Новые публикации

Fabrication and thermoelectric properties of SrTiO3–TiO2 composite ceramics

Zavjalov, A.P., Lyubas, G.A., Sharafutdinov, M.R., (...), Kriventsov, V.V., Kosyanov, D.Y.//Ceramics International//

https://doi.org/10.1016/j.ceramint.2022.08.210

The paper presents the results of preparing biphase SrTiO3–TiO2 ceramics as a promising system for n-type thermoelectrics using the features of a two-dimensional electron gas. Ceramics was obtained by reactive spark plasma sintering of SrCO3 and TiO2. The dynamics of phase transformations are shown; it is clarified that phase transformations are not the driving force of sintering. The mutual stabilization of the SrTiO3 and TiO2 phases is shown. Unique data on the assessment of the temperature gradient in the system have been obtained. A comparison of the thermoelectric characteristics of biphasic ceramics and its constituent phases allows concluding that the role of the two-dimensional electron gas is reduced to modulating the properties of bulk phases. Clear signs of size quantization were detected by the X-ray luminescence method, which is expressed in the blueshift of the luminescence spectrum by 22.3 ± 0.8 meV.

Crystal Structure Dynamics of RFe3(BO3)4 Single Crystals in the Temperature Range 25–500 K

Alekseeva, O.A., Smirnova, E.S., Frolov, K.V., (...), Lyubutin, I.S., Gudim, I.A.// Crystals//

 https://doi.org/10.3390/cryst12091203

The multiferroic RFe3(BO3)4 family is characterized by diverse magnetic, magnetoelectric, and magnetoelastic properties, the fundamental aspects of which are essential for modern electronics. The present research, using single-crystal X-ray diffraction (XRD) and Mössbauer spectroscopy (MS) in the temperature range of 25–500 K, aimed to analyze the influence of local atomic coordination on magnetoelectric properties and exchange and super-exchange interactions in RFe3(BO3)4. Low-temperature, single-crystal XRD data of the magnetically ordered phase of RFe3(BO3)4 at 25 K, which were obtained for the first time, were supplemented with data obtained at higher temperatures, making it possible to draw conclusions about the mechanism of the structural dynamics. It was shown that, in structures with R = Gd, Ho, and Y (low-temperature space group P3121), a shift in oxygen atoms (O2, second coordination sphere of R atoms) was accompanied by rotation of the B2O3 triangle toward R atoms at low temperatures, and by different rearrangements in iron chains of two types, in contrast to Nd and Sm iron borates (space group R32). These rearrangements in the structures of space group P3121 affected the exchange and super-exchange paths at low temperatures. The MS results confirm the influence of the distant environment of atoms on the magnetoelectric properties of rare-earth iron borates at low temperatures.

Formation of Noble Metal Phases (Pt, Pd, Rh, Ru, Ir, Au, Ag) in the Process of Fractional Crystallization of the CuFeS2 Melt

Sinyakova, E.F., Vasilyeva, I.G., Oreshonkov, A.S., Goryainov, S.V., Karmanov, N.S.// Minerals//

https://doi.org/10.3390/min12091136

The quasi-equilibrium directional crystallization of the melt composition (at. %): Cu 24.998, Fe 25.001, S 49.983, with Ag 0.002, Pd 0.003, Ru 0.004, Rh 0.006, and Au, Pt, Ir (each as 0.001) was carried out. The crystallized cylindrical ingot consisted of two primary zones and three secondary zones with different chemical and phase compositions. The compositions of the primary zones corresponded to high-temperature intermediate solid solution (zone I) and liquid enriched in sulfur (zone II). The compositions of the secondary zones corresponded to low-temperature intermediate solid solution and chalcopyrite (zone Ia), the same intermediate solid solution with chalcopyrite and bornite (zone Ib), and again with bornite, chalcocite, and idaite (zone II). We plotted the distribution curves of Fe, Cu, and S along the ingot, calculated the distribution coefficients of the components during directional crystallization, and clearly showed that, from the initial stoichiometric composition CuFeS2, the intermediate solid solution enriched in Fe and depleted in S is crystallized. Based on the data of directional crystallization and thermal analysis, a cross section was constructed in the intermediate solid solution-sulfide melt region of the Cu-Fe-S system. With solubility in the solid Cu-Fe sulfides lying below detection limit of scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS), noble elements occurred as individual phases of a size more often <10 µm. They were identified as Ag, RuS2, PdS, Au* (an Au based alloy), (Rh, Ir, Ru)3S8, (Rh, Ir)3S8, Rh3S8, and (Cu, Fe)~2(Pt, Rh)1S~5 phases by electron microprobe. Based on ab initio calculations of crystal structure, electronic band structure, and lattice dynamics of idealized laurite RuS2 phase and the idealized Ir3S8, Rh3S8, and Ru3S8 phases, the interpretation of Raman spectrum of the cation-mixed (Ru, Rh, Ir)S2 sulfide was presented for the first time. 

