Nanoscale switching characteristics of nearly tetragonal BiFeO3 thin films

TL;DR

This study explores the nanoscale ferroelectric switching and phase transition behaviors of strain-engineered BiFeO3 thin films, revealing complex polarization dynamics and reversible structural changes with potential technological applications.

Contribution

It provides new insights into the ferroelectric switching mechanisms and phase transitions in nearly tetragonal BiFeO3 films, highlighting deviations from ideal symmetry and reversible phase changes.

Findings

Ferroelectric switching occurs with polarization deviating from the expected axis.

Large reversible tetragonal to rhombohedral phase transition observed.

Monoclinic (Cc) symmetry identified instead of P4mm tetragonal symmetry.

Abstract

We have investigated the nanoscale switching properties of strain-engineered BiFeO3 thin films deposited on LaAlO3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicate that the nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy we provide clear evidence of ferroelectric switching of the tetragonal phase but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. We also demonstrate a large and reversible, electrically-driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material which is promising for a plethora of applications.