Topic
Flexoelectricity
About: Flexoelectricity is a research topic. Over the lifetime, 881 publications have been published within this topic receiving 25291 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this paper, a theory of the relationship between curvature strains and electric polarization in liquid crystals is developed in analogy to piezoelectric theory in ordinary crystals, which may explain some recently observed phenomena in nematic liquid crystals.
Abstract: A theory of the relationship between curvature strains and electric polarization in liquid crystals is developed in analogy to piezoelectric theory in ordinary crystals. The theory may explain some recently observed phenomena in nematic liquid crystals.
911 citations
TL;DR: Flexoelectricity is a universal effect allowed by symmetry in all materials as discussed by the authors and has been studied in many nanoscale systems, and potential applications of this electromechanical phenomenon have been discussed.
Abstract: Flexoelectricity—the coupling between polarization and strain gradients—is a universal effect allowed by symmetry in all materials. Following its discovery several decades ago, studies of flexoelectricity in solids have been scarce due to the seemingly small magnitude of this effect in bulk samples. The development of nanoscale technologies, however, has renewed the interest in flexoelectricity, as the large strain gradients often present at the nanoscale can lead to strong flexoelectric effects. Here we review the fundamentals of the flexoelectric effect in solids, discuss its presence in many nanoscale systems, and look at potential applications of this electromechanical phenomenon. The review also emphasizes the many open questions and unresolved issues in this developing field.
767 citations
Book•
17 Dec 1993
TL;DR: In this paper, the effect of an electric field on the structure of liquid crystals has been studied in terms of the effect on the phase transition temperature and the elasticity of the liquid crystal.
Abstract: 1 Liquid Crystalline State.- 1.1 Structure of Liquid Crystal Phases.- 1.1.1 Molecules.- 1.1.2 Thermotropic Mesophases Formed by Achiral Rod-Like Molecules.- 1.1.3 Thermotropic Chiral Mesophases.- 1.1.4 Mesophases of Disc-Like and Lath-Like Molecules.- 1.1.5 Polymer Liquid Crystals.- 1.1.6 Lyotropic Liquid Crystals.- 1.2 Mixtures.- 1.2.1 Nematic Eutectics.- 1.2.2 Reentrant Phases.- 1.2.3 Mixtures of Smectics.- 1.2.4 Nemato-Cholesteric Compositions.- 1.2.5 Ferroelectric Mixtures.- 1.3 Liquid Crystalline Materials.- 1.3.1 Chemical Classes.- 1.3.2 Chemical Structure and Transition Temperatures.- 1.3.3 Material.- 1.4 Direct Influence of an Electric Field on the Structure of Liquid Crystals.- 1.4.1 Field-Induced Shifts of the Phase Transition Temperatures.- 1.4.2 Influence of the Field on the Order Parameters.- 1.4.3 Field-Induced Changes in Symmetry.- References.- 2 Properties of the Materials.- 2.1 Dielectric Permittivity.- 2.1.1 Isotropic Liquids.- 2.1.2 Dielectric Anisotropy of Nematics.- 2.1.3 Nematic Mixtures.- 2.1.4 Other Phases.- 2.2 Electrical Conductivity.- 2.2.1 Dependence on Impurity Concentration.- 2.2.2 Conductivity Anisotropy.- 2.3 Optical Anisotropy and Dichroism.- 2.3.1 Optical Anisotropy.- 2.3.2 Dichroism.- 2.4 Viscoelastic Properties.- 2.4.1 Elasticity.- 2.4.2 Viscosity.- 2.4.3 Diffusion Coefficients.- References.- 3 Surface Phenomena.- 3.1 Structure of Surface Layers.- 3.1.1 Surface-Induced Changes in the Orientational Order Parameter.- 3.1.2 Surface-Induced Smectic Ordering.- 3.1.3 Polar Surface Order and Surface Polarization.- 3.2 Surface Energy.- 3.2.1 Wetting of a Solid Substrate.- 3.2.2 Surface Energy and Anchorage of a Nematic Liquid Crystal.- 3.2.3 Techniques for Measuring Anchoring Energies.- 3.3 Cells and Orientation.- 3.3.1 Electrooptical Cells.- 3.3.2 Liquid Crystal Orientation.- 3.3.3 Anchoring Transitions.- References.