New Publications

https://doi.org/10.1134/S1070363224060094

Using the methods of X-ray diffraction, Mössbauer spectroscopy, and temperature-programmed reduction with hydrogen, the relationship between the phase composition, structural characteristics of the phases, and the reactivity with respect to hydrogen was investigated for calcium ferrites-based catalysts. The catalyst samples were prepared via solid-state synthesis from CaO and Fe₂O₃ at 900 and 1000°C by varying the Fe₂O₃ content in the CaO–Fe₂O₃ system. The phase composition of the resultant samples corresponds to the CaO‒Ca₂Fe₂O₅, Ca₂Fe₂O₅‒CaFe₂O₄, and CaFe₂O₄‒α-Fe₂O₃ regions. In the CaO–Ca₂Fe₂O₅ samples the lattice parameters of Ca₂Fe₂O₅ and its activity with respect to hydrogen depend on the phase ratio. The activity of CaFe₂O₄ is higher in Ca₂Fe₂O₅‒CaFe₂O₄ compared to CaFe₂O₄‒α-Fe₂O₃ catalysts.https://doi.org/10.1134/S1070363224060094

https://doi.org/10.1134/S1062873824707190

Results are presented from investigating the structure of Mn_2.25Co_0.75BO₅ via powder neutron diffraction. Crystals of ludwigite Mn_2.25Co_0.75BO₅ are grown by flux method using a Bi₂Mo₃O₁₂-based solvent diluted with Na₂CO₃ carbonate. Boric acid H311BO3 is used as the boron-containing reagent. Powder neutron diffraction measurements are made at a temperature of 100 K on powder prepared by grinding grown single crystals. Rietveld studies show that the grown Mn_2.25Co_0.75BO₅ crystals belong to Pbam space group. Crystallographic sites occupied by cobalt and manganese ions are identified by analyzing powder neutron diffractograms. A bottleneck regime is observed in the temperature dependence of the EPR spectra.

https://doi.org/10.1103/PhysRevB.110.045102

EuAl4 is a rare-earth intermetallic in which competing itinerant and/or indirect exchange mechanisms give rise to a complex magnetic phase diagram, including a centrosymmetric skyrmion lattice. These phenomena arise not in the tetragonal parent structure but in the presence of a charge-density wave (CDW), which lowers the crystal symmetry and renormalizes the electronic structure. Microscopic knowledge of the corresponding atomic modulations and their driving mechanism is a prerequisite for a deeper understanding of the resulting equilibrium of electronic correlations and how it might be manipulated. Here, we use synchrotron single-crystal x-ray diffraction, inelastic x-ray scattering, and lattice-dynamics calculations to clarify the origin of the CDW in EuAl4. We observe a broad softening of a transverse acoustic phonon mode that sets in well above room temperature and, at 𝑇CDW=142 K, freezes out in an atomic displacement mode described by the superspace group 𝐼⁢𝑚⁡𝑚⁡𝑚⁡(00⁢𝛾)⁢𝑠⁢00. In the context of previous work, our observation is a clear confirmation that the CDW in EuAl4 is driven by electron-phonon coupling. This result is relevant for a wider family of BaAl4 and ThCr2⁢Si2-type rare-earth intermetallics known to combine CDW instabilities and complex magnetism.

DOI 10.1209/0295-5075/ad56c3

We revisit the problem of two-terminal transport of non-interacting Fermi particles in a mesoscopic device. First, we generalize the transport problem by taking into consideration relaxation processes in contacts (which are characterized by the contact self-thermalization rate γ) and then solve it by using the master equation approach. In the limit �→0 the obtained results are shown to reproduce those of the Landauer theory. Thus, the presented analysis proves correspondence between the Landauer and master equation approaches to quantum transport —a problem which has been waiting for a solution for decades.

https://doi.org/10.1134/S1062873824706858

Water-soluble organic luminophores based on 3-(1,3-benzothiazol-2-yl)-4-hydroxybenzenesulfonic acid were studied both experimentally and by density functional theory for the first time. Because of peculiarities in chemical structure, one of them has a large Stokes shift, which results from excited state intramolecular proton transfer.

