Resonance and Relaxational Dispersions around the Domain Freezing Temperature in KH₂PO₄

The resonance and the relaxational dielectric dispersions of KH 2 PO 4 found in the ferroelectric phase were examined for ordinary and lossy specimens. The magnitudes of these two dispersions decreased markedly with crystal defects as well as with a d.c. bias field. A universal relation between the free dielectric constant ε x and the elastic stiffness C E 66 was found regardless of the specimens and their states examined. The small C E 66 and the large ε x were obtained for the specimens with high densities of domain walls. The mean value and the standard deviation of the energy parameter E in the relaxation time, τ=τ 0 exp { E /( T - T 0 )}, as well as the Vogel-Fulcher temperature T 0 decreased with the crystal defects. A possible model for the domain freezing is proposed in connection with these two dispersions.