Inorganic Materials (v.51, #9)
Key features of the phase size effect in a metal–silicon disperse system during nanowhisker growth by V. A. Nebol’sin; A. I. Dunaev; S. S. Shmakova; A. Yu. Vorob’ev; E. V. Bogdanovich (855-861).
We demonstrate that Si nanowhiskers with the participation of Au and Sn nanoparticles form at substrate temperatures of 623 and 498 K, which is below the eutectic temperature in the binary systems Au–Si and Sn–Si. With a decrease in the characteristic size (an increase in the dispersity) of liquid catalyst particles, the phase equilibrium lines in the M–Si phase diagrams shift to lower limiting solute concentrations. The eutectic temperature in the Au–Si system decreases with an increase in the dispersity of the catalyst particles.
Modeling of the influence of defects on the electronic structure of silicon nanoclusters by E. V. Sokolenko (862-869).
The total and partial electron densities of states of defect-free and imperfect silicon clusters have been calculated by a semiempirical method. The local centers produced in the band gap of silicon by doping have been shown to be determined predominantly by the intrinsic states of silicon.
Spatial structure and electron energy spectrum of HfGe n – (n = 6–20) clusters by N. A. Borshch; S. I. Kurganskii (870-876).
This paper presents spatial structure optimization results and calculated electronic spectra for HfGe n – (n = 6–20) anion clusters. Comparison of the calculation results and available experimental data makes it possible to identify the most likely spatial structures of clusters detected in experiments. Cage structures of the clusters, with an encapsulated hafnium atom, are stable for n ≥ 12. The clusters with n ≥ 12, 14, 15, and 18 are “magic” in the series of germanium–hafnium anion clusters.
T–x phase diagram and electrical conductivity of solid solutions in the TlInSe2–TlGaTe2 system by N. A. Alieva; A. I. Najafov; T. G. Mamedov (877-883).
Using detailed physicochemical characterization results, we have mapped out the T–x phase diagram of the TlInSe2–TlGaTe2 system. The system has been shown to have eutectic phase relations, with limited solid solubilities of its constituent components. The extent of the TlInSe2-based solid solution is 30.0 mol %, and that of the TlGaTe2-based solid solution is 25.0 mol %. The eutectic is located at 55.0 mol % TlGaTe2 and melts at a temperature of 973 K. The electrical conductivity of crystalline samples of the solid solutions has been measured as a function of temperature.
Optical and electrical properties of ZnSe films grown by hydrochemical deposition by E. M. Sofronova; V. V. Starikov; D. S. Sofronov; E. I. Kostenyukova; A. M. Lebedynskiy; P. V. Mateychenko (884-890).
Zinc selenide films have been produced by hydrochemical deposition through reaction between zinc oxide and selenium in the presence of hydrazine and sodium sulfite in an alkaline solution. Independent of deposition conditions, the films consist of sphalerite ZnSe and have a band gap in the range 2.6–2.7 eV. With increasing sodium sulfite concentration in solution, the average grain size increases to 0.75 μm (at Zn2+:SO 3 2− = 1: 10).
Thermal decomposition of vanadyl acetylacetonate by R. N. Nenashev; N. E. Mordvinova; V. P. Zlomanov; V. L. Kuznetsov (891-896).
Using thermogravimetry, differential scanning calorimetry, X-ray diffraction, mass spectrometry, and Fourier transform IR spectroscopy, we have determined the composition of VO(acac)2 thermal decomposition products and gained insight into the bond breaking sequence in this compound. A two-step annealing procedure has been proposed to ensure control over VO(acac)2 to VO2 conversion processes without changing the oxidation state of vanadium in the preparation of VO2 films by a sol–gel process.
Synthesis of thin silicon carbonitride films from hexamethyldisilazane in an inductively coupled plasma reactor by Yu. M. Rumyantsev; M. N. Chagin; M. L. Kosinova; F. A. Kuznetsov (897-902).
