Inorganic Materials (v.48, #5)

Ion beam deposition of photoactive nanolayers for silicon solar cells by L. S. Lunin; S. N. Chebotarev; A. S. Pashchenko; L. N. Bolobanova (439-444).
The ion beam deposition of photoactive silicon nanolayers through the bombardment of a single-crystal silicon target with an Ar+ ion beam has been analyzed using computer simulation. The model thus derived is consistent with experimental data on the growth of silicon nanolayers on 100-mm-diameter c-Si(p) substrates. The process conditions have been optimized experimentally: pressure, 10−4 Pa; substrate temperature, 550 ± 50°C; target-substrate distance, 240 ± 5 mm; target-beam angle, 45° ± 2°; accelerating voltage, 450–600 V. Under these conditions, the radial asymmetry of 300-nm-thick c-Si(n) layers is within 10 nm, which reduces the efficiency of c-Si(n +)/c-Si(p)/c-Si(p +) solar cells by no more than 0.3%.

Hydrogenated microcrystalline silicon for solar cells by R. G. Sharafutdinov; V. G. Shchukin; O. I. Semenova (445-450).
We report a detailed study of the deposition, composition, structure, and photoelectric properties of low-temperature microcrystalline silicon layers produced by a novel method, which takes advantage of the activation of gas mixtures in an electron-beam plasma and the transport of the activated particles to the deposition zone at a supersonic speed. Under optimal conditions, we have reached deposition rates above 5 nm/s on substrates 150 × 150 mm in dimensions. The method under development is potentially attractive for the fabrication of thin-film solar cells through roll-to-roll processing on cheap substrates.

The etching behavior of zinc selenide has been studied at temperatures from 20 to 90°C in inorganic acid solutions of different concentrations, with additions of H2O2 as an oxidant. The kinetic data obtained have been used to identify the mechanisms of the reactions involved and develop a chemical mechanical polishing procedure for polycrystalline zinc selenide.

Percolation effect in copper- and nickel-doped Bi2Te3 crystals by F. K. Aleskerov; K. Sh. Kakhramanov; S. Sh. Kakhramanov (456-461).
The (0001) surface morphology of Bi2Te3〈M〉 (M = Cu, Ni) layered crystals has been studied using atomic force microscopy (AFM) and scanning electron microscopy. Two- and three-dimensional AFM images reveal charge transport paths through inhomogeneities created by nanostructured elements (5–20 nm) in the Te(1)-Te(1) interlayer spaces. The nanoparticle distribution in the (0001) plane is similar to the arrangement of model two-dimensional percolation clusters on a square lattice. The carrier mobility in Bi2Te3〈0.5 wt % Ni〉 crystals varies anomalously between 80 and 120 K.

The dispersion laws of the optical and acoustic branches in diamond-like crystals have been derived using idealized models of crystal lattices. Two types of analytical expressions have been proposed, whose parameters can be derived from inelastic neutron scattering experiments and the properties of acoustic waves. The calculation results are in satisfactory agreement with experimental data for the crystallographic directions [100], [110], and [111]. The group velocities of optical and acoustic phonons have been determined, and expressions for the effective mass of optical phonons have been derived.

This paper examines the growth of aligned ZnO nanorod arrays through chemical deposition from solution and the vapor phase. The nanorod alignment is ensured primarily by a thin layer of seeds—zinc oxide nanoparticles produced by decomposing zinc acetate directly on the substrate and aligned with their c axes normal to the substrate surface. The acetate route was used to produce nanorod arrays 1 × 1 mm in dimensions on substrates with photoresist.

A negative refraction effect has been found in opal photonic crystals in the visible range. We have calculated the dispersion branches of a photonic crystal and determined the position of its photonic band gap. The frequency range has been identified where the refractive index of the opal is negative. An experimental arrangement is proposed for focusing a light beam by passing it through a plane-parallel opal photonic crystal and experimental evidence is presented in favor of negative refraction in the visible range.

Ferroin adsorption on TiO2-based photocatalytic materials by T. A. Sedneva; E. P. Lokshin; M. L. Belikov (480-487).
We have studied ferroin adsorption on photocatalytically active nanocomposites based on TiO2 doped with Fe3+, Nb5+, or W6+. The results demonstrate that the mass of an adsorbed organic substance correlates with the photocatalytic activity of the photocatalysts. High-temperature heat treatment of the nanocomposites increases manyfold the mass of an organic substance adsorbed from an aqueous solution for unit free surface area of the photocatalyst.

