Induced smectic C* phases

Induced ferroelectric S*C phases are formed by non-chiral SC host phases doped with chiral dipolar guest molecules. In those mixtures the spontaneous polarization P s and the tilt angle Θ has been investigated as a function of the mole fraction x G of the chiral dopant. In most cases the reduced polarization P 0 = P S/ sin Θ has been found to depend linearly on x G. The polarization power which is defined by δ P=(∂P 0/∂x G)ΔT is discussed in terms of the molecular structure of the chiral dopants. There are systems in which P 0(x G) deviates positively from linearity. This behaviour can be understood by considering a local field correction to P 0. By assuming a local field of Lorentz type a theoretical relation for P 0(x G) has been derived which explains the experimental results. The effect of a local field is considerable if the transverse dipole moment and the polarizability of the chiral dopant are large.