Inorganic Materials (v.47, #2)

We have evaluated the thermodynamic properties of solid solutions of titanium, chromium, cobalt, and nickel in silicon using a two-sublattice model. Our results demonstrate that the thermodynamic data obtained can be used in thermodynamic calculations.

Thermal oxidation of InP with V2O5 + PbO nanolayers of different compositions by A. A. Samsonov; I. Ya. Mittova; D. P. Valyukhov; E. V. Tomina; A. N. Lukin (100-106).
Data are presented on the thermal oxidation of (V2O5 + PbO)/InP structures which demonstrate that the combined effect of the oxides deposited by magnetron sputtering does not follow the additivity rule and that this behavior is due to the formation of a quasi-liquid phase (maximum) and lead vanadate (minimum) (IR spectroscopy, Auger electron spectroscopy). The effective activation energy for the oxidation of the (V2O5 + PbO)/InP structures is shown to systematically decrease with increasing initial vanadium oxide content. The oxidation of the structures follows a partially catalytic mechanism, with V2O5 acting as a catalyst (oxidation kinetics, IR spectroscopy, ultrasoft X-ray emission spectroscopy).

ZnS:Mn2+ films differing in surface morphology have been grown on glass substrates by magnetron sputtering and laser deposition, and the effect of surface roughness on the spectral characteristics and decay time of yellow luminescence in the films has been studied. The results demonstrate that luminescence interference at the upper and lower boundaries of the films influences not only the shape of their emission spectrum but also the manganese ion radiative recombination kinetics. The difference in emission decay time between ZnS:Mn2+ crystals and films can be understood in terms of the local density of photon states.

Radiative recombination in CdGa2S4 single crystals by A. N. Georgobiani; T. G. Kerimova; R. A. Guliev (112-115).
We have studied the effects of light polarization and temperature on the photoluminescence spectrum of CdGa2S4 single crystals at temperatures from 77 to 300 K. Based on analysis of the present experimental data in conjunction with earlier band structure, optical absorption, and photoconductivity data, we have identified the mechanism of radiative recombination in CdGa2S4.

Crystals of (FeIn2S4)1 − x (In2S3) x solid solutions consisting of large blocks have been grown by directional solidification (horizontal Bridgman process). FeIn2S4, In2S3, and the solid solutions are shown to crystallize in the spinel structure. The composition dependence of their unit-cell parameter a follows Vegard's law. The local states of the Fe ions in the solid solutions have been studied by Mössbauer spectroscopy in a transmission geometry.

A facile photochemical route for the synthesis of gold nanoparticles by Changming Cheng; Baoqiang Lv; Yi Li; Jun Wang; Jie He; Hongyan Yuan; Dan Xiao (121-127).
Synthesis of high-quality, water-dispersed gold nanoparticles (AuNPs), has been prepared employing luminol as a special reductant, via direct irradiation of the molecular precursors rather than traditional heat of the solvent. The final quality of the photochemically generated nanomaterial was characterized by transmission electron microscopy, resonance light scattering spectra, and cyclic voltammetry. AuNPs could enhance the chemiluminescence intensity of the luminol-H2O2 system, attributing to their catalysis. On the basis, we developed a nanoparticle-based chemiluminescence method for the determination of H2O2. The results demonstrated that it was possible to detect hydrogen peroxide in the range of 10−8–10−3 M.

We report an experimental study of carbon nanotube (CNT) growth via catalytic pyrolysis of acetylene. Surface free energy is shown to play a key role in determining the catalytic activity of the liquid droplet on the CNT tip and to be responsible for the constant nanotube diameter. A vapor-liquid-nanotube model is proposed for CNT growth.

The oxidation of tungsten carbide powders ranging in average particle size -D from 20 to 6000 nm has been studied by thermal analysis. Independent of particle size, the WC powders oxidize to the higher oxide WO3. With decreasing particle size, the oxidation rate increases, and the exothermic peak temperature decreases. Empirical relations are presented for the peak temperature and activation energy of oxidation as functions of the particle size of the powders.

Pb distribution in multistep bismuth refining products by Yu. V. Shevtsov; N. F. Beizel’ (139-142).
Significant amounts of lead impurities have been removed from bismuth using a multistep refining process involving bismuth electrorefining in a hydrochloric acid solution, melting of a cathodic bismuth sponge, and pyrometallurgical processing of molten bismuth in an inert atmosphere. The Pb distribution between bismuth and the products forming in different refining steps has been studied.

