In this study, a piezoelectric composite is fabricated from a Ba0.67Sr0.33TiO3 (BST) composition and air, and measured at room temperature (24°C) where the BST is in its paraelectric centric phase. The charge separation mechanism is flexoelectricity, driven by the strain gradient introduced by the pyramidal boundary shapes of each BST building unit of the composite. In spite of the macro (millimeter) dimensions of the building units that inhibit a steep strain gradient, the composite is sufficiently active to be measured by using a conventional Berlincourt d33 meter. The measured values are in good agreement with expectation from the earlier measured flexoelectric coefficient μ11 of the BST and the finite element simulation results of the strain gradient in the pyramid BST units.

Recent experimental studies have shown that some inhomogeneously strained bulk solid dielectrics have large flexoelectric coefficients. Here we report the experimental observation of the converse flexoelectric effect, i.e., the elastic stress induced in a Ba0.67Sr0.33TiO3 (BST) composition trapezoid block under the inhomogeneous electric fields generated by its chosen boundary shape. This BST composition has a very high electric susceptibility value χ and a ferroelectric Curie point that is close to room temperature. The quantitative measurement of the flexoelectric coefficient μ11 at a temperature just above the Curie point indicates that an enhanced converse flexoelectric effect exists in the BST sample in good agreement with the earlier measured direct effect. This observed phenomenon agrees with the theoretical predictions of Tagantsev’s phenomenological model. Furthermore, our experimental results suggest that we may be able to develop a method to design some unusual but useful piezocomposites with microscale artificial geometry shapes, which are completely fabricated from nonpiezoelectric materials.

We report observation of the giant direct flexoelectric effect in α-phase polyvinylidene fluoride (PVDF) films. This unexpected phenomenon was detected in the α-phase PVDF film undergoing elastic tensile stretching. Our results have shown that the physical mechanism behind the flexoelectricity in polymers might be more complicated than the one proposed for solid crystalline dielectrics.