Jaroslavas Belovickis

Polarization reversal in organic-inorganic ferroelectric composites: Modeling and experiment

Tailoring of ferroelectric properties of copolymer P(VDF-TrFE) by incorporation of ceramic inclusions in the polymer matrix is promising for advanced applications in sensorics. We have observed experimentally that in composites of P(VDF-TrFE) with barium-doped lead zirconate titanate (BPZT), the remanent polarization increases, while the coercive field substantially decreases in comparison with the pure polymer samples. Results of simulation in framework of the modified Weiss model have shown that the changes of the hysteresis loops characteristics are due to increase of the dielectric susceptibility of the composite as compared to pure PVDF-TrFE. This originates from the strong dispersion of the mean field constant α, which describes the feedback of the polarization on the electric field at the location of the dipoles and is closely related with the local increase of composite susceptibility in the vicinity the BPZT inclusions. This phenomenon effectively becomes macro-scale due to the long-range nature of the inhomogeneous elastic and electric fields occurring at the interfaces between the matrix and inclusions.

Dielectric Spectroscopy of Polymer Based PDMS Nanocomposites with ZnO Nanoparticles

Dielectric spectroscopy results of organic polymer Polydimethylsiloxane (PDMS) with different ZnO nanoparticle concentrations are presented in wide temperature range. Dielectric loss was measured as a function of electromagnetic field frequency at various temperatures. Our measurements have shown that the value and position of dielectric loss peak on a temperature scale depends on the concentration of ZnO nanoparticles within PDMS. The temperature behaviour of dielectric losses was compared with temperature dependencies of ultrasonic attenuation in the samples. It is shown that the maximum of dielectric losses in PDMS nanocomposite is described according to the Vogel-Fulcher law and the glass transition increases with ZnO concentration.

Acousto-optic interaction with leaky surface acoustic waves in Y-cut LiTaO3 crystals.

The acousto-optic interaction with leaky surface acoustic wave radiation into the bulk of YX-cut LiTaO(3) crystals has been investigated. The light incidence and diffraction angles corresponding to the strongest acousto-optic interaction were calculated and measured as functions of the acoustic wave frequency. The dependencies of the diffracted light intensity on the amplitude of radio-frequency voltage applied to the interdigital transducer (IDT) were studied. Our acousto-optic measurements revealed generation, by the IDTs, of slow shear bulk acoustic waves propagating at different angles depending on their frequency. A secondary acousto-optic interaction from the bulk waves radiated by the receiving IDT has been studied.

Leaky-surface-wave generated acoustic beam displacement upon reflection in lithium tantalate crystals

The non-specular reflection of a leaky surface acoustic wave radiated beam from the surface of piezoelectric lithium tantalate crystal has been investigated using an acoustoelectric and acousto-optic technique. The Schoch-type beam displacement upon reflection strongly depends on whether the surface is free or metalized. This effect is attributed to the excitation (on the reflecting surface) of the leaky surface wave, the acoustoelectric attenuation of which strongly depends on the surface conductivity.

Effect of thermal cycling on ferroelectric phase transition of PVDF-TrFE based composites as investigated by ultrasonic spectroscopy

ABSTRACT In this paper we report on the investigation of longitudinal ultrasonic wave attenuation, velocity and ultrasonically induced piezoelectric voltage in P(VDF-TrFE) composites with fillers of conductive carbon nanotubes (CNT). Moreover, temperature dependences of ultrasonic attenuation in the composites were shown to be sensitive to thermal cycling over the ferroelectric phase transition.

Ultrasonic and dielectric studies of polymer PDMS composites with ZnO and onion-like carbons nanoinclusions

The ultrasonic and dielectric temperature investigations were performed in polydi- methylsiloxane (PDMS) with zinc oxide (ZnO) and onion-like carbon (OLC) nanocomposites. In the glass transition region, the ultrasonic velocity dispersion and large ultrasonic attenuation maxima were observed. The positions of ultrasonic attenuation peaks were slightly shifted to higher temperatures after doping PDMS with OLC and ZnO nanoparticles. The ultrasonic relaxation was compared to that of dielectric and such behaviour was described by Vogel- Fulcher law. The upshift of the glass transition temperature with addition of nanoparticles was confirmed by both methods. The additional increase of ultrasonic attenuation in composites doped with OLC and ZnO was observed at room temperature and such behaviour we attributed to ultrasound-nanofiller interaction in polymer matrix.

Ultrasonic studies of onion-like carbons/polydimethysiloxane composites

The temperature dependencies of longitudinal ultrasonic velocity and attenuation in polydimethysiloxane (PDMS) with onion-like carbons (OLC) composites have been measured. In the region of the glass transition the ultrasonic velocity dispersion and large ultrasonic attenuation maxima were observed. The positions of ultrasonic attenuation peaks were slightly shifted to higher temperatures after doping PDMS with OLC nanoparticles. A significant increase of ultrasonic attenuation with increasing OLC concentration was observed at room temperature and such behavior can be attributed to ultrasonic - OLC interaction in polymer matrix.