Influence of optical purity on the Smectic-C*_β phase of antiferroelectric liquid crystals

The Smectic-C*_β (SmC*_β) phase, which appears between the SmA and SmC*_A phases in an optically pure liquid crystal of MHPOBC, has been studied by means of simultaneous measurements of the dielectric constant ε and the electroclinic coefficient κ under a dc bias electric field. The result of electroclinic coefficient measurement shows that the SmC*_β phase is obviously different from the SmC* phase and can be considered as a ferrielectric phase. From the simultaneous measurement of ε and κ, we can observe the difference in the phase transition behaviors between pure and slightly racemized MHPOBC samples and confirm that the decrease of optical purity causes the change from the SmC*_β phase to the SmC* phase.