Effective piezoelectric response of twin walls in ferroelectrics

TL;DR

This paper calculates the piezoelectric response of twin walls in tetragonal ferroelectrics, revealing significant enhancement factors and the influence of polarization gradients, with implications for nanoscale electromechanical characterization.

Contribution

It introduces a theoretical framework for predicting the piezoelectric response of twin walls considering polarization gradients, electrostriction, and flexoelectric effects.

Findings

Piezoelectric response can be enhanced up to 1000 times near twin walls.

Response is insensitive to flexoelectric coupling but sensitive to polarization gradient coefficients.

Local electromechanical response can inform about gradient terms and pinning mechanisms.

Abstract

The effective piezoelectric coefficients of twin walls in tetragonal ferroelectric are calculated in the framework of decoupling approximation and Landau-Ginzburg-Devonshire theory allowing for polarization gradient terms, electrostriction and flexoelectric coupling. Using an example of piezoelectric response of a1-a2 twins to a homogeneous electric field, we show that the response is almost independent on the flexoelectric coupling, but is very sensitive to the values of polarization gradient coefficients. This behavior originates from the strong coupling between local dielectric susceptibility and the gradient coefficients. The enhancement of piezoelectric response from 10% up to a factor of 103 times is predicted. The local electromechanical response of the domain walls can thus provide information on the gradient terms in GLD expansion and pinning mechanisms of the ferroelectric domain walls. The observability of these effects by the piezoresponse force microscopy of electroded structures and impact on the functional properties of the systems with dense domain structures is analyzed