Ligand Engineering Triggered Efficiency Tunable Emission in Zero-Dimensional Manganese Hybrids for White Light-Emitting Diodes

Ren, Q., Zhang, J., Mao, Y., Nanomaterials(...), Zhou, G., Zhang, X.-M.// Nanomaterials//

 https://doi.org/10.3390/nano12183142

Zero-dimensional (0D) hybrid manganese halides have emerged as promising platforms for the white light-emitting diodes (w-LEDs) owing to their excellent optical properties. Necessary for researching on the structure-activity relationship of photoluminescence (PL), the novel manganese bromides (C13H14N)2MnBr4 and (C13H26N)2MnBr4 are reported by screening two ligands with similar atomic arrangements but various steric configurations. It is found that (C13H14N)2MnBr4 with planar configuration tends to promote a stronger electron-phonon coupling, crystal filed effect and concentration-quenching effect than (C13H26N)2MnBr4 with chair configuration, resulting in the broadband emission (FWHM = 63 nm) to peak at 539 nm with a large Stokes shift (70 nm) and a relatively low photoluminescence quantum yield (PLQY) (46.23%), which makes for the potential application (LED-1, Ra = 82.1) in solid-state lighting. In contrast, (C13H26N)2MnBr4 exhibits a narrowband emission (FWHM = 44 nm) which peaked at 515 nm with a small Stokes shift (47 nm) and a high PLQY of 64.60%, and the as-fabricated white LED-2 reaches a wide colour gamut of 107.8% National Television Standards Committee (NTSC), thus highlighting the immeasurable application prospects in solid-state display. This work clarifies the significance of the spatial configuration of organic cations in hybrids perovskites and enriches the design ideas for function-oriented low-dimensional emitters. 

Effect of deuteration on the barocaloric properties of complex vanadates (NH4)3VOxF6−x (x: 1, 2)

Bogdanov, E.V., Gorev, M.V., Flerov, I.N.// Solid State Sciences//

https://doi.org/10.1016/j.solidstatesciences.2022.107022

We report on the analysis of intensive and extensive barocaloric properties and their sensitivity to deuteration of complex oxyfluorides (NH4)3VOxF6−x (x: 1, 2) undergoing a similar sequence of structural phase transitions. Due to the high sensitivity to hydrostatic pressure and the strong disordering of six-coordinated anionic fluoro-oxygen species, (NH4)3VO2F4 and (ND4)3VO2F4 crystals demonstrate the highest barocaloric efficiency at low pressure, p = 0.1 GPa, during the phase transition from the initial cubic phase: barocaloric coefficients reach large values |ΔSBCE|/p ≈ 400 J/(kg K GPa) and ΔTAD/p ≈ 80 K/GPa. Anionic, [VOF5] → [VO2F4], and cationic, [ND4] → [NH4] substitutions are accompanied by a decrease in the disorder of structural units in the cubic phase, which leads to a decrease in changes in entropy and temperature under pressure. The contribution of thermal expansion of the crystal lattice to the total intensive and extensive barocaloric effects is large and amounts to about 30–40%.

Rheological properties of colloidal suspensions of alumina nanofibers

Minakov, A.V., Pryazhnikov, M.I., Simunin, M.M., (...), Khartov, S.V., Voronin, A.S.// Journal of Molecular Liquids//

https://doi.org/10.1016/j.molliq.2022.120385

We have studied the rheological properties of colloidal suspensions based alumina nanofibers (ANF) with a mass fraction of 0.125–2 wt%. The ANFs used in this work are stand out by a high aspect ratio L/D ∼ 106–107 (dry ANF before dispersion) and ease of dispersion due to the self-organized aligned structure of ANF, which is characteristic of our synthesis method. It was shown that ANF suspensions are characterized by high colloidal stability, zeta potential has a significant dependence on ANF volume fraction. ANF have a strong effect on the shear viscosity of colloidal suspensions; non-Newtonian behavior is observed in suspensions with an ANF mass fraction of 0.5 wt%. A comprehensive study of the propagation of ultrasound in ANF suspensions was carried out. Based on experimental results on the scattering of ultrasound in suspensions and theoretical calculations, data on the bulk viscosity of ANF suspensions were obtained for the first time. The results of the study allow us to judge the possibility of using ANF as a promising fibrous additive to optimize the rheological properties of suspensions for various technical purposes, which include drilling muds, paint and varnish compositions, concrete-cement mixtures.

