Nanosecond Phase Transition Dynamics in Compressively Strained Epitaxial BiFeO3

TL;DR

This study demonstrates nanosecond electric field pulses can reversibly induce phase transformations in strained BiFeO3 thin films, revealing rapid dynamics and measurable piezoelectric responses, with insights from density functional theory.

Contribution

It introduces a method for ultrafast, reversible phase switching in BiFeO3 using nanosecond electric pulses, supported by experimental and theoretical analysis.

Findings

Up to 20% of BFO volume transforms between phases with electric pulses.

Transformation occurs on nanosecond timescales limited by charging time.

Piezoelectric expansion reaches up to 0.1% strain.

Abstract

A highly strained BiFeO3 (BFO) thin film is transformed between phases with distinct structures and properties by nanosecond-duration applied electric field pulses. Time-resolved synchrotron x-ray microdiffraction shows that the steady-state transformation between phases is accompanied by a dynamical component that is reversed upon the removal of the field. Steady-state measurements reveal that approximately 20% of the volume of a BFO thin film grown on a LaAlO3 substrate can be reproducibly transformed between rhombohedral-like and tetragonal-like phases by electric field pulses with magnitudes up to 2 MV/cm. A transient component, in which the transformation is reversed following the end of the electric field pulse, can transform a similar fraction of the BFO layer and occurs rapidly time scale limited by the charging time constant of the thin film capacitor. The piezoelectric expansion of the tetragonal-like phase leads to a strain of up to 0.1%, with a lower limit of 10 pm/V for the piezoelectric coefficient of this phase. Density functional theory calculations provide insight into the mechanism of the phase transformation showing that imparting a transient strain of this magnitude favors a transformation from rhombohedral-like to tetragonal-like phase.