PhC-2022

N.A. Pan'kin
National Research Ogarev Mordovia State University

Abstract: The melting of titanium nanoclusters Ti_n (n = 3599, 28725, 97045) with different heating rates (from 0,1 to and 10,0 TK/s) was studied by the molecular dynamics method. Molecular dynamics simulation was carried out using the LAMMPS program on a multiprocessor computer. A many-particle potential of interatomic interaction was used. The crystal structure of a titanium nanocluster upon heating passes into the liquid phase through the formation of a system of atoms (islands) with an ordered local environment near the melting point. The appearance of the latter is due to the non-equilibrium of the simulated heating process – the system does not have time to relax to an equilibrium state for a chosen temperature. The melting temperature was taken as the average value between the temperatures of the beginning and finishing of the phase transition process. The temperature of the beginning of melting corresponded to the state of completion of formation of individual islands. At the end of melting, the nanostructure is characterized by a completely disordered structure. It is noted that the melting temperature increases with the size of the nanoparticle and the rate of its heating. The limiting temperatures of the considered phase transition (at N → ∞) are significantly lower than the melting temperature of the bulk titanium.
Keywords: titanium, nanocluster, melting point, heating rate, structure, islands, molecular dynamics method

N.V. Vostrov¹, A.V. Solnyshkin¹, I.M. Morsakov², A.N. Belov³, P.N. Krylov^1
1 Tver State University
² JSC "SPC "Tvergeofizika"
³ National Research University of Electronic Technology

Abstract: In this work, we searched for the optimal way to create ferroelectric nanostructured composite materials based on 4D-printed polyvinylidene fluoride polymer films. Method fused deposition modeling allow using polyvinylidene fluoride and its copolymers not only in microelectronics as pyroelectric and piezoelectric sensors, as well as creating dynamic memory elements, organic solar cells and used in robotics. At the first stage of the work, the authors were selected optimal extrusion parameters for the manufacture of a thread from powder and granules. The next stage of the work included the analysis and determination of printing parameters by the method of layer-by-layer filament deposition to obtain the best quality of polymer films. Using scanning electron microscopy, the existence of two phases, a polar β-phase and a nonpolar α-phase, is shown, where the crystalline phase is observed in the form of lamellar crystals chaotically oriented in the α-phase matrix. Pyroelectric measurements performed by the dynamic method showed the presence of a noticeable pyroelectric response in polyvinylidene fluoride films obtained using additive technologies, bypassing the orientation extraction stage. The calculation of the pyroelectric coefficient gives values corresponding to the values of the pyroelectric coefficient for polyvinylidene fluoride samples obtained by traditional methods.
Keywords: composite, polymer ferroelectric, additive technologies, 4D printing, 3D printing, spontaneous polarization, piezoelectric effect, pyroelectric effect, scanning electron microscope

Yu.Ya. Gafner, D.A. Ryzhkova
Katanov Khakas State University

Abstract: The process of synthesis of CuAu nanoclusters from a high-temperature gas phase was simulated. The molecular dynamics method was used. 91124 Cu and Au atoms were used as the initial configuration. The atoms were arranged randomly in space, the average distance between them was 30 Bohr radii. The set of parameters was chosen in such a way as to simulate the conditions of the inert gas condensation. This system was cooled with a thermal energy removal rate of 10⁸ K/s. Based on the data obtained, conclusions were drawn about the main stages of the evolution of the model system. It is shown that the initial stage of synthesis consists of five different stages, which gradually lead to the formation of primary spherical nanoparticles of the CuAu binary alloy. At the final stage, the eventual transformation of the formed primary nanoparticles takes place. The initial atomic atmosphere almost completely disappears and spherical binary nanoparticles are formed, a characteristic feature of which is the displacement of gold atoms to the surface.
Keywords: nanotechnology, nanopowders, computer simulation, tight-binding model, nanoparticles, copper, gold

