Single-crystal growth of Ti–Nb–Ta–Zr–O alloys and measurement of elastic properties

Single crystals of β-type Ti alloy system Ti–Nb–Ta–Zr–O have been grown successfully in an Ar gas flow by a floating zone method. The growth orientations were determined approximately by using seed crystals with the desired orientations. The various growth conditions were realized by choosing the gas purity, the gas flow rate, and the growth rate as variables. Composition analysis of the grown crystals was done to check any variation from the values of the raw material along with the bulk homogeneity, followed by measurements of the lattice parameter and the hardness, which provides the following results: (1) the composition of oxygen varies with respect to the flow rate, or is increased as the purity is degraded, (2) the lattice parameter is increased with increasing composition of oxygen, (3) which is also the case with the hardness. Measurements of Young's moduli were performed to investigate the elastic properties. The results indicate that the crystals exhibit the anisotropy which was expected previously. The elastic constants were estimated from the moduli, giving the ideal stress 1.7–1.9 GPa which is on a level with the real strength. Additionally, the tensile stress–strain curve for the crystallographic direction 〈1 1 0〉 exhibited nonlinear elasticity and hysteresis.     

Electron microscopy study of the microstructure of Ni–W substrate surface

The surface microstructure of Ni–W alloy tapes, which are used as substrates to form films of high-temperature superconductors and photovoltaic devices, has been studied. Several samples of a Ni₉₅W₅ tape (Evico) annealed under different conditions were analyzed using scanning electron microscopy, energy-dispersive X-ray microanalysis, electron diffraction, and electron energy-loss spectroscopy. NiWO₄ precipitates are found on the surface of annealed samples. The growth of precipitates at a temperature of 950°С is accompanied by the formation of pores on the surface or under an oxide film. Depressions with a wedge-shaped profile are found at the grain boundaries. Annealing in a reducing atmosphere using a specially prepared chamber allows one to form a surface free of nickel tungstate precipitates.     

Nanocrystallization effects on the specific heat of Fe–Co–Nb–B amorphous alloy

Specific heat at constant pressure, C_P, was measured on amorphous, nanocrystalline and fully crystalline samples of Fe₆₀Co₁₈Nb₆B₁₆ alloy. Magnetic and calorimetric measurements agree, describing a continuously decreasing Curie temperature of the amorphous phase. A clear enhancement of C_P over the Dulong–Pettit limit has been observed (from 14% to 25 %). Part of the enhancement is due to magnetic (mainly amorphous phase) and electronic contributions, although an excess volume can be inferred from the high value of the slope of C_P versus temperature.     

Microstructure and thermal properties of the GeS2–In2S3–CsI glassy system

A new series of chalcohalide glasses in the GeS₂–In₂S₃–CsI pseudo-ternary system were prepared by conventional melt-quenching method. The glass-forming region was determined and it is mainly situated in the GeS₂-rich domain. The glasses have relatively high glass transition temperatures (T_g ranges from 335 to 405 °C) and good thermal stabilities. Based on the Raman spectra, it can be speculated that the glassy net is mainly constituted by [GeS₄] and [InS_4?xI_x] tetrahedra, which are interconnected by the bridging sulfur atoms. And the ethane-liked structural units [S₃Ge–GeS₃] can be formed because of the lacking of sulfur. Cs⁺ ion, which was added from CsI, exists as the nearest neighbor of I^? ion.     

Electron effects of the substituents on the structure of 4,4′-dipyridylium dications

The crystal structure of N,N′-di(2-hydroxyethyl)-4,4′-dipyridylium diperchlorate C₁₄H₁₈Cl₂N₂O₁₀ is determined by X-ray diffraction at 293 K. The crystals are monoclinic, a = 6.446(1) Å, b = 14.479(3) Å, c = 9.912(1) Å, β = 99.24(2)°, space group P2₁/c, and Z = 2; 1562 reflections measured; and wR2 = 0.086 and R1 = 0.033 for 1209 reflections with F > 4σ(F). It is found that, in the absence of charge transfer from the counterion to the dication, the planarity of the dipyridylium skeleton of the molecule is primarily due to the conjugation between the lone electron pairs of the hydroxyl groups and the π system of the dication. This inference is supported by the intramolecular O?N contact (2.847 Å).     

