Flexoelectricity

Abstract

Professor Pradeep Sharma will give a Plenary Lecture for Track 7 Dynamics, Vibration and Control at the IMECE Congress of the ASME in Columbus, OH, on Tuesday, November 1, 9:15AM - 10:00AM with title: Flexoelectricity and Electrets. The Abstract and Bio can be found at https://event.asme.org/IMECE/Program/Track-Plenary-Speakers. The lecture is sponsored by the Applied Mechanics Division of the ASME.

Dear colleagues,
We invite you to see the preprint of our new paper "Flexoelectricity in soft elastomers and the molecular mechanisms underpinning the design and emergence of giant flexoelectricity" that will appear in PNAS. Here we present a molecular-to-continuum scale theory for the flexoelectric effect in elastomers. The theory unveils a mechanism for achieving giant flexoelectricity--which finds support in prior experimental results; it is then leveraged for designing elastomers for 1) piezoelectricity, 2) tuning the direction of flexoelectricity, and 3) flexoelectricity which is invariant with respect to spurious deformations (https://doi.org/10.1073/pnas.2102477118).

Abstract

Abstract

Can the mere crumpling of a paper produce electricity? An inhomogeneous strain can induce electrical response in all dielectrics and not just piezoelectric materials. This phenomenon of flexoelectricity is rather modest unless unusually large strain gradients are present. In this paper, we analyze the crumpling of thin elastic sheets and establish scaling laws for their electromechanical behavior to prove that an extremely strong flexoelectric response is achieved at submicron length scales.

I would like to share our recent work published in Nature Communications.

I would like to share our recent work published in Physical Review Letters.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.205502

Beyond piezoelectricity: Flexoelectricity in solids

Jiawang Hong

School of Aerospace Engineering, Beijing Institute of Technology

1. Introduction

Bones generate electricity under pressure, and this electromechanical behavior is thought to be essential for bone's self-repair and remodeling properties. The origin of this response is attributed to the piezoelectricity of collagen, which is the main structural protein of bones. In theory, however, any material can also generate voltages in response to strain gradients, thanks to the property known as flexoelectricity.

Abstract

This paper presents a design methodology based on a combination of isogeometric analysis (IGA),

level set and point wise density mapping techniques for topology optimization of piezoelectric /

flexoelectric materials. The fourth order partial differential equations (PDEs) of flexoelectricity,

which require at least C 1 continuous approximations, are discretized using Non-Uniform Rational

B-spline (NURBS). The point wise density mapping technique with consistent derivatives is

This work has been recently published in Nature Nanotechnology. 

Cracks generate the largest strain gradients that any material can withstand. Flexoelectricity (coupling between strain gradient and polarization) must therefore play an important role in fracture physics. Here we use a self-consistent continuum model to evidence two consequences of flexoelectricity in fracture: the resistance to fracture increases as structural size decreases, and it becomes asymmetric with respect to the sign of polarization. The latter phenomenon manifests itself in a range of intermediate sizes where piezo- and flexoelectricity compete.

Flexoelectricity is an electromechanical effect coupling polarization to strain gradients. It fundamentally differs from piezoelectricity because of its size-dependence and symmetry. Flexoelectricity is generally perceived as a small effect noticeable only at the nanoscale. Since ferroelectric ceramics have a particularly high flexoelectric coefficient, however, it may play a significant role as piezoelectric transducers shrink to the sub-micrometer scale.

Flexoelectricity is a size-dependent electromechanical mechanism coupling polarization and strain gradient. It exists in a wide variety of materials, and is most noticeable for nanoscale objects, where strain gradients are higher. Simulations are important to understand flexoelectricity because experiments at very small scales are difficult, and analytical solutions are scarce.

Most technologically relevant ferroelectrics typically lose piezoelectricity above the Curie temperature. This limits their use to relatively low temperatures. In this Letter, exploiting a combination of flexoelectricity and simple functional grading, we propose a strategy for high-temperature electromechanical coupling in a standard thin film configuration.

In a piezoelectric material an applied uniform strain can induce an electric polarization (or vice-versa). Crystallographic considerations restrict this technologically important property to non-centrosymmetric systems. It can be shown both mathematically and physically, that a non-uniform strain can potentially break the inversion symmetry and induce polarization even in non-piezoelectric dielectrics.