Polarization Instability in Polydomain Ferroelectric Epitaxial Thin Films and the Formation of Heterophase Structures

TL;DR

This paper develops a thermodynamic theory explaining how misfit strain induces polarization changes and heterophase structures in ferroelectric thin films, revealing stability conditions and dielectric anomalies associated with structural transformations.

Contribution

It introduces a new thermodynamic framework for understanding polarization instability and heterophase formation in epitaxial ferroelectric films under strain.

Findings

Critical misfit strain causes instability in domain structures.

Heterophase structures form at specific strain and temperature conditions.

Dielectric anomalies are linked to strain-induced structural changes.

Abstract

A thermodynamic theory is developed for dense laminar domain structures in epitaxial ferrolectric films. It is found that, at some critical misfit strain between the film and substrate, the 90 degrees c/a/c/a domain structure becomes unstable with respect to the appearance of the polarization component parallel to domain walls, which results in the formation of a heterophase structure. For PbTiO_3 and BaTiO_3 films, the stability ranges of polydomain and heterophase states are determined using "misfit strain - temperature" diagrams. Dielectric anomalies accompanying misfit-strain-driven structural transformations are described.