Adolf Sergeevich Nogai

The article investigates the dielectric and conductive properties of the polar α-phase of Na₃Fe₂(PO₄)₃ polycrystals synthesized by solid-phase (sample type 1), melt (type 2), and melt-quenching (type 3) methods. To enable a rapid assessment of the dielectric properties of the polar α-phase of Na₃Fe₂(PO₄)₃, the thermo-polarization mobility parameter μ_Tp(T, E(ω)) was introduced. By studying the dielectric properties, it was concluded that the polar α-phase of type 1 samples consists of large and small dipoles and ordered sodium cations, which possess low values of μ_Tp(T, E(ω)), indicating the presence of strong interaction forces between the crystal lattice and the cationic part of the polycrystal. Additional studies of the samples’ conductivity confirm this conclusion. Studies of the polar α-phase of Na₃Fe₂(PO₄)₃ in type 2 samples have established that their structure contains dipoles and sodium cations with higher values of μ_Tr(T, E(ω)), and also exhibits higher conductivity than Type 1 samples. These data indicate a weakening of the interaction forces between the cationic and anionic components in type 2 polycrystals due to a partial increase in crystal symmetry. The results of studies of the polar α-phase of type 3 samples show that their structure contains dipoles and sodium cations with higher values of μ_Tr(T, E(ω)), and also exhibits higher conductivity than type 2 samples. It is concluded that the structure of type 3 samples is characterized by weak interaction forces between the cationic and anionic parts as a result of an increase in the symmetry of the polar α-phase of Na₃Fe₂(PO₄)₃, caused by sharply graded temperature conditions during the synthesis of polycrystals. By studying the dielectric properties of cathode materials, it is possible to obtain information on the extent of interactions between the cationic and anionic components in polycrystals. It is, therefore, appropriate to use this approach when investigating a wide range of new dielectric and ion-conducting materials.

This paper studies the structural parameters and electrophysical properties (dielectric and piezo electric, as well as currents of thermostimulated depolarization) of samples of composition 0.20BiScO₃·0.45PbTiO₃·0.35PbMg_1/3Nb_2/3O₃ (or in short 0.20BS·0.45PT·0.35PMN) obtained by ceramic and melt-hardening methods of synthesis. In the ceramic method, the samples were obtained from the starting oxides by two-stage firing. In the melt method, amorphous precursors were first obtained from heat-treated and non-heat-treated starting oxide mixtures by melting and subsequent quenching under sharply gradient temperature conditions. Samples were obtained after grinding, pressing, and thermal annealing of the synthesized precursors, and four types of samples differing in size and shape of the intermediate precursor particles (crystallites) were obtained. The X-ray phase analysis showed that the predominant phase in the studied samples is the perovskite phase; in both types of samples, up to 5 wt.% of impurity phase with pyrochlore structure was also present. The samples of 0.20BS·0.45PT·0.35PMN exhibit dielectric properties characteristic of relaxor ferroelectrics, and the polarized samples exhibit a pronounced piezo effect with a piezo modulus value of d₃₃~200 pC/N. A comparative analysis of the properties of the samples obtained by different methods has been carried out. The essential advantage of the melt method is that its use allows obtaining varieties of four kinds of ferroelectric relaxors and reduces the time of synthesis of samples by 2–3 times.

