Inorganic Materials (v.44, #6)
Effect of the line tension at the vapor-liquid-solid boundary on the growth of silicon nanocrystals by V. A. Nebol’sin; A. I. Dunaev; M. A. Zavalishin (559-562).
We examine the thermodynamic aspects of the effect of the line tension at a bent vapor-liquid-solid boundary on quasi-one-dimensional growth of silicon nanowires. Experimental data demonstrate that there is a limiting size of solvent nanodrops below which they cannot exist in equilibrium and that there is a limiting nanowire diameter starting at which the increase in line tension with decreasing diameter prevents nanocrystal growth at a given supersaturation.
Photoluminescence of Ga2S3:Sm2+ crystals by A. N. Georgobiani; B. G. Tagiev; O. B. Tagiev; Kh. B. Ganbarova (563-565).
The photoluminescence spectra of Ga2S3:Sm2+ crystals have been measured in a wide temperature range (77–450 K). The results have been used to identify the mechanisms of the luminescence and energy transfer from the host to the rare-earth ion.
Temperature-gradient-driven silver transport in the superionic conductor Ag1.9Cu0.1Se by M. Kh. Balapanov; G. R. Akmanova; R. A. Yakshibaev; R. Kh. Ishembetov (566-568).
A steady state silver transport in the superionic conductor Ag1.9Cu0.1Se in a temperature gradient has been analyzed. The parameters of the Soret effect have been determined, and the conditions for silver precipitation have been identified. The rate of silver precipitation is shown to increase with increasing temperature gradient and heat of silver transport.
Silver solubility in PbTe crystals by M. K. Sharov (569-571).
Silver solubility in lead telluride single crystals has been determined using electron microscopy, x-ray microanalysis, microhardness tests, and hydrostatic density measurements. The results indicate that the limit of the Pb1 − x Ag x Te solid-solution series is near x = 0.006. With increasing silver content, the density of the Pb1 − x Ag x Te solid solutions drops, while their microhardness rises.
Evaluation of charge displacement and the radii of Wigner-Seitz spheres for the components of A-Te (A = Ge, Sn, Pb) melts by E. A. Dolgopolova (572-575).
Thermodynamic and structural data for A-Te (A = Ge, Sn, Pb) melts are used to evaluate the charge displacement (in Tamaki’s approach) and the radii of Wigner-Seitz spheres. The results indicate that the interaction between dissimilar components and the formation of the ATe compounds prevail in the melts. In the Ge-Te system, there is a tendency toward the formation of Ge0.85Te0.15 and Ge0.33Te0.66 associates, in which, respectively, covalent and ionic bonding prevails.
PbTe-VTe2 phase diagram and properties of (PbTe)1 − x (VTe2) x solid solutions by A. A. Vinokurov; A. I. Artamkin; S. G. Dorofeev; T. A. Kuznetsova; V. P. Zlomanov (576-581).
The T-x phase diagram along the PbTe-VTe2 join of the Pb-V-Te system has been studied. Vanadium-doped lead telluride crystals have been grown, and the longitudinal vanadium and carrier profiles in the crystals have been investigated. The temperature dependences of resistivity for the crystals lend support to the conclusion drawn earlier that PbTe〈V〉 is in a semi-insulating state at low temperatures. The crystals offer a high 20-K electron mobility, on the order of 105 cm2/(V s), which attests to high electrical homogeneity of the material and stabilization of the Fermi level.
Growth of cerium-containing films on titanium and aluminum by V. S. Rudnev; T. P. Yarovaya; T. A. Kaidalova; P. M. Nedozorov (582-586).
Cerium-containing films have been grown via plasma electrolytic oxidation in aqueous electrolytes containing Ce(III) polyphosphate complexes and have been characterized by x-ray microanalysis and x-ray diffraction. The films are shown to contain crystalline monazite, CePO4. Under certain conditions, multilayer surface structures grow on titanium. Air annealing of titanium/film structures at 750°C leads to crystallization of NaTi2(PO4)3 and CeP5O14.
Formation of intermetallic phases during mechanical alloying and annealing of Cr + 20 wt % al mixtures by J. S. Kim; Y. S. Kwon; G. V. Golubkova; O. I. Lomovsky; D. V. Dudina; L. S. Davlitova; V. V. Malakhov; S. F. Tikhov; V. V. Usol’tsev; V. A. Sadykov (587-591).
