№ 5 (2025)

It is shown that there was a preferential formation of nanocrystals of solid solutions M–Pt of face-centered cubic structure when co-reduction of metal precursors (M²⁺ (M = Fe, Co, Ni) and [PtCl₆]²⁻) by alkaline hydrazine hydrate solution was. It was demonstrated by methods of elemental analysis, X-ray diffraction, and high-resolution transmission electron microscopy. Content of Fe and Co in the phase of solid solutions was ≈ 11.5 ± 0.5 and ≈ 16.9 ± 1 at. %, respectively. By comparing the results of high-resolution transmission electron microscopy, elemental analysis, X-ray phase analysis, and X-ray structural analysis, it was established that in the Fe—Pt and Co—Pt systems, in addition to the M—Pt solid solutions with a face-centered cubic structure revealed by X-ray diffraction methods, nanodispersed metallic phases, practically inaccessible for registration, are formed in the regions above and below the limiting Fe and Co contents. However, as for nanostructured Ni—Pt system, there was not upper limit of Ni content in the solid solutions of face-centered cubic structure, up to 40 at. %. Therefore, the phase compositions were represented by two types of face-centered cubic structures, i.e. pure Ni phase and solid solution phases, with Ni content of 10–12 and 40 at. %. The key points about the nature of these structure-phase features reviewed in the article.

Rigorous calculations of the absolute diffraction efficiency η, performed earlier using two commercial computer solver based on electromagnetic methods, have shown that the maximum η of neutron gratings with sinusoidal and lamellar groove profiles can exceed known analytical limits. Thus, for a sinusoidal grating with a period of d = 50 μm, a groove depth of h = 53.4 nm at an incidence angle of θ = 89.72° (θc = 89.53°), η(−1) = 46.8% was obtained at a wavelength of λ = 1 nm, which is 38.5% higher than the maximum scalar efficiency. For a similar lamellar grating, η(−1) = 46.05% was obtained, which is 13.7% higher than the scalar one. In this work, for copper, one of the promising materials for cold neutron optics, not only gratings with sinusoidal and lamellar groove profiles were investigated, but also the most efficient gratings with a triangular profile ("with blaze") were considered. For a grating with d = 50 μm and h = 41.1 nm, η(−1) = 79.2% was obtained for θ = 89.37° and λ = 1 nm. The data calculated using both codes with an accuracy of ~0.1% for the main diffraction orders of gratings of all groove profiles converge well and correspond to the estimates obtained using the phenomenological approach.

The first results of combined deposition of coatings from a beam of accelerated C₆₀ fullerene ions and fluoroplastic vapor (polymetrized tetrafluoroethylene, PTFE) are presented. The coatings were formed by condensation of thermally evaporated PTFE on a Si substrate in vacuum under irradiation with a C₆₀ ion beam with an energy of 5 keV, passed through a mass spectrometer. The calculated ratio of C₆₀ ions and molecular fragments condensing on the substrate (–CF₂–CF₂–) was chosen close to 1:1. The structure and chemical bonds have been studied by Raman scattering and X-ray photoelectron spectroscopy, according to which the coating contains about 8.6 at. % fluorine. The coating contains ~35% sp³ bonds, with a sp³/sp² ratio of ~0.76, and the main part (up to 50%) of fluorine–carbon bonds is concentrated in the form of polymer chains –CF₂–CF₂–, which are located in a solid carbon matrix, that is, the coating structure is nanocomposite. Mechanical tests showed high hardness of the coating H~32 GPa with an H/E ratio of ~0.16 (E is Young's modulus). The coating is characterized by a high contact angle of wetting with distilled water (CA = 98°). Tribological tests showed a coefficient of friction close to 0.18, with low wear of less than 10^–7 mm³/N m.

The crystallographic texture of bainitic and martensitic steels determined at room temperature is related to the texture of the prior austenite owing to the orientation relationship between the parent and daughter phases. This allows, in particular, judging the deformation of austenite and recrystallization. It becomes possible to analyze the effect of hot rolling on the austenite structural state, which precedes quenching. The structures and textures of bainitic and martensitic steels have been analyzed using electron backscatter diffraction. In the case of single-pass rolling, the state of prior austenite can be estimated based on the morphology of austenite grains reconstructed on the basis of the electron diffraction data. In the case of multi-pass hot rolling, which proceeds with a gradual decrease in temperature, such an estimate is difficult due to peculiarities of structure development. At the same time, this can be performed based on of the analysis of crystallographic texture of steel. As a quantitative characteristic of the structural state of austenite, a scalar parameter is proposed that depends on the relative intensity of texture components formed during the phase transformation.

