Новые публикации

https://doi.org/10.1016/j.jmmm.2024.172193

The magnetic properties of ordered MAX phases Mn₂(Al_xGa_1−x)C (x = 0.125, 0.25, 0.5, 0.75 and 0.875) have been studied within the DFT-GGA. We have found that increase of Al atom at A-site leads to the formation of the ferromagnetic phase with large magnetization of about 3.6 μ_B/f.u. The investigation of the phase stability is performed by comparing the total energy of the MAX phases with that of a set of competitive phases for calculation of the phase formation enthalpy. Up to a concentration of Al atoms x = 0.7 the compound remains thermodynamically stable. The exchange constants analysis shows the crucial role of exchange interactions between manganese atoms along the c-axis in forming of ferromagnetism. The magnetic transition temperature of Mn₂(Al_xGa_1−x)C alloys increases with increase of the aluminum concentration.

https://doi.org/10.1021/acs.chemmater.4c00548

Strong magnetic coupling interactions originating from a short Mn–Mn distance in some heavy Mn²⁺-doped matrices have important effects on luminescence of single Mn²⁺ ions and close-knit Mn²⁺–Mn²⁺ pairs. However, the intrinsic mechanism of controlling spectral regulation remains elusive since the underlying relationship among Mn–Mn distances, magnetic coupling interactions, and optical properties is unclear. Herein, we create an unusual red emission (620 nm) of Mn²⁺ in a typical tetra-coordinated lattice of Li₂CdGeO₄ by simply enhancing the Mn²⁺-doped level in addition to regular green emission (528 nm). Although the dual emission peaks occupy the same tetra-coordinated crystallographic lattice of CdO₄, different temperature-dependent emission behaviors are observed, which expands a possibility in optical thermometry sensors. Detailed Mn–Mn distances are calculated via Rietveld refinement analysis, and their effects on the Mn–Mn coupling interactions are evaluated. Furthermore, the Mn–Mn coupling interaction types are identified through electron spin resonance and magnetic measurements. The continuously decreasing distances between Mn²⁺ ions strengthen the dipole–dipole coupling effect, resulting in the atypical red emission in a tetra-coordinated lattice environment. These findings elucidate the spectral regulation mechanism from the perspective of magnetic coupling interactions, providing a new pathway to regulate Mn²⁺-related emission.

DOI: 10.1039/D4VA00040D 

We explored the role of biomineralization in industrial waste sludge formation, using the laboratory cultivation of Desulfovibrio sp. OL sulfate reducing species isolated from the Komsomolsky waste sludge (Russia). The most frequently reported sulfate-reducing bacteria (SRB) biomineralization products are various iron sulfides. Here we present first studies of the products of Desulfosporosinus metallidurans, acidophilic SRB from acid mine drainage. We analyzed the biomineralized sample using X-ray diffraction, electron microscopy, X-ray absorption and Mössbauer spectroscopies, and magnetization measurements via First-Order Reversal Curve (FORC) diagram analysis. Our findings show that the biomineralization occurring under pure culture conditions leads to the formation of greigite (Fe₃S₄) nanorods, along with larger microbially mediated crystals of vivianite (Fe₃(PO₄)₂·8H₂O) and siderite (FeCO₃). Energy dispersive X-ray spectroscopy revealed that the crystal sizes of vivianite and siderite were comparatively larger than those of the nanorod-shaped greigite. Transmission electron microscopy and Mössbauer spectroscopy detected ultrafine ferrihydrite (Fe₂O₃·nH₂O) superparamagnetic nanoparticles with an average size of 2.5 nm. FORC analysis showed significant magnetic interactions among these nanoparticles, suggesting their potential for magnetic separation applications. The current study demonstrates that ferrihydrite nanoparticles have a strong magnetic affinity for other crystal phases produced by Desulfosporosinus metallidurans. Therefore, we believe that the investigated bacterial species can be exploited in advanced magnetic separation techniques. This offers a cost-effective and environmentally friendly method for purifying sediments in industrial waste sludge.