Jahn–Teller Lattice Distortions and Asymmetric Electron Density Distribution in the Structure of TmB12 Dodecaboride in the Temperature Range of 85–293 K

Crystallography Reports - The structure of single-crystal dodecaboride TmB12, which possess metallic properties, has been studied by X-ray diffraction at nine temperatures in the range of...     

Investigation of directional solidified Al–Ti alloy

Al–1 wt% Ti alloy was directionally solidified upwards under argon atmosphere under the two conditions; with different temperature gradients (G = 2.20–5.82 K/mm) at a constant growth rate (V = 8.30 μm/s) and with different growth rates (V = 8.30–498.60 μm/s) at a constant temperature gradient (G = 5.82 K/mm) in a Bridgman furnace. The dependence of characteristic microstructure parameters such as primary dendrite arm spacing (λ₁), secondary dendrite arm spacing (λ₂), dendrite tip radius (R) and mushy zone depth (d) on the velocity of crystal growth and the temperature gradient were determined by using a linear regression analysis. A detailed analysis of microstructure development with models of dendritic solidification and with previous similar experimental works on dendritic growth for binary alloys were also made.     

The effect of degree of amorphousness on electronic transport behaviors in the Ni–Nb–Zr–H glassy alloys with subnanometer-sized clusters

Material and electronic properties of Ni–Nb–Zr–H glassy alloys were investigated as a function of the rotating wheel speed in the amorphous ribbon-preparation method. Increase in density and amorphous colony size indicates that the degree of amorphousness increases with increase in the rotating speed. Supercooling, which reached by rotating wheel speed of 10,000 rpm (104.7-m/s), of the molten alloy produces a ballistic conductor with electrical conductivity of about 0.1 nΩ cm (× 10^? 9 Ω cm, 0.01% of silver (1.62 μΩ cm)) for (Ni_0.36Nb_0.24Zr_0.40)_94.6 H_5.4 glassy alloy and a room-temperature discrete Coulomb oscillation for (Ni_0.36Nb_0.24Zr_0.40)_91.6H_8.4 glassy alloy. The increase in degree of amorphousness by supercooling induces uniformity of cluster morphology.     

Peculiarities of the Electron Structure of Pseudobinary Alloys (GeTe)m–(Sb2Te3)n

Crystallography Reports - The electron band structure of GeTe, Sb2Te3, GeSb2Te4, and Ge2Sb2Te5 compounds has been calculated by the electron density functional method using the WIEN2k software...     

Glass formation of Ti–Ni–Sn ternary alloys correlated with TiNi–Ti3Sn pseudo binary eutectics

Glass-forming ability (GFA) of Ti–Ni–Sn ternary alloys was investigated. Applying recent models based on atomic size ratio and efficient packing, the composition favoring the glass formation is predicted. Our experiments indicate that the optimized glass-forming composition is located at Ti₅₆Ni₃₈Sn₆, with the critical thickness of complete glass formation approaching 100 μm for the melt-spun ribbons. The Ti₅₆Ni₃₈Sn₆ metallic glass exhibits a sizable supercooled liquid region (ΔT_x) of about 35 K and a reduced glass transition temperature (T_rg) of 0.52. We demonstrate that the glass formation of the Ti₅₆Ni₃₈Sn₆ alloy correlates with the (L → TiNi + Ti₃Sn) pseudo binary eutectic reaction in Ti–Ni–Sn ternary system, which has an invariant temperature and composition at ～1370 K and ～Ti₅₈Ni₃₄Sn₈, respectively. With respect to Sn-free Ti–Ni binary alloys, the GFA is enhanced for the Ti–Ni–Sn ternary alloys, but the improvement is limited possibly due to changes in the crystalline phases competing with glass formation.     

The Electron Diffraction Investigation of the Phase Structures in the Systems MF2–RF3 (CaF2–ErF3, SrF2–LaF3)

Crystallography Reports - The electron diffraction investigation of two-component phases in the systems MF2–RF3 (CaF2–ErF3, SrF2–LaF3) and components of the systems CaF2, SrF2,...     

