Dynamics of the surface composition and structure of InP oxidized in the presence of V and V<Subscript>2</Subscript>O<Subscript>5</Subscript>

Structure of the surface layers of V₂O₅(20, 38 nm)/InO and V(25, 15 nm)/InP heterostructures, including surface morphology, distributions of elements over the oxidized-layer thickness, phase composition, and the interface quality, are studied both before and after oxidation. According to the Auger-and IR-spectroscopy data, the layers obtained as a result of the oxidation are mainly indium phosphates and vanadates with nonuniform distributions of elements over the oxide-film thickness. Results describing the kinetics of heterostructure oxidation are obtained. The solid-phase diffusion of the substrate components is shown to be the governing process. This implies that the considered process is catalytic. The reaction rate is weakly dependent on the catalyst amount.     

Influence of iron additives on the corrosion resistance of Al<Subscript>87</Subscript>Gd<Subscript>5</Subscript>Ni<Subscript>8</Subscript> amorphous metal alloy

Based on the results of voltammetric investigations, we have shown that the partial replacement of nickel by 4 at. % Fe in Al₈₇Gd₅Ni₈ amorphous alloy leads to a decrease in the corrosion currents and an increase in the polarization resistance, which demonstrates the higher corrosion resistance of Al₈₇Gd₅Ni₄Fe₄ alloy. Using the method of electrochemical impedance spectroscopy, we have studied the durability and protective capacity of passivation oxide layers at electrodes made of this alloy in 0.1 M NaCl aqueous solution. We have also selected an impedance model of the formation of interfaces oxide–0.1 M NaCl and amorphous metal alloy–0.1 M NaCl. We have established that active diffusion redox reactions, described by the Warburg element, take place at the interface oxide film–0.1 M NaCl. The diffusivities of anions from the solution into the surface oxide layer have been calculated. Finally, we show that, with increase in the time of electrochemical reaction in 0.1 M NaCl aqueous solution, diffusion decreases due to the compaction of the surface oxygen-containing layers.     

Fabrication of a plane-parallel interface in Ni/PbZr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>O<Subscript>3</Subscript> heterostructures

A process has been proposed for producing a plane-parallel ferromagnetic/ferroelectric interface, which ensures a reproducible magnetoelectric performance of Ni/PbZr_0.2Ti_0.8O₃ (PZT) heterostructures. Its principle is to smooth the initial surface profile of the PZT ceramic substrate to a submicron level by sequential deposition/sputtering of three layers 0.2, 0.1, and 0.05 μm in thickness through ion beam sputtering of a target having the same composition as the substrate, followed by the growth of a nickel film on the smoothed surface. This allows one to preclude film bulging and spalling and ensures high quality of the interface.     

Preparation of ZnGa<Subscript>2</Subscript>S<Subscript>4</Subscript> by reacting GaI<Subscript>3</Subscript> and ZnI<Subscript>2</Subscript> with sulfur

We have carried out thermodynamic modeling of the GaI₃–S and ZnI₂–S systems by the method of equilibrium constants and calculated the chemical compositions of the condensed and vapor phases in the temperature range 200–500°C. Our experimental data demonstrate the feasibility of preparing zinc thiogallate by reacting gallium(III) iodide and zinc(II) iodide with sulfur. Synthesis was carried out at a temperature of 450°C over a period 2 h, followed by calcination of the product at 650°C in order to remove the residual iodine. The practical ZnGa₂S₄ yield was 92–94%.     

Time-Dependent Diffusion Coefficient of Fe in MgB<Subscript>2</Subscript> Superconductors

The iron (Fe) diffusion in superconducting MgB₂ bulk samples has been studied for sintering time durations of 15 min, 30 min, 1 h, 2 h, and 4 h at 900^°C. Fe coating bulk polycrstalline superconducting MgB₂ samples for Fe coating were prepared by pelletizing and used in the diffusion experiments with initial sintering at 800^°C for 1 h. A thin layer of Fe was coated on MgB₂ pellets by evaporation in vacuum. Effects of Fe diffusion on the structural, electrical, and superconducting properties of MgB₂ have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), energy-dispersive X-ray spectroscopy (EDS), and resistivity measurements. Fe diffused samples have slightly increased critical transition temperatures and have larger lattice parameter c values, in comparison with bare samples. Fe diffusion coefficients were calculated from depth profiles of c parameter and room temperature resistivity values. Depth profiles were obtained by successive removal of thin layers from Fe diffused surfaces of the samples. Our results have shown that the Fe diffusion coefficient decreases with increasing sintering time and resistivity measurements can be utilized for determination of diffusion coefficient.     

