Inorganic Materials (v.45, #6)

Data are presented on the targeted synthesis of novel substrate materials based on rare-earth-containing mixed-oxide solid solutions for epitaxy of high-T c superconductors. Property-structure relationships are analyzed, and the key features of the synthesis process are outlined, with examples of practical applications.

The process of obtaining a silicon single crystal grown with crucibleless zone melting and heated with the use of a preheating inductor is studied. The preheating inductor electromagnetic field strength and temperature gradient within the single crystal are simulated.

Carrier mobility in Si1 − x Ge x crystals by E. V. Khutsishvili; L. L. Gabrichidze; O. A. Tsagareishvili; N. V. Kobulashvili (599-601).
We have studied the 300-K carrier mobility in Czochralski-grown single crystals of undoped and heavily boron doped Si1 − x Ge x (0 < x < 0.02) alloys. Comparison of our experimental data with theoretical predictions indicates that the Ge atoms in dilute Si1 − x Ge x alloys do not act as neutral scattering centers. The carrier mobility related to the scattering by Ge atoms is governed by disorder (alloy) scattering. The carrier mobility in the boron-doped Si1 − x Ge x alloys is much lower than that in the undoped alloys, depends very little on Ge content, and is governed by ionized impurity scattering.

It is established that the partial substitution of gallium for manganese (3 mol %) in TlGaS2 single crystals leads to a decrease in width of the band gap (from 2.62 to 2.5 eV), broadening of the peak of intrinsic photocurrent, and appearance of a broad band of extrinsic photocurrent over the photon energy range hν = 1.7–2.4 eV. Upon the partial substitution Ga → Mn in TlGaS2, the X-ray sensitivity coefficient increases significantly (by a factor of 24–57) within an irradiation dose of 0.75–78 R/min, and the current-dose characteristics of TlGa0.97Mn0.03S2 have good reproducibility.

Properties of CdSe single crystals activated with selenium by ion implantation by A. N. Georgobiani; B. N. Levonovich (606-610).
Selenium ion implantation has been used to produce p-type layers on cadmium selenide single crystals. Their conductivity is governed by acceptor levels at E ν + 0.05 eV and E ν + 0.32 eV, due to native point defects in the ion-implanted layer.

Transport properties and thermal expansion of TlIn1 − x Gd x Se2 (0 < x ≤ 0.09) solid solutions by E. M. Gojaev; E. A. Allakhyarov; S. S. Osmanova; Kh. S. Khalilova (611-615).
TlInSe2-TlGdSe2 alloys have been characterized by X-ray diffraction, and their electrical conductivity, Hall coefficient, thermoelectric power, and thermal expansion have been measured as functions of temperature. The results have been used to determine the carrier concentration and Hall mobility in the alloys and their band gap. Partial gadolinium substitution for indium in TlInSe2 increases the lattice parameters of the material and reduces its band gap. The thermal expansion coefficient of the TlIn1 − x Gd x Se2 alloys exhibits no anomalies in the temperature range 77.3–400 K.

Distribution of N+ centers in synthetic diamond single crystals by Yu. V. Babich; B. N. Feigelson (616-619).
The distribution of N+ centers in synthetic diamond grown by the temperature-gradient method in a nickel-containing metal-carbon system has been studied using FTIR mapping. The results clearly demonstrate that the distribution has a complex nature and is directly related to the sectorial structure of the crystal and linear growth rate, whose effects are analyzed with consideration for literature data. The aggregation rate of N+ single nitrogen is slower than that of neutral substitutional nitrogen (C centers).

Impact of shift potential applied to substrate on the film structure HfB2 by V. A. Konovalov; D. N. Terpii; V. V. Petukhov (620-625).
Using methods of X-ray diffractometry, electronic microscopy, roentgenography by the photomethod, and secondary ion mass spectrometry, the structures, substructures, and composition of hafnium diboride films obtained by nonreactive high-frequency magnetron sputtering are studied. The effect of the character and value of the shift potential applied to the substrate on the structure of the forming surfaces is shown.

Interaction between BNc and titanium in vacuum by B. V. Korzun; O. V. Ignatenko; S. A. Lebedev (626-630).
The thermal stability of cubic boron nitride in vacuum at temperatures up to 1470 K in contact with titanium is studied by means of the differential thermal, X-ray phase, and chemical analyses. It is found that, in the system Ti-BNc, the reverse phase transition of boron nitride from the cubic to hexagonal structure, followed by formation of titanium borides and nitrides, is observed.