Microstructure and properties of spark plasma sintered Fe–Cr–Mo–Y–B–C bulk metallic glass

Fabrication of Fe-based amorphous alloy using spark plasma sintering (SPS) process has been reported. Fully amorphous compacts with ～95% relative density were successfully sintered at temperature about 100 °C lower than glass transition temperature (T_g: 575 °C). Formation of crystalline Fe₂₃(C, B)₆ phases within near-fully dense (～99%) amorphous matrix is observed at sintering temperatures (>550 °C) close to glass transition temperature. Microstructure evolution in sintered compacts indicated that density, degree of crystallinity, and mechanical properties can be effectively controlled by optimizing SPS parameters.     

Structural investigations of nitrided Nb2O5 and Nb2O5–SiO2 sol–gel derived films

Sol–gel derived xNb₂O₅–(100 ? x)SiO₂ films (where x = 100, 80, 60, 50, 40, 20, 0 mol%) were nitrided at various temperatures (800 °C, 900 °C, 1000 °C, 1100 °C and 1200 °C). The structural transformations occurring in the films as a result of ammonolysis were studied using X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The XRD results have shown that the temperatures below 1100 °C were too low to obtain a pure NbN phase in the samples. The AFM observations indicate that the formation of the NbN phase and the size of NbN grains are related to the silica content in the layer. NbN grains become more regular and larger as the niobium content increases. The maximum grain size of about 100 nm was observed for x = 100. Preparation of the Nb₂O₅–SiO₂ sol–gel derived layers and the subsequent nitridation is a promising method of inducing crystalline NbN in amorphous matrices. It follows from the XPS results that a small amount of Nb₂O₅ remains in the films after nitridation at 1200 °C and that nitrogen reacted not only with Nb₂O₅ but also with SiO₂.     

Specific Features of Microstructure Formation in Co–Cr–Ni–W–Ta Alloys and Their Mechanical Properties

Crystallography Reports - The microstructure and mechanical properties of three experimental compositions of a new heat- and corrosion-resistant cast cobalt-based alloy have been investigated. It...     

Fabrication and ionic conductivity of amorphous Li–Al–Ti–P–O thin film

Li⁺ ion conducting Li–Al–Ti–P–O thin films were fabricated on ITO-glass substrates at various temperatures from 25 to 400 °C by RF magnetron sputtering method. When the substrate temperature is higher than 300 °C, severe destruction of ITO films were confirmed by XRD (X-ray diffraction) and the abrupt transformation of one semi-circle into two semi-circles on the impedance spectra. These as-deposited Li–Al–Ti–P–O solid state electrolyte thin films have an amorphous structure confirmed by XRD and a single semicircle on the impedance spectra. Good transmission higher than 80% in the visible light range of these electrolyte thin films can fulfill the demand of electro-chromic devices. Field emission scanning electron microscopy and atomic force microscopy showed the denser, smoother and more uniform film structure with the enhanced substrate temperature. Measurements of impedance spectra indicate that the gradual increased conductivity of these Li–Al–Ti–P–O thin films with the elevation of substrate temperature from room temperature to 300 °C is originated from the increase of the pre-exponential factor (σ₀). The largest Li-ion conductivity can come to 2.46 × 10^? 5 S cm^? 1. This inorganic solid lithium ion conductor film will have a potential application as an electrolyte layer in the field such as lithium batteries or all-solid-state EC devices.     

Effect of rare-earth elements on the plasma etching behavior of the RE–Si–Al–O glasses

The effect of rare-earth elements on the plasma etching behavior of oxide glasses were investigated to develop the window glass for a plasma processing chamber in the semiconductor industry. Aluminosilicate glasses with various rare-earth elements (Y, Gd and La) were prepared and their optical transmittance and plasma etching depth were evaluated. The plasma etching behavior of the glasses was estimated by X-ray photoelectron spectroscopy analysis at the fluorine plasma exposure surface of the glasses. The rare-earth element in the glass was highly related to various properties such as density, molar volume, mechanical properties and plasma etching depth. The cationic field strength of the rare-earth element more strongly affected the plasma etching depth of the glasses than the sublimation point of the fluorine compounds and this may be related to the plasma etching condition.     

