On Antiferroelectric Smectics Exhibiting Successive Phase Transitions in the Electric Field

The phase diagram of the axial next nearest neighbour Ising model with the third nearest neighbour interaction in an electric filed is obtained to study the phase transitions occurring in antiferroelectric smectic liquid crystals. Under suitable conditions, the jumps of the order parameters are small, though the transitions are necessarily of the first order in the absence of the electric field. The instability line of the ferroelectric phase, showing instability of the uniform phase with respect to periodic perturbation is also tested. The phase diagrams strongly suggest that the structure of the intermediate ferrielectric phase FI H has the wave number 2/7, and are also consistent with the previous result on FI L .