Inorganic Materials (v.46, #2)

Using thermal and activation analysis techniques, we have constructed the liquidus curves in the primary crystallization fields of silicon in the Si-Sr and Si-Ba systems. The Sr and Ba solid solubilities in silicon have been determined using microhardness measurements, and have been shown to exhibit retrograde behavior. At 1573 K, the solubility of Sr in silicon is 1.15 at %, and that of Ba is 0.98 at %. The solidus and liquidus curves have been analyzed using thermodynamic modeling and the known thermodynamic properties of the melt and intermediate phases. We assume that the large deviations of the melts from ideal behavior are due to the formation of Zintl polyanions (or clathrates), and describe a model for the chemical structure of the silicon-rich melts.

The phase diagram of the Pb-NiSb system is presented. The system is pseudobinary, with a limited series of NiSb-based solid solutions: ≃1 mol % Pb at 300 K. In the temperature range ≃520–670 K, the system contains un unstable compound, Ni3Pb2Sb3. At 1320 K, a monotectic transformation occurs (≃15–71 mol % NiSb). Electrical and thermal conductivity measurements reveal an additional contribution to the lattice thermal resistivity of the (NiSb)1 − x Pb x solid solutions and show that electrons and phonons in these materials are scattered elastically.

The electrical properties (loss tangent (tanδ), real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity, and ac conductivity across the layers (σac)) of (TlGaS2)1 − x (TlInSe2) x (x = 0.005, 0.02) layered single crystals have been studied in the frequency range f = 5 × 104 to 3.5 × 107 Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. Almost throughout the frequency range studied, their ac conductivity follows the relation σacf 0.8, characteristic of hopping conduction through localized states near the Fermi level. The Fermi-level density of states (N F ), the spread of their energies, the mean hop time τ and distance R, and the concentration of deep traps determining the ac conductivity of the crystals (N t ) have been estimated. With increasing x in (TlGaS2)1 − x (TlInSe2) x , N F and N t increase, while τ and R decrease.

Diffusion coefficient of Fe2+ in single-crystal ZnSe by N. N. Il’ichev; P. V. Shapkin; E. S. Gulyamova; L. A. Kulevsky; A. S. Nasibov (112-115).
The diffusion coefficient of Fe in single-crystal ZnSe has been measured in the temperature range 886–995°C. The 995°C diffusion coefficient is (47 ± 5) × 10−11 cm2/s, and the average activation energy for Fe diffusion is 2.9 ± 0.3 eV.

Electric-field and temperature effects on electric currents in polycrystalline ZnGa2Se4 by A. N. Georgobiani; B. G. Tagiev; O. B. Tagiev; T. G. Kerimova; S. A. Abushov; S. G. Asadullaeva (116-119).
The current (electrical transport) through In/ZnGa2Se4/In structures has been measured as a function of temperature and applied electric field at temperatures from 77 to 400 K in fields from 10 to 3 × 104 V/cm. The results are analyzed in terms of the Poole-Frenkel effect and space-charge-limited currents. The activation energy of traps and trap concentration in ZnGa2Se4 and its refractive index are determined to be E t= 0.8 eV, N t = 4 × 1013 cm−3, and n = 2.4, respectively.

Composition and properties of compounds in the PbSe-Bi2Se3 system by L. E. Shelimova; O. G. Karpinskii; P. P. Konstantinov; E. S. Avilov; M. A. Kretova; G. U. Lubman; I. Yu. Nikhezina; V. S. Zemskov (120-126).
To identify the compounds existing in the PbSe-Bi2Se3 system, Bridgman-grown ingots and annealed polycrystalline samples have been characterized by X-ray diffraction. The results indicate that the first solidified portion of the Bridgman-grown ingots consists of a PbSe-based solid solution with a cubic structure. Further directional solidification involves peritectic reactions that lead to the formation of the ternary compounds Pb5Bi6Se14 and Pb5Bi12Se23, which have monoclinic structures. The structural data have been used to refine the phase diagram of the PbSe-Bi2Se3 system. The thermoelectric properties of Pb5Bi6Se14, Pb5Bi12Se23, and Pb5Bi18Se32 have been studied using annealed polycrystalline samples. Their Hall coefficient and resistivity have been measured in the temperature range 80–670 K, and their thermoelectric power, electrical conductivity, and thermal conductivity have been measured from 80 to 370 K. The ternary compounds in the PbSe-Bi2Se3 system have low lattice thermal conductivity, which can be understood in terms of the key features of their crystal structure.

Transformation of onion-like carbon from nanodiamond by annealing by Q. Zou; Y. G. Li; B. Lv; M. Z. Wang; L. H. Zou; Y. C. Zhao (127-131).
Onion-like carbon (OLC) was synthesized by annealing nanodiamond in low vacuum (1 Pa) at the temperatures from 500 to 11400°C. The high-resolution transmission electron microscope images, X-ray diffraction patterns and Raman spectra showed that, when the annealing temperatures were lower than 900°C, there was no OLC fabricated. The amorphous carbon and the nanodiamond coexisted. The graphitization started from the surfaces of the nanodiamond particles. When the annealing temperatures were higher than 900°C, the OLC was fabricated. At 900°C, OLC began appearing and the size of the OLC particles was smaller than 5 nm. At the annealing temperature of 1400°C all the nanodiamond particles were transformed into OLC. The OLC particles exhibited similarity to the original nanodiamond particles in shape. Based on these results, a mechanism for the OLC synthesis by the method of annealing in vacuum was provided.

