Novel Temperature Dependences of Helical Pitch in Ferroelectric and Antiferroelectric Chiral Smectic Liquid Crystals

A variety of temperature dependences of helical pitch were found in ferroelectric SmC * and antiferroelectric SmC A * chiral smectic liquid crystals with large spontaneous polarization. In the vicinity of the transition temperatures of the materials showing the second-order SmA-SmC * or SmA-SmC A * phase transition, the pitch gradually increases with decreasing temperature over several degrees. In the materials which show the first-order phase transition from SmA to SmC * or to SmC A * , the maximum pitch suddenly appears at the transition. It was also confirmed in all of the materials used that the helix undergoes a discontinuous change in the pitch length and its handedness at the SmC * -SmC A * phase transition. The molecular orientational structure of the ferrielectric phase is also discussed on the basis of the temperature dependence of the pitch of ( S )-MHPOBC.