CRITICAL SLOWING-DOWN PROCESS OF DIELECTRIC RELAXATION IN ANTIFERROELECTRIC CU(HCOO)2.4H2O

The real and imaginary parts of the dielectric constants of antiferroelectric Cu(HCOO)2̇4H22O were measured in its transition temperature region. The measurements were made by using a capacitance bridge for the frequency range between 3 × 10 2 and 3 × 106 Hz and an admittance meter at the microwave frequency of 1 × 109 Hz. The experimental results obtained for ε′ and εb′ 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 (εb″) max upwards in the paraelectric phase. This can well be accounted for as due to dominant contribution of a relaxation time n, to the observed relaxation time r. The latter (τ) is characterized by critical slowing-down process near the transition temperature, while the former (τ0) does not relate to this process.