New Publications

Full article

Thermoelectric effects in the solid solution Mn_1-xLu_xS (x ≤ 0.2) in a wide temperature range without a field and in a magnetic field of 12 kOe are studied. The temperatures at wich a change in the sign of the thermoelectric power and the maxima of the Seebeck coefficient below Neel temperature in a magnetic field are found. The thermal expansion coefficients are measured to establish a correlation with the thermoelectric power. The thermoelectric power anomalies are explained within the framework of the orbital glass model and a change in the type of magnetic order in a magnetic field in a magnetically ordered region.

https://doi.org/10.3390/molecules30224482

Structure transformations in cholesteric droplets with planar anchoring induced by an electric field are studied experimentally. The radial spherical structure is formed initially, then it transforms into the quasi-nematic untwisting state under the action of an electric field 𝐸 =1.75 V/μm. The dependence of structure transformations on the voltage switching-off mode is examined. At the one-step voltage-off mode, the Lyre structure is realized in cholesteric droplets at the relative chiral parameter in the range 4.3 ≤𝑁 ≤8.5. The axis-symmetric bipolar structure and the low-symmetric planar bipolar structure are obtained at the multi-step voltage-off mode. The possibility of forming such structures and their stability are determined by the type of voltage switching-off mode, the N value, the surface anchoring strength (the value of cholesteric helix pitch), and the presence of the surface point defects.

https://doi.org/10.3390/polym17223064

In this study, we demonstrated chloroprene rubber (CR)-based composites with the addition of synthesized alumina nanofibers (AONF) with a high aspect ratio (>1000). AONF were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). AONF were introduced by pre-dispersion. The resulting chloroprene rubber/aluminum oxide nanofiber (CR/AONF) composites were subjected to tensile and shear adhesive bonding tests. The tensile test results for the CR/AONF composites are 81% greater than those of the original CR composite (0.85 MPa and 1.54 MPa, respectively). Shear adhesive bonding tests were conducted for glass and steel. CR/AONF demonstrates a 213% (for steel) and 262% (for glass) increase in shear strength. The main strengthening mechanisms are reinforcement, CR adsorption on the AONF surface, and crack arrest. These results may expand our understanding of the potential of sealant strengthening using AONF.

https://doi.org/10.1016/j.jallcom.2025.185110

Complex investigations of a solid-state reaction process were carried out in bilayer and multilayer thin films of Al/Pt and (Al/Pt)₁₅ by the methods of simultaneous thermal analysis, transmission electron microscopy, in situ electron diffraction, and X-ray diffraction. The solid-state reaction between the aluminum and platinum layers was found to start with the formation of an amorphous a-Al₂Pt phase. The sequence of the phase formation in the solid-state reaction was determined to be the following: Al+Pt→a-Al₂Pt→Al₃Pt₂→Al₂₁Pt₈→Al₄Pt. Thermokinetic modeling of the solid-state reaction was made in the Al/Pt films under study. The “An” type of reaction (n-dimensional formation of grains followed by crystallite growth) was shown to most accurately correspond to the formation of the a-Al₂Pt phase. The formation of the Al₃Pt₂ phase was revealed to occur in two sequential stages: the first stage corresponds to the “Bna” type of reaction (a chain mechanism of grain formation followed by fast crystallite growth), while the second stage belongs to the “R3” type of reaction (three dimensional diffusion along grain boundaries and/or a reaction on grain boundaries which proceeds according to the type of a contracting sphere). With regard to the Al₂₁Pt₈ and Al₄Pt phases, their formation process can be best described by a kinetic model which consists of two parallel reactions. The “An” type of reaction corresponds to the formation of the Al₂₁Pt₈ phase, with the “Cn-Х” type of reaction (a reaction with autocatalysis with grain formation following the chain mechanism) corresponding to the formation of the Al₄Pt phase. Kinetic parameters of the phase formation for a-Al₂Pt, Al₃Pt₂, Al₂₁Pt₈ and Al₄Pt, were determined, with those for Al₂₁Pt₈ and Al₄Pt found for the first time.

