Inorganic Materials (v.44, #2)

The effect of H3AsO4 concentration in ethylene glycol on the electrical properties of p-n junctions in silicon has been studied. The results can be used to select the orthoarsenic acid concentration for producing arsenic diffusion layers with a predetermined junction depth, sheet resistance, and arsenic concentration. The maximum value of N s As, 4.1 × 1019 cm−3, is lower than the surface phosphorus concentration, N s P ∼ 2 × 1020 cm−3, which is tentatively attributed to the significant arsenic vaporization from anodic oxide films and also to the fact that the arsenic concentration in doped anodic oxide films is lower than the phosphorus concentration because, in the case of phosphate electrolytes, the sorption capacity of a monolayer is a factor of 2.7 higher.

Thermal conductivity of extruded Bi85Sb15 doped with Gd and Pb by Z. F. Agaev; G. D. Abdinova; G. Z. Bagieva; M. M. Tagiev; D. Sh. Abdinov (97-99).
Doping with low concentrations (∼0.01 at % and below) of Gd and Pb is shown to have little effect on the lattice thermal conductivity χph of extruded Bi85Sb15. This finding suggests that the χph of solid solutions can be determined using doping with low concentrations of electroactive impurities.

Effect of gamma irradiation on the electrical conductivity of the layered compound GaS by R. S. Madatov; A. I. Najafov; T. B. Tagiev; A. R. Mobili (100-103).
Gamma irradiation of p-GaS at 300 K has been shown to produce both donors and acceptors. Their effect on the electrical properties of p-GaS depends on the gamma dose and the defect system in the unirradiated material. Low gamma doses (30–50 krad) reduce the hole concentration, which is due to the compensation of native acceptors by radiation-induced donors (sulfur interstitials). Studies of defect annealing in gamma-irradiated p-GaS at temperatures from 300 to 600 K indicate that this process occurs in three steps.

CuGa3Se5 single crystals have been grown by the Bridgman-Stockbarger method, and their composition has been determined. The near-edge transmission spectrum of CuGa3Se5 has been measured in the range 10–300 K, and the results have been used to determine its band gap as a function of temperature. The thermal expansion of CuGa3Se5 has been studied by dilatometry using single-crystal samples oriented parallel and perpendicular to its tetragonal axis.

Photo- and thermoluminescence of BaGa2S4:Eu2+ and BaGa2S4:Eu2+,Ce3+ crystals by A. N. Georgobiani; B. G. Tagiev; S. A. Abushov; O. B. Tagiev; Zheng Xu; Suling Zhao (110-114).
Data are presented on the photo- and thermoluminescence of polycrystalline BaGa2S4:Eu2+ and BaGa2S4:Eu2+, Ce3+ at temperatures from 77 to 300 K. The broad photoluminescence band at 505 nm in BaGa2S4:Eu2+ is shown to be due to the 4f 65d → 4f 7 transition. The broad emission bands at 460 and 510 nm in BaGa2S4:Ce3+ arise from the 5D (2 D 3/2) → 4f 2(2 F 5/2) and 5D (2 D 3/2) → 4f 2(2 F 7/2) transitions. Codoping of BaGa2S4 with Eu2+ and Ce3+ increases the luminescence efficiency owing to energy transfer from Ce3+ to Eu2+. The thermoluminescence data were used to evaluate the energies of the traps involved: 0.26, 0.31, 0.42, 0.57, and 0.64 eV in BaGa2S4:Eu2+ and 0.28, 0.32, 0.54, 0.61, and 0.65 eV in BaGa2S4:Eu2+, Ce3+.

Electrical and thermoelectric properties of Cu0.75Ni0.125FeTe2 by F. F. Aliev; G. G. Guseinov; G. P. Pashaev; G. M. Agamirzoeva; A. B. Magerramov (115-120).
The electrical conductivity, Hall coefficient, and thermopower of Cu0.75Ni0.125FeTe2 have been measured between 80 and 500 K. The results have been interpreted in terms of a three-band model which takes into account, in addition to the conduction band, two overlapping valence subbands. We have determined the energy spacing between the subbands (Δ0 K = 0.002 eV), its temperature coefficient (dΔ/dT = 1 × 10−4 eV/K), and the effective masses of the heavy and light holes and electrons. With the interband scattering of light holes taken into account, the conductivity has a minimum at ∼190 K.

Microstructure and strength of carbon fibers surface-modified with titanium carbide by N. I. Baklanova; T. M. Zima; A. T. Titov; T. M. Naimushina; V. P. Berveno (121-128).
Continuous titanium carbide barrier coatings have been grown on UKN-5000 and VMN-4 carbon fibers using chemical vapor transport. The surface morphology and microstructure of as-received and TiC-coated fibers have been studied by scanning electron microscopy. The coating process is shown to raise the tensile strength and Weibull modulus of the fibers.

