Новые публикации

 https://doi.org/10.1002/adfm.202401860

Hybrid metal halides (HMHs) have emerged as a promising platform for optically functional crystalline materials, but it is extremely challenging to thoroughly elucidate the electron transition coupled to additional ligand emission. Herein, to discover sequences of lead-free HMHs with distinct optically active metal cations are aimed, that is, Sb³⁺ (5s²) with the lone-pair electron configuration and In³⁺ (4d¹⁰) with the fully-filled electron configuration. (Me₂NH₂)₄MCl₆·Cl (Me = −CH₃, M = Sb, In) exhibits the superior temperature/component-dependent luminescence behaviors resulting from the competition transition between triplet-states (T_n-S₀) self-trapped excitons (STEs) of inorganic units and singlet-state (S₁-S₀) of organic cations, which is manipulated by the optical activity levels of [SbCl₆]³⁻ and [InCl₆]³⁻. The bonding differences between Sb³⁺/In³⁺ and Cl⁻ in terms of electronic excitation and hybridization are emphasized, and the different electron-transition mechanisms are established according to the PL spectra at the extreme temperature of 5 to 305 K and theoretical calculations. By fine-tuning the B-site Sb³⁺/In³⁺ alloying, the photoluminescence quantum yield (PLQY = 81.5%) and stability are optimized at 20% alloying of Sb³⁺. This research sheds light on the rules governing PL behaviors of HMHs, as well as exploring the optical-functional application of aviation temperature sensors and access-control systems.

 https://doi.org/10.1039/D4TC01477D

The discovery of novel Mn²⁺-based metal halides with excellent luminescence properties and thermostability is particularly of great importance for solid-state lighting (SSL). Herein, a novel one-dimensional hybrid manganese chloride (TMA)MnCl₃ of a hexagonal system with a P6₃/m space group is synthesized via a simple saturation crystallization method. Under 443 nm excitation, (TMA)MnCl₃ single crystals exhibit a strong broad-band red emission peak at 645 nm originating from the ⁴T₁ → ⁶A₁ transition of Mn²⁺ ions with a full width at half maximum of 99 nm and a photoluminescence quantum yield (PLQY) of 98.6%. Moreover, (TMA)MnCl₃ shows a high anti-thermal quenching behavior, and the integrated PL intensity still retains 100% of the initial intensity measured at 300 °C, caused by the high structural rigidity. Benefiting from its strong blue light excitation, high PLQY, and excellent thermal stability, a stable white light-emitting diode device is fabricated by combining a 465 nm blue LED chip, green-emitting Lu₃Al₅O₁₂:Ce³⁺ and the (TMA)MnCl₃ red phosphor with a high color rendering index of 94.3% and a correlated color temperature of 3995 K. This work develops a novel hybrid manganese chloride red-emitter and paves a new path to explore high-performance phosphors excited by blue light for SSL.

https://doi.org/10.1016/j.jallcom.2024.175104

Hydrated iron fluoridotitanate (FeTiF₆ × 6 H₂O) single crystals are fascinating magnetic materials with unique properties. To understand the underlying mechanisms, this study combines X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) techniques, complemented by density functional theory (DFT) calculations. Polarization-dependent X-ray absorption spectroscopy, encompassing XANES and XMCD, is a powerful technique for probing the local structures and magnetic properties of materials. It is element-selective, bulk-sensitive, and compatible with a wide range of experimental conditions. In this study, we used XANES and XMCD spectroscopies to investigate the local structures and magnetic properties of Fe and Ti in FeTiF₆ × 6 H₂O single crystals. XANES analysis revealed distinct local environments around Fe and Ti, providing insights into their coordination environments. Element-selective magnetization measurement at the Fe K-edge demonstrated that iron sites in the oxidation state Fe²⁺ have an unambiguous paramagnetic contribution to the magnetization along the b-axis. Notably, the absence of an XMCD signal at the Ti K-edge confirmed the absence of a magnetic moment in Ti atoms within the crystal. DFT calculations corroborate the experimental findings and provide insights into the electronic structure and magnetic interactions. The combined results provide a comprehensive understanding of the dynamic Jahn-Teller effect in FeTiF₆ × 6 H₂O single crystals, highlighting the significance of polarization-dependent X-ray absorption spectroscopy in unraveling the intricate magnetic behavior of such materials. This study contributes to the fundamental understanding of magnetism in these materials and paves the way for the development of novel magnetic materials with tailored properties.

