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Surface engineering is known as an effective strategy to enhance the catalytic properties of Pt-based nanomaterials. Herein, we report on surface engineering Ni-Pt nanoalloys with a facile method by varying the Ni doping concentration and oleylamine/oleicacid surfactant-mix. The alloy-composition, exposed facet condition, and surface lattice strain are, thereby manipulated to optimize the catalytic efficiency of such nanoalloys for methanol oxidation reaction (MOR). Exemplary nanoalloys including Ni0.69Pt0.31 truncated octahedrons, Ni0.45Pt0.55 nanomultipods and Ni0.20Pt0.80 nanoflowers are thoroughly characterized, with a commercial Pt/C catalyst as a common benchmark. Their variations in MOR catalytic efficiency are significant: 2.2 A/mgPt for Ni0.20Pt0.80 nanoflowers, 1.2 A/mgPt for Ni0.45Pt0.55 nanomultipods, 0.7 A/mgPt for Ni0.69Pt0.31 truncated octahedrons, and 0.6 A/mgPt for the commercial Pt/C catalysts. Assisted by density functional theory calculations, we correlate these observed catalysis-variations particularly to the intriguing presence of surface interplanar-strains, such as {111} facets with an interplanar-tensile-strain of 2.6% and {200} facets with an interplanar-tensile-strain of 3.5%, on the Ni0.20Pt0.80 nanoflowers.

Ultrathin single crystalline nanoplates of Ni12P5 are synthesized via a facile, template-free, wet chemical method. The thickness is about 6 nm with sizes tunable from 5 to 50 nm. The exposed plate surface is formed of { 2 ¯ 11 } lattice plane. Benefitting from the high electrical conductivity and the two dimensional (2D) nanostructures, the Ni12P5 nanoplates exhibit excellent supercapacitor properties. The specific capacity is about 697 C/g at the current density of 1 A/g. Even at 20 A/g, it is measured as 446 C/g, with 64.0% retention indicating an outstanding rate capability. The charge storage mechanisms include a battery-type behavior related to the bulk redox processes and a double-layer capacitance arising from the 2D geometric morphology. In particular, the morphological effects accounts for about 63% of the total charge storage effects at the voltage sweep rate of 2 mV/s in the cyclic voltammetry measurement, and is even higher percentage-wise at a higher sweep rate. This is, by far, the best performance with facile synthesis techniques for single crystalline nickel phosphides.

Elaborate design of highly active catalysts from earth-abundant elements is important for the development of water-splitting devices. We have synthesized { 1 1} high index-faceted Ni12P5 nanoplates and Ni12P5 spherical nanoparticles (SNPs) by the one-step solvothermal method. The Ni12P5 nanoplates show enhanced hydrogen evolution reaction activity with a lower overpotential of −128 mV and a smaller Tafel slope of 60.6 mV dec−1 compared to Ni12P5 SNPs. Stability tests reveal exceptional durability of the catalyst. This study offers an attractive catalytic material for large-scale hydrogen production technology.

A simple yet general one-step solvothermal method is applied to synthesize sub-7 nm monodispersed single-crystal NiPt2 nanoparticles (NPs) with the morphology of truncated octahedrons in the alloying state of disordered atomic arrangements. The effective magnetic moments of these NPs exhibit an anomalous temperature dependency, increasing from approximately 0.9 μB/atom at 15 K to 1.9 μB/atom at 300 K. This is an increase by a factor of more than three compared with bulk Ni. On the basis of experiments involving X-ray absorption near-edge spectroscopy of the L3 edge for Pt and density functional theory calculations, the observed novel magnetism enhancement and its anomalous temperature dependence are attributed to the electron transfer arising from the thermal-activation effects.

