Enhancement mechanism of flexoelectric effect in barium titanate

Flexoelectric effect refers to the phenomenon of electric polarization under the action of material deformation gradient. When the material is strained, the local strain gradient will cause the electric dipole moment to rearrange, thereby generating an electric field in the material. Different from the piezoelectric effect, the flexoelectric effect is not limited by the symmetry of materials. Furthermore, the flexoelectric effect exhibits a significant size effect, allowing for huge flexoelectric signals to be obtained in nanoscale systems. Therefore, the flexoelectric effect has a wider application prospect and development space. There are differences in the number dimension between the flexoelectric coefficient and the piezoelectric coefficient, but both flexoelectric and piezoelectric effects result in the induction of electric dipole moments. In analogy to the piezoelectric effect, the polarization intensity may influence the flexoelectric coefficient. In this study, we selected the typical piezoelectric material barium titanate (BaTiO₃) and employed the forward/reverse and continuous polarization method to regulate the dipole moment arrangement. We measured the piezoelectric-like effect and flexoelectric-like effect under different polarization voltages with using a quasi-static $d_{33}$ measuring instrument and a two-step dot-loop method. The results confirmed that the polarization process intrinsically enhances the flexoelectric coefficient. At a polarization voltage of 600 V, the flexoelectric-like coefficient reached 180 pC/N, which is more than twenty times stronger than that of the non-polarized sample (7 pC/N). This study provides a simple and feasible idea for the enhancement of macroscopic flexoelectric coefficients.