Properties of carbon-carbon composites based on exfoliated graphite by D. V. Savchenko; S. G. Ionov; A. I. Sizov (132-138).
We report the first study of the mechanical and electrical properties of carbon-carbon composites based on flexible graphite foils modified with pyrolytic carbon. Our results demonstrate that slight densification with pyrolytic carbon enhances the chemical and thermal stability of the graphite foils, increases their Young’s modulus by a factor of 2.5, and reduces their resistivity by 25%. Decomposition of the polymeric carbon precursors poly(hydridocarbyne) and poly(naphthylhydridocarbyne) in an exfoliated graphite matrix increases the tensile strength of the composite by a factor of 2 compared to the as-prepared graphite foil.

Composites based on chitosan- and gold-modified carbon fibers by L. A. Zemskova; A. V. Voit; T. A. Kaidalova; N. N. Barinov (139-143).
We report the fabrication of composite materials containing gold particles deposited on the surface of carbon fibers, in particular, immobilized in films of chitosan, a natural biopolymer. The fabrication process involves gold-chitosan electrocodeposition on unmodified fibers or gold deposition on chitosan-carbon materials used as electrodes. Scanning electron microscopy, energy dispersive X-ray analysis, and X-ray diffraction results are used to gain insight into the role of ion exchange, complexation, and electrochemical factors in the formation of the composites.

We report the critical current of superconducting Nb3Sn coatings produced by electrocodeposition from molten salts and its anisotropy in transverse magnetic fields. The anisotropy is quantified by the ratio of the critical currents measured in magnetic fields parallel and normal to the coating surface, k. The effect of doping with tantalum and nitrogen on the microstructure, critical current, and anisotropy factor k of Nb3Sn coatings is examined. The k of the undoped and tantalum-doped coatings ranges from 0.4 to 1.0, and that of the nitrogen-doped coatings, from 0.4 to 1.4. The critical current anisotropy is interpreted in terms of the microstructure of the coatings.

Phase equilibria in the K2O-MgO-B2O3 system by R. V. Kurbatov; B. G. Bazarov; A. K. Subanakov; Zh. G. Bazarova (151-153).
Subsolidus (500–700°C) phase relations in the K2O-MgO-B2O3 system have been studied by X-ray diffraction. The results are used to construct the phase compatibility diagram of the K2O-MgO-B2O3 system in the range 650–700°C. A new ternary compound of composition K2Mg3B2O7, with the constituent oxides in the molar ratio 1: 3: 1, is identified.

Growth of thin ZnO films by ultrasonic spray pyrolysis by V. V. Kireev; L. N. Dem’yanets; L. E. Li; V. V. Artemov (154-162).
We report the growth of high-quality thin ZnO films with controlled microstructure on Si(111) substrates by ultrasonic spray pyrolysis of Zn-containing solutions.

Tuning the band gap of ZnO nanoparticles by ultrasonic irradiation by R. S. Yadav; P. Mishra; A. C. Pandey (163-167).
In this present paper, we report the tunability of ZnO nanoparticles by ultrasonic irradiation. Different sized ZnO nanoparticles viz. 2.58–2.97 nm have been synthesized with variation of ultrasonic irradiation time 75–270 min in presence of Histidine as capping agent. UV and visible spectroscopy study revealed that as ultrasonic irradiation time increases, there is increase in amount of formed ZnO nanoparticles and also there is red shift in absorption edge. This confirms the tunability of bandgap of histidine capped ZnO nanoparticles with ultrasonic irradiation. Growth mechanism for controlling the size of ZnO nanoparticles are also discussed.

High-temperature hydroxyapatite-titanium interaction by A. A. Egorov; V. V. Smirnov; L. I. Shvorneva; S. V. Kutsev; S. M. Barinov (168-171).
Hydroxyapatite-titanium interaction has been studied in the temperature range 700 to 1200°C with a view to designing biocompatible dispersion-hardened hydroxyapatite-matrix materials for bone implants. The sequence of phase transformations in hydroxyapatite-titanium powder mixtures during heating in air has been identified using IR spectroscopy, differential thermal analysis, and X-ray diffraction. It is shown that hydroxyapatite decomposition can be inhibited via heat treatment in an atmosphere containing carbon monoxide.

Effect of Al2O3 on the properties of nanocrystalline ZrO2 + 3 mol % Y2O3 powder by E. V. Dudnik; A. V. Shevchenko; A. K. Ruban; V. P. Red’ko; L. M. Lopato (172-176).
We have studied the properties of nanocrystalline ZrO2〈3 mol % Y2O3〉 and 90 wt % ZrO2〈3 mol % Y2O3〉-10 wt % Al2O3 powders prepared via hydrothermal treatment of coprecipitated hydroxides at 210°C. The results demonstrate that Al2O3 doping raises the phase transition temperatures of the metastable low-temperature ZrO2 polymorphs and that the structural transformations of the ZrO2 and Al2O3 in the doped material inhibit each other.

