A. S. Bogatin

High dielectric permittivity in AFe1/2B1/2O3 nonferroelectric perovskite ceramics (A=Ba, Sr, Ca; B=Nb, Ta, Sb)

AFe1/2B1/2O3(A=Ba, Sr, Ca; B=Nb, Ta, Sb) ceramics were synthesized and temperature dependences of dielectric permittivity were measured at different frequencies. The experimental data obtained show very high values of dielectric permittivity in a wide temperature interval that is inherent to so-called high-k materials. Analyses of these data establish a Maxwell–Wagner mechanism as a main source for the phenomenon observed.

Dielectric and Mössbauer Studies of High-Permittivity BaFe1/2Nb1/2O3 Ceramics with Cubic and Monoclinic Perovskite Structures

Ceramic samples of monoclinic and cubic modifications of ternary perovskite BaFe 1/2 Nb 1/2 O 3 have been obtained by solid-state reaction route. Mossbauer 57 Fe spectra and Neel temperature values appeared to be very similar for both modifications. The values and temperature dependences of the dielectric permittivity for BaFe 1/2 Nb 1/2 O 3 samples were found to depend primarily on their apparent resistivity values and not on their structure. Thus high permittivity values of BaFe 1/2 Nb 1/2 O 3 are due not to the ferroelectric relaxor behavior but rather to the relaxation of the Maxwell-Wagner type and/or relaxation contributed by the oxygen vacancies.

Random-Site Cation Ordering and Dielectric Properties of PbMg1/3Nb2/3O3-PbSc1/2Nb1/2O3

(1 − x)PbMg1/3Nb2/3O3-(x)PbSc1/2Nb1/2O3 (PMN-PSN) solid solution crystals have been grown by the flux method in the whole concentration range. X-ray supercell reflections due to B-cation ordering were observed for as-grown crystals from the 0.1 ≤ x ≤ 0.65 compositional range. Though the ordered domains are rather large (∼50 nm) the relaxor-like dielectric behavior is observed for compositions with x < 0.6. The diffusion of the dielectric permittivity maximum in as-grown crystals is the lowest at x = 0.6 and increases towards the end members of solid solution. Such behavior is explained within a Bragg-Williams approach by employing the random layer model. At x ∼ 0.6 the excitation energy determined from the Vogel-Fulcher relation exhibits a jump which we regard to changing the kind of the polar regions from PbMg1/3Nb2/3O3 to PbSc1/2Nb1/2O3 related type.

Electric properties in the range of ferroelectric phase transitions in Pb(Fe0.5Nb0.5)O3 crystals and ceramics

Abstract Transition between two ferroelectric phases in the range of 85°C was observed when studying dielectric and semiconductive properties of Pb(Fe0.5Nb0.5)O3 crystals and ceramics. It was found that electron space-charge polarization plays the important part in formation of dielectric properties. The reasons of ϵ (T) anomaly absence at 85°C in some ceramic samples are discussed.

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.

Cation Ordering and Dielectric Properties of PbMg 1/3 Nb 2/3 O 3 -PbSc 1/2 Nb 1/2 O 3 Solid Solution Crystals

(1 m x )PbMg 1/3 Nb 2/3 O 3 -( x )PbSc 1/2 Nb 1/2 O 3 solid solution crystals have been grown by the flux method. X-ray supercell reflections due to B-cation ordering were observed for crystals in the 0.1 < x < 0.65 compositional range. In as-grown crystals diffuseness of dielectric permittivity maximum is the lowest for x = 0.65 composition and increases toward the end members of solid solution. Such behavior is assumed to be due to the random-site ordering of B-site cations and non-monotonic dependence of the compositional order-disorder phase transition temperature on concentration.

Determination of electric, thermoelectric and other properties of grains and grain boundaries in ceramic ferroelectrics

Knowledge about the relation between physical parameters of phases constituting a heterophase system, and the effective parameters of the whole system is important for preparation of materials with desired properties. Particularly essential is determination of parameters of individual phases from those measured for the whole system.With the selected model of grain and grain-boundary distribution throughout the volume of ceramics, its electric, thermoelectric, galvanomagnetic and other parameters may be determined separately by application to a specimen of periodically variable electric, thermal, magnetic and other excitations. In this way, resistivity, permittivity, Seebeck coefficient were determined as functions of temperature for grains and grain boundaries of semiconducting barium titanate.

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.

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.