https://doi.org/10.1016/j.optcom.2025.132681

In the present work, we report the first experimental observation of Talbot effect caused by a linear periodic arrangement of fork-shaped dislocations. The presence of dislocations imposes phase discontinuities to the optical field given rise to forming an array of optical vortices co-propagating behind the structure. Two types of masks have been considered, with the same or alternating signs of topological charges. Unlike the mask with the same signs of topological charges, a multi-fork grating with alternating signs of dislocations exhibits the Talbot effect. The observed Talbot effect proved by correlation analysis is conditioned by the modality of an array of fork-shaped dislocations under consideration. Theoretical and numerical results are found to be in good correspondence with experimental data. By unveiling the intricate dependencies of optical vortex trajectories on configuration of dislocation arrangement and topological charge distribution therein, this work has advanced the state of the understanding of structured singular optics, paving the way for innovative applications in optical manipulation, communications, and complex light field engineering.

https://doi.org/10.1016/j.jallcom.2025.185110

Complex investigations of a solid-state reaction process were carried out in bilayer and multilayer thin films of Al/Pt and (Al/Pt)₁₅ by the methods of simultaneous thermal analysis, transmission electron microscopy, in situ electron diffraction, and X-ray diffraction. The solid-state reaction between the aluminum and platinum layers was found to start with the formation of an amorphous a-Al₂Pt phase. The sequence of the phase formation in the solid-state reaction was determined to be the following: Al+Pt→a-Al₂Pt→Al₃Pt₂→Al₂₁Pt₈→Al₄Pt. Thermokinetic modeling of the solid-state reaction was made in the Al/Pt films under study. The “An” type of reaction (n-dimensional formation of grains followed by crystallite growth) was shown to most accurately correspond to the formation of the a-Al₂Pt phase. The formation of the Al₃Pt₂ phase was revealed to occur in two sequential stages: the first stage corresponds to the “Bna” type of reaction (a chain mechanism of grain formation followed by fast crystallite growth), while the second stage belongs to the “R3” type of reaction (three dimensional diffusion along grain boundaries and/or a reaction on grain boundaries which proceeds according to the type of a contracting sphere). With regard to the Al₂₁Pt₈ and Al₄Pt phases, their formation process can be best described by a kinetic model which consists of two parallel reactions. The “An” type of reaction corresponds to the formation of the Al₂₁Pt₈ phase, with the “Cn-Х” type of reaction (a reaction with autocatalysis with grain formation following the chain mechanism) corresponding to the formation of the Al₄Pt phase. Kinetic parameters of the phase formation for a-Al₂Pt, Al₃Pt₂, Al₂₁Pt₈ and Al₄Pt, were determined, with those for Al₂₁Pt₈ and Al₄Pt found for the first time.

https://doi.org/10.1016/j.optcom.2025.132681

In the present work, we report the first experimental observation of Talbot effect caused by a linear periodic arrangement of fork-shaped dislocations. The presence of dislocations imposes phase discontinuities to the optical field given rise to forming an array of optical vortices co-propagating behind the structure. Two types of masks have been considered, with the same or alternating signs of topological charges. Unlike the mask with the same signs of topological charges, a multi-fork grating with alternating signs of dislocations exhibits the Talbot effect. The observed Talbot effect proved by correlation analysis is conditioned by the modality of an array of fork-shaped dislocations under consideration. Theoretical and numerical results are found to be in good correspondence with experimental data. By unveiling the intricate dependencies of optical vortex trajectories on configuration of dislocation arrangement and topological charge distribution therein, this work has advanced the state of the understanding of structured singular optics, paving the way for innovative applications in optical manipulation, communications, and complex light field engineering.

