Inorganic Materials (v.49, #10)

The thickness and optical constants of films grown through the thermal oxidation of V2O5/InP, (NiO + PbO)/InP, and (V2O5+ PbO)/InP structures produced by magnetron sputtering have been determined by spectral ellipsometry. The results demonstrate that the structures have sharp interfaces and their optical constants in the long-wavelength part of the spectrum are well described by the Cauchy model with a normal dispersion law, which allows one to determine the thickness of such nanofilms with high accuracy using high-speed ellipsometric characterization with a single-wavelength laser ellipsometer.

Dynamic chemical polishing of undoped and doped ZnSe crystals with H2O2-HBr-H2O solutions by V. N. Tomashik; A. S. Kravtsova; Z. F. Tomashik; I. B. Stratiichuk; S. N. Galkin (971-974).
We have studied the chemical interaction of the surface of undoped and doped ZnSe crystals with H2O2-HBr-H2O bromine-releasing solutions. The dissolution rate of the semiconductor materials has been measured as a function of etchant composition, stirring rate, temperature, and doping. The composition region of polishing solutions has been mapped out, and the surface condition after chemical etching has been examined by microstructural analysis. We have proposed and optimized polishing etchant compositions and conditions for chemical polishing of the semiconductors.

This paper examines the feasibility of using transition metal oxides (cobalt, iron, copper, molybdenum, and vanadium oxides) as catalysts for ammonia borane (AB) hydrolysis. In our experiments, we used an aqueous solution containing 0.24 wt % AB. The amount of oxide catalysts was 10–40 mg. The hydrolysis process was run in the temperature range from 35 to 80°C. The highest hydrogen evolution rate was observed at a temperature of 80°C in the presence of cobalt and iron oxides (Co3O4 and Fe2O3 · nH2O). The data obtained for the cobalt and iron oxides demonstrate that the reaction is first-order in ammonia borane. We determined the rate constants of the process and its apparent activation energy: 47.5 kJ/mol for Co3O4 and 60.2 kJ/mol for Fe2O3 · nH2O. The cobalt and iron oxides were shown to be efficient catalysts for hydrogen production from aqueous AB solutions.

Ag nanoparticles 10 to 60 nm in size have been prepared by reducing silver ions in aqueous tea leaf extract. The properties of the nanoparticles have been studied by ultraviolet spectroscopy, atomic absorption, surface-enhanced Raman spectroscopy, and atomic force microscopy. According to the Raman spectroscopy results, the equilibrium of the redox reaction is displaced to an antioxidant form of flavonoids. The presence of silver nanoparticles enhances the antioxidant and bactericidal properties of tea.

Preparation of biomorphic SiC by E. I. Istomina; P. V. Istomin; A. V. Nadutkin (984-987).
A carbon template has been silicided with gaseous SiO at 1350°C in vacuum using a mixture of silicon and silicon dioxide powders as a SiO source and pyrolyzed birch wood as a carbon template. The results demonstrate the feasibility of producing biomorphic SiC whose microstructure replicates the structure of the carbon template. The material thus obtained has a porosity of about 80% and an axial compressive strength of 35 MPa.

Photostimulated growth of In-In2O3 films by E. P. Surovoi; G. O. Ramazanova (988-992).
Exposure to light of intensity I =1.12 × 1015 to 7.0 × 1015 photons/(cm2 s) at λ = 360 nm and T = 293 K produces significant changes in the absorption and reflection spectra and weight of indium films 1 to 32 nm in thickness. Kinetic curves for the photochemical transformation of the indium films are adequately represented by a linear, inverse logarithmic, parabolic, or logarithmic rate law. We have measured the contact potential difference across the In and In2O3 films and the photovoltage in the In-In2O3 system. A model has been proposed which includes the generation and redistribution of nonequilibrium charge carriers in the In-In2O3 interfacial field, oxygen adsorption, In3+ diffusion, and In2O3 formation.

Phase composition and pore structure of nanoparticulate tin oxides prepared by AC electrochemical synthesis by V. V. Korobochkin; M. A. Balmashnov; D. A. Gorlushko; N. V. Usol’tseva; V. V. Bochkareva (993-999).
The effect of current density and sodium chloride concentration in solution on the phase composition and pore structure of the products of ac electrolysis of metallic Sn has been studied using X-ray diffraction, thermogravimetry, differential scanning calorimetry, electron microscopy, and low-temperature nitrogen adsorption measurements. The results demonstrate that the synthesis products consist of tin(II) and tin(IV) oxides and hydroxides, whose percentages depend on electrolysis conditions, and have a large specific surface area and mesoporous structure. The average particle size ranges from 10 to 30 nm.