https://doi.org/10.1021/acs.inorgchem.4c01341

Phase transitions can change the crystal structure and modify the physical properties of crystals. In this work, we investigate the phase transition behavior in BaGa₄Se₇, an important middle infrared (mid-IR) nonlinear optical (NLO) crystal, in the temperature range from room temperature to 1173 K. Interestingly, the BaGa₄Se₇ crystal undergoes a reversible ferroelastic phase transition at T = 528 K, resulting in the presence of a newly discovered phase (γ-phase) at the higher temperature. The experimental temperature dependence of optical birefringence, as well as the first-principles birefringence and NLO coefficients, reveals that the γ-phase exhibits larger birefringence and better NLO properties compared with those of the low-temperature phase (α-phase). This work demonstrates that phase-transition-induced structural modification can improve the mid-IR NLO properties, which would provide an effective avenue to obtain materials with good optoelectronic performance.

https://doi.org/10.1140/epjp/s13360-024-05155-6

The temperatures and enthalpies of the decomposition of EuLnCuSe₃ compounds (Ln = La–Lu) are determined for the first time as functions of the Ln³⁺ ionic radius (rLn³⁺). The EuLnCuSe₃ compounds with Ln = La and Ce decompose in the course of a solid-phase reaction to form EuSe, Ln₂Se₃, and Cu_2−xSe, whereas those with Ln = Tb, Dy, Ho, Tm, and Lu melt incongruently to form EuSe and a melt, for example, T_decay = 1175 K and ΔH_decay = 2.66 kJ/mol for EuLaCuSe₃, while T_melt = 1576 K and ΔH_melt = 2.69 kJ/mol for EuTbCuSe₃. When plotted as functions of rLn³⁺, the temperatures of thermal effects of these compounds exhibit a periodic dependence and a tetrad effect. The temperature dependence of electrical resistivity and that of the Seebeck coefficient are measured from 300 to 600 K. It is shown that the studied compounds are p-type semiconductors with bandgaps ranging from 0.4 to ~ 1 eV.

https://doi.org/10.1016/j.giant.2024.100288

The features of the degradation of the "green" plastic poly(3-hydroxybutyrate) [P(3HB)] in the soil of various geographical regions were studied: in red ferralitic soil under tropical conditions (Kerala, India) and in chernozem soil under conditions of a sharply continental climate (Eastern Siberia, Russia). Significant differences in the chemical composition, temperature, and humidity of the studied soils were revealed. The number of bacteria and mycelial fungi in the Siberian chernozem was higher than in the red soil of India, from 2-3 to 10 or more times. The degradation of P(3HB) films in the chernozem occurred faster than in the red soil, which was drier, with a low content of humus and minerals, and fewer microorganisms than the chernozem. The half-life of polymer samples in Siberia and India was 64.8 and 126.4 days, respectively. During degradation, a decrease in the molecular weight and an increase in the degree of crystallinity of polymer samples were revealed, which indicates a more active biodegradation of the amorphous phase of the polymer by soil microorganisms. The primary degraders of the polymer have been isolated and identified, and it has been shown that the complexes of degrading bacteria and fungi in different types of soils did not have common species. Despite the presence of species with pronounced depolymerase activity, the rate of film degradation in red ferralitic soils was slowed down by unfavorable environmental conditions. The obtained results confirm the importance of studying the process of PHA degradation in natural conditions.

https://doi.org/10.1016/j.apsusc.2024.160236

The morphology and magnetic properties as well as adsorption capacity and catalytic activity of Fe₃O₄-Ag nanoparticles synthesized by the solvothermal method were studied in dependence on the duration of the thermolysis process (3, 6, and 8 h). X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy measurements showed that the morphology of nanoparticles changed strongly as the duration of thermolysis increased. At 6 and 8 h duration, Fe₃O₄ nanocrystals grow and assemble into porous spherical globules with an Ag core (samples 2 and 3). These samples demonstrate high magnetization value and very low coercivity. The adsorption capacity of nanoparticles was studied with respect to two organic dyes: cationic methylene blue (MB) and anionic Congo red (CR). The particles showed preferential adsorption of the cationic dye. High catalytic activity towards four dyes: MB, methyl orange (MO), CR, and Rhodamine C (RhC) at the presence of NaBH₄ is the remarkable property of these samples. The rate constant of the catalytic reaction was 1.4 min⁻¹. Simultaneous exposure of CR and MO dyes to nanoparticles and NaBH₄ caused their irreversible 100 % degradation while in the case of MB and RhC, a transition to their leuco form occurred.

