Volume 53, Nº 12 (2017)

Phase equilibria in the In–Al–Ga–P–As system have been analyzed in terms of a simple solution model. We have calculated the stability limits of InAlGaPAs solid solutions on GaAs substrates in the temperature range 937–1223 K. The addition of indium to AlGaPAs solid solutions leads to a slight decrease in growth rate under diffusion control and a considerable increase under kinetic control. Moreover, the addition of indium to AlGaPAs solid solutions has been shown to reduce the full width at half maximum of their X-ray rocking curves and photoluminescence spectra and increase the photoluminescence intensity. Increasing the indium concentration in In_xAl_yGa_1–x–yP_zAs_1–z solid solutions to x > 0.3 extends their stability region, increases their band gap, and reduces the composition region of lattice-matched In_xAl_yGa_1–x–yP_zAs_1–z/GaAs heterostructures, but these become thermal expansion-matched. With increasing indium concentration in the solid solutions, the distribution coefficients of P and As decrease, whereas those of Al and In increase.

The morphology and microstructure of PbTe surfaces polished with H₂O₂–HBr–ethylene glycol solutions have been studied by atomic force and electron microscopy techniques. The surface of PbTe single crystals after chemical–mechanical and dynamic chemical polishing with bromine-releasing etchants has been examined by optical microscopy and profilometry. The structural perfection and composition of the PbTe surface after chemical treatment have been determined by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The mechanical properties of the crystals have been studied using microindentation. Using X-ray microanalysis, we have monitored the concentrations of the host elements (Pb and Te) and possible contamination with chemical compounds present in the etchants and the solutions used to rinse the samples.

The electrical properties of R-phycoerythrin modified with Ag⁰ nanoparticles (Ag⁰ • R-PE) as a candidate material for biosensors were studied were studied. Modification was ensured by a known procedure: synthesis of Ag⁰ nanoparticles in R-phycoerythrin channels through the addition of AgNO₃ to an aqueous R-phycoerythrin solution. According to electron microscopy results, the Ag⁰ • R-PE contains predominantly elongated Ag⁰ nanoparticles 6.2 ± 0.5 nm in length, which form structures similar to rows 20–60 nm in length. The electrical conductivity, dielectric permittivity, and dielectric loss of the Ag⁰ • R-PE have been measured in the frequency range from 0.01 Hz to 1 MHz. Filling the channels in R-phycoerythrin molecules with Ag⁰ nanoparticles has been shown to increase the alternating current electrical conductivity and dielectric loss of the material at low frequencies by more than 200 times and its dielectric permittivity by 40 times. Ag⁰ nanoparticles increase the direct current conductivity of R-phycoerythrin from 5 × 10^–14 to 2.5 × 10^–11 S/cm. The electrical properties of Ag • R-PE are comparable to those of conductive polymer composites that contain metallic nanowires and are used in designing multifunctional films and smart materials.

We have synthesized octacalcium phosphate (OCP) in the presence of inorganic additives (magnesium, strontium, and fluoride ions) and studied the composition, morphology, thermal stability, and dynamic dissolution of the samples thus obtained. It has been shown that, in addition to OCP, magnesium and strontium ions favor the formation of brushite and hydroxyapatite (HA), whereas fluoride ions favor the formation of HA and fluorohydroxyapatite (FHA). We have proposed a process for the preparation of powder materials whose resorption kinetics in corrosive liquid media are corrected by adding dopants capable of activating the dissolution process.

Three-dimensional flower-like SnO₂-based structures have been produced by the alkaline hydrothermal treatment of t-SnO₂ powder with no additive and in the presence of aminoterephthalic acid (ATPA). The synthesis products have been characterized by a variety of physicochemical techniques (scanning electron microscopy, transmission electron microscopy, Raman and IR spectroscopies, X-ray diffraction, and others). The results demonstrate that raising the ATPA concentration in the reaction mixture changes the morphology of the materials and leads to the SnO₂ → SnO₂/Sn₃O₄ → Sn₃O₄ phase transformation in the structures through the formation of SnO_x nonstoichiometric tin oxide phases with 1 < x < 2. Hydrothermal treatment of the starting reagents in the presence of ≤75 wt % ATPA leads to the formation of hierarchical structures dominated by a nonstoichiometric tin oxide, which is thermally unstable at t ≥ 500°C. The morphology and phase composition of the synthesized structures have been shown to have a significant effect on the electronic conductivity of the material.

Sr₂Ni_1–yMg_yMoO₆ mixed oxides with a double perovskite structure have been synthesized via the pyrolysis of glycerol–salt mixtures. The phase composition and structure of the samples have been determined using X-ray diffraction and Raman spectroscopy. The temperatures of phase transitions in Sr₂Ni_1–yMg_yMoO₆ with y = 0.25, 0.5, and 0.75 have been determined by high-temperature X-ray diffraction and dilatometry.

The incorporation of manganese difluoride as a heterovalent additive into an α-(Yb_1–ySc_y)F₃ solid solution has made it possible to stabilize a solid solution with the α-YF₃ (α-UO₃) structure. The 573-K ionic conductivity of Yb_0.49Sc_0.26Mn_0.25F_2.75 is σ = 3 × 10^–5 S/cm, with an activation enthalpy for ion transport ΔH_σ = 0.6 eV (523–767 K).

Planar silver layers have been produced on the surface of porous glass (PG) membranes by multiple impregnations with an aqueous AgNO₃ solution, followed by hydrogen reduction of the salt to silver metal. In all cases, electron emission from the surface of the metallized porous glasses is observed above threshold electric fields lower than 2 V/μm. The emittance of the Ag/PG membranes decreases as the amount of silver increases above a nominal monolayer.

A technique has been developed for the self-propagating high-temperature synthesis of lutetium oxide (Lu₂O₃) powders using citric acid, glycine, and lutetium acetate as fuels. We have carried out thermodynamic analysis of synthesis conditions and examined the effect of the nature of the fuel on the properties of the resultant powders. Using vacuum sintering at a temperature of 1780°C and powders prepared with glycine as a fuel and containing 25 mol % yttrium oxide and 5 mol % lanthanum oxide as sintering aids, we have obtained transparent lutetium oxide-based ceramics.

We have studied how the duration of the vibration comilling of a 80 vol % TiB₂ + 20 vol % TiNi powder mixture influences the particle size, morphology, and fine-structure parameters of its components. At a milling time of 60 h, we obtained a mixture containing 27 vol % nanoparticles, in which the cubic TiNi phase had a crystallite size of 1.1 nm. We believe that vibration-milled TiB₂ + TiNi mixtures are potentially attractive for the fabrication of composite materials by powder metallurgy methods.