Study of different modes of dielectric relaxation in a newly synthesized material exhibiting ferro-, ferri- and antiferro-electric phases

Abstract

Employing thermodynamical, optical and comprehensive dielectric studies, we have investigated a freshly synthesized chlorinated MHPOBC analogue antiferroelectric liquid crystal; it exhibits different chiral SmC sub-phases, viz. SmC_α*, SmC* and SmC_γ*, at considerably lower temperature in comparison with MHPOBC, and a wide range room temperature antiferroelectric SmC_A* phase. Dielectric spectroscopy investigations under planar molecular anchoring were carried out in the frequency range 1 Hz to 10 MHz. The data measured for low and high frequency regions were corrected by the method of fitting operation of the theoretical equations. Seven different modes of dielectric relaxation in the different phases were identified. Soft mode relaxation was identified in the SmA* and SmC_α* phases. The Goldstone mode, characteristic of the ferroelectric phase, was observed in the SmC* and SmC_γ* phases. Two characteristic peaks are seen in the spectrum of the SmC_A* phase: one, at high frequency, corresponds to fluctuation where the molecules in neighbouring layers are rotating in opposite phase; the other, at low frequency, arises due to phase fluctuation in the helicoidal superstructure.