Frequency-dependent electrical conductivity of nanocrystalline SnO2 by A. S. Chizhov; M. N. Rumyantseva; A. M. Gaskov (1000-1004).
Nanocrystalline SnO2 with a crystallite size of 3–4 and 5–6 nm has been prepared by a sol-gel process in aqueous solution. Its ac electrical conductivity has been measured in dry air at a temperature of 200°C. The observed frequency dependence of its conductivity has been interpreted in terms of the random potential barrier model. The data obtained indicate that the transport properties of the material are dominated by hopping conduction through disordered crystallite boundaries.

Effect of surface modification with palladium on the CO sensing properties of antimony-doped SnO2 whiskers by A. A. Zhukova; A. N. Shatokhin; F. N. Putilin; I. A. Petukhov; M. N. Rumyantseva; A. M. Gaskov (1005-1010).
Antimony-doped tin dioxide whiskers have been prepared by vapor growth in a tube furnace in a flowing mixture of argon and oxygen at a constant evaporation temperature. The antimony concentration was measured by laser mass spectrometry. Palladium was deposited by laser ablation. The palladium-modified whiskers exhibit a sensing response to CO at the level of its maximum allowable concentration in the workplace.

Effect of cobalt layer thickness on the magnetoelectric properties of Co/PbZr0.45Ti0.55O3/Co heterostructures by A. I. Stognij; N. N. Novitskii; S. A. Sharko; A. V. Bespalov; O. L. Golikova; A. Sazanovich; V. Dyakonov; H. Szymczak; M. N. Smirnova; V. A. Ketsko (1011-1014).
We have studied the magnetic properties and determined the optimal range of thicknesses of cobalt films grown on PbZr0.45Ti0.55O3 (PZT) ceramic substrates with smoothed surfaces. Using an ion-beam deposition-sputtering process, we have produced Co/PZT/Co heterostructures with smooth, thermally stable PZT/Co interfaces. The structures exhibit a reproducible magnetoelectric effect comparable in magnitude to that in known layered structures fabricated by splicing ferromagnetic and ferroelectric layers. A ferromagnetic layer of optimal thickness makes the largest contribution to the magnetoelectric effect. The structures can be used as elements of more complex, multilayer structures. The use of the ion-beam deposition-sputtering process allows one to scale up such heterostructures by microelectronic means in producing magnetoelectric devices.

The Y3+/Ho3+, Y3+/Dy3+, and Dy3+/Ho3+ interdiffusion coefficients in the YBa2Cu3O7 − δ-HoBa2Cu3O7 − δ, YBa2Cu3O7 − δ-DyBa2Cu3O7 − δ, and DyBa2Cu3O7 − δ-HoBa2Cu3O7 − δ systems have been determined in air at a temperature of 1233 K by the Boltzmann-Matano method from the yttrium/holmium, yttrium/dysprosium, and dysprosium/holmium concentration profiles across the diffusion zone between two pellets of the high-T c superconductors. The composition dependences of the interdiffusion coefficients in the solid-solution systems are presented.

Disintegration of microcrystalline Zn2SiO4:Mn phosphor powder by K. A. Petrovykh; A. A. Rempel; V. S. Kortov; A. A. Valeeva; S. V. Zvonarev (1019-1022).
Zn2SiO4:Mn (willemite) nanoparticles ∼30 nm in size have been prepared by disintegrating microcrystalline willemite powder in a planetary ball mill. X-ray diffraction and scanning electron micros-copy characterization showed that ball milling of the Zn2SiO4:Mn powder for 60 min or a longer time ensured complete disintegration of the microcrystalline material and that the crystal structure of the resultant nanoparticles was identical to that of the parent powder.

We have studied the accommodation of niobium and cerium variable valence cations in the Ln 2 3+ Ti 2 4+ O7 (3+/4+) (Ln = Dy, Yb) pyrochlores in air and in a 5% H2 + 95% Ar reducing atmosphere. The (Dy0.8Ca0.1Ce0.1)2Ti2O7 − δ and (Yb0.8Tb0.1Ca0.1)2[Ti1−x Nb x ]2O7 − δ (x = 0–0.3) oxygen ion conducting solid solutions were synthesized through coprecipitation followed by heat treatment in air for 4 h at temperatures of 1400 and 1550°C, respectively. According to X-ray photoelectron spectroscopy (XPS) data, the valence state of the niobium in the (Yb0.8Tb0.1Ca0.1)2[Ti1−x Nb x ]2O7 − δ (x = 0.05, 0.1) solid solutions is 4+ and, hence, isovalent niobium substitution for titanium takes place. During synthesis in air, the titanium sublattice of the (Yb0.8Tb0.1Ca0.1)2[Ti1−x Nb x ]2O7 − δ pyrochlores is stable when the Nb4+ content does not exceed 10% (x = 0.1). According to conductivity data for the high-conductivity material (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9 at low oxygen partial pressures, there is no reduction of pentavalent niobium and no increase in electronic conductivity, which is supported by XPS results that only Nb4+ is present in the solid solution. In pyrochlore-like (Dy0.8Ca0.1Ce0.1)2Ti2O7 − δ synthesized in air at 1400°C, the dysprosium site contains both tri- and tetravalent cerium, as supported by conductivity measurements under reducing conditions. The Ce4+ + e → Ce3+ reduction process led to a change in the color and disintegration of the sample when the oxygen partial pressure was reduced. In the 3+/4+ A2B2O7 pyrochlores, variable valence cations on the A site (eightfold coordination) more readily participate in redox processes than do those on the B site (sixfold coordination).

