Nanosecond Phase Transition Dynamics in Compressively Strained Epitaxial BiFeO3

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.