Low and high frequency dielectric spectroscopy on a liquid crystal with the phase sequence N*-S_A-S*_c

Abstract

Broadband dielectric measurements on a multicomponent ferroelectric liquid crystal mixture have been performed. The alignment was homeotropic and the cell and sample holder were the same in the whole frequency range. Two relaxation processes have been observed in all liquid crystal phases with shapes given by the Havriliak-Negami and inverted Havriliak-Negami functions. Strengths and frequencies of both modes have been obtained for the different phases. The values of the latter and their activation energies allowed us to assign the low and high frequency mechanism to the molecular reorientation around the transversal axis and around the longitudinal axis, respectively. The behaviour of this high frequency mode does not show any jump in the S_A-S*_c phase transition, neither in the amplitude nor in the frequency, indicating that the appearance of the spontaneous polarization in the S*_c phase is not the consequence of the freezing of this mode.