DOI: https://doi.org/10.1103/kcm2-2mz4

We investigate the impact of quantum noise on non-Hermitian resonators at an exceptional point. The system's irreversible Markovian dynamics is modeled using the Lindblad master equation, which accounts for the incoherent pump, radiative losses, and external monochromatic field. An exact analytic solution is derived in the form of the characteristic function of the Husimi distribution, enabling the calculation of all quantum mechanical observables associated with the bosonic degrees of freedom. Our analysis reveals that quantum noise strongly influences the system's response when the system exhibits 𝒫⁢𝒯 symmetry. Out of the 𝒫⁢𝒯-symmetric regime, however, the system demonstrates stability within a specific parametric domain, where the effects of quantum noise on the signal-to-noise ratio can be mitigated by increasing the external field.

DOI: https://doi.org/10.1103/xzzp-w7bd

The evolution of the role of lattice vibrations in the formation of the pseudogap state in strongly correlated electron systems has been investigated concerning changes in the electron-phonon coupling parameters and the concentration of doped charge carriers. We apply the polaronic version of the generalized tight-binding method to analyze the band structure of a realistic multiband two-dimensional model that incorporates the electron-lattice contributions of both Holstein and Peierls types. It has been demonstrated that the emergence of polaronic effects begins with the modulation of spectral function intensity. However, within a specific region of the phase diagram, a significant transformation of the electron band structure and pseudogap state occurs. It results from coherent polaron excitations that create a partially flat band near the Fermi level. This process leads to a change in the topology of the Fermi surface and the emergence of corresponding features in the density of states.

https://doi.org/10.1103/22j6-2p89

The electronic structure of the lightly hole-doped triangular-lattice moiré Hubbard model is studied within cluster perturbation theory (CPT) using 13-site clusters for a fixed doping concentration p=1/13 varying the Coulomb parameter U and the hopping phase parameter \phi related to the spin-orbital interaction. We have also developed a rather simple generalized mean-field approximation (GMFA) containing the amplitude of the spin correlations as a free parameter to fit the CPT this http URL evolution of the Fermi surface and the pseudogap with the parameters \phi and U is explained from the viewpoint of the short-range magnetic order. The geometric frustration and the additional model parameter related to the spin-orbital interaction result in a more rich physics of the pseudogap state compared to the case of a more conventional square lattice.

https://doi.org/10.1134/S1062873825713182

Nickel ferrite powders with a particle size of 4 nm were prepared by chemical coprecipitation. The imaginary part �″ of the magnetic susceptibility was measured at room temperature with a broadband ferromagnetic resonance spectrometer in the frequency range from 100 MHz to 10 GHz. The obtained frequency dependences of �″ are described within the framework of an isotropic superparamagnet model taking into account interparticle interactions.

Near-infrared (NIR) emitting phosphor-converted LEDs (pc-LEDs) have garnered significant interest due to their promising applications in diverse fields utilizing NIR spectroscopy. Fe³⁺ ions, as promising NIR activators, possess the advantages of being nontoxic and cost-effective, making them ideal candidates for NIR emission. In this work, NaAl_11-xO₁₇: xFe³⁺ phosphors were successfully synthesized, exhibiting a broad NIR emission band ranging from 650 to 850 nm, with the peak emission centered at approximately 770 nm. The phosphors demonstrate a high external quantum efficiency (EQE = 54.01 %) and excellent thermal stability. Distinct emission profiles were observed under three different excitation wavelengths, and four luminescent sites were discussed through low-temperature emission spectra. Furthermore, the electroluminescence (EL) spectrum of the fabricated pc-LEDs shows a strong spectral overlap with the absorption band of phytochrome P_fr, highlighting their great potential for plant lighting applications.