https://doi.org/10.1134/S0031918X23603025

The paper examines the impact of interparticle interactions on the superparamagnetic relaxation of ultrasmall nanoparticle ensembles, using Fe₂O₃∙nH₂O iron oxyhydroxide (ferrihydrite) nanoparticles as an example. Two samples were analyzed: ferrihydrite of biogenic origin (with an average particle size of ⟨�⟩ ≈ 2.7 nm) with a natural organic shell, and a sample (with ⟨�⟩ ≈ 3.5 nm) that underwent low-temperature annealing, during which the organic shell was partially removed. The DC and AC magnetic susceptibilities (χ′(T), χ′′(T)) in a small magnetic field in the superparamagnetic (SPM) blocking region of the nanoparticles were measured. The results show that an increase in interparticle interactions leads to an increase in the SPM blocking temperature from 28 to 52 K according to DC magnetization data. It is shown that below the SPM blocking temperature, magnetic interactions of nanoparticles lead to the formation of a collective state similar to spin glass in bulk materials. The scaling approach reveals that the dynamics of correlated magnetic moments on the particle surface slow down with increasing interparticle interactions. Simulation of χ′′(T) dependence has shown that the dissipation of magnetic energy occurs in two stages. The first stage is directly related to the blocking of the magnetic moment of nanoparticles, while the second stage reflects the spin-glass behavior of surface spins and strongly depends on the strength of interparticle interactions.

https://doi.org/10.1134/S0031918X24600088

The study investigates carbon-containing coatings of 3d-metals (Ni, Co, Fe) produced by chemical deposition method using arabinogalactan. The coatings were analyzed using X-ray diffraction, FMR, and M(H) magnetometry. Measurement of M(H) in plane and perpendicular to the plane of the magnetic coatings allowed determining the distribution of demagnetizing factor in the studied coatings. The obtained distributions of the demagnetizing factor were used to analyze the angular dependences of the ferromagnetic resonance field. The values of magnetization and perpendicular anisotropy field were estimated. The paper illustrates the effect of texture on the magnetic parameters.

https://doi.org/10.1002/andp.202400120

Light diffraction is studied numerically and experimentally on a double fork-shaped grating representing a periodic grating containing two spaced dislocations. The spatial dynamics of the phase singularities (optical vortices) has been investigated as a function of dislocation parameters. Produced optical vortices affect each other while propagating in a free space. For dislocations of the same topological charge, the propagation trajectories and their transverse displacement coordinates depend on the dislocation spacing, and the larger the dislocation spacing, the smaller the relative displacement of the optical vortices and the smaller their trajectory curvatures. For oppositely charged dislocations, three types of spatial behavior of optical vortices are found. The numerical results agree well with the experimental data.

https://doi.org/10.1016/j.ica.2024.122310

Acetate complexes of rare earth elements are extensively studied compounds known for their diverse properties and potential applications and lanthanum acetate hydrate is commercially available. In this work, a powdered anhydrous lanthanum acetate (La(CH₃COO)₃) sample was prepared by dissolving lanthanum oxide (La₂O₃) in an excess of acetic acid (CH₃COOH) and distilled water (H₂O), followed by direct evaporation at 150 °C. The decomposition of La(CH₃COO)₃ was studied, showing initiation around 300 °C and conclusion at ≥700 °C, with four distinct thermal events (I–IV) of mass loss. Gas phase identification revealed acetone and carbon dioxide as decomposition products, indicating pyrolytic decarboxylation. The final thermal effect (IV) is linked to the decomposition of La₂O₂CO₃ to La₂O₃. The DFT refinement of atomic coordinates of hydrogen atoms, which were unavailable from experiment, was successfully performed. Obtained structural data was checked using vibrational spectroscopy method. The calculated electronic band structure of La(CH₃COO)₃ indicates it as an indirect wide band gap material with values of direct transition close to indirect. The optical bandgap is found to be 5.49 eV, suggesting that the charge transfer in La(CH₃COO)₃ can be optically activated with wavelengths shorter than 226 nm, which falls within the deep UV (DUV) region.

