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

The dielectric properties of multilayer ferroelectric Langmuir-Blodgett films based on the copolymer vinylidene fluoride with trifluoroethylene with 70/30 composition are investigated. Good agreement with theoretical models on the basis of the phenomenological Landau-Ginzburg approach is demonstrated for the first time for ultrathin films. Expressions describing the temperature variation of the permittivity in the temperature range of hysteresis and giving quantitative agreement with experimental data are obtained. It is 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 walls. The jumps observed in the frequency dispersion at volume and low-temperature (surface) phase transitions are explained by a sharp increase in the relaxation times at the transition into the ferroelectric state.