Yu..Ya.. Gafner, D.A. Ryzhkova
Katanov Khakas State University

Abstract: The article considers the process of formation of binary Cu-Au nanoclusters with different target composition from a high-temperature gaseous medium. The molecular dynamics method was used. The main attention was paid to studying formation of the crystal structure in such clusters and determination its type. It is shown that an increase in the percentage of gold atoms in the primary gaseous medium significantly affects the formation of the internal structure of simulated nanoparticles. With a relatively small increase in the proportion of gold atoms, there is a complete disappearance of clusters with the fcc structure. The formation of nanoparticles with, as a rule, five-particle symmetry is observed. In this case, the Dh configuration prevails. If both precursors are evaporated at the same rate, then an increase in the percentage of gold atoms in the gas mixture leads to the fact that CuAu clusters are often unable to form any clearly distinguishable crystalline form, due to which approximately every fourth cluster was fixed in the amorphous state. We concluded that the cause of this phenomenon may be the separation of atoms of different types, which is typical for binary nanoparticles of the studied chemical composition.
Keywords: nanotechnologies, nanopowders, computer simulation, tight-binding model, nanoparticles, copper, gold

A.Yu. Karpenkov¹, P.A. Rakunov¹, I.I. Musabirov², G.G. Dunaeva^1
1 Tver State University
² Institute for Metals Superplasticity Problems of Russian Academy of Sciences

Abstract: This paper presents the results of complex studies of the effect of deformation obtained by the multiple isothermal forging method on the magnetocaloric properties of the Ni-Mn-Ga Heusler alloy system. Direct measurements of the adiabatic temperature change show that cycling the sample in a magnetic field μ0ΔH=1,85 T can decrease the maximum of ΔTad(T)0→H by the value corresponding to the latent heat of transition. Neglecting this transformation effect leads to an overestimation of the magnetocaloric effect of materials with the first-order transition. An analysis of the deformation treatment effect on the phase transformation temperatures and the magnitude of the magnetocaloric effect indicates that the application of multiple isothermal forging leads to a small decrease of the magnetization and the magnitude of the magnetocaloric effect. Deformation also causes a shift in the phase transition temperature towards low temperatures and decrease of the temperature hysteresis width.
Keywords: Heusler alloys, multiple isothermal forging, magnetocaloric effect, magnetostructural phase transition

O.V. Malyshkina, A.I. Ivanova, D.V. Mamaev
Tver State University

Abstract: The paper presents the results of studying the effect of paratellurite vapor during sintering on the dielectric properties of a multicomponent system based on sodium–potassium niobate ceramics (mKNN) with the general formula (Na_0,5K_0,49Li_0,05Sr_0,05)(Nb_0,9Ta_0,05Ti_0,05)O₃. The inclusion of paratellurite in mKNN ceramics changes the shape and increases the grain size by an order of magnitude. Thus, if grains containing only mKNN material have a cubic shape, then the presence of tellurium leads to the formation of grains in the form of sufficiently long tubes (when the length is several times greater than the diameter) with a porous internal structure. The addition of TeO₂ to the mKNN composition leads to the disappearance of the maximum observed for mKNN on the temperature dependence of the permittivity in the region of 220-250°C, which corresponds to a nonferroelectric structural phase transition in KNN ceramics, and to smoothing the resonant- antiresonant peak in the range of 5-15 MHz, which appears in the KNN system with the introduction of modifiers.
Keywords: piezoelectric ceramics of potassium sodium niobate, lead-free materials, grain structure, complex permittivity dispersion

A.V. Blinov, I.M. Shevchenko, M.A. Pirogov, A.A. Gvozdenko, A.B. Golik, P.S. Leontev
North Caucasus Federal University

Abstract: In this work the influence of the molar ratio on the dimensional and structural characteristics of cobalt hexacyanoferrate nanoparticles was studied. The synthesis was carried out by chemical method in an aqueous medium using potassium hexacyanoferrate and cobalt nitrate. As a result of the study of samples by the method of dynamic light scattering, the values of the hydrodynamic radius of the samples were obtained. It was found that the minimum size (R = 76 nm) has a sample with a molar ratio K₃[Fe(CN)₆] : Co(NO₃)₂= 4 : 1. Scanning electron microscopy revealed that cobalt hexacyanoferrate samples are irregularly shaped aggregates consisting of nanoparticles with a diameter of 50 to 150 nm. As a result of X-ray phase analysis, it was found that the samples have a face-centered cubic crystal structure (Fm 3 m). According to the Debye-Scherrer equation, the average size of crystallites in the samples is from 17 to 20 nm.
Keywords: transition metal hexacyanoferrates, cobalt hexacyanoferrate, cobalt nitrate, scanning electron microscopy, dynamic light scattering, powder diffractometry, hydrodynamic radius