This article studies the influence of solid-phase (type 1 samples) and melt-quenching (type 2 samples) technological modes of obtaining Na₃Fe₂(PO₄)₃ polycrystals on their structures and ion-conducting properties. α-Na₃Fe₂(PO₄)₃ polycrystals of the 1st type are formed predominantly under an isothermal firing regime, and the synthesis of the 2nd type is carried out under sharp temperature gradient conditions, contributing to the formation of glassy precursors possessing a reactive and deformed structure, in which the crystallization of crystallites occurs faster than in precursors obtained under isothermal firing. The elemental composition of α-Na₃Fe₂(PO₄)₃ type 2 polycrystals is maintained within the normal range despite the sharp non-equilibrium thermodynamic conditions of synthesis. The microstructure of the type 1 Na₃Fe₂(PO₄)₃ polycrystals is dominated by chaotically arranged crystallites of medium (7–10 μm) and large (15–35 μm) sizes, while the polycrystals of type 2 are characterized by the preferential formation of small (3–4 μm) and medium (7–10 μm) crystallites, causing uniaxial deformations in their structure, which contribute to a partial increase in their symmetry. The advantage of type 2 polycrystals is that they have higher density and conductivity and are synthesized faster than type 1 samples by a factor of 4. The article also considers the issues of crystallization in a solid-phase precursor from the classical point of view, i.e., the process of the formation of small solid-phase nuclei in the metastable phase and their growth to large particles due to association with small crystallites using phase transitions. Possible variants and models of crystallite growth in Na₃Fe₂(PO₄)₃ polycrystals, as well as distinctive features of crystallization between two types of samples, are discussed.

X-ray diffraction and dielectric studies were performed on synthesized ceramic samples of the section (1–x) (0.8PbMg[ ]Nb[ ]O[ ]BiScO₃)⋅ x(0.8PbTiO[ ]BiScO₃) with [ ]–1 of the ternary BiScO₃–PbTiO₃–PbMg[ ]Nb[ ]O₃ (BS–PT–PMN) system, including the temperature dependence of thermally stimulated depolarization currents (TSDC). It was found that the samples are solid solutions with a perovskite structure, which have cubic symmetry in the range of x = 0–0.587 and tetragonal symmetry in the range of x = 0.680–1. In the intermediate composition range of x = 0.587–0.680 (morphotropic region — MR), the samples consist of a mixture of solid solutions of different symmetries. Data on the change in dielectric properties and TSDC(T) dependencies of solid solutions with a change in their composition were obtained. It was found that samples of compositions x =0–0.625 and 0.6875–1 exhibit relaxor-ferroelectric and conventional ferroelectric properties, respectively, while samples of compositions x = 0.625–0.6875 combine ferroelectric and relaxor-ferroelectric properties.

The electrical conductivity of GMZ grade graphite irradiated by fast neutrons with fluence of 2.22*1019 n/cm2 in the temperature range of 298–448 K was studied. It is shown that the more neutrons fluence, than the more the electrical conductivity of the material decreases.

This article investigates the structures and conductive properties of polycrystals of Na₃Fe₂(PO₄)₃ obtained by solid-state and melt synthesis methods using concentrated optical radiation. It has been established that in the melt synthesis method, the material is synthesized under significantly non-equilibrium thermodynamic conditions, leading to the creation of deformations in the sample, which contribute to the enhancement of ionic conductivity. Additionally, the synthesis duration is reduced by half. Through a comparative assessment of the structural parameters and conductive properties of these materials, it is demonstrated that polycrystals obtained by the melt method exhibit better texture and higher ionic conductivity. The occurrence of deformations during the synthesis of α-Na₃Fe₂(PO₄)₃ under high temperature-gradient conditions indicates the elasticity of the crystalline framework {[Fe₂(PO₄)]³⁻}_3∞. It is concluded that the non-equilibrium thermodynamic conditions of α-Na₃Fe₂(PO₄)₃ synthesis promote the formation of deformations in the crystalline structure of polycrystals, leading to a partial increase in symmetry and ionic conductivity.

This article presents the results of studies of the structure and conductive properties of Na3Fe2(PO4)3 polycrystals synthesized by solid-phase and melt (using concentrated optical radiation) methods. It has been established that with the melt method, the synthesis of the material occurs under significantly nonequilibrium temperature-gradient conditions, which leads to the creation of deformations in the sample that contribute to an increase in ionic conductivity. The ability of the Na3Fe2(PO4)3 structure to adapt to anomalous deformations that occur under temperature-gradient conditions indicates the elasticity of the crystalline framework {[Fe2(PO4)]3-}3∞. Through a comparative assessment of the structural parameters and conductive properties of these materials, it is shown that polycrystals obtained by the melt method have a better texture and greater ionic conductivity. The advantage of this method is that the duration of the synthesis of α-Na3Fe2(PO4)3 is halved. It is concluded that this method is applicable to obtain effective polycrystals of other compositions.