Thermodynamic properties of Al-Mn melts by V. S. Sudavtsova; N. V. Kotova; L. A. Romanova (631-634).
The thermochemical properties of Al-Mn melts have been studied at 1835 ± 3 K by high-temperature calorimetry under isoperibolic conditions. The Δmix H and Δmix $$ overline H _i $$ , data obtained correlate well with earlier data obtained at a lower temperature of 1628 K. The enthalpies of formation of manganese aluminides determined by calorimetry agree only qualitatively with the Δmix H of Al-Mn melts. We have calculated the partial and integral entropies of mixing of Al-Mn melts. Analysis of the entire set of thermodynamic properties indicates that, in liquid Al-Mn alloys, the interaction between dissimilar atoms is significant even well above the liquidus temperature.

The effect of microgravity on the composition of SHS products of the mixture NiO + Ni + Al + WC by V. N. Sanin; V. I. Yukhvid; A. E. Sychev; N. V. Sachkova; M. Yu. Shiryaeva (635-644).
The structure formation of the liquid-phase products of the synthesis of the model SHS mixture of the thermite type NiO + Ni + Al under microgravity conditions aboard the International Space Station ALPHA is investigated. Comparative investigations of the microstructure and chemical and phase compositions of synthesis products formed on the Earth and under microgravity conditions are performed. In the process of terrestrial experiments, the main attention was paid to the search for optimal compositions capable of burning under reduced pressure with a minimal spread of combustion products.

Annealing effect on reflectivity spectra of opal photonic crystals by V. S. Gorelik; Yu. P. Voinov; G. A. Emel’chenko; V. M. Masalov; N. I. Yurasov; V. V. Gryaznov (645-650).
We analyze broadband visible reflectivity spectra of opal photonic crystals annealed in an argon atmosphere and air. Scanning electron microscopic examination has shown that the crystals consist of close-packed spheres with a mean diameter in the range 200–290 nm. Incorporation of even small amounts of carbon (≃0.5 wt %) increases the density of the opal matrix. The presence of carbon shifts the Bragg reflection peak of the opal and increases its intensity.

Treatment of nano-sized rutile TiO2 powder in hydrogen peroxide under microwave irradiation and investigation on its sonocatalytic activity by Jun Wang; Zhao Hong Zhang; Jia Li; Ying Peng Xie; Zhe Jiang; Rui Xu; Yan Hui Lv; Xiang Dong Zhang (651-658).
In this work, a novel nano-sized mixed-crystal TiO2 catalyst was obtained under microwave irradiation in hydrogen peroxide solution and its sonocatalytic activity was also investigated through degradation of congo red dye. It was found that the sonocatalytic degradation effect of congo red using nano-sized mixed-crystal TiO2 powder was much higher than that using pure nano-sized rutile phase TiO2 powder. At last, the congo red dyes in aqueous solution were degraded completely and became some simple inorganic ions such as NO 3 , SO 4 2− and so on. The experiments indicated that the degradation method using such treated nano-sized rutile TiO2 powder as sonocatalyst could be used to treat those non- or low-transparent wastewaters effectively.

Chemical vapor deposition of electrolyte thin films based on yttria-stabilized zirconia by N. V. Gelfond; O. F. Bobrenok; M. R. Predtechensky; N. B. Morozova; K. V. Zherikova; I. K. Igumenov (659-665).
Gas-tight electrolyte films are obtained by chemical vapor deposition for solid oxide fuel cells from yttria-stabilized zirconia (YSZ) with a thickness of 4–15 μm on supporting porous ceramic anodes (YSZ/NiO). Volatile metal complexes with dipivaloylmethane Zr(dpm)4 and Y(dpm)3 are used as precursors. On the basis of an analysis of thermal properties of the starting compounds, parameter ranges in deposition processes are determined. Dependences of the structure, composition, and electrical characteristics on deposition conditions are found for YSZ electrolyte films. Electrochemical solid oxide fuel cells that operate at low temperatures with an open circuit voltage of 0.98–1.08 V and specific power up to 440 mW/cm2 at 1073 K and 1200 mW/cm2 at 1173 K are constructed.

Lattice parameter, density, and defect system of VOy by D. A. Davydov; A. A. Rempel (666-670).
Vanadium monoxide, VO y has been studied within its homogeneity range using X-ray diffraction and pycnometric density measurements. The density and lattice parameter of VO y have been shown to vary in a complex manner with oxygen content near the stoichiometric composition VO1.0. The experimental data have been used to evaluate the vanadium and oxygen vacancy contents in VO y . We assume that two cubic phases close in lattice parameter coexist near the composition VO1.0 and form a solid solution.

Structural and superconducting properties of single-crystal Bi2Sr2Ca n − 1Cu n O2n + 4 + δ (n = 1–3) whiskers grown in gas-filled cavities by M. V. Golubkov; Yu. I. Gorina; G. A. Kalyuzhnaya; V. V. Rodin; N. N. Sentyurina; V. A. Stepanov; S. G. Chernook (671-677).
Using growth inside gas-filled cavities in KCl-fluxed melts, we have obtained free-standing phasepure Bi2Sr2Ca n − 1Cu n O2n + 4 + δ (n = 1–3) whiskers possessing superconducting properties in the as-grown state. Bi-2212 whiskers have been prepared in a wide range of doping levels, from underdoped (T c = 76.5 K) to optimally doped (T c = 84 K). The whiskers possess high structural perfection, as shown by X-ray diffraction. Annealing under optimal conditions raises the superconducting transition temperature of the underdoped Bi-2212 whiskers to T c max = 85.5 K (ΔT c = 1.8 K), without impairing their structural perfection.

