Low-symmetry monoclinic phase stabilized by oxygen octahedra rotations in thin strained EuxSr1-xTiO3 films

TL;DR

This study uses theoretical modeling to reveal a stable low-symmetry monoclinic phase in strained EuxSr1-xTiO3 thin films, characterized by oxygen octahedra rotations, in-plane polarization, and enhanced piezoelectric properties.

Contribution

It demonstrates the stabilization of a monoclinic phase by oxygen octahedra tilts in strained films, highlighting its impact on polarization and electromechanical responses.

Findings

Monoclinic phase stabilized by oxygen octahedra tilts in strained films.

Presence of multiple twin domains enhances piezoelectric response.

Additional polarization and electromechanical effects occur at twin boundaries.

Abstract

Using Landau-Ginzburg-Devonshire theory and phase field modeling, we explore the complex interplay between the long-range structural order parameter (oxygen octahedron rotations) and polarization in EuxSr1-xTiO3 thin epitaxial films. In biaxially tensile strained films, we discover the presence of a low symmetry monoclinic phase with in-plane ferroelectric polarization that is stabilized by antiferrodistortive oxygen octahedra tilts. The monoclinic phase is stable in a wide temperature range, and is characterized by the large number of energetically equivalent polar and structural twin domains, which stimulates easy twinning of the film and thus enhances its effective piezoelectric response. The flexoelectric coupling and rotostriction give rise to additional spontaneous polarization, piezo- and pyro-electricity in the ferroelastic twin boundaries.