Monodispersed NiPt hollow nanospheres with citric acid as surfactant were synthesized by a one-pot wet chemical method in water at room temperature. The diameter is adjustable from 13 to 100 nm with the shell thickness of 2–3 nm, roughly the size of nanocrystallites. The composition is also tunable with the ratio of Ni : Pt from 1 : 9 to 9 : 1. A phase formation mechanism is proposed for the controllability of the diameter from the sacrificial templates of intermediate Ni–B amorphous nanocompounds. Molecular dynamic calculations show that 2 nm is the lower-bound shell thickness for a stable hollow spherical structure to avoid distortion or collapse. Electrocatalytic properties for the oxidation of ethylene glycol are measured for 35 nm Ni50Pt50 hollow nanospheres. Its performance is apparently better than that using commercial Pt/C catalyst. This makes it a potential application as a fuel cell catalyst.

Chains of superparamagnetic (SPM) Ni nanoparticles of 20 and 33 nm in diameter are synthesized by a facile, template-free, wet chemical method in magnetic field. The blocking temperature for the sample of 20 nm appears at T(B) approximately 255 K, above which the sample exhibits SPM behaviors by a M(H) measurement. At T < T(B), the temperature dependent coercivity, Hc(T), is beyond the description by the simple two-well model proposed by Neel and Brown in the early day. In contrast, for the Ni nanochains of diameter larger than the coherence length, Lcoh approximately 25 nm, the magnetization reversal properties are well described by this model. The magnetization reversal behavior of the SPM Ni nanochains with the diameter much smaller than the coherence length is one of the interesting points to study. Possible transition from the localized magnetization reversal mode in the high temperature end to the coherently rotational mode at low temperature is discussed.

We report a controlled synthesis of Co2P nanostructures. The products showing Curie–Weiss paramagnetic behavior have an orthorhombic structure with novel morphology. Nanoneedles with a tip of less than 10 nm homogeneously grew out of the center. The effects of temperature and the morphological evolutions of the intermediates are investigated.

We present a facile and controllable method for the large-scale fabrication of highly-ordered octahedral Fe3O4 colloidal “single crystals” without the assistance of a substrate. Oleic acid is used to reduce the solubility of the nano-building blocks in colloidal solution and to induce a “crystallization” process. Our colloidal crystals are of multimicron size and show typical crystallographic characteristics. They have a very robust structure and can serve as a novel ordered magnetic mesoporous material with a relatively narrow pore size distribution. The sample possesses an extremely high Verwey transition temperature (T V) of 100 K and a high saturation magnetization (M S) of 86 emu/g at 5 K based on its good crystallinity, as well as the interparticle dipolar interaction behavior arising from its unique structure. Electrochemical measurements have demonstrated the excellent capacity of the mesoporous colloidal crystals when used in lithium-ion batteries.

Peapodlike Ni/Ni3S2 chains of about 30 nm in outer diameter, with Ni cores of 10–15 nm, can be synthesized by a sacrificial template route. The Ni3S2 shell exhibits paramagnetic properties with a mass susceptibility of χ ≈ 5 × 10−5 emu (gOe)−1, while the ferromagnetic Ni cores show a superparamagnetic behavior with a blocking temperature of TB ≈ 130 K. The shape anisotropy of the chainlike structure is determined as 5.0 × 104 J·m−3, which is larger than the bulk magnetocrystalline anisotropy by one order of magnitude. The demagnetization factor is determined as ΔN = 0.29. The sample provides an ideal structure for studying the magnetization reversal property by the chain-of-sphere model. The observations on the formation of the peapod structure verify a growth mechanism of the nanoscale Kirkendall effect. Based on the preparation of peapod chains, a series of nickel sulfide hollow chains with average diameters of 25, 50, and 100 nm are fabricated. In addition, the phase transition for hollow chains from Ni3S2 to NiS is studied.

