Frequency response due to the orientational motion of the director around the smectic cone in a surface stabilized ferroelectric liquid crystal

Abstract

We report the effects of the rotational motion of the director around the chiral smectic cone on the dielectric relaxation and polarization reversal process in a surface stabilized ferroelectric liquid crystal cell. Measurement was made at a fixed temperature (40°C), far below the SmA–SmC* transition temperature (62°C) of the ferroelectric liquid crystal material (CS‐1027). The amount of switchable polarization (ASP), during the polarization reversal, is found to decrease with increasing frequency of the applied signal until a typical value of frequency (f l) is reached. This behaviour is considered to be due to the time‐dependent rotational motion of the director. The ASP value was calculated by measuring polarization–voltage (P–V) and capacitance–voltage (C–V) hysteresis loops as a function of the applied signal frequency and then following the Preisach model for the ferroelectric capacitor. The peaks of the C–V hysteresis loop, which correspond to the reversal of polarization, are gradually converted into wells for frequencies greater than a critical value (f i). The hysteresis loops shows ‘frustrated’ behaviour for frequencies between f l and f i. The inversion of the C–V hysteresis loop at higher frequencies (>f i) is attributed to the inversion of the dielectric biaxiality and the corresponding ‘frustrated’ behaviour arising due to competition between the dielectric and ferroelectric torques. A suitable equivalent circuit can be designed to represent the frequency‐dependent C–V and magnitude of admittance (conductance) –voltage (G–V) hysteresis behavior.