We have studied phase-formation processes in mixtures of Cr and Al (20 wt %) powders in the course of mechanical alloying (MA) and the phase transformations of the samples during subsequent annealing at temperatures of up to 800°C. The resultant x-ray amorphous intermetallic phases were identified by a differential dissolution method, which allows one to follow the formation of x-ray amorphous and partially crystallized phases. During MA of Cr + Al mixtures, the first to form is x-ray amorphous Cr4Al, which then converts to partially crystallized Cr2Al through reaction with aluminum. The peritectoid decomposition of Cr4Al during heating of the MA samples is accompanied by heat release at 330–350°C. Heating to 420°C leads to the formation of Cr5Al8. At 800°C, Cr5Al8 reacts with Cr to form Cr2Al.
Atomic force microscopy study of surface-modified carbon fibers by B. N. Zaitsev; N. I. Baklanova; T. M. Zima (592-597).
Structural carbon fibers surface-modified with titanium carbide have been studied by atomic force microscopy (AFM). Using statistical analysis of AFM images, quantitative characteristics of fiber surfaces have been determined. The results demonstrate that surface modification has a significant effect on the surface topography of the fibers: their surface becomes smoother and more uniform, as evidenced by the decrease in roughness value and average height and the narrower height distribution.
Conductive composites based on exfoliated graphite by I. M. Afanasov; V. A. Morozov; A. N. Seleznev; V. V. Avdeev (598-602).
Conductive composites of exfoliated graphite (EG) and coal-tar pitch have been prepared by mixing the components. The electrical properties of the composites have been studied, and the results have been interpreted in terms of the percolation theory. The threshold EG content for electrical conduction is determined to be ≃ 1.5 wt %, independent of the properties of the pitch and EG.
Metallic impurities in germanium tetrafluoride and germanium dioxide prepared from it by A. D. Bulanov; A. Yu. Lashkov; A. M. Potapov; V. G. Pimenov; M. M. Lipatova; M. F. Churbanov; V. N. Kornoukhov; L. B. Bezrukov (603-607).
The composition and contents of metallic impurities (in nonvolatile form) in isotopically unmodified and 76Ge-depleted germanium tetrafluoride samples were determined by chemical atomic emission spectrometry. The germanium tetrafluoride samples were then converted to germanium dioxide. The impurity compositions of the resultant germanium dioxide samples were determined by laser mass spectrometry, atomic emission spectrometry, inductively coupled plasma mass spectrometry, and spark source mass spectrometry.
Heat treatment of nanometer anatase powder and its photocatalytic activity for degradation of acid red B dye under visible light irradiation by Jun Wang; Rong He Li; Zhao Hong Zhang; Wei Sun; Xiao Fang Wang; Zhi Qiang Xing; Rui Xu; Xiang Dong Zhang (608-614).
The phase transformation of nanometer TiO2 powder from anatase to rutile was realized by heat treatment, and a new nanometer TiO2 photocatalyst that could be excited by visible light was obtained. The heat-treated TiO2 powder at different transition stage was characterized by powder x-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. The test of photocatalytic activity of the heat-treated TiO2 powder was carried out by the photocatalytic degradation of acid red B dye in aqueous solution under visible light irradiation. The nanometer anatase TiO2 heat-treated at 500°C for 30 min exhibited much higher activity than those of pure anatase and mechanically mixed (anatase and rutile) TiO2. The remarkable improvement of photocatalytic activity was mainly illustrated by the special interphase between rutile and anatase, which not only restrains the recombination of photogenerated electron-hole pairs but also reduces the adsorbability of nanometer anatase TiO2 powder to a certain extent. More significantly, the anticipatory interlaced energy level of heat-treated TiO2 particles is convenient for capturing photons of low energy and thus achieves the intention of using visible light.
Phase transformations of Pb0.995La0.005[Zr0.95 − y Sn0.05(Mg1/3Nb2/3) y ]0.99875O3 solid solutions by E. A. Bikyashev; E. A. Reshetnikova; I. V. Lisnevskaya; T. G. Lupeiko (615-621).
