Dielectric Dispersion in Ferroelectric N2H5Al(SO4)2 · 12H2O

Abstract

The complex dielectric constant of N 2 H 5 Al(SO 4 ) 2 · 12H 2 O along the cubic [100] direction e * was measured in a frequency range between 10 kHz and 1 GHz. The critical slowing-down phenomenon of polarization was observed above the transition temperature 164.5 K ( T C ). The experimental result was analyzed on the basis of the dielectric formula which represents the sum of two independent relaxators characterized by relaxation times τ 1 and τ 2 . The static dielectric constant of one relaxator, e 1S , obeys the Curie-Weiss law with the Curie constant C 1 =1.75 ×10 2 K and the paraelectric Curie temperature T 01 =148 K, while that of the other, e 2S , hardly depends on temperature. The relaxation time τ 1 can be well explained by the relation τ 1 =τ 01 · T /( T - T 01 ) with τ 01 =( h / k B T ) ·exp (Δ F 1 / k B T ), and the activation free energy was estimated to be Δ F 1 =1.51×10 -20 J just above T C .