Inorganic Materials (v.48, #11)
Dopant microassociation mechanisms in Si〈Mn〉 and Si〈Ni〉 by S. Z. Zainabidinov; K. N. Musaev; N. A. Turgunov; A. R. Turaev (1065-1069).
This paper examines the mechanisms underlying the formation of Mn and Ni impurity microassociates in Si. Thermodynamic analysis of Si〈Mn〉 and Si〈Ni〉 suggests that the formation of various types of microassociates is mainly due to internal Coulomb forces. Theoretical models for the formation of microassociates adequately describe impurity microassociates revealed in silicon by IR microscopy, X-ray diffraction, and electron probe microanalysis.
Electrical properties of n-Cd1 − x Co x GeAs2 (x = 0.05–0.15) at high pressures by A. Yu. Mollaev; R. K. Arslanov; I. K. Kamilov; V. M. Novotortsev; S. F. Marenkin; R. G. Dzhamamedov; P. P. Khokhlachev; I. V. Fedorchenko (1070-1074).
The resistivity (ρ) and Hall coefficient (R H) of n-Cd1 − x Co x GeAs2 with x = 0.05–0.15 were measured as functions of temperature (at atmospheric pressure) and pressure (up to p = 7 GPa). The temperature-dependent ρ data were used to determine the ionization energy of a cobalt-related impurity center. In the ρ(p) and R H(p) curves, we identified structural semiconductor-semiconductor phase transitions under both increasing and decreasing pressure. Using a mixed-phase structure-effective medium model, we assessed the dynamics of the variation of phase composition with pressure.
Electronic structure of gold nanoparticles by V. G. Yarzhemsky; E. N. Murav’ev; M. A. Kazaryan; Yu. A. Dyakov (1075-1077).
Using the B3LYP/LANL2DZ method, we have calculated the spatial and electronic structures of a Au32 nanocluster with I h symmetry. The results suggest that the highest occupied orbitals have a significant density of d states, in agreement with angle-resolved photoelectron spectroscopy data for metallic gold. Relying on the densities of states obtained for the occupied and excited orbitals, we discuss optical electronic transitions in a laser based on gold nanoparticles.
Synthesis of Mg2Cu and MgCu2 nanoparticles in a KCl-NaCl-MgCl2 melt by L. S. Volkova; G. V. Kalinnikov; A. V. Ivanov; S. P. Shilkin (1078-1081).
The reaction between magnesium and nickel powders in a KCl-NaCl-MgCl2 ionic melt at 973 K (reaction time, 5 h) has been studied by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis, and chemical analysis. According to scanning electron microscopy data, the synthesized Mg2Cu and MgCu2 powders consist of particles ≃ 100 and ≃ 95 nm in size, respectively, in reasonable agreement with the equivalent particle diameters, ≃ 98 and ≃ 87 nm, determined from the specific surface area of the Mg2Cu and MgCu2 powders and with the crystallite sizes evaluated from X-ray diffraction data: D hkl ≃ 90 and 84 nm, respectively. The Mg2Cu synthesized in the ionic melt reacts with hydrogen under milder conditions than do Mg2Cu samples prepared through standard melting of magnesium and copper in an electric arc or vacuum induction furnace.
Ultrapurification of tellurium and cadmium by distillation and crystallization by N. A. Potolokov; V. A. Fedorov (1082-1087).
We have developed physicochemical principles of the ultrapurification of crude tellurium and cadmium by distillation and crystallization and determined the effective solid-liquid distribution coefficients of impurities in tellurium and cadmium. Based on the observed behavior of impurities in different ultrapurification processes, we have proposed a combined process for the preparation of high-purity (99.9999%) tellurium and cadmium.
Phase transformations in Ni + Al and Ni + Al + Cr mixtures during mechanochemical synthesis and subsequent heating by V. K. Portnoi; A. V. Leonov; A. N. Streletskii; A. V. Logachev (1088-1092).
