Dielectric properties near the smectic-C/emph>–smectic-Aphase transition of some ferroelectric liquid-crystalline systems with a very large spontaneous polarization

The frequency and temperature dependence of the complex dielectric constant was measured near the smectic-$C^{\mathrm{*}}$–smectic-A liquid-crystal phase (Sm-$C^{\mathrm{*}}$–Sm-A) transition for two ferroelectric liquid crystals with a very large spontaneous polarization. The dielectric strengths as well as the corresponding relaxation frequencies of the dielectric modes were determined. Due to the large polarization we were able to resolve the contributions from the soft mode and the Goldstone mode in a comparatively large temperature interval in the Sm-$C^{\mathrm{*}}$ phase close to the transition to the Sm-A phase. In the Sm-A phase, the relaxation frequency and the inverse dielectric strength of the soft mode decrease linearly when approaching $T_c$. Comparing the experimental data with a recent theoretical calculation of the complex dielectric constant, we conclude that we have a fairly good understanding of the behavior of the complex dielectric constant in the whole Sm-$C^{\mathrm{*}}$–Sm-A transition range.