Editor’s column

K.I. Sabanin², V.M. Skachkov¹, E.A. Bogdanova³, N.A. Sabirzyanov^1
1 Institute of Solid State Chemistry of the Ural Branch of RAS
² Ural Federal University named after the first President of Russia B. N. Yeltsin
³ JSC «Giredmet»

Abstract: The paper studies the effect of reinforcing additives of titanium and zirconium oxides, as in individually and with their combined effect, on the physico-chemical properties of dispersed-hardened composite materials based on nanoscale hydroxyapatite obtained by precipitation from solution, followed by a heat treatment over a wide temperature range from 25 to 1200°C. The composite materials under study have been obtained by means of mechanochemical synthesis with simultaneous mixing and grinding of materials. The synthesized samples were certified by X-ray phase analysis, differential thermal analysis, and dispersion analysis. The influence of the qualitative and quantitative composition of the composite material on the sintering processes, strength characteristics and morphology of studied samples is shown. It has been experimentally established that the introduction of reinforcing additives, both individually and in combination, makes it possible to thermally stabilize the material up to temperatures of ~1200°C, while maintaining a constant phase composition, preventing the decomposition of hydroxyapatite into tricalcium phosphate. It is shown that the presence of zirconium dioxide in the sample composition makes it possible to significantly increase the compressive strength of the material. However, it was found that the combined presence of titanium and zirconium oxides in the ceramic material leads to a decrease in the microhardness of the composite, which in the case of these additives makes the use of double composites as medical materials more promising.
Keywords: hydroxyapatite, nonstoichiometric titanium oxide, zirconium dioxide, composite biomaterials, microhardness

A.A. Provorkina, O.A. Golovanova
Omsk State University named after F.M. Dostoevsky

Abstract: Modern dentistry and regenerative medicine face the challenge of controlled removal of pathological calcium phosphate deposits and development of biocompatible materials for tissue restoration. This study presents a comprehensive investigation of lactic acid interaction with brushite (CaHPO₄ꞏ2H₂O) and hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂), which is crucial for developing dental calculus demineralization methods and creating resorbable implants. The research employed advanced analytical techniques including potentiometry with a Ca-selective electrode, X-ray phase analysis, thermogravimetric analysis, and infrared spectroscopy. Special emphasis was placed on thermodynamic modeling of dissolution processes by Gibbs free energy calculation (ΔG° = -61,8 kJ/mol). The key results demonstrated that the calcium phosphate dissolution efficiency is critically pH-dependent: at pH < 4, the protonated form of lactic acid dominates, enabling active interaction, while at pH > 8,2 the process virtually ceases. The thermal analysis revealed the formation of calcium pyrophosphate (Ca₂P₂O₇) at 400-800°C, which is significant for bioceramic material development. These findings provide new opportunities for creating pH-controlled demineralization systems and designing biomaterials with programmable resorption rates. The study has important practical implications for dentistry (dental calculus removal) and regenerative medicine (bone implants).
Keywords: hydroxyapatite, brushite, monetite, lactic acid, degradation

N.S. Kozhevnikova¹, E.A. Bogdanova², V.M. Skachkov¹, I.V. Baklanova¹, A.P. Tyutyunnik¹, L.Yu. Buldakova¹, M.Yu. Yanchenko^1
1 Institute of Solid State Chemistry of the Ural Branch of RAS
² JSC «Giredmet»

Abstract: The article discusses the possibility of obtaining functional composite materials with pronounced photocatalytic properties. A hybrid composite material has been developed by in-situ modification of nanostructured hydroxyapatite obtained by precipitation from solution with cadmium sulfide particles. The initial components and synthesized samples were certified using modern physicochemical methods of analysis: X-ray phase analysis, energy-dispersive X-ray analysis, Raman spectroscopy, scanning electron microscopy, and the Brunauer-Emmett-Teller method. The functional characteristics of the developed composite materials based on hydroxyapatite and cadmium sulfide, in particular, photocatalytic activity under the action of ultraviolet or visible radiation, have been studied. The efficiency of using the developed composite material as a photocatalyst was estimated by the oxidation rate of n-dihydroxybenzene (hydroquinone). Based on the obtained experimental data, the values of the reaction rate constants of photocatalytic oxidation of hydroquinone and its half-life under various conditions were calculated. It was proven that the developed composite material based on nanosized cadmium sulfide and hydroxyapatite has pronounced catalytic properties and is a promising material for use as a photocatalyst. A patent application has been filed for the developed composite material.
Keywords: cadmium sulfide, chemical condensation from aqueous solutions, hydroxyapatite, composite material, hydroquinone, photocatalysis

