Новые публикации

https://doi.org/10.1016/j.jmmm.2024.171906

Manifestations of quantum effects in the macroscopic properties of frustrated magnets keep attracting considerable interest. We have formulated and studied a simple model of a three-sublattice mixed-spin (�=1,1/2,1/2) ��(3)-ferrimagnet on triangular lattice in which the strong quantum fluctuations are developed due to combined effect of frustrated exchange bonds, reduced dimensionality and a single-ion easy-plane anisotropy in the spin-1 sublattice. To account correctly for the ��(3) algebra, the Hubbard operators representation of generators is used. Dependencies of the magnetic moments � and �� (for spin-1/2 and spin-1 sublattices respectively), the total magnetic moment �, as well as the quadrupole moment, on the anisotropy parameter � are calculated at zero temperature and different ratios �/� of exchange integrals from different sublattices. It is established that for �/�≪1 the critical value ��, at which the system enters the quadrupole antiferromagnetic phase, can be much smaller than both � and �. Besides, with an increase in � from zero to �� the total moment � can change its direction several times via taking zero value. Classification of four branches of the spin-wave excitation spectrum of the ��(3)-ferrimagnet is carried out and modification of the spectrum with change in the single-ion anisotropy is analyzed.

https://doi.org/10.1016/j.jssc.2024.124640

The NdF₃–Nd₂S₃ system attracts attention of researchers due to the possibility of using LnSF compounds (Ln = rare earth element) as possible new p- and n-type materials. The samples of this system were synthesized from NdF₃ and Nd₂S₃. The NdSF compound belongs to the PbFCl structural type, P4/nmm space group, unit cell parameters: a = 3.9331(20) Å, c = 6.9081(38) Å. The experimentally determined direct and indirect NdSF bandgaps are equal to 2.68 eV and 2.24 eV. The electronic band structure was calculated via DFT simulation. The NdSF compound melts congruently at T = 1385 ± 10°С, ΔН_m = 40.5 ± 10 kJ/mol, ΔS = 24.4 ± 10 J/mol. The NdSF microhardness is 455 ± 10 HV. Five phase transformations in the NdF₃–Nd₂S₃ system were recorded by DSC; their balance equations were derived. The liquidus of the system calculated from the Redlich–Kister equation is fully consistent with the DSC data.

 https://doi.org/10.1002/adom.202303235

Far-red (FR) region (beyond 700 nm) lighting sources possess special potential for plant lighting. However, it remains a challenge to obtain high-performance Cr³⁺-doped FR phosphors. This study developed a FR phosphor, Ca_1.8Mg_1.2Al₂Ge₃O₁₂:Cr³⁺ (CMAGG: Cr³⁺), using the cation substitution strategy. Under 438 nm blue light excitation, the phosphors display FR emission centered at 720 nm with a full width at half maximum (FWHM) of 91 nm. Benefit from the favorable match with the FR phytochrome (P_fr), the phosphor is combined with InGaN blue light chips to create a FR phosphor-converted light-emitting diode (pc-LED), which is used in Italian lettuce growth experiments and it results shown in a 15% increase in fresh weight and a 6.5% increase in dry weight. Notably, supplemental FR light modulated its growth morphology. The results of this study will be useful for further research on novel Cr³⁺-doped FR phosphors to meet the precise spectral requirements for plant growth.