https://elib.sfu-kras.ru/handle/2311/152806

Controlled drug delivery is one of the frontier areas of science, which uses an interdisciplinary approach. The delivery systems offer numerous advantages over conventional dosage forms, such as improved efficacy and patient compatibility, reduced toxicity, and ease of use. Such systems often use micro- and nanoparticles as carriers for drugs, the prolonged effect of which is achieved due to the controlled slow release of the encapsulated drug. This study investigated the effects of encapsulation of various antiseptics (brilliant green, miramistin, and furacilin) and the chemical composition of the polymer on the yield, structure, size, drug release kinetics, and antibacterial activity of microparticles produced from resorbable polyesters of microbiological origin, polyhydroxyalkanoates. Microparticles with a 5.6–94.8 μm diameter were produced. The form of the active substance molecule has been found to be the most significant factor affecting the characteristics of polyhydroxyalkanoate microparticles. The surface structure of particles is rather determined by the chemical composition of the polymer, and the release kinetics to the model medium depends on the encapsulated drug. Microparticles based on PHAs loaded with brilliant green and furacilin showed antibacterial effects in S. aureus and E. coli cultures. The study demonstrated that microparticles with antiseptics encapsulated in them have potential as prolonged drug delivery systems and are of interest for further research

https://doi.org/10.1007/s10853-024-09755-6

Mn₅Ge₃ is a ferromagnetic hexagonal crystal promising for spintronics and magnetocalorics. A systematic study and analysis of the magnetic properties of the Mn₅Ge₃ thin film grown on Si(111) were performed. The magnetic anisotropy of the film is determined by the shape anisotropy and the easy magnetization axis aligned along the c axis of the crystal. The uniaxial anisotropy constant K_u fully corresponds to that for a bulk single crystal, which indicates that c axis coincides with film normal. Mn₅Ge₃ film demonstrates high saturation magnetization M_S = 900 emu/cm³ (900 kA/m) at T = 100 K and magnetocaloric effect ΔS = 3.16 ± 0.22 J kg⁻¹ K⁻¹ at 300 K and B = 1.5 T. ΔS is comparable to that for multicomponent or Gd rare earth films. Furthermore, a different anisotropy of the magnetocaloric effect compared to bulk Mn₅Ge₃ was found, which may be related to the anisotropy of the film shape and, possibly, to the domain structure. The results obtained are promising for the design and development of magnetocaloric, spintronic, and spin-caloritronic devices on a silicon platform.

https://doi.org/10.1016/j.matchemphys.2024.129524

Magnetic nanocomposites containing iron oxide and gold components take great attention last years because of their relative biocompatibility and the ability to combine the magnetic properties of iron and the chemical bonding properties of gold for the possible drug delivery or diagnostics for various diseases. However, such particles have some toxicity to living cells, and the effect depends on many factors, including size, shape, the ratio of components in the composites, and the type of cells affected. And thus, the search for compositions and technologies for producing iron-gold particles with improved properties and reduced cytotoxicity remains relevant. The aim of the study was to synthesize and characterize Fe₃O₄/Au nanocomposites and evaluate their influence on living cells using the example of cell line HEK293.

Fe₃O₄ nanoparticles (NPs) were synthesized by co-precipitation of Fe²⁺/Fe³⁺ water solution in alkaline conditions and then boiled with HAuCl₄ in 0.1 M sodium citrate. The NPs properties were estimated by transmission electron microscopy (TEM), vibration magnetometry and ferromagnetic resonance (FMR).

According to magnetometric measurements, nanoparticles are mainly in a superparamagnetic state. By fitting magnetization curves, the magnetic characteristics of nanoparticles were determined: saturation magnetization (59.3 emu/g) and magnetic anisotropy constant (� = 0.86·10⁵ erg/cm³). The average particle size estimated from magnetic measurements was 8.7 nm. Considering the presence of a magnetically dead layer, this is in good agreement with the TEM results. The temperature dependence of the FMR linewidth was analyzed using two models. As a result, the parameters ��� and �/�� were determined. The models used showed good agreement. The values of the anisotropy constant (� = 1.06·10⁵ erg/cm³) and the average particle size (6.8 nm) are estimated.

