Critical Behaviour of the Polarization, Tilt Angle, Electric Susceptibility and the Specific Heat Close to the SmA- Ferroelectric SmC (SmC*) Phase Transitions

This study gives the temperature dependence of the two order parameters, namely, polarization P and the tilt angle θ, when there is a biquadratic coupling P ² θ ² in the expansion of the Landau free energy. This applies to the electric-field-induced SmA-Ferro-Electric SmC (SmC*) phase transition. From this expansion of the Landau free energy in terms of the polarization and the tilt angle, we obtain the temperature dependence of the electric susceptibility χ and the electric field dependence of the polarization P. These dependences of P, θ and χ are fitted to the experimental data for C7 and their critical behaviour in this liquid crystal is described close to the SmA- ferroelectric SmC (SmC*) phase transition.

Also, considering this P ² θ ² coupling in the Landau free energy, the temperature dependence of the specific heat C _P is obtained and using the experimental data for 2f + 3f, the critical behaviour of C _P in this liquid crystal is analyzed close to its SmA- ferroelectric SmC (SmC*) phase transition.

Values of the critical exponents which we obtain from our analysis of the SmA- ferroelectric SmC (SmC*) phase tansitions in C7 and 2f + 3f, are in agreement with those predicted by the Landau mean field model.

Keywords:

• AC* Phase Transition
• C7. 2f+3f.