Inorganic Materials最新文献

The wettability and work of adhesion of the Ge₂₈Sb₁₂Se₆₀ glass melt to stainless steel grades AISI 201 and AISI 430 with a conventional and nitrided surface, titanium and a tungsten carbide alloy YG8 in the temperature range of 480–530°C was studied. It was found that nitriding of the stainless steel surface leads to a 2–3-fold decrease in the adhesion of chalcogenide melts to the stainless steel surface. Among all the considered structural materials, the maximum adhesion of the Ge₂₈Sb₁₂Se₆₀ glass melt is observed to AISI 201 stainless steel, the minimum to AISI 430 nitrided steel.

A new technique has been developed for the synthesis of dimolybdenum pentaboride nanoparticles via reaction between molybdenum powder and amorphous boron in the molar ratio 2 : 5 after mechanochemical activation in argon. The reaction was run in ionic salt melts with various compositions at temperatures of 750, 800, and 850°C in a hydrogen atmosphere. Using X-ray diffraction, X-ray energy spectrometry, simultaneous thermal and elemental analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and specific surface area measurements, we demonstrate that the use of ionic melts makes it possible to obtain nearly spherical single-phase Mo₂B₅ particles ~30 nm in average diameter only at a reaction time of at least 28 h. The particles have a rhombohedral structure with unit-cell parameters a = 0.3007–0.3015 nm and с = 2.090–2.095 nm.

The structure of contacts was determined, and a method was developed for applying them to nanostructured thermoelectric materials. Contacts were formed by the chemical solution deposition (CSD) of nickel or cobalt on catalytically active surfaces from alkali solutions using hypophosphite ions as reducing agents. The nickel and cobalt CSD films 5 to 8 µm thick form continuous uniform coatings that contain at least 82 wt % metals and 7.4 to 9.1 wt % phosphorus. The phosphorus enhances the barrier properties of the contacts. The resistivity of cobalt and nickel films was 10 × 10^–8 and 12×10^–8 Ω m, respectively. The contacts had a high adhesive strength (up to 20 MPa) and low contact resistivity (at a level of 10^–9 Ω m²) and were thermally stable up to 600 K.

(La_1–xR_x)₃Ga₅SiO₁₄ single crystals and ceramic solid solutions where R = Gd–Ho and 0 ≤ х ≤ 0.4 (as-batch) were characterized by X-ray powder diffraction (XRD) and analytical electron microscopy in order to determine the solubility limits of lanthanides in the langasite structure. Langasite-based solid solutions are the dominant phase up to the highest concentrations, but at x ≥ 0.15 for holmium and x ≥ 0.2 for terbium, garnet R₃Ga₅O₁₂ and La₂SiO₅-type impurity phases start to precipitate. Langasite single crystals have homogeneous structure where Tb, Dy, or Ho substitutes for La up to х = 0.05, and where Gd does up to х = 0.2. At х > 0.1, however, inclusions of impurity phases with the above structures appear in (La_1–xTb_x)₃Ga₅SiO₁₄ crystals. The magnetization curves of (La_1–xR_x)₃Ga₅SiO₁₄ (R = Ho and Tb) crystals measured at 1.85–2 K exhibit strong magnetocrystalline anisotropy, where the magnetic moment per R³⁺ ion is roughly the same for all of the heavy lanthanide concentrations studied. The temperature-and-frequency dependent dielectric constant and dielectric loss tangent of (La_1–xHo_x)₃Ga₅SiO₁₄ (x ≤ 0.2) and (La_1–xTb_x)₃Ga₅SiO₁₄ (x ≤ 0.3) ceramic samples were studied in the range T = 77–700 K at frequencies f from 1 kHz to 1 MHz. Debye-type relaxation with an activation energy of about 2 eV was detected.

—Single-phase ceramic samples of new compositions (1 – x)(K_0.5Na_0.5)NbO₃–xSrZrO₃ (x = 0–0.15) modified with the addition of 2 wt % ZnO were obtained via the solid-state synthesis method. Their crystal structures, microstructures, dielectric, and nonlinear optical properties were studied. The modified samples were found to form a phase with a perovskite structure and a pseudocubic unit cell. A decrease in the average crystallite size (coherent scattering regions) from 91 to 54 nm was observed. Ferroelectric phase transitions were confirmed using dielectric spectroscopy. A reduction in the phase transition temperatures and a weakening of nonlinear optical properties were revealed with an increase in the strontium zirconate content in the samples.