In this paper influence of the excess Ca and Cu cations on the critical temperature (Tc) and critical transport current density (J_c) of high-temperature superconducting ceramics of the compositions (HTSC) Bi_1.6Pb_0.4Sr₂Ca_2.1Cu_3.1O_y, Bi_1.6Pb_0.4Sr₂Ca_2.25Cu_3.25O_y and Bi_1.6Pb_0.4Sr₂Ca₃Cu₄O_y synthesized by the glass-ceramic method has been studied. The synthesis of superconducting ceramics was carried out on the basis of the glass phase, obtained by ultra-fast quenching of the melt. Melting of the mixture of starting components was carried out without the use of a crucible under the influence of IR radiant heating. Analysis of the elemental composition of the samples of the initial precursors showed a significant deviation from stoichiometry in oxygen (increase), as well as a decrease in calcium content. The synthesis of HTSC ceramics was carried out at a temperature of 849–850 °C for 96 h with intermediate grinding every 24 h. Studies of the phase composition of ceramic samples by X-ray diffraction have shown that HTSC ceramics consist only of a superconducting high-temperature phase Bi-2223. Studies of current-carrying characteristics by the four-point probe method according to the criterion of 1 µV/cm² have shown that high-temperature superconducting ceramics of the compositions Bi_1.6Pb_0.4Sr₂Ca_2.1Cu_3.1O_y, Bi_1.6Pb_0.4Sr₂Ca_2.25Cu_3.25O_y and Bi_1.6Pb_0.4Sr₂Ca₃Cu₄O_y have an increased density of critical transport current of 9.12 A/cm², 7.62 A/cm² and 7.26 A/cm², respectively. At the same time, it was found that with a decrease in the content of Ca and Cu cations in HTSC ceramics, an increase in the critical current density is observed.

The paper presents the results of the synthesis of bismuth superconducting ceramics with compositions Bi1.6Pb0.4Sr2Can-1CunOy (n=2, 3, 5) based on amorphous ceramics obtained by ultrafast melt quenching. In order to increase the rate of formation of superconducting compounds, effective devices have been developed for melting and hardening melts under the action of IR radiation. The sample holder was made of platinum. Melting and hardening were carried out in a continuous mode in an oxidizing environment in a flowing air atmosphere. The study of the elemental composition of the precursor samples established a slight deviation towards a decrease in the cationic composition of the precursors (Bi, Pb and Ca), relative to the stoichiometric composition. An increase in oxygen content by 12–15 % was also found. Synthesis of superconducting compounds was carried out in the temperature range of 843–850 °C, depending on the composition. The study found that in the sample Bi1.6Pb0.4Sr2Ca4Cu5Oy (2245) the superconducting high-temperature phase 2223 crystallizes. It was found that the formation of the superconducting phase 2223 in the Bi1.6Pb0.4Sr2Ca4Cu5Oy composition occurs in a lower and wider temperature range (843–848 °C) compared to the Bi1.6Pb0.4Sr2Ca2Cu3Oy (2223) composition. The complete formation of the superconducting high-temperature phase 2223 in a sample with the nominal composition Bi1.6Pb0.4Sr2Ca2Cu3Oy (2223) was carried out in a narrow temperature range of 849–850 °C, in a strict temperature regime with the participation of the liquid phase. An increase in the rate of formation of the superconducting compound 2223 in both studied compositions by 1.5–2.5 times was established, compared with the solid-phase method and other melt methods

Problems of the dipole ordering and ionic conductivity of Na3Sc2(PO4)3 polycrystal that has three polymorphic phases—α, β, and γ—are studied. The features of the α-Na3Sc2(PO4)3crystal...