https://doi.org/10.3390/molecules29040848

Aptamers are currently being investigated for their potential to improve virotherapy. They offer several advantages, including the ability to prevent the aggregation of viral particles, enhance target specificity, and protect against the neutralizing effects of antibodies. The purpose of this study was to comprehensively investigate an aptamer capable of enhancing virotherapy. This involved characterizing the previously selected aptamer for vaccinia virus (VACV), evaluating the aggregation and molecular interaction of the optimized aptamers with the recombinant oncolytic virus VV-GMCSF-Lact, and estimating their immunoshielding properties in the presence of human blood serum. We chose one optimized aptamer, NV14t_56, with the highest affinity to the virus from the pool of several truncated aptamers and built its 3D model. The NV14t_56 remained stable in human blood serum for 1 h and bound to VV-GMCSF-Lact in the micromolar range (Kd ≈ 0.35 μM). Based on dynamic light scattering data, it has been demonstrated that aptamers surround viral particles and inhibit aggregate formation. In the presence of serum, the hydrodynamic diameter (by intensity) of the aptamer–virus complex did not change. Microscale thermophoresis (MST) experiments showed that NV14t_56 binds with virus (EC50 = 1.487 × 10⁹ PFU/mL). The analysis of the amplitudes of MST curves reveals that the components of the serum bind to the aptamer–virus complex without disrupting it. In vitro experiments demonstrated the efficacy of VV-GMCSF-Lact in conjunction with the aptamer when exposed to human blood serum in the absence of neutralizing antibodies (Nabs). Thus, NV14t_56 has the ability to inhibit virus aggregation, allowing VV-GMCSF-Lact to maintain its effectiveness throughout the storage period and subsequent use. When employing aptamers as protective agents for oncolytic viruses, the presence of neutralizing antibodies should be taken into account.

https://doi.org/10.46690/capi.2024.03.02

Experimental oil displacement as a result of spontaneous imbibition of silica nanosols has been carried out using two types of sandstone as the reservoir rock. The permeability of the cores ranged from 0.34 to 333 mD, while the porosity was 11% and 22%, respectively. During the research, the influence of the concentration and nanoparticle size, as well as the permeability of the rock, on the process of spontaneous imbibition, was studied. Silica nanosols were considered as an object of study. The nanoparticle size ranged from 10 to 35 nm. The mass concentration of nanoparticles varied from 0.01% to 0.25%. It was found that the use of silica nanosols significantly increases the rate of the spontaneous imbibition process. It was established that a silica nanosol with a nanoparticle size of 10 nm and a concentration of 0.25% allows to displace more than six times oil compared to the reservoir water model in the same time. As a result, it was shown that the oil displacement efficiency and the efficiency of spontaneous imbibition increase along with an increase in the nanoparticle concentration and a decrease in the nanoparticle size.

• DOI: 10.1016/j.ijbiomac.2024.130252

Properties of degradable polyhydroxyalkanoates with different monomer compositions

https://doi.org/10.1080/01431161.2024.2313993

This article investigated the possibility of remotely sensing the soil moisture profile in thawed soil from multi-angular dual-polarized brightness temperature (TB) observations at P-band frequencies of 750 MHz and 409 MHz using a modified Burke model. Moreover, it was found that an excellent agreement (coefficient of determination R² = 0.999 and root-mean-square error (RMSE) no more than RMSE = 0.6 K) could be achieved between the Njoku coherent brightness temperature model and the modified Burke model by introducing a reflectivity from the air-soil interface that takes into account the phases of the multiple re-reflected waves in the underlying layers. Based on the modified Burke model, the depths from which apparent moisture and temperature could be retrieved in a dielectrically-inhomogeneous, non-isothermal soil were investigated, being approximately ten times less than the depth for which apparent soil temperature could be retrieved. In general, the thickness of the emitting layer depends on the TB look angle and polarization, along with the moisture and temperature profiles of the soil. It was also shown that due to the effect of the Brewster angle, the H-polarization of TB was twice as sensitive (4 K/1%) to changes in volumetric soil moisture than V-polarization (1.9 K/1%). Based on multi-angular (10°-50°) observations of TB at H- and V-polarizations, a method of moisture profile retrieval in the top 5–15 cm soil (depending on surface moisture) was proposed using an exponential fitting function, the parameters of which are found in the course of solving the inverse problem. A decrease in the sensing frequency from 750 MHz to 409 MHz makes it possible to increase the accuracy of soil moisture profiles retrieval by a factor of two, being from RMSE = 1.6% (R² = 0.946) to RMSE = 0.85% (R² = 0.982) in the top 15 cm layer of soil. The conducted investigation shows the promise of using P-band observations of TB for soil moisture profile retrieval.

