Inorganic Materials最新文献

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.

The output voltage, position sensitivity, and spectral sensitivity of a photodetecting element based on high-resistivity photosensitive CdSe layers have been shown for the first time to decrease hyperbolically with increasing layer thickness (in the range 6–60 μm) and increase linearly with increasing input electric current. The high position and spectral sensitivity found in this study (70.8 mV/(mm μA mW) and 375 mV/(μA mW), respectively), which considerably exceeds that of cadmium telluride layers, demonstrate that high-resistivity CdSe layers have considerable potential as a material of position-sensitive photodetectors.

Adhesion/decohesion processes on the surface of dense metallic diffusion membranes in direct contact with hydrogen have been studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. The elemental composition of the alloys has been determined to be (wt %) Pd₉₃Y₇, Pd_{100 – х}Pb_х (х = 5, 20), and Pd₉₄Ru₆. We have revealed Pb emission from the surface of the Pd_{100 – х}Pb_х membranes and Pb adhesion to the surface of the Pd₉₃Y₇ membranes. No adhesion of yttrium particles to the surface of the palladium–lead membranes has been detected. The surface of Pd₉₄Ru₆ alloy has good stability to adhesion/decohesion processes.

This paper presents results of density functional calculations of the atomic structure and electronic spectrum of ({text{TaSi}}_{n}^{ - }) (n = 12–17) clusters with the use of three distinct functionals. We analyze how the choice of the functional influences cluster structure optimization results and compare calculated electronic spectra of the most stable cluster isomers with measured photoelectron spectra, which makes it possible to assess the adequacy of the calculation method and identify the structure of the clusters.

Liquid-assisted processes that occur in iridium–silicon carbide diffusion couples have been studied in the temperature range 1500–1800°C at different heat treatment times. We have examined the microstructure and determined the elemental and phase compositions of the diffusion zone forming above eutectic temperatures and/or the melting points of individual reaction products: iridium silicides. The microstructure of the diffusion zone forming under liquid formation conditions has been shown to differ from that forming under the conditions of solid-state reaction between iridium and silicon carbide. At temperatures above 1700°C, the silicon content of the Ir–Si melt exceeds 50 mol %, which leads to crystallization of the Ir₃Si₄ and Ir₃Si₅ phases during cooling. The carbon resulting from reaction between iridium and SiC undergoes graphitization with increasing heat treatment temperature and time.

Calcium vapor reduction of niobium oxide compounds has been studied at temperatures from 1023 to 1123 K. The adiabatic temperature of calcium reduction of niobium pentoxide (3020 K) and the Mg₄Nb₂O₉ niobate (2525 K) has been determined by thermodynamic modeling with the TERRA software suite. We have assessed the effects of process temperature, reduction time, and precursor powder particle size on the degree of reduction, specific surface area, and pore structure of the niobium powders.

The effect of ultrasonic treatment of the surface of membrane foil produced from a solid solution of the Pd–In–Ru system on hydrogen sorption by the foil and its hydrogen permeability has been studied using cyclic voltammetry, Auger electron spectroscopy, and atomic force microscopy. The results demonstrate that such treatment leads to an increase in hydrogen sorption by the surface layer of the foil, without changes in its hydrogen permeability. Ultrasonic treatment has been shown to influence neither the morphology, nor the composition, nor the structure of the foil.

We have studied broadband (1000–1600 nm) IR photoluminescence of polycrystalline corundum (α-Al₂O₃) samples containing copper impurity ions and additionally doped with ions of elements in the oxidation state 4+: Si⁴⁺, Ge⁴⁺, Ti⁴⁺, Zr⁴⁺, Hf ⁴⁺, and Sn⁴⁺. The results demonstrate that the IR photoluminescence intensity in corundum singly doped with copper is rather low. Additional doping of corundum with some tetravalent cations sharply increases the luminescence intensity. The largest increase in Cu²⁺ IR photoluminescence intensity is obtained in the case of additional doping with Ti⁴⁺, Ge⁴⁺, or Sn⁴⁺ cations. It seems likely that these ions ensure charge compensation when incorporated into the corundum lattice together with Cu²⁺ ions, so that the substitution process can be represented as 2Al³⁺ → Cu²⁺ + M⁴⁺ (M⁴⁺ = Ti⁴⁺, Ge⁴⁺, Sn⁴⁺,…). In this way, the additional doping of corundum with tetravalent ions raises Cu²⁺ solubility in α-Al₂O₃, leading to photoluminescence enhancement in the material.

Single crystals of Ba_{1 – x – y}Yb_xR_yF_{2 + x + y} (R = Tm, Ho) solid solutions have been grown by the Bridgman technique in vacuum using a CF₄ fluorination atmosphere. We have measured their thermal conductivity in the range 50–300 K and their refractive index from the visible to IR spectral region. As the ytterbium content increases from 2 to 14 mol %, the room-temperature thermal conductivity of the solid solutions with R = Tm and Ho decreases from 3.39 to 1.18 and from 3.11 to 1.18 W/(m K), respectively. Raising the holmium and thulium content of the solid solutions leads to a gradual increase in their refractive index, and it gradually decreases with increasing wavelength.