Modelling the microwave dielectric response of ‘normal’ ferroelectrics

Ferroelectric materials present a dielectric dispersion in the frequency range of 0.1–1 GHz, which has been attributed to either a relaxation or a resonance process. However, the results reported in the literature have not been conclusive enough to distinguish clearly each process. In this work, the dielectric response of La-modified lead titanate ferroelectric ceramics were carefully investigated in both unpoled and poled state in the frequency range of 0.05–1 GHz. The results revealed clearly that the dielectric dispersion is highly anisotropic and can be associated with an overdamped process (relaxation-like) or a damped resonance process, which depends on the measuring direction. It was found that the dielectric dispersion can be modelled as a resonance process, which is either damped or overdamped when the ferroelectric or the ferroelastic contribution prevails.