https://doi.org/10.1016/j.commatsci.2024.112859

The magnetic and electronic properties of transition metal borates Me₃B₂O₆ (Me = Mn, Fe, Co, Ni) with kotoite structure have been investigated at ambient and high pressures via a combination of representation analysis and density functional theory (DFT + U) calculations. Several magnetic configurations corresponding to the different irreducible representations have been considered. The total-energy calculations reveal that the magnetic ground state of Me₃B₂O₆ kotoites is composition-dependent. The lowest energy magnetic phase of manganese and nickel kotoites is characterized by the antiferromagnetic ordering of the transition metal magnetic moments along the c- axis and along the b-axis for cobalt and iron kotoites. The magnetic cell of Ni₃B₂O₆ kotoite corresponds to k = (1/2, 0, 1/2) vector and four time larger than the unit cell. The calculated exchange constants indicate the competition between ferromagnetic and antiferromagnetic interactions. At a critical pressure, Me ions undergo a high-spin to low-spin state crossover. This magnetic moments collapse is analyzed in terms of change in electronic structure under pressure.

DOI 10.1088/1361-648X/ad258c

Using local ferromagnetic resonance spectroscopy, we have studied the magnetic properties near edges of thin tangentially magnetized permalloy films, in which a well-defined uniaxial magnetic anisotropy was induced perpendicular to one of the edges. In the experiment, two samples with thicknesses of 90 and 300 nm and with slightly different compositions were examined. To explain the magnetization dynamics near edges, we propose a simple yet effective model of a film in the form of a rectangular prism, which yields the modified Kittel formula for the resonance frequency. In this formula, the locally averaged distance-dependent demagnetizing field that emerges near the edges is included as an additional uniaxial anisotropy term. The measurements reveal that at a certain distance from the edge, the resulting (apparent) anisotropy, determined from the angular dependencies of the resonance field, almost vanishes. Moreover, its easy axis reorients to become parallel to the edge. The model predictions agree well with these results, proving that the main resonance mode behavior near the film edges can be accurately described by introducing additional effective uniaxial anisotropy, provided the measuring area is relatively large. However, for the thick (300 nm) sample, additional precession modes are also observed. These modes distort the angular dependence of the main mode, thus demonstrating the limitations of the model.

DOI: https://doi.org/10.1039/D4DT00038B

The threshold structural transformation of the DUT-4 metal–organic framework (MOF) from an ordered to distorted phase during exposure to ambient conditions has been revealed. The in situ X-ray diffraction analysis, in situ Raman and FTIR spectroscopy, scanning electron microscopy and synchronous thermal analysis have been used for investigation. The reversible effect of exposure time and humidity on such a phase transition has been confirmed. We also demonstrated that the observed phase transition correlated well with changes in the optical and electronic properties of DUT-4, paving the way to a new family of MOF-based phase change materials for optoelectronic applications.

https://doi.org/10.1021/acs.inorgchem.3c04140

Optical thermometry has gained significant attention due to its remarkable sensitivity and noninvasive, rapid response to temperature changes. However, achieving both high absolute and relative temperature sensitivity in two-dimensional perovskites presents a substantial challenge. Here, we propose a novel approach to address this issue by designing and synthesizing a new narrow-band blue light-emitting two-dimensional perovskite named (C₈H₁₂NO₂)₂PbBr₄ using a straightforward solution-based method. Under excitation of near-ultraviolet light, (C₈H₁₂NO₂)₂PbBr₄ shows an ultranarrow emission band with the full width at half-maximum (FWHM) of only 19 nm. Furthermore, its luminescence property can be efficiently tuned by incorporating energy transfer from host excitons to Mn²⁺. This energy transfer leads to dual emission, encompassing both blue and orange emissions, with an impressive energy transfer efficiency of 38.3%. Additionally, we investigated the temperature-dependent fluorescence intensity ratio between blue emission of (C₈H₁₂NO₂)₂PbBr₄ and orange emission of Mn²⁺. Remarkably, (C₈H₁₂NO₂)₂PbBr₄:Mn²⁺ exhibited maximum absolute sensitivity and relative sensitivity values of 0.055 K^–1 and 3.207% K^–1, respectively, within the temperature range of 80–360 K. This work highlights the potential of (C₈H₁₂NO₂)₂PbBr₄:Mn²⁺ as a promising candidate for optical thermometry sensor application. Moreover, our findings provide valuable insights into the design of narrow-band blue light-emitting perovskites, enabling the achievement of single-component dual emission in optical thermometry sensors.

