Inorganic Materials (v.46, #9)
High-pressure magnetic phase transition and galvanomagnetic effects in the high-temperature ferromagnet p-Cd0.7Mn0.3GeAs2 by A. Yu. Mollaev; I. K. Kamilov; S. F. Marenkin; R. K. Arslanov; U. Z. Zalibekov; T. R. Arslanov; A. A. Abdullaev; I. V. Fedorchenko (919-923).
The ferromagnetic semiconductor Cd0.7Mn0.3GeAs2 undergoes a high-pressure ferromagnetic-to-antiferromagnetic phase transition. We have studied this transition at different temperatures. From magnetic-field dependences of the Hall resistance measured at different temperatures, we have derived the normal and anomalous Hall coefficients of the material as functions of temperature. Its transverse magnetoresistance changes from positive to negative near the ferromagnetic-to-antiferromagnetic phase transition.
Quantum-chemical modeling of interaction between gold nanoclusters and thiols by V. G. Yarzhemsky; Yu. V. Norov; S. V. Murashov; C. Battocchio; I. Fratoddi; I. Venditti; G. Polzonetti (924-930).
Ab initio calculations are used to model small Au n nanoclusters and Au m SH clusters. The results for the Au6, Au8, and Au20 clusters demonstrate that the substitution of a SH group for a Au atom gives a stable cluster of the same geometry if the Au atom has an acute bond angle and a negative effective charge. The example of the Au10 cluster suggests that SH substitution for Au has a stabilizing effect. The modeling results are discussed with application to self-organizing thiol monolayers on gold clusters.
Solid-state reactions underlying mechanochemical synthesis in the Fe-Al system by K. V. Tret’yakov; A. V. Leonov; V. K. Portnoi; S. A. Fedotov (931-941).
The sequence of solid-state transformations in the mechanochemical synthesis of Fe-Al intermetallics according to the reactions Fe + Al = FeAl, FeAl + 2Fe = Fe3Al, and 2FeAl + 3Al = Fe2Al5 in powder mixtures has been studied by X-ray diffraction, differential scanning calorimetry, and Mössbauer spectroscopy. The results indicate that the process involves the formation of atomic configurations that may become nuclei of stable or metastable intermediate phases. Prolonged milling leads to homogenization of the synthesis product and the formation of a solid solution or an intermetallic phase with a low degree of long-range order. Complete ordering of the intermetallic phase can as a rule be achieved by heating.
Microstructure and properties of SiC-whisker-reinforced Si3N4 ceramics with calcium aluminate additions by S. N. Ivicheva; Yu. F. Kargin; A. S. Lysenkov; O. V. Baranova (942-947).
Silicon-nitride-based ceramics containing Al2O3-CaO sintering aids and reinforced with silicon carbide whiskers have been prepared by hot pressing at 1650°C in a nitrogen atmosphere, and their microstructure, phase composition, and mechanical properties have been studied. The results indicate that the Si3N4 ceramic containing 15 wt % calcium aluminate additions and 10 wt % SiC fibers has a dense microstructure with a uniform distribution of skeletal and dendritic silicon carbide crystals. The observed variations in the morphology of the crystals are tentatively attributed to the secondary crystallization of silicon carbide from the eutectic calcium aluminate melt during cooling.
p-n junctions in ZnO implanted with group V ions by I. V. Rogozin; A. N. Georgobiani; M. B. Kotlyarevsky; V. I. Demin; A. V. Marakhovskii (948-952).
n-Type ZnO〈Ga〉 films were implanted with 150-keV N+ (As+) ions to a dose of 7 × 1015 cm−2 and then annealed in atomic oxygen at different temperatures. p-Type conductivity was obtained at annealing temperatures in the range 770–870 K. The parameters of the p-type layers were determined by photoluminescence spectroscopy, secondary ion mass spectrometry, and Hall effect measurements. According to the Hall data, the p-type layers had a resistivity of ∼30 Ω cm, carrier mobility of ∼2 cm2/(V s), and carrier concentration of ∼1018 cm−3. The electroluminescence spectra of the p-n junctions produced by ion implantation showed a band at 440 nm, due to recombination via donor-acceptor pairs.
The reaction conditions influence on hydrothermal synthesis of boehmite nanorods by Qi Yang (953-958).
Synthesis of boehmite (γ-AlOOH) nanorods were performed by using aluminum nitrate and sodium hydroxide as starting materials in conditions of controlled pH value of reaction mixture, temperature and holding time. X-ray diffraction, transmission electron microscope, high resolution transmission electron microscope, selected area electron diffraction and N2 adsorption-desorption analysis were used to characterize morphology and structure feathers of the obtained products. The results show that γ-AlOOH nanorods with diameter of 10–30 nm, length of 200–300 nm, aspect ratio of 5–15, regular shape and clear surface were synthesized at 200–220°C for 24 h under pH = 5. The effect of reaction conditions on the morphology of 1D boehmite nanomaterials was discussed.
