Nonlinear Dielectric Constants of Anti-Ferroelectric Liquid Crystals

Abstract

The linear and nonlinear dielectric constants and electroclinic coefficient of some antiferroelectric liquid crystals are simultaneously measured in various smectic phases, SmA, SmC_α^* and SmC_A^*. The critical behavior in the SmA phase near the SmA-SmC_α^* or SmA-SmC_A^* phase transition is well describable by the phenomenological theory of Landau type which is proved to be applicable to the SmA-SmC^* phase transition. We can calculate the phenomenological coefficient concerning to the ferroelectric order parameter. It is found that the third-order nonlinear dielectric constant in the SmC_A^* phase shows a positive sign which is in contrast with a negative sign in the SmC^* phase due to the Goldstone mode.