https://doi.org/10.1016/j.mtcomm.2025.114184

The energy and electronic characteristics, as well as crystal parameters of the (Cr_1-xMn_x)₂GeC MAX phase with x = 0.00, 0.25, 0.33, 0.50, 0.67, 0.75, and 1.00 were determined using quantum chemical calculations. As the manganese concentration increases, the stability of the compound is expected to decrease. However, the possibility of experimentally realizing a structure with x > 0.25 has been shown. Epitaxial thin (Cr_1-xMn_x)₂GeC MAX films with x up to 0.33 were synthesized by magnetron co-deposition at an increased technological carbon concentration. The samples were studied using electron spectroscopy, high-energy electron diffraction, X-ray diffraction, atomic force microscopy, high-resolution transmission electron microscopy and reflection spectral ellipsometry. The additional graphitic carbon is identified in the films and is attributed to the peculiarities of the deposition method. An increase in x results in an increase in the parameters of the crystal lattice, a deterioration of the crystalline order, and a decrease in optical conductivity. However, a low manganese concentration (x = 0.25) enhances epitaxy compared to Cr₂GeC. A threefold increase in the thickness of the (Cr_0.75Mn_0.25)₂GeC film results in an increase in the fraction of the secondary (013) structure and a weakening of the primary (00L) structure, though the single-phase nature of the film is preserved.

 https://doi.org/10.1007/s10948-025-07074-8

In a two-band system, both conventional sign-preserving �++ and unconventional sign-changing �± superconducting state may appear at low temperatures. Moreover, they may transform from one to another due to the impurity scattering. To study the details of such a transition here we derive the expression for the Grand thermodynamic potential Ω for a two-band model with nonmagnetic impurities considered in a �-matrix approximation. For the iron-based materials within the multiband Eliashberg theory, we show that the �±→�++ transition in the vicinity of the Born limit is a first order phase transition.

https://doi.org/10.48550/arXiv.2501.17432

Many microscopic models with the interaction between the next-nearest neighbours as a key parameter for cuprate physics have inspired us to study the diagonal superexchange interaction in a CuO layer. Our investigation shows that models with extended hopping provide a correct representation of magnetic interactions only in a hypothetical square CuO layer, where the diagonal superexchange interaction with the next-nearest neighbors always has the AFM nature. The conclusions are based on the symmetry prohibition on FM contribution to the diagonal superexchange between the next-nearest neighbors for a simple square CuO layer rather than for a real CuO layer, where diagonal AFM superexchange may be overestimated. We also discuss the reasons for magnetic frustration effects and high sensitivity of spin nanoinhomogeneity to square symmetry breaking.

 https://doi.org/10.1002/chem.202502070

https://arxiv.org/abs/2504.02452

DOI: https://doi.org/10.1103/PhysRevB.85.125307

DOI: https://doi.org/10.1103/1z7s-wcw6

We consider thermo-optic bistability in resonant excitation of high-quality modes in two-dimensional dielectric resonators. We develop a coupled-mode theory approach which account for the frequency shift due to a temperature dependent dielectric permittivity. The model is applied to rectangular and hexagonal resonators supporting an isolated high-quality resonant mode. The results are verified in comparison with straightforward finite-element simulations. It is shown that the model accurately describes the effect bistabily which occurs under variation of the angle of incidence or the intensity of the incident wave. In particular, it is demonstrated that variation of the incident angle can optimize the coupling between the resonator and the incident waves leading to bistabily with low intensity incident waves . The bistability threshold is shown to be extremely sensitive to the imaginary part of the dielectric permittivity .