https://doi.org/10.1021/acs.cgd.3c01154

nsights into the mechanical properties of DUT-8(Ni) MOF crystals capable of structural phase transitions are presented. The open and closed pore phases of DUT-8(Ni) are drastically different in their mechanical behavior. For the open-pore phase, a huge anisotropy of compressibility and shear modulus is observed, caused by the presence of two orthogonal motives formed by aromatic linkers bound with Ni atoms via Ni–O bonds. The possibility of easy shifting of linkers with breaking and formation of new Ni–O and Ni–N bonds at the application of shear stress, which is at the same time more stable at uniaxial stress, is shown on the basis of the stiffness tensor analysis. This fact assumes the flexibility of the open-pore phase crystals and their ability for structural transformation. The less prominent anisotropy of elastic moduli and the increased values of these moduli for the closed-pore phase crystals indicate the predominantly hardness and absence of flexibility of this phase.

DOI https://doi.org/10.1039/D3TC02823B

Phytochrome P_FR plays a key role in plant photomorphogenesis, and its perception of far-red light is essential, but how to obtain an efficient far-red phosphor to achieve accurate light filling remains a huge challenge. In this study, Gd_1−y−zAl_3−x(BO₃)₄:xCr³⁺,yLu³⁺,zSm³⁺ (GAB:xCr³⁺,yLu³⁺,zSm³⁺) series phosphors were synthesized by a high-temperature solid-state method. By doping Lu³⁺, the emission intensity of Cr³⁺ could increase as high as 20%. With the introduction of Sm³⁺, the emission intensity of Cr³⁺ was further increased by 29%. Particularly, the emission spectra can be tuned by varying the concentration ratio of Sm³⁺ and Cr³⁺, more suitable for the absorption spectrum of P_FR. Moreover, the internal quantum yield and external quantum yield of GL_0.1AB:0.03Cr³⁺ and GL_0.1AB:0.03Cr³⁺,0.003Sm³⁺ were 83.1% and 24.7% and 78.1% and 26.3%, respectively. There were high anti-thermal quenching properties in the prepared phosphors at 423 K, with 107.6% (GAB:0.03Cr³⁺), 103.1% (GL_0.1AB:0.03Cr³⁺), and 102.7% (GL_0.1AB:0.003Sm³⁺,0.03Cr³⁺). Finally, the phosphors were made into pc-LED devices, which can realize the adjustable orange-red and far-red luminescence and meet the needs of plant lighting applications. In the light-regulated plant growth experiment, compared with the control group, far-red light promoted root growth in plants, confirming the application potential of the prepared phosphors in indoor plant cultivation.

https://doi.org/10.1134/S0021364024600046

We consider the effect of the nematic order on the formation of the superconducting state in iron pnictides and chalcogenides. Nematic order with the B_2g symmetry is modelled as the d-type Pomeranchuk instability and treated within the mean-field approach. Calculated nematic order parameter depends on the nematic interaction coefficient and abruptly changes with the coefficient’s increase. The superconducting solution is obtained within the spin-fluctuation pairing theory. We show that the leading solution in the nematic phase has a s_π± structure. From the critical temperature T_c estimations, we conclude that the nematic superconducting state of the s_π± type is more favorable than the usual s_± and ��2−�2 type states appearing in the absence of the nematicity

Zhidkie Kristally i Ikh Prakticheskoe Ispol'zovanie, 23(4), pp. 49-57.

