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.

The relationship between the applied elastic strain gradient and the induced electric polarization in the α-phase polyvinylidene fluoride (PVDF) films under bending conditions has been investigated. Our experimental studies have shown that the flexoelectric polarization is linearly proportional to the strain gradient and the corresponding direct flexoelectric response is strong. It is reasonable to believe that the physical mechanisms behind the flexoelectric effects in polymers and solid dielectrics are different.

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Harvesting waste energy through electromechanical coupling in practical devices requires combining device design with the development of synthetic strategies for large-area controlled fabrication of active piezoelectric materials. Here, we show a facile route to the large-area fabrication of ZnO nanostructured arrays using commodity galvanized steel as the Zn precursor as well as the substrate. The ZnO nanowires are further integrated within a device construct and the effective piezoelectric response is deduced based on a novel experimental approach involving induction of stress in the nanowires through pressure wave propagation along with phase-selective lock-in detection of the induced current. The robust methodology for measurement of the effective piezoelectric coefficient developed here allows for interrogation of piezoelectric functionality for the entire substrate under bending-type deformation of the ZnO nanowires.

In this study, we explore the possibility of fabricating a kind of piezoelectric actuators by exploiting the converse flexoelectric effect. The phenomena of flexoelectricity demonstrate that inhomogeneous external stimuli (either mechanical or electric stimuli) can break the inversion symmetry and induce the piezoelectric response even in nonpiezoelectric materials. By using the finite element method, we approximately estimate the magnitude of the converse piezoelectric effect under such circumstances. Our simulation results have proved that the inhomogeneous electric field generated by the asymmetric configuration of electrodes can be manipulated to create the converse piezoelectric response in nonpiezoelectric dielectrics. It is also reasonable to expect that this method may provide an alternative way to overcome the negative influence of the Casimir force on micro- or nanoscale devices.