Editor’s column

D.S. Pavlenko¹, A.L. Bulanova¹, A.V. Pavlenko^2
1 Southern Federal University
² Southern Scientific Center of the RAS

Abstract: In this work, 0,91NaNbO₃–0,09SrZrO₃ (NZNO-0,09) thin films were grown on SrRuO₃/MgO(001) substrates using the high-frequency magnetron sputtering method in an O₂ atmosphere. A comprehensive study of their crystal structure, dielectric response, and polarization characteristics was carried out using X-ray diffraction analysis, dielectric spectroscopy, and measurements of dielectric hysteresis loops. It was established that the obtained films are single-phase, impurity-free, and at room temperature they exist in the antiferroelectric phase. At the same time, in contrast to ceramics of the same composition, they exhibit relaxor behavior in terms of the temperature–frequency dependence of the relative permittivity ε and dielectric loss tangent tg δ. Analysis of the dispersion of ε and tan δ in the temperature range T = 305-460 K and frequency range f = 0,2-500 kHz revealed the presence of contributions from two relaxation processes associated with different polarization mechanisms. A model describing the observed spectra is proposed. The paper discusses the origins of the observed features in the formation of dielectric properties, as well as the high energy efficiency of the NZNO-0,09 films. The obtained results are important for understanding the mechanisms governing the property formation in antiferroelectric nanoscale thin films in view of their application in modern functional electronics.
Keywords: antiferroelectric, dielectric properties, thin films, polarization, high-frequency magnetron sputtering method

V.M. Skachkov, S.A. Bibanaeva, N.A. Sabirzyanov
Institute of Solid State Chemistry of the Ural Branch of RAS

Abstract: The article discusses changes in the structure and microhardness of diffusion-hardening solder based on low-melting alloy gallium (68%) -indium (23,5%) -tin (8,5%) and a solid component from copper-tin alloy powder (5%) depending on the dosage of stainless steel powder. Stainless steel powder was added in an amount of 5, 10, 15, 20% by weight, solder samples were heat treated at temperatures of 125 and 600°C, and compared with a base solder composition of 30% by weight of gallium-indium-tin alloy and 70% by weight of copper-tin alloy powder. The X-ray phase analysis method determines the phases formed as a result of the interaction of solder components under different heat treatment modes. The method of differential thermal analysis revealed thermal effects in the formation of solid solutions and intermetallic compounds of gallium with transition metals in the temperature range of 17-600°C. It has been shown that thermal treatment at temperatures above 450°C promotes the transition of the solder to an equilibrium state, which leads to an increase in hardness, in particular, due to the uniform distribution of nanoscale inclusions. Scanning electron microscopy revealed that stainless steel has limited solubility in the composition of diffusion-hardening solder, but after high-temperature treatment (600°C) reduces its hardness due to violation of the composition of the gallium-copper solid solution.
Keywords: composite diffusion-hardening solders, metal powder, properties, microhardness, differential thermal analysis

A.A. Ostroushko, A.E. Permyakova, Yu. Zhulanova
Ural Federal University

Abstract: Parameters of the sintering process for compacted complex oxide powders based on lanthanum strontium manganite with a perovskite-type structure were studied: the temperature of intensive sintering and the achieved shrinkage of the workpiece. The studied complex oxide samples were obtained in the combustion reactions of nitrate-organic precursors (the so-called solution combustion method – SCS). During the synthesis, the composition of the precursors was varied: the nature of the organic component (polyvinyl alcohol, polyvinylpyrrolidone, glycine) and its relative content in relation to the stoichiometry of the combustion reaction with the formation of water vapor, molecular nitrogen and carbon dioxide as gaseous products. At the same time, positive or negative electric charges were generated in the precursors due to the formation and carry-over with the released gases of ionized molecular groups. The intensity of this process was monitored using an electrostatic field meter. The ground-precursor potential difference, depending on the composition of the initial composition, ranged from values   close to zero to several tens of volts. With intensive generation due to the accumulation of the excess surface energy of mutually repulsive nanoparticles of the complex oxide, the temperature of intensive sintering decreased by 350 degrees compared to that (1050°C) for materials obtained from precursors with a low intensity of charge formation. The relative shrinkage of samples of the first type increased from 3 to 23%. The established correlation was universal and practically independent of the sign of the generated charge.
Keywords: nanosized powders, synthesis of nitrate-organic precursors in combustion reactions, charge generation, sintering, complex oxides, lanthanum-strontium manganite

