Inorganic Materials最新文献

(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.

Fe₃C iron carbide nanoparticles and iron carbide-coated iron (Fe@Fe₃C) nanoparticles have been prepared from bulk iron by the induction flow levitation technique, which has a number of advantages: high production rate (up to 100 g/h), continuity of the process, contactless heating to 2500°C, and absence of harmful emissions. The size of the synthesized nanoparticles is under 24 nm. Two different reagents have been used to prepare iron carbide nanoparticles: acetylene and hexane. The Fe@Fe₃C core/shell nanoparticles have been obtained by reacting condensed nanoparticles with acetylene in a quartz reactor. The average size of their core is 7 nm. All of the synthesized nanoparticles have been characterized by a variety of physicochemical techniques: transmission electron microscopy, X-ray diffraction, BET surface area measurements, statistical thickness surface area method, and dynamic light scattering.

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.

Raman spectra of crystalline gallium arsenide grown by the Czochralski method have been studied. It has been demonstrated that the frequency of the coupled plasmon–phonon mode increases with increasing electron concentration n and approaches the frequency of the transverse vibration mode at n ~ 3 × 10¹⁸ cm⁻³. An increase in the hole concentration leads to a broadening of the longitudinal vibration peak. The relative intensity of the transverse mode decreases with an increase in the degree of disorder.

TiC nanoparticles less than 16 nm in size have been prepared in a single step from bulk titanium carbide by the induction flow levitation (IFL) method. The method has a number of advantages: high production rate (up to 100 g/h), the ability to vary the nanoparticle size in a wide range (0.5–500 nm), and contactless heating (up to 2500°C). Moreover, it meets green chemistry principles. In this gas phase method, a levitating metal is heated by a high-frequency electromagnetic field. The synthesized titanium carbide nanoparticles have been characterized by a variety of physicochemical techniques: transmission electron microscopy, scanning electron microscopy, X-ray diffraction, low-temperature nitrogen adsorption measurements, and dynamic light scattering. The results demonstrate that IFL is one of the most promising methods for the preparation of nanoparticles and ensures high purity and a small particle size of single-step synthesis products.

We have synthesized polycrystalline (TlGaSe₂)_1–x(TlGaS₂)_x (x = 0–1) solid solutions and used them to grow single crystals by the Bridgman–Stockbarger method. The dielectric properties of single-crystal samples of the solid solutions have been studied in ac electric fields in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. We have demonstrated relaxation behavior of the complex dielectric permittivity of the (TlGaSe₂)_1–x(TlGaS₂)_x solid solutions, found out the nature of the dielectric loss in them, and identified the hopping charge transport mechanism in them. With increasing x, the electrical conductivity of the (TlGaSe₂)_1–x(TlGaS₂)_x crystals and the average distance and time of carrier hopping between localized states in the band gap of the crystals decrease, whereas the scatter in the energy of Fermi level localized states and their density increase.

Nanoporous glass is a promising material for application in integrated optics and archival optical storage. Femtosecond laser pulses incident on porous glass can produce microstructures exhibiting form birefringence whose retardance and slow axis orientation depend on writing conditions. In this work, nanoporous glass was heat-treated at temperatures from 700 to 775°C to obtain samples differing in pore size and specific pore volume with the aim of further laser modification of their structure. The results demonstrate that, as the heat treatment temperature is raised, the retardance decreases and the range of femtosecond laser pulse energies where birefringent microregions can be produced narrows down. Analysis of the retardance and pore structure parameters has made it possible to demonstrate a critical effect of specific pore volume on the feasibility of local form birefringence writing. We have proposed heat treatment conditions that ensure protection of porous glass from the influence of adsorption of contaminants from the ambient atmosphere and allow the possibility of producing birefringent structures to be retained, which will extend the application area of nanoporous glass structured by a femtosecond laser beam.