Ferroelectric smectic- C* liquid-crystal phase: reexamination of the electric-field influence.

Calorimetric and dielectric experiments are presented near the recently proposed Lifshitz point in order to study the nature and properties of the newly suggested phase transitions in the electric-field-temperature (E-T) phase diagram. It was found that both calorimetric and dielectric results obtained across the recently proposed C1 - C2 transition line agree with the predictions of the extended Landau model, showing that the C1 - C2 transition line is not a true phase transition but is merely a continuous evolution similar to a supercritical evolution between two states possessing microscopically the same symmetry. However, it was confirmed in agreement with findings by Ghoddoussi et al. that in samples of finite thickness the extended Landau model cannot adequately describe some features of the E-T phase diagram and some other physical quantities such as the Goldstone mode temperature dependence and the polarization field dependence P (E) . These discrepancies are discussed within the frame of a relaxing mechanism of the helicoidal structure involving annihilation of pairs of +/-2pi disclination lines.