Engineering of Atomic-Scale Flexoelectricity at Grain Boundaries

TL;DR

This paper demonstrates how grain boundary engineering can induce significant atomic-scale flexoelectricity in dielectric materials, enabling tunable electromechanical properties at the nanoscale.

Contribution

It introduces a novel approach to generate large strain gradients at atomic scale via grain boundary manipulation, enhancing flexoelectric effects in non-piezoelectric materials.

Findings

Achieved a strain gradient of ~1.2 nm^-1 at grain boundaries.

Induced flexoelectric polarization up to ~38 μC/cm^2.

Showed general applicability across different dielectric materials.

Abstract

Flexoelectricity is a type of ubiquitous and prominent electromechanical coupling, pertaining to the response of electrical polarization to mechanical strain gradients while not restricted to the symmetry of materials. However, large elastic deformation in most solids is usually difficult to achieve and the strain gradient at minuscule is challenging to control. Here we exploit the exotic structural inhomogeneity of grain boundary to achieve a huge strain gradient (~ 1.2 nm-1) within 3 ~ 4 unit-cells, and thus obtain atomic-scale flexoelectric polarization up to ~ 38 {\mu}C/cm2 at a 24 LaAlO3 grain boundary. The nanoscale flexoelectricity also modifies the electrical activity of grain boundaries. Moreover, we prove that it is a general and feasible way to form large strain gradients at atomic scale by altering the misorientation angles of grain boundaries in different dielectric materials. Thus, engineering of grain boundaries provides an effective pathway to achieve tunable flexoelectricity and broadens the electromechanical functionalities of non-piezoelectric materials.