Polycrystalline magnetite hollow spheres with diameter of about 200 nm and shell thickness of 30–60 nm were prepared via a facile solution route. For the reaction, ethylene glycol (EG) served as the reducing agent and soldium acetate played the role of precipitator. In addition, polyvinylpyrrolidone (PVP) served as a surface stabilizer. The morphologies and structures were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The intermediate products at different stages were also studied to shed light on the evolution of phase formation. It revealed that the hollow structure formed via self-assembly of nanocrystallites (about 15 nm) using sodium acetate as mild precipitator. Evidences further pointed out that the Ostwald ripening process well explained the growth mechanism of the hollow structure. Magnetization measurements showed that the coercivity of magnetite hollow spheres at low temperature is about 200 Oe and the saturation magnetization is about 83 emu g−1, roughly 85% that of the bulk phase, close to the value of its solid counterpart. In addition, a freezing transition was observed at 25 K.

A series of highly uniform one-dimensional Ni nanochains, with diameters ranging from 20 to 200 nm, have been synthesized by a facile, template-free, wet chemical method at diverse temperature and magnetic field. Our results indicate that the crystallite size, diameter and length of the prepared nanochains depend critically on the reaction temperature. The characteristic thermodynamic cohesive energies, ΔED and ΔEL, are obtained for the formation of the Ni nanochains. In addition, the chain length also depends on the applied field because of the Zeeman energy of the magnetic Ni nanoparticles. For the morphology control, an external field is required in order to obtain axially aligned rather than dendritic nanochains. The size-dependent magnetic properties are studied systematically. The saturation magnetization is shown to reduce inversely with the chain diameter, attributable to a core−shell structure. The thickness of the shell which encloses the ferromagnetic Ni core is determined to be about 2.3−3.4 nm.

Highly uniform coalescent moniliforme-shape α-Fe2O3 straight nanochains built up of single crystal building blocks are synthesized via a facile one-pot solution-phase route at 180 °C using FeCl3, which have interesting magnetic behaviors based on their unique structure. Surprisingly, an exceptionally high TM (Morin transition temperature) is observed.

A series of pure Ni thin chains with particle diameters ranging from 15 to 80 nm were successfully synthesized by a wet chemical method. Magnetization measurements for the Ni chains reveal that the saturation magnetization increases and the coercivity decreases with increasing particle diameter. The magnetization reversal mechanism of both the samples with a diameter of 30 and 50 nm can be described by the model of “chain of spheres”. Using the fanning mode, the calculated coercivities and the remnant ratios agree well with the experimental results. Surprisingly, the coercivity is greatly enhanced, reaching as high as 790 Oe at T = 5 K for the Ni chains with a diameter of ∼15 nm, which are composed of single-crystal particles. Meanwhile, in the degradation of pentachlorophenol (PCP) solutions with Fe0 nanoparticles as reducing agents, Ni nanochains with a diameter of ∼80 nm were added, and the results indicate that the sample could serve as a good catalyst in dechlorination systems.

One-dimensional (1D) chainlike arrays of hollow magnetic Fe3O4 spheres have been prepared by simply aging magnetically preassembled Fe nanoparticles in aqueous solution at room temperature. The diameter of the 1D nanomaterials is about 100−200 nm, and the length is up to 1−3 μm, observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure and magnetic properties of the Fe3O4 hollow chains were characterized by X-ray powder diffraction (XRD) and via a superconducting quantum interference device (SQUID) magnetometer. Mechanism investigations on the time dependent process reveal these hollow nanostructures were formed based on the nanoscale Kirkendall effect. Besides the aqueous microenvironment, the partial pressure of oxygen is of great importance in the formation of 1D chainlike Fe3O4 hollow nanostructures.

Cu2O hollow spheres with thin shells were synthesized using poly(vinylpyrrolidone) (PVP) as the template in deionized water. In this process, CuAc2.H2O was reduced by acerbic acid in the presence of PVP and sodium hydroxide. Techniques, including XRD, XPS, TEM and HRTEM were used to characterize the morphology, structure and composition of the as-prepared nanomaterials. The results revealed that the average diameter of polycrystalline Cu2O hollow spheres is about 200 nm, with the shells as thin as approximately 10 nm. The formation mechanism, of these hollow spheres was studied. Magnetic property of the sample demonstrates a paramagnetic behavior at 15 K, and it might be attributed to the hollow-sphere structure of the diamagnetic Cu2O.

