Flexoelectricity induced increase of critical thickness in epitaxial ferroelectric thin films

TL;DR

This paper demonstrates that flexoelectricity can significantly increase the critical thickness of epitaxial BaTiO3 ferroelectric thin films, especially in tensile conditions, affecting their polarization stability.

Contribution

It introduces a phenomenological model showing flexoelectricity's role in enhancing critical thickness in ferroelectric thin films, a novel insight into ferroelectric stability.

Findings

Flexoelectricity increases the critical thickness in tensile films.

Flexoelectric effects are trivial in compressive films.

Films remain in a uni-polar state below the critical thickness.

Abstract

Flexoelectricity describes the coupling between polarization and strain/stress gradients in insulating crystals. In this paper, using the Landau-Ginsburg-Devonshire phenomenological approach, we found that flexoelectricity could increase the theoretical critical thickness in epitaxial BaTiO3 thin films, below which the switchable spontaneous polarization vanishes. This increase is remarkable in tensile films while trivial in compressive films due to the electrostriction caused decrease of potential barrier, which can be easily destroyed by the flexoelectricity, between the ferroelectric state and the paraelectric state in tensile films. In addition, the films are still in a uni-polar state even below the critical thickness due to the flexoelectric effect.