Vol 54, No 12 (2018)

The structure and chemical composition of cobalt impurity microinclusions in silicon have been studied by electron probe microanalysis using n- and p-type Si〈Co〉 samples prepared by diffusion doping and cooled at different rates after diffusion annealing. The cooling rate after diffusion annealing has been shown to have a significant effect on the structural parameters of the samples and the size of the forming impurity microinclusions. The size and shape of the impurity microinclusions determine their distribution over the bulk of the samples.

We have studied the mechanical and thermoelectric properties of samples of n-type Bi₂Te₃–Bi₂Se₃ solid solutions containing 8 and 20 mol % Bi₂Se₃; doped with excess tellurium, cadmium chloride, and antimony iodide; and prepared by hot-pressing and extruding granules produced through melt solidification in a liquid. The materials have been tested in compression at 300, 423, 523, and 623 K and in bending at 300 K. Their electrical conductivity, Seebeck coefficient, and thermal conductivity have been measured in the temperature range 100–700 K. We have obtained materials with a compressive strength of ~260 MPa and maximum thermoelectric figure of merit ZT ~ 0.9 in the range 320–390 K.

In this paper, we examine the key features of the preparation of graphene by chemical vapor deposition on copper substrates differing in geometry (foil and wire). Along with graphene, we analyze impurity structures forming on the surface of copper substrates as a result of graphene synthesis and discuss their origin and possible ways of eliminating them.

Nanodisperse modified titanium dioxide ranging in specific surface from 70 to 130 m²/g has been prepared by a sol–gel process using Al(NO₃)₃ and H₃PO₄ as modifying components and dodecylamine and ammonium carbonate as structuring components. Microwave drying of an intermediate product and pulverization in a planetary mill have been shown for the first time to be effective in reducing the bulk density of the material and improving its electrorheological activity. The effect of filler concentration (10–40 wt %) on the shear load and leakage current density of electrorheological dispersions has been examined.

Boehmite gel was prepared via hydrolysis of aluminum isopropylate in a water–alcohol solution. Electron-microscopic examination showed that the boehmite particles were highly uniform in diameter, at ~70 nm. X-ray fluorescence analysis demonstrated high purity of the material. The boehmite was heat-treated in air at 50, 165, 250, 400, 600, 800, 1000, and 1200°C and characterized by X-ray diffraction after each step. The crystallite size of the thermolysis products was found to increase from 1.1 to 3.6 nm in the range 50 to 1000°C. The gel sample dried at 50°C was characterized by simultaneous thermal analysis in combination with mass spectrometry of released gases. According to the thermal analysis results, the total weight loss in the sample was 45%. The mass spectrometry data allowed us to determine the overall formula of the synthesized gel. In the range 100–200°C, the gel lost the residual adsorbed isopropanol and isopropoxide groups, whereas water release continued up to 1000°C. We conclude that the degree of structural order, water content, and purity of the material influence the thermal stability of the metastable phases of aluminum oxide.

This paper presents a systematic Raman scattering study of novel nanostructured materials based on synthetic opal and Bi₂TeO₅ nanocrystals, which offer high photorefractive sensitivity. Bismuth tellurite was introduced into opal pores in a molten state. The crystal structure of the material in the opal pores was determined by Raman spectroscopy. Comparison of the measured Raman spectra of the opal–Bi₂TeO₅ nanocomposite and those of polycrystalline powders and single crystals made it possible to reveal a number of new bands and analyze their origin. The observed variation in the intensity of Raman bands from point to point on the sample surface can be interpreted as due to structural light focusing and excitation field localization at surface and volume defects of the photonic crystal structure of the material.

Ca_{0.75 + 0.5x}Zr_1.5Fe_0.5(PO₄)_{3 –x}(SiO₄)_x (x = 0–0.5) solid solutions have been synthesized by a sol–gel process and characterized by X-ray diffraction, IR spectroscopy, and differential scanning calorimetry. As expected, the synthesized phosphatosilicates crystallize in a NaZr₂(PO₄)₃-type structure (trigonal symmetry, sp. gr. R\(\bar {3}\)c). The thermal expansion of the solid solutions has been studied by high-temperature X-ray diffraction in the temperature range from 25 to 800°C. Their thermal expansion parameters have been calculated and analyzed as functions of composition. High-density ceramics based on the Ca_0.875Zr_1.5Fe_0.5(PO₄)_2.75(SiO₄)_0.25 phosphatosilicate have been produced by spark plasma sintering and their structure and properties have been studied in detail.

We have studied the effects of the preparation procedure, connectivity pattern, and weight ratio of components on the phase composition and properties of particulate PZT–Ni_0.9Co_0.1Cu_0.1Fe_1.9O_{4 – δ} magnetoelectric (ME) composites (where PZT stands for piezoelectric materials based on lead zirconate titanate of various industrial grades). The ME ceramics contain no foreign phases, but the use of fine piezoelectric powders leads to one-way doping of the piezoelectric with components of the ferrite. If macrocrystalline PZT is used, undesirable doping processes occur only on interfaces. The 0–3 connectivity composites with equal weight percentages of phases based on soft piezoelectric materials have improved piezoelectric parameters and high ME coupling efficiency (ΔE/ΔH = 110–140 mV/(cm Oe)), which exceeds that of the composites with the other connectivity patterns by at least a factor of 1.5. The use of hard piezoelectrics instead of the soft ones reduces ΔE/ΔH coefficients by a factor of 3 or more.

Solid-state transformations of a 3[Pd(NH₃)₄]Cl₂ + (NH₄)₂CrO₄ mixture at temperatures from 40 to 550°C in various media have been studied by thermal analysis and mass spectrometry. The results demonstrate that the solid thermolysis product obtained in an argon atmosphere consists of a single phase: palladium-based Pd_1 – xCr_x solid solution isostructural with palladium and having a unit-cell parameter a = 3.897(2) Å. Its formation proceeds through the formation of metallic Pd and Cr, as evidenced by the absence of chromium oxide phases in all of the solid intermediate thermolysis products. The solid thermolysis product obtained in air consists of the phases Pd and PdO. A model has been proposed for the transformations of the 3[Pd(NH₃)₄]Cl₂ + (NH₄)₂CrO₄ mixture through the formation of metallic palladium and chromium.