Measurement of Initial Dielectric Constant of KH2PO4 by Thermal Noise Method

The dielectric constant of KH 2 PO 4 along the ferroelectric axis is measured at 1 kHz between 90 K and 130 K by a thermal noise method by which one can obtain the dielectric constant without applying Chi external field. The results well agree with the values obtained by the usual bridge method, using the external field of 1 to 20 V/cm, when extrapolation has been made toward zero external field. In the ferroelectric phase, the initial dielectric constants of the multi-domain crystal thus determined are of the order of 10 2 times as large in magnitude as those of the single domain crystal. It is concluded that the most part of the initial dielectric constants of multi-domain KH 2 PO 4 crystal are due to the domain wall motion. A simple model is proposed to give a relation between the domain wall motion and the initial dielectric constant.