Inorganic Materials (v.51, #5)

Effect of oxidation on IR absorption spectra of silicon by E. V. Sokolenko; E. P. Kuznechenkov (413-418).
Infrared absorption spectra of clusters are calculated by a semiempirical method (with PM3 parameterization), and the effect of oxidation on the position and strength of absorption bands is examined.

Nonlinear optical conversion in synthetic opal by V. S. Gorelik; K. I. Zaytsev; V. N. Moiseenko; S. O. Yurchenko; I. N. Aliev (419-424).
This paper presents an experimental study of third optical harmonic generation processes in synthetic opal. Excitation was provided by ultrashort (∼10−13 s) laser pulses (λ = 1026 and 513 nm) with a high repetition rate (105 Hz), high peak power (up to 1 GW), and low pulse energy (10−5 J). The third optical harmonic intensity was shown to depend significantly on the diameter of the silica spheres, which determines the spectral position of the band gaps in the opal photonic crystal. The highest efficiency of the nonlinear optical conversion of excitation light to the third optical harmonic was observed when the excitation or optical harmonic wavelength was close to the spectral position of the band gap of the photonic crystal. This behavior can be accounted for by the presence of surface photon (Tamm) states of the optical field in opal photonic crystals in the spectral region corresponding to the band gap of the photonic crystal. The presence of photon Tamm states leads to the formation of high spectral intensity regions localized near the surface of the photonic crystal. This causes a considerable increase in nonlinear optical conversion efficiency, in particular, in the case of the third optical harmonic generation in the centrosymmetric structure of opal lattices.

Ammonia response of thin films grown on GaAs using PbO + Bi2O3 mixtures by V. F. Kostryukov; I. Ya. Mittova (425-429).
Thin oxide films exhibiting gas-sensing properties in an ammonia atmosphere have been grown on GaAs surfaces by chemically stimulated thermal oxidation. As shown by electrical measurements, the synthesized materials are n-type. We have studied the effect of thermal processes on the gas-sensing performance of the thin films grown on GaAs using PbO + Bi2O3 mixtures and obtained the temperature dependences of the carrier concentration and mobility in the films.

Template synthesis, structure, and properties of magnetically controlled, large surface area Fe3O4/TiO2 adsorbents by L. S. Semko; L. P. Storozhuk; S. V. Khutornoi; N. V. Abramov; P. P. Gorbik (430-435).
We have developed a process for the preparation of magnetically controlled Fe3O4/TiO2 nanocomposites with increased specific surface areas and investigated the structural, magnetic, and adsorption properties of the nanocomposites. The use of block-poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic-123) as a template in the synthesis process was shown to lead to a considerable increase in specific surface area (to 320 m2/g). After heat treatment, the materials containing 0.3–0.5 g of TiO2 and 0.0007–0.7 g of Pluronic-123 per gram of magnetite had a specific saturation magnetization in the range 3.75 to 3.96 μT m3/kg and coercive field from 1.47 to 1.61 kA/m.

SnO powder with a specific surface area of 2 m2/g has been prepared by microwave-assisted hydrothermal processing of an ammoniacal Sn6O4(OH)4 suspension. We have examined the effect of pressure rise rate in a reaction mixture on the surface morphology and photocatalytic activity of SnO. Raising the pressure has been shown to reduce the SnO synthesis time, without influencing the surface morphology of SnO or its photocatalytic activity for methyl orange photodegradation.

Fabrication and thermoelectric power of wires from a solid solution between bismuth and antimony tellurides by L. D. Ivanova; V. V. Molokanov; A. V. Krutilin; O. N. Uryupin; A. A. Shabaldin (441-444).
We have investigated conditions for the fabrication of glass-coated wires from the Bi0.5Sb1.5Te3 solid solution by the Taylor-Ulitovsky method and assessed the influence of the coating material and drawing rate on the formation and Seebeck coefficient (thermoelectric power) of wires of various diameters. We have optimized conditions for the fabrication of long wires (up to 1 m) 100 to 250 μm in core diameter, with geometric parameters stable along their length. The structure of fracture surfaces of the wires has been examined by scanning electron microscopy. Their Seebeck coefficient (α) has been measured in the temperature range 70–420 K. We have obtained wires with 400-K α from 100 to 140 μV/K by drawing from a melt with an open surface and α = 180 μV/K by drawing from a melt in a closed system (the parent ingot had α = 200 μV/K).

Preparation and characterization of hollow carbon nanospheres by Naing Min Tun; A. N. Morozov; I. M. Izvol’skii; E. G. Rakov (445-450).
Graphene particles in the form of hollow carbon nanospheres ranging in wall thickness from ≃1 to 12 nm have been produced via methane pyrolysis at temperatures from 500 to 900°C on spherical SiO2 nanoparticles 40 to 80 nm in average diameter, followed by dissolution of the template. We have prepared aqueous dispersions of the nanospheres with the Triton X-100 surfactant and demonstrated the possibility of producing electrodes from the nanospheres. The electrodes have been preliminarily tested for electrosorption from NaCl solutions.