We have constructed phase diagrams of Pb0.995La0.005[Zr0.95 − y Sn0.05 (Mg1/3Nb2/3) y ]0.99875O3 (y = 0–0.02) solid solutions in different electric fields. Our results demonstrate that, by cooling in a constant electric field, the low-temperature rhombohedral ferroelectric phase can be stabilized in a narrow temperature range. It is shown that the phase state below the Curie temperature strongly depends on the temperature-field history of the material. In particular, the low-temperature rhombohedral ferroelectric phase only appears during cooling. At the same time, the temperature-field stability region of the tetragonal antiferroelectric phase is much broader during heating.
Morphology and structure of hexagonal MoO3 nanorods by V. V. Atuchin; T. A. Gavrilova; V. G. Kostrovsky; L. D. Pokrovsky; I. B. Troitskaia (622-627).
We have prepared h-MoO3 nanocrystals in the form of well-faceted straight hexagonal rods with an aspect ratio of l/d ≃ 60. The nanocrystals have been characterized by x-ray diffraction, scanning and transmission electron microscopy, and IR/Raman spectroscopy. Their phase composition has been determined, and their morphology and spectroscopic properties have been studied in detail.
Growth and properties of LiCu2O2-NaCu2O2 crystals by A. A. Bush; K. E. Kamentsev; E. A. Tischenko; V. V. Cherepanov (628-634).
Platelike Li1 − x Na x Cu2O2 single crystals up to 2 × 10 × 10 mm in dimensions have been grown by slowly cooling (1 − x)Li2CO3·xNa2O2·4CuO melts in alundum crucibles in air. Li1 − x Na x Cu2O2 solid solutions in the LiCu2O2-NaCu2O2 system have been shown to exist in the composition range 0.78 < x < 1. The temperature stability ranges of NaCu2O2 and LiCu2O2 are 780–930 and 890–1050°C, respectively. The Mössbauer spectra and electrical conductivity of the crystals have been measured.
Nanostructure of CaMgSi2O6 (Diopside) and CaTiO3 (Perovskite) mechanically activated in carbon dioxide by A. M. Kalinkin; V. N. Nevedomskii; E. V. Kalinkina (635-640).
The micro- and nanostructure of materials resulting from mechanochemical interactions of natural diopside (CaMgSi2O6) and synthetic perovskite (CaTiO3) with CO2 have been studied by transmission electron microscopy (TEM) and high-resolution TEM. The results indicate that CO2 absorption is accompanied by CO2 “dissolution” in the form of CO 3 2− ions in the structurally disordered silicate or titanate matrix. The diopside activation product is a quasi-homogeneous amorphous carbonate-silicate phase. The mechanically activated perovskite is a nanocomposite consisting of CaTiO3 nanocrystals embedded in a carbonated amorphous titanate matrix.
Mechanochemical synthesis of BaTiO3 from barium titanyl oxalate by V. A. Zazhigalov; V. V. Sidorchuk; S. V. Khalameida; L. S. Kuznetsova (641-645).
The effect of mechanochemical processing in air and water on the physicochemical transformations of barium titanyl oxalate has been studied using X-ray diffraction, thermal analysis, FTIR spectroscopy, temperature-programmed argon desorption, and particle size measurements. The results demonstrate that mechanochemical processing of barium titanyl oxalate in air leads to the formation of structurally imperfect barium titanate. During subsequent air calcination at 550°C, this material transforms into well-crystallized cubic BaTiO3, whereas thermal decomposition of barium titanyl oxalate only yields cubic BaTiO3 starting at 800°C. Mechanochemical processing in water leads to partial amorphization of barium titanyl oxalate, and conversion of the product to BaTiO3 requires heat treatment at 700°C. All of the BaTiO3 samples obtained via mechanochemical processing have a larger specific surface in comparison with samples prepared by conventional calcination of barium titanyl oxalate or other known processes.
Crystal structure of the low-temperature forms of cesium and rubidium orthophosphates by V. I. Voronin; I. F. Berger; N. V. Proskurnina; D. V. Sheptyakov; B. N. Goshchitskii; E. I. Burmakin; S. S. Stroev; G. Sh. Shekhtman (646-652).
