Directly Observing the Evolution of Flexoelectricity at the Tip of Nanocracks

Abstract

As an electromechanical coupling between strain gradients and polarization, flexoelectricity is largely enhanced at the nanoscale. However, directly observing the evolution of flexoelectric fields at the nanoscale usually suffers from the difficulty of producing strain gradients and probing electrical responses simultaneously. Here, we introduce nanocracks in SrTiO 3, Ba 0.67 Sr 0.33 TiO 3, and TiO 2 samples and apply continuously varying mechanical loading to them, and as a result, huge strain gradients appear at the crack tip and result in a significant flexoelectric effect. Then, using atomic force microscopy, we successfully measure the evolution of flexoelectricity around the crack tips. For the case of SrTiO 3, the maximum induced electric field reaches 11 kV/m due to the tensile load increasing. The proposed method provides a reliable way to identify the significance of the flexoelectric effect. It may also open a new avenue for the study of flexoelectricity involving multiple physics phenomena including flexoelectronics, the flexo-photovoltaic effect, and others.

The transparent photovoltaic NiO/TiO2 orderly nanoarray pn junction via synergism of AgInS2 quantum dots and Ti3+ self-doping

“…20,21 In addition to the ease of preparation and physical-chemical stability enabling its use in various occasions, the unique electronic structure and higher intrinsic carrier concentration are significant factors. 22,23 For example, He et al have fabricated TiO 2 @MAPbI 3 nanoarrays with decent photovoltaic response, 24 and Zheng et al have fabricated n-TiO 2 /p-NiO heterojunctions for achieving remarkable self-powered UV photodetectors. 25 Compared with conventional film photovoltaic devices, orderly nanoarrays can further increase the solar efficiency and stability via its microstructure.…”

Nanoscale Enhancement of the Local Optical Conductivity near Cracks in Metallic SrRuO3 Film

“…Recently, there have been several reports on an emergent phenomena from nanocracks in insulating oxide materials. − For examples, Abdollahi et al . theoretically predicted the relationship between the direction of the polar axis and crack propagation in the piezoelectric material .…”

“…showed the evolution of strain relaxation and their flexoelectricity. 15 Yeo et al . reported that the electrical conductivity near the STO crack wall could be enhanced by a factor of 10 4 by the migration of oxygen vacancies.…”

“…By performing nanoindentation experiments on STO films, Xu et al . showed the evolution of strain relaxation and their flexoelectricity . Yeo et al .…”

“…14 By performing nanoindentation experiments on STO films, Xu et al showed the evolution of strain relaxation and their flexoelectricity. 15 Yeo et al reported that the electrical conductivity near the STO crack wall could be enhanced by a factor of 10 4 by the migration of oxygen vacancies. 16 Most of these works can be interpreted in terms of the microscopic charge redistribution in the insulating oxides near the nanocrack regions.…”