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.     

Porous piezoelectric composites with extremely high reception parameters

The reception parameters Q ₃₃ ^* and Q _h ^* of modified fiber composites based on high-e ₃₃ ^FC /c ₃₃ ^{FC, E} ferroelectric piezoceramics (e ₃₃ ^FC is the piezoelectric constant, c ₃₃ ^{FC, E} is the elastic modulus) are considered as functions of the electromechanical properties and the porosity of the components. Pore configurations at which the values (Q ₃₃ ^* )²≈(Q _h ^* )²≈7×10⁻⁹ Pa⁻¹ for the polymer matrices of 1-0-3 composites are much higher than for conventional ternary composites are analyzed.     

Synthesis of Ethyl 2,3-Anhydro-4,5:6,7-di-O-isopropylidene-D-arabino-heptonate by the Darzens Reaction

Ethyl 2,3-anhydro-4,5:6,7-di-O-isopropylidene-D-arabino-heptonate was prepared for the first time by the Darzens reaction from 2,3:4,5-di-O-isopropylidene-D-arabinose and ethyl chloroacetate under the action of metallic sodium in p-xylene. The reaction gives a number of by-products, including ethyl 3-chloro-2-deoxy-3-hydroxy-4,5:6,7-di-O-isopropylidene-D-arabino-heptonate.     

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.     

Strong and weak relaxation polarization in dielectric statistical mixtures of non-extended particles

The heterogeneous dielectric in the form of a statistical mixture of nonextended particles is considered; the existence of through conductivity in each component is examined, and an expression for the complex dielectric permeability of this system is obtained. The conditions for the development of strong relaxation polarization in such systems are found. The transition from strong to weak relaxation polarization is identified from an increase in the relationship between the contributions of the relaxation polarization and the fast polarization processes to the effective polarizability of a heterogeneous system and a change in the distribution parameter.     

Reversible permittivity of multicomponent PMN-PT-based ceramics

The reversible permittivity of Ba-doped ceramics of the multicomponent system mPMN-nPNN-yPZN-xPT (m = 0.1298–0.4844, n = 0.1266–0.4326, y = 0.0842–0.130, x = 0.25–0.40) is studied. The reversible permittivities of cubic, heterophase, and tetragonal ceramics are analyzed under various experimental conditions, such as the measuring ac electric field frequency and the time of residence in a dc bias electric field. The transformation of permittivity minima into a plateau and the subsequent disappearance of all anomalies as the lead titanate concentration decreases are assumed to be related to a change in the initial domain structure of the material. A diagram illustrating the dependence of the tunability coefficient on the lead titanate concentration is plotted, and the ceramic compositions that correspond to the characteristic dependences of reversible permittivity are determined.     

Heterogeneous multiferroics: Magnetoelectricity and piezoelectric effect

Physics of the Solid State - The concentration and frequency dependences of the effective magnetoelectric, dielectric, piezoelectric, and piezomagnetic constants of two-dimensional conducting...     

Dielectric relaxation and magnetic characteristics of the Bi0.5La0.5MnO3 ceramics

The complex permittivity ?* of ceramics of bismuth-lanthanum manganite Bi_0.5La_0.5MnO₃ has been measured in ranges of temperatures T = 10–200 K and frequencies f = 10²–10⁶ Hz. Clearly pronounced regions of the non-Debye dielectric relaxation have been revealed at low temperatures (T < 90 K). To describe them, the possible mechanisms have been proposed and discussed. The temperature dependences of magnetization, the anomalous behavior of which can be associated with the phase transition from the paramagnetic phase into the ferromagnetic phase occurring at T ～ 40–80 K, have been measured in the temperature range T = 10–120 K.     

Dielectric constant of polymer matrices containing isolated inclusions: Giant dielectric enhancement instead of collective resonance

A giant increase in the static dielectric constant and a giant dielectric relaxation are predicted for a heterogeneous medium consisting of matrix-isolated spheroids and described by the Maxwell-Garnett formula. The possibility of observing collective dielectric resonance in such a medium is also discussed.