Structure and electrical properties of liquid Sn, Sn0.962Ag0.038, Sn0.987Cu0.013, and Sn0.949Ag0.038Cu0.013 by S. I. Mudry; V. M. Sklyarchuk; Yu. O. Plevachuk; I. I. Shtablavyi (129-133).
We have studied the structure, electrical conductivity, and thermopower of liquid Sn, Sn0.962Ag0.038, Sn0.987Cu0.013, and Sn0.949Ag0.038Cu0.013 alloys, which are used as lead-free solders. Diffraction data have been used to develop structural models of the melts. The conductivity and thermopower data have been interpreted in terms of the proposed structural models and resonance s-d scattering.

Low-temperature heat capacity and magnetic phase transition of TbB2 by V. V. Novikov; A. V. Matovnikov (134-138).
The heat capacity of TbB2 prepared by high-temperature elemental synthesis has been measured from 5 to 300 K. The C p (T) curve has a broad anomaly near 100 K, due to the Schottky contribution, and a sharp peak at 143.28 K, arising from the ferromagnetic ordering of TbB2. The total heat capacity of terbium diboride has been represented as the sum of magnetic, lattice, and Schottky contributions, and their parameters have been determined.

Brightness of blue GaN-based light-emitting diodes by N. S. Grushko; A. V. Lakalin; A. P. Solonin (139-141).
We report the brightness characteristics of KPT-1608PBC (SMD) blue light emitting diodes and the key features of emission propagation through the SMD case. The luminosity pattern of the diode is presented. The external quantum yield is determined as a function of the current through the diode, and the quantum yield is shown to correlate with the mechanism responsible for the recombination current.

Chemical interaction between TiFe and ammonia by V. N. Fokin; E. E. Fokina; I. I. Korobov; B. P. Tarasov (142-145).
We have studied chemical interaction between the intermetallic compound TiFe and ammonia at temperatures from 150 to 500°C in the presence of NH4Cl as an activator of the process. We have derived schemes of the reactions involved and have shown that the use of ammonia for hydriding/nitriding enables the preparation of fine powders of TiFe and its hydride.

Mesoporous alumina with a narrow effective pore diameter distribution has been prepared using poly(N-vinylpyrrolidone)-modified sols of hydrous Al2O3 and Al2O3-ZrO2. We compare the microstructures of nanoporous aluminas prepared from electrochemically produced unmodified and modified sols of hydrous oxides and describe the formation of highly ordered mesoporous structures from a mixture of modified sols of hydrous metal oxides differing in chemical nature. Microstructural studies of uni-and biporous permeable nanosystems during heat treatment demonstrate that the pore diameter distribution in the mesoporous oxides prepared from the modified sols remains unchanged at calcination temperatures of 700°C and lower. The microstructure and phase composition of the oxides depend on the initial properties of the sols.

The reaction between a concentrated aqueous lithium nitrate solution and a cobalt-containing composite prepared through the thermal decomposition of [LiAl2(OH)6]2[CoEDTA] · 4H2O in vacuum at temperatures from 400 to 500°C has been studied using x-ray diffraction and chemical analysis. The results indicate that, first, the lithium-aluminum-oxygen species present in the composite react with water molecules in the lithium nitrate solution to form layered Li-Al hydroxides. The next step is a hydroxide for nitrate ion exchange, leading to the formation of a nitrate form of the hydroxides. A similar mechanism underlies the formation of a nitrate in the reaction between nickel-containing composites and aqueous lithium nitrate. The nickel-and cobalt-containing composites prepared via vacuum thermolysis of [LiAl2(OH)6]2[MEDTA] · 4H2O (M = Ni, Co) react with water to form a ferromagnetic carrier containing, in addition to a metallic phase, an aluminum lithium hydroxide and bayerite impurity.

Luminescent properties of synthetic opal by A. N. Gruzintsev; G. A. Emel’chenko; V. M. Masalov; M. Romanelli; C. Barthou; P. Benalloul; A. Maître (159-164).
We have studied the effect of the photonic band gap on the visible luminescence of opal photonic crystals. The results indicate that the position of the photonic band gap in the luminescence and reflection spectra of opal depends on the photon propagation direction. Optical measurements have been used to determine the refractive index of opal and the diameter of silica spheres. We have assessed the effect of oxygen annealing on the intrinsic luminescence spectra and crystal structure of opal. The emission centers in synthetic opal have been tentatively identified. The visible luminescence intensity in opal is shown to be anisotropic, in accordance with the frequency and angular dispersions of the first photonic band gap in opal.

The histogram for the size distribution of magnetite nanoparticles in a disperse system has been shown to be close to the frequency polygon. The parameters of the histogram have been optimized by least squares. The optimized histogram more accurately represents the size distribution of the nanoparticles and can be used to adequately evaluate the moments and parameters of the distribution and the magnetization of the system.

