Elucidating the Physics of Flexoelectricity Through First-Principles Calculations of Complex Materials

Suny At Stony Brook, Stony Brook NY

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports computational and theoretical research, and education on flexoelectricity. If a strain gradient is applied to a piece of an electrically insulating material, for example by bending it, a voltage will be created across the material. This effect, known as flexoelectricity, has attracted attention because of the possibility for technological applications such as actuators, deflection sensors, and energy harvesters. Also, flexoelectricity is important since modern nanoscale electronic devices may contain large unintentional strain gradients, and thus flexoelectricity may play a crucial role in their properties. A pivotal missing ingredient in developing a quantitative understanding of flexoelectricity has been the lack of an efficient and accurate computational methodology to predict the flexoelectric response of a material. In this project, the PI will build on predictive methodology he has developed with collaborators and apply it to explore and characterize the flexoelectric response in materials more complex than could be theoretically investigated before. The goal of this research is to better understand what materials properties lead to an especially large flexoelectric response, which can be utilized for technological applications. This will also help identify materials with a suppressed flexoelectric response, which will be useful in cases where the effects of unintentional strain gradients need to be mitigated. The research activities in this project serve as an ideal platform for the education and mentoring of graduate and undergraduate students in diverse aspects of condensed matter physics, materials science, and computational science. TECHNICAL SUMMARY This award supports computational and theoretical research, and education on flexoelectricity. The flexoelectric effect, where electrical polarization is induced by a strain gradient, is universal in all insulators. As devices shrink to the micro and nanoscale, large strain gradients can occur, and therefore the flexoelectric effect may play a significant role in their properties. Also, flexoelectricity can be exploited for novel paradigms of electromechanical manipulation of materials, such as the development of piezoelectric "metamaterials" constructed from nonpiezoelectric constituents, or mechanical switching of ferroelectric polarization. In this work, the PI will explore and elucidate the physics of flexoelectricity in complex materials, utilizing recently developed density functional perturbation theory methodology for accurately and efficiently calculating flexoelectric coefficients. The PI will investigate the flexoelectric response in two materials systems with the goal of addressing significant open questions relating to how flexoelectricity is generally manifested in materials. The PI will focus on two-dimensional, van der Waals bonded materials including, boron nitride and the transition-metal dichalcogenides, and "distorted" perovskite oxides with lower symmetry than the cubic parent structure. The PI will systematically explore how symmetry, mechanical, and dielectric properties influence the flexoelectric response, and how this response can be measured or manipulated by forming heterostructures or superlattices, or modifying surface properties. The materials study performed in this work, will enable the identification of specific materials and material systems that have large flexoelectric responses which may be useful for applications, as well as those with small responses, which are necessary in applications where gradients are present unintentionally and flexoelectricity must be mitigated. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.