https://doi.org/10.1134/S2075113324700400

By the example of α-Fe₂O₃ hematite, 5Fe₂O₃⋅9H₂O ferrihydrite, and γ-Fe₂O₃ maghemite powders, a microwave-radiation-induced powder system temperature growth ΔT_max of several degrees has been measured in the ferromagnetic resonance mode at a frequency of 8.9 GHz. The powders heat up the most in the external field H coinciding with the ferromagnetic resonance field. The value of the ΔT_max effect depends on the magnetization of a powder material. The results obtained allow us to propose a new magnetic hyperthermia method for biomedical applications.

 https://doi.org/10.3390/magnetochemistry10070047

The generally accepted model of the magnetic structure of an iron oxide core–shell nanoparticle includes a single-domain magnetically ordered core surrounded by a layer with a frozen spin disorder. Due to the exchange coupling between the shell and core, the spin disorder should lead to nonuniform magnetization in the core. Suppression of this inhomogeneity by an external magnetic field causes the nonlinear behavior of the magnetization as a function of the field in the region of the approach to magnetic saturation. The equation proposed to describe this effect is tested using a micromagnetic simulation. Analysis of the approach to magnetic saturation of iron oxide nanoparticles at different temperatures using this equation can be used to estimate the temperature evolution of the core–shell coupling energy and the size of the uniformly magnetized nanoparticle core and the temperature behavior of this size.

https://pubs.acs.org/doi/full/10.1021/acs.chemmater.4c01205

Negative-thermal-expansion (NTE) materials violate the common knowledge of “thermal expansion and cold contraction” in solids and embrace various physical mechanisms. In most phonon-driven NTE materials, an open-framework structure is necessary to accommodate the spatially anisotropic phonon excitations of the bridged atoms, but such a structural feature may result in structural instability at a high temperature. Herein, we focus on γ-LiBO₂ with a closed-framework diamond-like structure and identify its uniaxial NTE behavior over the largest temperature range (100−850 K) among this structural family. As the temperature increases, the synergetic structural modification of the constituent structural groups, i.e., the stretching and bending of the Li−O bonds in floppy [LiO₄] and the tension or rotation in the [BO₄] group, accounts for NTE along the c-axis. Our study unveils that, apart from the anisotropic phonon excitations of individual atoms, the preferred phonon excitations of structural groups are also able to generate NTE, which would update the understanding of the NTE mechanism and guide the further exploration of phonon-driven NTE materials.

https://doi.org/10.1063/5.0206742

The properties of charge transfer plasmons (CTPs) in periodic metallic nanoparticle arrays (PMNPAs) on the single-layer graphene surface are studied within a computationally efficient original hybrid quantum-classical model. The model is based on the proven assumption that the carrier charge density in doped graphene remains unchanged under plasmon oscillations. Calculated CTP frequencies for two PMNPA geometries are shown to lie within the THz range and to be factorized, i.e., presented as a product of two independent factors determined by the graphene charge density and the PMNPA geometry. Equations are derived for describing the CTP frequencies and eigenvectors, i.e., oscillating nanoparticle charge values. It is shown that the CTP plasmons having a band structure containing a wave vector and a band number, like to phonons in periodic media, can be divided into an acoustic mode and optical CTP modes. For the acoustic modes, the CTP group velocity tends to zero at �→0⁠, but reaches a value of ∼�Fermi in graphene inside the Brillouin zone, while for the optical modes, the group velocity dispersion is extremely weak, although their energy is higher than the acoustic plasmon energies. It is shown that the calculated dependence of CTP frequencies on the carrier concentration in graphene is in good agreement with experimental data. We believe that the proposed model can help in designing various graphene-based terahertz nanoplasmonic devices of complex geometry due to very high computational efficiency.