Highly uniform and well-aligned one-dimensional Ni nanochains with controllable diameters, including 33, 78, and 120 nm, have been synthesized by applying an external magnetic field without any surface modifying agent. The formation can be explained by the interactions of magnetic dipoles in the presence of applied magnetic field. Magnetic measurements demonstrate that the shape anisotropy dominates the magnetic anisotropy. The demagnetization factor, ∆N, is in the range of 0.23–0.36.

Co-doped ZnO single-crystalline nanorods with 80–100 nm in diameter and 1.5–2 μm in length have been prepared in a simple solution route. X-ray diffraction data and selected area electron diffraction pattern of the diluted magnetic semiconductor nanorods confirm the single crystallinity of Zn1−xCoxO solid solution without impurities of metallic Co or other phases. Magnetic results show that the Zn0.95Co0.05O nanorods exhibit a ferromagnetic characteristic with Curie temperature higher than 380 K. The high-temperature ferromagnetic properties allow this Zn1−xCoxO nanorods potential applications in future spintronic devices.

It is well-known that there is a relatively small temperature window for the growth of epitaxial and c -axis oriented YBCO thin films by various methods. In this study, this window was more precisely examined for YBCO film growths by photo-assisted MOCVD. At specified total reactor pressure of 4.6 torr, and specified respective partial pressures for the oxidizing agents, O 2 and N 2 O at 1.7 torr and 1.1 torr, the film growths were tested at several substrate temperature ( T s ) points from 780 °C to 864 °C. The film growth time for each test was 3 min. As to compositional purity, purity in c -axis orientation, and crystal structural quality of these tested films by using photo-assisted MOCVD technique, it was found that for the growth of purely c -axis oriented YBCO thin films with high crystalline quality, the appropriate growth temperature range (or “ T s window”) was from about 800 °C to 830 °C, at relevant pressures as specified above. T c and J c of a typical YBCO film sample grown within this “ T s window”, i.e., 810 °C, were found as 90 K and 1.32 MA/cm 2 (77 K, 0 Oe) respectively by magnetization measurements. It is noticeable that this film, and other purely c -axis oriented YBCO films are all single-crystal like and dense, with no SEM visible grain boundary or void. The causes of precipitates found on top surface of these c -axis oriented YBCO films are also discussed.

Donut- or ring-shaped Co nanomaterials were successfully synthesized using the polymer-modified method, by which PVP is used as a surface modifier reagent. The synthesized products were structurally and morphologically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), whereas the magnetic characterization was performed by temperature- and field-dependent magnetization measurements. The results show that the rings have a h-Co nanostructure. The outer diameter is about 400−500 nm, inner diameter 150−250 nm, and the ring plane thickness ∼120 nm. The magnetization measurements show a typical coercivity of about 112 Oe at 300 K and an almost vanishing coercivity, HC ≈ 0 at T = 5 K. Numerical calculations using the packeage of object oriented micromagnetic framework (OOMMF) reveal a magnetization ground-state of flux closure structure, as expected for the geometric structure of the submicrometer-sized Co rings. This explains the observed hy...

Nickel nanochains assembled with submicrometer-sized hollow spheres were synthesized through a mild polyol reduction method by using PVP as the soft template. The resulting fiberlike superstructures were characterized by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. A self-assembly mechanism of PVP-assisted bubble templating is responsible for the formation of hierarchical superstructures. It was found that PVP concentration plays a key role in determining both the morphology and the further self-assembly process of nickel hollow fibers. This first synthesis of such hierarchical structures implies a simple and inexpensive way to prepare transition metal superstructures on a large scale. Magnetic measurements by SQUID were also carried out to explore their magnetic properties; the micromagnetic simulation result by OOMMF code showed good agreement with the characters of our samples.