- 4 Electrooptical Effects Due to the Uniform Distortion of Nematic Liquid Crystals.- 4.1 Electrically Controlled Birefringence.- 4.1.1 Director Distribution.- 4.1.2 Tilted Directors at the Boundaries.- 4.1.3 Different Geometries. Simultaneous Action of Electric and Magnetic Fields.- 4.1.4 Effect of Electrical Conductivity.- 4.1.5 The Frederiks Transition for a Weak Anchoring at the Boundaries.- 4.1.6 Dynamics of the Frederiks Transition.- 4.1.7 The Frederiks Transition in Ferronematic Liquid Crystals.- 4.1.8 Optical Characteristics of the Electrically Controlled Birefringence Effect.- 4.2 Twist-Effect.- 4.2.1 Preparation of Twist Cells, Optical Properties at Zero Field.- 4.2.2 Transmission-Voltage Curve for Normal Light Incidence.- 4.2.3 Electrooptics of the Twist Cell for Oblique Incidence.- 4.2.4 Matrix Addressed Displays and Multiplexing Capability of Twist-Effect Materials.- 4.2.5 Dynamics of the Twist Effect.- 4.2.6 New Possibilities.- 4.3 Supertwist Effects.- 4.4 "Guest-Host" Effect.- 4.4.1 Change in Intensity of the Coloring.- 4.4.2 Colorimetry of "Guest-Host" Displays.- 4.4.3 Color Switching.- 4.4.4 Change in Fluorescence.- 4.5 The Flexoelectric Effect.- 4.5.1 Physical Reasons.- 4.5.2 Static Flexoelectric Distortion in Different Geometries Determination of Flexoelectric Moduli.- 4.5.3 Dynamics of the Flexoelectric Effect.- 4.5.4 Microscopic Approach to Determination of the Flexoelectric Coefficients.- 4.6 Reflectivity in an Electric Field.- 4.6.1 Optical Properties of Nontwisted Nematic Layers.- 4.6.2 Various Techniques.- 4.7 Field Behavior of the Isotropic Phase.- 4.7.1 The Kerr Effect in the Isotropic Phase.- 4.7.2 Reorientation of Surface Quasi-Nematic Layers.- 4.8 Electric Field Effects in Nematic Polymers.- 4.8.1 Thermotropic Mesophases.- 4.8.2 Lyotropic Polymers 212.- 4.9 Electrooptical Properties of Polymer Dispersed Liquid Crystal Films.- References.- 5 Modulated and Nonuniform Structures in Nematic Liquid Crystals.- 5.1 Orientational Modulated Structures.- 5.1.1 Flexoelectric Domains.- 5.1.2 Dielectric Two-Dimensional Structure in the Frederiks Transition.- 5.1.3 Other Types of Modulated Structures.- 5.2 Electrohydrodynamic Modulated Structures.- 5.2.1 Low-Frequency Limit The Kapustin-Williams Domains.- 5.2.2 Different Types of Low-Frequency Electrohydrodynamics.- 5.2.3 Electrohydrodynamic Instability in Nematics with Oblique Director Orientation at the Boundaries.- 5.2.4 Electrohydrodynamic Instability: "Chevron" Mode.- 5.2.5 Anisotropic Instabilities for Different Field and Cell Configurations.- 5.2.6 Allowance for Flexoelectricity in Anisotropic Domain Structures.- 5.2.7 High-Frequency Inertia Anisotropic Mode.- 5.2.8 Modulated Structures with Large Periods in Homeotropic Nematics.- 5.2.9 "Isotropic" Mechanism of the Excitation of Electrohydrodynamic Domains.- 5.2.10 Instabilities in Homeotropic Nematics with ?? >0.- 5.2.11 Classification of Threshold Conditions for Different Instabilities in Nematics.- 5.2.12 Electrohydrodynamic Instabilities in Polymer Nematics.- 5.2.13 The Instabilities above the Threshold Voltage. Dynamic Scattering of Light.- 5.3 Nematics in Spatially Nonuniform Fields.- 5.3.1 Homeotropic Orientation.- 5.3.2 Homogeneous Alignment.- 5.3.3 Twist Cells.- References.- 6 Electrooptical Properties of Cholesterics and Nonferroelectric Smectics.- 6.1 The Pitch of Helix and the Optical Properties of Cholesterics.- 6.1.1 Textures.- 6.1.2 Methods of Measuring the Pitch.- 6.1.3 Optical Properties of Planar Cholesteric Textures.- 6.1.4 Diffraction on the Focal-Conic Texture.- 6.1.5 Pitch Dependence on Cell Thickness.- 6.2 Field-Induced Dielectric Instabilities of Cholesterics.- 6.2.1 Texture Transitions.- 6.2.2 Instability of the Planar Cholesteric Texture.- 6.2.3 Field Untwisting of a Cholesteric Helix.- 6.2.4 Electrically Switched Bistable Structures.- 6.3 Electrohydrodynamic Instabilities in Cholesterics.