The Magnetic Properties of Fe4BO7 and Mn4BO7 Tetraborates in Three Structural Types

A. S. Shinkorenko// JETP Letters//

https://doi.org/10.1134/S0021364022601786

The crystal structure and magnetic properties of Fe4BO7 and Mn4BO7 tetraborates have been studied within DFT-GGA. The tetraborates can be found in several possible structural modifications. We considered here three of them, namely Pbca (α-ZnB4O7), Cmcm (β-ZnB4O7 structural type) and P6522 (γ-NiB4O7 structural type). The possible magnetic orderings in three structural types are described within group-theoretical analysis. The following DFT calculations allow find the lowest energy magnetic structure for Fe4BO7 and Mn4BO7 in three structural types. The total energy of tetraborates in three structural types was compared with and without taking into account of the spin-polarization. It was found that in non-spin-polarized case Mn4BO7 and Fe4BO7 have α-ZnB4O7 and γ-NiB4O7 structural types as lowest energy structure, correspondingly. However, taking into account magnetic structure results in the anitiferromagnetic α-ZnB4O7 phase appears to be the ground state for both tetraborates. The pressure behavior of enthalpy of Fe4BO7 and Mn4BO7 tetraborates were studied. We obtained that the applied pressure results in the arising of β-ZnB4O7 structural type as the lowest energy structure under pressure.

Desktop laboratory of bound states in the continuum in metallic waveguide with dielectric cavities

Bulgakov, E., Pilipchuk, A., Sadreev, A.// Physical Review B//

DOI: 10.1103/PhysRevB.106.075304

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

Josephson oscillation in the open two-site Bose-Hubbard system

Kolovsky, A.R.// Europhysics Letters//

DOI: 10.1209/0295-5075/ac8cae

We analyze Josephson's oscillation of Bose particles in the open two-site Bose-Hubbard system. First, we excite the system from the vacuum state into a state suitable for observing the oscillation by using a special protocol for external driving. Next, we switch off the driving and observe the oscillation. It is shown that the main mechanism for the decay of Josephson's oscillation is the dephasing due to the fluctuating number of particles in open systems. An analytical estimate for the decay time is obtained. 

Degradable Poly(3-hydroxybutyrate)—The Basis of Slow-Release Fungicide Formulations for Suppressing Potato Pathogens

Volova, T.G., Kiselev, E.G., Baranovskiy, S.V., (...), Vasiliev, A.D., Thomas, S.// Polymers//

https://doi.org/10.3390/polym14173669

Three-component slow-release fungicide formulations with different modes of action of the active ingredients for suppressing potato pathogens were constructed for the first time. The difenoconazole, mefenoxam, prothioconazole, and azoxystrobin fungicides were embedded in the degradable polymer P(3HB)/birch wood flour blend and examined using SEM, IR spectroscopy, X-ray analysis, DTA, and DSC. Results showed that no chemical bonds were established between the components and that they were physical mixtures that had a lower degree of crystallinity compared to the initial P(3HB), which suggested different crystallization kinetics in the mixtures. The degradation behavior of the experimental formulations was investigated in laboratory micro-ecosystems with pre-characterized field soil. The slow-release fungicide formulations were prolonged-action forms with a half-life of at least 50–60 d, enabling gradual and sustained delivery of the active ingredients to plants. All slow-release fungicide formulations had a strong inhibitory effect on the most common and harmful potato pathogens (Phytophthorainfestans, Alternarialongipes, Rhizoctoniasolani, and Fusariumsolani)

Double-Resolved Beam Steering by Metagrating-Based Tamm Plasmon Polariton

Bikbaev, R.G., Maksimov, D.N., Chen, K.-P., Timofeev, I.V.// Materials//

https://doi.org/10.3390/ma15176014

We consider Tamm plasmon polariton in a subwavelength grating patterned on top of a Bragg reflector. We demonstrate dynamic control of the phase and amplitude of a plane wave reflected from such metagrating due to resonant coupling with the Tamm plasmon polariton. The tunability of the phase and amplitude of the reflected wave arises from modulation of the refractive index of a transparent conductive oxide layer by applying the bias voltage. The electrical switching of diffracted beams of the ±1st order is shown. The possibility of doubling the angular resolution of beam steering by using asymmetric reflected phase distribution with integer and half-integer periods of the metagrating is demonstrated. 

Direct Observation of the Spin Exciton in Andreev Spectroscopy of Iron-Based Superconductors

Korshunov, M.M., Kuzmichev, S.A., Kuzmicheva, T.E.// Materials//

https:// doi.org/10.3390/ma15176120

Quasiparticle excitations provide viable information on the physics of unconventional superconductors. Higgs and Leggett modes are some of the classic examples. Another important bosonic excitation is the spin exciton originating from the sign-changing superconducting gap structure. Here we report a direct observation of the temperature-dependent spin exciton in the Andreev spectra of iron-based superconductors. Combined with the other experimental evidence, our observation confirms the extended s-wave (s±) order parameter symmetry and indirectly proves the spin-fluctuation mechanism of Cooper pairing.

