Field-induced heterophase state in PbZrO3 thin films

Abstract

Applications of epitaxial antiferroelectrics face scientific challenges, such as limited understanding of degraded (in comparison to bulk) switching behavior and its relation to nanoscale structural organization. We report on an unusual structural response of ${\mathrm{PbZrO}}_{3}/{\mathrm{SrRuO}}_{3}/{\mathrm{SrTiO}}_{3}$ (001) heterostructures to precritical (lower than required for switching) electric fields. In situ x-ray diffraction shows a ferrielectric-like structure, which forms gradually upon increasing the applied field and makes up a heterophase state with the host antiferroelectric phase. The field-induced structure is similar to the antiferroelectric parent phase in the octahedral-tilt pattern, but differs from it in the lead-ion displacement pattern. The latter can be encoded as $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\uparrow}\phantom{\rule{4pt}{0ex}}\ensuremath{\downarrow}\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}$ provided that the antiferroelectric structure is encoded as $\ensuremath{\downarrow}\ensuremath{\downarrow}\ensuremath{\uparrow}\ensuremath{\uparrow}$. We propose that the unusual commensurateness (as opposed to the more ubiquitous incommensuration in similar materials) between the modulation periods of host and guest phases can be explained by accounting for the energy of heterophase boundaries, which is important in dense nanostructures due to the high surface-to-bulk ratio of nanodomains. An analysis using the ab-initio-correlated, but empirical (parametrized) energy model suggests that the observed field-induced structure is likely to be selected in ${\mathrm{PbZrO}}_{3}$ instead of the others in the case when the above commensuration effect is at play. The results point to the mechanism leading to the smearing of polarization-field loops in such heterostructures and suggest a perspective for the controlled creation of delicate dipolar orderings for ferroic-based memory.