https://doi.org/10.1016/j.jeurceramsoc.2024.116769

The paper presents the results of detailed studies of thermal expansion of solid solutions (1-x)Na1/2Bi1/2TiO3-xBaTiO3 with x=0.04-0.97 in the temperature range from 100 to 900 K. A change in chemical pressure associated with the complex cationic substitution, (Na1/2Bi1/2)2+→ Ba2+, result in a very rapid decrease in the temperatures of the transformation �4��→�2��→�3� below 100 K which are characteristic of BaTiO3. Significant features in the behavior of thermal expansion were observed near two triple points in the �−� phase diagram where the phases ��3̄�, �4��, �4�� (x≈0.15-0.20) and �4��, �4��, �3� (x≈0,06) coexist, allow the studied solid solutions to be divided into three groups. The relationship between the effects of internal chemical pressure and external hydrostatic one is discussed. By analyzing the thermodynamic potential, the root-mean-square polarization �� is determined, which increases by about 16% with a decrease in the BT content from 0.97 to 0.4.

https://doi.org/10.1016/j.saa.2024.124801

The study of Na-carbonates stability and their transformations in aqueous carbonate fluid under high P–T conditions is relevant from the point of view of the understanding geochemical processes of the Na-assisted carbon circulation in the Earth’s crust and subduction zones. In situ Raman study of Na-bearing carbonate-water-Fe-metal system in diamond anvil cell (DAC) at high P–T conditions revealed that carbonates decompose with abiogenic formation of formates and other organic compounds that differs from behavior of carbonates in dry system. XRD and FTIR methods have been used additionally to determine the phase composition. Na-bearing carbonates (nahcolite NaHCO3, shortite Na2Ca2(CO3)3 and cancrinite Na7Ca[(CO3)_1.5Al6Si6O₂₄]⋅2H2O) in aqueous fluid decompose to form simple carbonates and formates (as dominant organic molecules) at moderate P–T parameters (above ∼0.2 GPa, 200 °C). Our experimental results directly confirm the hypothesis of Horita and Berndt (Science, 1999) about possible yield of organic formates in the carbonate-water-metal system.

Nahcolite NaHCO3 in aqueous fluid in the presence of Fe metal decomposes into anhydrous phases: natrite �-Na2CO3, siderite, magnetite (due to dissolution of Fe steel gasket), Na-formate and likely organic molecular crystalline solvate of Na-formate and methyl formate. Shortite decays into anhydrous phases: aragonite CaCO3, Na-Ca-formates and an amorphous phase. Cancrinite decomposes to unidentified carbonate-alumonosilicate phases, Na-Ca-formates and unknown organic molecular crystal. Magnetite is also formed in this system due to dissolution of Fe steel gasket used in DAC. The present study provides a new insight in processes of abiogenic formation of organic matter from carbonates in the crust and upper mantle.

https://doi.org/10.1002/adma.202406164

The quest for artificial light sources mimicking sunlight has been a long-standing endeavor, particularly for applications in anticounterfeiting, agriculture, and color hue detection. Conventional sunlight simulators are often cost-prohibitive and bulky. Therefore, the development of a series of single-phase phosphors Ca₉LiMg_1-xAl_2x/3(PO₄)₇:0.1Eu²⁺ (x = 0-0.75) with sunlight-like emission represents a welcome step towards compact and economical light source alternatives. The phosphors are obtained by an original heterovalent substitution method and emit a broad spectrum   spanning from violet to deep red. Notably, the phosphor with x = 0.5 exhibits an impressive full width at half-maximum of 330 nm. A synergistic interplay of experimental investigations and theory unveils the mechanism behind sunlight-like emission due to the local structural perturbations introduced by the heterovalent substitution of Al³⁺ for Mg²⁺, leading to a varied distribution of Eu²⁺ within the lattice. Subsequent characterization of a series of organic dyes combining absorption spectroscopy with convolutional neural network analysis convincingly demonstrates the potential of this phosphor in portable photodetection devices. Broad-spectrum light source testing empowers the model to precisely differentiate dye patterns. This points to the phosphor being ideal for mimicking sunlight. Beyond this demonstrated application, the phosphor's utility is envisioned in other relevant domains, including visible light communication and smart agriculture.

