Inorganic Materials (v.47, #6)
Structurally perfect silicon layers produced on sapphire by oxygen ion implantation by V. M. Vorotyntsev; E. L. Shobolov; V. A. Gerasimov (571-574).
We demonstrate that the structural perfection of silicon layers on sapphire can be improved through high-temperature solid-state recrystallization after preamorphization of the most imperfect silicon layer near the silicon/sapphire interface by high-energy oxygen ions, followed by high-temperature recrystallization in an inert atmosphere.
IR spectroscopic determination of the refractive index and thickness of hydrogenated silicon layers by S. P. Timoshenkov; V. P. Pelipas; B. M. Simonov; O. M. Britkov; V. V. Kalugin (575-578).
IR spectroscopic techniques widely used to determine the thickness and refractive index of layers and thin films of various materials are adapted for determining those of hydrogenated silicon layers. Based on a literature analysis, three formulas are chosen which enable the refractive index and thickness of such layers to be determined from reflection and transmission spectra. The formulas are applicable, with some restrictions, to other samples in the form of relatively transparent layers (films) on transparent substrates. Experimental data are presented that illustrate the use of the formulas.
Solid-state phase equilibria and thermodynamic properties of ternary compounds in the Tl-Sb-S system by Ya. I. Jafarov; I. M. Babanly; S. Z. Imamalieva; M. B. Babanly (579-582).
The Tl-Sb-S system has been studied in the composition region Tl2S-Sb2S3-S using differential thermal analysis, X-ray diffraction, and emf measurements on thallium concentration cells at temperatures from 300 to 390 K, and the 300-K isothermal section of its phase diagram has been mapped out. The existence of the ternary compounds TlSb5S8, TlSb3S5, TlSbS3, TlSbS2, Tl3SbS4, and Tl3SbS3 has been confirmed, and the position of the phase fields involving these compounds has been accurately determined. Using emf data, we have evaluated the partial molar functions ( $Delta ar G$ , $Delta ar H$ , $Delta ar S$ ) of the thallium in the alloys studied, the standard thermodynamic functions of formation of the ternary compounds, and their standard entropies.
Composition range and thermodynamic properties of Tl5Se2Br-based solid solutions by D. M. Babanly (583-587).
The equilibrium subsolidus phase diagram of the TlBr-Tl2Se-TlSe system has been mapped out using X-ray diffraction analysis and emf measurements on thallium concentration cells. Tl5Se2Br has been shown to have a broad homogeneity region. The emf results are used to evaluate the relative partial thermodynamic functions of the thallium in the alloys studied and the standard integral thermodynamic functions (ΔG 0(298 K), ΔH 0(298 K), S 0(298 K)) of the Tl5Se2Br-based solid solutions.
Luminescence properties of CdTe-based solid solutions in the CdTe-Ga2Te3 and CdTe-GaTe systems by I. N. Odin; M. V. Chukichev; M. V. Gapanovich; G. F. Novikov (588-591).
The extent of the cadmium-telluride-based solid solution along the CdTe-GaTe join at 737°C has been determined from the composition dependence of its unit-cell parameter. The cathodoluminescence spectra of CdTe-based solid solutions in the CdTe-GaTe and CdTe-Ga2Te3 systems have been measured. The 895-nm band observed in the 78-K spectrum of the Ga2Te3-containing solid solution is due to the [Ga Cd · V Cd] radiative defect complex. The spectra of the CdTe-GaTe solid solutions seem to show a superposition of two lines close in position, attributable to the [Ga Cd · V Cd] and [Ga Cd ′ V Te] defect complexes.
Structure and composition of hafnium diboride films by A. A. Goncharov; A. V. Agulov; V. A. Stupak; V. V. Petukhov (592-596).
The structure and composition of hafnium diboride films grown by rf magnetron sputtering have been studied by X-ray diffraction and secondary ion mass spectrometry. The results demonstrate that the key parameters of the process are the bias-dependent energy of incident particles and the substrate temperature. The substrate microstructure may also have a significant effect on the film growth process, when the first two factors are negligible. We have examined the microstructure effect on the elemental composition of the films. The secondary ion emission coefficient for boron in highly textured films is shown to be 20–25% above that in the powder target. At the same time, clustered amorphous films have a reduced boron content: B/Hf < 2.
Preparation of finely dispersed nanographite by Yu. V. Ioni; S. V. Tkachev; N. A. Bulychev; S. P. Gubin (597-602).