https://doi.org/10.1016/j.cocom.2024.e00918

The energies of various magnetically ordered structures for ludwigite Ni₂MnBO₅ have been calculated in the framework of the first-principles approach using the Wien2K program package, with the parameters of exchange interactions being determined. Two subsystems can be distinguished in the magnetic system, which are associated with the triads 4-2-4 and 3-1-3. The magnetic moments of the ions in both triads are antiferromagnetically oriented. The analysis of the exchange contribution to the energy shows that there occurs an increase of the magnetic cell relative to the crystallographic one due to antiferromagnetic ordering of the magnetic moments along the c axis in three-legged ladders formed by 4-2-4 triads. However, in three-legged ladders formed by 3-1-3 triads, the magnetic moments of the ions are ordered along the c-axis ferromagnetically. The predicted type of magnetic ordering in Ni₂MnBO₅ is similar to magnetic ordering in Fe₃BO₅. Non-collinear ordering of the magnetic moments of the subsystems at different temperatures is also likely to be observed in Ni₂MnBO₅, as is the case in Fe₃BO₅. Superexchange (indirect) interactions (No-O-B-O-Ni) influence the orientation of the magnetic moments of two 3-1-3 (4-2-4) triads within the unit cell. It is these interactions that may be responsible for the formation of long-range magnetic order in Co₃BO₅ and ferrimagnetic-antiferromagnetic spin-reorientation transition in Fe₃BO₅.

https://doi.org/10.1021/acs.inorgchem.4c00555

A luminescent zero-dimensional organic–inorganic hybrid indium halide (TUH)₆[In_1–xSb_xBr₆]Br₃ (TU = thiourea, 0 ≤ x ≤ 0.0998) was synthesized via the solvothermal method. In structures, resolved by single-crystal X-ray diffraction, isolated distorted [InBr₆]^3– and [SbBr₆]^3– octahedra are linked to organic TUH⁺ cations by intermolecular N–H···Br and N–H···S hydrogen bonds. The crystals were characterized by elemental analysis, TG-DSC, powder X-ray diffraction, FTIR analysis, and steady-state absorption and photoluminescence spectroscopy. (TUH)₆[In_1–xSb_xBr₆]Br₃ exhibits a broadband yellow-orange emission centered at 595–602 nm with a half-width of 141–149 nm (0.48–0.52 eV) and a large Stokes shift of 232–238 nm (1.33–1.35 eV). This emission can be attributed to the self-trapped exciton emission of triplet states of the octahedral anion [SbBr₆]^3– or [InBr₆]^3–. Two possible emission mechanisms were discussed. Doping with Sb³⁺ leads to a significant increase in photoluminescence quantum yield from 25.7 at x = 0 to 48.4% at x = 0.0065, when excited at 365 nm, indicating the potential use of (TUH)₆[In_1–xSb_xBr₆]Br₃ compounds in the field of photonics.

https://doi.org/10.1134/S2517751624020033

A procedure has been proposed for producing ceramic substrates for filtration membranes based on a narrow fraction of fine fly ash microspheres using cold uniaxial pressing followed by high-temperature firing. It has been shown that increasing the sintering temperature from 1000 to 1150°C leads to a decrease in open porosity from 40 to 24%, a decrease in the average pore size from 1.60 to 0.34 μm, and an increase in the compressive strength from 9.5 to 159 MPa. The resulting substrates are characterized by water permeability values of 1210, 310, 240, 170 L m⁻² h⁻¹ bar⁻¹ at sintering temperatures of 1000, 1050, 1100 and 1150°C, respectively. Experiments on filtration of aqueous suspensions of fine microspheres (d_av = 2.5 µm) and microsilica (d_av = 1.9 μm) through a substrate produced at a sintering temperature of 1150°C have shown the rejection close to 100%. The proposed methodology for using ash waste in the production of membrane materials promotes the development of technologies for the integrated processing of thermal energy waste.

https://doi.org/10.1103/PhysRevE.109.054703

A photonic crystal microcavity with the liquid crystal resonant layer tunable by heating has been implemented. The multiple vanishing resonant lines corresponding to optical bound states in the continuum are observed. The abrupt change in the resonant linewidth near the vanishing point can be used for temperature sensing.

