Inorganic Materials (v.45, #2)
Crystal structures of CaO-Al2O3-SiO2-H2O zeolites by T. N. Kol’tsova (99-115).
Analysis of the structures of CaO-Al2O3-SiO2-H2O zeolites demonstrates that Ca is always bonded to intraframework oxygens that link Si to Al if these atoms occupy different sites. The SiO2:“CaAl2O4” ratio plays an important role in zeolite formation. It is inappropriate to analyze the structural framework of zeolites with no consideration for the calcium-water component.
Temperature effect on the photoluminescence intensity and Eu2+ excited state lifetime in EuGa2S4 and EuGa2S4:Er3+ by A. N. Georgobiani; B. G. Tagiev; O. B. Tagiev; S. A. Abushov; F. A. Kazymova; T. Sh. Gashimova; Xu Xurong (116-122).
The photoluminescence (PL) spectra and Eu2+ excited state lifetime of EuGa2S4 and EuGa2S4:Er3+ have been studied in the range 78–500 K. The spectra show a band at 545 nm, due to the 4f 65d → 4f 7(8 S 7/2) transition. With increasing temperature, the full width at half maximum Γ(T) of the PL band of EuGa2S4 and EuGa2S4:Er3+ crystals increases from 0.15 to 0.22 and from 0.13 to 0.19 eV, respectively. Over the entire temperature range studied, Γ(T) is a linear function of T 1/2. The 545-nm emission intensity and Eu2+ excited state lifetime in EuGa2S4 and EuGa2S4:Er3+ vary exponentially with temperature. The luminescence quenching energies evaluated from the Arrhenius plots of I(103/T) and τ(103/T) coincide (0.10 eV) within the error of determination.
Extruded thermoelectric materials based on Bi2Te3-Bi2Se3 solid solutions by L. D. Ivanova; L. I. Petrova; Yu. V. Granatkina; V. S. Zemskov; O. B. Sokolov; S. Ya. Skipidarov; N. I. Duvankov (123-128).
Extruded n-type materials based on Bi2Te3-Bi2Se3 alloys containing 6 to 40 mol % Bi2Se3 have been investigated using microstructural analysis and thermoelectric measurements at room temperature and in the range 100–400 K. Their electrical properties have been compared to those of single-crystal analogs. Compositions have been found at which the extruded materials offer the highest thermoelectric performance in different temperature ranges.
Thermodynamic properties and homogeneity regions of Tl6SCl4 and Tl5Se2Cl by G. M. Guseinov; D. M. Babanly; F. M. Sadygov; M. B. Babanly (129-134).
In this activity system Tl-Tl2X-X (X = S, Se)are studied using emf measurements of concentration chains relative thallic electrode. The solid phase diagrams of these systems are clarified, homogeneity areas of the compounds Tl6SCl4 and Tl5Se2Cl are determined. On the basis of emf measurement results, relative partial molar functions of thallium in alloys and standard integral thermodynamic functions (ΔG 0(298 K), ΔH 0 (298 K), ΔS 0 (298 K)) of the ternary compounds Tl6SCl4 and Tl5Se2 Cl and phases of variable composition based on the latter are calculated.
Porous carbon materials based on exfoliated graphite by I. M. Afanasov; O. N. Shornikova; I. I. Vlasov; E. V. Kogan; A. N. Seleznev; V. V. Avdeev (135-139).
We have prepared low-density composites of exfoliated graphite and coke. The distribution of the coke particles in the composites and their structural perfection have been studied by scanning electron microscopy and Raman spectroscopy. The specific surface area of the materials have been determined as a function of burnoff value using low-temperature nitrogen adsorption measurements. The results demonstrate that the highest specific surface (400 m2/g) is offered by the composite with a burnoff value of 35%, which contains micropores of 1.4-nm radius.
Tungsten thin-film deposition on a silicon wafer: The formation of silicides at W-Si interface by S. V. Plyushcheva; G. M. Mikhailov; L. G. Shabel’nikov; S. Yu. Shapoval (140-144).
The interphase boundary formed in the process of tungsten thin-film deposition on a silicon wafer is investigated. These films are produced via (1) a CVD technique relying on hydrogen reduction of tungsten hexafluoride, (2) the same technique supplemented with plasmochemical action, and (3) magnetron deposition used for comparison purposes. It is shown that a nanometer tungsten silicide W5Si3 layer is formed at the tungsten-silicon interface only under gas-phase deposition. The effect of annealing on the specimen composition and surface resistance is investigated. It is shown that the formation and growth of a silicide WSi2 layer commences at 700°C for CVD films and at above 750°C for films obtained with plasmochemical deposition; this results in a drastic increase in their electrical resistance. Under optimal conditions, tungsten films of 8 × 10 −6 Ω cm resistivity are produced.
Composition and structure of the oxidation products of Mo-Pt alloys by S. N. Nesterenko; L. L. Meshkov; P. A. Zosimova; N. S. Nesterenko (145-150).
