  Polar discontinuities and structural changes at oxide interfaces can give
rise to a large variety of electronic and ionic phenomena. Related effects have
been intensively studied in epitaxial systems, including ferroelectric domain
walls and interfaces in superlattices. Here, we investigate the relation
between polar discontinuities and the local chemistry at grain boundaries in
polycrystalline ferroelectric ErMnO3. Using orientation mapping and different
scanning probe microscopy techniques, we demonstrate that the polycrystalline
material develops charged grain boundaries with enhanced electronic
conductance. By performing atom probe tomography measurements, we find an
enrichment of erbium and a depletion of oxygen at all grain boundaries. The
observed compositional changes translate into a charge that exceeds possible
polarization-driven effects, demonstrating that structural phenomena rather
than electrostatics determine the local chemical composition and related
changes in the electronic transport behavior. The study shows that the charged
grain boundaries behave distinctly different from charged domain walls, giving
additional opportunities for property engineering at polar oxide interfaces.