Современные проблемы дистанционного зондирования Земли из космоса. 2024. Т. 21. № 2. С. 51-60

Представлены результаты серии измерений амплитудно-временной зависимости интерференционного поля сигналов глобальных навигационных спутниковых систем (ГНСС) диапазона L1 (λ ≈ 0,19 м) при отражении от слоистых сред: снежно-ледового покрова пресноводного озера в зимне-весенний период и вблизи лесного массива. По результатам измерений выполнены: первичная выборка данных измерений с использованием облачного сервиса, последующая обработка данных путём быстрого фурье-преобразования (БФП) и дальнейший анализ результатов с помощью методик, применяемых в многолучевой ГНСС-рефлектометрии. Для анализа полученных рефлектограмм использована модель многолучевой интерференции в слоистых средах, для чего привлечена схема геометрической оптики. Это позволило, используя коэффициенты пропускания и отражения Френеля, рассчитать амплитуду и фазу волн, пришедших наряду с прямым сигналом на приёмную антенну. В дополнение к экспериментальным данным в работе представлены результаты вычислительного моделирования динамики снежно-ледового покрова, что позволило определить его температурный режим, состояние, другие термодинамические характеристики. Моделирование проведено на основе численного решения задачи Стефана в обобщённой постановке с учётом локальных климатических данных. Это позволило не только оценить текущее состояние слоёв, но и спрогнозировать их динамическое развитие с использованием метеорологических прогнозов. Результаты исследования могут применяться для мониторинга состояния ледового покрова от становления до таяния, а также лесных массивов с целью анализа их влажности, пожароопасности и густоты посадки.

https://doi.org/10.1016/j.jcrysgro.2024.127716

The phase formation of terbium chromoborate TbCr₃(BO₃)₄ in the bismuth trimolybdate and lithium tungstate melt–solutions has been studied. The absence of the terbium chromoborate trigonal phase in the bismuth trimolybdate-based system at all component ratios has been shown. The component ratio in the lithium tungstate-based system has been found at which the TbCr₃(BO₃)₄ trigonal crystals are formed at temperatures above 1100 °C; below this temperature, the monoclinic phase dominates. The structural and magnetic properties of the grown crystals have been studied. It has been established that the trigonal and monoclinic TbCr₃(BO₃)₄ crystals synthesized from the lithium tungstate-based solvent exhibit identical magnetic properties. At the same time, a significant difference of the magnetic properties of the single crystals synthesized from the bismuth molybdate melt–solution has been observed. This difference has been attributed to the effect of Bi³⁺ ions that partially replace Tb³⁺ ions.

https://doi.org/10.1016/j.inoche.2024.112449

The structure and properties of three layered heterometallic quaternary sulfides SrLaCuS₃, SrNdCuS₃ and SrTmCuS₃ were studied for the first time using first-principles calculations in the stoichiometric and nonstoichiometric approximations. The applied DFT-based computations were performed using a hybrid functional with the contribution of nonlocal exchange in the Hartree-Fock formalism. It was revealed that the nonstoichiometry of SrLaCuS₃ and SrNdCuS₃ must be considered for modeling phonon spectra, elastic properties and band gaps. The wavenumbers and types of the Raman and “silent” modes at the Г-point were determined. From the analysis of displacement vectors, the degree of participation of ions in each mode was determined. The elastic constants and elastic moduli of the reported sulfides were calculated.