YVO4:Eu3+ nanoparticles were synthesized by hydrothermal method at different conditions. The microstructures and photoluminescence (PL) properties of the as-prepared YVO4:Eu3+ nanoparticles were investigated by X-ray powder diffraction, field emission scanning electron microscopy and PL spectroscopy. The detailed relationship between the microstructures and luminescence properties was investigated. It has been found that the crystallinity, the grain size and the duty factor of Eu3+ play important roles in influencing the luminescence properties.

Magnetic properties and valence states of the Fe ions in Bi0.5Sr0.5FeO3 − y by V. V. Pokatilov; V. S. Pokatilov; A. S. Sigov; V. M. Cherepanov (683-688).
57Fe hyperfine interactions in the cubic perovskite Bi0.5Sr0.5FeO3 − y have been studied by Mössbauer spectroscopy in the temperature range 87–670 K. The results indicate that its magnetic ordering temperature is 637(3) K, which is close to the Néel point T N of bismuth ferrite. Below T N, the measured spectra have a partially resolved magnetic hyperfine structure with broadened lines, which is well represented by four sextets. Above T N, the spectra each consist of four quadrupole doublets. From the room-temperature hyperfine magnetic field B and isomer shift δ, it follows that all of the Fe ions are trivalent. The two sextets identical in isomer shift (δ1 ≃ δ2 = 0.37 mm/s) are due to Fe ions in octahedral oxygen coordination. The other two sextets correspond to squarepyramidal (δ3 = 0.25 m/s) and tetrahedral (δ4 = 0.17 mm/s) coordination.

Preparation of magnetic composites through SrO-Fe2O3-Al2O3-B2O3 glass crystallization by L. A. Trusov; D. D. Zaitsev; P. E. Kazin; Yu. D. Tret’yakov; M. Jansen (689-693).
Glasses with nominal compositions 11SrO · 5.5Fe2O3 · 4.5Al2O3 · 4B2O3 (1) and 15SrO · 5.5Fe2O3 · 4.5Al2O3 · 4B2O3 (2) were prepared by rapidly quenching oxide melts between counterrotating steel rollers. The glasses were then heat-treated in the range 650–950°C to produce glass-ceramic samples. The samples were characterized by X-ray diffraction, electron microscopy, and magnetic measurements. The phase composition of the glass-ceramics was determined, and their microstructure and magnetic properties were studied. The annealing temperature was shown to have a strong effect on the coercivity of the materials, which reaches 650 and 570 kA/m for compositions 1 and 2, respectively.

Microstructure and composition of SHS products of powder multicomponent oxide mixtures with aluminum and graphite by V. P. Kobyakov; T. V. Barinova; V. I. Ratnikov; I. P. Borovinskaya (694-701).
The microstructure and composition of products of SHS combustion of two types of multicomponent oxide mixtures with aluminum and graphite powders, differing in the presence or absence of a thermite additive, are studied. The combustion product—oxide carbide ceramic based on Al2O3/TiC—serves for immobilization of graphite-containing radioactive wastes. It is proposed to use results of the studies of “undercombusted” samples of such composites for analysis of the initial stages of the process of their front combustion. Procedures of combustion of the composites with the presence or absence of a thermite additive are specified. The problems of distribution in the combustion products of the impurities introduced into the original system, which simulate the most characteristic composition of nuclides in nuclear-fuel degradation products and in radiation-exposed graphite, are studied

Production and dielectric properties of lead-free ceramics with the formula [(Na0.5K0.5)1 − x Li x ](Nb1 − yz Ta y Sb z )O3 by I. A. Verbenko; O. N. Razumovskaya; L. A. Shilkina; L. A. Reznichenko; K. P. Andryushin (702-708).
The influence of past history on the possibility of obtaining high-density ferroelectric ceramics of solid solutions [(Na0.5K0.5)1 − x Li x ](Nb1 − yz Ta y Sb z )O at x = 0–0.14, y = 0, 0.1, 0.2, and z = 0–0.1 is identified. The dynamics of behavior of materials under a field in the process of polarization is evaluated. The relative dielectric permeability of samples in a wide range of temperatures (20–700°C) and frequencies (25 Hz-1 MHz) of a variable electric field is studied. On the basis of study of dielectric, piezoelectric, and elastic properties of solid solutions, prospective objects for further technological elaboration and modification of chemical composition with the goal of improving the electrophysical parameters are selected.