https://doi.org/10.1007/s10948-024-06802-w

Bi‒Sr‒Ca‒Cu‒O polycrystalline high-temperature superconductors with the 2–2-2–3 structure have been comprehensively studied, their properties have been described, and features of the small magnetic hysteresis in the investigated materials have been established. The small magnetic hysteresis is shown to be caused by the penetration of a magnetic flux into a superconductor and its capture in the region of boundaries between HTS crystallites and by Meissner currents flowing through these boundaries. It has been found that, at a certain magnetic prehistory, the small hysteresis collapses, i.e. its footprints disappear. This has been attributed to the interaction between two superconducting subsystems in the investigated polycrystalline HTS, specifically, the effect of the magnetic moments of HTS crystallites on the effective field in the regions of intercrystalline boundaries. The shape of the small magnetic hysteresis loop has been described within the critical state model.

https://doi.org/10.1134/S0021364024600812

The field dependence of the magnetization along the hard axes in a four-sublattice ferromagnet PbMnBO₄ is calculated by the numerical minimization of the ground state energy in the approximation of classical magnetic moments. The parameters of anisotropic interactions—the second-order single-ion anisotropy constants, the magnitude and direction of the antisymmetric exchange vector, and the symmetric anisotropic exchange tensor—are obtained by a comparison with experimental magnetization curves. The direction of the Dzyaloshinskii–Moriya interaction vector is close to the orthorhombic c axis. The symmetric exchange tensor has an almost uniaxial form with the easy axis perpendicular to the antisymmetric exchange vector. Changes in the energy of each anisotropic interaction during magnetization reorientation are calculated.

https://doi.org/10.1016/j.jlumin.2024.120795

Tuning the components and multiple activator sites possesses profound significances on the regulation for corresponding luminescent properties of target phosphors. However, it is still challenging to realize full-visible emission via single activator in a single phase owing to the matrix diversity and uncertainty for multi-site occupation. Herein, we developed a family of whitlockite-type solid-solution phosphors Ca₈MgGa_1-yLa_y(PO₄)₇: Eu²⁺(y = 0–1) via inducing the La³⁺ ions into Ca₈MgGa(PO₄)₇:Eu²⁺. The local environments of Eu²⁺ ions and corresponding tunable photoluminescent properties, decay times and thermal stability are revealed systematically in detail. Specially, the excitation and emission spectra of Ca₈MgGa_1-yLa_y(PO₄)₇: Eu²⁺ are broadened gradually, finally towards a full-visible emission with 152 nm bandwidth spectrum for the phosphor Ca₈MgLa(PO₄)₇: Eu²⁺. WLED with a high color rendering index (CRI = 95) and low color temperature (CCT = 3764 K) was fabricated based on the full-visible emission Ca₈MgGa_0.2La_0.8(PO₄)₇: 0.08Eu²⁺ phosphors under a 365 nm chip, indicating the prominent potentials for high-color-rendering WLEDs. These results in current work provide new ideas for synergetic manipulation of components and multiple activator sites towards a full-visible emission in single-phase applied for white lighting.

https://doi.org/10.1103/PhysRevB.110.045102

EuAl4 is a rare-earth intermetallic in which competing itinerant and/or indirect exchange mechanisms give rise to a complex magnetic phase diagram, including a centrosymmetric skyrmion lattice. These phenomena arise not in the tetragonal parent structure but in the presence of a charge-density wave (CDW), which lowers the crystal symmetry and renormalizes the electronic structure. Microscopic knowledge of the corresponding atomic modulations and their driving mechanism is a prerequisite for a deeper understanding of the resulting equilibrium of electronic correlations and how it might be manipulated. Here, we use synchrotron single-crystal x-ray diffraction, inelastic x-ray scattering, and lattice-dynamics calculations to clarify the origin of the CDW in EuAl4. We observe a broad softening of a transverse acoustic phonon mode that sets in well above room temperature and, at 𝑇CDW=142 K, freezes out in an atomic displacement mode described by the superspace group 𝐼⁢𝑚⁡𝑚⁡𝑚⁡(00⁢𝛾)⁢𝑠⁢00. In the context of previous work, our observation is a clear confirmation that the CDW in EuAl4 is driven by electron-phonon coupling. This result is relevant for a wider family of BaAl4 and ThCr2⁢Si2-type rare-earth intermetallics known to combine CDW instabilities and complex magnetism.