Phase composition and thermal properties of Ce1 − x Ln x O2 − d (Ln = Sm, Pr) solid solutions by A. A. Ostroushko; O. V. Russkikh; S. A. Petrova; R. G. Zakharov; M. V. Prosvetova (959-964).
Ce1 − x Ln x O2 − d (Ln = Sm, Pr; x = 0–0.30) oxides have been prepared through pyrolysis of polymer-salt systems, and their particle size and specific surface area have been determined. Their sintering behavior and thermal expansion have been studied using dilatometry. The thermal expansion of the Pr-containing materials is shown to vary considerably with temperature. X-ray diffraction data (obtained at various temperatures and oxygen pressures) suggest that the Ce1 − x Pr x O2 − d oxides undergo a low-temperature phase transition, presumably a reversible decomposition of one solid solution to two others. The structural parameters of the phases involved and the oxygen nonstoichiometry of the samples are determined.
Solar photocatalytic degradation of rhodamine B by heat-treated nanometer anatase TiO2 powder by Jun Wang; Chengwu Li; Liqun Zhang; Jia Li; Ying Li; Guangxi Han; Rui Xu; Xiangdong Zhang (965-970).
The partial phase transformation of nanometer TiO2 powder from anatase to rutile was realized by heat-treatment, and then a novel photocatalyst which could utilize solarlight was obtained. The heat-treated nanometer TiO2 powders at different transition stage were characterized by XRD, TEM and UV-vis spectra. In addition, the photocatalytic activity of heat-treated nanometer TiO2 powder was tested out through the degradation of Rhodamine B dye in aqueous solution under solarlight irradiation. The results reveal that the nanometer anatase TiO2 powder heat-treated at 500°C for 80 min exhibites the highest photocatalytic activity. That is, Rhodamine B dye can effectively degraded under solarlight irradiation in the presence of heat-treated nanometer TiO2 powder.
Effect of high-temperature annealing on solid-state reactions in hydroxyapatite/TiO2 films on titanium substrates by A. Yu. Berezhnaya; V. O. Mittova; E. V. Kukueva; I. Ya. Mittova (971-977).
Hydroxyapatite (HA) films 0.5 and 1 μm thick with a 0.2-μm TiO2 underlayer have been grown on titanium by rf magnetron sputtering. After annealing in an argon atmosphere at 900, 950, and 1000°C for 30 and 60 min, the phase composition, elemental composition, and surface morphology of the films have been determined by scanning electron microscopy, X-ray microanalysis, and X-ray diffraction. The surface microstructure of the films is shown to depend on annealing temperature. X-ray microanalysis results indicate that, at HA layer thicknesses of both 1 and 0.5 μm, the Ca/P ratio increases with annealing temperature. In addition, the Ca/P ratio in the films produced under identical conditions depends on the film thickness. X-ray diffraction data indicate the presence of reaction intermediates. A TiO2 interlayer in the HA/Ti system inhibits titanium oxidation, and the reaction intermediates forming during heat treatment improve the adhesion between the titanium and HA.
Redox modification of high-silica zeolites with chromium via multistep cluster synthesis by V. E. Vakhmistrov; A. B. Ponomaryov; M. V. Shostakovsky; V. N. Kalinin; S. P. Solodovnikov; E. S. Mortikov (978-982).
This paper examines the modification of zeolites with superstoichiometric amounts of metals using multistep cluster synthesis. Ion-exchange sites in zeolite MFI-50 (SiO2/Al2O3 molar ratio of 50) have been modified with hydrazonium cations. Subsequent redox reaction with chromate anions has yielded a chromium-containing zeolite. The sample prepared by three ion-exchange/redox cycles contains 10 wt % chromium (Cr-MFI-50). EPR results show that most of the chromium in Cr-MFI-50 is in the form of fine Cr2O3 particles. In addition, the material contains isolated Cr5+ ions and, presumably, Cr3+ stabilized at aluminum vacancies.
Luminescence of Ce3+ ion doped in SrZn2(PO4)2 phosphor under excitation of vacuum ultraviolet by Yonggang Cao; Yanlin Huang; Liang Shi; Hyo Jin Seo; Ye Tao (983-987).
Ce3+ doped SrZn2(PO4)2 was prepared by high temperature solid-state reaction. The phosphor was investigated by X-ray powder diffraction, scanning electron microscope, and FT-IR measurements. Spectroscopic properties of the phosphor were characterized by vacuum ultraviolet spectroscopy. According to the excitation spectrum, the five 5d levels corresponding to the 4f 1 → 4f 05d 1 transitions of Ce3+ ions were clearly identified. The observed excitation bands in the VUV region are due to the PO 4 3− anion groups of the host, in which energy transfer to Ce3+ ions is rather efficient. The emission bands corresponding to the 4f 1 → 4f 05d 1 transitions of Ce3+ ions were analyzed. The barycenter of Ce3+ ions, host absorption bands, crystal field splitting, emission wavelength and Stokes shift were calculated and discussed.
Composition, structural parameters, and color of langatate by I. A. Kaurova; G. M. Kuz’micheva; V. B. Rybakov; A. B. Dubovskii; A. Cousson (988-993).
