ANOMALOUS DIELECTRIC BEHAVIOR OF KH2PO4 TYPE CRYSTALS IN THE FERROELECTRIC PHASE

Experimental studies on the dielectric constants of KH2PO4 type ferroelectrics below the Curie temperature T(c) are reviewed with special emphasis to the anomalously large dielectric constant and its abrupt decrease in the low temperature region called domain freezing. The origin of the large dielectric constant below T(c) is explained in connection with the elastic softening in the multidomain crystals. The domain freezing is closely related to the dielectric dispersion observed in the multidomain crystals. The relaxation time tau of the dispersion obeys approximately the Vogel-Fulcher law, which is widely found in dipole glasses near their freezing temperatures. The anomalous increase in tau provides the abrupt decrease in the dielectric constant around the domain freezing temperature.