A.V. Shishulin, A.V. Shishulina
Nizhny Novgorod State Technical University named after R.E. Alekseev

Abstract: This paper examines the dependence of the vacancy formation energy and the activation energy of volume diffusion in the «skeleton» of a mesoporous material on the geometric characteristics (volume and shape) of the pores distributed within the material. The geometric features of the pores were defined within a fractal-geometric approach by their effective diameter and fractal dimension. The presented estimates indicate that the effect characteristic of nanoparticles, associated with the significant dependence of the vacancy formation energy and the activation energy of volume diffusion on the particle size and shape, can also occur in mesoporous materials (with a characteristic pore size from 5 to 50 nm), even though the mesoporous objects themselves can have macroscopic dimensions. Using porous gold as an example, it is shown that a decrease in the pore volume and a «complication» of their morphology lead to a noticeable reduction in the considered energy characteristics. The results were obtained within the framework of the cohesive energy-based model.
Keywords: vacancy formation energy, volume diffusion activation energy, mesoporous materials, fractal dimension, cohesion, size distribution, Hardy-Ramanujan-Rademacher formula

A.V. Shishulin, E.A. Vlyalkova, A.V. Shishulina
Nizhny Novgorod State Technical University named after R.E. Alekseev

Abstract: Due to their unique combination of physicochemical properties, heavy tungsten-based pseudo-alloys with an ultrafine-grained structure produced from nanoparticles by advanced powder metallurgy techniques have become a subject of considerable research interest. In this work, within the framework of a thermodynamic approach, we simulate the features of the phase composition in core-shell nanoparticles formed from a phase-separating solid solution, using the heavy W-Cr pseudo-alloy as a model system. For a binary system with limited solid-state solubility, a specific effect is demonstrated: in contrast to macroscopic systems, the equilibrium composition and volume fraction of the coexisting nanophases vary significantly depending on the chemical nature of the external environment. The environment dictates the surface energy of the outer interface. The set of considered modellin dispersion media includes argon (a common sintering atmosphere), hydrogen (an annealing atmosphere), and several others. For two distinct heterogeneous states of the core-shell structure, temperature dependences of the equilibrium phase composition in each state were obtained. A thermodynamic interpretation of the observed regularities is provided, based on three possible mechanisms for reducing the free energy of the system.
Keywords: nanoparticles, solution decomposition, chemical thermodynamics, solubility, core-shell, tungsten, chromium

A.N. Zaritovskii¹, E.N. Kotenko¹, S.V. Grishchuk¹, V.A. Glazunova¹, G.K. Volkova¹
Galkin Donetsk Institute for Physics and Engineering
¹ L.M. Litvinenko Institute of Physical Organic and Coal Chemistry

Abstract: The parameters of the synthesis of carbon nanostructures during microwave catalytic co-pyrolysis of polymer materials were studied. Polystyrene, which is a typical high-carbon synthetic polymer, and microcrystalline cellulose, a renewable environmentally friendly source of carbon of plant origin, were selected as carbon donors. The processes were carried out in the presence of a mixture of nickel and iron oxalates, which serve as metal catalysts precursors, using granulated activated carbon of AG-3 grade as a microwave absorber to convert electromagnetic energy into thermal energy. The effect of microwave acceptor concentration, treatment time and method of preparing the reaction mixture on the formation of multi-walled carbon nanotubes was investigated. It has been established that the optimal conditions for the synthesis process of the target product are achieved at a microwave acceptor concentration of 40% (wt.) and a cyclic exposure to microwave radiation with a power of 1000 W for 5-12 minutes. The results of studies were confirmed by the data of transmission electron microscopy and X-ray phase analysis.
Keywords: microwave co-pyrolysis, multi-walled carbon nanotubes, polystyrene, cellulose

A.N. Bolotov, O.O. Novikova
Tver State Technical University

Abstract: A generalized approach to calculating the service life of magnetic fluid tribological units operating in vacuum and gas environments is presented. The physical mechanisms of magnetic nanofluid degradation during dispersion medium evaporation and increasing solid phase concentration are examined. A statistical approach developed by Ya. I. Frenkel is used to estimate the rate of nanofluid liquid phase evaporation into a vacuum. An equation for the time dependence of the dispersed phase concentration in a magnetic fluid was obtained for calculating the durability of magnetic fluid devices in a vacuum. The dynamics of magnetic nanofluid mass loss upon contact with a gaseous medium was described using а diffusion mass transfer equation. An electrostatic analogy method was used to solve this equation. The time during which the volume content of the dispersed phase of the magnetic nanofluid increases to a limiting value was determined for magnetic fluid tribounits with an open fluid surface and those enclosed in a chamber with a small opening. Based on the obtained calculation relationships linking evaporation parameters with changes in the volume fraction of the dispersed phase and the maximum permissible viscosity criterion, an engineering methodology for assessing the service life of magnetic fluid bearings and seals has been developed. Recommendations for selecting magnetic fluid and operating modes that maximize its service life are provided.
Keywords: magnetic fluid, evaporation, dispersion medium, friction unit life, viscosity, plain bearing

