Octahedral rotation patterns in strained EuFeO3 and other Pbnm perovskite films: Implications for hybrid improper ferroelectricity

TL;DR

This study investigates how epitaxial strain influences octahedral rotation patterns in Pbnm-type perovskite films, revealing strain-dependent behaviors and substrate imprinting effects that impact hybrid improper ferroelectricity.

Contribution

It provides a comprehensive analysis of strain effects on octahedral rotations in EuFeO3 and related films, highlighting substrate imprinting as a robust method for controlling ferroelectric properties.

Findings

Compressive strain favors a-a+c- and a+a-c- rotation patterns.

Tensile strain weakly favors a-a-c+ structures.

Substrate imprinting can override strain effects in EuFeO3 films.

Abstract

We report the relationship between epitaxial strain and the crystallographic orientation of the in-phase rotation axis and A-site displacements in Pbnm-type perovskite films. Synchrotron diffraction measurements of EuFeO3 films under strain states ranging from 2% compressive to 0.9% tensile on cubic or rhombohedral substrates exhibit a combination of a-a+c- and a+a-c- rotational patterns. We compare the EuFeO3 behavior with previously reported experimental and theoretical work on strained Pbnm-type films on non-orthorhombic substrates, as well as additional measurements from LaGaO3, LaFeO3, and Eu0.7Sr0.3MnO3 films on SrTiO3. Compiling the results from various material systems reveals a general strain dependence in which compressive strain strongly favors a-a+c- and a+a-c- rotation patterns and tensile strain weakly favors a-a-c+ structures. In contrast, EuFeO3 films grown on Pbnm-type GdScO3 under 2.3% tensile strain take on a uniform a-a+c- rotation pattern imprinted from the substrate, despite strain energy considerations that favor the a-a-c+ pattern. These results point to the use of substrate imprinting as a more robust route than strain for tuning the crystallographic orientations of the octahedral rotations and A-site displacements needed to realize rotation-induced hybrid improper ferroelectricity in oxide heterostructures.