Vol 54, No 10 (2018)

This paper examines sources of carbon impurities in polycrystalline monoisotopic ²⁸Si prepared by a hydride method. Analytical data on the concentrations of carbon-containing impurities in volatile silicon compounds (²⁸SiH₄ and ²⁸SiH₄), process gases (Ar and H₂), and polycrystalline ²⁸Si are used to identify the major sources of carbon in the polycrystalline ²⁸Si prepared by the hydride method. These are the starting ²⁸SiH₄ and calcium hydride used in ²⁸SiH₄ conversion into ²⁸SiH₄. The rate of carbon intake into polycrystalline silicon from the apparatus material during the monosilane pyrolysis process does not exceed 9 × 10¹¹ cm^–2 h^–1. Polycrystalline silicon has been precipitated from monosilane with different concentrations of hydrocarbon impurities. At hydrocarbon concentrations in the range 10^–4 to 10^–3 mol %, the carbon concentration in the monosilane correlates with that in the silicon obtained from it. High-purity monosilane has been used to prepare polycrystalline ²⁸Si samples with concentrations of carbon impurities in the range (0.8–2.3) × 10¹⁵ cm^–3. Based on calculations of the carbon impurity distribution along the length of a zone-refined ingot, we examine the effect of the initial carbon concentration in the starting polycrystal on the yield of single-crystal monoisotopic ²⁸Si. Requirements are formulated for the carbon concentration in polycrystalline ²⁸Si which ensure a high yield of single crystals with parameters suitable for metrological applications.

This paper presents results of a ⁵⁷Fe probe Mössbauer spectroscopy study of the BiNi_0.96⁵⁷Fe_0.04O₃ nickelate. The spectra measured above its TN demonstrate that Fe³⁺ cations heterovalently substitute for Ni²⁺ nickel (←Fe³⁺), being stabilized on four sites of the nickel sublattice in the structure of BiNiO₃. Calculations in an ionic model with allowance for monopole and dipole contributions to the electric field gradient indicate that the parameters of electric hyperfine interactions between ⁵⁷Fe probe atom nuclei reflect the specifics of the local environment of the nickel in the structure of the unsubstituted BiNiO₃ nickelate. Below T^N, Mössbauer spectra transform into a complex Zeeman structure, which is analyzed in terms of first-order perturbation theory with allowance for electric quadrupole interactions as a small perturbation of the Zeeman levels of the ⁵⁷Fe hyperfine structure, as well as for specific features of the magnetic ordering of the Ni²⁺ cations in the nickelate studied.

The effect of defect complexes related to the presence of protons on the optical properties of LiNbO₃:Y(0.24):Mg(0.63) and LiNbO₃:Gd(0.25):Mg(0.75) (wt %) crystals has been studied using IR absorption spectroscopy, photoinduced light scattering, and laser conoscopy. The results indicate that the absorption bands at frequencies of 3483 and 3486 cm^–1 correspond to vibrations of a V_Li^-–OH⁻ defect complex. To a Mg _Li⁺ - Mg _Nb^3-–OH⁻defect complex in the LiNbO₃:Gd(0.25):Mg(0.75) crystal correspond bands at frequencies of 3526 and 3535 cm^–1. In the LiNbO₃:Y(0.24):Mg(0.63) crystal, we have detected an anomalous opening of the speckle structure of the photoinduced light scattering indicatrix.

Mg_0.5Zr₂(AsO₄)_x(PO₄)_{3 − x} arsenate phosphates have been prepared by a sol–gel process and characterized by X-ray diffraction, IR spectroscopy, and impedance spectroscopy. The results indicate the formation of a continuous series of solid solutions with the Sc₂(WO₄)₃ structure (sp. gr. P2_1/n) in the composition range 0 < x < 3. The unit-cell parameters of the solid solutions increase linearly with composition, as a consequence of arsenic substitution for phosphorus, which has a smaller ionic radius. The number of observed stretching and bending bands of the AsO₄^3- and PO₄^3- ions in the IR spectra of the solid solutions agrees with that predicted by factor group analysis for space group P2_1/n. The observed gradual shift of the absorption bands of the AsO₄ tetrahedra to lower frequencies with increasing arsenic content on the tetrahedral site supports the X-ray diffraction evidence of the formation of substitutional solid solutions. The cation conductivity of Mg_0.5Zr₂(AsO₄)_x(PO₄)_{3 − x} with 0 ≤ х ≤ 1 has been shown to exceed the conductivity of the parent magnesium zirconium arsenate.

This paper reports results of studies aimed at developing physicochemical principles of the preparation of high-purity arsenic (99.9999 (6N) and 99.99999 wt % (7N) purity) from standard (As₂S₃ and As₄S₄ sulfide ores) and unconventional raw materials (lewisite disposal (detoxification) products, nonferrous metals industry waste, and III–V semiconductor fabrication waste). We present data on the behavior of impurities in arsine ultrapurification processes and substantiate integrated approaches to the preparation of high-purity arsine and arsenic from various raw materials.

A new method of doping of spinel nanopowders with LiF sintering additive has been proposed, consisting in its introduction via solution technology, which leads to improved sinterability of the ceramic. The effect of LiF doping on densification behavior, microstructure, and optical and mechanical properties of hot-pressed MgAl₂O₄ ceramics has been studied. Samples of MgAl₂O₄ optical ceramics with density close to that theoretically achievable have been produced by hot pressing of 0.5 wt % LiF-doped nanopowders at 1600°C for 1 h. It has been shown that addition of LiF changes crack propagation in spinel ceramic from transgranular to intergranular.

A NiV₂O₆–25 wt % V₂O₅ molten-oxide material has been prepared and characterized, and its transport properties (electrical conductivity, oxygen ion transport number, and oxygen permeability) have been studied in the temperature range 680–700°C. The results demonstrate that the molten-oxide membrane material obtained possesses high selective oxygen permeability (KO₂ = (2.5–5.6) × 10^–10 mol/(cm s) in the range 680–740°C and \(\frac{{{j_{{O_2}}}}}{{{j_{{N_2}}}}}\) ~ 1500) and can be used in separators for the preparation of extrapure oxygen from air.

It has been shown by means of EBSD techique that fracture of ferritic steel in ductile-brittle transition temperature region, along with the formation of previously discribed cleavage microcracks, results in the formation of ductile microcracks. It has also been shown that microstructure of plastic zones under brittle and ductile fracture components produced by the main crack propagation differ significantly. Better developed plastic zone under ductile fracture component protects steel from overstress. The plastic zone under brittle fracture surface, apparently, has a reduced local plasticity. Consequently, the cleavage microcracks formation precedes the fracture process. During the main crack formation such microcracks occur in steel microvolumes located both in front of its tip and in adjacent to its edges microvolumes. Further propagation of the main crack is realized in steel which already contains scattered cavities and reduces to ductile fracture of the connections between them.