Papers by Keyword: Flexoelectricity

Abstract: General 2D boundary value problems of piezoelectric nanosized structures with cracks under a thermal load are analyzed by the finite element method (FEM). The size-effect phenomenon observed in nanosized structures is described by the strain-gradient effect. The strain gradients are considered in the constitutive equations for electric displacement and the high-order stress tensor. For this model, the governing equations are derived with the corresponding boundary conditions using the variational principle. Uncoupled thermoelasticity is considered, thus, the heat conduction problem is analyzed independently of the mechanical fields in the first step. A numerical example is presented and discussed to demonstrate the effects of the strain-gradient.

Abstract: The size-dependent features concerning the mechanical behavior of the micro/nanoelectronic structures are well known from experiments. They are described by the strain-gradient effect in this paper since the classical elasticity theory fails to capture the size effect of the nanostructures. The electric field-strain gradient coupling is considered in the constitutive equations of the material and the governing equations are derived with the corresponding boundary conditions using the variational principle. The path independent J-integral is derived for fracture mechanics analysis of piezoelectric solids described by the gradient theory.

Abstract: 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.

Abstract: The difference between e1 and e3 parameters for flexoelectric polarization, as originally defined byMeyer, is measured for nematic liquid crystal materials E7 and BL087 in Twisted Nematic (TN) cells with In-Plane Switching (IPS) electric fields using the crystal rotation method, which measures transmission as a function of angle of incidence. Values of e₁ − e₃ for E7 and BL087 are found to be 7.2±1.0 pCm⁻¹ and 9.4±1.0 pCm⁻¹ respectively.