Effect of 90° Domain Walls on the Low-Field Permittivity of PbZr0.2Ti0.8O3 Thin Films

We report on the contribution of 90 degrees ferroelastic domain walls in strain-engineered PbZr0.2Ti0.8O3 thin films to the room-temperature permittivity. Using a combination of phenomenological Ginzburg-Landau-Devonshire polydomain thin-film models and epitaxial thin-film growth and characterization, the extrinsic or domain wall contribution to the low-field, reversible dielectric response is evaluated as a function of increasing domain wall density. Using epitaxial thin-film strain we have engineered a set of samples that possess a known quantity of 90 degrees domain walls that act as a model system with which to probe the contribution from these ferroelastic domain walls. We observe a strong enhancement of the permittivity with increasing domain wall density that matches the predictions of the phenomenological models. Additionally, we report experimentally measured bounds to domain wall stiffness in such PbZr0.2Ti0.8O3 thin films as a function of domain wall density and frequency.