We have made a precision measurement to obtain dielectric functions ε' and ε'' in the dipole glass system of deuterated rubidium ammonium dihydrogen phosphate (DRADP-x, x=0.4) in the frequency range from 10mHz to 10MHz. Tikhonov regularization method was applied in the analysis of the experimental data to obtain the relaxation time distribution g(τ, T), from which we could calculate the temperature dependence of 〈τ〉, distribution width, and distribution asymmetry. The weighted average relaxation time 〈τ〉 was found to follow the Vogel-Fulcher law with the static freezing temperature $T_0=16.5±1.2K$ for the DRADP-x(x=0.4) system. As for a non-Debye type relaxation function, a form derived by chamberlin from percolation theory for spin glass and glass forming liquid system was applied in the analysis of dielectric data of DRADP-x. We discuss the fitting result in comparison with the glass forming liquid system.
Ultralow frequency dielectric dispersion recently observed in the ferroelectric phase of $KH_2PO_4$(KDP) crystal and attributed by Chaves et al. as due to the heat diffusion central peak(HDCP) contribution was reexamined. Our temperature dependence study of dielectric relaxations in the same low frequency region for a natural multidomain KDP crystal confirms that major part of this low frequency dielectric dispersion should be attributed not to the heat diffusion central peak but to the domain wall relaxations as already reported by Paul et al..
We have performed a careful measurement of both pyroelectric currents and static charges to obtain the dielectric susceptibility of a deuterated rubidium ammonium dihydrogen phosphate ( DRADP-x, x=0.4) in the region of glass transition. We have found an inadequacy of the pyroelectric measurements to define the field cooled susceptibility $ε_FC$. Instead we have applied the static charge measurement to obtain $ε_FC$ and come to a different conclusion from the previous one: the field cooled susceptibility $ε_FC$ remains to be equal to the zero-field cooled susceptibility $ε_ZFC$ across the glass transition temperature within the accessible time scales of static charge measurements.
