Dielectric response in the Smectic A and Smectic C* phases of a ferroelectric liquid crystal, 12CN5(R*)

This paper reports the results of the dielectric relaxation studies performed in the Smectic A (SmA) and Smectic C* (SmC*) phases of the ferroelectric liquid crystal, 12CN5(R*) in the frequency range 5Hz to 13MHz. Planar orientation used throughout the study was achieved by rubbed polyamide coating on the surfaces of the dielectric cell. Transition temperatures determined from the derivative of this dielectric permittivity agrees with that obtained using thermal polarizing microscopy. The dielectric spectrum in the SmA phase shows single relaxation, whereas the SmC* phase has two relaxations, viz., the low frequency Goldstone mode and the high frequency soft mode. Special attention was paid to the study of the low frequency Goldstone mode relaxation. From the Cole-Cole plots, the temperature dependence of dielectric strength (Δε), the relaxation frequency (f_R) and the distribution parameter (x) ralevant to the Goldstone mode have been estimated. The relaxation frequency follows the Arrhanius relation in the asymptotic regions far from the transition. Results of the bias-dependent dielectric, measurements of the Goldstone made relaxation, have also been presented.