Vol 55, No 7 (2019)

We have studied the effect of HBr concentration in (H₂O₂–HBr–EG)/EG etching mixtures on chemical–mechanical polishing (CMP) and dynamic chemical polishing (DCP) of single-crystal PbTe and Pb_{1 –x}Sn_xTe solid solutions. The CMP and DCP rates have been measured as functions of solution composition, and the effect of initial HBr concentration on the composition range of polishing etchants, surface quality, and surface condition after polishing has been assessed by measuring surface roughness. We have optimized the composition of polishing mixtures and processing conditions for obtaining high-quality polished surfaces.

This paper reports the synthesis of RNi_{1 –x}Si_x-based (R = Dy, Gd; x = 0.05, 0.02) intermetallic hydrides. The amount of absorbed hydrogen in the hydride phases is three to four atoms per formula unit. According to X-ray diffraction data, the synthesized hydrides have a crystal lattice with the FeB structure (sp. gr. Pnma, no. 62) at R = Dy and the CrB structure (sp. gr. Cmcm, no. 63) at R = Gd.

Using a variety of characterization techniques (differential scanning calorimetry, X-ray diffraction, high-resolution transmission electron microscopy, resistivity measurements, nanoindentation, and uniaxial tension testing), we have studied structural changes produced in the amorphous phase of the Fe₇₇B₇Nb_2.1Si₁₃Cu_0.9 alloy by heating in vacuum to 750°C and lamp processing (LP) with the use of pulsed xenon lamps to a fluence F = 120 J/cm² on the sample surface. Increasing the temperature or fluence leads to three stages of structural transformations: structural relaxation of the amorphous phase below 450°C and two stages of crystallization, which show up as nonmonotonic behavior of the hardness and local plasticity of the samples. With a common character of the structural changes, the effect of LP shows up as an increase in crystallization rate (the processing time is 200 times shorter). In both cases, the fraction of plastic strain in indentation work in amorphous and crystallized samples is 25% larger than that in amorphous–crystalline composites. It has been shown that irreversible deformation of amorphous samples by uniaxial tension leads to structural relaxation and an increase in the size of the relaxation zone.

In this paper, we examine processes for producing mesoporous Fe₂O₃–SiO₂ silica-matrix composites with different fractions of ferric oxide and demonstrate the effect of the synthesis procedure on the structure, textural characteristics, particle size, and magnetic properties of the materials. We assess the thermal stability of the composites. A ferric-oxide-rich material (Fe : Si = 0.6 : 1) prepared by hydrothermal synthesis (THS) exhibits ferrimagnetic properties after high-temperature holding (t = 1000°C) for 3 h.

Published experimental data are used to assess the feasibility of adding bismuth to (R,Bi)₃(Fe,M)₅O₁₂ (R = Ln, Y; M = Ga, Al) multicomponent solid solutions with the garnet structure using various synthesis techniques. We demonstrate that the existing approaches for producing (R,Bi)₃(Fe,M)₅O₁₂ films and coatings are incapable of ensuring reproducibility of their chemical composition and phase stability.

IR absorption spectra of zinc-doped LiNbO₃ crystals in the stretching region of OH groups, Raman spectra of the crystals, and their optical absorption spectra provide evidence of drastic changes in the mechanism responsible for the incorporation of Zn into the structure of the crystals and the nature of hydrogen bonds and the corresponding proton-containing charged defect complexes (\(V_{{{\text{Li}}}}^{ - }\)–OH^–, Nb_Li–OH⁻, and \({\text{Zn}}_{{{\text{Nb}}}}^{{{\text{3}} - }}\)–OH⁻) near a concentration threshold at ≈6.76 mol % ZnO in the melt.

We have studied EPR spectra of MnO₂-activated fluorozirconate and fluorohafnate glasses in order to determine the oxidation state and distribution of the manganese ions. The effect of activator concentration on the ratio of the percentage of free Mn⁴⁺ ions to that of ions in clusters in the glasses has been investigated for the first time. The results demonstrate that, at high activator concentrations, the manganese ions in the glasses are clustered, and only a small fraction of them are present as isolated ions. Reducing the manganese concentration leads to an increase in the percentage of free Mn⁴⁺ ions. Devitrification is accompanied by dissociation of the clusters and a transition of the ions to an isolated state.

We have studied structural, morphological, and phase transformations in the surface layer of compact zirconium nitride-based ceramics during high-temperature annealing in vacuum, nitrogen, and air. The formation of oxygen-containing phases during heat treatment of ZrN is controlled by bulk and grain-boundary oxygen diffusion. At the beginning of the process, oxygen is supplied by an amorphous surface layer, which always forms during the ceramic preparation process. In air, the process is driven by oxygen indiffusion from the gas phase across an initially forming porous oxide layer. Grain-boundary oxygen diffusion leads to the formation of a crystalline zirconium oxide layer on grain boundaries and crack nucleation.

We have studied the influence of melt heat treatment, initial cooling temperature (t_cooling 0), and cooling schedule for a melt containing 50 mol % Bi₂O₃ and 50 mol % GeO₂ on the phase composition, macrostructure, and microstructure of crystallizing solid phases. According to X-ray diffraction, optical microscopy, and scanning electron microscopy data, the phase composition of the crystallization products is represented by either the metastable bismuth germanate Bi₂GeO₅ or a mixture of metastable and stable phases, depending on melt cooling conditions. The crystallization behavior of phase-pure Bi₂GeO₅ under identical cooling conditions has been shown to be influenced by not only t_cooling 0 but also isothermal preholding of the melt for 1 h at a temperature of 1160°C.