https://doi.org/10.1016/j.matchemphys.2024.129400

Huntite-like borates are versatile and promising materials with wide range of applications in frequency conversion, UV light generation, lighting, displays, quantum information storage, and more, demonstrated by their various properties and uses in scientific research. In this work, EuAl₃(BO₃)₄ powder was prepared through multi-stage solid-state reaction method using high-purity starting reagents: Eu₂O₃, Al₂O₃ and H₃BO₃, considering a 20 wt% excess of H₃BO₃ to compensate for B₂O₃ volatilization. Obtained samples undergo several treatments at varying temperatures and their phase purity is subsequently verified through powder X-ray diffraction analysis. The scanning electron microscopy reveals that resulting EuAl₃(BO₃)₄ powder consists of granules exhibiting irregular morphologies with dimensions of 0.5–8 μm. The electronic band structure of EuAl₃(BO₃)₄, calculated using the GGA PBE method, reveals f-states of Eu near 4 eV. These states do not produce emphasized peaks on simulated absorbance spectra. Using of DFT + U for the f-states of Eu pushed up f-bands above 6 eV and the charge transfer from p-O to d-Eu was obtained (E_g^direct = 5.63 eV, E_g^indirect = 5.37 eV using U_eff = 4 eV). The variation of U_eff has a weak influence on the position of the bottom of the conduction band. The experimental bandgaps of EuAl₃(BO₃)₄ crystalline powder, both direct and indirect, are found to be 3.96 and 3.67 eV, correspondingly. These values are lower than theoretical values what is associated with limitations of DFT calculations involving f electrons. The Raman spectrum of EuAl₃(BO₃)₄ powder is discussed, detailing the contributions of different ions to specific spectral bands. Investigation of high-resolution luminescence spectra shows the possibility to estimate the content of defects by the testing the violation of the prohibition of ultranarrow ⁵D₀ → ⁷F₀ line that is forbidden in the ideal crystalline structure of trigonal EuAl₃(BO₃)₄.

https://doi.org/10.1016/j.jallcom.2024.174683

Single crystals of LaCr₃(BO₃)₄ were synthesized through spontaneous nucleation from a K₂Mo₃O₁₀ flux melt. The crystal structure was determined using single-crystal X-ray diffraction (XRD) at temperatures of 293 K and 85 K. LaCr-borate crystallizes in the monoclinic C2/c space group with unit cell parameters a = 7.47980(5) Å, b = 9.55180(7) Å, c = 11.48330(8) Å, β= 104.0060(6)°, V = 796.04(1) ų (for C1, T = 293 K), and a = 7.47380(5) Å, b = 9.55520(7) Å, c = 11.47100(8) Å, β = 103.9330(6)°, V = 795.08(1) ų (for C2, T = 85 K), each with Z = 4. The temperature dependence of the unit cell parameters, including the monoclinic angle (β) and the unit cell volume (V), was investigated over the range of 85–293 K. No structural phase transitions were observed in the low-temperature region down to 85 K. Differential scanning calorimetry (DSC) measurements revealed no high-temperature phase transitions between 50 and 1350°C. Infrared (IR) spectroscopy confirmed the monoclinic structure of LaCr₃(BO₃)₄ crystals, revealing characteristic absorption bands, including the lowest frequency mode associated with the translational vibrations of the La³⁺ ion.

https://doi.org/10.1134/S106287382370627X

Ferrihydrite nanoparticles are synthesized and characterized. The dependences of heating of powders are studied upon pumping by a high-frequency electromagnetic field on a dc magnetic field. It is shown that the experimental dependence of the temperature of particles on a dc magnetic field is consistent with the theory of ferromagnetic resonance for an isotropic superparamagnet.

https://doi.org/10.1134/S1062873823706244

Results are presented from investigating the ferromagnetic resonance spectra of arrays of Co‒Ni and Co‒Fe‒Ni wires with different composition gradients, deposited into polycarbonate track-etched membranes. The effect interfaces and concentration gradients have on the effective fields of the investigated wires is examined. An anomalous angular dependence of the fields of ferromagnetic resonance is observed for the wire arrays at a pore density of ~18% in the membrane.

