Dielectric properties of antiferroelectric liquid-crystalline mixtures

Antiferroelectric liquid crystalline mixtures having smectic C-A* phase in very broad temperature range have been investigated. Measurements of dielectric relaxation and spontaneous polarization were performed. Two absorption peaks in the existence range of the antiferroelectric C-A* phase in the kHz-MHz range of frequency were observed. Both peaks are quite week and of Debye type. Their characteristic dielectric strengths are almost temperature independent. The peaks are probably related to the motions of molecules on the side of a cone, defined by the molecular tilt angle. The slower process is related to the motions of molecules, tilted in opposite directions in subsequent layers and moving in the same direction (in-phase motions). The process with shorter relaxation time is attributed to the movement of molecules in opposite directions (anti-phase motions). Both modes are active in dielectric measurements due to small residual polarization being a consequence of the helical superstructure.