K. A. Verkhovskaya

Switching in one monolayer of the ferroelectric polymer

The switching in one monolayer of ferroelectric vinylidene fluoride-trifluoroethylene copolymer P[VDF-TrFE] is observed. The kinetics of switching is well described by Landau-Khalatnikov (LK) equation.

Photovoltaic and Photorefractive Phenomena in Ferroelectric Rb2ZnBr4

The first observation of the anomalous photovoltaic effect and the photorefractive effect in a Rb 2 ZnBr 4 crystal is reported. The Glass constant and the photovoltaic current in this crystal has been found to be of the same order of magnitude as those in LiNbO 3 : Fe, although the spontaneous polarization of Rb 2 ZnBr 4 is very low, that is, three orders of magnitude lower than that in oxygen octahedra ferroelectrics. Neither photovoltaic effect nor photorefractive effect is observed in the incommensurate phase. The photorefractive effect in this crystal is understood to be caused by the photovoltaic effect.

Dielectric Dispersion in Langmuir-Blodgett Ferroelectric Polymer Films

The dynamic permittivity of vinylidene fluoride-trifluoroethylene (70:30) copolymer films is measured over wide ranges of frequencies and temperatures. It is revealed that 15-to 45-nm-thick Langmuir-Blodgett films of the vinylidene fluoride-trifluoroethylene copolymer undergo a Debye-type dielectric relaxation. The relaxation time τ increases as the temperature increases and the ferroelectric phase transition is approached. This effect is interpreted as a result of critical slowing down. The influence of gamma irradiation on the dielectric response of Langmuir-Blodgett films consisting of 10 and 30 monolayers is investigated.

Phase transition in ferroelectric nanocrystals of the poly(vinylidene fluoride-trifluoroethylene) copolymer

The dielectric dispersion of nanocrystals of the poly(vinylidene fluoride-trifluoroethylene) copolymer with the 70/30 composition has been studied. It has been found that the phase transition in ferroelectric nanocrystals takes place at T = 100°C. The observed broad temperature hysteresis indicates the occurrence of a first-order phase transition.

Glass transition of Langmuir-Blodgett polymer films

The dielectric dispersion of vinylidene fluoride-trifluoroethylene copolymer P(VDF/TrFE) (70/30) films obtained by the Langmuir-Blodgett technique was investigated in the low-temperature range from 20 to −100°C. The thickness of the explored films was 40 nm. A glass-transition range from −25 to −40°C was detected; this indicates the presence of an amorphous phase in the LB films.

Dielectric Dispersion in Ultrathin Ferroelectric Polymer Films

Dynamic dielectric measurements were carried out for Langmuir-Blodgett films based on vinylidene fluoride with trifluoroethylene copolymers P(VDF/TrFE). Debye-type dielectric relaxation has been revealed for all films of different composition and thickness. The values of the relaxation time and the damping coefficient depend on the film thickness. Frequency and temperature dependences of conductivity have been investigated.

Dielectric dispersion of ultrathin polymer Langmuir-Blodgett films

Dielectric dispersion is studied in films made of vinylidene fluoride/trifluoroethylene copolymer [P(VDF/TrFE)], which are obtained by the Langmuir-Blodgett technique in the temperature range from −90 to +132°C. The thickness of the films studied is ∼7 nm. A glass transition is observed in the temperature range from −40 to −50°C; this indicates the presence of an amorphous phase in the ultrathin Langmuir-Blodgett films.

Dielectric Relaxation in Polymer Ferroelectric Nanostructures

The dielectric dispersion of ultrathin films and nanocrystals of the poly(vinylidene fluoride-trifluoroethylene) copolymer with the 70/30 composition has been studied. It has been found that the phase transition in ferroelectric nanocrystals takes place at T = 100°C. The observed broad temperature hysteresis indicates the occurrence of a first order phase transition.

Dielectric spectroscopy of ultrathin ferroelectric polymer films

The dielectric dispersion of poly(vinylidene fluoride-trifluoroethylene) copolymer films prepared using the Langmuir-Blodgett technique is studied. All films of different compositions and thicknesses undergo a Debye-type dielectric relaxation. The phenomenon of critical slowing down is investigated. It is found that the relaxation time τ and the kinetic coefficient ξ depend on the thickness of the film.

Optically sensitized ferroelectric polymers

The new photoferroelectric material is prepared by means of dye sensitization of ferroelectric vinylidene fluoride trifluoroethylene copolymers VDF/TrFE. The photoconductivity and bulk photovoltaic effects have been observed in the spectral bands connected with dye molecules absorption. At the ferroelectric phase transition the sharp changes of absorption and fluorescence spectra of sensitized films VDF/TrFE are revealed. These effects are denoted as structural optic effects. The influence of an external electric field on the fluorescence of VDF/TrFE doped by rhodamine 6G is revealed. This phenomena is explained by the influence of polarization on the radiationless electron transitions in the dye molecules.