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.