https://doi.org/10.1134/S0031918X23601439

Powders of maghemite γ-Fe₂O₃ with an average diameter of 8 nm, γ-Fe₂O₃/SiO₂ composites with an agglomerate diameter of about 50 nm and a size of interspersed γ-Fe₂O₃ particles of 6 nm, and γ‑Fe₂O₃/SiO₂/aptamer(FAS9) composites were synthesized by chemical deposition. Mössbauer spectra were measured, the static and dynamic magnetic properties of the powders were studied, and the coercive force was determined, which decreases from 14 Oe for γ-Fe₂O₃ powders to 3 Oe for the γ-Fe₂O₃/SiO₂ composite. It is shown that the particle blocking temperature is close to room temperature. The increment of temperature of the powders was measured in the ferromagnetic resonance mode; the temperature of the Fe₂O₃/SiO₂ composite (ΔT ≈ 16°C) turned out to be higher than that of the pure γ-Fe₂O₃ powder (ΔT ≈ 10°C). It has been experimentally shown that temperature increment ΔT is proportional to the square of the microwave field amplitude. It has been shown that the composition γ-Fe₂O₃/SiO₂/aptamer FAS9 is able to effectively bind to tumor cells, and FMR hyperthermia leads to a decrease in the viability of tumor cells.

https://doi.org/10.1134/S0031918X2360135X

Auger electron spectroscopy was used to determine the phase composition of Cr₂GeC MAX phase thin films. A distinctive feature of the formation of carbon-containing MAX phases is the shape of carbon Auger peaks, which is characteristic of metal carbides spectra. Features of the Auger spectra in the presence of secondary phases of chromium germanides are found. Their presence can manifest itself in an increase in the energy of the germanium peaks, which is caused by a chemical shift during the formation of the Cr–Ge bond. Moreover, we have detected the accumulation of electronic charge, which can be explained by the features of the surface morphology.

https://doi.org/10.1134/S0031918X23601385

In this paper, we solve the inverse problem of magneto-optical ellipsometry for thin ferromagnetic films with optical uniaxial anisotropy. We work within the framework of the approach we developed earlier analyzing magnetoellipsometric data without using fourth-order M-matrices. We work with ellipsometric relations, in which we take into account the magneto-optical contribution as perturbations, and ellipsometric measurements are carried out on a setup with a simple dipole scheme based on the transverse magneto-optical Kerr effect. We add the magneto-optical response to the expressions known in the literature for the reflection coefficients of anisotropic thin films, which are related to the parameters measured by magneto-optical ellipsometry. As a result, by analyzing the obtained expressions for the reflection coefficients, we obtain information on the total permittivity tensor of a thin film.

https://doi.org/10.31857/S0205961423020021

Создана диэлектрическая модель, основанная на рефракционной диэлектрической модели смеси талых и мерзлых лесных органических почв корневой зоны для частоты 435 МГц. Модель разработана на основе диэлектрических измерений четырех почв, в которых содержание органического вещества варьировалось от 15 до 31%. Диэлектрические измерения были проведены в диапазоне массовой влажности от 0 до 0.6 г/г и диапазоне температур от –30 до 25°С. Коэффициент детерминации (R²) между рассчитанными с использованием модели и измеренными значениями действительной (ε') и мнимой (ε") частями комплексной диэлектрической проницаемости составил 0.97. Нормированное среднеквадратическое отклонение составило 16 и 21% для действительной и мнимой частей комплексной диэлектрической проницаемости соответственно. Разработанная диэлектрическая модель может быть применена в алгоритмах дистанционного зондирования при восстановлении значения влажности лесных почв корневой зоны из данных радарного и радиометрического зондирования.

https://doi.org/10.1103/PhysRevB.109.014421

In the substituted ${\mathrm{Nd}}_{1-x}{\mathrm{Tb}}_x{\mathrm{Fe}}_3{\left({\mathrm{BO}}_3\right)}_4$ $(x=0.1\text{and}x=0.2)$, possessing almost easy-axis magnetic structure at low temperatures, an unusual two-step transition in fields along the trigonal $c$ axis was observed by magnetization and single-crystal neutron diffraction studies. At the first step, only part of the Tb Ising-type moments flip to the $c$ axis, which is accompanied by a significant deviation of the antiferromagnetic Fe spins from the $c$ axis. At the second step, the remaining Tb moments flip and the Fe moments flop into the basal plane. The ob- served evolution is qualitatively explained by a model assuming small deviations of Tb moments from the trigonal axis due to local environment distortions, which leads to nonequivalence of the Tb ions with respect to effective Tb-Fe exchange and external field. Thus, an intrinsic “hidden” instability of the magnetic system in the magnetic field occurs.

