Field-induced phase transitions in an antiferroelectric liquid crystal using the pyroelectric effect

The antiferroelectric liquid crystal (AFLC) under investigation possesses d ifferent helical polar phases. Measurements of pyroelectric response of the se phases as a function of temperature and bias field have elucidated the a bility of this method for investigating the nature of antiferroelectric pha ses and phase transitions under the bias field. The pyroelectric signal as a function of the bias field at fixed temperatures and as a function of tem perature for fixed bias fields was measured for different phases of the inv estigated AFLC material. A theoretical model describing the pyroelectric re sponse in different phases of AFLC is given, and the experimental results a re interpreted. The threshold fields for field induced phase transitions ar e determined. The type of field induced phase transition from the AF phase in particular is found to be dependent on the temperature within its range. The properties of an unusual ferrielectric phase existing between ferriele ctric chiral smectic-C (SmC*) and antiferroelectric AF phases are studied i n a great detail. The results confirm that this phase is one of the incomme nsurate phases, predicted by the axial next-nearest neighbor Ising model an d Landau model for this temperature region.