  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.