The effect of the NPs on the HEK293 cells was studied by MTT-assay, flow cytometry and RT-PCR. The exposure with the NPs lead to a significant decrease of cell metabolic activity in HEK293 cell culture, but this effect was not accompanied by cell death. It was shown that the expression of antioxidant enzymes SOD1 and GPX1 was reduced at the mRNA stage. So the NPs synthesized may affect gene expression and metabolism of HEK293 cells, but this does not have fatal consequences for cell viability.

https://doi.org/10.48550/arXiv.2404.14726

The levitation of a cylindrical permanent magnet over a high-temperature superconductor cooled by liquid nitrogen can be accompanied by spontaneous oscillations and rotation. The reason for spontaneous rotation of the magnet is magnetization inhomogeneity induced by the temperature gradient. An experiment was carried out on the levitation of Nd-Fe-B magnets over a composite high-temperature superconductor. The experimental results confirm that the rotation frequency depends on the difference in the magnetization values in the upper and lower halves of the magnet. Methods for controlling the rotation frequency of a levitating magnet are proposed.

https://doi.org/10.1007/978-981-99-6105-4_22

People have been exposed to airborne nanosized materials (100 nm) for thousands of years, but since the industrial revolution, particularly with regard to combustion operations, the level of exposure has significantly increased. Since the advent of nanotechnology, two decades ago, the danger of exposure to nanomaterials by ingestion, absorption through the skin, absorption through the dermis, and medication administration utilizing designed nanoparticles, has grown. Nanomaterials acquire new mechanical, electrical, optical, catalytic, and, last but not least, biological capabilities when they shrink from bulk to nanoscale. The creation, usage, and disposal of the product, as well as the toxicological impacts of nanomaterials, must all be studied. Basic multidisciplinary research including materials scientists, toxicologists, medical professionals, and environmental engineers is necessary to better understand the health risks and safety concerns of nanoparticles.

https://doi.org/10.1134/S0361768824010067

wolfram cellular automata are considered and their operation is demonstrated using an example of traffic flow simulation. For the class of one-dimensional elementary cellular automata, the concept of linearity is introduced in the language of Zhegalkin operators. An algorithm for finding linear Zhegalkin operators with multipliers of three variables is presented. The algorithm is implemented in Python.

https://doi.org/10.1134/S1062873824706573

The authors propose a way of reconstructing the Raman tensor by studying the angular dependences of the intensities of the Raman lines of unoriented microcrystals. The technique is verified using familiar calomel Hg₂Cl₂ crystals. It is shown that the lines on DUT-8 (Ni) crystals indicating phases with open and closed pores have different types of symmetries. The technique can be used to reconstruct the Raman tensor for any unoriented crystalline sample.

https://doi.org/10.1016/j.jtice.2024.105560

Crystal structure of rare-earth LaCoO₃ cobalt oxide subjected to high energy mechanical activation has been studied. In the temperature range of 300–800 K, the electrical conductivity and Seebeck coefficient were measured. Thermal conductivity was measured at 300–480 K.

https://doi.org/10.1134/S0030400X24700206

Using a generalized refractive mixture dielectric model, the influence of the relative permittivity spectra of bound and unbound water in mineral soil on the nature of the temperature dependence of the relative permittivity of natural mineral soil, with a clay fraction content of 41.3%, was studied in the electromagnetic field frequency range from 50 MHz to 15 GHz. The causes of the emergence of intersections in the relative permittivity spectra of mineral soil, obtained at different temperatures but for a sample of the same moisture content, have been studied. It has been proved that the emergence of such an intersection point in the frequency range up to 1.5 GHz is due to the Maxwell–Wagner effect in bound water. The dependences of the frequency of the intersection point of the relative permittivity spectra of mineral soil on the temperature and volumetric content of bound and unbound water have been studied.

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.