We have developed a convenient single-step method for producing stable nanographite dispersions from natural graphite in various solvents using high-power sonication. Nanographite dispersions in water are shown to be stable for several weeks, and aqueous nanographite dispersions containing a surfactant are stable for several months. Nanographite samples prepared from aqueous nanographite dispersions have been characterized by various physicochemical techniques (including X-ray diffraction and Raman spectroscopy). Interference microscopy, transmission and scanning electron microscopy, and atomic force microscopy have been used to examine the morphology and determine the size of nanographite particles. The nanographite platelets are 300–500 nm in lateral size and 20–40 nm in thickness, which corresponds to 30–50 graphene layers.
Zirconia-modified exfoliated graphite by I. M. Afanasov; G. Van Tendeloo (603-608).
Zirconia has been incorporated into exfoliated graphite (EG) through the anodic polarization in the natural graphite-ZrO(NO3)2-HNO3-H2O system, followed by flash heating. The thermal properties of the oxidized graphites employed as precursors to EG have been studied by thermogravimetry in combination with differential scanning calorimetry, and the distribution of ZrO2 particles in the EG has been assessed by scanning and transmission electron microscopy. Conditions are described for the preparation of EG with bulk densities in the range 1.3–4.7 g/l and ZrO2 contents in the range 4–34 wt %.
Surface modification of carbon fibers with nitric acid solutions by A. S. Tikhomirov; N. E. Sorokina; V. V. Avdeev (609-613).
We have studied the surface modification of carbonized carbon fibers with nitric acid solutions, compared the effects of 60 and 98% HNO3, and examined the influence of the anodic polarization of the fiber for surface functionalization. Unmodified and surface-modified carbon fibers have been characterized by a variety of physicochemical techniques.
Transmission electron microscopic study of multiwalled carbon nanotubes by E. M. Baitinger; N. A. Vekesser; I. N. Kovalev; O. V. Slobodchikov; V. V. Viktorov (614-617).
Multiwalled carbon nanotubes have been studied by transmission electron microscopy, selectedarea electron diffraction, and transmission electron energy loss spectroscopy (EELS). The results demonstrate that the walls of carbon nanotubes consist of graphite-like layers with an increased interlayer spacing compared to graphite. The local density distribution in the CNTs has been evaluated from EELS scans over the nanotubes.
Synthesis and electrocatalytic activity of platinum nanoparticle/carbon nanotube composites by O. Yu. Ivanshina; M. E. Tamm; E. V. Gerasimova; M. P. Kochugaeva; M. N. Kirikova; S. V. Savilov; L. V. Yashina (618-625).
Pt/CNT nanocomposite materials with an average platinum particle size of 3–5 nm and platinum content of 13–28 wt % have been prepared by reducing chloroplatinic acid, H2PtCl6, in the presence of conical carbon nanotubes. The effect of synthesis conditions on the average platinum particle size, total platinum content, and surface composition of the nanocomposites has been studied using X-ray photoelectron spectroscopy, IR spectroscopy, electron microscopy, X-ray diffraction, and thermogravimetry. The materials have been tested as catalysts for hydrogen oxidation and oxygen reduction. Their performance has been assessed by cyclic and steady-state voltammetric techniques. The structure and composition effects on the electrocatalytic properties of the nanocomposites are discussed.
Preparation of nanomaterials from metalorganic compounds of tungsten and molybdenum by A. G. Ermilov; E. V. Bogatyreva; T. A. Sviridova (626-632).
We have studied the sequence of phase transformations of the thermolysis products of tungsten- and molybdenum-containing metalorganic compounds and examined the influence of various phases on the formation of nanocrystalline carbide materials and the possibility of controlling the particle size of forming phases. We have obtained WC and WC/Co materials ranging in crystallite size from 13 to 26 nm and high-porosity (up to 80%) molybdenum, nickel-molybdenum, and titanium-molybdenum materials ranging in strength from 5 to 26 MPa.
Evaluation of the mineralogical composition of gabbro rocks from chemical analysis data by I. Z. Babievskaya; N. F. Drobot; S. V. Fomichev; V. A. Krenev (633-636).
A procedure proposed earlier for calculating the mineralogical composition of basalts from chemical analysis data has been developed further. We have calculated the mineralogical compositions of various gabbro occurrences in Russia. The calculation results correlate well with earlier data on the mineralogical composition of the rocks in these occurrences.