Dielectric properties of colemanite by N. D. Gavrilova; A. M. Lotonov; A. A. Kornilova (171-175).
Rapid cooling of colemanite crystals is shown to create a metastable state with a number of unusual anomalies in dielectric properties. The dielectric properties of colemanite show a significant thermal hysteresis. A number of parameters are calculated, and the origins of the observed anomalies are discussed.

The thermal expansion coefficient of the M4 ± x V6O16 ± x (M = K, Rb, Cs) polyvanadates is a nonmonotonic function of temperature, with sharp minima at 663, 558, and 713 K, respectively, which are accompanied by no changes in cell symmetry (tetragonal) or a/c axial ratio. The polyvanadates are shown to be ionic-electronic conductors. The activation energy for electronic conduction in the three polyvanadates is 0.43 ± 0.02 eV. In the range 675–740 K, the conductivity of K4.2V6O16.2 shows metallic behavior. Rubidium polyvanadate has a narrower temperature range of unactivated conduction, and Cs3.8V6O15.8 has no such range. The conclusion is made that these phases undergo cation disordering due to deviations from the M4V6O16 stoichiometry.

Structural, electrical, and magnetic properties of La0.7Ca0.3 − x Na x MnO3 ± γ solid solutions by O. Z. Yanchevskii; A. I. Tovstolytkin; O. I. V’yunov; A. G. Belous (181-188).
La0.7Ca0.3 − x Na x MnO3 ± γ (LCNM) solid solutions with x = 0, 0.04, 0.06, 0.08, and 0.10 have been synthesized (rhombohedral structure, sp. gr. R $$ overline 3 $$ c). Sodium volatility during sintering is shown to lead to the formation of vacancies on the lanthanum and oxygen sites. Ca2+ → Na+ substitution does not increase the fraction of Mn4+ in LCNM, but the increase in the concentration of lanthanum vacancies with increasing sodium content leads to an increase in ferromagnetic ordering temperature T C and magnetoresistance, which depend, in addition, on heat-treatment conditions on account of the sodium volatility.

Electrical conductivity of a CaF2-BaF2 nanocomposite by N. I. Sorokin; I. I. Buchinskaya; P. P. Fedorov; B. P. Sobolev (189-192).
A CaF2-BaF2 nanocomposite material has been prepared via 70CaF2 · 30BaF2 (mol %) melt solidification. The material has a lamellar structure due to the eutectoid decomposition of the solidified melt. The 500°C ionic conductivity of the composite is 25 and 330 times higher than those of the parent BaF2 and CaF2, respectively. The enhanced conductivity of the composite can be understood in terms of the electrical properties of its interfaces.

Using mathematical modeling of crystal growth processes, we have analyzed the chemical homogeneity of single crystals grown from solution by conventional techniques. The results indicate that all of these techniques are, in principle, unsuitable for the growth of homogeneous single crystals. A mathematical model has been developed for a continuous isothermal growth process which insures constant solution growth conditions and chemical homogeneity of the growing crystal. The key conditions of a continuous isothermal growth process have been formulated which insure an intended uniform distribution of intentional and unintentional impurities in the bulk of the growing single crystal.

Energy stored in mineral raw materials during mechanical activation by E. V. Bogatyreva; A. G. Ermilov (197-202).
For a number of inorganic compounds, we evaluate and compare several approaches to calculating the lattice and atomization energies. Using mechanical activation of SiO2 in copper-containing concentrate as an example, we demonstrate that the milling-induced energy gain can be evaluated using the lattice and atomization energies per unit volume. We describe a procedure for calculating the milling-induced energy gain in individual phases present in mineral raw materials. As the input data for such calculations, one can use x-ray diffraction data for the starting and milled materials. The results of such calculations are shown to correlate with literature data.

Fabrication of silica membranes with controlled pore structure by M. V. Lyubavin; T. M. Burkat; V. N. Pak (203-206).
Alkaline leaching of porous glasses is shown to involve three consecutive steps: removal of secondary silica from the pores, disruption of the surface (boron-enriched) layer of the channel walls, and etching of the silica skeleton of the porous glass. The effect of the alkaline leaching time on the porosity and effective pore radius in the glasses depends significantly on the heat-treatment temperature of the parent sodium borosilicate glass, which enables control over the pore structure of membranes produced from such glasses.

Problems are addressed that relate to the use of standard processes (involving several consecutive steps) for the fabrication of calcium phosphate bioceramics: process duration (up to 72 h), low chemical yield (notably lower than 100%), and a large amount of byproducts (largely in the form of alkaline (pH ∼ 10) aqueous solutions). A new, environmentally friendly, one-step process is proposed for the preparation of calcium phosphate bioceramics.