Mechanochemical processing of elemental mixtures with the compositions Ni75Al25, Ni70Al25Cr5, and Ni75Al20Cr5 (5 at % Cr in the mixtures instead of the equivalent amount of Ni or Al) leads to the formation of nanocrystalline nickel-based solid solutions (crystallite size in the range ≃ 7–12 nm). Comparison of experimentally determined lattice parameters of the solid solutions with Vegard’s law values and with the lattice parameters evaluated using the Bozzolo-Ferrante rule, which takes into account the bulk moduli of constituent elements, suggests that the atoms in the solid solutions are bonded more strongly. Heating the synthesized ternary solid solutions in a calorimeter to 1000°C leads to the formation of an ordered γ′-phase (L12). Analysis of the relative intensity ratio of superlattice and fundamental reflections indicates that the Cr atoms always reside in the Al sublattice, independent of the composition of the starting mixture. When 5 at % Cr is incorporated instead of Ni, the chromium atoms force out aluminum from the Al sublattice, and the Ni deficiency in the Ni sublattice is compensated by the Al atoms. The ordered phases remain nanocrystalline (crystallite size in the range ≃ 40–70 nm).
Preparation of high-purity single-crystal W and W〈Nb〉 via chemical vapor transport by V. P. Smirnov; D. S. Kiselev (1093-1095).
High-purity single-crystal W and W〈Nb〉 have been prepared using chemical vapor transport. The impurity composition of the materials has been determined using spark source mass spectrometry and high-temperature vacuum extraction. The radial Nb profile in the alloy has been investigated by electron microscopy.
Effect of polymethyl methacrylate on the grinding of a metal-polymer system by V. P. Reva; D. V. Moiseenko; D. V. Onishchenko (1096-1101).
We demonstrate that grinding of metallic turnings in the presence of a destroyable high-molecular-weight compound intensifies the grinding process and contributes to plasticization of the metal. The grinding of the metal-polymer system is accompanied by reduction reactions and desulfurization of the metal being dispersed.
Nanomaterials from shungite rocks by V. V. Zyryanov; V. V. Kovalevski; S. A. Petrov; A. A. Matvienko (1102-1110).
Size fractions of shungite rock modified by heat treatment in argon at 1400°C have been characterized by X-ray diffraction; scanning electron microscopy in combination with energy dispersive X-ray microanalysis; transmission electron microscopy; optical microscopy; and IR, Raman, and Mössbauer spectroscopies. The material consists largely of a mixture of carbonaceous material (a variety of imperfect nanostructures), silicon carbide, quartz, glass, and carbon-encapsulated Fe and FeC x . The size fractions obtained using an electro-mass-classifier and magnetic separator are of interest as fillers for composite materials. A significant percentage of the carbonaceous material is associated with iron in porous globules, which allows it to be concentrated by magnetic separation. The Mössbauer spectrum of the magnetic component has low intensity, due not only to the low iron content but also to the small particle size of the iron and the loose state of the matrix. Some of the iron-carbon solid solution is in a superparamagnetic state, which transforms into a ferromagnetic state as the temperature is lowered.
Optical homogeneity of Ti:Sapphire crystals grown by horizontal directional solidification by S. V. Nizhankovskiy; E. V. Krivonosov; V. V. Baranov; A. T. Budnikov; V. N. Kanishchev; L. A. Grin’; G. T. Adonkin (1111-1114).
We have found conditions for the growth of Ti:sapphire crystals with a uniform dopant profile by horizontal directional solidification (HDS) in protective gaseous atmospheres of different compositions at different pressures. The results demonstrate that the HDS process enables the growth of large Ti:sapphire laser crystals with high optical homogeneity and wavefront distortions in the range λ/10 to λ/5.
Formation of complex oxides in the W-O2 system at temperatures from 2000 to 2500 K and a pressure of 105 Pa by D. V. Kostomarov; Kh. S. Bagdasarov; E. V. Antonov (1115-1119).
