Kazuoki Kuramoto

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 e 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 e 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.

Dielectric dispersion accompanied with the domain freezing in KH2PO4 single crystal

Dielectric dispersion relating to the “domain freezing” of KH 2 PO 4 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=τ 0 exp { E /( T - T 0 )}, with a Gaussian distribution of the activation energy, \(f(E){=}(\sqrt{2\pi}\sigma)^{-1} \exp \{-(E-E_{0})^{2}/2\sigma^{2}\}\). 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.

Mechanism of domain freezing in KDP type ferroelectrics

Abstract The dielectric relaxation time τ of KH2PO4 and CsH2AsO4 was investigated in the ferroelectric phase through measurements of the complex dielectric constants in the frequency range between 103 Hz and 109 Hz. Anomalous increase in τ near the domain freezing temperature Tf , considered together with the relation between the free dielectric constant ec and the the elastic stiffness C 66 E , suggests that dipolar reorientation in the domain walls has a close relation to the hardening of the crystal around Tf , which originates the domain freezing.

Nonlinear dielectric constant of KH2PO4 in the ferroelectric phase

Abstract Nonlinear components of the dielectric constant of KH2PO4 along the c-axis have been measured in the ferroelectric phase, using the Digital Fourier Transform technique. The digital sampling of the P-E curve at 0.1 Hz was made for thick (6.47 mm) and thin (0.10 mm) specimens down to about 80 K. Contributions of the nonlinear components are important in the thick specimen even when the small electric field of less than 1 V/cm is applied.

Dielectric Dispersion in KH2PO4 below 10 K

Complex dielectric constants of KH 2 PO 4 along the c - and a -axes have been measured in the frequency range from 10 Hz to 20 kHz. Dielectric dispersions of relaxation type with small loss peaks have been observed at temperatures below 10 K in both directions. Arrhenius plots of the relaxation frequencies give extremely small values of activation energies, 0.014 eV for the c -axis and 0.004 eV for the a -axis, respectively.

Isotope effect of domain freezing in KH2PO4 single crystals

Abstract Complex dielectric constants along the c-axis were measured in mixed crystals K(H1−x D x )2PO4(x = 0 ∼ 0.9). Remarkable effect of deuteration on domain freezing was recognized.