Strain-Driven Structure-Ferroelectricity Relationship in hexagonal TbMnO$_3$ Films

TL;DR

This study investigates how strain influences the structural and ferroelectric properties of hexagonal TbMnO$_3$ thin films, revealing phase transitions and microstructural inhomogeneities driven by temperature and stress relaxation.

Contribution

It provides new insights into the strain-driven phase transitions and ferroelectric behavior in high-quality epitaxial h-TMO films, combining multiple characterization techniques.

Findings

Identified a phase transition from P63mc to P63mcm at ~800 K.

Observed ferroelectric domain vanishing at 410 K.

Showed stress relaxation affects structure and ferroelectricity.

Abstract

Thin films and heterostructures of hexagonal manganites as promising multiferroic materials have attracted a considerable interest recently. We report structural transformations of high quality epitaxial h-TMO/YSZ(111) films, analyzed by means of various characterization techniques. A phase transition from P63mc to P63mcm structure at TC~800 K was observed by temperature dependent Raman spectroscopy and optical ellipsometry. The latter probing directly electronic system, indicates its modification at the structural phase transition likely due to charge transfer from oxygen to Mn. In situ transmission electron microscopy (TEM) of the lamella samples displayed an irreversible P63mc-P63mcm transformation and vanishing of ferroelectric domains already at 410 K. After the temperature cycling (300K-1300K-300K) the room temperature TEM of h-TMO films revealed an inhomogeneous microstructure, containing ferroelectric and paraelectric nanodomains with P63mc and P63mcm structure, respectively. We point out a strong influence of stress relaxation, induced by temperature and by constrained sample geometry onto the structure and ferroelectricity in strain-stabilized h-TMO thin films.