 https://doi.org/10.3390/polym13101553

The study reports results of using a CO₂-laser in continuous wave (3 W; 2 m/s) and quasi-pulsed (13.5 W; 1 m/s) modes to treat films prepared by solvent casting technique from four types of polyhydroxyalkanoates (PHAs), namely poly-3-hydroxybutyrate and three copolymers of 3-hydroxybutyrate: with 4-hydroxybutyrate, 3-hydroxyvalerate, and 3-hydroxyhexanoate (each second monomer constituting about 30 mol.%). The PHAs differed in their thermal and molecular weight properties and degree of crystallinity. Pristine films differed in porosity, hydrophilicity, and roughness parameters. The two modes of laser treatment altered these parameters and biocompatibility in diverse ways. Films of P(3HB) had water contact angle and surface energy of 92° and 30.8 mN/m, respectively, and average roughness of 144 nm. The water contact angle of copolymer films decreased to 80–56° and surface energy and roughness increased to 41–57 mN/m and 172–290 nm, respectively. Treatment in either mode resulted in different modifications of the films, depending on their composition and irradiation mode. Laser-treated P(3HB) films exhibited a decrease in water contact angle, which was more considerable after the treatment in the quasi-pulsed mode. Roughness parameters were changed by the treatment in both modes. Continuous wave line-by-line irradiation caused formation of sintered grooves on the film surface, which exhibited some change in water contact angle (76–80°) and reduced roughness parameters (to 40–45 mN/m) for most films. Treatment in the quasi-pulsed raster mode resulted in the formation of pits with no pronounced sintered regions on the film surface, a more considerably decreased water contact angle (to 67–76°), and increased roughness of most specimens. Colorimetric assay for assessing cell metabolic activity (MTT) in NIH 3T3 mouse fibroblast culture showed that the number of fibroblasts on the films treated in the continuous wave mode was somewhat lower; treatment in quasi-pulsed radiation mode caused an increase in the number of viable cells by a factor of 1.26 to 1.76, depending on PHA composition. This is an important result, offering an opportunity of targeted surface modification of PHA products aimed at preventing or facilitating cell attachment.

DOIhttps://doi.org/10.1039/D4CE00091A

A series of single crystals of Ni_3−xCo_xB₂O₆ compounds with the kotoite structure and with different concentrations of transition metal ions (x = 0; 0.19; 0.6; 0.93 and 2) were obtained. The lattice parameters and atomic coordinates were determined using X-ray diffraction. The theoretical calculations using the WIEN2k package predict that nickel ions tend to occupy the 4f crystallographic position, while cobalt ions tend to occupy the 2a crystallographic position. The study of the diffuse scattering spectra and comparison of the Racah parameters for the compounds Ni₃B₂O₆ and Co₂NiB₂O₆ provides experimental evidence that nickel ions occupy crystallographic position 4f.

 DOIhttps://doi.org/10.1039/D4NR00710G

Light-trapping devices have always been a topic of intense interest among researchers. One such device that has gained attention is the hot-electron photodetector with a tunable detection wavelength. Photodetectors based on plasmon nanostructures that provide excitation of surface plasmon polaritons are challenging to manufacture. To address this issue, a planar hot-electron photodetector based on a Tamm plasmon polariton localized in a metal–semiconductor-multilayer mirror structure has been proposed in this study. The parameters and materials of the structure were adjusted to ensure perfect absorption at the resonance wavelength. As a result, the photoresponsivity of the proposed device can reach 42.6 mA W⁻¹ at 905 nm. For the first time, the photosensitivity was calculated analytically by solving the dispersion law for the Tamm plasmon polariton.

