S. A. Kovrigina

Bias Field Effect on the Dielectric and Pyroelectric Response of Pb(Fe0.5Ta0.5)O3 Relaxor Multiferroic Ceramics

Dielectric and pyroelectric studies of PbFe0.5Ta0.5O3 ceramics have been carried out under different bias field values. E,T-phase diagram has been constructed using these data. It has been found out that PbFe0.5Ta0.5O3 combines the properties of both relaxors and usual ferroelectrics. The results obtained show that the origin of the relaxor-like behavior in PbFe0.5Ta0.5O3 seems to be somewhat different as compared to canonical relaxors.

The Effect of PbO-Nonstoichiometry on Dielectric and Semiconducting Properties of PbFe0.5Nb0.5O3-Based Ceramics

Dielectric, X-ray and electric resistivity studies of nonstoichiometric PbFe0.5Nb0.5O3-based ceramics obtained by solid-state reaction route with PbO/(Fe0.5Nb0.5O2) molar ratio differing from 0.6 to 1.2 have been carried out. Deviation from stoichiometric PbFe0.5Nb0.5O3 composition leads to formation of diphase mixtures containing ferroelectric perovskite PbFe0.5Nb0.5O3 phase and nonferroelectric PbO or pyrochlore Pb3Nb4O13 phases and to decreasing of the dielectric permittivity values. The electric resistivity of PbFe0.5Nb0.5O3 ceramics decreases dramatically when the sintering temperature increases. The formation of the pyrochlore phase decreases the room temperature resistivity values while the anomaly of the positive temperature coefficient of resistivity above the ferroelectric Curie temperature gradually diminishes with the increase of the pyrochlore content.

Effect of the Conductivity on Dielectric Spectra at the Relaxation Process with the Fröhlich Relaxation Times Distribution

The effect of conductivity on dielectric spectra of relaxing polarization processes described by the Fröhlich relaxation times distribution is studied. It is shown that in this case the dielectric relaxation processes subdivide into strong and weak ones. Borders between these relaxation processes are established. The physical reason of the division of the relaxation processes is determined.

Dielectric and polarization studies of magnetoelectric coupling in non-relaxor Pb(Fe1/2Ta1/2)O3 multiferroic ceramics

ABSTRACT Dielectric permittivity ϵ and polarization / electric field hysteresis loops of highly-resistive Li-doped non-relaxor Pb(Fe1/2Ta1/2)O3 ceramics obtained by one-step sintering of the mechanically activated mixture of starting oxides and Li2CO3 have been studied. Antiferromagnetic phase transition temperature TN ≈ 150 K was determined using Mossbauer spectroscopy studies at different temperatures. Though no anomalies in ϵ(T) curve at TN were observed, 1/ϵ(T) dependence exhibits change of the slope in the vicinity of TN. Anomalies in the temperature dependences of coercive field EC and derivative of the spontaneous polarization PS are observed near TN as well. These anomalies are attributed to magnetoelectric coupling.

Negative Capacity of a Dielectric as a Result of the Development of Relaxation Polarization

The reasons for the emergence of negative capacitance in matter are discussed. The relaxation polarization in matter, accompanied by the creation of an electric field of the inverse directivity, is named one of the possible reasons for the emergence of a negative capacitance. This field can appear in local areas of a substance after development of the polarization of ionic displacement. Calculated dielectric spectra of matter characteristic of such relaxation polarization are presented.

Impedance Description of the Processes of Electromigration in a Substance

Equivalent electrical circuits for all types of electromigration are proposed: pass-through conductivity, fast polarization processes, and relaxation polarization. The principle of the superposition of currents allows circuits to be designed with the simultaneous development of several processes of electromigration. The possibility of identifying the processes of electromigration developing in a substance from the experimental impedance spectra is discussed.

Frequency control of the dielectric temperature coefficient of resistance in the process of relaxation polarization

It is shown that the dielectric temperature coefficient of resistance (TCR) can be changed in the process of relaxation polarization. The TCR frequency dependences are calculated using the Debye model of polarization. When the signal frequency is altered, both the value and the sign of the TCR change. The effect of the change in the value and sign of the TCR when the frequency is altered is discovered experimentally in doped semiconductor barium titanate.

Strong relaxation polarization in a double-layer capacitor

In dielectrics, strong relaxation polarizations develop that contribute much to the polarization of the substance. Such great contributions should be expected in heterogeneous dielectrics. Relaxation polarization is studied in the simplest of heterogeneous dielectrics: a double-layer capacitor. The areas of concentration of the development of strong relaxation polarizations, the locations of which depend on the ratios of permittivities and the through electrical conductivities of the layers, are determined. The transition to strong relaxation polarization in this case also occurs in accordance with criteria developed earlier.

Determining the form of a relaxator distribution by extrapolation

AbstractА new way of determining types of relaxator distribution and their parameters is proposed. It is based on calculating the slopes of high-frequency and low-frequency asymptotes in the frequency dependences of the real and imaginary parts of complex dielectric permittivity and conductivity in dielectrics with polarization relaxation.

Determining the relaxation polarization parameters in dielectrics with high electrical conductivity

In dielectrics with high steady leakage of conductivity, the frequency–temperature dependences of the dielectric loss tangent generally allow us to determine the relaxation time and activation energy of relaxation process only when they are strong. With weak relaxation processes, there are no extrema in the frequency dependence of the dielectric loss tangent. In such cases, the parameters of the relaxation processes are initially determined from the frequency behavior of the imaginary parts of the electrical module or impedance. However, the frequency dependences of these quantities when there is electrical conduction can contain three extrema. Identifying the maxima associated with relaxation polarization therefore requires additional research.