Author: norAdmin

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

Abstract: In our work, we used the finely dispersed polystyrene to produce porous samples of the piezoelectric ceramics. Samples of the sodium potassium niobate ceramics with pore concentrations of the 10, 20, 25, 30 and 40 volume percent were produced. The structure was analyzed and the temperature and frequency dependences of the dielectric constant of the obtained samples were investigated. It has been established that the presence of polystyrene in the process of sintering piezoceramic samples plays the role of a binder, which evaporates during high-temperature processing. At the same time, the binder contributes to stabilization of the dielectric properties of the ceramics. In the porous samples, there are no fluctuations of the permittivity in the low-frequency region, and the frequency range in which the permittivity values are independent of the frequency increases. It was found that already 34 volume percent of the pores worsen the mechanical strength of the sample. It is shown that the use of a simple problem of percolation theory does not allow assessing the mechanical strength of porous samples depending on the pore concentration.
Keywords: piezoelectric ceramics, porous materials, potassium sodium niobate, permittivity, nanostructure, 3-3 composites

E.V. Medyanik, F.F. Malyavin, V.A. Lapin, A.A. Kravtsov, V.E. Suprunchuk, L.V. Tarala
North-Caucasus Federal University

Abstract: In this work, ceramic samples based on lutetium-aluminum garnet doped with erbium (content 1 at.%) were manufactured. In the manufacture of ceramic material, the chemical precipitation method was chosen. The influence of two types of sintering additives, MgO and CaO, on the microstructure and optical properties of ceramic samples obtained at vacuum sintering temperatures of 1800, 1850, 1875°C was studied. The article discusses in detail how the microstructure and optical transmission of ceramics with sintering additives MgO and CaO change at different vacuum sintering temperatures. It was found that magnesium oxide allows to achieve a higher optical transparency of ceramics (about 80%), while calcium oxide more effectively inhibits the grain growth. An increase in the sintering temperature for samples with MgO from 1800 to 1850°Ccontributed to an increase in the light transmission of samples from 10 to 80% and an increase in grain size from 1,80 to 3,03 microns. Earlier no such a phenomenon was not observed for samples with CaO, samples obtained at sintering temperatures of 1850 and 1875°C had approximately the same microstructure, containing some residual microporosity.
Keywords: lutetium-aluminum garnet doped with erbium, optical ceramics, sintering, light transmittance coefficient, luminescence

O.D. Novik¹, N.D. Gavrilova¹, O.V. Malyshkina^2
1 M.V. Lomonosov Moscow State University
² Tver State University

Abstract: In this work, we present the results of our studies of temperature-frequency behaviour of dielectric permittivity ε, conductivity σ, relaxation time τ_μ, thermodepolarisation currents j, and pirocurrents γ in hydrophilic polymers and crystals with a hydrogen-bond network OH…O in the ranges of 0,01–10⁷ Hz and 20-140°С. Analysis of the obtained data has revealed temperature anomalies of ε(T), σ(T), τ_μ(T), j(T), and γ(T) around «threshold» points at 20, 36, 50, 65, and 85°С, where the destruction of water clusters (and, if above 100°С, of water molecule itself) takes place, and thereby the release of deep traps, the change of the charge carriers (Н₃O⁺, ОН^–, etc.) composition and of their trajectories in volume are observed. In this study, we draw an analogy between the temperature behaviour of ε, σ, τ_μ, j, and γ in «threshold» points having a characteristic single resonance peak and the dipole resonance of photoabsorption in clusters of Ag, Mg, and Sm metals, which is manifested in thebroadening of resonance, single peak splitting, and in the formation of single-domain ATGS+Cr³⁺ crystal (0,06 wt.% Cr). We also discuss a possible onset of collective nuclear excitements during irradiation with photons or an onset of internal electrical displacement field E_dp in a sudden sample cooling or warming. The entanglement of photons by polarization is also considered.
Keywords: giant dipole resonance, discrete energy levels of double-well potential, dielectric permittivity and conductivity, coherent collective excitements of nuclei, splitting of resonance maxima of ε, σ and of conductivity relaxation time τμ, spin probability field

