Strain Gradients in Epitaxial Ferroelectrics

TL;DR

This study investigates how internal strain gradients in epitaxial ferroelectric thin films affect their properties, emphasizing the importance of controlling strain gradients to maintain bulk-like ferroelectric behavior.

Contribution

It introduces a functional form for strain profiles in ferroelectric films and links strain gradients to property degradation via flexoelectric coupling.

Findings

Strain gradients are present across film thickness.

Strain gradients influence ferroelectric property degradation.

Controlling strain gradients is crucial for thin film performance.

Abstract

X-ray analysis of ferroelectric thin layers of Ba1/2Sr1/2TiO3 with different thickness reveals the presence of internal strain gradients across the film thickness and allows us to propose a functional form for the internal strain profile. We use this to calculate the direct influence of strain gradient, through flexoelectric coupling, on the degradation of the ferroelectric properties of thin films with decreasing thickness, in excellent agreement with the observed behaviour. This work highlights the link between strain relaxation and strain gradients in epitaxial films, and shows the pressing need to avoid strain gradients in order to obtain thin ferroelectrics with bulk-like properties.