A comparative study of the structural and spectral characteristics of ZnO nanoparticles dispersed in isopropanol and polyethylene by E. G. Nebukina; E. M. Khokhlov; M. A. Zaporozhets; A. G. Vitukhnovskii; S. P. Gubin (143-147).
We have developed a process for the preparation of zinc oxide nanoparticles in isopropanol and high-pressure polyethylene (HPPE) and investigated the structural and spectral properties of the ZnO-isopropanol disperse system and ZnO-HPPE nanocomposite. The results demonstrate that the luminescence properties of ZnO quantum dots can be maintained intact when the quantum dots are transferred to a chemically inert HPPE matrix. We believe that the process for the fabrication of ZnO-HPPE nanocomposites can be employed in the development of UV and visible luminescence standards.

ω(k) dispersion curves are calculated for electromagnetic waves in a photonic crystal (at normal incidence). The calculations rely on a model of a one-dimensional periodic layered medium with two refractive indices. The ω(k) dispersion law thus derived is used to find the frequency-dependent reflectance of the photonic crystal. Approximations are proposed that allow the dispersion law ω(k) to be obtained in explicit form.

We examine chemical reactions that lead to the oxidation of tungsten in the W-Al2O3 system at T = 2350–2500 K and p = 1–105 Pa. The results indicate that, for p ≥ 10 Pa, tungsten oxidizes through reactions with both Al2O3 vapor and dissociation products (Al2O2, Al2O, AlO2, and AlO). For p ≤ 10 Pa, oxidation is due to direct reaction of tungsten with O and/or O2. For p ≤ 2 Pa, tungsten may react with molten Al2O3. A detailed analysis of tungsten oxidation processes is intended to optimize parameters of the melt growth of corundum crystals.

Crystallization from high-temperature solutions in the K2O-P2O5-V2O5-Bi2O3 system by N. A. Gorodylova; V. N. Baumer; I. V. Zatovsky; A. A. Babarik; N. S. Slobodyanik; O. V. Shishkin (156-162).
We have studied general trends of crystallization from high-temperature solutions in the K2O-P2O5-V2O5-Bi2O3 system at P/V = 0.5−2.0, K/(P + V) = 0.7−1.4, and Bi2O3 contents from 25 to 50 wt % and identified the stability regions of BiPO4, K3Bi5(PO4)6, K2Bi3O(PO4)3, and K3Bi2(PO4)3 − x (VO4) x (x = 0−3) solid solutions. The synthesized compounds have been characterized by X-ray powder diffraction and IR spectroscopy, and the structure of two solid solutions has been determined by single-crystal X-ray diffraction (sp. gr. C 2/c): K3Bi2(PO4)2(VO4), a = 13.8857(8), b = 13.5432(5), c = 6.8679(4) Å, β = 114.031(7)°; K3Bi2(PO4)1.25(VO4)1.75, a = 13.907(4), b = 13.615(2), c = 6.956(2) Å, β = 113.52(4)°.

Thermal conductivity and heat capacity of α- and β-BaB2O4 single crystals by P. A. Popov; N. V. Moiseev; A. E. Kokh; K. A. Kokh (163-166).
The thermal conductivity of β- and α-BaB2O4 single crystals has been measured at temperatures from 50 to 300 K by a steady-state axial flow technique. The 300-K thermal conductivity of the β-polymorph along and across its c axis is 1.64 ± 0.08 and 1.24 ± 0.06 W/(m K), respectively, and that of the α-polymorph along its c axis is 1.65 ± 0.08 W/(m K). Swirls and twin boundaries have an insignificant effect on the thermal conductivity of α-BaB2O4 crystals. The heat capacity of α-BaB2O4 measured in the range 56–300 K using adiabatic calorimetry differs little from that of the β-polymorph.

Synthesis of high-purity aluminosilicates using aluminosiloxane precursors by P. A. Storozhenko; G. I. Shcherbakova (167-171).
Using cohydrolysis of aluminum alkyls with tetraethyl orthosilicate, we have synthesized aluminosiloxane oligomers, which have been pyrolyzed to give homogeneous high-purity aluminosilicates with a controlled Al: Si molar ratio.

Phase transitions and thermal expansion of apatite-structured compounds by N. G. Chernorukov; A. V. Knyazev; E. N. Bulanov (172-177).
The phase transitions and thermal expansion of apatite-structured compounds with the general formula M 5 II (AVO4)3L (MII = Ca, Sr, Cd, Ba, Pb; AV = P, V; L = F, Cl) have been studied by high-temperature X-ray diffraction and differential thermal analysis. The Pb-containing apatites are shown to undergo phase transitions involving a reduction in unit-cell symmetry from hexagonal to monoclinic. The thermal expansion anisotropy in the hexagonal phases increases in the order Ca < Sr < Ba < Pb < Cd, and the monoclinic phases are less anisotropic but have larger thermal expansion coefficients in comparison with the hexagonal phases.

