Study Of The Flexoelectric Aging Behavior And Its Related Mechanism In Ferroelectric Ceramics

Flexoelectric effect describes the electric polarization phenomenon which is caused by strain gradient.This effect,has significant size effect(because the smaller the size,the larger the strain gradient)and no crystal symmetry limitation,could be widely used in micro/nano actuating and sensing devices.However,up till now,the critical issue regarding the relationship between the structure and performance of flexoelectric materials still remains unclear,and hence restricts its further application.This thesis,focused on the service properties of flexoelectric materials and devices,and systematically studied the flexoelectric fatigue and aging behaviors and their mechanism in ferroelectric ceramics.The main research contents and conclusions are listed below.The ferroelectric ceramics such as K0.5Na0.5NbO3(KNN)and BaTiO3(BTO),which are typical perovskite materials of ABO3 type,are selected as the research objects.The quantum paraelectric material SrTiO3(STO)is selected as the counterpart.We doped the variable valence element into the B-site elements in order to tune the oxygen vacancy concentration of the above materials.We summarized the interplay of continuous bending vibration on the material properties(we called it as flexoelectric fatigue or flexoelectric aging),and studied the dependence of flexoelectric coefficient of materials on vibration period,vibration time and vibration frequency.By comparing the flexoelectric fatigue with the ferroelectric and dielectric fatigue/aging in the ferroelectric materials,we made the following conclusions:1.The flexoelectric coefficient of KNN and BTO ferroelectric ceramics decrease with the increase of vibration period and aging time and can be well fitted by the exponential decay function.The aging and fatigue regulation of flexoelectricity are similar with that of the ferroelectricity and dielectric constant.It is proved that the flexoelectric aging(fatigue)of ferroelectric ceramics is closely related to the defect structure(oxygen vacancy).2.The results show that the flexoelectric fatigue(aging)may come from the ferroelectric fatigue(aging),and it can also reveal that the origin of enhanced flexoelectricity in ferroelectric materials is correlated to ferroelectricity.This work could be benefit for the comprehensive understanding of the relationship between structure and property in ferroelectric materials and promote the exploration of flexoelectric devices in the future.