https://doi.org/10.1021/acs.chemmater.4c00514

Halide double perovskites like Cs₂NaBiCl₆ are good host materials for luminescent dopants like Mn²⁺. The nature of photoluminescence (PL) depends on the local structure around the dopant ion, and doping may sometimes influence the global structure of the host. Here, we unveil the correlation between the temperature-induced (global) structural phase transition of Mn²⁺-doped Cs₂NaBiCl₆ with the local structure and PL of the Mn²⁺ dopant. X-ray diffraction analysis shows Mn²⁺-doped Cs₂NaBiCl₆ is in a cubic (Fm3m) phase between 300 and 110 K, below which the phase changes to tetragonal (I4/mmm), which persists at least until 15 K. The small (∼1%) doping amount does not alter the phase transition behavior of Cs₂NaBiCl₆. Importantly, the phase transition does not influence the Mn²⁺ d-electron PL. The PL peak energy, intensity, spectral width, and lifetime do not show any signature of the phase transition between 300–6 K. The hyperfine splitting in temperature-dependent electron paramagnetic spectra of Mn²⁺ ions also remain unchanged across the phase transition. These results suggest that the global structural phase transition of the host does not influence the local structure and emission property of the dopant Mn²⁺ ion. This structure–property insight might be explored for other transition-metal- and lanthanide-doped halide double perovskites as well. The stability of dopant emission regardless of the structural phase transition bodes well for their potential applications in phosphor-converted light emitting diodes.

https://doi.org/10.1134/S0031918X23602883

The distribution of Co²⁺ ions over sublattices and structurally nonequivalent positions in the unit cell of the crystal lattice of a single crystal of lithium gallium spinel Li_0.5Ga_2.5O₄ is shown. This distribution determines the properties of both mono- and nanocrystalline substances. The distribution is obtained by a special technology and is manifested in the electron paramagnetic resonance (EPR) spectra. The distribution of Co²⁺ ions depends on the structural and magnetic nonequivalence. The structural and magnetic nonequivalence causes a multiminimum behavior of the crystal field potential in the unit cells of single crystals at the locations of Co²⁺ ions. The Co²⁺ ions are found in complexes with tetrahedral and octahedral oxygen ions. Three types of EPR spectra of Co²⁺ ions have been found and investigated. The [Math Processing Error]Cotetr2+ spectrum is attributed to the Co²⁺ ion, which replaces the Ga³⁺ ion located in a tetrahedral oxygen environment. The spectrum of the [Math Processing Error]Cooct2+ ion located in the crystal field with axial symmetry belongs to the Co²⁺ ion replacing the Li⁺ ion located in an octahedral oxygen environment. The spectrum of the [Math Processing Error]Cooct2+ ion located in a low symmetry crystal field belongs to the Co²⁺ ion replacing the Ga³⁺ ion located in an octahedral oxygen environment. The nearest cationic environment of the ion creates rhombic distortions due to the different valence numbers of Li⁺ and Ga³⁺. The results of studying the angular dependences of the spectra show the presence of four and twelve magnetically nonequivalent positions in the unit cells.

Журн. СФУ. Сер. Матем. и физ., 17:2 (2024), 162–168

Предложена новая конструкция ВТСП ограничителя мощности с двумя рабочими полосами. Ограничитель содержит два микрополосковых полосно-пропускающих фильтра. Каждый фильтр состоит из двух четвертьволновых резонаторов, которые связаны между собой через составной полуволновый резонатор, содержащий пленку из высокотемпературного сверхпроводника. Макет устройства в открытом режиме имеет ширины рабочих полос пропускания 10% и 11% с центральными частотами 1.48 ГГц и 2.03 ГГц. Минимальные вносимые потери составили 1.9 дБ и 1.7 дБ для НЧ- и ВЧ-каналов соответственно. Передаточные характеристики устройства были исследованы до уровня СВЧ-мощности 3.15 Вт.

https://doi.org/10.1080/1536383X.2024.2338524/

A fullerene mixture was enriched with endohedral metallofullerenes (EMF) using Lewis acid (TiCl₄), which took 22 min, whereas the standard method requires about 8 h. An algorithm for assessing small-area chromatographic peaks has been proposed, which has improved the accuracy of determination. For example, the area of the C₈₄ peak was 4.24% using the developed program, while the use of chromatograph software estimated the area of this peak to be 1.78%.