A novel approach has been proposed for producing model catalysts via oxidation of molybdenum- platinum alloys. The effect of alloy composition on the structure and morphology of the oxidation products has been studied, and heat-treatment conditions have been optimized to achieve a uniform distribution of fine platinum particles in the resulting molybdenum oxide.
Properties of amorphous silica generated by the fluoride method by L. P. Demyanova; A. Tressaud; J. -Y. Buzare; C. Martineau; C. Legein; Yu. N. Malovitski; V. S. Rimkevich (151-156).
A study of amorphous silica generated from mineral material by the fluoride method and by different procedures of analysis, i.e., x-ray diffraction, x-ray fluorescence, IR spectroscopy, and nuclear magnetic resonance, is reported. Direct fluoridation of amorphous silica was performed by using gaseous F2 and different conditions of processing, which allowed us to assess the reduction of impurities in amorphous silica and to show that (NH4)(Si(NH3)F5) was not present in the sample as an impurity.
Obtaining nanodisperse powders of neodymium-activated yttrium aluminum garnet by self-propagating high-temperature synthesis method by S. S. Balabanov; E. M. Gavrishchuk; V. V. Drobotenko; A. M. Kut’in; V. S. Polyakov; T. I. Storozheva (157-161).
Nanosized slightly agglomerated powders of neodymium-activated yttrium aluminum garnet (YAG:Nd) were obtained by a self-propagating high-temperature synthesis method. An increase in content of reducing substituents in metal-organic complexes as compared to oxidizing substituents leads to an increase in average size of the forming grains from 23 to 70 nm; thereupon, a decrease in powder agglomeration degree is observed. Firing of x-ray amorphous powders results in formation of polycrystalline YAG:Nd without forming intermediate phases.
Correlations between admixtures and color centers created upon irradiation of natural beryl crystals by E. M. Ibragimova; N. M. Mukhamedshina; A. Kh. Islamov (162-167).
Colorless samples of natural beryl which are of little value were irradiated by a neutron flux from a reactor, gamma rays from a shutdown reactor, and gamma rays from a 60Co source to impart gem color to them. As a result of selection of irradiation conditions for samples of pale aquamarines and emeralds, different sample colors were obtained. It was shown using neutron activation and x-ray radiometric methods that the acquired colors and hues of beryl crystals depend on the presence and content of Ca, Sc, Ti, V, Fe, and Co admixtures. It was established from optical absorption, reflection, and luminescence spectra that the induced color centers are related to replacement of cation site of structure by impurities.
Synthesis of BaCO3 with different morphologies using amphiphilic PS-PAA copolymer as medium by Dalai Jin; Xiaojing Yu; Linhai Yue; Ping Sun (168-172).
Barium carbonate (BaCO3) with multiple morphologies were synthesized using BaCl2 and Na2CO3 in the presence of a copolymer of poly(styrene) (PS) and poly(acrylic acid) (PAA), an amphiphilic copolymer, by a simple solvent reaction route. X-ray powder diffraction and field emission scanning electron microscopy were used to characterize the obtained products. The mole ratio of the PS/PAA was found to play an important role in determining the morphologies of the final products.
Phase equilibrium and properties of solid solutions of PbTiO3-PbZrO3-PbNb2/3Mg1/3O3-PbGeO3 system by L. A. Reznitchenko; L. A. Shilkina; O. N. Razumovskaya; E. A. Yarovtseva; S. I. Dudkina; I. A. Verbenko; O. A. Demchenko; Yu. I. Yurasov; I. N. Andryushina; A. A. Esis (173-181).
Phase diagrams of three sections of the four-component system PbTiO3-PbZrO3-PbNb2/3Mg1/3O3-PbGeO3 are plotted (at 20°C) and electrophysical properties of solid solutions are studied. It is found that morphotropic areas, in which dielectric, piezoelectric, and elastic properties are extreme, have a wider concentration interval than in binary systems serving as the base for the studied solid solutions. In monophase areas, isosymmetrical fields (phase states) divided by areas of constant structural parameters are revealed. An explanation of the observed effects based on the real defect structure of objects is proposed.
Raman spectra and structure of tungsten-oxygen groups in crystalline, molten, and glassy NaIn(WO4)2 by Yu. K. Voronko; A. A. Sobol; V. E. Shukshin; P. P. Fedorov; A. E. Kokh; N. G. Kononova (182-188).
Room-temperature polarized Raman spectra of NaIn(WO4)2 single crystals have been studied in detail. We have identified all of the vibrational modes corresponding to the assumed C2/c space group of this material. Using high-temperature Raman spectroscopy, we have studied the structure of NaIn(WO4)2 in the range 300–1600 K. The results indicate that NaIn(WO4)2 melts incongruently at 1253 K, with the formation of solid In2(WO4)3. Above 1350 K, the melt becomes homogeneous. In contrast to crystalline NaIn(WO4)2, which contains tungsten in octahedral oxygen coordination, the tungsten-oxygen groups in the homogeneous melt have the form of isolated [WO4] tetrahedra. Quenching of a homogenized NaIn(WO4)2 melt is found to result in the formation of a glassy phase.
