Vortex domain structures induced by strain gradient reduce ferroelectric brittleness

The shear failure of ferroelectric material is hard to investigate because of the electromechanical properties of the material and its high speed at the nanoscale. The brittleness of the material also limits the potential applications of these materials in ferroelectric devices. In this work, we use atomic simulations to investigate simultaneously the dynamic process of shearing and domain evolution to clarify how these affect the dielectric properties of the material. On the atomic scale, an apparent polarization vortex-like domain structure appears at the tip of the shear band with 180 degrees and 90 degrees domain walls on each side. These complex domain structures are attributed to the flexoelectric effect induced by a strain gradient. An external electric field is introduced to hinder domain switching and prevent misfit strain regions, which accelerates the shearing process by reducing accumulated energy. The results reveal that polarization vortices impede shear failure and the mechanism allows us to toughen ferroelectric materials by manipulating the domain structure.