Vol 55, No 4 (2019)

This paper presents results of a comparative experimental study aimed at producing GaAs/GaInP and GaAs/AlGaAs quantum wells (QWs) by metalorganic vapor phase epitaxy. The photoluminescence signal of the GaAs/GaInP QWs is shown to have a higher intensity (by a factor of 50–100) and, at the same time, a larger width (by a factor of ~2.5) in comparison with the GaAs/AlGaAs QWs. We analyze different approaches to controlling emission spectra of these QWs.

We have studied the electroluminescence (EL) properties of p-GaSe〈REE〉 single crystals doped with N ≤ 0.1 at % gadolinium or dysprosium and exhibiting a switching effect (SE). The results demonstrate that, at such values of N, EL and SE parameters and characteristics are independent of the chemical nature of the rare-earth dopant (gadolinium or dysprosium). Rare-earth doping levels in the range N ≈ 10^–2 to 10^–1 at % ensure high stability and reproducibility of the EL and SE parameters. We have examined the feasibility of using p‑GaSe〈REE〉 single crystals for the fabrication of high-performance light switches and sources with S‑shaped current–voltage characteristics.

A new technique has been proposed for TiO₂ synthesis via oxidative hydrolysis of TiN powder. We have examined the effect of factors determining the rate of TiN dissolution (temperature, concentration, and nature of the oxidant) on the phase composition and particle size of resulting TiO₂ powders and assessed the photocatalytic activity of the synthesized powders in comparison with commercially available photocatalysts.

This paper presents a systematic study of Raman spectra of nanocomposite photonic crystals produced using opal matrices or anodic aluminum oxide and filled with various inorganic compounds. We compare Raman spectra of the starting inorganic compounds (K₂Cr₂O₇, CrO₃, and KIO₃) and nanocomposite photonic crystals whose pores are filled with the inorganic substances. Our results open up the possibility of producing high-performance sensors of inorganic substances introduced into the pores of photonic crystals, based on analysis of enhanced Raman scattering in a nanocomposite photonic crystal.

The IR absorption spectrum of LiNbO₃:Mg(5.05 mol %):Fe(0.009 mol %) crystals has been shown to be noticeably shifted (by ~50 cm^–1) to higher frequencies, corresponding to stretching vibrations of OH^– groups, in comparison with the spectrum of congruent LiNbO₃ crystals. Analysis has shown that the shift is due to the formation of \({\text{Mg}}_{{{\text{Li}}}}^{ + }\)–\({\text{Fe}}_{{{\text{Nb}}}}^{{2 - }}\)–OH^– and \({\text{Mg}}_{{{\text{Li}}}}^{ + }\)–\({\text{Mg}}_{{{\text{Nb}}}}^{{3 - }}\)–ОН^– defect complexes.

We have studied interaction between the microwave activation product of gibbsite and an aqueous cobalt nitrate solution at room temperature, atmospheric pressure, and pH 8.0 ± 0.3. The results demonstrate that, under such conditions, the reaction in the near-surface region of the microwave-activated gibbsite particles leads to the formation of an aluminum cobalt oxyhydroxide with fragments of spinel structure and the composition Со_2.3Al_0.7O₄, and a Со_{6 –x}Al_{2 –x}(OH)_1.5 · 3.5H₂O (0 ≤ x ≤ 1) nonstoichiometric hydrotalcite. The morphology of such compounds is determined by 2D nanoparticles in the form of bent sheets 2–5 nm in thickness and 500 nm or more in length. After calcination at 500°C, the composition of the reaction products corresponds to the aluminum cobalt oxide Со_2.3Al_0.7O₄ with the spinel structure.

The results of obtaining by plasma processing of spherical, including hollow, particles of cermet powder with high content of carbide inclusions have been presented. The phase composition of particles has been determined, their morphology and internal structure has been studied. An explanation of formation of a hollow particle has been proposed.

This paper presents a study aimed at determining the weight ratio of oxide additives for obtaining high-voltage ceramics in the ZnO–Bi₂O₃–Sb₂O₃–Al₂O₃–Co₃O₄ system containing 90 wt % ZnO, with a leakage current density under 1 μA/cm². The ceramic containing the oxide additives in the ratio Bi₂O₃ : Sb₂O₃ : Al₂O₃ : Co₃O₄ = 0.25 : 0.17 : 1.4 : 1.4 has a nonlinearity coefficient as high as α = 69, a leakage current density as low as I_l = 0.4 μA/cm², and a breakdown voltage V_b = 4.1 kV/mm.

TiAl-based composite materials have been produced by spin-casting self-propagating high-temperature synthesis metallurgy methods using thermite-type mixtures, general relationships in the formation of their composition and structure have been investigated, the synthesis conditions have been optimized, a method for obtaining large ingots has been proposed, and their composition and structure have been determined. We have obtained cast Nb- and Cr-doped TiAl-based composite materials using mixtures of Ti, Nb, Cr, and Ca oxides with a combined reducing agent (Al and Ca) under the effect of an overload above 200g. It has been shown that partial Ca substitution for Al in the starting mixture ensures complete reduction of the TiO₂, and the resultant metallic phase contains calculated amounts of Ti and Al. Mixtures of optimized composition make it possible to produce a cast composite material similar in composition to alloy 4822.