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.

The object of this study is the process of deorbiting the KazEOSat-1 spacecraft, which has completed its active service life in low Earth orbit. The main problem is the lack of an effective technique to deorbit KazEOSat-1, taking into account its technical characteristics, orbital parameters, and the need to minimize risks to the environment and other objects in orbit. As part of the work, a software model was built that takes into account the initial orbital parameters of the device, which are essential for planning and performing deorbiting maneuvers. The model is designed to accurately calculate the descent trajectory, taking into account the laws of celestial mechanics and the influence of atmospheric conditions. The optimal deorbiting strategy was selected based on an analysis of various methods for calculating orbital maneuvers aimed at reducing fuel consumption and minimizing environmental risks. This included a comparative analysis of existing approaches and the selection of the most suitable ones under the given mission parameters. The results of the simulation using precise modeling methods in the MATLAB software environment allowed us to determine the main deorbiting parameters, such as the altitude at which the maneuvers begin, the required velocity impulses, the total fuel consumption, and the expected time before entering the dense layers of the atmosphere. Based on the obtained data, practical recommendations were formulated for the KazEOSat-1 deorbit. The first stage, the active controlled deorbit, is carried out by operating the low-thrust engine and braking by the Earth’s atmosphere, allowing the spacecraft to descend from 758 km to 444 km in 2.5 days. The second stage, the passive uncontrolled deorbit, continues the descent to 103 km in 969 days, using only atmospheric braking. The third stage, the uncontrolled drop, begins after reaching 103 km and ends with a drop to the Earth in 834 seconds

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.

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.

In this work, the features of the structure-conductivity relationship in polar (α) and ion-conducting (β and γ) phases of Na3Fe2(PO4)3 polycrystals obtained by the melt-quenching method have been investigated. Na3Fe2(PO4)3 polycrystals are synthesized by isothermal firing of glassy precursors (after grinding and pressing). The glassy precursors were prepared by melting a pre-calcined (350 C) mixture of initial reagents under the influence of thermal and infrared radiation energy and rapid cooling of the melt (or quenching). It was found that the deformations of the structure of polycrystals α-Na3Fe2(PO4)3 during synthesis by melt-quenching lead to an increase in the conductivity in polar (α) and ion-conducting (β and γ) phases because they contribute to the reduction of structural distortions of the samples. Polycrystals Na3Fe2(PO4)3 obtained by the melt-hardening method have high-quality crystallites, high density, and conductivity, and their synthesis is faster than samples obtained by other methods. The established advantages of synthesized polycrystals of α-Na3Fe2(PO4)3 are probably connected with deformations of structure and chemical activity of glassy precursors caused by nonequilibrium thermodynamic conditions of synthesis. For the first time, it was possible to detect domain structures in polycrystals of α-Na3Fe2(PO4)3 obtained by the melt-quenching method, which confirms the polarity of the α-phase, the appearance of which is associated with the ordered displacement of the cationic sublattice relative to the anionic sublattice under the influence of monoclinic distortion of the crystal framework.