Flexoelectricity Research Articles

Magneto-electro-elastic vibration analysis of modified couple stress-based three-layered micro rectangular plates exposed to multi-physical fields considering the flexoelectricity effects

In this paper, based on the CPT, motion equations for a sandwich plate containing a core and two integrated face-sheets have derived. The structure rests on the Visco-Pasternak foundation, which includes normal and shear modules. The piezo-magnetic core is made of CoFe2O4 and also is subjected to 3D magnetic potential. Two face sheets at top and bottom of the core are under electrical fields. Also, in order to obtain more accuracy, the effect of flexoelectricity has took into account at face sheets' relations in this work. Flexoelectricity is a property of all insulators whereby they polarize when subject to an inhomogeneous deformation. This property plays a crucial role in small-scale rather than macro scale. Employing CPT, Hamilton's principle, flexoelectricity considerations, the governing equations are derived and then solved analytically. By present work a detailed numerical study is obtained based on Piezoelectricity, Flexoelectricity and modified couple stress theories to indicate the significant effect of length scale parameter, shear correction factor, aspect and thickness ratios and boundary conditions on natural frequency of sandwich plates. Also, the figures show that there is an excellent agreement between present study and previous researches. These finding can be used for automotive industries, aircrafts, marine vessels and building industries.

Bio Focus: Flexoelectricity found in bone

Bio Focus: Flexoelectricity found in bone

Mixed Finite Elements for Flexoelectric Solids

Flexoelectricity (FE) refers to the two-way coupling between strain gradients and the electric field in dielectric materials, and is universal compared to piezoelectricity, which is restricted to dielectrics with noncentralsymmetric crystalline structure. Involving strain gradients makes the phenomenon of flexoelectricity size dependent and more important for nanoscale applications. However, strain gradients involve higher order spatial derivate of displacements and bring difficulties to the solution of flexoelectric problems. This dilemma impedes the application of such universal phenomenon in multiple fields, such as sensors, actuators, and nanogenerators. In this study, we develop a mixed finite element method (FEM) for the study of problems with both strain gradient elasticity (SGE) and flexoelectricity being taken into account. To use C0 continuous elements in mixed FEM, the kinematic relationship between displacement field and its gradient is enforced by Lagrangian multipliers. Besides, four types of 2D mixed finite elements are developed to study the flexoelectric effect. Verification as well as validation of the present mixed FEM is performed through comparing numerical results with analytical solutions for an infinite tube problem. Finally, mixed FEM is used to simulate the electromechanical behavior of a 2D block subjected to concentrated force or voltage. This study proves that the present mixed FEM is an effective tool to explore the electromechanical behaviors of materials with the consideration of flexoelectricity.

Flexoelectricity in Bulk and Nanoscale Polar and Non-Polar Dielectrics

Piezoelectricity (PE) is defined as the polarization under homogeneous application of stress on polar/non-centrosymmetry/no-inversion symmetry dielectrics, whereas it has been commonly accepted that flexoelectricity (FLX) is the induced polarization due to strain gradient in any polar/nonpolar dielectrics, the latter effect is universal and can be generated in any materials under inhomogeneous stress. Flexoelectricity is inversely proportional to the size of materials and devices which further suggests that giant FLX effects may develop in nanoscale materials. Flexoelectricity represents the polarization due to strain gradient and have significant effects on the functional properties of nanoscale materials, epitaxial thin films, one-dimensional structure with various shape and size, liquid crystals, polymers, nanobio-hybrid materials, etc. Till late sixties, very few works on flexoelectricity have been reported due to very weak magnitude compared to piezoelectricity. Advancement in nanoscale materials and device fabrication process and highly sophisticated electronics with detection of data with high signal to noise ratio lead the scientists/researchers to get several orders of higher flexoelectric coefficients compared to the proposed theoretical limits. Recently, giant FLX have been observed in nanoscale materials and their magnitudes are six to seven orders larger than the theoretical limits. In this review article, we describe the basic mechanism of flexoelectricity, brief history of discovery, theoretical modeling, experimental procedures, and results reported by several authors for bulk and nanoscale ferroelectric and dielectric materials.

