Nonlinear dielectric measurements in the smectic-A-smectic-C-alpha* phase transition

We have performed precise measurements of the third-order dielectric consta nt in an antiferroelectric crystal MHPOCBC. In the vicinity of the SmA- SmC alpha* phase transition point an anomalous increase of it was observed. We have developed a Landau theory taking into account the pretransitional fluc tuations and shown that the fluctuation can contribute to the third-order r esponse. The anomalous behavior near the transition point was discussed on the basis of the theoretical results.