Study of strain effect on in-plane polarization in epitaxial BiFeO3 thin films using planar electrodes

TL;DR

This study investigates how epitaxial strain influences in-plane polarization in BiFeO3 thin films, using innovative planar electrodes to directly measure polarization, supported by first-principles calculations, revealing large in-plane polarization at high strain levels.

Contribution

It introduces a novel planar electrode method for direct in-plane polarization measurement in ultrathin strained films, validated by experimental and theoretical agreement.

Findings

Large in-plane polarization (~44 μC/cm²) at high misfit strain (-4.4%.)

Pure Tetragonal-like phase observed under high strain.

Method enables direct measurement of in-plane properties in ultrathin films.

Abstract

Epitaxial strain plays an important role in determining physical properties of perovskite ferroelectric oxide thin films. However, it is very challenging to directly measure properties such as polarization in ultrathin strained films using traditional sandwich capacitor devices, because of high leakage current. We employed a planar electrode device with different crystallographical orientations between electrodes along different electric field orientation to directly measure the in-plane polarization-electric field (P-E) hysteresis loops in fully strained thin films. At high misfit strains such as -4.4%, the pure Tetrogonal-like phase is obtained and its polarization vector is constrained to lie in the (010) plane with a significantly large in-plane component, ~44 {\mu}C/cm2. First-principle calculations are carried out in parallel, and provide a good agreement with the experimental results. Our results pave the way to design in-plane devices based on T-like BFO and the strategy proposed here can be expanded to study all other similar strained multiferroic ultrathin films.