Dielectric Dispersion Accompanied with the Domain Freezing in KH2PO4 Single Crystal

Dielectric dispersion relating to the “domain freezing” of KH₂PO₄ crystals has been observed in the frequency range from 110 Hz to 1 GHz. A clear dispersion of a relaxational type is found in the ferroelectric phase above the piezoelectric resonant frequency. This dispersion can be described with the relaxation time τ which obeys a Vogel-Fulcher law, τ{=}τ₀ \exp \{E/(T-T₀)\}, with a Gaussian distribution of the activation energy, f(E){=}(\sqrt{2π}σ)^-1 \exp \{-(E-E₀)²/2σ²\}. When the temperature is lowered, the relaxation times become longer; and crossover of the relaxational dispersion and the piezoelectric resonance arises around 100 K below which the dielectric constant of the free crystal decreases remarkably. It is concluded that the “domain freezing” is caused by the Vogel-Fulcher behavior of the relaxational dispersion.