC/m increased to 65.0μC/m）,while the flexoelectric coefficient of non-stoichiometric Fe-BTO ceramics remains essentially stable,which is attributed to the effects of different lattice defects after excluding the secondary effects of external factors.The results show that oxygen vacancies contribute significantly to the enhancement of flexoelectricity rather than trap charge defects,and this enhancement effect can be explained by the selective orientation of defective dipoles formed by oxygen vacancies.2.Using high-valent Nb⁵⁺as a dopant,Ba Ti_1-xNb_xO₃ doped ceramics were designed through a stoichiometric ratio.Meanwhile,the concentration of weak electron lattice defects introduced into BTO doped ceramics was controlled through changes in dopant concentration.The effect of weak electron concentration on the flexoelectric properties of BTO ceramics was systematically investigated.XRD,and SEM test methods verified the solid solution of Nb⁵⁺in BTO materials,and showed the small differences caused by Nb⁵⁺doping on the structure of the materials.Impedance spectroscopy,XPS and I-V curves verified the introduction of weak electron defects and the variation of material semi-conductivity in Nb-BTO ceramics.The results show that the concentration of weak electron defects is maximum when the dopant concentration is 0.3 mol%,and the degree of semiconducting of the material is maximum,when the material exhibits the best electrical properties with an order of magnitude increase in dielectric constant at room temperature（from～2500 to～80000）and an increase in flexural electric coefficient from9.5μC/m to 387.28μC/m.Meanwhile,the thickness experiments further verify the barrier layer mechanism of the flexoelectric enhancement effect in semiconducting ceramics.The interaction between lattice defects and flexoelectricity explored in this article not only helps to understand the physical mechanism of flexoelectric properties,but also provides a feasible strategy for the design of new flexoelectric materials and related devices with high flexoelectric coefficients.