SiC x N y :H films have been grown by inductively coupled plasma chemical vapor deposition via hexamethyldisilazane decomposition at substrate temperatures from 50 to 450°C and rf powers from 100 to 500 W. The growth rate and physicochemical properties of the films (their elemental composition, refractive index, optical band gap, and optical transmittance) have been shown to be weak functions of process conditions. The process offers high stability, and the films are uniform in thickness over the entire substrate surface. The SiC x N y :H films have a polymer-like structure, high transmission, a refractive index near 2.0, and hardness of 8–9 GPa, which is typical of films produced from hexamethyldisilazane by low-temperature plasma deposition processes.
Stability of the solid–liquid interface under constitutional undercooling in the crystal growth of TlCl–TlBr and TlBr–TlI solid solutions by P. P. Fedorov; E. V. Chernova (903-907).
Using phase diagram data for the TlCl–TlBr and TlBr–TlI systems, we have calculated the stability functions of the solid–liquid interface under constitutional undercooling for solid solutions of these systems. The curves thus obtained are typical of systems containing continuous series of solid solutions and having minima in their liquidus and solidus curves. The curves can be used to evaluate technologically important process parameters necessary for the growth of crystals of high optical quality.
Magnetic microstructure of Fe3–x Al x O4 superparamagnetic magnetites by V. V. Korovushkin; G. A. Frolov; I. V. Trunina; M. N. Shipko; V. G. Kostishin (908-912).
We have studied superparamagnetic magnetites with various isomorphous aluminum contents, identified the cation distribution in their structure, and demonstrated nonlinear variations in their unit cell parameter and density and also a nonlinear variation in their magnetization, with a maximum at an aluminum content of 3.6% (x = 0.3). The conclusion has been made that the properties of the superparamagnetic magnetites with isomorphous aluminum can be used in optimizing the composition of nanocomposite materials with tailored magnetic properties.
Effect of growth conditions on the optical homogeneity of KTiOPO4 crystals by S. A. Guretskii; I. M. Kolesova; A. V. Kravtsov; A. I. Mit’kovets; E. L. Trukhanova; A. A. Linkevich (913-915).
We have optimized the growth of KTiOPO4 (KTP) crystals by a modified Czochralski technique. It has been shown that, as the crystal–melt interface shifts to a larger depth owing to more effective forced melt convection, the optical homogeneity of the crystals improves.
Synthesis of powders of solid solutions between barium, strontium, and lead titanates and zirconates by V. I. Ivanenko; E. N. Yakubovich; S. V. Vladimirova; E. P. Lokshin (916-922).
We have studied the crystallization conditions of single-phase nanopowders of solid solutions between mixed oxides based on titanium(IV), zirconium(IV), and divalent metals (barium, strontium, and lead). Our results demonstrate that hydrous ammonium-containing oxohydroxo precursors to titanium(IV) and zirconium(IV) have considerable potential for use in the synthesis of such materials.
Ion exchange synthesis of lanthanum zirconate by E. A. Bovina; D. V. Tarasova; F. Kh. Chibirova (923-927).
We have studied the formation of lanthanum zirconate through ion exchange in aqueous solutions of lanthanum and zirconyl chlorides and the AV-17-8 anion exchanger. The results demonstrate that the ion exchange leads to the formation of hydrosol of an amorphous lanthanum zirconium compound in the form of spherical particles about 4 nm in diameter. Heat treatment of the hydrosol at 700°C leads to crystallization of lanthanum zirconate with the fluorite structure, which transforms into the pyrochlore structure at higher temperatures.
Determination of oxygen nonstoichiometry in La0.7Sr0.3MnO3–δ on oxide substrates by structural refractometry by A. A. Tikhii; S. V. Kara-Murza; Yu. M. Nikolaenko; V. A. Gritskikh; N. V. Korchikova; I. V. Zhikharev (928-932).
A semiempirical method has been proposed for evaluating oxygen deficiency δ in La0.7Sr0.3MnO3–δ (LSMO) films on oxide substrates by comparing a measured refractive index with the refractive index calculated as a function of δ.
Synthesis of cadmium sulfide CdS nanoparticles in a silicate glass matrix by Yu. V. Kuznetsova; A. A. Rempel (933-938).