Surface Energy Dissipation in Homeotropic Nematic Layers: The Role of Flexoelectricity and Surfactant Desorption

Homeotropic nematic layers of MBBA have been studied by a phase-sensitive flexoelectric spectroscopy method. They have been oriented by films of dilauroyl phosphatidyl choline (DLPC) and cetyl trimethyl-ammonium bromide (CTAB) self-assembled onto the cell glass plates. Using continuum theory, the transmitted light versus excitation frequency spectral shapes have been derived in terms of space variation of the nematic parameters (elastic constant, flexoelectric coefficient, rotational viscosity, and birefringence). These viscoelastic spectra contain information about the surface dissipation of the orientational energy for different aligning films that partially desorb from the surface and dissolve in the nematic, producing a gradient of the surfactant. A new type of flexoelectric effect dependent on the space derivative of flexo-coefficients has been identified. This effect consists of a bulk flexo-torque source that substantially influences the apparent liquid crystal anchoring. Static and dynamic cases have been analyzed for a steplike surfactant distribution. Resulting spectra have been successfully compared with the experiment, yielding information about the surfactant gradient. These results provide new insights on the interfacial physics of nematic liquid crystals and solid surfaces, where flexoelectricity and desorption play a fundamental role.

Piezoelectricity versus flexoelectricity and electrostriction in cholesteric and chiral smectic liquid‐crystalline elastomers

Piezoelectricity versus flexoelectricity and electrostriction in cholesteric and chiral smectic liquid‐crystalline elastomers

Influence of flexoelectricity on the stable configuration of a nematic layer with opposite boundary conditions

We discuss the influence of flexoelectricity on the critical thickness of a hybrid aligned nematic liquid crystal cell. We show that the critical thickness is independent of the flexoelectrical properties of the nematic only under the hypothesis that the distorted-undistorted transition is of second order. Afterall, the only effect of flexoelectricity is to introduce a very large elastic anisotropy. On the other hand, if first order transitions are considered, the flexoelectricity may play an important role. We also consider the surface polarization which can be different from zero for symmetry considerations. The analysis shows that its influence on the critical thickness or on the order of the transitions is negligible when there is no applied electric field. Some considerations on the terms connected with the surface polarization are also reported. The analysis is performed by supposing the nematic material a perfect insulator Discussion de l'influence de la flexoelectricite sur l'epaisseur critique d'une cellule nematique hybride: cette epaisseur n'est independante des proprietes flexoelectriques que si la transition distordu/non distordu est du 2eme ordre, la flexoelectricite n'introduisant qu'une forte anisotropie elastique, mais la flexoelectricite joue un role important sur une transition du 1er ordre. Analyse de l'effet de la polarisation de surface, qui peut etre non nulle a cause de la symetrie du systeme

The Different Aspects of Flexoelectricity in Nematics

Abstract We report on an experimental investigation of the thermal dependence of the flexoelectric coefficient in the nematic phase of several compounds. It is found to vary essentially like the angular order parameter S. For the first time a symmetric compound (pp' hexyloxytolan) is shown to exhibit a “regular” flexoelectric behavior. All these observations are consistent with the quadrupolar interpretation, but we also define cases in which the dipolar contribution shows up. Nous communiquons des résultats concernant la dépendance thermique du coefficient flexo-électrique dans la phase nématique de plusieurs composés. Nous trouvons qu'il varie essentielle-ment comme le paramètre d'ordre angulaire S. Nous montrons aussi, pour la première fois, qu'un composé symétrique (le pp' hexyloxytolane) a une actívité flexoélectrique “normale”. Ces observations sont compatibles avec l'interprétation quadrupolaire du phénomène, mais nous définissons aussi des cas dans lesquels il est possible de mettre en évidence la contribution dipolaire.