G. S. Radchenko

Giant Piezoelectric and Dielectric Enhancement in Disordered Heterogeneous Systems

Effective complex piezoelectric and dielectric constants of disordered heterogeneous systems, such as statistical mixtures consisting of spheroidal particles of the same orientation but with random distribution in space, are studied. It is found for the first time that, in such systems, there exists giant piezoelectric enhancement accompanied by giant relaxation of piezoelectric coefficients and permittivity. The piezoelectric and dielectric spectra differ considerably from the Debye spectra and have a Cole-Cole character. The dependence of the effects considered on the aspect ratios of the spheroids is investigated. The physical mechanisms responsible for the anomalous behavior of the piezoelectric coefficients and permittivity are considered.

Maxwell-Wagner Relaxation of Elastic Constants of Layered Polar Dielectrics

This paper reports on the results of investigations into the effective complex elastic compliances of a composite in the form of a multilayer piezoactive medium consisting of layers of polar dielectrics connected in series. Exact solutions for normal and inverse Maxwell-Wagner relaxations of elastic compliances are derived for the first time. The mechanical hysteresis loops corresponding to either a decrease or an increase in the elastic energy are analyzed. It is demonstrated that relaxation of elastic constants occurs only in piezoactive media.

Dielectric spectra of disordered ferroelectric systems: Polycrystals and composites

The dielectric spectra of heterogeneous systems that have very large dielectric constants and exhibit the Maxwell-Wagner relaxation are analyzed. The spectra of the disordered systems are found to be of a non-Debye type, and attempts to fit them using either the Cole-Cole or Davidson-Cole equations sometimes fail to produce satisfactory results. Experimental spectra of disordered systems are proved to be close to the spectra obtained by computer simulation of statistical mixtures and ferroelectric ceramics. A new formula is suggested to describe the dielectric relaxation in polycrystalline and composite materials, and reasons for the non-Debye nature of the dielectric spectra are examined.

Giant Piezoelectric Effect in Layered Ferroelectric-Polymer Composites

The giant piezoelectric effect and giant piezoelectric relaxation are revealed for the first time in structures consisting of ferroelectric and polymer layers connected in series. Under these effects, the composites exhibit giant static permittivities. The physical mechanisms responsible for the unusual behavior of the piezoelectric coefficients and permittivities are considered.

A theory of the inverse magnetoelectric effect in layered magnetostrictive–piezoelectric structures

A theory of the inverse magnetoelectric effect in layered structures has been presented. The theory is based on solving the equations of elastodynamics and electrostatics separately for the magnetostrictive and piezoelectric phases, taking into account the conditions at the interface between the phases. Expressions for the coefficient of inverse magnetoelectric conversion through the parameters characterizing the magnetostrictive and piezoelectric phases have been obtained. Theoretical dependences of the inverse magnetoelectric conversion coefficient on the frequency of the alternating-current electric field for the three-layer PZT–Ni–PZT structure and the two-layer terfenol-D–PZT structure have been calculated. The results of the calculations are in good agreement with the experimental data.

Magnetoelectric effect in layered disk-shaped magnetostrictive–piezoelectric structures: Theory and experiment

Theoretical and experimental studies of the magnetoelectric effect in a disk-shaped magnetostrictive–piezoelectric structure in the electromechanical resonance region are presented. An expression for the magnetoelectric voltage coefficient is derived based on the simultaneous solution of elastodynamic and electrostatic equations separately for magnetostrictive and piezoelectric layers. The conditions at the interface were taken into account based on the premise that the interaction between layers is implemented by shear. It is shown that the inhomogeneity of the voltage and strain distribution over the sample thickness, caused by the interface, leads to a significant contribution to the effect in the case of thick layers. The theoretical and experimental dependences of the frequency characteristic of the effect are presented for the permendur–lead zirconate-titanate–permendur structure. The theoretical calculations are in good agreement with experimental data.

Electromechanical Properties of Ferroactive Composites near the Percolation Threshold

This paper deals with the fundamental problem of electromechanical response in conducting disordered systems with different dimensions. We show that the dielectric and piezoelectric spectra of such systems have very different relaxation frequencies. The Havriliak-Negami empirical equation is applied for fitting such spectra. The Cole-Cole diagrams are derived and discussed. The physical processes responsible for the unusual behavior of basic effective constants are analyzed.

Inverse multimodal magnetoelectric effect in piezomagnetostrictive rings

The theoretical investigation of the frequency dependence of the inverse magnetoelectric effect in piezomagnetostrictive rings in the region of radial resonances has been presented. The analytical expression for the coefficient of the inverse magnetoelectric conversion for ring-like samples with the axial polarization has been derived. It has been shown that the energy is redistributed between the modes depending on the structure geometry, which results in the formation of regions where some modes are absent while the amplitude of other ones increases. The voltage transfer coefficient, which can considerably exceed this parameter in the samples shaped as a continuous disc, has been theoretically predicted.

Elastic Constants Relaxation in Disordered Heterogeneous Systems

Using self-consistent effective-medium theory, we studied the complex elastic compliances of conducting disordered heterogeneous piezoelectric-polymer systems. The considered system is a random mixture of piezoelectric spheroids and polymer ones with the same orientation. The proximate cause of the effective elastic constants frequency dependencies was considered. The nature of the obtained spectra was analyzed.

Giant Piezoelectric and Dielectric Relaxations in Statistical Mixtures

The effective complex piezoelectric and dielectric constants of disordered heterogeneous systems of the type of statistical mixtures with the components in the form of spheroid-shaped particles equally oriented but randomly arranged in space were studied. It has been found for the first time that in such systems there appears a giant piezoelectric enhancement accompanied by a giant relaxation of piezoelectric coefficients and the dielectric permittivity. Piezoelectric and dielectric spectra differ significantly from the Debye ones and are of Davidson-Cole type. The influence of the aspect ratio of spheroids on the effects under consideration was studied. The physical mechanisms responsible for the anomalies in the behavior of piezoelectric coefficients and the dielectric permittivity were considered.