Dielectric critical slowing down in ferroelectric (C(3)N(2)H(5))(5)Sb(2)Br(11)

Abstract

Dielectric dispersion studies have been carried out on the pentakis(imidazolium) undecabromodiantimonate(III), (C(3)N(2)H(5))(5)Sb(2)Br(11), single crystal in the audio-frequency region. It is found that low-frequency dielectric dispersion, observed for the field along the a-axis of the monoclinic symmetry (P 2(1)/n), reveals a polydispersive nature near the paraelectric-ferroelectric phase transition temperature (T(c) = 145 K). The dielectric dispersion results can be fitted with the Cole-Cole formula. Unexpectedly, the mean relaxation frequency obeys the Vogel-Fulcher law with freezing temperature of 143 K. Near the ferroelectric phase transition temperature, the process of dielectric critical slowing down was observed. Such a dynamic dielectric response is characteristic of ferroelectrics with an 'order-disorder' transition mechanism.