On the basis of experimental data, we calculate the diffusion coefficients of titanium and oxygen through rutile, which is synthesized in the process of oxidative construction of thin-wall ceramics (OCTWC), and titanium through a K-layer (a solid solution of oxygen in the metal). It is shown that, at the beginning of the exponential stage, the process rate is determined by the rate of titanium diffusion through the K-layer. Near the bifurcation point, the diffusion conductivities of the OCTWC rutile and K-layer become equal, which leads to a stepwise variation in the process rate.

Microwave synthesis of SnO2 nanocrystals on the surface of fine polymer fibers by G. V. Lysak; I. A. Lysak; T. D. Malinovskaya; G. G. Volokitin (183-186).
Nanocrystals of stable, tetragonal tin dioxide have been synthesized using microwave processing, and the effect of microwave heating on the structural phase transformations of the tin compounds involved has been examined. The results are used to determine microwave heating parameters that ensure strong bonding of nanocrystals to the surface of polymer fibers.

It is shown that mesolite, scolecite, and metascolecite have essentially identical structural frameworks, and the distinctions between their structures are related to differences between the calcium-water, sodium-water, and calcium (sodium)-intraframework oxygen bonds. As a result of the sodium substitution for one-third of the calcium atoms, the calcium-water networks are separated by a layer of sodium-water chains. The substitution leads to significant displacements of some of the calcium atoms within the nine-membered channels and insignificant displacements of the intraframework atoms (silicon, aluminum, and oxygen). Thermal analysis and X-ray diffraction data indicate that the first step of dehydration is the removal of the water from the calcium channels and disruption of the calcium-water network, followed by disruption of the sodium-water chains.

We have developed a procedure for the synthesis of phase-pure α- and β-Cu2V2O7. Thermal analysis and X-ray diffraction demonstrate that the β-phase (monoclinic structure) exists at low temperatures (stability range 25–610°C), while α-Cu2V2O7 (orthorhombic structure) is stable in the range 610–704°C. The α-phase observed during cooling, in particular at room temperature, is in a metastable state. The melting of the high-temperature phase γ-Cu2V2O7, which forms between 704 and 716°C, has the highest rate in the range 770–785°S and is accompanied by peritectic decomposition and oxygen gas release. Subsequent cooling gives rise to four exothermic peaks, one of which (780.9°C) is attributable to the crystallization of the peritectic melt, one (620.1°C) is due to the γ → α → β phase transformations of Cu2V2O7, and the other two arise from the crystallization of multicomponent low-melting-point eutectics containing α- and β-Cu2V2O7, CuVO3, and other compounds.

Mn(VO3) powders was successfully synthesized by an effective and simple route-rheological phase reaction method and investigated as a cathode material for lithium-ion batteries. The structures, morphologies, phase purity of the prepared powder were characterized by X-ray diffraction, transmission electron microscope and X-ray photo-electron spectrometry, respectively. The results showed that the different heat temperatures could influence the particle size and crystallinity of the product. The charge-discharge experiments were performed to investigate the electrochemical properties of Mn(VO3)2 powder at a constant current density of 1.0 mA/cm2 in a potential range of 0.0 and 3.5 V. The discharge capacity (441.1 mAh/g) showed only 31.7% losses of the initial discharge capacity (645.9 mAh/g) after 40 cycles.

Stoichiometry and doping effects on cation ordering in LiNbO3 crystals by E. P. Fedorova; L. A. Aleshina; N. V. Sidorov; P. G. Chufyrev; A. A. Yanichev; M. N. Palatnikov; V. M. Voskresenskii; V. T. Kalinnikov (206-211).
The cation disorder in stoichiometric and congruent lithium niobate crystals and also in congruent crystals doped with Y3+ or Gd3+ has been studied by X-ray diffraction and Raman scattering spectroscopy using vacancy models. The results indicate that the structural disordering induced by doping with Y3+, revealed by both X-ray diffraction and Raman spectroscopy, can be understood in terms of the mechanism of yttrium incorporation into the cation sublattice of the crystal. Yttrium substitution for Nb5+ on its normal lattice site causes Nb5+ to occupy vacant octahedra, thereby increasing the cation and vacancy disorder along the polar axis and distorting the octahedra because the ionic radius of Y3+ exceeds that of Nb5+.

Crystalline and induced anisotropy and structural defects in single-crystal spinel ferrite films by L. A. Mitlina; A. A. Sidorov; Yu. V. Velikanova; M. R. Vinogradova; G. S. Badrtdinov (212-215).
The crystalline and uniaxial anisotropy constants of single-crystal manganese and magnesium manganese ferrite spinel films have been determined experimentally. The results indicate that the structural perfection of the films, influenced by the film composition and growth conditions, has a significant effect on their anisotropy constants.