ELECTRICAL AND OPTICAL-RESPONSES OF AN ANTIFERROELECTRIC LIQUID-CRYSTAL IN SMA, SMC-ALPHA-ASTERISK AND SMC-ASTERISK PHASES

The SmA, SmC alpha and SmC* phases of an antiferroelectric liquid cry stal 4-(1-methylheptyloxycarbonyl) phenyl 4'-octyloxybiphenyl-4-carbox ylate (MHPOBC) have been studied by means of simultaneous measurements of the dielectric constant and the electroclinic coefficient under a de bias electric field. From the three dimensional representation of t he electroclinic coefficient as a function of de electric field and te mperature, it is confirmed that there is no helix with a long pitch in the SmC alpha phase and the electric field-temperature phase diagram for these phases is obtained. In the SmA phase near the phase transit ion temperature, the temperature dependences of the dielectric constan t and the electroclinic coefficient are analyzed in terms of the pheno menological theory of Landau type and the parameters appearing in the theory are determined.