  We demonstrate a novel approach to the structural and electronic property
modification of perovskites, focusing on Pr$_2$CuO$_4$, an undoped parent
compound of a class of electron-doped copper-oxide superconductors. Currents
were passed parallel or perpendicular to the copper-oxygen layers with the
voltage ramped up until a rapid drop in the resistivity was achieved, a process
referred to as "flash". The current was then further increased tenfold in
current-control mode. This state was quenched by immersion into liquid
nitrogen. Flash can drive many compounds into different atomic structures with
new properties, whereas the quench freezes them into a long-lived state.
Single-crystal neutron diffraction of as-grown and modified Pr$_2$CuO$_4$
revealed a $\sqrt{10}$x$\sqrt{10}$ superlattice due to oxygen-vacancy order.
The diffraction peak intensities of the superlattice of the modified sample
were significantly enhanced relative to the pristine sample. Raman-active
phonons in the modified sample were considerably sharper. Measurements of
electrical resistivity, magnetization and two-magnon Raman scattering indicate
that the modification affected only the Pr-O layers, but not the Cu-O planes.
These results point to enhanced oxygen-vacancy order in the modified samples
well beyond what can be achieved without passing electrical current. Our work
opens a new avenue toward electric field/quench control of structure and
properties of layered perovskite oxides.