P.A. Rakunov, M.B. Lyakhova, E.M. Semenova, A.Yu. Karpenkov
Tver State University

Abstract: The results of experimental studies of magnetic properties and magnetization reversal processes of a series of alloys Sm-Gd-Zr-Co-Cu-Fe are presented. The studied samples were subjected to prolonged isothermal annealing for 24 hours, which made it possible to achieve the formation of a certain nanostructure that affects the hysteresis properties of the material and allows to achieve a high coercivity state. According to the magnetic measurements data obtained by the method of a vibrating magnetometer, the hysteresis loops are constructed, the dependence of the saturation magnetization, and the coercive force on chemical composition, and the values of the temperature coefficient of magnetization change depending on the relative content of Sm and Gd are determined. It is shown that the substitution of a part of samarium atoms for gadolinium atoms increases the effect of the mechanism of irreversible rotation of the spontaneous magnetization vector on the remagnetization of samples. Application of the studied samples in various devices puts serious demands on the stability of their magnetic properties at high temperatures. Our researches allow us to conclude that compounds with gadolinium concentration x=0,5 have the greatest coercive force, and compounds with gadolinium concentration in the range x=0,5-0,6 have the highest temperature stability.
Keywords: rare earth intermetallic compounds, hard magnetic materials, hysteresis, coercive force, magnetization, magnetization reversal processes

A.Yu. Salomatina^1,2, A.Yu. Fedotov¹, O.Yu. Severyukhina¹, F.A. Vinogradov^2
1 Udmurt Federal Research Center UB RAS
² Kalashnikov Izhevsk State Technical University

Abstract: In this paper, a comparative analysis of the characteristics, advantages and disadvantages of five different types of magnetoresistive random access memories has been carried out. An optimal mathematical model for investigation of composition and structure of materials for spintronics devices is selected. A review of the combined mathematical model consisting of the molecular dynamics method and the model of spin dynamics of particles with interatomic interaction potential based on a modified embedded atom method is presented. An analysis is performed of modeling of magnetic properties of cobalt and iron bilayer film under conditions of the uniform external magnetic field. The iron layer was characterized by the formation of skirmions, while regions with different magnetic domains were found in the cobalt nanofilms. The overall magnetization of the Co-Fe system was found to be low due to the lack of the priority direction of the magnetic moment. The magnetizationrates of cobalt, iron of different thicknesses and the Co-Fe system as a whole were compared separately.
Keywords: spintronics, magnetoresistive random access memory, mathematical modeling, molecular dynamics, spin dynamics, modified embedded atom method, LAMMPS, skirmions

N.V. Sidorov¹, L.A. Bobreva^1,2, M.N. Palatnikov¹, A.Yu. Pyatyshev³, M.K. Tarabrin⁴, A.A. Bushunov^4
1 Tananaev Institute of Chemistry  Subdivision of the Federal Research Centre «Kola Science Centre of the Russian Academy of Sciences»
² Murmansk Arctic University
³ P.N. Lebedev Physical Institute of the Russian Academy of Sciences
⁴ Bauman Moscow State Technical University