Liquid-phase epitaxy of NdAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> and Yb-doped YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Epitaxial layers of NaAl₃(BO₃)₄ (NAB) and YAl₃(BO₃)₄〈Yb〉 (YAB〈Yb〉) containing up to 10 at % Yb have been grown by liquid-phase epitaxy on YAB substrates. Their growth kinetics have been studied at relative supersaturations of the high-temperature solution from 2 × 10^?2 to 16 × 10^?2. The ytterbium concentration in YAB〈Yb〉 has been shown to vary little during the epitaxial process. Near the edges of the substrate, the surface morphology of the layers is complicated by vicinals, which have a spiral form in the case of YAB〈Yb〉. On \(\{ 10\overline 1 1\} \) YAB substrates, homogeneous single-crystal NAB films have been grown.     

A Study of the Crystal Structure of Co<Subscript>40</Subscript>Fe<Subscript>40</Subscript>B<Subscript>20</Subscript> Epitaxial Films on a Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> Topological Insulator

Laser molecular-beam epitaxy has been used to form Co₄₀Fe₄₀B₂₀ layers on Bi₂Te₃ topological insulator substrates, and their growth conditions have been studied. The possibility of growing epitaxial ferromagnetic layers on the surface of a topological insulator is demonstrated for the first time. The CoFeB layers have a body-centered cubic crystal structure with the (111) crystal plane parallel to the (0001) plane of Bi₂Te₃. 3D mapping in the reciprocal space of high-energy electron-diffraction patterns made it possible to determine the epitaxial relationships between the film and the substrate.     

Effect of V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoislands on the surface composition and structure of InP during thermal oxidation

The evolution of the surface morphology and composition during the thermal oxidation of InP in the presence of V₂O₅ nanoislands has been studied by scanning tunneling microscopy and Auger electron spectroscopy. The results demonstrate that the effect of the islands is strongest in the initial stage of the process and persists in later stages. Auger electron spectroscopy and kinetic data strongly suggest that the oxidation of InP in the presence of vanadium oxide nanoislands follows a catalytic mechanism.     

Thermal oxidation of InP with V<Subscript>2</Subscript>O<Subscript>5</Subscript> + PbO nanolayers of different compositions

Data are presented on the thermal oxidation of (V₂O₅ + PbO)/InP structures which demonstrate that the combined effect of the oxides deposited by magnetron sputtering does not follow the additivity rule and that this behavior is due to the formation of a quasi-liquid phase (maximum) and lead vanadate (minimum) (IR spectroscopy, Auger electron spectroscopy). The effective activation energy for the oxidation of the (V₂O₅ + PbO)/InP structures is shown to systematically decrease with increasing initial vanadium oxide content. The oxidation of the structures follows a partially catalytic mechanism, with V₂O₅ acting as a catalyst (oxidation kinetics, IR spectroscopy, ultrasoft X-ray emission spectroscopy).     

Analysis of morphology and microstructure of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> layers

The paper presents the characterization of obtaining Al₂O₃ oxide layers on AlMg₂ aluminum alloy as a result of hard anodizing by the electrolytic method in a three-component electrolyte. The Al₂O₃ layers obtained on the AlMg₂ alloy in the three-component SBS electrolyte were subjected to detailed microstructural investigations (by means of a scanning electron microscope). By using X-ray diffraction, the phase compositions of obtained oxide layers were examined. It was found that the Al₂O₃ oxide layers obtained via hard anodizing in a three-component electrolyte are amorphous. The chemical composition of the Al₂O₃ layers is presented and compared with the results of stechiometric calculations for the Al₂O₃ layer. Surface morphologies of the obtained oxide layers are characterized and discussed in nano- and microscopic scales. The surface morphologies of the layers obtained have a significant influence on their properties, including their susceptibility to further modification (e.g., to incorporation of graphite), their wear resistance, and the capacity for sorption of lubricants.     

Preparation of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Buffer Layer on LaAlO<Subscript>3</Subscript> Substrate by TFA-MOD Method

Chemical solution deposition is a promising technique for fabrication of high-temperature superconducting films and oxide buffer layers due to its reproducibility and low cost. In this work, Y₂O₃ buffer layers were prepared on (100) LaAlO₃ substrates by mental organic deposition method using trifluoroacetate. The resulting Y₂O₃ films crystallized as a single phase at 900°C and showed a low degree ofc-axis orientation. The scanning electron micrography showed that the surface of the films was smooth with a uniform grain size of approximately 10 nm.     

Electroluminescent layers based on ZnS:Cu deposited into matrices of porous anodic Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

It is suggested to use a new nanocomposite material—nanostructures of copper-doped zinc sulfide in a matrix of porous aluminum oxide—as a light-emitting layer of electroluminescent sources of light. The material was deposited by thermal evaporation in a vacuum. The microstructure of the layers, impurity distribution in the electroluminescent-phosphor layer, and electroluminescence spectra at various copper concentrations in ZnS:Cu were studied.     