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TiO2 photonic crystal nanostructure films are anodic synthesized with pulsed and stepwise voltage changes. The obtained photonic structures were activated by cyclic voltammetry in 0.5M Na2SO4. The photoelectrochemical activity of the electrodes was studied in the water splitting reaction in the wavelength range 360–700 nm. Activation leads to a change in the band gap energy, a red shift in the IPCE spectrum and an increase in its values in the studied wavelength range

https://doi.org/10.1134/S1063774523601296

MnBi₂Te₄, Mn(Bi,Sb)₂Te₄, and MnBi₂Te₄(Bi₂Te₃)_m (m ≥ 1) are assigned to magnetic topological insulators. Successful application of these materials in nanoelectronic devices calls for comprehensive investigation of their electronic structure and magnetic properties in dependence of the Bi/Sb atomic ratio and the number m of Bi₂Te₃ blocks. The magnetic properties of the surface of MnBi₂Te₄, MnBi₄Te₇, and Mn(Bi1−�Sb_x)₂Te₄ compounds (x = 0.43 and 0.32) have been studied using the magneto-optical Kerr effect. It is shown that the temperatures of magnetic transitions on the surface and in the bulk of MnBi₄Te₇ and Mn(Bi, Sb)₂Te₄ differ significantly.

https://doi.org/10.1016/B978-0-32-395195-1.00012-0

We consider dielectric cavities whose radiation space is restricted by two parallel metallic planes. The TE solutions of the Maxwell's equations of the system are equivalent to the solutions of periodical arrays of dielectric cavities. The system readily allows to achieve bound states in the continuum (BICs) of any type, including topological BICs that depends on the position and orientation of the cavities relative to the planes. This facilitates experimental studies immensely compared to infinite arrays of the cavities. We show the effect of merging topologically protected BICs, which pushes the square asymptotic of the Q-factor to the power degree of 4 or even 6.

https://doi.org/10.1134/S1061933X23601294

Due to their unique properties, organosols of silver nanoparticles are widely used in optical and semiconductor devices, to produce electrically and thermally conductive films, as catalysts, antibacterial materials, etc. This work proposes a simple and highly productive method for the preparation of silver organosols, which have a metal concentration as high as 1800 g/L and contain spherical nanoparticles with low polydispersity and a median size of 9.1 nm. The method consists in the initial preparation of silver nanoparticle hydrosols with a concentration of higher than 30 g/L followed by the transfer of the NPs into an organic phase of o-xylene. A set of physical research methods has been employed to study the regularities of the extraction of silver nanoparticles with o-xylene in the presence of cetyltrimethylammonium bromide (CTAB) and ethanol and to determine the optimal process conditions, under which the extraction degree is as high as 62.5%. It has been found that bromine anions contained in CTAB molecules cause the aggregation of some amount of silver nanoparticles with the formation of silver metal sediment in the aqueous phase. According to X-ray photoelectron spectroscopy data, the sediment contains bromide ions (up to 4 at %) on the particle surface. Organosols synthesized under optimal conditions are stable for more than 7 months and withstand repeated cycles of drying and redispersing. Silver organosols have been used to obtain metal films with an electrical conductivity of about 68 500 S/cm, which increases to 412 000 and 509 500 S/cm (87.8% of the electrical conductivity of bulk silver) after thermal treatment at 150 and 250°C, respectively.

https://doi.org/10.1134/S0021364023604244

The magnetic structure of Fe₅O₆ is studied using a combination of the group-theoretical analysis and DFT + U calculations of the electronic spectrum. The calculations are performed for the magnetic k = (0, 0, 0) vector. The magnetic ground state corresponds to the orthogonal ordering of two magnetic subsystems:  the magnetic moments of Fe²⁺/Fe³⁺ ions located at the octahedral sites (slabs of octahedra) are directed along the c axis and are antiferromagnetically ordered, whereas the magnetic moments of Fe²⁺ ions in trigonal prisms forming one-dimensional chains are directed along the b axis and are antiferromagnetically coupled along the c axis. The formation of a nonzero antiferromagnetic component of magnetic moments in the slabs of octahedra directed along the b axis is caused by the effect of magnetic chains on the three-dimensional magnetic structure.