Using a wet chemical method, we have synthesized chain-like structure with diameters of 200–250 nm and lengths of ∼10 μm formed by assembly of small cobalt nanoparticles. The chain-like structures were realized via reaction of CoCl2˙6H2O and N2H4 in the presence of PVP in an ethylene glycol solution. Magnetic measurements show a coercivity of about 122 Oe at 300 K. We also propose a possible mechanism for the formation of the chain-like structures.

One-dimensional Ni/Ni3C core-shell nanoball chains with an average diameter by around 30 nm were synthesized by means of a mild chemical solution method using a soft template of trioctylphosphineoxide (TOPO). It was revealed that the uniform Ni nanochains were capped with Ni3C thin shells by about 1 to 4 nm in thickness and each Ni core consists of polygrains. The coercivity of the core-shell nanochains is much enhanced (600 Oe at 5 K) and comparable with single Ni nanowires due to the one-dimensional shape anisotropy. Deriving from the distinctive structure of Ni core and Ni3C shell, this architecture may possess a possible bi-functionality. This unique architecture is also useful for the study on the magnetization reversal mechanism of one-dimensional magnetic nanostructure., Comment: 17 pages, 6 figure

Flower-like Ni particles about 1 µm in diameter have been synthesized by means of a mild chemical solution method with a soft template of hexadecyltrimethy-lammonium bromide (CTAB). Analysis of the structures by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) reveal that they are composed of particles with an average diameter of 250 nm. The particles are composed of grains 20–30 nm in size. Based on a series of experiments, the growing process of the flower-like structure is described briefly. The coercivity of the as-grown product at 300 K is about 90 Oe. It is small in comparison with that of the reported flower-like microstructure composed of nickel nanotips, ∼232 Oe. This is attributed to its shape anisotropy and polycrystalline structure. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Manganese oxides are important materials in many applications. We describe, for the first time, the facile one-pot synthesis of highly crystallined λ-MnO2 nanodisks assembled from nanoparticles through a novel wet chemical route. Morphology evolutions, magnetic properties, and phase transitions are also studied by transmission electron microscopy, scanning electron microscopy and thermal gravimetric analysis. A mechanism for the formation of the λ-MnO2 nanodisks as well as their inner structure is proposed based on controlled experiments. The key to the successful preparation of this novel MnO2 nanostructure has been a synergic control of a surfactant, polyvinylpyrrolidone, and a solvent, dimethyl sulfoxide, capable of stabilizing the microreactors and promoting the assembly of manganese nanoparticles.

The effect of the size of the B powder and the Mg powder on MgB2 phase formation has been studied by the technique of in situ high-temperature resistivity (HT-ρ(T)) measurement. Two characteristic temperatures indicating the phase formation, the onset point, Tonset, and the completion point, TPF, were directly determined during the continuous heating process. These two temperatures of the samples synthesized using nanometer-size B powder (Nano-B) and micrometer-size B powder (Micro-B) with nanometer-size Mg (Nano-Mg) are almost the same, i.e. Tonset = 713 K and TPF~763 K, respectively, indicating that the phase formation temperature of MgB2 does not primarily depend on the particle size of the B powder. A similar process was then carried out on Mg powders with the same B powder. An exponential relationship between the onset phase formation temperature and the Mg powder size is clearly shown, which can be fully fitted by a modulated diffusion equation and which gives Q = 421 kJ mol−1 describing the grain boundary activation energy of Mg diffusing into B. We also find that the MgB2 crystallites along the [101] direction have the lowest formation energy, revealed by x-ray diffraction (XRD) analysis on raw Mg powders, and the corresponding MgB2 crystallites aligned along [101] will be formed preferentially in the sintering process. This result is useful for the understanding of MgB2 phase formation in the solid reaction process.

