PhC-2024

E.V. Barabanova, N.M. Ospelnikov, A.I. Ivanova
Tver State University

Abstract: Introduction of dopants is a classic method for modifying the properties of materials, in particular, complex oxides of the perovskite family with the general formula ABO₃. Ions located in positions A and/or B are substituted. In this case, their valence can coincide with the valence of the basic ion (isovalent substitution) or differ (heterovalent substitution). Sodium niobate (NaNbO₃) is a convenient basis for producing ferroelectric solid solutions. Doping changes the properties of sodium niobate in a wide range, allowing the production of functional materials for various applications. In this paper, the effect of Bi³⁺ doping upon substitution of niobium ion Nb⁵⁺ on the structure and electrophysical properties of sodium niobate is studied. It has been shown that such compositions are characterized by a significant increase in electrical conductivity with increasing the doping concentration, a decrease in the Curie temperature, and a change in the grain structure. The dopant concentration is more than 10 mol. % leads to the formation of some secondary phases.
Keywords: ionic conductivity, ferroelectric solid solutions, sodium niobate, dielectric permittivity

V.P. Bezverkhniy, A.Y. Gagarina, E.N. Muratova, A.I. Maximov, V.A. Moshnikov
Saint Petersburg Electrotechnical University «LETI»

Abstract: As a part of the research work, inorganic lead-containing halide perovskite nanocrystals with the CsPbX₃ structure were obtained by the hot injection. The alloying of single crystals of perovskites was carried out by solution methods, zinc and indium ions acted as dopants. The photoluminescence spectra and optical density spectra of the obtained colloidal solutions were studied. Our studies have shown that doping of perovskite nanocrystals with metal ions leads to an increase in photoluminescence as well as to a shift in the maximum of photoluminescence relative to the reference composition by 4 and 12 nm for bromides and iodides, respectively. Also, it has been shown that the magnitude of the shift does not depend on the type of dopant. It is noted that within the framework of this work, doping does not lead to a change in the position of the edge of its own absorption.
Keywords: perovskites, solar energy, nanocrystals, alloying, optical properties

L.A. Bobreva¹, R.A. Titov¹, M.V. Smirnov¹, I.V. Biryukova¹, S.M. Masloboeva¹, A.Yu. Pyatyshev², N.V. Sidorov¹, M.N. Palatnikov^1
1 Tananaev Institute of Chemistry – Subdivision of the Federal Research Centre «Kola Science Centre of the RAS»
² P.N. Lebedev Physical Institute of the RAS

Abstract: Comparative studies of double-doped LiNbO₃:Er:Zn crystals of different genesis have been carried out using infrared absorption spectroscopy (in the region of OH^–-group stretching vibrations) and Raman spectroscopy. A LiNbO₃:Er(0,53 mol.%):Zn(4,02 mol.%) crystal obtained by solid-phase doping and a LiNbO₃:Er(0,75 mol.%):Zn(3,82 mol.%) crystal obtained by homogeneous doping were used in the study. No significant changes have been recorded in the infrared absorption spectra and Raman spectra of crystals obtained using different technologies. Minor changes in the main parameters of the absorption bands with frequencies of 3483 and 3492 cm^-1 have been detected in the infrared absorption spectra. This may be due to the higher concentration of zinc dopant in the LiNbO₃:Er (0,53 mol.%):Zn(4,02 mol.%) crystal. Measuring the half-width parameter of the band with a frequency of 271 cm^-1 in the Raman spectra of the studied crystals helped to establish that the LiNbO₃:Er(0,53 mol.%):Zn(4,02 mol.%) crystal has a higher ordering of the structural units of the cation sublattice compared to the LiNbO₃:Er(0,75 mol.%):Zn(3,82 mol.%) crystal.
Keywords: lithium niobate, solid phase doping, homogeneous doping, erbium, zinc, double doping, Raman scattering, complex defects, infrared spectroscopy

L.A. Bobreva¹, R.A. Titov¹, M.V. Smirnov¹, I.V. Biryukova¹, S.M. Masloboeva¹, A.Yu. Pyatyshev², O.V. Palatnikova¹, N.V. Sidorov¹, M.N. Palatnikov^1
1 Tananaev Institute of Chemistry – Subdivision of the Federal Research Centre «Kola Science Centre of the RAS»
² P.N. Lebedev Physical Institute of the RAS

