Ferroelectric ceramics: defects and dielectric relaxations

Dielectric relaxations in ferroelectric ceramics occur at various frequenci es, depending on the type of chemical or physical defects. These defects de pend on either intrinsic or extrinsic heterogeneities due to special heat t reatments (quenching, annealing,...), ionic substitutions, grain size addit ives, and grain boundary nature. The value of the relaxation frequency f(r) increases from about 10(2) to 10(12) Hz as the scale of the defect phenome non decreases from microstructure, to nanostructure, to unit-cell, to atomi c vibrations. This type of study requires a pluridisciplinary approach invo lving solid state chemistry, materials science, solid state physics and var ious industrial aspects. The applications in the area of electronic ceramic s are related to the value of f(r). In absorbants, the usable frequency is close to f(r), whereas it is far from f(r) in good insulators. In view of n umerous experimental examples, a classification is proposed to predict whic h materials may be suitable for a given application.