Toroidal spin ordering in BiFeO3, GaFeO3, and Cr2O3 in the Faddeev model with a magnetic field by A. N. Kalinkin; V. M. Skorikov (189-192).
The Fadeev model is used for describing the recently discovered toroidal spin ordering in piezoelectric and ferrimagnetic GaFeO3 and piezo- and magnetoelectric Cr2O3 and BiFeO3. A stable toroidal solution of the Faddeev model with the topological charge Q= 1 in an external homogeneous magnetic field was obtained using the trial function method. The energy of a toroid as a function of its radius (R) was determined at various values of the external magnetic field (H). It was shown that the energy minimum is shifted toward smaller R’s with an increase in H. At a critical field value, the torus collapses so that the local spin structure disappears. It is suggested to use magnetic field for controlling the torus size in multiferroics, promising materials of spintronics.
Synthesis of silver sulfide nanowires in ethylene glycol through a sacrificial templating route by Shancheng Yan; Yuping Zhang; Yong Zhang; Zhongdang Xiao (193-197).
In this study, Ag2S nanowires were prepared in ethylene glycol using single-crystal silver nanowires as a sacrificial templating and choosing suitable sulfur sources for the sulfuration reaction. X-ray powder diffraction and a transmission electron microscope equipped with an energy dispersive X-ray analysis were used to characterize the products. The results indicated Ag2S nanowires with diameters of about one hundred nanometers and lengths up to several micrometers could be obtained through this method. The selected area electron diffraction pattern and high-resolution transmission electron microscope imaging indicated that the Ag2S nanowires thus formed were crystalline.
Recombination luminescence of CaI2 crystals activated with Eu2+, Gd2+, Tl+, Pb2+, and Mn2+ by S. S. Novosad; I. S. Novosad (198-202).
The spectral characteristics of thermostimulated luminescence, steady-state roentgenoluminescence and photostimulated luminescence (PSL) buildup and decay kinetics, and the effect of IR irradiation on the roentgenoluminescence yield and glow curves of CaI2:Eu2+, CaI2:Gd2+, CaI2:Tl+, CaI2:Pb2+, CaI2:Mn2+, and CaI2: Pb2+, Mn2+ crystals grown by the Bridgman-Stockbarger method have been studied in the temperature range 90–295 K. Coupled with earlier data, the present results on the influence of oxygen and hydrogen impurities on the spectral characteristics of CaI2 indicate that the activation of calcium iodide with Eu2+, Gd2+, Tl+, Pb2+, and Mn2+ leads to the formation of cation impurity-native defect complexes, which act as carrier traps and are responsible for the thermostimulated luminescence in the range 150–295 K. IR exposure after 90-K x-ray excitation gives rise to flash PSL and influences the thermostimulated luminescence light sum. The nature of the emission and trapping centers involved and the mechanisms of recombination luminescence excitation in the crystals are discussed.
Synthesis and conductivity of Zn2SnO4-based cermet material by T. V. Barinova; I. P. Borovinskaya; V. I. Ratnikov; A. F. Belikova (203-207).
SHS synthesis of Zn2SnO4-based cermet material from Zn + NiO + SnO2 compacted powder mixtures has been studied. The final product is obtained as a monolithic cylindrical block composed of a ZnO-based outer layer and Zn2SnO4-based central part, in which the metal phase is distributed. The phase composition and microstructure of combustion products have been studied by x-ray phase analysis (XPA), electron microscopy, and microprobe techniques. It is established that the structure of the obtained cermet material has a dramatic effect on their conductivity.
Effect of annealing of starting polycarbosilanes on the properties of resulting SiC ceramics by E. G. Kononova; N. V. Chizhova; I. M. Petrova; N. N. Makarova (208-210).
The effect of changes in the fragment composition of poly- and copolyorgano-silaalkanes with cyclic and linear fragments in the chain produced by annealing in an inert medium on the properties of resulting SiC ceramics is analyzed. On the basis of IR spectroscopy data, it is found that the polymethylcarbosilane skeleton is rearranged, and an inorganic framework (the precursor of SiC ceramics) forms during a stepwise increase in temperature.
Self-propagating high-temperature synthesis of Al2O3/TiC-based ceramic materials by V. P. Kobyakov; T. V. Barinova; V. I. Ratnikov (211-219).
Dense Al2O3/TiC composite ceramic materials are synthesized using the SHS compaction of mixtures based on TiO2 + Al + C. Mineralizing and heating additives are introduced into compounds. The phase composition and microstructure of combustion products are investigated by x-ray phase analysis, electron microscopy, and microprobe techniques. Two Al2O3 modifications are revealed. Special attention is devoted to the presence of residual graphite. The mechanisms of phase formation and formation of the microstructure of combustion products are considered.