DOI https://doi.org/10.1039/D4DT00038B

The threshold structural transformation of the DUT-4 metal–organic framework (MOF) from an ordered to distorted phase during exposure to ambient conditions has been revealed. The in situ X-ray diffraction analysis, in situ Raman and FTIR spectroscopy, scanning electron microscopy and synchronous thermal analysis have been used for investigation. The reversible effect of exposure time and humidity on such a phase transition has been confirmed. We also demonstrated that the observed phase transition correlated well with changes in the optical and electronic properties of DUT-4, paving the way to a new family of MOF-based phase change materials for optoelectronic applications.

https://doi.org/10.1016/j.jmmm.2024.171781

Contributions of different magnetic subsystems formed in the systems of synthetic ferrihydrite nanoparticles (characterized previously) with an average size of < d> ≈ 2.7 nm coated with polysaccharide arabinogalactan in different degrees have been separated by measuring the dependences of their magnetization M on magnetic field H of up to 250 kOe on vibrating sample and pulsed magnetometers. The use of a wide measuring magnetic field range has been dictated by the ambiguity in identifying a linear M(H) portion for such antiferromagnetic nanoparticle systems within the conventional field range of 60–90 kOe. The thorough analysis of the magnetization curves in the temperature range of 100–250 K has allowed the verification of the contributions of (i) uncompensated magnetic moments µ_un in the superparamagnetic subsystem, (ii) the subsystem of surface spins with the paramagnetic behavior, and (iii) the antiferromagnetic susceptibility of the antiferromagnetically ordered ferrihydrite particle core. As a result, a model of the magnetic state of ferrihydrite nanoparticles has been proposed and the numbers of spins corresponding to magnetic subsystems (i)–(iii) have been estimated. An average magnetic moment μ_un of ∼ 145 μ_B (μ_B is the Bohr magneton) per particle corresponds approximately to 30 decompensated spins of iron atoms in a particle (about 3 % of all iron atoms), which, according to the Néel’s hypothesis μ_un ∼ <d>^3/2, are localized both on the surface and in the bulk of an antiferromagnetically ordered particle. The fraction of free (paramagnetic) spins is minimal in the sample without arabinogalactan coating of the nanoparticle surface (7 %) and is attained 20 % of all iron atoms in the sample with the highest degree of spatial separation of particles. According to this estimation, paramagnetic spins are located mainly on the edges and protruding areas of particles. Most magnetic moments of iron atoms are ordered antiferromagnetically and the corresponding magnetic susceptibility of this subsystem behaves as in an antiferromagnet with the randomly distributed crystallographic axes, i.e., increases with temperature.

https://iopscience.iop.org/article/10.1088/1361-6463/ad211b

Double fluoride salts (NH₄)₃M⁴⁺F₇ (M⁴⁺: Sn, Ti, Ge, Si) demonstrate a high efficiency of using chemical pressure as a tool for control and tuning structural ordering/disordering, sensitivity to hydrostatic pressure, successions of the phase transitions, etc and, as a result, for purposeful variation within a wide range of parameters of barocaloric effect (BCE). The conventional and inverse BCEs near the triple points were found on the T − p phase diagrams, combination of which can be used to construct original cooling cycle in narrow temperature and pressure ranges. Reconstructive transformation between two cubic phases, , realized in (NH₄)₃SnF₇ at atmospheric pressure and in (NH₄)₃TiF₇ at  0.4 GPa are characterized by rather low thermal hysteresis,  = 1 K, and a great entropy change,  = 110–152 J (kg · K)⁻¹, depending on the size of the central atom. At above 300–350 K, a contribution to BCE associated with the regular thermal expansion of the crystal lattice becomes comparable to entropy and temperature changes under pressure in the region of the phase transitions. An analysis of the absolute, relative and integral barocaloric characteristics of (NH₄)₃M⁴⁺F₇ compounds showed their high competitiveness with respect to other barocaloric materials considered as promising solid-state refrigerants.