DOI:https://doi.org/10.1103/PhysRevB.110.035410

We study the effects of relaxation/decoherence processes on quantum transport of noninteracting Fermi particles across the disordered tight-binding chain, where we distinguish between relaxation processes in the contacts (external decoherence) and those in the chain (internal decoherence). It is shown that external decoherence reduces conductance fluctuations but does not alter the Anderson localization length. This is in strong contrast with the effect of internal decoherence which is found to suppress Anderson localization. We also address quantum transport in chains with particle losses which are of considerable interest for laboratory experiments with cold atoms.

https://doi.org/10.1016/j.mtcomm.2024.109623

Utilizing density functional theory (DFT), we embarked on a comprehensive investigation of the structural, electronic, and optical properties characteristic of the ferroelectric hybrid (Me2NH2)[NaFe(CN)5(NO)] crystal. The geometry of the crystal structure in the ���21 phase was optimized. We simulated the electronic band structure within the first Brillouin zone. The calculated band gap for the indirect U-X transition is 2.401 eV, indicative of a wide band gap semiconductors. We also simulated the density of electronic states across the Brillouin zone. The simulation of the electronic structure revealed that the crystal comprises both ionic and covalent bonds. We accurately predicted various optical parameters including the dielectric function, conductivity, reflectivity, loss function, absorption, and refractive index. The reflectivity of the crystal does not exceed 21 percent. All calculated optical properties of the (Me2NH2)[NaFe(CN)5(NO)] crystal are anisotropic.

https://doi.org/10.1016/j.jmmm.2024.172287

The structural, electrical, magnetic, magneto-optical properties and magnetoresistance of {[(Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆]/[ZnO]}_n multilayer structures, where n = 50 is the number of bilayers (Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆ nanocomposite and ZnO have been studied. The thicknesses of (Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆ nanocomposite layers as well as ZnO spacers were varied in a wide range. The samples were synthesized by ion-beam sputtering onto glass ceramic substrates. The (Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆ composite have an amorphous structure and the semiconductor ZnO interlayers have a hexagonal crystalline structure with the p63mc symmetry group. The nanocomposite layers containing a ferromagnetic component far from the percolation threshold are in a superparamagnetic state. The presented in the paper data of magnetization, magneto-optical transverse Kerr effect and magnetoresistance indicates that long-range ferromagnetic order does not form down to 77 K both for references ZnO films and studied multilayers with thin and thick ZnO interlayers. An increase in the magneto-optical signal in multilayers compared to references (Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆ composite films has been detected at 1.2 eV. The magnetoresistance of {[(Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆]/[ZnO]}_n multilayers with thick (>32 nm) ZnO interlayers is lower than in reference (Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆ nanocomposite, while at thin ZnO interlayers magnetoresistance is significantly higher and reaches 12 % at temperatures of 77 К. Possible mechanisms of ferromagnetic and antiferromagnetic ordering, enhancement of the magneto-optical response and magnetoresistance in {[(Co₄₀Fe₄₀B₂₀)₃₄(SiO₂)₆₆]/[ZnO]}_n multilayer nanostructures are discussed.

http://dx.doi.org/10.2139/ssrn.4805398

Ni2CrBO5 has been synthesized and investigated by X-ray diffraction, dc magnetization, and specific heat measurements. The unusual cation distribution has been established: the M1 and M3 sites are occupied by Ni2+ ions, the M2 site is by Cr3+ ions, and the M4 site is mixed, featuring both Ni2+and Cr3+ ions. The magnetic order onsets at TN=140 K, which is confirmed by a λ-type peak in specific heat, followed by the dome-shaped anomaly of the magnetization at about 30 K. In the magnetically ordered state, a remarkable sequence of temperature-induced magnetization reversal sensitive to the measurement’s regime is observed. Dominant antiferromagnetic interactions are characterized by the Weiss temperature θ = -73 K. The effective magnetic moment of 5.37 μB per formula unit is close to the spin-only one. The effect of the cation distribution on the magnetic properties is discussed.

