DIELECTRIC STUDY AND HELICAL PITCH MEASUREMENTS ON A NEW ANTIFERROELECTRIC LIQUID-CRYSTAL

The dielectric dispersion in the ferroelectric and antiferroelectric p hases of a new liquid crystal (S)-4-(1-methylheptyloxycarbonyl)-phenyl 4-(4-dodecyloxybenzoyloxy)benzoate has been investigated in the frequ ency range from 10 Hz to 10 MHz. The behaviour of the soft mode in SmA and the Goldstone mode in SmC have been determined.;Two dielectric r elaxations have been recognized in the antiferroelectric SmCA phase : the first one between 5 kHz and 50 kHz and the second one, also obser vable in the ferrielectric SmCFI phase, around 1 MHz. In SmCFI*, a dr astic change in the behaviour of the low frequency response has been f ound depending on whether the sample was heated or cooled. A sign reve rsal of the helical pitch has been determined inside the SmCFI phase, leading to low pitch values of opposite sign in SmCA and SmC*.