Study of the Effect of Modified Aluminum Oxide Nanofibers on the Properties of PLA-Based Films

Sukhanova, A., Boyandin, A., Ertiletskaya, N., (...), Volochaev, M., Pyatina, S.// Materials//

 https://doi.org/10.3390/ma15176097

To find out whether Al2O3 nanofiller is effective in improving the characteristics of polymer composites, composite polymer films based on biodegradable polylactide and epoxidized aluminum oxide nanofibers were obtained by solution casting. Surface morphology, mechanical and thermal properties of composites were studied by SEM, IR-Fourier spectroscopy, DSC and DMA. It was shown that, below and above the percolation threshold, the properties of the films differ significantly. The inclusion of alumina nanoparticles up to 0.2% leads to a plasticizing effect, a decrease in the crystallization temperature and the melting enthalpy and an increase in the tensile stress. An increase in the content of alumina nanoparticles in films above the percolation threshold (0.5%) leads to a decrease in the crystallinity of the films, an increase in stiffness and a drop in elasticity. Finding the percolation threshold of alumina nanoparticles in PLA films makes it possible to control their properties and create materials for various applications. The results of this study may have major significance for the commercial use of aluminum oxide nanofibers and can broaden the research field of composites.

Solid-state Synthesis of Cu6Sn5 Intermetallic in Sn/Cu Thin Films

Bykova Liudmila E., Myagkov Victor G., Balashov Yuri Yu., Zhigalov Victor S., Patrin Gennady S.// Journal of Siberian Federal University - Mathematics and Physics//

DOI: 10.17516/1997-1397-2022-15-4-493-499

The study results of solid-state synthesis of the Cu6Sn5 intermetallic in the Sn/Cu thin-film systems during vacuum annealing from room temperature to 300 °C are presented. The initiation and finishing temperatures of the solid-state reaction between the Cu and Sn nanolayers and the phase composition of the reaction products were determined. The synthesized thin films were monophasic and consisted of the hexagonal η-Cu6Sn5 phase. It is assumed that the initiation temperature of the solid-state reaction in Sn/Cu thin films is associated with the start temperature of the reverse polymorphic transformation η′ → η between the monoclinic and hexagonal Cu6Sn5 phases. © Siberian Federal University. All rights reserved.

Strategy to Construct High Thermal-Stability Narrow-Band Green-Emitting Si-CDs@MAs Phosphor for Wide-Color-Gamut Backlight Displays

Jianying Chen,Xikun Zou,Wei Li,Haoran Zhang,Xuejie Zhang,Maxim S. Molokeev,Yingliang Liu,Bingfu Lei// Advanced Optical Materials//

 https://doi.org/10.1002/adom.202200851

Developing innovative narrow-band green-emitting phosphors featuring low thermal quenching and eco-friendliness for white light-emitting diode (WLED) backlights is a pivotal challenge. Benefitting from narrowband and low toxicity of green-emitting silanized carbon dots (Si-CDs), an efficient confinement and protection strategy through embedding Si-CDs in mesoporous aluminas (MAs) is proposed to construct MAs and Si-CDs composites (Si-CDs@MAs) with superior luminescence properties. Si-CDs@MAs phosphor exhibits green emission at 526 nm with narrow full width at half maximum of 51 nm, zero-thermal quenching even up to 423 K (104.1%@423 K of the emission peak intensity at 298 K), and the internal quantum efficiency of 64.46%. Compared with broad-band yellow-emitting solid-state Si-CDs (S-Si-CDs), the thermal stability, photostability, and water stability of Si-CDs@MAs phosphor are remarkably improved due to surface protection. The WLED backlight is fabricated with optimized Si-CDs@MAs phosphor, which shows high luminous efficacy of 117.43 lm W−1 and wide color gamut (107% NTSC). Furthermore, this work provides the design principles of realizing stable narrow-band solid-state fluorescence carbon dots, suggesting its great potential for wide-color-gamut display application.

