Using a generalized Landau type of free-energy density, we develop a theoretical model which, in a unified way, describes the general features of the tilt, polarization, pitch, dielectric susceptibility, and heat capacity of ferroelectric liquid crystals. Rewriting the equations into dimensionless form, we show that six parameters are needed in order to account properly for the temperature dependence of the quantities in question. It is also shown that the introduction of a biquadratic coupling between the tilt and the polarization in the free-energy density, which is an essential part of the model, implies a crossover behavior of the polarization when plotted as a function of temperature.

• Received 22 April 1987

DOI:https://doi.org/10.1103/PhysRevA.36.1484