Influence of the bias field on dielectric properties of the SmC_A* in the vicinity of the SmC*–SmC_A* phase transition

Abstract

In a large class of smectic mixtures prepared at our University, the phase transition between chiral ferroelectric smectic C (SmC*) and chiral antiferroelectric smectic C (SmC_A*) phases can be observed on cooling. Under bias field the temperature of the phase transition SmC*−SmC_A* decreases (ca. 100°C in the investigated mixture). The transition is called: unwound SmC*−twisted SmC_A* phase transition. The Goldstone mode in SmC* phase is reduced by a direct current field while two modes (P_H and P_L) in the SmC_A* phase are amplified. The amplitude of the fast X mode observed in the SmC_A* phase is reduced. The aim of this paper is to show how parameters of the modes in SmC_A* phase (calculated from Cole–Cole model) change with bias voltage—when twisted structure in SmC_A* phase is gradually unwound. The character of the modes observed in SmC_A* is discussed. A new effect is shown: a high value of dielectric loss is detected in the unwound SmC* phase, which is very close to SmC_A*.

Keywords:

• phase transition
• dielectric modes
• ferroelectrics and antiferroelectrics
• Cole–Cole model
• bias field

Acknowledgements

This work was conducted in 2011 under financial support from the Polish Ministry of Sciences and Higher Education, Key Project POIG.01.03.01−14−016/08 ‘New photonic materials and their advanced application’.