A.N. Zaritovskii, E.N. Kotenko, S.V. Grishchuk
L.M. Litvinenko Institute of Physical Organic and Coal Chemistry

Abstract: Carbon nanomaterials are a key component of developing nanotechnologies due to their unique characteristics and diverse applications. The production of biomass-based carbon nanostructures is considered a promising research area. Lignocellulosic materials are abundant carbon-rich renewable resources and have a sufficiently high potential to be converted into valuable carbon nanomaterials by various methods and technologies. Microwave pyrolysis is characterized as a process of thermochemical biomass conversion with improved energy efficiency and rapid heating. In this study, the catalytic synthesis of carbon nanotubes accompanying microwave pyrolysis of cellulose-containing feedstock using catalysts that are metal-modified graphite was investigated. It has been established that for obtaining multi-walled carbon nanotubes, the optimal metal content in the catalyst is 23-32%. Experiments studying the effect of microwave processing time on carbon nanostructure synthesis have demonstrated that carbon nanotubes formation mainly occurs during the first 3 minutes of exposure to ultra-high-frequency electromagnetic radiation. The possibility to exert a directed influence on the structure and morphology of the forming carbon nanomaterials by changing the synthesis parameters was shown. The products of microwave pyrolysis of cellulose have been characterized by transmission electron microscopy and X-ray phase analysis.
Keywords: carbon nanotubes, synthesis, cellulose, microwave pyrolysis, composite metal-carbon catalysts

O.A. Golovanova, S.V. Simonov
Dostoevsky Omsk State University

Abstract: A study of composition, properties and characteristics of gallstones extracted from the human body has been conducted. An analysis of the chemical composition and properties of stones has been established using a set of physico-chemical methods, which may contribute to a deeper understanding of mechanisms of their formation, which are still unknown. X-ray phase analysis showed that the stones under study are mixed, with a predominance of cholesterol in their composition. Special attention is paid to the detection of calcium phosphate, which may be a key factor in understanding the pathogenesis of gallstone disease, as this compound has not previously been detected in gallstones from different collections. To confirm the group composition of the stones, infrared Fourier spectroscopy was used, which revealed the conditions of absorption of bilirubin, represented as sodium bilirubinate. In addition, the average hydrodynamic radius of the nanopowder particles from the stones in the studied collection was determined by photon correlation spectroscopy, which made it possible to evaluate their dimensional characteristics. The study also carried out selective dissolution nanopowder from stones in order to identify the most effective solvent, which is of practical importance for understanding the properties and methods of lysis. The results of the work open up new horizons for further research in the field of bioorganic nanochemistry.
Keywords: gallstones, composition, mechanisms of formation, cholesterol, degradation, hydrodynamic radius

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

Abstract: The defect structure of a series of LiTaO₃ crystals, LiTaO₃:Cr (0,005 wt.%), LiTaO₃:Cr(0,06):Nd (0,20 wt.%), LiTaO₃:Cr(0,09)Nd (0,25 wt.%), LiTaO₃:Cr(0,1):Nd (0,25 wt.%), LiTaO₃:Cr(0,2):Nd (0,45 wt.%), was studied using infrared absorption spectra in the frequency range of stretching vibrations of hydrogen atoms in OH hydroxyl groups. It was found that the spectra of all crystals contain lines with frequencies in the ranges of 3462-3464 and 3476-3480 cm^-1, corresponding to stretching vibrations of hydrogen atoms in OH hydroxyl groups. Such minor differences in the line frequencies are due to differences in the stoichiometry of the crystals (the ratio R=[Li]/[Ta]) and the formation of complex defects (V_Li^–)-OH. It was found that the absorption band with a frequency of ≈ 3504 cm^-1 is associated with the appearance of complex defects Cr_Li²⁺-OH-Cr_Ta^2-. The Klavier method was used to determine the volume concentration of OH- groups in the crystals, which is maximum for the LiTaO₃:Cr(0,09)Nd (0,25 wt%) crystal due to the presence of two types of complex defects (Cr²⁺_Li)-OH-(Cr^2-_Ta) and (V_Li^–)-OH.
Keywords: lithium tantalat, double doping Cr and Nd, valence fluctuations in hydrogen atoms of it- groups, point structural defects, complex defects, infrared spectroscopy