We examine the main processes that lead to the formation of (WO3) n (n = 2–5) complex tungsten oxides at T = 2000–2500 K and p = 105 Pa. Our results demonstrate that the (WO3) n oxides form not only through WO3 polymerization and WO2 disproportionation but also presumably through tungsten oxidation or reactions of the oxides WO, WO2, and WO3 with each other. We show that WO has a dual nature, participating in both (WO3) n formation and decomposition. We determine the (WO3) n concentrations and interpret the decrease in total (WO3) n concentration with increasing temperature and the increase in W2O6 concentration relative to the other (WO3) n oxides.
Temperature-dependent emissivity of coatings produced from mixtures of BaCO3 and TiO2 powders and ZrO2 micro- or nanoparticles by M. M. Mikhailov; T. A. Utebekov (1120-1125).
We have determined temperature-dependent emissivity of coatings produced from annealed mixtures of BaCO3 and TiO2 powders and ZrO2 micro- or nanoparticles. The results demonstrate that the best coatings have been obtained using ZrO2 microparticles.
Oxygen ion conductivity of (Yb0.9 − x Tb x Ca0.1)2Ti2O7 − δ solid solutions by A. V. Shlyakhtina; D. A. Belov; S. Yu. Stefanovich; O. K. Karyagina; L. G. Shcherbakova (1126-1130).
We have studied terbium substitution for ytterbium in (Yb0.9 − x Tb x Ca0.1)2Ti2O7 − δ (x = 0.1, 0.2, 0.3, 0.4) pyrochlore solid solutions synthesized through coprecipitation followed by firing at 1550°C. The results indicate that only a small amount of terbium (less than 10%) can be incorporated into the pyrochlore structure of (Yb0.9Ca0.1)2Ti2O6.9 because of the large difference in ionic radius between the terbium and ytterbium cations: Δr = r(Tb CN 8 3+ ) − r(Yb CN 8 3+ ) = 0.055 Å. The oxygen ion conductivity of the (Yb0.9 − x Tb x Ca0.1)2Ti2O7 − δ solid solutions has been determined by impedance spectroscopy in air in the temperature range 300 to 900°C. At high temperatures (t > 640°C), their bulk conductivity was essentially independent of the Yb/Tb ratio. The observed decrease in density and microstructural changes were insignificant. At relatively low temperatures (t < 640°C), the bulk conductivity decreased slightly, and the decrease depended little on terbium concentration.
Crystal structure and dielectric properties of (1 − x)(NaBi)1/2TiO3 · xBi(ZnTi)1/2O3 perovskite solid solutions by Yu. V. Radyush; N. M. Olekhnovich; A. V. Pushkarev (1131-1135).
(1 − x)(NaBi)1/2TiO3 · xBi(ZnTi)1/2O3 ceramics have been prepared by solid-state reactions. In the composition range x < 0.2, we obtained (NaBi)1/2TiO3-based solid solutions with a rhombohedrally distorted perovskite structure. With increasing x, the degree of rhombohedral distortion, the angle of antiphase tilts of oxygen octahedra about the hexagonal axis in the unit cell, and the octahedral strain decrease systematically and the unit-cell parameters a H and c H increase. We have studied the dielectric properties of the solid solutions using ceramic samples. The results demonstrate that the ceramics undergo a high-temperature diffuse ferroelectric phase transition. Near the temperature of the maximum in the real part of the dielectric permittivity (510–610 K), the ceramics have low ɛ′ dispersion and low dielectric losses. At low temperatures (below 500 K), the dielectric response of the materials exhibits ferroelectric relaxor behavior.
Micropore formation in lead zirconate titanate films by I. Yu. Tentilova; E. Yu. Kaptelov; I. P. Pronin; V. L. Ugolkov (1136-1140).