A.V. Parashchuk, E.P. Shehin
Moscow Institute of Physics and Technology (National Research University)

Abstract: The processes of gas release from titanium and titanium-vanadium getter materials used in electrovacuum devices were studied using thermodesorption spectroscopy. Two consecutive heating cycles were performed at a rate of 5°C/min, followed by an isothermal annealing at the end of the heating process. The activation energies of desorption for H₂, H₂O, CO₂ and CH₄ were calculated using the Redhead method. It has been shown that during secondary heating after 5 days of keeping in a vacuum, the hydrogen peaks are restored, some new high-temperature water peaks appear, and methane is formed, which was not present during the primary heating. For the Ti-V alloy, all desorption processes are shifted to lower temperatures (maximum of 550°C) with an activation energy of 2,52 eV compared to 3,62 eV for pure titanium. It has been established that during exposure at room temperature, getters sorb hydrogen, oxygen, and carbon-containing gases from the residual atmosphere, and the sorbated components enter into chemical interaction.
Keywords: thermodesorption spectroscopy, getter, titanium, titanium-vanadium alloy, activation energy, desorption, sorption, electrovacuum devices, Redhead method

D.V. Bespalov, O.A. Golovanova
Omsk State University named after F.M. Dostoevsky

Abstract: The combined application of quantum-chemical methods of density functional theory (DFT/B3LYP) with the 6‑31G(d,p) basis set and the semiempirical GFN2‑xTB method allowed to construct a reliable model of an isolated molecule of the zinc glycine complex. The structure was optimized, and the thermodynamic characteristics and infrared spectrum of the studied complex were calculated. Using potentiometric titration according to the Calvin-Melchior method, the stability constants of the complexes in the zinc–glycine system were determined. The ZnGly₂ complex was synthesized. The 1:2 molar ratio was confirmed by complexometric and formol titration methods. The infrared spectra of the synthesized compound are presented. A comparison of the experimental and theoretical infrared spectra confirmed the reliability and consistency of the selected quantum-chemical methods. X‑ray phase analysis was used to determine the probable composition of the complex, and the unit cell parameters were calculated using the dichotomy method. The presence of a water molecule in the crystal lattice was confirmed by calculating the van der Waals volumes of atoms, and the average crystallite size was determined using the Scherrer method. The obtained data expand the understanding of the coordination chemistry of zinc and provide a basis for the rational design of bioactive compounds aimed at regulating homeostasis. These data can be used in medicine to prevent pathologies associated with impaired zinc metabolism and the formation of some nanoscale aggregates.
Keywords: synthesis, amino acids, zinc complexes, glycine, density functional method, molecular modeling

A.V. Shishulin, A.V. Shishulina
Nizhny Novgorod State Technical University n.a. R.E. Alekseev

Abstract: Complex random number generators that combine rapid pseudorandom sequence generation with hardware entropy sources have numerous practical applications in stochastic process modeling, machine learning, and information security. This paper presents a method for generating pseudorandom sequences based on a physical model of particle diffusion within a nanoscale periodic structure featuring a nonlinear potential and thermal noise, which serve as sources of dynamic chaos. The sequence of thermally activated transitions between potential minima exhibits irregular and chaotic behavior. The sequence generation is achieved through the digitalization of the particle’s stochastic motion along the energy landscape of the nanostructure. Particle diffusion in a nanostructured medium is described by the Langevin equation and is integrating by using the Verlet method. Additionally, a software implementation of the suggested algorithm is provided in the Ruby programming language. The obtained results demonstrate the potential for using a «pseudophysical» approach, which is based on nonlinear potentials of various physical natures, as a viable alternative to a «purely mathematical» methodology in the tasks involving the generation of random number sets.
Keywords: nanostructures, diffusion, nonlinear potential, dynamic chaos, pseudorandom numbers