Abstract: A comparative analysis of the photoluminescent properties, concentration of OH^–-groups and optical quality of double-doped crystals obtained from charges of different genesis has been performed. In a LiNbO₃:Er(0,53 mol.%):Zn(4,02 mol.%) crystal obtained by solid-phase doping, the content of OH^–-groups is higher than in a LiNbO₃:Er(0,75 mol.%):Zn(3,82 mol.%) crystal obtained by homogeneous doping. These changes occur as a result of the simultaneous formation of two types of complex defects in the LiNbO₃:Er (0,53 mol.%):Zn(4,02 mol.%) crystal structure: Zn_Nb^3--OH and V_Li- OH. It has been established that photoluminescence in the visible region is caused by radiative transitions of Er³⁺ without the manifestation of the host’s own luminescence in the studied crystals. For the LiNbO₃:Er:Zn crystal obtained by solid-phase doping, the luminescence intensity is 77% higher than in the crystal obtained by homogeneous doping. This may be due to the participation of OH^–-groups in the energy transfer between the host and the Er³⁺ ions.
Keywords: lithium niobate; double doping; photoluminescence; hydroxyl groups; rare earth and non- photorefractive dopant; point and complex defects

N.N. Bolshakova¹, A.I. Ivanova¹, N.Yu. Druginina², E.M. Semenova¹, S.S. Schipilov^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 an experimental study of the dielectric and switching characteristics of some initial and annealed alanine-doped crystals of the triglycine sulfate group at room temperature. The results of measurements and calculations of the effective permittivity, switchable polarization, coercive and bias fields, unipolarity coefficient and dielectric loss tangent are presented. It was found that for most samples before and after annealing, the dielectric hysteresis loops are unipolar and shifted along the abscissa axis. This indicates a preferential orientation of domains and the presence of bias fields. As a result of annealing, the values of the coercive field and the unipolarity coefficient of the crystals decrease, and the switchable polarization increases. It is shown that the field dependences of the effective permittivity of the crystals before annealing have extrema lying in the field range of (5-7,5) ∙ 10⁴ V∙m^-1 and in the range (5-12) ∙ 10⁴ V∙m^-1 after their annealing.
Keywords: triglycine sulfate crystals, hysteresis, switching processes, permittivity

A.M. Guseva, A.I. Sinkevich, S.D. Smetannikova, E.M. Semenova, Yu.G. Pastushenkov
Tver State University

Abstract: The results of an experimental study of the magnetic domain structure on the basal plane of RFe₁₁Ti single crystals (R=Y, Gd, Ho, Er) by magnetic force microscopy are presented. At room temperature, the compounds are characterized by magnetocrystalline anisotropy of the «easy axis» type. Based on the magnetic force microscopy data, the sizes of domains on the basal plane of the samples were determined. Using the Bodenberger-Hubert method, the surface energy density of domain walls γ was determined for all compounds based on the magnetic force microscopy data: YFe₁₁Ti – 4,05 mJ/m², GdFe₁₁Ti – 5,93 mJ/m², HoFe₁₁Ti – 4,97 mJ/m², ErFe₁₁Ti – 2,98 mJ/m². The cube counting method was used to calculate the fractal dimension D_L of the stray fields of the domain structure at different heights from the surface (0,1 – 9 μm). D_L on the surface of the z(0) sections has values of 2,62 for compounds with R = Y, Gd, Ho and 2,72 for R=Er. For all samples, D_L has a maximum near the surface.
Keywords: rare earth intermetallic compounds, domain structure, magnetic force microscopy, fractal dimension

G.G. Dunaeva, A.Yu. Karpenkov
Tver State University

Abstract: This paper presents the results of complex studies, including direct experiment and computer modeling, of the magnetization reversal processes of a SmCo₅ single crystal and a (GdBiLu)₃(FeGa)₅O₁₂ ferrite-garnet film. The analysis of images of the domain structure in the external magnetic field of both samples allowed us to construct the field dependences of magnetization. It was found that the field dependence of the magnetization of the ferrite-garnet film coincides with the magnetometry data. For the SmCo₅ single crystal the saturation field of the surface corresponds to the saturation field obtained from the measurements on a vibrating sample magnetometer, however, the view of the field dependence M(H) differs. Image analysis of the main domains of a single crystal in an external magnetic field and computer modeling have shown that the values of the domain structure disappearance fields on the surface of the film located above the single crystal are significantly less than the saturation fields according to magnetometry data. The application of an external magnetic field of 0,02 T leads to saturation of the entire volume of the ferrite-garnet film in the direction of the field, which does not allow further observation of the transformation of the main domain structure of the bulk sample and limits the applicability of the indicator film method.
Keywords: ferrite-garnet film, single crystal, magnetic domain structure, Kerr effect, magnetization reversal processes