Cadmium sulfide (CdS) nanoparticles have been synthesized in a silicate glass matrix containing ZnO additions. Annealing conditions in the temperature range of the glass transition have been shown to determine the final size of the CdS nanoparticles. The particle size, in turn, influences the optical properties, color, and fundamental absorption edge of the glass. The present results demonstrate that, with increasing CdS nanoparticle size, the absorption edge of the glass experiences a redshift from 330 to 530 nm and its luminescence peak shifts from 450 to 750 nm.
X-Ray fluorescence analysis of Ge–As–Se glasses using X-Ray and electron-beam excitation by G. A. Bordovsky; A. V. Marchenko; P. P. Seregin; K. U. Bobokhuzhaev (939-943).
The quantitative content of germanium, arsenic, and selenium in As1–x Se x , Ge1–x Se x , and Ge1–x–y As y Se x (As y (Ge1–z Se z )1–y ) glassy alloys has been determined by X-ray fluorescence analysis with fluorescence excitation by bremsstrahlung X-rays and an electron beam. The use of these techniques has made it possible to determine the quantitative composition of the glasses (x, y, and z) with an accuracy of ±0.0002 in a surface layer 0.1 mm (under X-ray excitation) to 0.1 μm (under electron beam excitation) in thickness.
Synthesis, structure, and properties of Ca3Co3.85M0.15O9 + δ (M = Ti–Zn, Mo, W, Pb, Bi) layered thermoelectrics by A. I. Klyndyuk; I. V. Matsukevich (944-950).
We have prepared Ca3Co3.85M0.15O9 + δ (M = Ti–Zn, Mo, W, Pb, Bi) solid solutions, investigated their crystal structure and microstructure, assessed their thermal stability in air, and measured their thermal expansion, electrical conductivity, and thermoelectric power in air at temperatures from 300 to 1100 K. The results demonstrate that the Ca3Co3.85M0.15O9 + δ cobaltites are p-type semiconductors and that their unitcell parameters decrease with an increase in the number of d electrons in the 3d transition metal ion and with an increase in the average oxidation state of the cobalt. Their thermoelectric power increases with increasing temperature, reaching the highest value in the Ca3Co3.85Pb0.15O9 + δ solid solution: 380 μV/K at a temperature of 1100 K. The Ca3Co3.85Bi0.15O9 + δ solid solution has the largest thermoelectric power factor among the materials studied, 206 μW/(m K2) at a temperature of 1100 K, which is twice the power factor of the unsubstituted calcium cobaltite Ca3Co4O9 + δ.
Studying structure and determining permeability of materials based on X-Ray microtomography data (using porous ceramics as an example) by K. M. Gerke; D. V. Korost; R. V. Vasilyev; M. V. Karsanina; V. P. Tarasovskii (951-957).
Modern noninvasive methods for probing the three-dimensional structure of materials, such as X-ray tomography, make it possible not only to obtain precise data on the structure of a sample but also to use them for assessing effective properties of the material by numerical methods. We have studied the pore structure of three samples of permeable porous ceramics by X-ray microtomography and numerically determined the permeability by solving the Stokes equation in the three-dimensional geometry of the pore structure. The data thus obtained are in excellent agreement with results of laboratory measurements. Morphological analysis of the pore structure (pore size distribution) allowed us to explain the results obtained for three samples of ceramics produced from granules of various sizes and shapes.
Thermodynamic analysis of the self-propagating high-temperature synthesis of scandium and lutetium oxides nanopowders by E. M. Gavrishchuk; O. N. Klyusik; A. M. Kut’in; D. A. Permin (958-963).
Using the method of valence states of atoms in a chemical compound, we have calculated the standard enthalpies of formation for the reaction systems lutetium nitrate–lutetium acetate, scandium nitrate–scandium acetate, scandium nitrate–scandium acetylacetonate, and scandium nitrate–glycine. To optimize the composition of precursors for the self-propagating high-temperature synthesis of Sc2O3 and Lu2O3 nanopowders, we have analyzed the influence of the nature of the fuel and the oxidant to fuel ratio in the starting mixture on the adiabatic temperature and thermodynamically substantiated composition of reaction products.