Inorganic Materials最新文献

The thermodynamic modeling of the GaI₃–Se and ZnI₂–Se systems was carried out by the equilibrium constant method in the temperature range of 200–500°C. The equilibrium degrees of conversion of iodides to Ga₂Se₃ and ZnSe were found to be 21 and 0.7%, respectively. Molecular iodine was the major component of the vapor phase in both systems. A preparation method of Ga₂Se₃, ZnSe, and ZnGa₂Se₄ by the reaction of GaI₃ and ZnI₂ with selenium in an evacuated quartz reactor with two temperature zones was developed. The selective withdrawal of iodine from the reaction melt made it possible to attain a practical yield of selenides of 86–90% at 450°C. The residual content of iodine in the products was 0.2–1 at %.

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.

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.

Nickel and aluminum powders have been deposited for the first time on steel 35 by electrospark deposition. We have studied the effect of the ratio of the Ni and Al powders in the anodic mixture on the structure, oxidation resistance, and corrosion behavior of the coatings and also on their friction coefficient and wear resistance. The results demonstrate that, as the fraction of aluminum powder in the anodic mixture increases from 30 to 70 at %, the average aluminum content of the coatings increases steadily from 39 to 63 at %, whereas the nickel content decreases from 46 to 26 at %. The use of such coatings allows the oxidation resistance of steel 35 parts at a temperature of 700°C to be raised 13 to 34 times. The most aluminum rich coating has been shown to have the highest hardness, wear resistance, and heat resistance.

A single crystal of a Pb_1−xSc_xF_2+x heterovalent solid solution with x = 0.1 (nominal composition) has been grown by vertical directional solidification (Bridgman technique), its elemental and phase compositions and crystallographic parameters have been determined, and the interrelation between its thermal and electrical conductivities has been analyzed. The composition of the solid solution has been found to vary from x = 0.08 in the bottom (cone) of the crystal to x = 0.095 in its top. The Pb_1−xSc_xF_2+x crystal has been shown to have low thermal conductivity (k = 0.7 W/(m K) at 300 K), with “glass-like” behavior of thermal transport, atypical of the crystalline state, in combination with high fluoride ion electrical conductivity (σ_dc = 0.012 S/m at 293 K) and relatively low activation enthalpy for electrical conduction (ΔH_σ = 0.378 ± 0.005 eV). The observed behavior of the thermal and electrical conductivities of the Pb_1−xSc_xF_2+x solid solution is due to structural disorder in the fluorine sublattice—which persists at room temperature—as a result of heterovalent substitutions of Sc³⁺ for Pb²⁺ cations. The thermal and electrical conductivities of single crystals of Pb_1−xSc_xF_2+x and Pb_1−xCd_xF₂ two-component solid solutions (CaF₂ structure) are compared to those of the β-PbF₂ (CaF₂ structure) and ScF₃ (ReO₃ structure) single-component fluorides.

This paper presents models of the hysteresis effects occurring on the wetting perimeter of a liquid-metal catalyst drop due to the effects caused on the contact angles by the edge of the end (tip) face of a nanowires (NW) and the linear tension of the three-phase contact interface. The contact angle hysteresis of the catalyst liquid drop on the end of an NW grown by the vapor → liquid → solid (VLS) scheme is due to its indifferent equilibrium at the wetting perimeter. The conclusion is drawn that the contact angle hysteresis in the catalyst drop wetting the NW crystal surface has a dual, not strictly equilibrium nature.

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.

We have grown single crystals of solid solutions based on the layered compound semiconductor TlGaS₂ containing up to 2 mol % praseodymium and characterized them by X-ray diffraction. The optical absorption edge of the TlGaS₂〈Pr〉 solid solutions has been studied in the temperature range 100–200 K, and the edge exciton peak position has been determined as a function of temperature for all of the TlGaS₂〈Pr〉 compositions studied.