Control of domain states in rhombohedral PZT films via misfit strains and surface charges

TL;DR

This study uses Landau-Ginzburg-Devonshire theory to numerically analyze how misfit strains, surface charges, and flexoelectric effects influence domain structures and polarization in rhombohedral PZT thin films, revealing strain-dependent phases and topological states.

Contribution

It provides a detailed numerical analysis of the combined effects of misfit strain, surface charges, and flexoelectricity on domain configurations in rhombohedral PZT films, highlighting the formation of topological states.

Findings

Misfit strain determines domain structure and polarization directions.

Surface screening influences domain closure and single-domain states.

Flexoelectric effect significantly impacts skyrmion topological states.

Abstract

Using the Landau-Ginzburg-Devonshire theory, an influence of the misfit strain and surface screening charges, as well as the role of the flexoelectric effect, have been studied by numerical modelling in the case of a rhombohedral lead zirconate-titanate ferroelectric/ferroelastic thin film with an anisotropic misfit produced by a substrate. It was established that the magnitude and sign of the misfit strain influence the domain structure and predominant directions of the polarization vector, providing misfit-dependent phases with different favourable polarization components. Whilst strong enough compressive misfit strains favour a phase with an orthorhombic-like polarization directions, strong tensile misfits only yield in-plane polarization components. The strength of surface screening is seen to condition the existence of closure domain structures and, by increasing, supports the single-domain state depending on the value of the misfit strain. The flexoelectric effect exhibits a weak influence on the phase diagram of multi-domain states when compared with the phase diagram of single-domain states. Its effect, however, becomes significant in the case of skyrmion topological states, which spontaneously form near the film surface when compressive misfit strains are applied. Cooperative influence of the misfit strain, surface screening charges and temperature can set a thin rhombohedral ferroelectric film into a number of different polar and structural states, whereby the role of the flexoelectric effect is pronounced for topologically nontrivial structures.