Dielectric Spectroscopy of Ferro- and Antiferroelectric Phases of (S)-(+)-4′- (1-Methylheptyloxycarbonyl)Biphenyl-4-yl 4-(6-heptanoyloxyhex-1-oxy) Benzoate

Abstract

Frequency and temperature dependent dielectric spectroscopy of a newly synthesized highly tilted AFLC material named as (S)-(+)-4′-(1-methylheptyloxy carbonyl)biphenyl-4-yl 4-(6-heptanoyloxyhex-1-oxy)benzoate (acronym 6H6B) under planar and homeotropic anchoring conditions has been carried out in order to determine the different dielectric parameters of the various modes of dielectric relaxations. Paraelectric SmA* phase shows soft mode of relaxation related with the amplitude fluctuation (amplitudons). Its relaxation frequencies are highly temperature dependent and decreases with decrease in the temperature. Dielectric strength is small (∼ 4-5) but increases with decrease in the temperature and follows Curie Weiss' law. Ferroelectric SmC* phase shows Goldstone mode having large dielectric strength (∼ 140). Two modes of dielectric relaxation have been clearly observed in anti ferro-electric SmC _A * phase. Lower frequency mode observed in kHz range has been assigned as P _L mode whereas the higher frequency mode observed at about 100 kHz has been assigned as P _H mode. DC field effect has also been studied in various phases.

Keywords:

• Antiferroelectric liquid crystal
• dielectric relaxation
• Goldstone mode
• soft mode

Acknowledgments

Financial assistance from Department of Science and Technology under the project No. SR/FTP/PS-06/2003 is thankfully acknowledged.