This paper presents results of a theoretical study of the electronic structure of a number of Cd-substituted silicon-based clathrates. Linearized augmented plane wave calculations are used to examine their band structure and the total and partial densities of electronic states in the clathrates. We analyze how the number of cadmium substituent atoms and their crystallographic position in the unit cell influence the electron energy spectrum of the clathrates.

We have studied the effect of heat treatment in an oxidizing medium and under vacuum on the properties of Russian-made silicon carbide fiber. The fiber has been characterized by a variety of physicochemical analysis techniques, including scanning electron microscopy, Raman spectroscopy, IR spectroscopy, and X-ray diffraction, before and after heat treatment under vacuum and in air. The kinetics of fiber oxidation in air have been studied in the range 900–1000°C. The activation energy for the oxidation process has been determined to be 72.0 ± 7.8 kJ/mol. The tensile strength of the fiber has been determined before and after heat treatment in different media. The results demonstrate that heat treatment under vacuum and in an oxidizing medium causes substantial degradation of the properties of the fiber.

Hybrid nanoparticles based on nonferrous metal oxides and gold are of interest for application in catalysis and biomedicine, in particular, for magnetic hyperthermia and targeted drug delivery. In this paper, we describe methods for the preparation of oxide (CuO and CuFe₂O₄) cores and hybrid (CuO/Au and CuFe₂O₄/Au) nanoparticles having gold nanoclusters ~2 nm in size on their surface. The hybrid nanoparticles were synthesized using L-methionine, an amino acid that acts as a reducing agent and an “anchor” between the oxide core and gold clusters. The proposed method for the preparation of CuO and CuFe₂O₄ oxide cores—anion exchange resin-assisted precipitation—is simple, fast, and easy to reproduce under ordinary laboratory conditions. It has been shown that anion exchange resin-assisted Cu²⁺ precipitation with no polysaccharide leads to the formation of elongated copper(II) oxide nanoparticles 85 ± 3 nm in length and 15.1 ± 0.3 nm in thickness, whereas anion exchange resin-assisted precipitation of Cu²⁺ and Fe³⁺ in the presence of a polysaccharide (dextran-40) and subsequent heat treatment (850°C) of a stoichiometric precursor yields copper ferrite nanoparticles 18.3 ± 0.4 nm in size. Evaluation of the biocompatibility of all the synthesized materials (CuO, CuFe₂O₄, CuO/Au, and CuFe₂O₄/Au) with the use of Escherichia coli and Bacillus subtilis as test microorganisms has shown that the presence of gold improves their biocompatibility and makes them suitable for biomedical applications.

Photoionization cross-sections of atomic shells are essential for studying the electronic structure of materials using X-ray photoelectron spectroscopy. In the chemical bonding of lanthanoids with other atoms, electrons from both the ground-state configurations and excited states participate. However, existing tables only include photoionization cross-sections for the ground-state configurations of lanthanoids. In this work, photoionization cross-sections were calculated for both the ground and, for the first time, the excited states of lanthanoid atoms for photon energies of 1253.6 and 1486.6 eV. The calculations were based on relativistic wavefunctions of the self-consistent field obtained using the Dirac–Fock method. The application of these results to experimental X-ray photoelectron spectra of lanthanoid compounds is discussed, exemplified by the experimental spectrum of CeO₂ and the first calculated spectrum of cluster Ce₆₃O₂₁₉.

The technological foundations for producing the MAX phase Nb₂AlC by the method of self-propagating high-temperature synthesis (SHS) from powdered mixtures of Nb + Al + C with an energy additive Mg + Mg(ClO₄)₂ have been developed. As a result of the synthesis, a multiphase powder is formed, containing the target phase Nb₂AlC and secondary phases NbC, Nb₂C, AlNb₂, MgO, and MgAl₂O₄. It has been shown that the phase composition of the product and the yield of the target phase are controlled by the carbon content in the charge. Reducing the carbon content in the charge relative to its stoichiometric ratio leads to a decrease in the niobium carbide content in the product. Optimal component ratios have been determined to obtain, after acid leaching, a powder containing ~82 wt % Nb₂AlC.