https://doi.org/10.3390/bios15100644

Diabetes has become a global health challenge, driving the demand for innovative, non-invasive diagnostic technologies to improve glucose monitoring. Urinary glucose concentration, a reliable indicator of metabolic changes, provides a practical alternative for frequent monitoring without the discomfort of invasive methods. In this simulation-based study, we propose a novel asymmetric photonic structure that integrates Tamm plasmon polariton (TPP) modes and a cavity mode for high-precision refractive index sensing, with a conceptual focus on the potential detection of urinary glucose. The structure supports three distinct resonance modes, each with unique field localization. Both the TPP modes, confined at the metallic–dielectric interfaces, serve as stable references whose wavelengths are unaffected by refractive-index variations in human urine, whereas the cavity mode exhibits a redshift with increasing refractive index, enabling high responsiveness to analyte changes. The evaluation of sensing performance employs a sensitivity formulation that leverages either TPP mode as a reference and the cavity mode as a probe, thereby achieving dependable measurement and spectral stability. The optimized design achieves a sensitivity of 693 nm·RIU⁻¹ and a maximum figure of merit of 935 RIU⁻¹, indicating high detection resolution and spectral sharpness. The device allows both reflectance and transmittance measurements to ensure enhanced versatility. Moreover, the coupling between TPP and cavity modes demonstrates hybrid resonance, empowering applications such as polarization-sensitive or angle-dependent filtering. The figure of merit is analyzed further, considering resonance wavelength shifts and spectral sharpness, thus manifesting the structure’s robustness. Although this study does not provide experimental data such as calibration curves, recovery rates, or specificity validation, the proposed structure offers a promising conceptual framework for refractive index-based biosensing in human urine. The findings position the structure as a versatile platform for advanced photonic systems, offering precision, tunability, and multifunctionality beyond the demonstrated optical sensing capabilities.

https://doi.org/10.1134/S1062873825712942

Two-layer films in the Fe–Bi system were experimentally studied, which differed in the order of deposition of the magnetic and nonmagnetic layers. Electron magnetic resonance showed that additional magnetic anisotropy of the easy-plane type arises in Fe–Bi films. The observed changes are explained by the formation of a granular iron layer with strong magnetic anisotropy at the interface with bismuth.

https://doi.org/10.1016/j.jssc.2025.125716

Ionic conductivity of triple molybdates Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Cd) is studied by the method of impedance spectroscopy in the frequency range from 1 Hz to 1 MHz and in the temperature range of 300–830 K. The molybdates Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Cd) are prepared in the form of fine crystalline powder by solid state synthesis from Tl₂MoO₄, CaMoO₄ (or CdMoO₄), and Hf(MoO₄)₂ at 723–823 K. The conductivity of Tl₅Ca_0.5Hf_1.5(MoO₄)₆ ceramic samples σ = 2.69‧10⁻⁴ S/cm (at 830 K); Tl₅Cd_0.5Hf_1.5(MoO₄)₆ ‒ 8.5‧10⁻⁵ S/cm (at 830 K). The σ vs. T curve demonstrates an anomaly which corresponds to thermal effects in this temperature range. The ionic conductivity of Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Cd) is due to Tl ⁺ ions localized in channels of the framework structure. The crystal structures of Tl₅A_0.5Hf_1.5(MoO₄)₆ (A = Ca, Cd) are obtained by Rietveld method. The following unit cell parameters are calculated for Tl₅Ca_0.5Hf_1.5(MoO₄)₆: a = 10.68493(26), c = 38.3943(11) Å, V = 3796.13(22) ų, Z = 6 and for Tl₅Cd_0.5Hf_1.5(MoO₄)₆: a = 10.66890(17), c = 38.25443(73) Å, V = 3770.96(14) ų, Z = 6.

https://doi.org/10.1021/acsabm.5c00587

The development of magnetic particles for cell separation is a promising and actively developing direction. An important requirement for this method of isolation is the preservation of cell viability for the possibility of further study. The aim of the work was to develop magnetic composites based on iron oxide for single-stage cell separation and to evaluate the possibilities of further study of these cells using molecular and cellular biology methods. The particles were synthesized by the precipitation method; the magnetic cores were embedded in silica using TEOS and APTES reagents. Anti-EpCAM antibodies were immobilized on the surfaces of the obtained composites. T24 cells containing this antigen on the surface of some cells were used as a model suspension. It was shown that incubation of particles with the cells led to a decrease in the proportion of EpCAM-positive cells in the suspension and their binding to the magnetic composites. During the first hour of incubation with the particles, a decrease in the proportion of living cells in the suspension and a change in the mRNA level of the BCL2 gene were noted. However, after 2 h of incubation, cell adaptation and restoration of viability were noted. The separation procedure resulted in a stable decrease in the expression of the BIRC5 gene. The cells that were immobilized were subsequently successfully cultured. Thus, the proposed particles do not have high requirements for synthesis but allow for the isolation of living cells that can be used for further studies

