Electromechanical analysis of direct and converse flexoelectric effects under a scanning probe tip. (September 2020)

• Record Type: Journal Article
• Authors: Liu, Wenyuan; Deng, Feng; Xie, Shaoxiong; Shen, Shengping; Li, Jiangyu
• Is Part Of: Journal of the mechanics and physics of solids. Volume 142(2020)
• Publication Date: 2020-09
• Subjects: Flexoelectric effect -- Piezoresponse force microscopy -- Mixed finite element method; Mechanics, Applied -- Periodicals; Solids -- Periodicals; Mechanics -- Periodicals; Mécanique appliquée -- Périodiques; Solides -- Périodiques; Mechanics, Applied; Solids; Periodicals; 531.05
• DOI: 10.1016/j.jmps.2020.104020
• Languages: English
• ISSNs: 0022-5096

Abstract

Highlights: Mixed finite element method to analyze flexoelectricity under a scanning probe Mixed FEM validated by analytic solutions for simple axially-symmetric tubes Flexoelectricity accounts for less than 20% of the typical measured piezoresponse Mechanical switching via flexoelectricity only possible for upward polarization Mechanical switching zone confined to a small region under PFM tip Abstract: Flexoelectricity refers to phenomena that polarization is coupled with strain gradient and stress is coupled with electric gradient. It occurs in all dielectrics, and becomes significant under a sharp conductive tip in piezoresponse force microscopy (PFM), under which large gradients in electromechanical field naturally arise. Here we analyze direct and converse flexoelectric effects under such a scanning probe, using mixed finite element method (FEM) developed under the phenomenological continuum framework. The FEM was first validated by analytic solutions for simple axially-symmetric tubes, and then applied to analyze two different modes of PFM experiments. It reveals that the flexoelectric effect accounts for less than 20% of the measured piezoresponse in a typical piezoelectric material, while mechanical switching via flexoelectricity is only possible for ferroelectric materials having upward polarization, with the switching zone confined to a small region near surface. These analyses explain a number of experimental observations well, and shed insight into complex electromechanical phenomenon under a sharp PFM tip. The theoretical and computational framework developed can also be applied to study flexoelectric effect in other structural configurations.