Critical slowing down at ferroelectric transitions

Abstract

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.

Low-Frequency Dielectric Loss of Triglycine Sulfate

“…Unruh and Wahl, who claim Debye relaxation, report at the same temperature r-2x 10" 10 sec. 2 Hill and Ichiki, 2 who indicate a more complicated relaxation behavior, nevertheless find r ~ r 0 /2nr= 3 xlO" 10 sec, in excellent agreement with Unruh. Similarly, O'Brien and Litovitz 2 obtain from ultrasonic measurements r-2xl0" 10 sec, and an exponent r <*t' L .…”

Dynamic Critical Behavior of Ferroelectric Triglycine Sulfate from Dielectric Loss Measurements

“…The dielectric dispersion of TGS has been the object of several papers. 7 " 9 Luther and Muser's 8 data on this crystal show, in contrast to those of Hill and Ichiki, 7 a monodispersive behavior, with a single Debye relaxation time. Unruh and Wahl's 9 data confirm this monodispersive behavior and report a temperature dependence of the relaxation time r s ~e s x~\ (T-T c )/T c \ x with x^ 1.08.…”

On the validity of the molecular field theory in ferroelectrics

“…We repeated the measurement on TGS under the influence of the dc field (5) and found the same results. In contrast to these results, Unruh and Wahl (6,7) ob- The a r e a of the samples was about 1 cm and its thickness about 1 mm. The faces perpendicular to the ferroelectric axis were completely covered by vacuum evaporated A1 electrodes, Before insertion of the sample into the cell the crystal faces parallel to the ferroelectric axis were repolished.…”