S.V. Belibikhin, N.N. Konobeeva
Volgograd State University

Abstract: In this paper, we study the evolution of electromagnetic waves in an anisotropic optical medium with carbon nanotubes and polymers. The relevance of the work is due to the active use of such nanocomposites in modern nanophotonics and optoelectronics, where control of femtosecond light pulses is required. The main attention is paid to the influence of anisotropy of optical properties, which occurs due to a certain orientation of carbon nanotubes in a polymer matrix. This phenomenon significantly modifies the nonlinear response of the medium. The system of wave equations for two components for the vector potential is supplemented by a term that takes into account the effect of polymers on an extremely short optical pulse. The dependences of the output pulse parameters on the degree of anisotropy and concentration of nanotubes in the composite are established. It is shown that by controlling the orientation of carbon nanotubes, it is possible to purposefully influence such parameters of an extremely short optical pulse. This opens up significant prospects for the design and creation of new active elements, such as ultrafast optical shutters, modulators, laser radiation limiters and sensors based on controlled nonlinear properties of materials.
Keywords: carbon nanotubes, polymer, extremely short laser pulses, optical anisotropy

I.V. Baklanova, V.N. Krasil’nikov, Y.V. Baklanova
Institute of Solid State Chemistry Ural Branch of the RAS

Abstract: Erbium-doped ytterbium aluminum garnet has been synthesized by a precursor method. The samples were characterized by Infrared spectroscopy and scanning electron microscopy. Under infrared excitation at 980 nm, the compounds exhibit intense upconversion red luminescence in the visible range. According to the concentration dependences of upconversion luminescence, the optimal concentration of erbium in Yb_3-xEr_хAl₅O₁₂ compounds was x=0,3. The thermoluminescent characteristics for Yb_2,7Er_0,3Al₅O₁₂ garnet were determined by the ratio of band intensities in the visible and near-infrared ranges due to transitions from non-thermal coupled energy levels ⁴F_9/2 and ⁴I_9/2 of Er³⁺ ion. The maximum values of absolute and relative sensitivity in the temperature interval of 25-225°C have been determined. The results obtained show that it is reasonable to use the method of comparing two luminescent lines assigned to non-thermal coupled energy levels of lanthanide ions for optical thermometry and that phosphors based on Yb_3-xEr_хAl₅O₁₂ garnet hold promise as materials for temperature sensors.
Keywords: ytterbium aluminum garnet, erbium, precursor synthesis, luminescence, upconversion

I.N. Egorshin¹, V.I. Ivanov^2
1 Pacific State University
² Far Eastern State Transport University

Abstract: Studying concentration profiles induced by sedimentation is an effective way to obtain an equation of state of a colloidal suspension, to study fine details of the phase diagram and obtain information about the nature of metastable phases. Optical sedimentation methods have a number of advantages over the gravity method or centrifugation. In particular, an effective method of sedimentation in transparent nanosuspensions provides the use of the light pressure. In the case of nanoparticles, the light pressure force can exceed gravitational ones by orders of magnitude even when using continuous radiation sources. Calculation of the concentration profile for sufficiently high radiation intensities, when the volume fraction of nanoparticles at the bottom of the cuvette can reach unity, requires taking into account the interaction (repulsion) of nanoparticles. In this paper, the simplest model for taking into account the finite volume of the nanophase, the hard sphere model, is considered. As a result of the analytical solution of the problem of light-induced mass transfer, an expression is obtained that allows calculating the steady-state concentration profile. The proposed model demonstrates the need to take into account the finite volume of nanoparticles when calculating the parameters of optical deposition in dense nanosuspensions at high (superthermal) radiation
intensities. The results obtained are of interest for the development of new methods for obtaining nanomaterials, photonic crystals and chemical sensors, as well as for improving the methods of optical
diagnostics of nanomaterials.
Keywords: nanoparticle sedimentation, light pressure, nanosuspensions, sedimentation profile, hard sphere model, photonic crystals, optical diagnostics

N.N. Bolshakova, D.A. Pavlov, E.M. Semenova
Tver State University

Abstract: The paper presents the results of an experimental study of switching processes in niobium- containing BaTiO₃ crystals. It is shown that increasing the niobium concentration in BaTiO₃:Nb⁵⁺ in the range from 0,1 to 0,9 mol.% leads to an increase in the values of the switchable polarization of crystals by 20-30% compared to pure barium titanate. Coercive fields also increase: the maximum increase in the coercive field by 95% is observed for crystals with the niobium concentration of 0,9 mol.%. The field frequency has a significant effect on the switching processes: with an increase in the frequency of the repolarizing field E = 9,6ꞏ10⁴ Vꞏm^-1, the values of the switched polarization decrease monotonically to frequencies of the order of 500 Hz, and the dielectric viscosity coefficient – to 200 Hz. If we continue to increase the field frequency, the values of the polarization and the dielectric viscosity coefficient remain practically unchanged. It was found that in the frequency range from 30 Hz to 90 Hz, the domain structure of the BaTiO₃ crystal actively participates in its repolarization processes.
Keywords: barium titanate crystals, hysteresis, switching processes, permittivity, viscosity, domain structure