AISI304 steel samples cut from a forged rod were rolled at room temperature using longitudinal and cross schemes, after which they were subjected to various heat treatments with cooling from temperatures of the two-phase α+γ- and single-phase γ-regions to fix different phase compositions. The phase composition was studied, the volume fractions of austenite and α-martensite, crystallographic texture, structure and substructure of two-phase steel were determined, uniaxial tension tests of rolled sheets in different directions were carried out to evaluate the anisotropy of mechanical properties. It was found that the occurrence of γ → α phase transformations during deformation significantly depended on the rolling scheme and conditions, and the amount of remaining austenite varied within 15–29%. The reverse α → γ phase transformation initiated by annealing in the single-phase γ-region leads in the case of longitudinal rolling to the multiplication of the γ-phase texture components and the appearance of an additional orientation {113}<332>, while in the cross scheme the texture of deformed austenite is preserved. Quenching in the two-phase region at 700°C does not lead to a fundamental change in the austenite texture, but ensures the appearance of additional martensite components {110}<001> and {112}<111>. The texture features affect the anisotropy of elastic properties and yield strengths: the anisotropy of the Young's modulus of samples consisting entirely of austenite is higher (E_TD/E_RD = 1.67) compared to 1.25 for samples of quenched two-phase steel.

In this work, single-phase monocrystalline and thin-film samples of lead selenide were synthesized. Methods have been developed for the creation of surface oxidized lead selenide with a conductivity different from the base PbSe. Using oxidized lead selenide as an interface, Ag/Pb₃OSeO₃/PbSe heterostructures were made, demonstrating stable memristive characteristics. The obtained heterojunctions were investigated for the detection of resistive switching, the volt-ampere characteristics and the temperature dependence of the resistance of the structures were measured. By changing the external parameters: frequency, magnitude of the electric field voltage applied to the heterocontact, different metastable states are realized. Dynamic effects were studied, and the transition times from one metastable state to another were determined. Single crystal-based memristors were more stable than film structures, reproducible characteristics in single crystal-based memristors were observed for several months.

Structural transformations in Ni–Ag bimetallic nanoparticles sized 5 nm were investigated after a cycle of sequential phase transitions corresponding to melting and crystallization. The initial configuration of the Ni–Ag bimetallic nanoparticles corresponded to a Janus structure. Two alternative methods — molecular dynamics and Monte Carlo methods — were used to simulate the thermally induced effects. The tight binding potential was used as the intermolecular interaction potential. It was shown that for Ni–Ag bimetallic nanoparticles, surface segregation of Ag atoms is characteristic, and specific features of the segregation behavior of Ag atoms at different concentrations were identified. The obtained regularities are compared with the experimental results for Ni–9 wt. % Ag nanoparticles synthesized by the method of electric explosion of wires, which is characterized by the formation of particles with a "core–shell" structure. Based on the analysis of calorimetric curves of the potential part of the specific internal energy, hysteresis of the melting and crystallization temperatures was revealed, allowing for the estimation of the starting and finishing temperatures of the corresponding phase transition, as well as determining the thermal stability intervals. In addition, it was found that with an increase in the number of nickel atoms in the composition of the particles, the width of the hysteresis of the melting and crystallization temperatures increases.

Besides the standard application of ion thrusters for the Near-Earth space exploration and cruise missions, there is a problem of removing man-made space debris objects from the Near-Earth space by a weakly diverging ion beam, i.e. by a contactless impact. However, for stable operation of the ion-extraction system of both the ion thruster and the ion source, it is necessary to predict and take into account the thermal deformations of electrodes of the ion-extraction system. The increase in the number of man-made space debris objects in the Near-Earth space hinders the long-term sustainable development of space activities. Many different methods have been proposed for removing large objects into disposal orbits or into low orbits for their further destruction in the dense layers of the Earth's atmosphere. To remove space debris, a service spacecraft can be used, which could approach the space debris to be removed and tow it to the disposal region by a contactless impact. A radio-frequency ion source forming a weakly diverging ion beam, under the influence of which the space debris objects would move in the direction of the disposal orbit, can be used as an onboard device designed for this purpose. Such radio-frequency ion source is in fact a radio-frequency ion thruster. The development of thermal and thermomechanical models of ion thruster and ion source taking into account the requirements for the reliable operation and integration of ion source with service spacecraft systems to provide contactless space debris transportation in space and integrations of ion thruster with onboard systems to provide attitude control or ensure cruise missions is one of the problematic scientific and technical issues. In terms of design, the ion-extraction system of ion thruster and ion source is the most complex unit. When developing the ion-extraction system design, it is necessary to take into account the peculiarities of electrode operation.