Study Of Flexoelectric Grain Size Effect In Ferroelectric Ceramics

The flexoelectric effect is a mechanoelectric coupling effect of electrical polarization induced by a strain gradient.Compared with the piezoelectric effect,it is not limited by the symmetry and size effect of crystal materials.It has important application potential in micro-nano sensing and driving and energy recovery.As a relatively new research field,the academic research on flexoelectric is still in its infancy,especially on the structure-activity relationship between flexural electricity-performance and structure.Therefore,in-depth study of flexoelectric structure performance relationship has important scientific significance.In this paper,the typical ferroelectric ceramic Ba Ti O₃（BTO）is selected as the research object,and strontium titanate ceramic Sr Ti O₃（STO）as the control.Taking the dielectric grain size effect of these two kinds of materials as the breakthrough,trying to establish the physical image between flexoelectricity and grain size effect.The main innovations and conclusions of this paper are as follows:1.The grain size of BTO ceramics increases with the increase of sintering temperature,and its dielectric and piezoelectric properties show a classical grain size effect,but the flexoelectric coefficient at room temperature increases gradually.The results show that the source of this flexoelectric enhancement effect is related to the reversal of 180°domain in ferroelectric ceramics.With the increase of grain size,the number of grain boundaries in the ceramics decreases,and the pinning effect of the domain wall weakens,which makes the 180°domain more easily flipped and oriented in the direction of the flexural electric field,which shows the enhancement of the flexoelectric effect macroscopically.2.With the increase of sintering temperature,the grain size of STO ceramics increases gradually,the dielectric properties increase at first and then decrease,and the flexoelectric coefficient at room temperature also increases at first and then decreases.It is found that the flexoelectric effect is consistent with the change of dielectric properties with grain size,which proves that the flexoelectricity of STO materials comes from the intrinsic flexoelectric properties of materials.At the same time,it is indirectly proved that the main contribution of the grain size effect of the flexoelectric properties of ferroelectric material BTO comes from the reversal of180o domain in the grain.The relevant data of this thesis show that both ferroelectric BTO ceramics and cis-electric STO ceramics have significant flexoelectric grain size effect,which further shows the dependence of flexoelectricity on the dielectric and ferroelectricity of the materials.Taking the crystal size effect as the control can provide theoretical reference for the subsequent development of high-performance flexoelectric materials and their devices.