Jan Kulek

Dielectric relaxation in ferroelectric PZT–PVDF nanocomposites

Abstract Composites of electroactive ceramics and ferroelectric polymers are important for applications since they combine the most important features of the both phases and their properties can be easily tailored to various requirements. As the dielectric permittivity is involved in figures of merit of the quantities important for applications we studied dielectric response of Pb(Zr 0.5 Ti 0.5 )O 3 –polyvinylidene fluoride nanocomposites over a wide frequency and temperature range. It was found that though the permittivity value of the composites is high due to the high permittivity of the ceramics, the glass transition of the polymer and dielectric relaxation related to the wide-angle oscillation of polar groups attached to the main polymer chain determine the dielectric behaviour of the composites.

Dielectric and Pyroelectric Response of PLZT-P(VDF/TrFE) Nanocomposites

Dielectric response (100 Hz–1 MHz) and pyroelectric response (light modulation frequency range 10 Hz–1 kHz) of ferroelectric P(VDF/TrFE)(50/50) copolymer loaded with relaxor PLZT 9.5/65/35 ceramic powder of 10 nm crystallite size and ∼700 nm aggregates was studied. Though the dielectric permittivity of the composites increases due to high permittivity of the ceramic, their dielectric response is determined by dielectric relaxation processes of the polymer matrix. The dispersive dielectric anomalies of PLZT-0.9/65/35 relaxor ceramic affect mainly the dielectric absorption of the composites in the range of dipolar relaxation in the crystallite phase of the copolymer. The composites exhibit pyroelectric activity proper for application in operation frequency up to 1 kHz and temperature range 290–310 K.

The method of matching resonance frequencies in coupled transmitter PVDF/TRFE diaphragms

The influence of thermal aging on the resonance frequency and electric impedance of polyvinylidenefluoride (PVDF) type polymer films was studied with the aim to apply thermal treatment to modify and tune the parameters of polymer electromechanical transducers. Results of our study show that thermal treatment of PVDF/TRFE 75/25 copolymer in the temperature range 50 to 125/spl deg/C (10 min) can be applied for matching the resonance frequencies of coupled transducers. The resonance frequency of the copolymer was found to increase linearly with the rise of the annealing temperature by /spl sim/12%, whereas the related decrease in the electromechanical coupling coefficient does not exceed /spl sim/11%.

Dynamic pyroeffect and resonance phenomena in pvdf based diaphragm-type systems: Physical and application aspects

Abstract Frequency dependence of pyroelectric response of polarized P(VDF/TFE) (0.98/0.02) 70 μm foil was studied and its amplitude-phase analysis is provided. A low frequency pyroelectric resonance is discovered. The resonance is observed in the case of thermal excitation of the foil close to the electrode being grounded during poling. The effect is explained by nonhomogeneous distribution of pyro- and piezoelectric activity. Moreover, influence of acoustic and electric field on the pyroelectric response is discussed from the application point of view.

Dielectric Relaxation in K0.5Na0.5NbO3-PVDF Composites

K1−x Na x NbO3 is considered as an alternative system for lead-based functional ceramics widely used in transducers, sensors and actuators. In some applications however, the composites of electroactive ceramic and polymer, with low acoustic impedance and dielectric permittivity that can be tailored to various requirement, are more useful. We studied dielectric relaxation processes in polyvinylidene fluoride (PVDF) loaded with K0.5Na0.5NbO3 powder in wide temperature and frequency range. The powder was prepared by solid state synthesis and characterized by HRTEM and NIR Raman spectroscopy. The dielectric response of (K0.5Na0.5NbO3)0.32(PVDF)0.68 composite, of (0–3) connectivity, was found to be determined by the relaxation processes of the polymer matrix with an additional broad low-frequency anomaly at ∼ 305 K that we relate to a response of water absorbed by the shell of KNN grains.

Relation between the pyroelectric response and the dielectric heterogeneity of PVDF foil

Abstract Dynamical response to an applied electric and heat field is important in pyroelectric application of polymers, particularly due to their complex heterogeneity. We studied the effect of nonuniform poling of PVDF film on the dielectric and pyroelectric behaviour. Heterogeneous distribution of polarization results in pyroelectric coefficient anomaly in the frequency range 102 - 104 Hz observed when the electrode grounded during poling, is illuminated. The effect of the crystalline heterogeneity of the samples on the dielectric behaviour (β-relaxation) is apparent in the MHz range at room temperature.

Dielectric and pyroelectric response of BaTiO3-PVDF nanocomposites

Abstract Dielectric response of (0–3) type composites, made of BaTiO 3 particles with mean size of 20–30 nm and polyvinylidene fluoride was found to be determined by the response of BaTiO 3 with a broad Curie point anomaly at TC ≈ 317 K. The dielectric anomaly appears in the same temperature range where the decrease in the wave number of the strongest Raman band at ∼520 cm−1 was observed. HRTEM images revealed a core-shell structure of the BaTiO 3 particles and in some grains greater than ∼20 nm fine 180° domain structure was observed.

Piezoelectric, dielectric and pyroelectric properties of 0-3 ceramic-polymer composites

Abstract The circular samples of composites were made from PZT ceramic grains dispersed in polymers (epoxy or rubber). Pressure dependencies of the hydrostatic piezoelectric coefficient dh and permittivity ε were measured in the range up to 60 MPa. The hydrostatic strain coefficient dh, the hydrostatic voltage coefficient gh and figure of merit dh.gh were determined using the static method. The pressure dependence of the hydrostatic coefficients was measured for several successive cycles. Experimental dependence of the charge on pressure and temperature was fitted by multi parameter function. The pressure and temperature dependencies of the hydrostatic dh and pyroelectric p3 coefficients were determined. It was found that the hydrostatic strain coefficient dh and hydrostatic voltage coefficient gh decreased and pyroelectric coefficient p3 increased with pressure at constant temperature.

Simple electric equivalent circuit method to determine piezoelectric and elastic properties of piezoelectric polymer film

A simple method is proposed to determine the parameters of a piezoelectric resonator equivalent circuit in the frequency range from 1 MHz to 1 GHz. Traditional methods use an electronic setup which always involves significant frequency range limitations. The present method overcomes this limitation by simultaneous measurement of the reflectivity coefficient of two samples with HP4191A RF impedance analyzer. The measurements are carried out on films of polyvinylidenefluoride (PVDF) and its copolymer (PVDF/trifluoroethylene (TRFE))(0.75/0.25) which were corona charged as well as corona charged and then thermally aged. Piezoelectric and elastic constants are calculated using the parameters of the piezoelectric resonator equivalent circuit.

Time-domain terahertz and infrared spectroscopy of BaTiO3–PVDF nanocomposites

Several composites of BaTiO3 nanoparticles obtained by mechanosynthesis embedded into a PVDF matrix were studied using time-domain THz and FTIR spectroscopies and microwave measurements with the split-post-resonator technique. No indication of the ferroelectric phase transition could be seen in the temperature dependence of the effective dielectric response, in agreement with expectations based on various effective medium models. The effective soft-mode frequency is strongly shifted up and smeared. No conclusion on the size effect of ferroelectricity can be drawn from the effective dielectric response.