Concentration and state of light elements in titanium carbide nanopowders by K. V. Grigorovich; A. V. Alpatov; B. A. Rumyantsev; A. V. Kasimtsev; N. Yu. Tabachkova; S. N. Yudin; E. A. Skryleva (451-459).
We have studied the effect of process parameters (temperature) in the reduction of titanium oxide with calcium hydride and calcium carbide on the concentrations and state of light elements (H, O, N, C, and S) in the reaction product and identified the oxygen-containing phases present in the titanium carbide (TiC) nanopowders obtained by reducing TiO2 with calcium hydride and calcium carbide. The oxygen present in the powders can be divided qualitatively and quantitatively into oxygen in adsorbed water, oxygen in organic compounds on the surface, and oxygen in the oxide layer on the surface of the carbide nanoparticle. We have performed fractional gas analysis for carbon in the titanium carbide nanopowders and assessed the effect of synthesis temperature on the average particle size and oxygen content of the nanopowders.

Thermochemical stability and adhesive strength of CuMoO4/basalt fiber composite catalysts by N. V. Lebukhova; E. A. Kirichenko; P. G. Chigrin (460-465).
This paper presents a comparative study of the adhesion of copper molybdate catalytic coatings produced on basalt fibers by different methods and their stability to high-temperature exposure to SO2 gas and water vapor. The CuMoO4/basalt fiber composites obtained in this study possess high catalytic activity for soot oxidation and are not subject to inhibition by reactive gases. A CuMoO4 layer produced by an extraction-pyrolysis process had poor adhesion to the fiber surface. When a polymer gel was used as an impregnating solution, the attachment of the catalyst to the support ensured partial Fe leaching from the basalt, which was accompanied by the formation of a porous structure in the fibers. Subsequent pyrolysis led to the formation of an intermediate iron molybdate layer and the Cu3Mo2O9 and Fe x Cu3 − x Mo2O9 phases, which decomposed to CuMoO4 and the corresponding oxides CuO and Fe2O3 during catalytic soot combustion.

A new lanthanum oxysulfide-based IR phosphor with a controlled luminescence decay time by O. Ya. Manashirov; E. M. Zvereva; A. N. Lobanov (466-472).
We have identified general aspects of the variation of the decay time for the IR Stokes luminescence of (La1 − xy Nd x Pr y )2O2S solid solutions under pulsed excitation at a wavelength of 0.810 μm. The results have been used to develop a new, lanthanum-oxysulfide-based IR phosphor with a luminescence decay time tunable from 50 to 107 μs in the ranges 1.03–1.12 and 1.30–1.45 μm.

Effect of dopant concentration on the phase composition and luminescence properties of Eu2+- and Ce3+-doped AlONs by N. S. Akhmadullina; A. S. Lysenkov; A. A. Ashmarin; Yu. F. Kargin; A. V. Ishchenko; V. V. Yagodin; B. V. Shul’gin (473-481).
Herein we report the synthesis of aluminum oxynitride (Al5O6N) doped with Eu2+ and Ce3+ and examine the effects of the dopant concentration and the nature of the rare-earth-containing precursor (europium and cerium oxides, Eu(acac)3, and Ce(acac)3) on its properties. At dopant concentrations above the solubility limit of rare-earth aluminates (EuAl12O19 and CeAl11O18) in aluminum oxynitride, we observed the formation of aluminum nitride and aluminum oxide (α-Al2O3) as individual phases. The concentration of the latter phase was higher when the rare-earth oxides were used. The emission intensity in the cathodoluminescence spectra of the samples was shown to have a maximum at Eu2+ and Ce3+ concentrations from 0.1 to 0.5 at %. Concentration quenching of luminescence was observed.

(BaSiO3)0.75(Er2O3)0.25-(BaSiO3)0.75(ErF3)0.25 join in the ErOF-ErF3-BaSiO3 system by I. B. Bakhtiyarly; S. G. Asadullaeva; K. O. Tagiev; V. P. Zlomanov (482-485).
The (BaSiO3)0.75(Er2O3)0.25-(BaSiO3)0.75(ErF3)0.25 join in the ErOF-ErF3-BaSiO3 system has been studied using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements.

Heat capacity and thermodynamic properties of LuVO4 in the range 404–908 K by L. T. Denisova; Yu. F. Kargin; L. G. Chumilina; V. M. Denisov (486-489).
The molar heat capacity of LuVO4 has been determined by differential scanning calorimetry in the temperature range 404–908 K. The C p (T) curve has been shown to have no extrema. The experimental data have been used to evaluate the thermodynamic functions of lutetium orthovanadate in the temperature range studied.