This paper presents an experimental study of the pyrochlore-to-perovskite phase transition in ferroelectric lead zirconate titanate (PZT) films grown on silicon substrates by rf magnetron sputtering and annealed in air or in an inert (argon) atmosphere at temperatures of up to 600°C and atmospheric pressure. Simultaneous thermal analysis results demonstrate that annealing in air leads to release of the latent heat of the phase transition, which is due to the conversion of lead oxide to lead orthoplumbate in the bulk of the PZT film. This transition is accompanied by changes in the densities of the perovskite phase and parent (pyrochlore) phase. In this case, the possibility of phase transformation should be ensured by changes in the volume of the system. The change in the volume of the film leads to the formation of micropores in the bulk of thin PZT films. The micropore size has been determined by scanning electron microscopy, and the phase composition of the films has been assessed by X-ray diffraction. We present experimental evidence that micropore nucleation and growth at the interface between the new and old phases in thin PZT films is due to the difference in density between these phases.
Stability of bioactive hydroxyapatite films on titanium substrates in physiological buffer solutions by A. Yu. Berezhnaya; V. O. Mittova; I. Ya. Mittova; A. V. Kostyuchenko (1141-1146).
Hydroxyapatite/titanium (HA/Ti) structures heat-treated and then incubated in CaCl2 (3 mM Ca2+) and KH2PO4 + Na2HPO4 (20 mM; pH 6, 7, 8) solutions have been characterized by X-ray diffraction, X-ray microanalysis, scanning electron microscopy, and pX measurements. The insoluble phases CaTiO3 and CaTi4O9 have been identified. After prolonged incubation (96 h), the heat-treated structures were found to be biologically resistant. Thermostating the structures in the physiological buffer solutions studied does not rupture the bioactive film, and the HA/Ti structure is stable in such solutions.
Structural and magnetic properties of BaFe12 − 2x Co x Sn x O19 modified M-type hexaferrites by E. D. Solov’eva; E. V. Pashkova; A. E. Perekos; A. G. Belous (1147-1152).
We have studied the effect of heterovalent substitution of a Co2+ + Sn4+ combination for Fe3+ on the crystal chemistry and magnetic properties of M-type barium hexaferrite (BHF). The results demonstrate that 2Fe3+ → Co2+ + Sn4+ heterovalent substitution allows one to tune the magnetic properties of M-type BHF (to reduce its coercive force (H c), while maintaining its magnetization (M s) at the level of unsubstituted BHF (x = 0)).
Synthesis and IR spectroscopic characterization of fluorinated graphite intercalation compounds with chlorinated derivatives of methane and ethane by D. V. Pinakov; N. I. Alferova; G. N. Chekhova (1153-1157).
We have synthesized (C2F x Br0.01 · yG) n intercalation compounds with (C2F x Br0.01) n as a host and G (dichloromethane, chloroform, carbon tetrachloride, and dichloroethane) as a guest (x and y are stoichiometric coefficients). The behavior of the functional groups in the guest and host subsystems has been studied by IR spectroscopy. We have examined the influence of the degree of fluorination of the polymer host (0.5 < x < 1.0) and the nature of the guest on the vibrational frequencies of the C-F and C-Cl bonds.
Hot-pressed Si3N4 ceramics containing CaO-Al2O3-AlN modifying additives by Yu. F. Kargin; A. S. Lysenkov; S. N. Ivicheva; V. V. Zakorzhevskii; I. P. Borovinskaya; S. V. Kutsev; K. A. Solntsev (1158-1163).
We have studied the influence of SHS aluminum nitride content (5–15%) and particle size on the fabrication conditions (hot pressing in a nitrogen atmosphere) of Si3N4-based ceramics containing CaO-Al2O3-AlN sintering aids. The results demonstrate that the reaction of Si3N4 with a eutectic calcium aluminate mixture during liquid-phase sintering leads to the formation of α-sialon-based intergranular phases: Ca m/z Si12 − (m − n)Al(m + n)O n N16 − n . The addition of AlN to starting mixtures contributes to a more complete conversion of the calcium aluminate sintering aid to Ca-α-sialon and influences the relationship between α-Si3N4 and β-Si3N4 in the ceramics. We examine the influence of synthesis conditions and the percentages of added calcium aluminates and aluminum nitride on the density, porosity, and bending strength of the ceramics. Thermogravimetric analysis data demonstrates that the Si3N4 + Ca-α-sialon composites obtained are stable to oxidation in air up to 1300°C.