Application of BiFeO3 and Bi4Ti3O12 in ferroelectric memory, phase shifters of a phased array, and microwave HEMTs by A. N. Kalinkin; E. M. Kozhbakhteev; A. E. Polyakov; V. M. Skorikov (1031-1043).
This paper examines the main applications of bismuth ferrite and bismuth titanate and demonstrates their potential applications in spintronics and radioelectronics.

Ga- and Ti-containing Ni4Nb2O9-based solid solutions for Ni-Selective electrodes by A. L. Podkorytov; S. A. Shtin; A. S. Kashapova; A. A. Luppov; N. S. Shubina (1044-1047).
Gallium- and titanium-containing niobates with the compositions Ni4 − x Ga2/3x Nb2O9 and Ni4 − x Ti x/2Nb2O9 have been synthesized and their physicochemical properties have been studied. Their unitcell parameters have been determined by X-ray diffraction and their electrical conductivity has been measured as a function of temperature. According to thermomechanical analysis data, the niobates undergo no phase transitions. Some of the solid solutions have been used to fabricate Ni-selective electrodes, which have been tested in ion-selective measurements. In a number of cases, satisfactory results have been obtained.

Synthesis of Li x Na1 − x Ta y Nb1 − y O3 and LiTa y Nb1 − y O3 perovskite and pseudoilmenite solid solutions by M. N. Palatnikov; N. V. Sidorov; O. V. Makarova; V. T. Kalinnikov (1048-1054).
This paper compares the solid-state reactions underlying the synthesis of LiTa y Nb1 − y O3 and Li x Na1 − x Ta y Nb1 − y O3 solid solutions with the use of Ta2y Nb2(1 − y)O5 niobium tantalum pentoxides and a mechanical mixture of the Ta2O5 and Nb2O5 pentoxides. Our results demonstrate that the synthesis with the use of Ta2y Nb2(1 − y)O5 allows phase-pure solid solutions to be obtained at substantially lower temperatures in comparison with a mechanical mixture of Ta2O5 and Nb2O5.

Preparation of metal-polymer composites through the thermolysis of Fe(II), Co(II), and Ni(II) maleates by L. I. Yudanova; V. A. Logvinenko; N. F. Yudanov; N. A. Rudina; A. V. Ishchenko; P. P. Semyannikov; L. A. Sheludyakova; N. I. Alferova; A. I. Romanenko; O. B. Anikeeva (1055-1060).
Metal-polymer composites have been prepared through the thermolysis of the [M1(H2O)2(C4H2O4)] · H2O (M1 = Co(II), Ni(II)) neutral maleates and [M2(H2O)4(C4H3O4)2] (M2 = Fe(II), Co(II), Ni(II)) acid maleates. In the polymer matrix of the Fe-containing composite, we identified metal, Fe2O3, and Fe3O4 particles, with slight densification of the matrix around them. The polymer matrix of the cobalt maleate-derived composite contained four types of nanoparticles: α-Co, β-Co, and CoO in polymer shells and Co3O4 with no polymer shell. The decomposition of the nickel maleates yielded homogeneous nickel nanoparticles (4–5 nm) covered with two to five graphene layers. The Co-containing composite was found to be a dielectric. The Ni-containing composite exhibited variable range hopping conduction in the range T ≤ 50 K.

Preparation of transparent oxyfluoroborate glass-ceramics containing CaF2〈Eu〉 crystals by A. V. Egorysheva; A. P. Melekhov; V. D. Volodin; I. A. Gerasimov; T. B. Kuvshinova; G. S. Bogdanov; I. P. Sipailo; T. D. Dudkina; D. V. Lavrukhin (1061-1065).
The glass-forming region in the CaF2-Bi2O3-B2O3 system has been determined for the first time. We have prepared glasses of various compositions, investigated their physicochemical properties, and examined the effect of rare-earth (La, Nd, Eu, Dy, Er, Tm, Yb) doping on the crystallization behavior of the glasses. Transparent glass-ceramics containing ∼40-nm Ca1 − x Eu x F2 and Ca1 − x La x F2 crystallites have been obtained. The luminescence properties of the glasses and glass-ceramics have been studied.