Vol 52, No 10 (2016)

Variations in the contours of pores produced in n-type silicon by electrochemical etching in hydrofluoric acid solutions are interpreted in terms of the mechanism underlying the chemical interaction of the etchant with silicon and the anisotropy of the etchant–silicon system. Mathematical expressions are proposed which describe the contours and limiting radial sizes of pores forming at the very beginning of the etching process (~10–15 s).

Nanostructured titanium disilicide (TiSi₂) powders with semiconducting properties have been prepared via cold fusion of silicon and titanium nanopowders and mechanochemical activation of TiSi₂ powders prepared by self-propagating high-temperature synthesis. The semiconducting properties of TiSi₂ have been shown to be determined by the nanocrystallite size. Basic to the formation of TiSi₂ as a semiconductor material is a change in its band structure upon the conversion of the conductor to a semiconductor. The transformation takes place when the crystallite size decreases from microns to the nanometer range (≤70 nm). Such crystallites are nanoclusters with distorted order in the arrangement of the silicon and titanium atoms.

We have studied the effect of the hydrothermal synthesis temperature on Al₂O₃ structure formation and examined the role of the phase composition of the precursor gel and surfactant in the formation of the pore structure of Al₂O₃. A technique has been proposed for the synthesis of TiO₂/Al₂O₃ binary xerogels, and the effect of TiO₂ content on the pore structure parameters and adsorption properties of TiO₂/Al₂O₃ has been investigated.

To ensure high-speed analytical support to the technology of cadmium tungstate single crystal growth, we have developed an electrothermal atomic absorption spectrometry technique for analysis of high-purity cadmium and cadmium oxide for the technologically important impurities Ag, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Sn with detection limits from 2 × 10^–7 to 6 × 10^–6 wt %.

We have studied the optical absorption, luminescence, and electron paramagnetic resonance of EuF₃- and EuF₂-activated fluorohafnate glasses. The glasses prepared with EuF₂ contain both di- and trivalent europium. The fraction of divalent europium clusters in the glass host decreases with decreasing EuF₂ concentration. Eu²⁺ luminescence in the fluorohafnate glasses is quenched, which is due the overlap of Eu²⁺ excited state levels with the conduction band of the glass, resulting in nonradiative relaxation through Hf³⁺ levels in the conduction band. The Eu³⁺ luminescence spectra contain lines corresponding to transitions from several levels of the ⁵D multiplet to levels of the ⁷F multiplet. The relationship between transitions from different ⁵D levels depends on europium concentration and temperature.

Phase formation processes along the YBa(Co, Cu)₄O_{7 + x} section of the Y–Ba–Co–Cu–O system have been studied in the temperature range 900–1150°C under atmospheric oxygen pressure. We have located the boundaries of the homogeneity range of the YBaCo_4–yCu_yO_{7 + x} (114) phase and determined the temperature- dependent copper solubility in this phase, y_max(t) (y_max ≈ 0 at 900°C; the highest solubility is y_max ≈ 0.7, at t = 1000–1050°C). Using X-ray diffraction data for quenched samples, we have identified the phases that coexist with YBaCo_4–yCu_yO_{7 + x} in the phase regions adjacent to its homogeneity range. The results demonstrate that, if the percentage of copper in a starting mixture, y₀, exceeds the copper solubility limit in the 114 phase at a given synthesis temperature, the excess copper concentrates in copper-rich phases: YBaCo_2–yCu_yO_{5 + x} (112), Co_1–yCu_yO_{1 + x} (001), and Y₂Cu₂O_{5 + x} (202). At temperatures in the range 900 ≤ t ≤ 1050°C and compositions in the range y₀ ≤ 0.9, the system can be thought of as ternary, with a constant Y: Ba ratio of 1: 1 (that is, only the 114, 112, and 001 phases are present at equilibrium). Beyond this region, phases with other Y: Ba ratios appear.

In this paper, we analyze the relationship between the microstructure of new polycrystalline electron–proton conductors, Ln_6–xZr_xMoO_{12 + δ} (Ln = La, Nd, Sm; x = 0.2, 0.6), and the reduction and hydration processes in these materials in humid atmospheres (air and argon). The La_5.8Zr_0.2MoO_12.1 solid solution with a rhombohedral structure possesses not only the highest electrical conductivity among the materials studied here but also high stability in various dry and humid, oxidizing (air) and reducing atmospheres. La_5.8Zr_0.2MoO_12.1 ceramic grains have a twin microstructure, and the conductivity of this material along the grain boundaries, consisting of ordered domains, differs little from its bulk conductivity. It seems likely that we observe a “domain wall” effect, typical of La_0.95Sr_0.05Ga_0.9Mg_0.1O_3–δ (LSGM) oxygen ion conductors [1]. In studies of Ln_6–xZr_xMoO_{12 + δ} (Ln = Nd, Sm; x = 0.2, 0.6) ceramics in humid atmospheres, we detected a grain-boundary contribution, which limited the total conductivity, like in perovskite BaZr_0.8Y_0.2O_3–δ. We believe that such conditions lead to a reduction process in these materials and that Mo⁶⁺ is reduced before Nd³⁺ and Sm³⁺. The process first occurs on grain boundaries.

Co (Ni) films on ceramic lead zirconate titanate (PbZr_0.45Ti_0.55O₃) ferroelectric substrates and single-crystal GaAs piezoelectric substrates are shown to exhibit a giant magnetoelectric response, which reaches 200 V/A at room temperature and mechanical Q of at least 1000. These findings are interpreted in terms of the formation of stable interfaces in thin-film heterostructures owing to good adhesion of dissimilar materials to substrate surfaces after ion beam sputtering/deposition processing. This will allow one to extend the applicability of the magnetoelectric effect at room temperature to commercially available microelectronic materials and integrate related hybrid structures into single-chip signal generation/processing devices.

We have proposed synthesis of polydisperse particles of poorly soluble substances through precipitation in pores of a water-soluble matrix. As a matrix, we used sucrose pressed under mass production conditions. In its pores, we obtained highly dispersed BaSO₄ particles precipitated by reacting Ba(NO₃)₂ and Na₂SO₄. The BaSO₄ particles were separated from the aqueous phase using a track-etched membrane filter and characterized by electron microscopy.