Characteristics of heteroepitaxial Cu2−xMnxO/Nb–SrTiO3 p–n junction

Mn-doped cuprous oxide Cu_2?xMn_xO (CMO), where x = 0.03, is a p-type diluted magnetic semiconductor (DMS) with Curie temperature above room temperature [M. Wei, N. Braddon, et al., Appl. Phys. Lett. 86 (2005) 0725141; Y.L. Liu, S. Harrington, et al., Appl. Phys. Lett. 87 (2005) 222108]. We have grown CMO (x = 0.03) thin films of about 200 nm thick on n-type semiconducting (0 0 1)Nb–SrTiO₃(NSTO) single crystal substrates by pulsed laser deposition. Cubic crystalline phases of CMO layers were obtained in a narrow deposition pressure window of about 20 mTorr at growth temperature of 650 °C. X-ray diffraction and TEM studies of these heterostructures reveal a cube-on-cube epitaxial relationship of [CMO]₀₀₁/[NSTO]₀₀₁. All the oxide p–n junctions with the size of 500 × 500 μm were fabricated by the shadow masking technique. These junctions show highly asymmetric I–V characteristics. The rectification ratio at room temperature is about 10³ at ±2 V. Leakage current density of 10^?4 A cm^?2 at ?1 V is observed. No apparent junction breakdown is recorded at reverse bias voltages down to ?5 V. From the 1/C²–V plots, the forward bias turn on voltage is ～1.4 V. Clear junction current rectifying property is maintained at up to 200 °C. Our results have demonstrated that epitaxial CMO films can be fabricated on lattice matched cubic substrates. They are suitable DMS for above room temperature spintronic junction applications.     

Structure and properties of NaPO3–ZnO–Nb2O5–Al2O3 glasses

In an effort to design low-melting, durable, transparent glasses, two series of glasses have been prepared in the NaPO₃–ZnO–Nb₂O₅–Al₂O₃ system with ZnO/Nb₂O₅ ratio of 2 and 1. The addition of ZnO and Nb₂O₅ to the sodium aluminophosphate matrix yields a linear increase of properties such as glass transition temperature, density, refractive index and elastic moduli. The chemical durability is also significantly, but nonlinearly, improved. The glass with the highest niobium concentration, 55NaPO₃–20ZnO–20Nb₂O₅–5Al₂O₃ was found to have a dissolution rate of 4.5 × 10^? 8 g cm^? 2 min^? 1, comparable to window glass. Structural models of the glasses were developed using Raman spectroscopy and nuclear magnetic resonance spectroscopy, and the models were correlated with the compositional dependence of the properties.     

Simulation of the spinodal phase separation dynamics of the Bi–Zn system

In the phase separation occurring at the miscibility gap (at the spinodal region) of an alloy a discrete symmetry is spontaneously broken and a domain wall network is formed. Field theory simulations are often used to study the dynamics of topological defects networks appearing in different physical contexts. In this work, we focus on the dynamics of the two immiscible liquids appearing on the phase diagram of the Bi–Zn system, one of the basic systems of lead free solders. We use phase field simulations to quantitatively simulate the dynamics of the two liquids separation in the Bi–Zn system, at different temperatures and for different concentrations. We obtain the miscibility gap curve and the domain morphologies of the system as a function of time, temperature and component concentrations using simulations.     

Electron spin resonance of Mn2+ IN As–Se and As–Te glasses

The electron spin resonance of Mn has been studied in As_xSe_100?x with 0 ? x ? 70 and As_xTe_100?x with 40 ? x ? 70. All samples, except those with x < 20 in As_xSe_100?x, exhibit six hyperfine lines centered at g = 4.3. A g = 2.0 line is observed in As–Se with largely scattered linewidth by samples, but not in As–Te unless oxygen contamination is included in the samples. The g = 4.3 line in As–Se is closely related to a formation of As₂Se₃-type layer structure and interpreted as being caused by Mn situated at the interlayer position and surrounded by four Se atoms in an arrangement of rhombic symmetry. In As–Te, a similar model by four Te atoms is valid in composition near As₂Te₃, but the surrounding Te is replaced by As as As content increases. The g = 2.0 line is concluded to come from phase-separated antiferromagnetic particles of Mn–O and MnSe. The linewidth is scattere by differences in the relative amounts of the two kinds of particles and in particle size.