Critical Slowing-Down and Static Dielectric Constant of Monoclinic RbD₂PO₄

Abstract

The real and imaginary parts of the complex dielectric constant along the b axis of monoclinic RbD 2 PO 4 were measured in a frequency range between 10 6 Hz and 10 9 Hz. It was found that RbD 2 PO 4 shows dielectric critical slowing-down near the ferrielectric phase transition point. In addition, the static dielectric constants ( ε 0 ) of RbD 2 PO 4 and the partially deuterated crystal Rb(D 0.3 H 0.7 ) 2 PO 4 were also measured at 10 4 Hz. A theoretical expression of ε 0 for a ferrielectric phase transition was obtained on the basis of the quasi-one-dimensional Ising model with assumed two sublattices. The remarkable deviations of ε 0 from the Curie-Weiss law observed in these crystals were analyzed successfully by the present theoretical result and the experimental results were discussed.