Phase transformations in the TiO2-NiO system by V. V. Viktorov; E. A. Belaya; A. S. Serikov (488-493).
The anatase-rutile phase transition in fine-particle TiO2-NiO oxides has been studied using physicochemical characterization techniques (X-ray diffraction, differential thermal analysis, and mass spectrometry). The results demonstrate that NiO additions considerably increase the rate of the anataserutile polymorphic transformation. Nickel titanate formation depends on the procedures used to prepare both titanium dioxide and nickel oxide. In the temperature range 700–850°C, the anatase to rutile phase transition prevents nickel titanate formation.

Synthesis of nanocrystalline ZrO2 with tailored phase composition and microstructure under high-power sonication by A. D. Yapryntsev; A. E. Baranchikov; N. N. Gubanova; V. K. Ivanov; Yu. D. Tret’yakov (494-499).
The effect of sonication on the composition and properties of zirconia precipitated from aqueous zirconyl nitrate solutions at various pH values has been studied using thermal analysis, X-ray diffraction, and low-temperature nitrogen adsorption measurements. The results demonstrate that acoustic processing considerably reduces the content of sorbed ions in amorphous ZrO2 · xH2O gels and allows one to control the composition and microstructure of the nanocrystalline zirconia produced through thermal decomposition of the gels.

Synthesis and properties of yttrium hydroxyacetate sols by S. S. Balabanov; E. M. Gavrishchuk; D. A. Permin (500-503).
We report a process for the preparation of yttrium hydroxyacetate sols by sonicating yttria nanopowder in aqueous acetic acid. The dependences of the rheological characteristics and electrokinetic potential of the sols on the pH of the medium and the concentration of chloride and sulfate anions are used to identify the mechanism underlying the coagulation stability of the sols. The thermal decomposition of the yttrium hydroxyacetate xerogel obtained by drying the sol is analyzed in detail.

Heat capacity and thermodynamic properties of crystalline SrB4O7 by N. V. Moiseev; P. A. Popov; V. D. Solomennik; A. I. Zaitsev; A. V. Cherepakhin (504-507).
The heat capacity of a strontium tetraborate (SrB4O7) single crystal has been determined in the temperature range 55–300 K by adiabatic calorimetry, and its Debye characteristic temperature, entropy change, enthalpy increment, and phonon mean free path have been calculated as functions of temperature.

Structure effect on the absorption and circular dichroism spectra of Sm14B6Ge2O34 crystals by V. A. Krut’ko; V. I. Burkov; L. N. Alyabeva; M. G. Komova; G. A. Bandurkin (508-512).
The spectroscopic and chiroptical properties of rare-earth-rich borate germanate crystals of composition Sm14B6Ge2O34 have been studied for the first time. The absorption and circular dichroism spectra of the crystals have been measured. For some of the f-f transitions involved, we have calculated the dipole strength and optical rotatory power.

Lithium diffusion in materials based on LiFePO4 doped with cobalt and magnesium by D. V. Safronov; S. A. Novikova; T. L. Kulova; A. M. Skundin; A. B. Yaroslavtsev (513-519).
We have studied lithium intercalation/deintercalation kinetics in magnesium- and cobalt-doped lithium iron double phosphates in a cathode material for lithium ion batteries. The results demonstrate that the incorporation of divalent cations reduces the charge and discharge capacities of the samples, the effect being stronger in the magnesium-doped materials. In addition, magnesium doping markedly increases the resistivity of the material in both the lithiated and delithiated states, whereas the resistivity of the cobalt-doped materials is considerably lower in comparison with the undoped material, which leads to an increase in the charging/discharging rate of batteries despite the marked increase in particle size. These findings can be understood in terms of different doping mechanisms: it seems likely that cobalt substitutes for iron, whereas magnesium is accommodated predominantly in the lithium site.

