Dielectric Relaxation Mechanism in NaNO₂

Abstract

The dielectric relaxation in NaNO₂ is analyzed on the basis of the time dependent statistics of the Ising system, where the Ising variable corresponds to two stable orientations of the polarization carried by each molecular unit. The dynamical susceptibility is calculated with the random phase approximation in terms of the potential barrier ΔU between two stable orientations. The observed temperature and frequency dependences of the complex dielectric constants above the antiferroelectric transition temperature T_N are explained reasonably well by taking ΔU as ΔU≅7.4kT_N. The relaxation time of the flipping motion of each NO₂⁻ ion at high temperatures where the correlation between molecules is negligible is of the order of 10⁻¹¹ sec. The observed slow relaxation near the transition temperature is accounted for as due to the thermodynamical slowing down process of the correlated fluctuation of polarization. The monodispersive character is discussed in terms of the long range nature of interdipolar interaction and the antiferroelectricity.