Inorganic Materials最新文献

The effect of the characteristic size of nanoparticles, nanofiber (nanowire), and thin films of the AmO₂, CmO₂, NpO₂, PaO₂, PuO₂, ThO₂, and UO₂ actinide dioxides on their band gap has been studied quantitatively by a nanothermodynamic method. The size effect is essential in the case of ThO₂ nanoparticles, nanofiber, and thin films and NpO₂, PuO₂, and CmO₂ nanoparticles and nanofiber even at a characteristic size of about 20 nm. The size effect is significant for AmO₂, PaO₂, and UO₂ nanoparticles if their diameter is about 7–8 nm. The maximum attainable band gap of nano-objects is shown to be twice the band gap of the corresponding bulk material. The band gap of nano-objects having the same characteristic size decreases in the sequence nanoparticles > (nanofiber) nanowire > thin films. It is shown that, using mixed actinide oxides and varying their stoichiometry, characteristic size, and morphology, one can control the band gap of nano-objects in a wide range of permissible values.

Ceramic samples with compositions along the (1 – 2x)BiScO₃·(2 – y)xPbTiO₃∙yxPbMg_1/3Nb_2/3O₃ (y = 1.2, 1.0, 0.9, 0.5) sections in the BiScO₃–PbTiO₃–PbMg_1/3Nb_2/3O₃ (BS–PT–PMN) system have been characterized by X-ray diffraction and dielectric, piezoelectric, and thermally stimulated depolarization current measurements. The materials with 1 – x ≲ 0.5 have been shown to consist of perovskite solid solutions. With increasing BS content, the symmetry of the solid solutions rises from tetragonal to cubic. In the intermediate composition region (morphotropic region (MR)), the samples consist of a mixture of solid solutions differing in symmetry. We have located the MR boundaries and examined the effect of composition on the dielectric and piezoelectric properties of the solid solutions.

Ceramic nitride samples of tailored composition and shape have been prepared by controlled nitridation of Ti–V metal pairs. We have obtained kinetic and current–voltage curves for the interaction of the Ti–V metal pairs with nitrogen. In different parts of the metal pairs, the nitridation process follows different mechanisms. In the case of the pure metals, the formation of nearly stoichiometric ceramics involves the formation of three- and two-layer graded structures. Nitridation of the junction region, containing a Ti–V solid solution, is determined by the chemical affinity of titanium and vanadium for nitrogen. The formation of titanium nitride leads to decomposition of the Ti–V solid solution in the junction and vanadium metal separation on grain boundaries. The rate of vanadium nitridation increases as the titanium content of the solid solution decreases. The thermoelectric voltage of the Ti–V system in the temperature range from –195.7 to +550°C has been evaluated as a function of the degree of nitridation. The thermoelectric voltage and Seebeck coefficient of metal–ceramic and ceramic structures have been determined as functions of temperature. Characteristically, the thermoelectric voltage of all the nitrided pairs rises monotonically over the entire temperature range studied. Nitrided titanium–vanadium pairs with tailored composition can be used as ceramic thermoelectric converters.

A multielement inductively coupled plasma atomic emission spectrometry (ICP-AES) technique has been proposed for high-speed monitoring of the preparation of pure antimony, and analytical lines of analytes with the weakest spectral effects have been chosen. We have studied the effect of matrix component concentration (5 to 40 g/L) on the analytical signals of impurity elements. Changes in excitation conditions in the plasma at a varied antimony concentration in solution and varied ICP power have been assessed using the ICP robustness. The robustness was evaluated from the intensity ratio of the magnesium ionic and atomic lines. The presence of 40 g/L of antimony in solution has been shown to reduce the ICP robustness by up to 5%. The adequacy of the proposed technique has been confirmed by the standard addition method and comparison with results obtained by an independent method. The proposed technique for analysis of antimony allows one to determine 56 impurity elements with detection limits from n × 10^–7 to n × 10^–4 wt %.