Structure and luminescent properties of Cs2Sr(VO3)4:Mn2+ by B. V. Slobodin; A. V. Ishchenko; R. F. Samigullina; B. V. Shul’gin; M. A. Melkozerova; E. V. Zabolotskaya (520-524).
We have developed a procedure for thermally stimulated synthesis of a cesium strontium metavanadate, Cs2Sr(VO3)4:Mn2+ (0.01, 0.50, 1.00, 5.00 at % Mn2+), using MnO-containing starting mixtures. The EPR spectrum of the material containing 0.01 at % Mn2+ shows a hyperfine structure due to the incorporation of a small amount of manganese into the diamagnetic double metavanadate host. The luminescent and optical properties of Cs2Sr(VO3)4:Mn2+ depend on manganese content. In contrast to higher doping levels, doping with 0.01 at % Mn2+ increases the integrated emission intensity of the vanadate by 10% and improves its chromaticity characteristics (approaching them to those of white light). We assume that this is due to the reduction in the density of vacancy-type growth defects, such as oxygen vacancies.

Cation distribution in nanocrystalline Ni x Zn1 − x Fe2O4 spinel ferrites by A. P. Kazin; M. N. Rumyantseva; V. E. Prusakov; I. P. Suzdalev; A. M. Gaskov (525-530).
We have studied the cation distribution over the tetrahedral and octahedral sites in the spinel structure of nanocrystalline Ni x Zn1 − x Fe2O4 ferrites prepared by spray pyrolysis. 57Fe Mössbauer spectroscopy data for the ferrites demonstrate that, depending on the composition of the materials, the tetrahedral site may accommodate only Fe3+ (inverse spinel, x ≥ 0.4) or both Fe3+ and Zn2+ cations (mixed spinel, x = 0 and 0.2), which accounts for the fact that the composition dependence of the unit-cell parameter for the ferrites deviates from Vegard’s law.

Synthesis of ultrafine fluorite Sr1 − x Nd x F2 + x powders by A. A. Luginina; P. P. Fedorov; S. V. Kuznetsov; M. N. Mayakova; V. V. Osiko; V. K. Ivanov; A. E. Baranchikov (531-538).
We have identified conditions that ensure the preparation of ultrafine Sr1 − x Nd x F2 + x powders uniform in phase composition. The powders were characterized by X-ray diffraction and scanning electron microscopy. The powder particles have the form of faceted nano- and microcubes and range in size from 30–100 nm to 0.3–2.5 μm, depending on precipitation conditions.

Luminescent properties and stability of europium ions in Ca2BO3Cl:Eu by I. V. Berezovskaya; N. P. Efryushina; A. S. Voloshinovskii; S. I. Vdovenko; I. P. Kovalevskaya; V. P. Dotsenko (539-543).
We have studied the luminescent properties of Eu2+ and Eu3+ in the calcium chloride borate Ca2BO3Cl under optical and synchrotron excitation. The results demonstrate that a reductant should be present during synthesis in order to stabilize Eu2+ in Ca2BO3Cl and provide insight into the factors responsible for the long-wavelength position of the luminescence band (λmax = 577 nm) and the relatively low Eu2+ stability in Ca2BO3Cl.

Effect of ripening time on the sintering of CaCO3 powders and the properties of the resultant ceramics by V. V. Smirnov; N. V. Bakunova; S. M. Barinov; M. A. Gol’dberg; S. V. Kutsev; L. I. Shvorneva (544-548).
We have studied the effect of the ripening time in the synthesis of calcium carbonate powders through mechanochemical activation on the characteristics and sintering behavior of the powders. The results demonstrate that increasing the ripening time leads to recrystallization of the precipitate and formation of larger, more perfect crystals. This impairs the sinterability of the powder and, as a consequence, leads to an increase in the porosity of the ceramics and a reduction in their strength. We have obtained calcium carbonate ceramics with a grain size of 1–3 μm and bending strength of up to 73 MPa, potentially attractive for bone tissue regeneration.

Heat release in the preparation of TiC-Al2O3 ceramics by V. P. Kobyakov; T. V. Barinova; L. B. Mashkinov; M. A. Sichinava (549-551).
Mixtures for the self-propagating high-temperature synthesis of TiC-Al2O3 ceramics for radioactive waste immobilization have been studied using a modified BKS-3 combustion bomb calorimeter.