Structural and thermoelectric properties of Zr1 − x Er x NiSn solid solutions by Yu. V. Stadnyk; A. M. Goryn’; V. V. Romaka; Yu. K. Gorelenko; L. P. Romaka; N. A. Mel’nichenko (637-644).
We have studied the electronic and crystal structures and temperature-dependent resistivity and thermopower of Zr1 − x Er x NiSn (x = 0–0.20) substitutional semiconductor solid solutions (so-called half-Heusler alloys) in the temperature range 80–380 K. Heavily erbium doped semiconductors with the MgAgAs structure are described in terms of an amorphous semiconductor model. The erbium atoms in Zr1 − x Er x NiSn are shown to act as acceptors. Density of states calculation results for the Zr1 − x Er x NiSn alloys are consistent with experimental data.
Ultrapurification of archaeological lead by R. S. Boiko; V. D. Virich; F. A. Danevich; T. I. Dovbush; G. P. Kovtun; S. S. Nagornyi; S. Nisi; A. I. Samchuk; D. A. Solopikhin; A. P. Shcherban’ (645-648).
Based on purification efficiency calculations for lead distillation, we developed a combined process for the ultrapurification of archaeological lead. We obtained pilot amounts of high-purity archaeological lead and PbO with the following contents of detrimental impurities: U, <2 ppb; Th, <1 ppb; Ni, Cu, Fe, Si, Ti, Mg, Al, Mn, Cr, V, Co, < 0.1 ppm; K, Ca, Zn, Cd, Ag, Sb, < 1 ppm. Lead of such purity can be used in low-background experiments as a protective shield material and in the growth of low-background PbWO4 and PbMoO4 scintillator crystals. From an isotope ratio, we were able to identify the origin of the archaeological lead.
Growth and Raman spectra of doped ZnO single crystals by L. N. Dem’yanets; R. M. Zakalyukin; B. N. Mavrin (649-653).
ZnO:M n+(M n+ = Cd2+, Co2+, Ni2+, Sc3+, In3+, Ga3+, Fe3+, Te4+, V5+) single crystals have been grown under hydrothermal conditions in ZnO-M x O y -KOH-LiOH-H2O systems, and their Raman spectra have been measured under visible (514.5 nm) and near-IR (1064 nm) excitation. The anomalous band between 500 and 600 cm−1 in the Raman spectra of ZnO:Mn2+ has A 1 symmetry and is due to vibrations involving Mn2+.
Optimal algorithm for constructing the embedded atom method potential for liquid metals by D. K. Belashchenko (654-659).
An optimal algorithm has been developed for calculating the embedding potential in the embedded atom method (EAM) with the aim of describing not only the temperature-dependent density of a liquid metal but also its energy up to its critical temperature. The algorithm is based on the unification of the form of the potential and calculation of its parameters from known density and energy data for the liquid metal. The basis of the algorithm is the use of least squares fitting of the pressure and energy in molecular dynamics simulations to data for a series of states of the liquid along an isobar. To describe liquid potassium, the pair contribution to the potential is represented by a power series in interparticle distance. Data on the properties of potassium at 343, 473, 723, 1000, 1500, 2000, and 2200 K were used. The embedding potential was expanded in terms of 1 − ρ, where ρ is the effective electron density in the EAM. In least squares fitting, fifteen equations were included: eight for the energy and seven for the pressure. The number of unknown coefficients was seven. Iterative calculations allow one to find optimal expansion coefficients and construct equilibrium models through molecular dynamics simulations. It is shown that the discrepancy in energy between simulations and the real metal at high temperatures can be eliminated by taking the electron excitation energy into consideration. The difference between the actual energy of a metal and the energy obtained in EAM simulations is very close to the contribution of the electron heat capacity.
Preparation of eutectics by directional solidification of quaternary melts by V. I. Kosyakov; E. F. Sinyakova (660-664).
