Dielectric Dispersion in KH2PO4Single Crystal at Low Temperatures

Complex dielectric constants of KH 2 PO 4 single crystals along the a - and the c -axes have been measured in the temperature range from 2.5 K to 30 K at frequencies between 10 Hz and 20 kHz. Dielectric dispersions with small loss peaks are observed in both directions. The dispersion along the c -axis (dispersion C) is found only in the multidomain crystal, whereas the dispersion along the a -axis (dispersion A) is insensitive to the domain structure. The relaxation frequency of the dispersion C obeys the Arrhenius' relation with the extremely small activation energy of 0.019 eV. A large deviation from the Arrhenius' relation is found for the dispersion A. The temperature dependence of the dispersion frequency and the profile of the dispersion curves of the dispersion A are well explained by a damped oscillator model with a Gaussian distribution of the resonant frequencies.