The crystal structure of the low-temperature forms of the Cs3PO4 and Rb3PO4 orthophosphates has been determined for the first time by neutron diffraction using the Rietveld method. Cs3PO4 and Rb3PO4 are shown to be isostructural with K3PO4: orthorhombic cell (sp. gr. Pnma, Z = 4); lattice parameters a = 1.23177(6) nm, b = 0.88948(4) nm, c = 0.64197(3) nm for Cs3PO4; a = 1.17362(2) nm, b = 0.81046(1) nm, c = 0.615167(9) nm for Rb3PO4.
Dielectric properties of (1 − x)KNbO3 · xBiZn2/3Nb1/3O3 (x ≤ 0.4) perovskite solid solutions by I. I. Moroz; N. M. Olekhnovich; Yu. V. Radyush; A. V. Pushkarev (653-658).
(1 − x)KNbO3 · xBiZn2/3Nb1/3O3 ceramic materials have been prepared by solid-state reactions. The materials with x < 0.5 have been shown to be phase-pure perovskite solid solutions. Their average lattice parameter increases linearly with x. Below 300 K, the solid solutions with 0.1 < x ≤ 0.4 are ferroelectric relaxors. M″-M′ diagrams, representing the relationship between the real and imaginary parts of the complex electric modulus, have been used to evaluate the Curie temperature of the solid solutions and the temperature of their transition to the paraelectric phase. The Arrhenius plots of dc conductivity for the solid solutions show breaks corresponding to their phase transitions. Below 400 K, the dc conductivity is low, and its contribution to the dielectric response of the solid solutions is insignificant.
Luminescence spectra and kinetics of LiF〈U〉-O crystals by L. A. Lisitsyna; S. N. Putintseva; V. M. Lisitsyn; V. I. Oleshko (659-663).
The promising phosphor LiF〈U〉-O has been studied by nanosecond-resolution pulsed spectrometry. The uranium and oxygen luminescence buildup and decay characteristics have been measured at 300 K. The uranium luminescence buildup under nanosecond electron excitation has been shown to involve two steps. The effect of pulsed electron irradiation on the activator luminescence efficiency has been assessed.
Effect of BiI3 doping on the optical properties of CaI2 by S. S. Novosad; I. S. Novosad; O. S. Novosad; I. A. Khvyschun (664-668).
The effect of BiI3 doping on the optical absorption spectra and roentgeno-, photo-, and thermoluminescence of CaI2 scintillator crystals has been studied in the temperature range 90–295 K. The crystals were grown by the Bridgman-Stockbarger method. Doping of CaI2 with BiI3 from the melt gives rise to absorption bands centered at 466, 400, and 350 nm, which can be interpreted as the A, B, and C bands due to electronic transitions from the 1 S 0 state to the 3 P 1, 3 P 2, and 1 P 1 levels of a free Bi3+ ion. The absorption band at 270–290 nm is assignable to near-activator excitons. Changes in spectral composition and the reduction in luminescence intensity caused by Bi3+ doping of CaI2 are associated mainly with the reabsorption of the emission from centers characteristic of the host by activator centers. Under x-ray excitation, the spectrum of heavily doped crystals shows, in addition, a weak emission centered around 620 nm, which is probably due to an impurity phase. The light sum of CaI2:Bi3+ under x-ray excitation is small and is due to shallow traps. Upon Bi3+ substitution on the cation site of CaI2, the excess charge of the activator is probably compensated by unintentional O2− impurity and vacancy pairs near Bi3+ centers—one vacancy in a neighboring cation site and the other in a neighboring anion site.
Effect of Mn2+ doping on the temperature coefficient of capacitance of TiO2/SiO2-doped BaTiO3 ceramics by Tang Bin; Zhang Shu-Ren; Zhou Xiao-Hua (669-672).
The effect of Mn2+ on the temperature coefficient of capacitance (TCC) of TiO2/SiO2-doped BaTiO3 ceramics has been investigated. The experiment has shown that the high temperature peak of TCC exhibited a continuous enhancement when Mn2+ concentration increased and X8R specification was gradually met. The secondary phase Ba2TiSi2O8 was found in all samples. SEM and XRD analyses have proved that Mn2+ could depress the crystallization of TiO2/SiO2 in BaTiO3 ceramics. The microstrain study through MAUD analysis depicted that the high temperature peak of TCC was dependent on the microstrain of samples to a certain extent. The Mn2+ could be a useful dopant for ameliorating the TCC of TiO2/SiO2-doped BaTiO3 ceramics.