This paper presents a theoretical analysis of quasi-equilibrium directional solidification of a quaternary melt. We consider the variation in the composition of phases in each portion of the sample and changes in phase composition for various types of phase reactions. The results indicate that the melt trajectory during directional solidification may belong only to those phase diagram elements corresponding to the crystallization of binary, ternary, or quaternary eutectics or single-phase crystallization regions. Using the directional solidification of a melt with the composition (at %) Cu 29.37, Ni 17.72, Fe 5.91, and S 47.00, we obtained a sample consisting of zones with different phase compositions: [Ni z (Fe,Cu)1 − z ]S1 ± δ single-phase zone, [Ni z (Fe,Cu)1 − z ]S1 ± δ + Cu5 ± x Fe1 ± x S4 binary eutectic mixture, and [Ni z (Fe,Cu)1 − z ]S1 ± δ + Cu5 ± x Fe1 ± x S4 + (Ni z Fe1 − z )S2 ternary eutectic mixture. In going from one zone to another, new phases appear and the average composition of the sample changes sharply, whereas the compositions of the melt and solid solution present in neighboring zones vary continuously. These results are consistent with theoretical concepts.
Low-loss, high-purity (TeO2)0.75(WO3)0.25 glass by A. N. Moiseev; V. V. Dorofeev; A. V. Chilyasov; V. G. Pimenov; T. V. Kotereva; I. A. Kraev; L. A. Ketkova; A. F. Kosolapov; V. G. Plotnichenko; V. V. Koltashev (665-669).
By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO2)0.75(WO3)0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 102 cm−3, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm−1. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.
Synthesis and properties of magnetoresistive (La,Sr)MnO3-based glass-ceramic borate-matrix composites by A. V. Vasiliev; A. A. Eliseev; P. E. Kazin; Yu. D. Tret’yakov (670-673).
Magnetic glass-ceramic borate-matrix composites containing micron-sized lanthanum strontium manganite grains have been prepared by ceramming amorphous La2O3-SrO-MnO x -B2O3 materials at 800 and 900°C. The glass-ceramics had a magnetization of up to 48.7 A m2/kg in a magnetic field of 400 kA/m. Their relative magnetoresistance reached 6.2% at 290 K in a magnetic field of 80 kA/m and 16% at 77 K in a field of 160 kA/m.
Sintering mechanism for high-density NZP ceramics by M. V. Sukhanov; V. I. Pet’kov; D. V. Firsov (674-678).
We have studied the shrinkage kinetics and mechanism of NaZr2(PO4)3 containing inorganic additives. The sintering of NaZr2(PO4)3 containing ZnO microadditives is shown to follow a liquid-phase mechanism. Effective sintering aids include oxides of metals in the oxidation states 2+ and 3+ that are capable of reacting with sodium zirconium phosphate to form solid solutions. Ceramics having a relative density of 96–99% and isostructural with NaZr2(PO4)3 can be prepared by adding 0.75–2.0 wt % ZnO as a sintering aid capable of influencing the structure of grain boundaries in ceramic materials, pressing green bodies at 200–300 MPa, and sintering them at 1000–1100°C for 7–15 h.
Phase composition, microstructure, and properties of Na1 − y NbO3 − y/2 ceramics by O. Yu. Kravchenko; G. G. Gadzhiev; Z. M. Omarov; L. A. Reznichenko; Kh. Kh. Abdullaev; O. N. Razumovskaya; L. A. Shilkina; V. D. Komarov; I. A. Verbenko (679-685).
We have studied the phase composition, microstructure, and dielectric and thermophysical properties of Na1 − y NbO3 − y/2 (0 ≤ y ≤ 0.20) ceramics and identified a complicated sequence of phase transformations within the homogeneity range of sodium niobate (y ≤ 0.10), accompanied by anomalous variations in its physical properties. At low y values, discontinuous secondary recrystallization occurs. We conclude that dielectric effects above the Curie temperature are related to the electrical conductivity of the material and that those at low temperatures are governed by the motion of domain walls and interfaces. The temperature-dependent structural, dielectric, and thermophysical properties of the materials studied are shown to correlate.
Microstructure and Young’s modulus of high-pressure Li x Na1 − x TayNb1 − y O3 ceramics by M. N. Palatnikov; O. B. Shcherbina; V. V. Efremov; N. V. Sidorov; A. N. Salak (686-689).
The microstructure and elastic properties of ceramic samples of high-pressure Li x Na1 − x Ta y Nb1 − y O3 perovskite solid solutions have been studied for the first time in relation to their composition and the synthesis temperature. The results demonstrate that, with increasing sintering temperature, the Young’s modulus of the Li0.17Na0.83Ta y Nb1 − y O3 solid solutions decreases, which can be understood in terms of the recrystallization behavior of the disordered solid solutions under high-pressure synthesis conditions.