Langatate crystals with the nominal composition La3(Ga0.5Ta0.5)Ga5O14 grown by Czochralski pulling along 〈0001〉 have been studied by X-ray and neutron diffraction before and after postgrowth annealing in air and vacuum. Their compositions are determined, the relationship between the Ga/Ta ratio and unit-cell parameters is established, and their color (colorless, yellow, and orange crystals) is shown to depend on their oxygen content and the growth and annealing conditions. Vacuum annealing at sufficiently high temperatures leads to precipitation of a green phase, La(Ta,Ga)3+O3.
MCVD of fluorosilicate glass by V. A. Aksenov; G. A. Ivanov; V. A. Isaev; M. E. Likhachev (994-997).
Preforms with a fluorosilicate glass core produced by the modified chemical vapor deposition process with SiF4 as the fluorination agent were used to study the effect of initial vapor mixture composition on the refractive-index difference Δn between the fluorosilicate and silica glasses and the glass deposition rate. The results indicate that Δn can reach about −0.01. The marked reduction in the deposition rate of fluorosilicate glass with increasing SiF4 concentration seems to be due to chemical reactions that lead to the formation of stable gaseous chlorofluorosilanes.
Vapor composition over nonstoichiometric crystals studied by vapor pressure measurements by V. N. Guskov; A. D. Izotov (998-1000).
This work examines a direct procedure, referred to as vapor pressure scanning (VPS), for assessing the composition of nonstoichiometric crystals and calculating the vapor composition from experimental vapor pressure data. A VP phase analysis procedure is proposed as a precision technique for determining the phase composition of samples. Single-phase samples can be prepared by an “equalization” method.
Structural defects and band-structure parameters of CdAs2, ZnAs2, Cd1 − x Zn x As2, and Zn1 − x Cd x As2 single crystals by S. F. Marenkin; V. A. Morozova; O. G. Koshelev (1001-1006).
Structurally perfect CdAs2, ZnAs2, Cd1 − x Zn x As2, and Zn1 − x Cd x As2 single crystals have been grown, and the main parameters of their band structure have been determined. We have proposed band structure models for the crystals and presented evidence in favor of the models of structural defects responsible for the donor and acceptor levels in CdAs2, ZnAs2, Cd1 − xZn x As2, and Zn1 − x Cd x As2.
Heat capacity of GaBV and InBV (BV = P, As, Sb) above 298 K by A. S. Pashinkin; V. A. Fedorov; A. S. Malkova; M. S. Mikhailova (1007-1012).
The heat capacity of indium phosphide has been measured from 350 to 750 K. The results are used to more accurately determine the best fit equation for the C p (T) of InP. We analyze our and others’ heat capacity data for the III–V compounds (except for the Group III nitrides) at temperatures above 298 K and recommend the most reliable C p (T) results.
High-power InP/GaInAsP buried heterostructure semiconductor laser with a modulation band of up to 10 GHz by M. G. Vasil’ev; A. M. Vasil’ev; A. A. Shelyakin (1013-1018).
As a continuation of our studies aimed at designing InP/GaInAsP heterostructures based on semi-conductor solid solutions, we consider the design and fabrication aspects of laser emitters with a high average-power bandwidth product. We describe in detail experimental studies of the microwave parameters of laser emitters and present their power-current curves, spectral response, and frequency modulation characteristics at frequencies of up to 10 GHz.
Subsolidus phase relations of Mg-Ga-Fe-O spinel solid solutions by G. D. Nipan; V. A. Ketsko; T. N. Kol’tsova; M. A. Kop’eva; A. I. Stognii; A. V. Trukhanov (1019-1024).
The phase relations of Mg-Ga-Fe-O spinel solid solutions have been analyzed in a topological approach using composition diagrams. Oxides with the nominal compositions Mg1 − x Ga2 − 2x Fe3x O4 + δ and Mg1 − x Ga2x Fe2 − x O4 + δ (with x varied in steps of 0.1) prepared by a pyrohydrolytic process and air-annealed at 1270 K have been studied by X-ray diffraction.
Heat capacity of Li x Ni2 − x O2 solid solutions by A. L. Emelina; M. A. Bykov; M. L. Kovba; K. S. Gavrichev (1025-1030).
We have synthesized Li x Ni2 − x O2 oxides in the range x = 0.1–0.84 and showed that the solid-solution system contains a two-phase region. The heat capacity of Li x Ni2 − x O2 has been determined by differential scanning calorimetry.
Low-temperature heat capacity of Li x Ni2 − x O2 solid solutions by K. S. Gavrichev; A. V. Tyurin; M. A. Ryumin; A. S. Bogomyakov (1031-1037).
The heat capacity of Li x Ni2 − x O2 (x = 0.40–0.76) oxides has been measured using an adiabatic calorimeter, and their thermodynamic functions have been determined. The results indicate that the lithium nickelate solid-solution series contains a two-phase region and that near-stoichiometric LiNiO2 has a layered structure, in accordance with earlier results.