Abstract: LiNbO₃:Cu (0,005 wt.%), LiNbO₃:Cu (0,015 wt.%), LiNbO₃:Cu (0,022 wt.%), LiNbO₃:Cu (0,042 wt.%), LiNbO₃:Cu (0,46 wt.%) crystals were studied by IR absorption spectroscopy in the region of stretching vibrations of OH^–-groups. These crystals were grown by the Czochralski method using the technology of direct doping of a charge of congruent composition. It has been established that the recorded absorption bands in the infrared spectrum in the frequency range 3469-3490 cm^-1 are associated with a deviation in the composition of the LiNbO₃:Cu crystal from the stoichiometric one. Such changes occur due to a deficiency of Li⁺ cations in the crystal structure. The incorporation of Cu²⁺ dopant leads to disordering of the cation sublattice and noticeable deformation of oxygen octahedra. This occurs due to an increase in the O–O bond lengths. In this case, a newabsorption band with a frequency of 3487 cm^-1, corresponding to the V_Li-OH complex defect, is recorded in the IR spectrum. Calculation of the volume concentration of OH^–– groups showed the highest value for crystals ofLiNbO₃:Cu (0,005 wt.%), LiNbO₃:Cu (0,015 wt.%), LiNbO₃:Cu (0,022 wt.%). These changes occur due to the simultaneous formation of two types of complex defects in the crystal structure: Cu⁺-OH-Cu^3- and V_Li-OH. A change in the mechanism of entry of a doping impurity into the structure of a LiNbO₃:Cu crystal (0,042 wt.%) leads to a decrease in the concentration of OH^–– groups.
Keywords: lithium niobate, photorefractive impurity, point defects, complex defects, infrafed spectroscopy

M.V. Staritsyn¹, V.P. Pronin², I.I. Khinich², A.N. Krushelnitsky², S.V. Senkevich^2,3, E.Y. Kaptelov³, I.P. Pronin^3
1 NRC «Kurchatov institute» – CRISM «Prometey»
² Herzen University
³ Ioffe Institute

Abstract: The paper presents the results of the microstructure study of spherulitic islands in thin films of lead zirconate titanate, characterized by either a non-uniform radial rotation of the crystal lattice (radiant microstructure) or a uniform rotation, which allows one to detect Kikuchi lines of electron channeling. Thin lead zirconate titanate films were obtained by a two-stage method of radio-frequency magnetron sputtering of a ceramic target: deposition onto a «cold» platinized silicon and glassceram substrates, followed by high-temperature annealing to obtain islands of the perovskite phase surrounded by a matrix of the low-temperature pyrochlore phase. To study the cross section, a lamella was prepared, the study of the microstructure of which showed that the rotation of the crystal lattice in the perovskite spherulite occurs uniformly throughout the entire thickness, and it is not a manifestation of some near-surface effects. It was found that the rate of rotation of the crystal lattice in spherulites with a radial-radiant structure is approximately two times less than in spherulites with a radiallyuniform rotation; a model of translational rotation of the crystal lattice with the formation of dislocations and partial relaxation of mechanical stresses is proposed; it is assumed that the lattice rotation velocity is limited by the elasticity limit of the thin film. It is assumed that the Kikuchi image in spherulitic islands consisting of crystalline grains is determined by both the identical growth texture and the orientational correlation of the grains in the plane of the film; an analysis and interpretation of Kikuchi electron channeling lines has been carried out, which makes it possible to determine the orientation of the crystal lattice planes and growth axes in thin films.
Keywords: thin films of lead zirconate titanate, spherulites, radially-radiant microstructure, electron Kikuchi channeling

N.A. Teplyakova, N.V. Sidorov, M.N. Palatnikov
Tananaev Institute of Chemistry  Subdivision of the Federal Research Centre «Kola Science Centre of the Russian Academy of Sciences»

Abstract: This work examines the main reasons for the appearance of an «extra» band with a frequency of ~737 cm^-1 in the Raman spectra of lithium niobate crystals. The following stand out among the reasons: the presence of clusters (microstructures); the presence of microinclusions of impurity phases of other lithium niobates (LiNb₃O₈ and Li₃NbO₄); strong anharmonicity of some fundamental vibrations of the Raman spectrum. The structure of clusters differs from the structure of the crystalline matrix. It has been shown that the appearance of a line with a frequency of ~737 cm^-1 in the Raman spectrum cannot be unambiguously associated with the existence of regions with reduced symmetry in the structure of doped crystals. These regions are the result of uneven incorporation of dopants into the crystal. The existence of these areas is also not explained in terms of the photorefractive effect. The results of studying the features of the defect structure, stoichiometry, optical uniformity and photorefractive effect confirm a correlation between the band with a frequency of ~737 cm^-1 and Nb_Li defects in the structure of the lithium niobate crystal.
Keywords: lithium niobate, crystal, defects, clusters, Raman spectroscopy, anharmonicity of fundamental vibrations, «extra» lines