https://doi.org/10.1007/s11182-025-03583-0

This work focuses on the improvement of the global navigation satellite system reflectometry (GNSS-R) methods of the underlying terrestrial surfaces. An integrated approach based on a multipath GNSS‑R is applied to determine the parameters of near-surface layered structures, including ice and snow and continuous forest covers. At the same time, experimental measurements of amplitude-time dependencies of signals from navigation satellites are processed by fast Fourier transform and then analyzed using a mathematical apparatus based on the multipath reflection model within geometric optics. In combination with the GNSS‑R technique, numerical modeling of near-surface layers, is based on local meteorological data. This allows assessing not only the current state of layered near-surface structures, but also predicting their dynamics.

DOI: 10.6060/ivkkt.20256811.7219

This work is devoted to the study by Raman spectroscopy of the features of the structural organization of molecular fragments in products of thermal solvolysis of coal in hydrocarbon solvents. The samples were obtained by dissolving GZhR grade coal in an environment of high-boiling fractions of hydrocarbon residues from coal and oil refining at a moderate temperature of 380 °C, without the use of hydrogen and catalysts. The solvent series included coal tar of high-temperature coking of coal, anthracene fraction of coal tar, heavy gas oil of catalytic cracking of petroleum raw materials and a mixture of coal tar with heavy gas oil of catalytic cracking. Pitch sampels were obtained by vacuum distillation of distillate fractions from the products of thermal dissolution. The macromolecular carbon structure of the thermal dissolution products and pitch samples was characterized by Raman spectroscopy. The calculation and analysis of the main numerical characteristics of the structure of the obtained products are performed: the degree of graphitization, the measure of sample disorder, and the size of crystallites in the basic plane of carbon atoms. It has been established that the obtained samples represent a complex carbon matrix with graphite-like fragments included in its composition. Products obtained in a solvent environment of coal origin are characterized by an increased proportion of ordered graphite structures compared to products obtained in an petroleum solvent. For pitch products, there was an increase in the degree of graphitization compared with thermal dissolution products, while the indicator characterizing the measure of disorder decreased, which allowed us to conclude that more ordered graphite structures were formed in pitch products. A correlation has been established between the indicators of the ordering of structured carbon fragments according to Raman spectroscopy data and the characteristics of the molecular structure of products obtained by FTIR-spectroscopy. Products characterized by higher aromaticity and a lower degree of substitution of aromatic rings according to FTIR data show a higgher degree of graphitization and a lower degree of disorder according to Raman spectroscopy.

 https://doi.org/10.1002/lpor.202501813

Flexible thermal sensors are crucial for monitoring the important thermodynamic parameter of temperature in daily life, industrial production, and scientific research. However, significant challenges remain in simultaneously achieving reproducible, sensitive, real-time, and in situ temperature sensing capabilities. Herein, a Mn⁴⁺ mono-doped CsNaNbOF₅:Mn⁴⁺ (CNNOFM) phosphor is designed and synthesized as a dual-mode optical thermometric material, showing high luminescence efficiencies and excellent temperature-dependent behaviors. Combined density functional theory calculations and experimental characterization reveal the isovalent group substitution mechanism between [MnF₆]²⁻ and [NbOF₅]²⁻ octahedrons, eliminating charge compensation defects in the CNNOFM system and thereby leading to enhanced luminescence efficiencies. Furthermore, CNNOFM exhibits remarkable water resistance, retaining 88.12% of its luminescent efficiency after 4 h of water immersion. The CNNOFM demonstrates high relative sensitivity in both fluorescence intensity ratio and lifetime modes, with S_r values of 0.37% K⁻¹ and 5.8% K⁻¹ at 440 K, respectively. Finally, a flexible composite fluorescent fiber temperature sensor is fabricated based on the CNNOFM phosphor to monitor the temperature of an ice-water mixture, exhibiting satisfactory performance. This work not only provides a promising thermally sensitive material for optical thermometry but also offers a new pathway for the development of flexible optical temperature sensors.

