Ferrielectricity in Chiral Smectic Cβ of an Antiferroelectric Liquid Crystal

Abstract

The switching current behavior and the complex dielectric constant under DC electric bias field and domain structures ofan antiferroelectric liquid crystal, 4-(1-methylheptyloxycarbonyl) phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC), wereinvestigated as a function of optical purity and cell thickness, and the ferrielectricity of the chiral smectic Cβ phase (SmCβ*) was discussed. Optically pure samples show two-step decrease in the real part of complex dielectric constant with increasing DC bias field. The first decrease corresponds to the suppression of the ferroelectric Goldstone mode, which is also suppressed by decreasing cell thickness. The second step, which is observed even in the chiral smectic Cα phase (SmCα*), corresponds to the suppression of a new relaxation mode induced by DC electric bias field. Three peaks of the switching current were observed in SmCβ* and also in the lower-temperature region of SmCα*. Temperature dependence curves of the peak positionsare continuously connected together at the phase transition temperature between SmCβ* and SmCα*. It can be said that the antiferroelectricity of SmCα* is conserved in SmCβ*, and that the ferrielectricity of SmCβ* may consist of the ferroelectricityof SmC* and the antiferroelectricity of SmCα*. Striped domains observed in SmCβ* after removing the DC electric bias field can be considered to be the SmCα* phase.