Dielectric relaxation studies in ferro-, ferri- and antiferro-electric phases of (S)-4^′-octyloxybiphenyl-4-carboxylic acid 3-chloro-4-(1-methylheptyloxycarbonyl)phenyl ester

Abstract

Temperature-dependent dielectric spectroscopy of (S)-4^′-octyloxybiphenyl-4-carboxylic acid 3-chloro-4-(1-methylheptyloxycarbonyl)phenyl ester (chlorinated MHPOBC analogue) has been carried out in the frequency range from 1 Hz to 10 MHz for sample thicknesses 5, 10 and 20 µm during heating and cooling runs. This compound shows a rich and complex dielectric response, with several active modes in each subphase. Goldstone-mode relaxation has been observed for

,

and

subphases; however, another relaxation mode (apparently a soft mode) has also been observed in these subphases. It has been found that the dielectric strength corresponding to a relaxation mode increases with increasing thickness of the sample, whereas the relaxation frequency remains invariant. The activation energy of the molecular rotation about their short axes has been determined. It has been found that the molecular reorientation about the short axes is more hindered in chiral smectic C (tilted) subphases than in orthogonal

phase.

Keywords:

• Dielectric spectroscopy
• Antiferroelectric phase
• Polar phases
• Collective modes
• Molecular modes

Acknowledgements

We thank the University Grants Commission (UGC), New Delhi, for the financial assistance under a project. One of us (MBP) thank UGC especially for the research fellowship.