Vol 53, No 9 (2017)

This paper presents results on the kinetics and mechanism of the physicochemical interaction of InAs, InSb, GaAs, and GaSb semiconductor surfaces with (NH₄)₂Cr₂O₇–HBr–C₄H₆O₆ etching solutions under reproducible hydrodynamic conditions in the case of laminar etchant flow over a substrate. We have identified regions of polishing and nonpolishing solutions and evaluated the apparent activation energy of the process. The surface morphology of the crystals has been examined by microstructural analysis after chemical etching. The results demonstrate that the presence of C₄H₆O₆ in etchants helps to reduce the overall reaction rate and extend the region of polishing solutions.

Iron nanopowders ranging in particle size from 20 to 100 nm have been synthesized by reducing a 1-mm-thick iron(III) hydroxide layer in flowing hydrogen at 400°C and then passivated for 6–60 min in flowing argon containing 3% air. Our results demonstrate that the passivated iron nanopowders do not oxidize in air for six months. The iron nanoparticles have been characterized by X-ray diffraction (crystallite size evaluation), Auger electron spectroscopy, and polymolecular adsorption. The passivated iron nanoparticles have been shown to consist of a metallic core and oxide shell 2–4 nm in thickness.

Using data on the crystal symmetry of iron pnictides, we have calculated possible symmetries of singlet two-electron states corresponding to the superconducting order parameter. It has been shown that the octet line node structure observed in photoemission spectra is due to interaction between pairs of the same symmetry and that the presence of an odd component of a superconducting state in NMR spectra is associated with states on the Brillouin zone boundary.

The influence of low concentrations (1 mol %) of co-dopants (Y, Ce, Gd, Er, La, Zn, Mn, Co and Cu) on the microhardness and fracture toughness of Zr_0.81Sc_0.19O_2–δ (10.5ScSZ) solid electrolyte was studied by the indentation method. It was shown that co-doping of 10.5ScSZ by the rare-earth elements (Y, Ce, Gd, Er) results in microhardness increase on 4–45% due to stabilization of cubic phase in the grains, while the microhardness changing upon transition metals (Mn, Cu, Co, Zn) introduction is caused by the grain boundaries modification. The microhardness decreases on ~4 and 10% upon doping by Mn and Cu, accordingly, whereas the introduction of Co and Zn results in its increase approximately by 2 times. It was shown also that the influence of all investigated dopants on the fracture toughness is insignificant. The maximal effect observed for Cu was the fracture toughness increase from 2.1 up to 2.6 MPa m^0.5.

A series of Gd_11–x–yYb_xEr_yGeP₃O₂₆ germanate phosphates differing in the ratio of the Yb³⁺ and Er³⁺ active ions have been synthesized, and their luminescence spectra have been measured. According to X-ray diffraction characterization results, all of the synthesized germanate phosphates are single-phase and have a triclinic structure (sp. gr. P1). We have measured upconversion luminescence spectra due to the Er³⁺²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 radiative transitions in the synthesized gadolinium ytterbium erbium germanate phosphates and determined the luminescence upconversion energy yield (B_en) in Gd_11–x–yYb_xEr_yGeP₃O₂₆. The effects of the concentrations and ratio of the dopants in the Gd₁₁(GeO₄)(PO₄)₃O₁₀ germanate phosphate host on B_en and the ratio of the luminescence intensities in the red and green spectral regions (R/G) have been assessed.

A technique has been developed for fluorinating the pyrochlore oxide Bi_1.8Fe_0.2FeSbO₇, and a compound with the composition Bi_1.8Fe_1.2SbO_7–x/2F_x has been obtained. The synthesized oxyfluoride also has the pyrochlore structure (sp. gr. Fd3m), with a lattice parameter a = 10.4443(1) Å (R_wp = 5.2). It has been shown that the charge balance upon fluorine substitution for oxygen is maintained not through partial reduction of Fe³⁺ to Fe²⁺ but through the incorporation of fluorine into oxygen vacancies. The magnetic behavior of the fluorinated pyrochlore phase is determined by the persisting frustration of the octahedral sublattice, which is responsible for the development of a spin glass state below T_f = 12 K. The fluorination-induced changes in the anion sublattice led to an increase in the antiferromagnetic exchange interaction between neighboring Fe³⁺ ions and changes in the dynamic properties of the spin glass phase.

We have studied the effect of water glass prepared by a wet-chemical process on the principal properties of structural materials using alkali-activated mineral binders and determined the optimal hydrothermal leaching time for tripoli, corresponding to the maximum SiO₂ concentration in the water glass slurry. We have investigated the initial structure of the tripoli and the leaching-induced structural changes in its mineral component. The influence of three types of mixing agents has been analyzed in the context of the preparation of materials: water glass in the form of slurry, water glass slurry filtrate, and the filtered-off insoluble residue of the slurry in the form of thick mass. The strength of the obtained materials increases in the following order: insoluble residue < filtrate < slurry. The present results demonstrate that the materials have high strength characteristics and that water glass prepared by a wet-chemical process is potentially attractive for practical application.

This paper examines the feasibility of using electrophoretic deposition for producing thin films of cathode materials based on lanthanum nickel oxides (with the lanthanum nickelate La₂NiO_{4 + δ} (LNO) as the predominant phase). We have determined the particle size and zeta potential of nonaqueous suspensions of LNO micro- and nanopowders prepared by solid-state reactions, pyrolysis of liquid precursors, and laser evaporation of a target. Using ultrasonic processing, we have obtained stable LNO nanopowder suspensions in acetylacetone and an isopropanol + acetylacetone mixture, which have zeta potentials of +25 and + 38 mV, respectively. Electrophoretic deposition on a dense model cathode has produced thin bilayer coatings from electrode and electrolyte materials (LNO and Се_0.8(Sm_0.75Sr_0.2Ba_0.05)_0.2O_2–δ), which are of interest for solid oxide fuel cell technology.