Converse flexoelectricity around ferroelastic domain walls

TL;DR

This paper reveals that converse flexoelectricity plays a crucial role in shaping the asymmetric structures of ferroelastic domain walls, challenging traditional LGD theory and providing a new way to quantify flexoelectric coefficients.

Contribution

It introduces the incorporation of converse flexoelectricity into LGD theory to explain asymmetric ferroelastic domain wall structures and quantifies flexoelectric coefficients through combined experimental and computational methods.

Findings

Asymmetric structure of ferroelastic DWs explained by converse flexoelectricity.

Quantitative determination of flexoelectric coefficients around DWs.

Converse flexoelectricity is essential for understanding ferroelectric boundary phenomena.

Abstract

Domain walls (DWs) are ubiquitous in ferroelectric materials. Ferroelastic DWs refer to those who separate two domains with unparalleled polarizations (or two different ferroelastic variants). It is long believed that the structures of ferroelastic DWs can be simply explained from the perspective of mechanical and electric compatibilities in the framework of the Landau-Ginzburg-Devonshire (LGD) theory. Here we show that the converse flexoelectricity must be taken into account for fully describing the nature of ferroelastic DWs. In our work, an unexpected asymmetric structure is identified, which is beyond the prediction of the conventional LGD theory. By incorporating the converse flexoelectricity into the LGD theory and using it to analyze high-resolution images acquired by the aberration-corrected transmission electron microscope (TEM), we demonstrate that it is the converse flexoelectricity that result in the asymmetric structure. Moreover, the flexoelectric coefficient is derived by quantifying the converse flexoelectricity around the DWs. This quantification is deterministic in both the magnitude and sign of flexoelectric coefficients, by the mutual verification of atomic mapping and first-principles calculations. Our results suggest that the converse flexoelectricity cannot be neglected for understanding the ferroelastic DWs and other boundaries in ferroelectric materials.