Converse Flexoelectric Effect Research Articles

Fabrication and measurement of a flexoelectric micro-pyramid composite

A fabrication method by combining precision mechanical dicing and wet etching was developed to prepare micro-pyramid structures based on (Ba0.67Sr0.33)TiO3 ceramics. The effective piezoelectric properties of flexoelectric pyramid structures in ten micrometers scale were investigated and measured through converse flexoelectric effect. The scaling effect of the flexoelectric response was demonstrated as the structure size shrinks down. The results do suggest the great potential of flexoelectric micro pyramids as an alternative to lead-free piezoelectric material.

Converse flexoelectric effect in the SrTiO3 single crystal

The converse flexoelectric effect in the SrTiO3 single crystal as a response of inhomogeneous strain (bending strain) to an applied electric field has been studied. The temperature dependence of the effect in the temperature range of 77–450 K has been obtained.

Exact Solutions for Flexoelectric Response in Nanostructures

This paper is concerned with the derivation of the exact solutions for the static responses of the simply supported flexoelectric nanobeams subjected to the applied mechanical load and applied voltage difference across the thickness of the beams. Considering both the direct and the converse flexoelectric effects, the governing equations and the associated boundary conditions of the beams are derived to obtain the exact solutions for the displacements and the electric potential in the beams. Due to the converse flexoelectric effect, the active beams significantly counteract the applied mechanical load. The normal and the transverse shear deformations in the beams are affected by the converse flexoelectric effect in the beams resulting in the coupling of bending and stretching deformations in the beams. For the particular values of the length of the beam and the applied voltage, the deflection of the nanobeam due to the converse flexoelectric effect significantly increases with the decrease in the thickness of the beam. But the deflection of the beam remains invariant with the change in length of the beam for the particular values of the thickness of the beam and the applied voltage. Also, for the particular values of the thickness of the beam and the applied mechanical load, the induced transverse electric polarization on the surface of the beam is independent of the variation of the length of the beam and the value of the polarization increases with the decrease in the thickness of the beam. The benchmark results presented here may be useful for verifying further research and the present study suggests that the flexoelectric nanobeams may be effectively exploited for advanced applications as smart sensors and actuators at nanoscale.

Converse flexoelectric coefficient f1212 in bulk Ba0.67Sr0.33TiO3

The converse flexoelectric effect, referred as the electric field gradient induced strain, widely exists in dielectric materials, but its experimental studies have been reported by few research groups so far. In this Letter, we report our studies on the converse flexoelectric behavior of (Ba0.67Sr0.33)TiO3 ceramics and present the measured value of its flexoelectric coefficient f1212. In the experiments, the electric field gradient was generated by applying an electric field across the two lateral sides of trapezoid (Ba0.67Sr0.33)TiO3 samples. The shear displacement was measured using a laser vibrometer. The converse flexoelectric coefficient f1212 was found to be 124 ± 14 μC/m at room temperature. This result was in good agreement with the theoretical prediction of the flexoelectricity of the (Ba, Sr)TiO3 ceramics.

Backflow in flexoelectric nematic layers deformed by electric field

Coupling between director reorientation and flow appearing in nematic layers during arising and decay of electric field-induced deformations, known as backflow, was analysed numerically. Nematics possessing flexoelectric properties, in which the converse flexoelectric effect occurred, were considered. The velocity of the nematic liquid, as well as the director orientation angle, was calculated as functions of time and coordinate in the layer after applying a voltage step, as well as by switching off the voltage. Homeotropic and planar layers were taken into account. Several distinct forms of the backflow were found which differ from those observed for the non-flexoelectric nematic. Correlations between the flow patterns and the director distributions were determined.

Converse flexoelectric effect in homeotropic nematic layers with asymmetric surface anchoring

The dc electric field-induced deformations of conducting flexoelectric nematic layers were studied numerically. Asymmetric boundary conditions expressed by different anchoring strengths on the limiting surfaces were assumed. Nematic material was characterised by negative dielectric anisotropy. Both signs of the sum of flexoelectric coefficients were taken into account. The electric properties of the layer were described in terms of a weak electrolyte model. Mobility of cations was assumed to be one order of magnitude lower than that of anions. Quasi-blocking electrode contacts were assumed. The threshold voltages for the deformations and the director distributions in the deformed layers were calculated for low, moderate and high ion concentrations. The director distributions were also determined. The results show that asymmetry caused by difference between the anchoring strengths and by difference between mobilities of anions and cations lead to two threshold values for a given layer corresponding to two polarities of the bias voltage. Additionally, the values of both thresholds depend on the sign of the flexoelectric parameter. In every case under consideration, the threshold is significantly lowered when the ion concentration is high.

Converse flexoelectric effect in comb electrode piezoelectric microbeam

We demonstrate the converse flexoelectric effect in a lead zirconate titanate microbeam. The fringe electric field of a comb electrode induces converse flexoelectric responses in uniformly poled and depoled beams. The simulated electric field distribution shows that bending of the beam is induced by piezoelectric and μ11, μ12 flexoelectric coefficients. Simulations indicate that piezoelectric displacement occurs in different directions in the two opposite poled samples while flexoelectric displacement remains the same. This finding is verified by the displacement measurement results.