Recently, nanosized ferrites with spinel structure have been actively discussed as possible magnetically controlled catalysts, sorbents, and biomedical materials. For the large-scale practical use of ferrites, it is necessary to find simple, reproducible, and cost-effective methods that allow one to control the characteristics of nanosized ferrites with spinel structure to obtain samples with a large number of active centers for catalysis and sorption, low toxicity for biomedical applications, and good magnetic properties required to control such materials by an external magnetic field. This review summarizes the results of scientific studies (predominantly over the last 5–10 years) focused on different methods of synthesis of nanosized ferrites with spinel structure and composite materials, and considers approaches to control their catalytic, sorption, and magnetic characteristics and prospects of their application as magnetically sensitive catalysts (Fenton-like processes), sorbents (extraction of heavy metals, separation of ions, separation of valuable metals), and materials for drug delivery, hyperthermia, and MRI contrast.

In this paper, we report the preparation of high-purity ²⁸Si silicon and ⁷²Ge germanium isotopes and their volatile hydrides with controlled concentrations of the ²⁹Si and ⁷³Ge nonzero nuclear spin isotopes for producing Si/SiGe heterostructures for quantum computers employing the nuclear spin state as a qubit. We have prepared ²⁸SiH₄ and ²⁸Si samples containing about 99.9, 99.99, and 99.999% ²⁸Si as a major isotope and 340 ± 8, 41.1 ± 4.3, and 11.4 ± 0.1 ppm of the ²⁹Si isotope. In addition, we obtained high-purity ⁷²GeH₄ and ⁷²Ge samples containing about 99.9% ⁷²Ge as a major isotope and 109.9 ± 9.6 ppm of the ⁷³Ge isotope.

Y₃Fe_{5 – x}Al_xO₁₂ (х = 0, 0.5, 1.0, 1.5, 2.0) materials prepared by sol–gel synthesis have been characterized by scanning electron microscopy, X-ray diffraction, Raman and Mössbauer spectroscopies, field- and temperature-dependent saturation magnetization measurements, and magnetocaloric measurements in an ac magnetic field. We have examined the effect of aluminum concentration on the magnetic and crystal structures and magnetothermal properties of the garnet ferrite particles.

The magnetic susceptibility of Fe_{1 – x}Co_xCr₂S₄ solid solutions in the FeCr₂S₄-rich part of the FeCr₂S₄–CoCr₂S₄ system has been studied by static and dynamic methods. The magnetic measurements were performed at temperatures from 5 to 300 K in static (50 Oe and 45 kOe) and ac magnetic fields (field amplitude H_ac = 1 Oe; ac field frequencies ν = 100, 1000, and 10 000 Hz). We have determined the temperatures of the magnetic transformations in the system and identified their nature. The results demonstrate that the temperature of the ferrimagnetic phase transition (T_C) in Fe_{1 – x}Co_xCr₂S₄ increases with increasing cobalt content. The materials with x = 0–0.5 have been shown to undergo a transition to a spin glass state, evidenced by a shift of maxima in temperature dependences of the imaginary part of their dynamic susceptibility.

Two-phase thin-film composites consisting of Cd_xPb_{1 – x}S (0.007 ≤ x ≤ 0.068) substitutional solid solutions with a B1 cubic structure (sp. gr. (Fmbar {3}m)) and amorphous cadmium sulfide (CdS) have been produced by chemical deposition. The surface topography of the films has been studied by atomic force microscopy, and the results have been used to calculate surface microtopography parameters. A correlation has been found between the composition and functional properties of thin CdS–PbS films. The sensitivity of Cd_xPb_{1 – x}S/CdS two-phase films to ammonia (NH₃) in air has been assessed for the first time. The room-temperature detection limit for ammonia has been determined to be 10 ppm (6.22 mg/m³).

An approach is proposed which makes it possible to lower the silicon melt infiltration temperature in the fabrication of silicon carbide/zirconium diboride matrix ceramic composites via the formation of a silicon–yttrium low-temperature eutectic. Using thermodynamic calculations, we have substantiated the addition of yttrium to a siliciding agent and demonstrated its advantages. Silicon melt infiltration into composites has been carried out for the first time at a temperature below the melting point of silicon, which has ensured a decrease in the degree of carbon fiber degradation, while allowing the matrix to retain high density and uniformity.