 
 
 
 
 
 
 

Features of Characteristics of Second-Order Bandpass Filters Based on Half-Wave and Quarter-Wave Microstrip Resonators

Belyaev, B.A., Balva, Y.F., Leksikov, A.A., (...), Khodenkov, S.A., Shumilov, T.Y.// Russian Physics Journal//

https://link.springer.com/article/10.1007/s11182-022-02633-1

A comparison is made of the characteristics of bandpass filters consisting of two interacting resonators, which are either half-wave or quarter-wave segments of microstrip transmission lines with the same widths of strip conductors. Plates with a thickness of 0.5 mm made of TBNS high-frequency ceramics with a relative permittivity ε = 80 were used as substrates for microstrip structures. The structures having a maximum coupling region of the resonators and the maximum value of their coupling to external ports with a wave impedance of 50 Ω were studied. The filters were tuned by selecting the gap between the strip conductors so that the maximum reflection level in the passband was equal to –20 dB. Electromagnetic simulation of 3D models showed that the fractional bandwidth of filters based on quarter-wave resonators is almost 2 times wider than the bandwidth of filters based on half-wave resonators, and this fact is confirmed by the measurement results. The discovered effect is explained by twice the characteristic impedance of a quarter-wave resonator relative to a half-wave one. 

Dynamic processes of the water sublattice in FeTiF6·xH2O·yD2O crystal

Gerasimova Yu.V.,Krylov A.S.,Vtyurin A.N.,Laptash N.M.,Pogoreltsev E.I.,Dubrovskiy A.A.,Gerasimov M.A.// Journal of Raman Spectroscopy//

https://doi.org/10.1002/jrs.6430

Phase transition in (Formula presented.) crystals has been studied by Raman spectroscopy. The 611 cm−1 line corresponding to mode (Formula presented.) of (Formula presented.) system does not exhibit anomalous behavior associated with the phase transition. The temperature studies showed that below the phase transition temperature, the equivalence of D2O molecules in (Formula presented.) octahedron is broken. The phase transition mechanism in the compound under study is associated with (Formula presented.) complex. 

Magnetic Frequency Doubler

Govorun, I.V., Afonin, A.O., Ugryumov, A.V., (...), Leksikov, A.A., Boev, N.M.// International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices, EDM//

https://ieeexplore.ieee.org/document/9855072

This article presents the compact magnetic frequency doubler based on a quarter-wavelength stepped-impedance microstrip resonator with a 125-nm-thick permalloy (Ni 70 Fe 30 ) magnetic film. For the first time, the implementation of a frequency doubler operating at the high-field peak is shown. To produce a uniform magnetic field in the thin magnetic film plane, the magnetic system consisting of individual permanent magnets and based on the circular Halbach array was developed. The uniformity of the magnetic field in the region of 10×10 mm 2 was 4.9%. Two bandpass filters were developed. The input filter serves to purify the input signal from parasitic harmonics. The output filter blocks the input signal in the resonator. The resonator, magnetic system, input and output filters are integrated into a single device. The maximum measured conversion efficiency was 0.97% (at 1 GHz) at the input power of 4800 mW. The −3 dB fractional bandwidth of the magnetic frequency doubler was 2.15%.

Multibeam Antenna Implementation Using Anisotropic Metasurfaces

Chesnitskiy, A.V., Kosmynin, A.N., Kaigorodov, O.M., (...), Kosmynina, K.N., Lemberg, K.V.// International Conference of Young Specialists on Micro/Nanotechnologies and Electron Devices, EDM//

https://ieeexplore.ieee.org/document/9855123

This study is devoted to the development and research of multibeam antennas based on anisotropic metasurfaces with one or several feed points. An innovative technique for synthesizing the tensor impedance distribution for the formation of three beams from a radiating metasurface was proposed. Prototypes of the proposed antennas in the Ku-band frequency with one and three feed points were fabricated, and their characteristics were experimentally investigated. The gain of the manufactured multibeam antennas reaches 23 dBi. Good agreement between the results of the numerical simulation and experimental data was achieved, which indicates the reproducibility of the synthesis method in practice. Multibeam antennas on anisotropic metasurfaces can be scaled to high frequencies and effectively used at operating frequencies up to the sub-terahertz range. Such antennas are promising for the development of terrestrial communication infrastructure as 5/6G transmitters and repeaters, as well as for use as a payload of low-orbit satellite systems.

T − E phase diagrams and electrocaloric effect in PNN-PT solid solutions

Gorev, M.V., Bondarev, V.S., Flerov, I.N., Bormanis, K., Birks, E.// Journal of Alloys and Compounds//

https://doi.org/10.1016/j.jallcom.2022.167032

Using the sixth-order free energy expansion of the Landay thermodynamic potential, T − E phase diagrams and the electrocaloric effect (ECE) in solid solutions (1-x)Pb(Ni1∕3Nb2∕3)O3-xPbTiO3 (PNN-PT) were studied under an electric field along the crystallographic directions [001], [101] and [111]. The composition of the samples, temperature range, as well as magnitude and direction of the electric field significantly affect the sequence of phase transitions, stability of various crystalline phases and electrocaloric properties. Direct measurements of the intensive ECE in the 0.8PNN-0.2PT compound were carried out by the method of adiabatic calorimetry at electric field strength E = 6 kV/cm. The large electrocaloric coefficient ΔT∕ΔE = 10 μK ⋅ cm/kV indicates that this compound and other PNN-PT solutions are promising for application as solid-state refrigerants.

