Dielectric Spectroscopy of Para‐, Ferro‐, and Anti‐Ferro‐Electric Phases of (S)‐(+)‐(1‐Methylheptyloxycarbonyl)Phenyl 4′‐(6‐Perfluoropentanoyloxyhex‐1‐Oxy) Biphenyl‐4‐Carboxylate

Abstract Frequency and temperature dependent dielectric studies have been carried out in the para‐, ferro‐, and anti‐ferro‐electric phases of a liquid crystal compound, namely "(S)‐(+)‐(1‐methylheptyloxycarbonyl)phenyl 4′‐(6‐perfluoropentanoyloxyhex‐1‐oxy) biphenyl‐4‐carboxylate." Dielectric spectroscopy in the frequency range of 1 Hz to 10 MHz under planar anchoring conditions of molecules suggests five different collective modes of relaxations in various phases. The para‐electric SmA* phase shows soft mode relaxation related with the tilt fluctuation of the molecules. Relaxation frequency of the observed soft mode is highly temperature dependent and decreases with decrease in the temperature. On the other hand, relaxation frequency of the observed Goldstone mode in the ferro‐electric SmC* phase is almost invariant at about 3.5 kHz. Two modes of dielectric relaxations have been detected in the anti‐ ferro‐electric SmCA *phase. High frequency mode of the SmCA *phase has been assigned to the phase fluctuation of the residual polarization of anti‐tilt pair whereas the low frequency mode relates to anti‐phase azimuthal angle fluctuations of the anti‐tilt pairs of the molecular directors. Arrhenius plots of the relaxation frequencies suggest that energy required to activate low frequency mode is almost double (∼114 kJ/mole) to that required for high frequency mode (∼60 kJ/mole). Keywords: Anti‐ferro‐electric liquid crystalDielectric spectroscopyGoldstone modeRelaxationSoft mode ACKNOWLEDGMENTS We thank the University Grants Commission (UGC), New Delhi for financial assistance under the research grant No. F. 30‐83/2006 (SA‐II) under the National Research Award Scheme. One of us (AD) thanks UGC for a fellowship under the scheme. We are grateful to Prof. I. M. L. Das, In‐charge Impedance Spectroscopy Laboratory and Prof. Pradip Kumar (Head), Physics Department, Allahabad University, Allahabad for providing the dielectric measurement facility.