Experimental study of nonlinear dielectric relaxation spectra of ferroelectric liquid crystals in the smectic c phase

Nonlinear dielectric relaxation spectra of two kinds of ferroelectric liquid crystals (FLC) are investigated in the chiral smectic C (SmC*) phase. The linear spectrum shows the relaxation of Debye type and the third-order nonlinear spectrum also shows the relaxation of Debye type generalized to the nonlinear case. The third-order nonlinear dielectric increment is found to be negative, which indicates that the dielectric nonlinearity of FLCs in the SmC* phase mainly originates from the saturation of molecular dipole moments induced by the applied electric field. The profiles of linear and nonlinear spectra remain almost unchanged throughout the SmC* phase. In the vicinity of the SmA-SmC* phase transition temperature, the linear spectrum shows the critical behavior of Curie- Weiss type and the third-order spectrum shows a sharp peak.