Chemistry of vinylidene complexes—XXVII—new µ-vinylidene MnPt complexes with platinum-coordinated 1-adamantyl isocyanide ligand: spectroscopic, structural and electrochemical study

Victor V. Verpekin, Oleg S. Chudin, Alexander A. Kondrasenko, Galina V. Burmakina, Alexander D. Vasiliev, Dmitry V. Zimonin & Anatoly I. Rubaylo // Transition Metal Chemistry//

https://doi.org/10.1007/s11243-022-00511-w

New binuclear MnPt µ-vinylidene complexes Cp(CO)2Mn(µ-C=CHPh)Pt(CN–Ad)(L) [L=PPh3 (1a), P(OPri)3 (2a)] bearing a terminal platinum-coordinated 1-adamantyl isocyanide ligand were prepared by the treatment of Cp(CO)2Mn(µ-C=CHPh)Pt(CO)(L) [L=PPh3 (1b), P(OPri)3 (2b)] with CN-Ad. At the same time the reaction between Cp(CO)2Mn(µ-C=CHPh)Pt(L)2 [L=PPh3 (1c), P(OPri)3 (2c)] and CN-Ad did not proceed. The new complexes were characterized by IR and 1H, 13C, 31P NMR spectroscopy. The molecular structure of Cp(CO)2Mn(µ-C=CHPh)Pt(CN–Ad)[P(OPri)3] (2a) was determined by an X-ray diffraction study. The redox properties of the new complexes and their reactions of chemical oxidation were studied. An influence of the platinum-coordinated 1-adamantyl isocyanide ligand on the properties of the synthesized µ-vinylidene compounds 1a and 2a was revealed.

Effect of ligand environment of rare-earth ions on temperature measurement performance of SrAO4:xEu3+ (A = Mo and W) phosphors

Gao, H., Molokeev, M.S., Chen, Q., (...), Wang, X., Ma, B.// Ceramics International//

https://doi.org/10.1016/j.ceramint.2022.08.247

Molybdate and tungstate with scheelite-type structure are excellent self-luminescent materials, which can be used as ideal hosts for the doping of rare-earth ions. In this study, a series of Eu3+-activated SrAO4 (A = Mo and W) phosphors were successfully synthesized, and their crystal structures, photoluminescence properties, and temperature measurement performance were analyzed in detail. These phosphors were excited by UV light (291 nm and 247 nm, respectively), with clear energy transfer (ET) (MoO42−→Eu3+ or WO42−→Eu3+). According to fluorescence intensity ratio (FIR) and Judd–Ofelt (J–O) theory, compared to SrWO4:0.01Eu3+ phosphor, SrMoO4:0.01Eu3+ phosphor exhibited better thermal stability, with relatively low Sa value (maximum values were 5.082 %K−1 and 20.74 %K−1, respectively), and their Sr values were not significantly different (maximum values were 0.864 %K−1 and 0.83 %K−1, respectively). Sa value was negatively correlated to central asymmetry of Eu3+, but the optimal Sr value tended to be more suitable for central asymmetry of Eu3+. In addition, Eu3+ exhibited stronger central asymmetry as well as covalency of Eu–O bond in SrMoO4. Results reveal that SrMoO4:xEu3+ and SrWO4:xEu3+ can be used for luminescent thermometers.

Low-Frequency Spectrum of the Gyrotropic Modes of a Finite Chain of Interacting Ferromagnetic Disks

V. A. Orlov, V. S. Prokopenko, R. Yu. Rudenko & I. N. Orlova// Technical Physics//

https://doi.org/10.1134/S1063784222050085

The problem of the frequency spectrum of collective gyrotropic modes in a finite linear chain of magnetostatically interacting ferromagnetic disks has been considered. It has been shown that by analyzing the frequency spectrum, one can derive information about the magnetization eddy state for each of the nanodisks in the chain. The feasibility of recording the frequency spectrum as a tool for data readout in magnetic memory devices has been discussed.