https://doi.org/10.48550/arXiv.2307.07208

We analyse the stationary current of Bose particles across the Bose-Hubbard chain connected to a battery, focusing on the effect of inter-particle interactions. It is shown that the current magnitude drastically decreases as the strength of inter-particle interactions exceeds the critical value which marks the transition to quantum chaos in the Bose-Hubbard Hamiltonian. We found that this transition is well reflected in the non-equilibrium many-body density matrix of the system. Namely, the level-spacing distribution for eigenvalues of the density matrix changes from Poisson to Wigner-Dyson distributions. With the further increase of the interaction strength, the Wigner-Dyson spectrum statistics changes back to the Poisson statistics which now marks fermionization of the bosonic particles. With respect to the stationary current, this leads to the counter-intuitive dependence of the current magnitude on the particle number.

https://doi.org/10.1063/5.0178247

Metal nanoparticle (NP) complexes lying on a single-layer graphene surface are studied with a developed original hybrid quantum–classical theory using the Finite Element Method (FEM) that is computationally cheap. Our theory is based on the motivated assumption that the carrier charge density in the doped graphene does not vary significantly during the plasmon oscillations. Charge transfer plasmon (CTP) frequencies, eigenvectors, quality factors, energy loss in the NPs and in graphene, and the absorption power are aspects that are theoretically studied and numerically calculated. It is shown the CTP frequencies reside in the terahertz range and can be represented as a product of two factors: the Fermi level of graphene and the geometry of the NP complex. The energy losses in the NPs are predicted to be inversely dependent on the radius R of the nanoparticle, while the loss in graphene is proportional to R and the interparticle distance. The CTP quality factors are predicted to be in the range ∼10−100⁠. The absorption power under CTP excitation is proportional to the scalar product of the CTP dipole moment and the external electromagnetic field. The developed theory makes it possible to simulate different properties of CTPs 3–4 orders of magnitude faster compared to the original FEM or the finite-difference time domain method, providing possibilities for predicting the plasmonic properties of very large systems for different applications.

https://doi.org/10.1016/j.jre.2022.11.004

We report on the novel heterometallic quaternary selenide EuCeCuSe₃, the fabrication of which has been a challenge until this work. The structure of the reported selenide was elucidated from the powder X-ray diffraction data, which revealed the formation of EuCeCuSe₃ with excellent yield (96.7%) accompanied with a minor fraction of CeSe₂ (3.3%), and was best solved in orthorhombic space group Pnma with the BaLaCuS₃ structural type. Thus, the crystal structure of the title compound completes the row of the heterometallic quaternary selenides EuRECuSe₃ (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y), of which the cerium-based derivative exclusively belongs to the BaLaCuS₃ structural type. The distortion of the CuSe₄ polyhedron was compared for the whole series of EuRECuSe₃ compounds using the τ₄-descriptor for four coordinated ions, which revealed the highest degree of distortion for the Ce³⁺-containing selenide, followed by the La³⁺-based derivative. Furthermore, the crystallographic and geometrical parameters of the reported selenide were discussed in comparison to the Ce³⁺-based sulfides SrCeCuS₃ and EuCeCuS₃. Ab initio calculations of the crystal structure, a phonon spectrum and elastic constants for the crystal of EuСeCuSe₃ were also performed. The types and wavenumbers of fundamental modes were determined and the involvement of ions participating in the phonon modes was assessed. The experimental IR spectrum of the reported selenide was interpreted and found to be in agreement with the calculated spectrum. The experimental direct band gap of EuCeCuSe₃ was measured to be 1.36 eV that is consistent with the concept of its origin due to interband transitions between orbitals emerging mainly from 4f (valence band) and 5d (conduction band) levels of the Eu²⁺ cation. The dependence of the Young's modulus on the direction demonstrates the anisotropy of the elastic properties, while the Vickers hardness for EuCeCuSe₃ was calculated to be 5.2 GPa. Finally, the title compound is paramagnetic above 4 K.

