Quantitative 3D mapping of chemical defects at charged grain boundaries in a ferroelectric oxide

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.