Spectral analysis: A new method to measure the spontaneous polarization of ferroelectric liquid crystals

Abstract

A dielectric mode in electroclinic liquid crystalsA new method to measure the spontaneous polarization density P S of ferroelectric liquid crystals as a function of the temperature is described. It is based on the spectral decomposition of the polarization and measurement of the different temporal harmonics using a lock-in amplifier. It is particularly adapted to measure small values of P S in regions where different nonlinear process compete. This condition is fulfilled at temperatures around the SmC*-SmA transition temperature in liquid crystals. The method has a quantitative procedure to evaluate the saturation state of the sample's polarization at a given applied electric field. It overcomes the difficulty of the subjective evaluation of the hysteresis loop present in the usual methods. The accuracy in the measurement of P S of the ZLI-3654 ferroelectric liquid crystal in the region of about 0.5 nC/cm 2 is approximately one order of magnitude larger than that obtained with conventional hysteresis loop methods.