Effect of Surfactants on the Structure, Phase Composition, and Magnetic Properties of Fe xS y Nanoparticles Synthesized by Thermal Decomposition

Ivantsov, R.D., Lin, C.-R., Chen, Y.-Z., (...), Sukhachev, A.L., Edelman, I.S.// Nanobiotechnology Reports//

https://doi.org/10.1134/S2635167622030089

The effect of surfactants on the structure, morphology, and magnetic properties of FexSy iron-sulfide nanoparticles synthesized by thermal decomposition is studied. Oleylamine, hexadecylamine, and octadecylamine are used as surfactants. It is established by X-ray and electron-diffraction analysis combined with Mössbauer spectroscopy that, in samples 1 and 2 prepared using oleylamine and hexadecylamine, respectively, the Fe3S4 greigite phase dominates, with an inverse spinel structure isostructural to the iron oxide Fe3O4 magnetite with minor Fe9S11 impurities. Deviations in the distribution of iron cations over the tetrahedral and octahedral sites relative to the bulk greigite crystals are observed. The nanoparticles synthesized using octadecylamine (sample 3) are found to be multiphase with a greigite fraction of ~20%. In all three cases, as showed the results of transmission electron microscopy and Fourier transform infrared spectroscopy together with thermogravimetry analysis, the magnetic nanoparticles have an organic shell chemically bonded to their magnetic core, which prevents the agglomeration of the particles. This shell is much more massive in samples 2 and 3. The magnetization values for samples 1 and 2 are similar to those of greigite nanoparticles reported in publications, while the magnetization of sample 3 is several times lower, in accordance with the greigite fraction in it. The combination of fairly high magnetization with a massive organic shell allows one to consider hexadecylamine to be a promising surfactant for the synthesis of iron-sulfide nanoparticles protected from external impact and agglomeration.

Effect of substitution of Mn and Ga atoms by Fe atom in the Mn2GaC MAX phase

Draganyuk, O.N., Zamkova, N.G., Zhandun, V.S.//Journal of Magnetism and Magnetic Materials//

https://doi.org/10.1016/j.jmmm.2022.169860

The magnetic properties of ordered and disordered MAX-phase Mn2-xFe2xGaC and Mn2Ga1-xFexC (x = 12.5, 25, and 50 at.%) have been studied within DFT-GGA. The investigation of phase stability of M2AX phases is performed by comparing the total energy of MAX phases to that of the set of competitive phases for calculation of the phase formation enthalpy. At the small concentration of Fe atoms (x = 12.5 %) compound remains stable. We have found that introducing Fe atom at A-site leads to the forming of ferromagnetic phase with large magnetic moments on magnetic atoms and magnetization. Through detailed group-theoretical analysis we have obtained that only ferromagnetic ordering is possible when Fe atom ordering over Ga sites. The study of exchange constants shows that the out-of-plane Fe-Mn exchange gives the main contribution in appearance of ferromagnetic phase. The temperature dependences of magnetization reveal the increase of Curie temperature in Mn2GaC with Fe atom incorporated into Ga-site. 

High-Efficiency Continuous-Luminescence-Controllable Performance and Antithermal Quenching in Bi3+-Activated Phosphors

Gao, P., Li, Q., Zhou, C., (...), Zhou, Z., Xia, M.// Inorganic Chemistry//

https://doi.org/10.1021/acs.inorgchem.2c01784

Recently, Bi3+-activated phosphors have been widely researched for phosphor-converted light-emitting diode (pc-LED) applications. Herein, novel full-spectrum A3BO7:Bi3+ (A = Gd, La; B = Sb, Nb) phosphors with a luminescence-tunable performance were achieved by a chemical substitution strategy. In the La3SbO7 host material, a new luminescent center was introduced, with Gd3+ replacing La3+. The photoluminescence (PL) spectra show a large blue shift from 520 to 445 nm, thus achieving regulation from green to blue lights. Moreover, a series of solid solution-phase phosphors La3Sb1–xNbxO7:Bi3+ were prepared by replacing Sb with Nb, and a PL spectral tunability from green (520 nm) to orange-red (592 nm) was realized. Temperature-dependent PL spectra show that La3–xGdxSbO7:Bi3+ phosphors have excellent thermal stability. Upon 350 nm excitation, the PL intensity of La3–xGdxSbO7:Bi3+ phosphors at 150 °C remained at more than 93% at room temperature. With Gd3+ doping, the thermal stability gradually improved, and LaGd2SbO7:0.03Bi3+ represents splendid antithermal quenching (135.2% at 150 °C). Finally, a full-visible spectrum for pc-LED with a high color-rendering index (Ra = 94.4) was obtained. These results indicated that chemical substitution is an effective strategy to adjust the PL of Bi3+, which is of great significance in white-light illumination and accurate plant lighting.