D.A. Zernitsa¹, V.G. Shepelevich^2
1 Mozyr State Pedagogical University named after I.P. Shamyakin
² Belarusian State University

Abstract: The article presents the results of studying the microstructure of rapidly solidified foil of Sn_55,18Zn_44,50Si_0,23Al_0,09 alloy. The phase composition of rapidly solidified foil was studied. A uniform distribution of alloying silicon and aluminum in tin in the form of a solid solution was established. The formation of the (100) texture of tin and (1010) of zinc was revealed, associated with the predominant growth of crystallites, in which the close-packed planes of tin and zinc are perpendicular to the direction of heat removal during crystallization. An analysis of the structure and properties of the foil during isothermal annealing and natural aging was performed, with a description of the processes occurring. Formation of a dispersed structure due to high degree of supercooling of liquid phase with increase of degree of dispersion of zinc during isothermal annealing (average chord d on sections of zinc phases is 1,24 μm before heat treatment and 0,42 μm after isothermal annealing for 170 min at 150°C) along with invariance of texture during heat treatment is established. Change of the microhardness of foil during natural aging, noticeable formation of large number of clusters of precipitations of tin and zinc phases due to their supersaturation, as well as reinforcing action of alloying elements (Si, Al) are explained. During heat treatment zinc dissolves in the matrix phase, with decrease of its volume, while share of softening phase of tin increases which leads to a decrease in the microhardness.
Keywords: rapidly solidified structures, multicomponent alloy, zinc, tin, supersaturated solution, structure, isothermal annealing, silicon, aluminum

A.I. Ivanova, A.V. Dudilovskaya, O.E. Zhuravlev, A.D. Kaphtanov
Tver State University

Abstract: This article presents the results of studying non-conducting biological, crystalline objects, powders, and glass composite samples using an ionic liquid by scanning electron microscopy. Ionic liquids based on alkylpyridinium dicyanamides studied in the work were obtained by a metathesis reaction. A solution of ionic liquid in acetone was used as a conductive coating for dielectrics. It was found that the use of ionic liquid is an alternative to the methods of metal and carbon sputtering on dielectric samples. Scanning electron microscopy images of samples obtained by such microscopy methods as low vacuum mode, the use of metal sputtering (Pt) on samples, and a study of samples without a conductive coating are presented. A comparative analysis of the results obtained by traditional methods and the method of applying ionic liquid to samples is carried out. It is shown that the use of electrically conductive ionic liquids with the thermal and chemical stability makes it possible to obtain high-resolution electron microscopic images and also allows visualization of the topographic and compositional contrast of the studied dielectric samples.
Keywords: ionic liquid, sample preparation, dielectric samples, surface microstructure, scanning electron microscopy

Yu.V. Kabirov¹, A.A. Utoplov¹, N.V. Lyanguzov¹, E.N. Sidorenko¹, N.V. Prutsakova², E.V. Chebanova^2
1 Southern Federal University
² Don State Technical University

Abstract: The paper studies the dependence of the magnetoresistance and Seebeck coefficient of the composite magnetoresistive composition near the percolation threshold of 80%La_0,7Sr_0,3MnO₃/20%GeO₂ on the constant magnetic field strength up to 3,8 kOe and temperature in the range from 25°C to 150°C. The 80%La_0,7Sr_0,3MnO₃/20%GeO₂ samples have the p-type conductivity, a the positive sign of the Seebeck coefficient and a dielectric character of the change in the electrical resistance with temperature. The activation energy of such compositions is of about 0,35 eV. The magnetoresistance of such a composition decreases with an increase in the temperature difference between the hot and cold edges and disappears in the region of the phase transition temperatures of 90°C. It was found that in a constant external magnetic field of 3,8 kOe, a decrease in the Seebeck coefficient of the 80%La_0,7Sr_0,3MnO₃/20%GeO₂ compositions by 11% is observed at a temperature difference of 10 K. The dependence of the Seebeck coefficient on the magnetic field decreases with an increase in the hot edge temperature and also disappears in the temperature range of 90°C, which is associated with the ferromagnetic-paramagnetic phase transition of lanthanum manganite La_0,7Sr_0,3MnO₃ and the suppression of spin-dependent electron tunneling.
Keywords: Seebeck coefficient, magnetoresistive composite, constant magnetic field, lanthanum- strontium manganite, percolation