A.A. Utoplov¹, N.V. Prutsakova², A.G. Rudskaya¹, A.V. Nazarenko³, M.V. Belokobylsky¹, Yu.V. Kabirov^1
1 Southern Federal University
² Don State Technical University
³ Federal Research Centre Southern Scientific Centre of the Russian Academy of Sciences

Abstract: Electrical, structural and magnetoresistive properties of ceramic composites with different mass ratios of components were synthesized and studied: (Cu₂O+CuO)_x/(La_0,7Sr_0,3MnO₃)_1-x (x = 0,17; 0,22; 0,33; 0,43; 0,48; 0,53; 0,58; 0,63; 0,68; 0,72; 0,77; 0,82; 0,86; 0,91; 0,99), and Ag_y/(La_0,7Sr_0,3MnO₃)_1-y (y = 0; 0,02; 0,06; 0,08; 0,10; 0,12; 0,25; 0,50). The composites with copper oxides were synthesized using an original technology for sample preparation using dispersed copper and a pre-prepared ferromagnetic oxide with the perovskite structure La_0,7Sr_0,3MnO₃. Pressed mixtures with a copper content of less than 45% by weight were annealed at a temperature of 1050°C. At higher copper contents, annealing was performed at 1000°C. The compositions with silver nanoparticles were prepared by reduction from silver nitrate. The composites were synthesized using an original technology for sample preparation using dispersed copper and La_0,7Sr_0,3MnO₃ manganite with annealing at 1000-1050°C. It was shown that the synthesized composites with a mass ratio of components (Cu₂O+CuO)_0,43/(La_0,7Sr_0,3MnO₃)_0,57 exhibit the highest magnetoresistance values of about 7% in a constant magnetic field of 14 kOe at room temperature. The maximum magnetoresistance correlates with a special region of change in the dependence of electrical resistance on the component ratio in these compositions. In the Ag_0,08/(LSMO)_0,92 composition, the magnetoresistance values reach 5,5%.
Keywords: ceramic composites, magnetoresistance, lanthanum-strontium manganite, copper oxides, silver nanoparticles, percolation

A.M. Apekov¹, I.G. Shebzukhova², L.A. Khamukova^1
1 North-Caucasus Center for Mathematical Research, North-Caucasus Federal University
² Kabardino-Balkarian State University named after H.M. Berbekov

Abstract: Understanding the energy characteristics at the metal-organic interface is of great importance for the development of equipment and technologies in various industries. In this regard, there is a great interest in studying the processes occurring at this interface. Particularly noteworthy is the rapid growth of studies on the properties of metal-organic framework structures, which is associated with the possibility of synthesizing these structures with the desired properties by varying the lengths of the organic molecules connecting the atoms of metals or their oxides, as well as by selecting the chemical composition. In this paper, the values of the interfacial energy at the boundaries of the faces of an aluminum crystal with organic liquids are obtained within the framework of the electron-statistical method, taking into account the polarization of metal ions and molecules of the organic liquid, as well as the dispersion interaction of Wigner-Seitz cells on the interface. The dependence of the interfacial energy and corrections to the interfacial energy on the permittivity of the liquid and the orientation of the metal crystal is obtained. It is found that the dispersion correction makes a positive contribution while the polarization correction reduces the interfacial energy.
Keywords: interfacial energy, polarization correction, dispersion correction, electronic statistical method, nonpolar organic liquid, aluminum