Re-entrant ferroelectric phases in binary mixtures of ferroelectric and antiferroelectric homologues of a series with three chiral centers

In binary mixtures composed of homologues from a series derived from 4-alko xybiphenyl- 4'-carboxylic acid exhibiting ferroelectric (FE) and antiferroe lectric (AF) phases, a re-entrant FE phase may be induced in a certain conc entration region, which is miscible with the SmC* phase. Dielectric spectro scopy study revealed a softening of the antiphase mode in the AF phase, whi ch is responsible for the appearance of the re-entrant phase. The helix twi st inversion occurs at the low temperature limit of the (AF) phase so that the helix handedness of the upper and lower temperature FE phases have oppo site sense. The values of spontaneous polarization and the spontaneous tilt angle evolve continuously with the concentration, while dielectric strengt h exhibits a maximum for a certain concentration of homologues. All phase t ransitions existing in the binary mixtures are sharp and divide homogeneous phases in contrast to results reported in E. Gorecka [Phys. Rev. Lett. 81 2946 (1998)], where a frustrated cluster phase exists. The reason is in dif ferent behavior of interlayer interactions at the FE-AF phase transition. ( C) 2001 American Institute of Physics.