The dielectric dispersion of ferroelectrics is investigated within the scope of a model developed by Thomas, describing the phase transitions in solids as feedback phenomena. The relations between the eigenfrequencies of the uncoupled and the coupled systems are given and the physical importance of electric boundary conditions is demonstrated. The dielectric relaxation of triglycine sulfate is reexamined. It could be proved that this material shows a simple Debye type relaxation even in the immediate vicinity of the Curie point. No deviations occur with respect to the results of the molecular field approximation.
Multilayer piezoelectric ceramics promise to close the gap between the high electric field strengths required to generate the largest possible deformation in piezoelectric ceramics and the low supply voltages (5 V to 15 V) conventional in present-day electronics.Multilayer PZT ceramics with ceramic layer thicknesses down to 30 pm were prepared using a metal injection process which, especially from the economic aspect, is of very great interest.In small-signal operation these multilayer ceramics exhibit a piezoelectric strain constant that is only about 10% to 15% smaller than that of plain PZT of like composition. Using a series model this can be traced back to the clamping effect of the inactive electrodes. At large signal amplitudes the increased no-load deflection of piezoelectric actuators otherwise caused by 90" domain wall displacements is not fully effective. Multilayer ceramic actuators attain the same blocking forces as those of actuators made of plain ceramic.
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