Том 52, № 12 (2016)

We have studied arsenic incorporation from tris(dimethylamino)arsine into epitaxial CdTe layers in a metalorganic chemical vapor deposition (MOCVD) process. Arsenic incorporation into the layers has been shown to depend on the crystallographic orientation of their growth. Incorporation effectiveness increases in the order (111)B < (211)B < (100) < (310) < (211)A. Arsenic concentration in the CdTe layers is proportional to the tris(dimethylamino)arsine flow rate to the power 3/2. The dependence of arsenic incorporation on the ratio of the metalorganic tellurium and cadmium precursors in the vapor phase suggests that arsenic is incorporated predominantly into the anion sublattice. The maximum concentration of free charge carriers, p₂₉₅ = (1–2) × 10¹⁷ cm^–3, was observed after annealing of the arsenic-doped CdTe layers in an argon atmosphere.

In this paper, we report a detailed study of the thermal properties of a peritectic Ag–Sn alloy electrochemically deposited onto copper and titanium plates in order to produce soldered contact structures. A comparative analysis of Ag and Sn codeposition and layer-by-layer deposition processes is presented.

Titanium samples 60.0 mm in length and 3.0 × 0.3 mm in cross section were heated in a nitrogen gas atmosphere for 60 min at temperatures from 1300 to 2100°C. At temperatures below 2000°C, the titanium nitridation process comprised two stages. The lower temperature limit of exponential nitridation kinetics was determined to be ~1000°C. At temperatures above the melting point of the metal, the presence of liquid phase in the bulk of the material has no significant effect on the titanium nitridation process.

V_xTi_1–xO₂ (x = 5 and 10 mol %) solid solutions have been synthesized through supercritical drying in isopropanol at t = 250°C and p = 10 MPa. Their physicochemical properties and photocatalytic performance have been compared to those of an earlier synthesized Zn_xTi_1–xO₂ aerogel containing 10 mol % Zn [1]. It has been shown that increasing the vanadium content of V_xTi_1–xO₂ from 5 to 10 mol % leads to a decrease in hydrogen evolution rate in methanol/water splitting reaction under UV irradiation from 190 to 32 µL/(min g_catal), whereas in the case of the anatase-based aerogel solid solution containing 10 mol % Zn an opposite picture is observed: the hydrogen evolution rate in methanol/water splitting reaction under UV irradiation increases sharply to 700 µL/(min g_catal).

We have studied reactions of metallic magnesium with ethyl cellosolve and a mixture of ethyl cellosolve and tetraethyl orthosilicate and demonstrated the possibility of preparing a mixed magnesium–silicon cellosolvate that can be used as a precursor for the synthesis of forsterite and enstatite.

The formation of the spinel oxide compounds CuCrAlO₄ and CuFeAlO₄ has been studied at the nanolevel using thermal analysis, X-ray diffraction, high-resolution elemental microscopy, and differential dissolution. The results demonstrate that, in the case of the synthesis procedure used in this study, spinel structures are formed by solid-state reactions. We have studied the dynamics of changes in the chemical and phase compositions, lattice parameters, structure, and morphology of spinel particles at temperatures of 600 and 900°C. Our findings are of practical interest in adjusting conditions for the formation of mixed oxide compounds with the spinel structure.

We have studied the thermal behavior, proton conductivity, and structural properties of composite proton electrolytes based on KH₂PO₄, the mixed salt K_0.97Cs_0.03(H₂PO₄)_0.97(HSO₄)_0.03, and silicon dioxide with a pore size of 70 Å in a wide composition range. The results demonstrate that the proton conductivity of the (1–x)KH₂PO_4–xSiO₂ (x = 0.1–0.5) composite systems increases by more than two orders of magnitude, reaching 3 × 10^–3 S/cm at a temperature of 225°C. The increase in conductivity is due to the formation of a disordered amorphous state of the salts as a result of partial KH₂PO₄ dehydration and the formation of K₄H₆(PO₄)₂P₂O₇ as an intermediate product. In the composites based on the highly conductive, disordered K_0.97Cs_0.03(H₂PO₄)_0.97(HSO₄)_0.03 mixed salt, close in composition to KH₂PO₄, heterogeneous doping causes no increase in conductivity, and the conductivity decreases with increasing doping level, which is caused by dispersion of the salt and the dehydration process, leading to the formation of K₄H₆(PO₄)₂P₂O₇ and KPO₃.

The dielectric and piezoelectric properties and electrical conductivity of initially multidomain LiNbO₃:ZnO crystals have been studied in a wide range of dopant concentrations with the aim of determining the composition range of the anomalous increase in unipolarity. The results demonstrate that the development of spontaneous unipolarity during high-temperature annealing takes place only in LiNbO₃:ZnO crystals grown from melts in a “near-threshold” composition range (~5.4 < C_m ≤ 6.76 mol % ZnO). The effect is accompanied by a considerable and reproducible increase in the static piezoelectric modulus d₃₃₃. The increase in the piezoelectric modulus, Δd₃₃₃, rises linearly with increasing jump in electrical conductivity, Δσ, near a temperature T* ≈ 800 K.

Using electrophoretic deposition (EPD), we have produced YSZ individual ceramic coatings and YSZ/Al₂O₃ composite coatings for a wide range of applications in modern materials research. YSZ and Al₂O₃ nanopowders were prepared by high-energy physical dispersion techniques, namely, by a laser evaporation–condensation process and electroexplosion of wire, respectively. Stable nonaqueous suspensions for the EPD process have been prepared using YSZ and Al₂O₃ nanopowders with an average particle size of 11 and 22 nm, respectively. The YSZ/Al₂O₃ composite coating produced by sintering at 1200°C has been shown to have higher density in comparison with the YSZ individual coating produced at the same temperature. X-ray diffraction characterization showed that the YSZ/Al₂O₃ composite coating consisted of two crystalline phases: α-Al₂O₃ (corundum) (42 wt %) and cubic ZrO₂〈Y₂O₃〉 (58 wt %). Quantitative analysis of electron micrographs of the surface of the films showed that the YSZ individual coating produced by sintering at 1200°C had a loose structure and contained pores (9%), as distinct from the composite coating, which had a dense, porefree grain structure.