D.P. Bernatskii, V.G. Pavlov
Ioffe Institute

Abstract: Modification of the emission surface on a nanometer scale during adsorption of barium atoms on the surface of a rhenium field emitter was investigated using field electron and desorption microscopy. Field electronic images of the emitter surface reflecting the localization of barium atoms on the emitter surface, representing the quasi-spherical surface of a rhenium single crystal, were obtained. The influence of the temperature of the emitter with adsorbed barium on the change in the emitter work function is shown. Deposition at room temperature leads to the appearance of a dependence of the work function on the concentration of adsorbate with a minimum in the area of optimal coating. Annealing of the emitter at T = 600 K after deposition of each portion of barium causes the minimum to disappear. After reaching the minimum value (optimal coverage with adsorbed atoms), the work function remains constant with an increase in the number of adsorbed barium atoms on the surface of the emitter. A sharp change in the localization of barium atoms due to a phase transition with the formation of islands in the region of the rhenium face was detected on the field electronic image. The change in the nature of the dependence of the work function is associated with a phase transition in the barium film with the formation of barium islands. The concentration of barium in the islet is constant and corresponds to the optimal coating.
Keywords: field emitters, field electron and desorption microscope, adsorption, rhenium, barium

N.N. Bolshakova¹, N.Yu. Druginina², A.I. Ivanova¹, D.N. Pavlova¹, B.B. Ped`ko¹, E.M. Semenova^1
1 Tver State University
² Military Academy of Air and Space Defense named after Marshal of the Soviet Union G. K. Zhukov

Abstract: The paper presents the results of the analysis of experimental dielectric hysteresis loops and field dependens of polarization switching of initial and annealed crystals of triglycine sulfate, doped copper (the concentration range (4,2–8,7) 10^-3 wt.%). It has been experimentally established that their dielectric hysteresis loops do not have distortions. It has been found that the relative and effective permittivities and switchable polarization increase with increasing impurity concentration in crystals of TGS:Cu²⁺. The field dependences of the effective permittivity have extrema: before annealing the samples, the maxima of the ε_eff(E) curves correspond to a field value of about (20-40)∙10_³ V∙m^-1, and for annealed samples these fields have a value of ~(15-30)∙10³V∙m^–1. Annealing of the samples increases the mobility of domain walls, which promotes the transformation of lenticular nuclei of domains into lamellae.
Keywords: triglycine sulfate, repolarization, domain structure, switching processes, hysteresis, permittivity

N.M. Barbin^1,2, L.V. Yakupova¹, D.I. Terent’ev¹, V.T. Kuanyshev^2
1 Educational and Scientific Department, Ural Institute of the State Fire Service, The Ministry of the Russian Federation for Civil Defence, Emergencies and Elimination of Consequences of Natural Disasters
² Ural Technical Institute of Communications and Informatics, Siberian State University of Telecommunications and Informatics in Yekaterinburg

Abstract: A study of the behavior of С₂₈ fullerene when heated in a nitrogen atmosphere was conducted. The calculations were made using the thermodynamic modeling method, which consists in a complete thermodynamic analysis of the system using the TERRA software complex. The range of minimum and maximum heating temperatures was 273-3373 K and pressure was 0,1 MPa. A graph of the carbon balance in the С₂₈ – N₂ system was built, chemical reactions were determined, temperature intervals were allocated for each reaction. Temperature intervals of the thermal stability of carbon nanoparticles in the condensed and vapor phases are established. In the gas phase, С₂₈ steam shows increased thermodynamic stability and only reacts with vapors at high temperatures, as evidenced by a sharp decrease in its content. The equilibrium constants of the reactions are calculated, and graphs of the dependence of the equilibrium constants of the reactions on temperature are given. For each reaction, the calculated data were approximated by the linear dependence.
Keywords: fullerenes, carbon nanoparticles, thermodynamic modeling, physical and chemical process