Thermodynamic properties of NaZr2(AsO4)3 by V. I. Pet’kov; D. V. Firsov; A. V. Markin; M. V. Sukhanov; N. N. Smirnova (178-182).
The heat capacity C p 0 of crystalline NaZr2(AsO4)3 has been measured in the range 7–650 K using precision adiabatic calorimetry and differential scanning calorimetry. The experimental data have been used to calculate the standard thermodynamic functions of the arsenate: C p 0 , enthalpy H 0(T) − H 0(0), entropy S 0(T), and Gibbs function G 0(T) − H 0(0) from T → 0 to 650 K. The standard entropy of its formation from elements is Δf S 0(NaZr2(AsO4)3, cr, 298.15 K) = −1087 ± 1 J/(mol K).

Polymorphism and properties of Bi2W1 − x Mo x O6 aurivillius phases by V. I. Voronkova; E. P. Kharitonova; O. G. Rudnitskaya (183-191).
A continuous series of Bi2W1 − x Mo x O6 solid solutions between the n = 1 Aurivillius phases Bi2WO6 and Bi2MoO6 with a polar orthorhombic structure (γ-phase) have been prepared by solid-state reactions at 850 (0 < x ≤ 0.3) and 530–640°C (0.3 ≤ x < 1), and their thermal and electrical properties have been studied throughout their stability region, between room temperature and 960°C, with the aim of gaining detailed insight into their polymorphism. The results demonstrate that the tungsten-rich (0 ≤ x ≤ 0.2) materials undergo a ferroelectric and a reconstructive phase transition like bismuth tungstate, Bi2WO6. The temperatures of both transitions decrease with increasing molybdenum content. The molybdenum-rich materials in the composition range 0.9 ≤ x ≤ 1 are similar in properties to bismuth molybdate, Bi2MoO6. In the composition range 0.3 ≤ x ≤ 0.8, neither ferroelectric nor reconstructive phase transition was detected.

The metal stoichiometry ranges of the Ln2 − x Mn x O3 ± δ (Ln = Y, Ho, Er) manganites have been determined using X-ray diffraction analysis of ceramic samples prepared by reacting oxide mixtures in air at temperatures from 900 to 1400°C. The results are represented as partial phase diagrams of the Ln-Mn-O systems in air. Comparison of the phase diagrams demonstrates that the phase boundaries of the manganites are determined not only by the effective cation radius of the rare-earth metal. The solubilities of the binary oxides Y2O3, Ho2O3, and Mn3O4 in yttrium and holmium manganites increase with temperature, with significant quantitative distinctions. The Er2O3 and Mn3O4 solubilities in erbium manganite remain unchanged over the entire temperature range studied. The LnMn2O5 solubility in LnMnO3 ± δ is an intricate function of temperature. We analyze the possible causes of the Ln2O3, Mn3O4, and LnMn2O5 solubility in the LnMnO3 ± δ (Ln = Y, Ho, Er) manganites.

Effect of A-site vacancies on the magnetoresistive Effect in La1 − x − y Ca x Na y MnO3 ± δ by O. Z. Yanchevskii; D. A. Durilin; D. M. Polishchuk; A. I. Tovstolytkin; A. G. Belous (196-203).
We have studied the effect of composition and heat-treatment conditions on the structural and transport properties of La1 − x − y Ca x Na y MnO3 ± δ solid solutions. The materials obtained offer a magnetoresistance of about 48% in a magnetic field of 1.2 MA/m.

Properties of Mg(Fe0.8Ga0.2)2O4 + δ ceramics and films by A. I. Stognij; A. V. Trukhanov; V. A. Ketsko; G. D. Nipan (204-207).
The magnetic and semiconducting properties of homogeneous ceramic samples of the diluted magnetic semiconductor Mg(Fe0.8Ga0.2)2O4 + δ have been studied as functions of temperature and magnetic field. The results suggest that spinel phases with this combination of cations are potential candidates for spintronic applications. Using ion-beam sputtering of a ceramic Mg(Fe0.8Ga0.2)2O4 + δ target, we obtained chemically homogeneous films similar in properties to the source material.

K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9) perovskite compounds by E. Yu. Peresh; V. I. Sidei; O. V. Zubaka; I. P. Stercho (208-212).
We systematize available experimental data on the crystal structure of the ternary halides K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9), analyze the general trends in the properties of their single crystals, and examine the key features of the physicochemical interaction in related systems.