Dielectric Dispersion of Ferroelectric Ceramics and Single Crystals by Sound Generation in Piezoelectric Domains

Periodic domain configurations with alternating 180° and 90° domains are not completely mechanically clamped up to microwave frequencies. Above the acoustic resonance of the ferroelectric sample, therefore, the dielectric constant comprises contributions which can be attributed to the free dielectric constant. Up to microwave frequencies the domains are piezoelectrically active; they emit longitudinal and shear thickness waves into the surroundings which cause dielectric loss in the sample. The dielectric step from the free condition to the clamped condition at the relaxation frequency is on the order of Δε∼ 10–100. This step is much smaller than the step caused by the emission of shear waves from 90° domain walls.