DOI: https://doi.org/10.1039/D5CP01311A

Li₂Ge₇O₁₅ is a ferroelectric and acousto-optical crystal. The lattice dynamics of the ferroelectric and paraelectric phases of the Li₂Ge₇O₁₅ crystal have been investigated using density functional theory calculations and Raman spectroscopy. The symmetry analysis of the phonon modes at the center of the Brillouin zone of both phases was performed. The phonon dispersions of both phases of the Li₂Ge₇O₁₅ crystal were simulated. The unstable modes in the paraelectric phase were determined. Temperature studies of the low-frequency region of the Raman spectra were repeated using a dynamic regime. The behavioral features of the soft mode were demonstrated, clearly showing how they depend on the orientation of the sample. The experimental behavior of the low-frequency modes has been explained. The theoretical data have been analyzed in comparison with our experimental data and the data of other authors. This study significantly improved the understanding of the lattice dynamics of both phases of the Li₂Ge₇O₁₅ crystal.

DOI: 10.47475/2500-0101-2025-10-3-595-604

FeNi/Dy/FeNi three-layer films were studied by the ferromagnetic resonance method in the temperature range from 4 to 300 K. Acoustic and optical peaks detected in the microwave spectra indicated the presence of exchange coupling between the ferromagnetic FeNi layers in the planar structure, which allowed determining the sign and value of the interlayer exchange interaction constant J12. The temperature dependence of J12 of the three-layer film with the thickness of Dy interlayer equal to 15 nm demonstrated a number of features (a change in the sign and an extremum point of the J12(T) function), which was indicative of transformations of the Dy magnetic structure.

https://doi.org/10.1134/S0036023625601989

Hitherto undescribed copper(II) hexamethylenetetramine (HMTA) complexes of tungstophosphate metalates Rb₅[PW₁₁O₃₉Cu(H₂O)]‧9H₂O (I), Rb₅[PW₁₁O₃₉Cu(C₆H₁₂N₄)]‧10H₂O (II), Rb₅[PW₁₁O₃₉Zn_0.95Cu_0.05(H₂O)]‧9H₂O (III), and Rb₅[PW₁₁O₃₉Zn_0.95Cu_0.05(C₆H₁₂N₄)]‧10H₂O (IV) were prepared and characterized by IR and electronic spectroscopies, X-ray powder diffraction, and electron paramagnetic resonance (EPR). The copper-ion absorption peak in the spectrum shifts to the longer wavelengths in going from [Cu(H₂O)₆]²⁺ through [PW₁₁O₃₉Cu(H₂O)]^5– [PW₁₁O₃₉Zn_0.95Cu_0.05(H₂O)]^5–, and [PW₁₁O₃₉Cu(C₆H₁₂N₄)]^5–, to [PW₁₁O₃₉Zn_0.95Cu_0.05(C₆H₁₂N₄)]^5– because of the changing ligand-field strength in the inner sphere of the complex. Electron paramagnetic resonance showed a significant difference between the magnitudes of the ligand field around the octahedrally coordinated Cu²⁺ ions in complexes (III) and (IV): the height of the crystal field potential barrier at the location of the Cu²⁺ ion differs more than twofold due to the replacement of a water molecule by an HMTA molecule C₆H₁₂N₄. The results of the studies can be helpful in the preparation and structure determination of other tungstate polyoxometalates with inner-sphere paramagnetic ions.

https://doi.org/10.1107/S2052520625007413

Cover illustration: Crystal structure of Cu2FeO2(BO3) represented in terms of cation- and oxo-centered polyhedra in comparison with figures of eigenvalues of thermal expansion tensor at 300 K (green color) and 1000 K (red color). The anisotropy of thermal expansion is explained by (i) the preferable orientation of the [BO3]3− units, (ii) the theory of shear deformations of the monoclinic ac plane and (iii) an arrangement of the oxo-centered double chains.