Phase transitions and low-frequency dielectric dispersion in ferroelectricLangmuir-Blodgett films of the copolymer vinylidene fluoride with trifluoroethylene

The dielectric properties of multilayer ferroelectric Langmuir-Blodgett fil ms based on the copolymer vinylidene fluoride with trifluoroethylene with 7 0/30 composition are investigated. Good agreement with theoretical models o n the basis of the phenomenological Landau-Ginzburg approach is demonstrate d for the first time for ultrathin films. Expressions describing the temper ature variation of the permittivity in the temperature range of hysteresis and giving quantitative agreement with experimental data are obtained. It i s shown that the Langmuir-Blodgett films are conducting. This conductivity does not depend on the frequency of the field. The results are explained by the fact that the motion of charge in the films is not bounded by domain w alls. The jumps observed in the frequency dispersion at volume and low-temp erature (surface) phase transitions are explained by a sharp increase in th e relaxation times at the transition into the ferroelectric state. (C) 2000 MAIK "Nauka/ Interperiodica".