https://doi.org/10.1134/S1063776123120075

The magnetic-field dependence of the superparamagnetic-blocking temperature T_B of systems of antiferromagnetically ordered ferrihydrite nanoparticles has been investigated and analyzed. We studied two powder systems of nanoparticles: particles of “biogenic” ferrihydrite (with an average size of 2.7 nm), released as a result of vital functions of bacteria and coated with a thin organic shell, and particles of biogenic ferrihydrite subjected to low-temperature annealing, which cause an increase in the average particle size (to 3.8 nm) and burning out of the organic shell. The character of the temperature dependences of magnetization, measured after cooling in a weak field, as well as the shape of the obtained dependences T_B(H), demonstrate peculiar features, indicating the influence of magnetic interparticle interactions. A detailed analysis of the dependences T_B(H) within the random magnetic anisotropy model made it possible to estimate quantitatively the intensity of magnetic particle–particle interactions and determine the magnetic anisotropy constants of individual ferrihydrite particles.

https://doi.org/10.1134/S1990793123060064

The results of a study of water absorption processes by samples of polymer composite materials (PCMs) based on fiberglass, subjected to low-speed impact with controlled impact energy and alternating temperature cycling are presented. Using magnetic resonance imaging (MRI), the distribution of absorbed water in the fiberglass structure is visualized and the dynamics of its accumulation in various areas of the sample are studied. It is found that mechanical impact leads to a nonuniform distribution of the absorbed water in the samples and a significant accumulation of free water in the areas of destruction and adjacent layers in the event of a violation of the integrity of the outer layer of the material. It is shown that cyclic alternating temperature effects do not lead to a noticeable change in the water absorption processes and are comparable in effect to mechanical nondestructive impacts. The results obtained using MRI are in close agreement with the data of traditional weight measurements, which shows the effectiveness of the method in diagnosing defects and mechanical damage to PCMs exposed to the humid environment.

https://doi.org/10.3390/ijms25020708 

Gd@C₈₂O_xH_y endohedral complexes for advanced biomedical applications (computer tomography, cancer treatment, etc.) were synthesized using high-frequency arc plasma discharge through a mixture of graphite and Gd₂O₃ oxide. The Gd@C₈₂ endohedral complex was isolated by high-efficiency liquid chromatography and consequently oxidized with the formation of a family of Gd endohedral fullerenols with gross formula Gd@C₈₂O₈(OH)₂₀. Fourier-transformed infrared (FTIR) spectroscopy was used to study the structure and spectroscopic properties of the complexes in combination with the DFTB3 electronic structure calculations and infrared spectra simulations. It was shown that the main IR spectral features are formed by a fullerenole C₈₂ cage that allows one to consider the force constants at the DFTB3 level of theory without consideration of gadolinium endohedral ions inside the carbon cage. Based on the comparison of experimental FTIR and theoretical DFTB3 IR spectra, it was found that oxidation of the C₈₂ cage causes the formation of Gd@C₈₂O₂₈H₂₀, with a breakdown of the integrity of the parent C₈₂ cage with the formation of pores between neighboring carbonyl and carboxyl groups. The Gd@C₈₂O₆(OOH)₂(OH)₁₈ endohedral complex with epoxy, carbonyl and carboxyl groups was considered the most reliable fullerenole structural model.

https://doi.org/10.1007/s11433-023-2282-8

High-Q optical cavity is an indispensable component of many photonic devices, such as lasers, sensors, harmonic generation and photon emission, and chiral dichroism. Conventional way of realizing ultrahigh Q-factor relies on Fabry-Pérot resonators, photonic crystal nanocavities fabricated by a CMOS-compatible process, or whispering gallery modes.