- 6.4 Flexoelectric Effects.- 6.4.1 Fast Linear-in-Field Rotation of the Cholesteric Helix.- 6.4.2 Flexoelectric Domains.- 6.5 Electrooptical Effects in Blue Phases.- 6.5.1 Optical Features.- 6.5.2 Field Behavior.- 6.6 Electric Field Behavior of Nonferroelectric Smectics.- 6.6.1 The Frederiks Transition in a Smectic A.- 6.6.2 Dielectrically Induced Texture Transitions.- 6.6.3 The Frederiks Transition in a Smectic C.- 6.6.4 Electrohydrodynamic Instabilities in Smectics A and C.- References.- 7 Ferroelectric Liquid Crystals.- 7.1 The Physical Properties of Ferroelectric Liquid Crystals. Methods of Measurement.- 7.1.1 The Symmetry.- 7.1.2 The Microscopic Approach. Ferroelectric Mixtures.- 7.1.3 Physical Parameters.- 7.1.4 Tilt Angle.- 7.1.5 Spontaneous Polarization.- 7.1.6 Flexoelectric Polarization.- 7.1.7 Rotational Viscosity.- 7.1.8 Helix Pitch.- 7.1.9 Dielectric Properties.- 7.1.10 Optical Properties.- 7.1.11 Total Free Energy with Allowance for Anchoring.- 7.2 Electrooptical Effects in Ferroelectric Liquid Crystals.- 7.2.1 The Clark-Lagerwall Effect.- 7.2.2 Deformed Helix Ferroelectric Effect.- 7.2.3 Electroclinic Effect Near the Smectic A ? C* Phase Transition.- 7.2.4 Other Electrooptical Effects.- 7.2.5 Orientation of Samples.- 7.2.6 Problems of Bistability Realization.- 7.3 Ferroelectric Liquid Crystal Polymers.- 7.3.1 Introductory Remarks.- 7.3.2 Chemical Structures.- 7.3.3 Ferroelectricity.- 7.3.4 Electrooptical Switching.- References.- 8 Applications of Electrooptical Liquid Crystalline Materials.- 8.1 Displays.- 8.1.1 Active Matrix Addressed Displays.- 8.1.2 Supertwist Displays for Personal Computers.- 8.1.3 Projection Displays.- 8.1.4 Guest-Host Large Area Information Boards.- 8.1.5 General Trends in Display Applications.- 8.2 Optical Data Processing Devices.- 8.2.1 Light Valves.- 8.2.2 Modulators, Shutters.- 8.2.3 Deflectors of Light.- 8.2.4 Integrated Optical Devices.- 8.2.5 Matrix Spatial Light Modulators or Controlled Transparencies.- 8.2.6 Liquid Crystal Logic Elements.- 8.2.7 Optical Filtration.- 8.2.8 Application of Polymer Liquid Crystals in Optoelectronics.- 8.3 Other Applications.- 8.3.1 Storage Devices.- 8.3.2 Stereoscopic Liquid Crystal Sytems.- 8.3.3 Nondestructive Testing.- 8.3.4 Large Area Glass Light Shutters on Polymer Dispersed Liquid Crystal Films.- References.
692 citations
TL;DR: It is demonstrated that the stress gradient generated by the tip of an atomic force microscope can mechanically switch the polarization in the nanoscale volume of a ferroelectric film, enabling applications in which memory bits are written mechanically and read electrically.
Abstract: Ferroelectric materials are characterized by a permanent electric dipole that can be reversed through the application of an external voltage, but a strong intrinsic coupling between polarization and deformation also causes all ferroelectrics to be piezoelectric, leading to applications in sensors and high-displacement actuators. A less explored property is flexoelectricity, the coupling between polarization and a strain gradient. We demonstrate that the stress gradient generated by the tip of an atomic force microscope can mechanically switch the polarization in the nanoscale volume of a ferroelectric film. Pure mechanical force can therefore be used as a dynamic tool for polarization control and may enable applications in which memory bits are written mechanically and read electrically.
632 citations
TL;DR: This work has shown that not only the intensity of the response of the immune system to carbon dioxide but also its ability to reprogram theresponse of the nervous system to accommodate high levels of carbon dioxide.
Abstract: Note: Tagantsev, Ak Af Ioffe Engn Phys Inst,Leningrad 194021,UssrPart 2E4504Times Cited:19Cited References Count:16 Reference LC-ARTICLE-1986-010doi:10.1103/PhysRevB.34.5883 Record created on 2006-08-21, modified on 2017-11-27
583 citations