Some physical properties and Vickers hardness measurements of Fe diffusion-doped Bi<Subscript>1.8</Subscript>Pb<Subscript>0.35</Subscript>Sr<Subscript>1.9</Subscript>Ca<Subscript>2.1</Subscript>Cu<Subscript>3</Subscript>O<Subscript>y</Subscript> superconductors

In this study we have investigated the influence of iron diffusion and diffusion-annealing time on the mechanical and the superconducting properties of bulk Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃O_y superconductors by performing X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers hardness, dc resistivity (ρ-T) and critical current density (J_c) measurements. The samples are prepared by the conventional solid-state reaction method. Doping of Bi-2223 was carried out by means of iron diffusion during sintering from an evaporated iron film on pellets. Then, the Fe layered superconducting samples were annealed at 830 °C for 10, 30 and 60 h. The mechanical properties of the compounds have been investigated by measuring the Vickers hardness (H_v). The mechanical properties of the samples were found to be load dependent. The load independent Vickers hardness (H₀), Young’s modulus (E), yield strength (Y), and fracture toughness (K_IC) values of the samples are calculated. These all measurements showed that the values of the Vickers hardness, critical current density, and critical transition temperature and lattice parameter c increased with increasing Fe doping and diffusion-annealing time.     

Synthesis and crystal structure of Cu<Subscript>2</Subscript>{(UO<Subscript>2</Subscript>)<Subscript>3</Subscript>[(S,Cr)O<Subscript>4</Subscript>]<Subscript>5</Subscript>}(H<Subscript>2</Subscript>O)<Subscript>17</Subscript>

Cu₂{(UO₂)₃[(S,Cr)O₄]₅}(H₂O)₁₇ crystals were prepared by evaporation of aqueous solutions. The crystal structure was solved by the direct method and refined to R ₁ = 0.064 (wR ₂ = 0.177) for 8120 reflections with ¦F _hkl¦ 4 ¦F _hkl¦. Rhombic system, space group Pbca, a = 18.0586(8), b = 19.9898(9), c = 20.5553(8) Å, V = 7420.2(6) ų. The structure is based on {(UO₂)₃[(S,Cr)O₄]₅}^4– anionic layers, formed by combination of UO₇ pentagonal bipyramids and TO₄ tetrahedra through common vertices. The { (UO₂)₃ [(S,Cr)O₄]₅}^4– layers are parallel to the (010) plane. The Cu²⁺ (H₂O)₆ octahedra and additional water molecules are located in the interplanar space and provide binding of the layers in the structure by hydrogen bonds. Based on the occupancy of tetrahedral positions, more accurate chemical formula of the compound should be written as Cu₂{(UO₂)₃[(S_0.804 Cr_0.196)O₄]₅} (H₂O)₁₇.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 408–411.Original Russian Text Copyright © 2004 by Krivovichev, Burns.     

Crack propagation in layered Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> composites prepared by electrophoretic deposition

Crack propagation through layered Al₂O₃/ZrO₂ composites was studied. The specimens were prepared via electrophoretic deposition of alumina and zirconia powders from suspensions with monochloroacetic acid and isopropanol. The kinetics of electrophoretic deposition could be described fully if the electrophoretic mobility and conductivity of suspensions were known. The conductivity of suspensions increased in the course of deposition. Adjusting to properly controlled kinetics of deposition and sintering, deposits were prepared with strongly bonded layers of different pre-defined thicknesses and, consequently, with different magnitudes of residual stress. Cracks, produced by an indentation technique, propagated askew towards layer interfaces deflected towards the interface in the Al₂O₃ layers and away from the interface in the ZrO₂ layers. Changes in the direction of crack propagation were described for the whole range of angles of incidence (0°–90°). The biggest change in the crack propagation was observed for the angle of incidence 45° and was ca. 15°, irrespective of the magnitude of residual stress in the layers.     

Effect of high pressure on the metal-dielectric transition and the pseudo-gap temperature range in oxygen deficient YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−δ</Subscript> single crystals

The effect of high hydrostatic pressure on the electric resistance in the ab-plane of the oxygen deficient YBa₂Cu₃O_7−δ single crystals is investigated. It is shown that the pressure induced redistribution of the labile oxygen results in the strengthening of the phase immiscibility in layers. This process is accompanied with structural relaxation and ascending diffusion processes within the volume of the experimental sample. We observe a significant displacement of the temperature range that corresponds to metal-dielectric type transitions and the pseudo-gap realization regime.     

