Dynamic nonlinearity in epitaxial BaTiO3 films

Dynamic dielectric and piezoelectric constants of ferroelectrics increase proportionally to the amplitude of alternating electric field as a result of hysteretic Rayleigh-type motion of domain walls. Here a hysteresis-free quadratic field dependence of the dynamic dielectric response is experimentally demonstrated in the absence of domain walls in epitaxial BaTiO3 films. This extraordinary behavior is related to polar entities, whose presence is confirmed by the Vogel-Fulcher relaxation. The polar entities are ascribed to polarization fluctuations associated with lattice inhomogeneity.