Anisotropic Thermal Expansion and Electronic Structure of LiInSe2

Atuchin, V.V., Isaenko, L.I., Lobanov, S.I., (...), Jiang, X., Lin, Z.// Molecules//

 https://doi.org/10.3390/molecules27165078

Optical quality cm-sized LiInSe2 crystals were grown using the Bridgman–Stockbarger method, starting from pure element reagents, under the conditions of a low temperature gradient of 5–6 degrees/cm and a slight melt overheating. The phase purity of the grown crystal was verified by the powder XRD analysis. The thermophysical characteristics of LiInSe2 were determined by the XRD measurements in the temperature range of 303–703 K and strong anisotropy of the thermal expansion coefficients was established. The following values of thermal expansion coefficients were determined in LiInSe2: αa = 8.1 (1), αb = 16.1 (2) and αc = 5.64 (6) MK−1. The electronic structure of LiInSe2 was measured by X-ray photoelectron spectroscopy. The band structure of LiInSe2 was calculated by ab initio methods.

Enhancement of Thermoelectric Performance in Bi0.5Sb1.5Te3Particulate Composites Including Ferroelectric BaTiO3Nanodots

Yiming Cheng, Junyou Yang, Yubo Luo, Wang Li, Alexander Vtyurin, Qinghui Jiang*, Steve Dunn, and Haixue Yan// ACS Applied Materials and Interfaces//

https://doi.org/10.1021/acsami.2c10424

An increasing number of studies have reported producing composite structures by combining thermoelectric and functional materials. However, combining energy filtering and ferroelectric polarization to enhance the dimensionless figure of merit thermoelectric ZT remains elusive. Here we report a composite that contains nanostructured BaTiO3 embedded in a Bi0.5Sb1.5Te3 matrix. We show that ferroelectric BaTiO3 particles are evenly composited with Bi0.5Sb1.5Te3 grains reducing the concentration of free charge carriers with increasing BaTiO3 content. Additionally, as a result of the energy-filtering effect and ferroelectric polarization, the Seebeck coefficient was improved by ∼10% with a ∼10% improvement in power factors. The BaTiO3 phase can effectively scatters phonons reducing lattice thermal conductivity κl (0.5 W m–1 K–1) and increasing ZT to 1.31 at 363 K in Bi0.5Sb1.5Te3 composites with 2 vol % BaTiO3 content giving an improvement of ∼25% over pure Bi0.5Sb1.5Te3. Our work indicates that the introduction of ferroelectric nanoparticles is an effective method for optimizing the ZT of Bi0.5Sb1.5Te3-based thermoelectric materials.

Unfolding the terahertz spectrum of soft porous crystals: rigid unit modes and their impact on phase transitions

Hoffman, A.E.J., Senkovska, I., Wieme, J., (...), Kaskel, S., Van Speybroeck, V.// Journal of Materials Chemistry A//

https://pubs.rsc.org/en/content/articlelanding/2022/TA/D2TA01678H

Phase transitions in flexible metal–organic frameworks or soft porous crystals are mediated by low-frequency phonons or rigid-unit modes. The alteration of specific building blocks may change the lattice dynamics of these frameworks, which can influence the phase transition mechanism. In this work, the impact of building block substitution on the rigid-unit modes in flexible MIL-53 analogs with a winerack topology will be investigated via ab initio lattice dynamics calculations. First, the accuracy of the theoretical simulations is verified via experimental Raman measurements, which provide unique fingerprint vibrations in the terahertz range to characterize the phase transition. Following analysis of the low-frequency vibrations shows that there exists a set of universal rigid-unit modes inducing translations and/or rotations of the building blocks. The theoretical results demonstrate that linker substitutions have a large effect on the rigid-unit mode frequencies, whereas this is less so for inorganic chain substitutions. These findings may help to rationally tune the phonon frequencies in soft porous crystals.

Temperature- and Field-Induced Transformation of the Magnetic State in Co2.5Ge0.5BO5

Kazak, N., Arauzo, A., Bartolomé, J., (...), Patrin, G., Ovchinnikov, S.// Inorganic Chemistry//

https://doi.org/10.1021/acs.inorgchem.2c01193

A tetravalent-substituted cobalt ludwigite Co2.5Ge0.5BO5 has been synthesized using the flux method. The compound undergoes two magnetic transitions: a long-range antiferromagnetic transition at TN1 = 84 K and a metamagnetic one at TN2 = 36 K. The sample-oriented magnetization measurements revealed a fully compensated magnetic moment along the a- and c-axes and an uncompensated one along the b-axis leading to high uniaxial anisotropy. A field-induced enhancement of the ferromagnetic correlations at TN2 is observed in specific heat measurements. The DFT+GGA calculation predicts the spin configuration of (↑↓↓↑) as a ground state with a magnetic moment of 1.37 μB/f.u. The strong hybridization of Ge(4s, 4p) with O (2p) orbitals resulting from the high electronegativity of Ge4+ is assumed to cause an increase in the interlayer interaction, contributing to the long-range magnetic order. The effect of two super–superexchange pathways Co2+-O-B-O-Co2+ and Co2+-O-M4-O-Co2+ on the magnetic state is discussed.

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