https://doi.org/10.1016/j.jssc.2024.124880

Lanthanum selenidofluorides belong to wide-gap semiconductors and are promising for optoelectronics. La₂F₄Se, B–LaFSe compounds were obtained by the ampoule method from binary compounds. Crystals La₂F₄Se, R-3m, a = 4.18245(11) Å, c = 23.2939(6) Å, Z = 3, B–LaFSe P6₃/mmc, a = 4.21989(5) Å, c = 8.19140(10) Å, Z = 2 have a layered grain structure, their microhardnesses are 340 and 450 HV, which allows samples processing. The optical bandgap of La₂F₄Se is 4.5 eV. The optical bandgaps of La₂F₄Se and B–LaFSe were analyzed by comparing the calculated absorption spectra and the experimental Kubelka-Munk Functions. It was shown that this approach is attractive in explaining optical properties in the vicinity of fundamental absorption onset and in neighboring regions. In LaF₃–La₂Se₃ system, temperatures and enthalpies of five phase transformations were determined, and their balance equations were obtained. It was shown that La₂F₄Se, B–LaFSe compounds melt incongruently and that an eutectic is formed between the phases. A phase diagram of LaF₃–La₂Se₃ system was constructed. The liquidus calculated by Redlich-Kister polynomial agrees with the data of differential scanning calorimetry.

https://doi.org/10.1016/j.jallcom.2024.175500

The kinetics of diffusion and formation of Al-Au intermetallic compounds in a solid-state reaction between layers of aluminum and gold has been studied by the method of in situ electron diffraction. The phase sequence in the solid-state reaction in Al/Au thin films is found to depend on the atomic ratio of aluminum and gold at the initial state. Specifically, with the atomic ratio being Al:Au=2:1, one observes the formation sequence: Al₃Au₈→AlAu₂→Al₂Au, while with the ratio Al:Au=1:4, the sequence is Al₃Au₈→AlAu₄. The observed change in the sequence is explained using the theoretical model of EHF (Effective Heat of Formation). The kinetic parameters of the diffusion of gold through the layer of reaction products in the Al/Au thin films have been determined, including the apparent activation energy of the diffusion E_a=1.17 eV and pre-exponential factor D₀=120 cm²/s. Based on the data obtained by in situ electron diffraction, the kinetic parameters of the phase formation have been estimated by the Kissinger-Akahira-Sunose method. In addition, the kinetic parameters of the formation of the Al-Au intermetallic compounds have been determined (apparent activation energy E_a, pre-exponential factor A) in the solid-state reaction in the Al/Au thin films, namely, E_a = 0.77 eV, log(A, s⁻¹) = 9 for Al₃Au₈; E_a = 1.08 eV, log(A, s⁻¹) = 13 for AlAu₂; E_a = 1.13 eV, log(A, s⁻¹) = 13 for Al₂Au; and E_a = 1.35 eV, log(A, s⁻¹) = 16 for the phase AlAu₄. The kinetic parameters of the formation of the AlAu₄ phase have been estimated for the first time.

Liquid crystal cells, in which the planar director orientation is specified by SU-8 polymer films treated by the stamp nanoprinting method, have been studied. The orienting film surface after texturing represents a comb-shaped lattice, the profile of which depends on the processing temperature. In cells filled with nematic LC E7, a homogeneous orientational structure with a small number of surface linear defects on both substrates is formed. These defects do not appear in LC cells with asymmetric substrates, when one of them is coated with an SU-8 film, and the other one is covered with a rubbed nylon-6 film. It has been shown that the director pre-tilt angle on the studied SU-8 films is close to zero and the films set a strong polar anchoring energy for the nematic E7. The results obtained are of interest for the development of methods for manufacturing LC devices using technologies for nanoprinting of orienting polymer films.