Prolonged Stochastic Resonance in Single Ion Channel Recordings

Stochastic resonance refers to the improved signal transduction through a system due to the addition of noise to that system. By prolonged stochastic resonance, we refer to the continued enhancement of signal transduction beyond the typical stochastic resonance maximum with increasing input noise. We present evidence of this phenomenon from single Alamethicin ion channels. Identification of the single channel in the presence of voltage noise was accomplished by extracting the conductance of the system by simultaneous voltage and current recording. We determined that, when applying low levels of voltage noise, no more than a single ion channel conducted at any given time. Further, we provide evidence that the prolongation of stochastic resonance in this system is due to the mechanotransductive effects of Alamethicin ion channels. It is well known that Alamethicin channels respond to mechanical tension in the lipid bilayer [1,2]. By extracting the capacitance of the system (again, via simultaneous voltage and current recordings), we record changes in membrane area with respect to applied voltage noise. We find that increasing voltage noise yields larger capacitances due to expansion of the lipid bilayer via the converse flexoelectric effect [3]. This areal expansion induces tension on the ion channel, increasing its conductance and enhancing signal transduction through the system. We therefore find that applied voltage noise affects Alamethicin ion channels by two means: directly, via the channel's voltage-gated nature; and indirectly, through the converse flexoelectric effect. This two-fold effect of voltage noise on channel conductance prolongs the signal transduction enhancement with increasing noise, and thus prolongs the effect of stochastic resonance in the system.[1] Stava, et al., Lab on a Chip, in press.[2] Opsahl and Webb, Biophys. J. (1994).[3] Todrov, et al., J. Phys. Chem. (1994).

Converse piezoelectric responses in nonpiezoelectric materials implemented via asymmetric configurations of electrodes

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.

Converse Flexoelectric Effect in Bent-Core Nematic Liquid Crystals

We report on the converse flexoelectric effect in two bent-core nematic liquid crystals with opposite dielectric anisotropies. The results are based on electro-optic investigations of inplane field-driven distortions in homeotropic samples (the Helfrich method). They are interpreted by an extension of the Helfrich theory that takes into account the higher order distortions. The bend flexocoefficient for both the compounds is of the usual order of magnitude as in calamitics, unlike in a previously investigated bent-core nematic for which giant values of the bend flexocoefficient are reported. In order to resolve this discrepancy, we propose a molecular model with nonpolar clusters showing quadrupolar flexoelectricity. The study also includes measurements on surface polarization instabilities in the dielectrically positive material; the splay flexocoefficient thereby deduced is also of the conventional order.

Separate control of direct and converse piezoelectric effects in flexoelectric piezoelectric composites

The fabrication of piezoelectric composites driven by the flexoelectric charge separation has aroused considerable interest recently. In earlier oral presentations, we have posited that, in such composites, even though the direct and the converse flexoelectric effects are thermodynamically equivalent, it is possible to separately control the direct and converse piezoelectricities. Here, we would like to demonstrate how this separation can be accomplished through the control of the texture symmetry and that the result does not violate reciprocity as two different phases are involved in those two effects.

Experimental studies of the converse flexoelectric effect induced by inhomogeneous electric field in a barium strontium titanate composition

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.

Flexoelectricity and photoflexoelectricity in model and biomembranes

Flexoelectricity provides an exact relationship between electric and mechanical degree of freedom of a bilayer membrane, i.e. between transmembrane voltage and membrane curvature. Detailed studies by means of laser stroboscopic interferometry technique of direct flexoelectric effect in dipolar, zwitterionic and charged black lipid membranes (BLMs) and first observation of converse flexoelectric effect in an uranyl acetate-stabilized BLM are reviewed and theoretically interpreted. A new effect also involving another, optical degree of freedom of BLM, i.e. photo-flexoelectricity, was discovered very recently. It is observed in a composite BLM containing in-situ generated photo-semiconductor CdS nanosized particles (mimicking integral proteins of biomembranes) upon bandgap illumination. Light-dependent flexoelectric response is rationalized in terms of curvature-modulated BLM photo-potential. Possible applications of these new effects in membrane sensors (for sound, light, chemical species), in membrane actuators and their biological relevance are discussed.

First Observation of the Converse Flexoelectric Effect in Bilayer Lipid Membranes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFirst Observation of the Converse Flexoelectric Effect in Bilayer Lipid MembranesA. T. Todorov, A. G. Petrov, and J. H. FendlerCite this: J. Phys. Chem. 1994, 98, 12, 3076–3079Publication Date (Print):March 1, 1994Publication History Published online1 May 2002Published inissue 1 March 1994https://doi.org/10.1021/j100063a004RIGHTS & PERMISSIONSArticle Views277Altmetric-Citations49LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts