Coexistence of multi-scale domains in ferroelectric polycrystals with non-uniform grain-size distributions

Engineering of ferroelectric domain structures enables direct control over the switching dynamics and is crucial for tuning the functional properties of ferroelectrics for various applications, ranging from capacitors to future nanoelectronics. Here, we investigate the domain formation in poly- and single-crystalline improper ferroelectric hexagonal DyMnO3. We show that a non-uniform grain-size distribution in the polycrystal facilitates the coexistence of multi-scale domains, varying by up to one order of magnitude in size. This unusual domain structure originates from an inverted domain-size/grain-size dependence that is intrinsic to the hexagonal manganite polycrystals, expanding previous studies toward non-uniform grain-size distributions. Our results demonstrate that the micrometer-sized grains in DyMnO3 represent individual ferroelectric units with a characteristic domain structure, giving a new dimension to domain engineering in ferroelectric polycrystals with non-uniform microstructures.