S. P. Kubrin

Dielectric, magnetoelectric, structure, and dissipative properties and the Mössbauer effect in PbFe1/2Nb1/2O3 ceramics in wide frequency and temperature ranges

High-quality fine-grained ceramic samples of classical multiferroics PbFe1/2Nb1/2O3 (PFN) were synthesized. Their dielectric, magnetoelectric, and magnetic characteristics, including the Mössbauer effect, were measured over wide ranges of temperatures (10–1000 K) and field frequencies (from 25 Hz to 1 MHz). The temperature dependence of the dielectric loss exhibits a maximum between 150 and 170 K, likely due to magnetic ordering. The dependence of ɛ on the magnetic field displays an anomalous increase near the Curie temperature (370 K) that rises to 40% upon heating.

The crystal and grain structure and physical properties of Bi1 − xAxFeO3 (A = La, Nd) solid solutions

High-quality ceramics were synthesized on the basis of Bi1 − xAxFeO3 (A = La, Nd; 0.00 ≤ x ≤ 0.20) solid solutions. Their crystal and grain structure, Mössbauer spectra, and other dielectric and magnetic characteristics were studied. It was shown that an increase in the content of A elements in the studied samples considerably enhanced their magnetic susceptibility and magnetoelectric effect.

Dielectric spectroscopy of Pb1–xBax(Mg1/3Nb2/3)m(Zn1/3Nb2/3)y(Ni1/3Nb2/3)nTizO3 solid solutions in a wide temperature interval

The dielectric spectra of Pb1–xBax(Mg1/3Nb2/3)m(Zn1/3Nb2/3)y(Ni1/3Nb2/3)nTizO3 (x = 0–0.15, m = 0.4541, y = 0.0982, n = 0.1477, and z = 0.3) ceramic samples have been studied in wide intervals of temperature (10–873 K) and frequency of the measurement electric field (0.1–1000 kHz). It has been found that an increase in the Ba2+(x) content leads to a reduction in the phase transition temperature (from 418 K at x = 0 to 256 K at x = 0.15), to the transition from the normal ferroelectric state to the relaxor ferroelectric one (at x ≥ 0.025), and to the disappearance of temperature hysteresis of dependences of the relative dielectric permittivity. It has been hypothesized that a tricritical point is present near x ∼ 0.125 in the x–T phase diagram of the studied solid solutions.

Structure and dielectric characteristics of PbFe0.5Nb0.5O3 single crystals grown under different conditions

The structure and dielectric and magnetic characteristics of plumbum ferroniobate crystals grown from a solution–melt containing potassium fluoride have been investigated. The obtained crystals have a cubic shape, 4-mm edges, and a rhombohedral structure at room temperature. Iron ions in the samples have the valence state of Fe3+. A change in the Mössbauer spectra with a change in temperature has been registered; this is indicative of strong diffusion of the magnetic phase transition in the range from–130 to–230°C, which is enhanced due to incorporation of fluorine atoms into the structure of the basic compound accompanying the synthesis process and clusterization of this structure. The latter phenomena also lead to a decrease in the temperature of transition from the ferro- to paraelectric phase.

The relaxation dynamics, iron valence state, and Mössbauer effect in PFN ceramics

The dielectric properties, X-ray emission spectra, and Mössbauer effect in ceramics made of PbFe1/2Nb1/2O3 (PFN) compound were studied. The relaxation dynamics revealed above Curie temperature TC at a frequency of 3 × 10−2–105 Hz is described in detail. Analysis of the X-ray emission and Mössbauer spectra showed that at room temperature (T = 300 K), the iron ions in PFN are mainly in the high-spin valence state Fe3+. The Mössbauer spectral parameters obtained at T = (300, 353, and 393 K) indicate an octahedral environment for Fe3+ in both the ferroelectric and paraelectric phases.

Relaxation dynamics, microwave absorption, and secondary periodicity in properties of rare-earth-modified bismuth ferrites

Based on an analysis of the structure and physical properties of bismuth ferrite (BiFeO3) modified by rare-earth (RE) elements, solid solutions characterized by the presence of spontaneous magnetization, low- and high-temperature relaxation, and maximum microwave absorption have been found. It is established that these materials exhibit a secondary periodicity in their properties. The observed effects are related to the appearance of symmetry phase transitions, specific features of the crystal chemistry of RE elements, and changes in the type of solid solutions.

Structure, dielectric, magnetoelectric, and dissipative properties of AFe2/3W1/3O3 (A = Ba, Sr, Pb) ceramics in wide frequency and temperature ranges

High-density impurity-free AFe2/3W1/3O3 (A = Ba(BWF), Sr(SWF), Pb(PWF)) ceramics with well-developed microstructures were synthesized. Their structures and dielectric properties were investigated over wide temperature (10–973 K) and frequency (25 Hz-1 MHz) ranges. These materials are found to be almost transparent in the microwave range. They were characterized by weak magnetoelectric interactions; ɛ(BWT) ≈ 50 up to 400 K and ɛ(BWT) and ɛ(PWT) have second maxima between 400 and 600 K. All properties are easily reproduced, regardless of slight variations in synthesis conditions.

Peculiarities of the dielectric, elastic, and anelastic properties of the PbFe1/2Nb1/2O3 ferroelectromagnet at the antiferromagnetic phase transition

Peculiarities in the behavior of the dielectric, elastic, and anelastic properties of the PbFe1/2Nb1/2O3 ceramic ferroelectromagnet have been found and investigated near the antiferromagnetic phase transition (Néel temperature TN = 160 K). It is established that the transition to the antiferromagnetic phase leads to a decrease in the permittivity and elastic compliance. The anomaly of permittivity found near TN indicates the presence of magnetoelectric interaction in the magnetically ordered phase.

X-ray photoelectron and mössbauer spectroscopy studies of the valence state of transition metal ions in Co1–xFexCr2O4 (x = 0.1, 0.2, 0.5) ceramics

The valence state of transition metal ions in the Co1–xFexCr2O4 (x = 0.1, 0.2, 0.5) system has been investigated using X-ray photoelectron and Mössbauer spectroscopy. It has been shown that, in this system, there are Fe2+ and Fe3+ ions. The relative Fe3+/Fe2+ contents have been determined by fitting the experimental Fe 2p photoelectron spectra by a superposition of theoretical spectra of the Fe2+ and Fe3+ ions, as well as using Mössbauer spectroscopy.

Phase formation and the formation of microstructures and macroscopic responses in BST ceramics

Patterns of phase formation and the formation of microstructure and macroscopic responses in (1–х)BaTiO3–xSrTiO3 (0.00 ≤ х ≤ 1.00) ceramics are established.