Dielectric and electro-optical response of a room temperature tri-component antiferroelectric mixture

Abstract

Frequency- and temperature-dependent dielectric and switching parameters of a room temperature tri-component antiferroelectric liquid crystal mixture W-287 have been determined. Dielectric, optical texture and thermodynamic studies show wide room temperature range antiferroelectric SmC*_a (˜91.1°C to <–25°C) phase in addition to high temperature paraelectric SmA* (˜2.6°C) and ferroelectric SmC* (˜4.4°C) phases. The dielectric studies carried out in the frequency range of 1–35 MHz under planar anchoring condition of the molecules show five different relaxation modes appearing in the SmA*, SmC* and SmC*_a phases. Using Curie–Weiss law fit, ferroelectric SmC* to paraelectric SmA* transition temperature has been found to be 91.8°C. The dielectric response of SmC*_a phase exhibits unusually three relaxation modes due to collective as well as individual molecular processes in addition to phason mode in the SmC* phase and amplitudon mode in the SmA* phase. Spontaneous polarisation, switching time and rotational viscosity have also been determined. The maximum value of P_S is ˜300 nC/cm², whereas viscosity is moderate. Switching time is of the order of few milli seconds.

Keywords:

• antiferroelectric liquid crystal
• dielectric permittivity and loss
• soft and Goldstone modes
• spontaneous polarisation
• switching time

Acknowledgements

Avneesh Mishra thanks DAE-BRNS especially for a Junior Research Fellowship under the project.

Funding

We thank Department of Atomic Energy, Board of Research in Nuclear Sciences (DAE-BRNS), for financial assistance under a research grant [grant number 2010/34/38/BRNS].