DOI: 10.18083/LCAppl.2024.1.90

Исследовано фотоиндуцированное изменение ориентационной структуры хирального нематика на основе ЛН-396, допированного хиральными добавками S811 и cChD. Продемонстрировано, что использование планарно-конических граничных условий позволяет реализовать плавное изменение угла закрутки его структуры вследствие изменения шага спирали. Показано, что при коническом сцеплении, задаваемом полимером ПиБМА для исследуемого хирального нематика, закрутка структуры на угол более 240° приводит к появлению ондуляций структуры. Обнаружено, что полимер ПтБМА задает для исследуемого хирального нематика тангенциальные граничные условия, позволяющие директору легко поворачиваться в плоскости образца. Представленные результаты могут быть перспективными для разработки жидкокристаллических систем с тонко настраиваемыми и перестраиваемыми полярным и азимутальным углами директора.

DOI:10.18083/LCAppl.2024.2.54

In order to gain an adequate understanding about the nature of spectral and optical properties of uniaxial molecular (polymer) films, the data about the energy structure of molecules (monomers) and the long-range orientation order of dipole moments m_q of electronic/vibrational transitions are needed. This order is characterized by the order parameters U_q of moments m_q with respect to the optical axis n of the film. Until now, components n_j(omega), k_j(omega) of refractive indices N_j(omega) = n_j(omega) – ik_j(omega) or components epsilon_(1,2)j(omega) of dielectric constants epsilon_j(omega) = epsilon_1j(omega) – iepsilon_2j(omega) of the film for the light-wave polarizations along (j = ||) and across (j = perpendicular) the axis n had been used as indirect sources of such data. The direct information about the energy structure of molecules (monomers) and parameters U_q is contained in the components gamma_(1,2)j(omega) of ensemble-averaged polarizabilities gamma_j(omega) = gamma_1j(omega) – igamma_2j(omega) of molecules (monomers). In this work, components P_(1,2)j(omega) of polarizabilities densities P_j(omega) = [epsilon_j(omega) – 1]/f_j(omega) = 4PiNgamma_j(omega) = P_1j(omega) – iP_2j(omega) are used for receiving such information. Here, f_j(omega) = 1 + L_j[epsilon_j(omega) – 1] are the local-field tensor components for the light wave in the film; the Lorentz-tensor components L_j are obtained using the dependences n_j(omega) in the transparency region of the film; N is the number of molecules (monomers) per unit volume of the film. Methods for determining parameters U_q for molecular transitions were developed using the dependences P_(1,2)j(omega) within the isolated absorption bands corresponding to the transitions. The methods were confirmed for the uniaxial films of the conjugated polymer F8BT with the preferred orientation of macromolecules in the film plane XY with the optical axis n||Z and the known dependences n_j(omega), k_j(omega) in the transparency and lowfrequency electronic absorption ranges. The spectral-invariant correlations connecting functions P_(1,2)j(omega) and epsilon_(1,2)j(omega) were established.

https://doi.org/10.2174/0113852728296495240409062733

Synthesis of new hybrid organosilicon compounds based on the amides 1- naphthylacetic acid was described. N-Organyl-2-(1-naphthyl)-N-[(triethoxysilyl)methyl]- acetamides were obtained by the reaction of 1-naphthylacetyl chloride with α-silylamines RNHCH₂Si(OEt)₃ (R = Me, i-Pr and Ph). Their subsequent interaction with N(CH₂CH₂OH)₃ led to the formation of N-organyl-2-(1-naphthyl)-N-(silatranylmethyl)acetamides. The structure of these hybrid compounds was characterized by ¹H, ¹³C, and ²⁹Si NMR spectroscopy. The structure of N-methyl- and N-isopropyl-2-(1-naphthyl)-N-(silatranylmethy)acetamides was confirmed by X-ray diffraction analysis. Results of computational screening showed that these silatranes are bioavailable and have drug-likeness.