Ionic conductivity of KMgFe(MoO4)3 crystals by N. I. Sorokin (490-493).
The electrical conductivity of KMgFe(MoO4)3 crystals has been determined in the temperature range 296–828 K using impedance spectroscopy (5 to 5 × 105 Hz). The potassium magnesium iron molybdate was prepared by solid-state reaction between MgMoO4 and KFe(MoO4)2 at 900 ± 25 K over a period of 200 h. The ionic conductivity of KMgFe(MoO4)3 ceramic samples is σ = 3 × 10−4 S/cm at 573 K and the activation enthalpy for ionic transport is E a = 0.53 ± 0.03 eV. After heating in vacuum, electrical measurements indicated electronic conduction, which shunted the original impedance of the samples.

This paper presents a physicochemical study of Na1 − x Mg1 − x Sc1 + x (MoO4)3 (0 ≤ x ≤ 0.5) glassceramics and oxide glasses containing different amounts of bismuth oxide and having broad glass-forming regions, which allows the composition and properties of the materials to be varied over a rather wide range. We have studied Eu3+ luminescence under ultraviolet excitation in glass-ceramics containing a crystalline phase with the composition Na1 − x Mg1 − x Sc1 + x (MoO4)3:Eu3+ (0 ≤ x ≤ 0.5). The highest Eu3+ luminescence intensity is offered by the NaMgSc(MoO4)3 and Na0.5Mg0.5Sc1.5(MoO4)3 materials. With increasing Eu2O3 concentration, the luminescence intensity increases, reaching the highest level at 5 mol %. The glass-ceramics have trigonal symmetry (sp. gr. $$Rar 3c$$ ). The emission band at 614 nm (Eu3+ 5 D 07 F 2 transition) has high intensity, whereas the bands at 592 and 596 nm (5 D 07 F 1 transition) are rather weak. This suggests that Na1 − x Mg1 − x Sc1 + x (MoO4)3:Eu3+ (0 ≤ x ≤ 0.5) glass-ceramics are potentially attractive, bright red phosphors.

Thermal oxidation of the decahydro-closo-decaborate anion B10H 10 2− in a silicate matrix by V. K. Skachkova; L. V. Goeva; A. V. Grachev; V. V. Avdeeva; E. A. Malinina; A. Yu. Shaulov; A. A. Berlin; N. T. Kuznetsov (498-502).
We have studied the thermal oxidation of composites produced by reacting sodium water glass with the B10H 10 2− anion owing to multicenter contacts and possessing a spatially branched structure. The results demonstrate that, in air between 300 and 500°C, some of the decahydro-closo-decaborate anions present in the water glass/B10H 10 2− system oxidize, which is accompanied by a large exotherm and leads to the formation of a surface borosilicate layer preventing further oxygen diffusion into the bulk of the sample and oxidation of the B10H 10 2− anion. Samples protected by a coating produced during thermal oxidation possess thermal and deformation stability up to 600°C.

Synthesis, structure, and electrical and mechanical properties of Nb2(1 − y)Ta2y O5 ceramics by M. N. Palatnikov; O. B. Shcherbina; V. V. Efremov; N. V. Sidorov (503-511).
The structural, mechanical, and electrical properties of ceramics based on coprecipitated Nb2(1 − y)Ta2y O5 pentoxides have been studied by scanning probe microscopy, Raman spectroscopy, and impedance spectroscopy. We have examined the effect of high-intensity light processing on the structure and properties of the Nb2(1 − y)Ta2y O5 ceramics.

The electrical properties of stoichiometric and nonstoichiometric samples of barium lead titanate ferroelectric ceramics with the initial composition Ba0.95Pb0.05TiO3 have been studied by impedance spectroscopy in weak electric fields at temperatures from 295 to 620 K and frequencies from 0.3 to 103 kHz. In addition, the optical properties of the samples have been investigated in the infrared spectral region at room temperature. The measurements were made before and after vacuum quenching, which helped to produce nonequilibrium point defects: oxygen vacancies.

Preparation of high-voltage ZnO varistor ceramics by O. G. Gromov; Yu. A. Savel’ev; E. L. Tikhomirova; A. N. Danilin; V. V. Kolobov; E. P. Lokshin; V. T. Kalinnikov (516-519).
We have examined the effect of dopant concentration on the properties of ZnO varistor ceramics and determined the composition and conditions of the synthesis of ceramic powders and sintering of ceramics at a temperature of 925°C. We obtained a breakdown voltage of 2.8–3.0 kV/mm and nonlinearity coefficient in the range 48–55.

A model for the heat balance of an infinitely long whisker by O. D. Kozenkov; V. V. Gorbunov (520-524).
We have proposed a model for the heat balance of an infinitely long whisker. The model examines crystallization-related incoming heat flows to the liquid phase and the outgoing heat flow from the lateral surface of the crystal as a result of its heating through thermal conduction. The temperature is assumed to be constant throughout the cross section of the whisker. Using this model, we determined the tip temperature as a function of whisker radius for an infinitely long whisker and evaluated the whisker length at which thermal coupling to the substrate can be neglected. The whisker tip temperature decreases with decreasing whisker radius because of the increase in heat removal rate as a result of the increase in the proportion of the crystal surface. In the case of nanowhiskers, heat effects are insignificant, because the whisker tip temperature is essentially identical to the temperature of the ambient medium.