First principles study of three-component SrTiO<Subscript>3</Subscript>/BaTiO<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> ferroelectric superlattices

The geometrical, chemical and ferroelectric properties of a new nanoscale short-period three-component SrTiO₃/BaTiO₃/PbTiO₃ perovskite superlattice are investigated using a first principles density functional approach. The study focuses on varying the thickness of each component in the superlattice and determining the resulting lattice distortion and total polarization. Thicknesses of up to three unit cells in a single component are considered and the in-plane lattice constants normal to the [001] stacking direction are fixed to the bulk SrTiO₃ values to simulate a rigid substrate. It is found that the PbTiO₃ layers play a key role in strain and polarization enhancement. By increasing the amount of PbTiO₃ in the superlattices the strain in the other components increases significantly resulting in an enhanced total polarization of the superlattice relative to bulk BaTiO₃. Increasing the number of BaTiO₃ layers also improves the overall polarization. All the SrTiO₃ layers in each superlattice are found to be highly polarized. Many of the calculated features are similar to those found previously by others for the SrTiO₃/BaTiO₃/CaTiO₃ superlattice, although in the present study significantly greater enhancement factors and polarization values are found. The predicted enhancement of the polarization is mostly attributed to lattice strain due to mismatch of the in-plane lattice constant of the three-component materials.     

Effects of Nd concentration on structural and magnetic properties of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Zinc ferrite nanomaterials have been received significant attention in recent years on account of their potential applications in the fields of electronics, optoelectronics and magnetics. To enhance the magnetic properties of zinc ferrites, Nd-doped zinc ferrites (ZnFe_2?xNd_xO₄, x?=?0, 0.01, 0.02, 0.03) nanoparticles (NPs) have been prepared by the sol–gel method. The effects of Nd doping concentration on the structural and magnetic properties of zinc ferrites were studied. The results of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy indicated that the Nd ions were incorporated into the crystal lattice of ZnFe₂O₄ and substituted for the Fe³⁺ sites. Unlike pure zinc ferrites with paramagnetism, Nd doped ZnFe₂O₄ NPs were superparamagnetic at room temperature. Vibrating sample magnetometry results showed, with the increase of Nd content, the saturation magnetization of Nd doped ZnFe₂O₄ NPs increased.     

Antireflecting coating from Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> and SiO<Subscript>2</Subscript> multilayer films

Sol-gel method is important for depositing antireflective coating that allows control over thickness as well as the index of refraction. Antireflective coatings which are produced from Ta₂O₅ and SiO₂ multi-layer thin films using sol-gel spin coating method are presented. The refractive index and the thickness are controlled by the composition and the concentration of the solution respectively. The thickness, refractive index and extinction coefficient of the films were calculated through transmission and reflection measurement by an NKD analyser. Mechanical properties of the films were checked by the cross tape test and dry sun test at 760 W/m². The result shows that the sample heat treated at 450^∘C for 15 min approaches a reflectance with less than 0.5% at around 840 nm.     

Strain-induced artificial multiferroicity in Pb(Zr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>/Pb(Fe<Subscript>0.66</Subscript>W<Subscript>0.33</Subscript>)O<Subscript>3</Subscript> layered nanostructure at ambient temperature

Layered nanostructures (LNs) of the commercial ferroelectric Pb(Zr_0.53Ti_0.47)O₃ (PZT) and the natural ferroic relaxor Pb(Fe_0.66W_0.33)O₃ (PFW) were fabricated with a periodicity of PZT/PFW/PZT (~5/1/5 nm, thickness ~250 nm) on MgO substrates by pulsed laser deposition. The dielectric behavior of these LNs were investigated over a wide range of temperatures and frequencies, observing Debye-type relaxation with marked deviation at elevated temperatures (>400 K). High dielectric constant and very low dielectric loss were observed below 100 kHz and 400 K, whereas the dielectric constant decreases and loss increases with increase in frequency, similar to relaxor ferroelectrics. Asymmetric ferroelectric hysteresis loops across UP and DOWN electric field were observed with high remanent polarization (P_r) of about 33 μC/cm². High imprint (~5–7 V across 250 nm thin films) were seen in ferroelectric hysteresis that may be due to charge accumulation at the interface of layers or significant amount of strain (~3.21) across the layers. Room temperature ferromagnetic hysteresis was observed with remanent magnetization 5.32 emu/cc and a coercive field of ~550 Oe. Temperature and field dependent leakage current densities showed very low leakage ~10⁻⁷–10⁻⁵ A/cm² over 500 kV/cm. We observed imprint in hysteresis that may be due to charge accumulation at the interface of layers or active role of polar nano regions (PNRs) situated in the PFW regions.