Critical Slowing-Down Process of Dielectric Relaxation in Antiferroelectric Cu(HCOO)2·4H2O

Abstract

The real and imaginary parts of the dielectric constants of antiferroelectric Cu(HCOO)₂·4H₂O were measured in its transition temperature region. The measurements were made by using a capacitance bridge for the frequency range between 3 × 10² and 3 × 10⁶ Hz and an admittance meter at the microwave frequency of 1 × 10⁹Hz. The experimental results obtained for ${\epsilon }_b\prime$ and ${\epsilon }_b″$ were analyzed both for the paraelectric and antiferroelectric phases on the basis of time‐dependent statistics in a molecular‐field approximation. It is shown that the dielectric relaxation observed in the paraelectric phase can be described to good approximation by monodispersive process, while in the antiferroelectric phase it can be described qualitatively by a monodispersive process. The increase of frequency results in the temperature shift of ${\mathrm{(\epsilon }}_b{\mathrm{″)}}_{\max }$ upwards in the paraelectric phase. This can well be accounted for as due to dominant contribution of a relaxation time ${\tau }_0$ to the observed relaxation time $\tau$ . The latter $\mathrm{(\tau )}$ is characterized by critical slowing‐down process near the transition temperature, while the former ${\mathrm{(\tau }}_0)$ does not relate to this process.