A novel Co complex [Co(NH3)6Cl3] nanorods with diameters of 150–200 nm and 2–2.5 μm in length were synthesized successfully through a simple solution chemical route. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and superconducting quantum interference device (SQUID) system. We propose a possible reaction process for the formation of Co(NH3)6Cl3. A control experiment shows that PVP plays a soft-template to uniform the morphology and size of the products.

Co-based (Co and Co 3 O 4 ) nanoparticles were self-integrated into SiO 2 nanotubes with a methodology based on the use of a Co salt as a template structure for the formation of SiO 2 nanotubes. Within the confinement of tubular matrix of SiO 2 , the nanofibres of cobalt precursor, i.e., [Co(NH 3 ) 6 ](HCO 3 )(CO 3 )·2H 2 O, were treated in a H 2 atmosphere with different parameters. With a sufficient reduction on the cobalt precursor, sphere-like Co-based nanoparticles are obtained, being well aligned in the interior space of the SiO 2 nanotubes. With an insufficient reduction, platelet-like Co-based nanoparticles are formed, being arranged in a random manner inside the SiO 2 nanotubes. The sufficiently reduced Co–SiO 2 nanocomposite exhibits an open hysteresis loop in the low field region ( 3 kOe) at 300 K. An observed wide separation between the zero-field-cooling (ZFC) and field-cooling (FC) curves over the whole temperature region has demonstrated a characteristic feature of ferromagnetism with a magnetically anisotropic barrier diverting the easy axis from the axis of the applied field. The predominant factor leading to this anisotropic potential barrier is attributed to the shape anisotropy native to the one-dimensional arrangement of Co-based nanoparticles within the tubular matrix, i.e. SiO 2 nanotubes.

High-density MgB2 (HD-MgB2) superconducting samples (D ⩾ 2.2 g/cm3), using different sources of magnesium powder as raw material, were synthesized in ambient pressure in a rich Mg environment. The magnesium powders used in the fabrication process include nanometer-sized magnesium particles, powders from Alfa Aesar, ordinary off-the-shelf powder, and magnesium chip. The fabrication procedure involved a double-sintering process in a rich-Mg environment. A transition temperature Tc of 39 K was observed. Samples with the equally high density and matching superconducting properties were obtained as well by a triple sintering process of the MgB2 powder directly from Alfa Aesar.

Magnetic chains up to 10 μm in length formed of hollow cobalt mesospheres (480-850 nm) with a 60 nm thick shell are synthesized by a new soft-assembly protocol. The obtained chains show a saturation magnetization of 37.5 emug -1 , a remnant magnetization of 1.55 emu g -1 , and a coercivity of ca. 66 Oe at 300 K. A possible mechanism for the formation of the chainlike hollow structures is proposed.

We have made a progress in fabricating MgB 2 films, ∼25 μm, on the stainless steel substrate by hybrid physical–chemical vapor deposition. The superconducting transition temperature is, T C (onset) = 39.6 K with a transition width, Δ T = 0.5 K. The characterization by scanning electron microscope and X-ray diffraction indicates that its structure is polycrystalline. At T = 0 K, the upper critical field H C2 is determined as 15.2 T by extrapolation from a polynomial fitting to the transition temperatures under various applied fields, T C ( H ). In the self field, the critical current density J C is determined as 3.74 MA/cm 2 at T = 15 K by a magnetic measurement according to the Bean model.

Thick MgB2 films have been grown on Cu substrates by the technique of hybrid physical?chemical vapour deposition (HPCVD). The films are about 2?3??m thick and are quite dense. The Tc (onset) is as high as 37?38?K and sharp, ~0.7?K. X-ray diffraction indicates that the films show a highly textured polycrystalline character. The upper critical field, Hc2(0) at T = 0?K, is extrapolated as 15.3?T. The controlled growth of MgB2 film on Cu substrate provides an alternative route for the preparation of MgB2 tape materials.

Magnetism of a very thin antiferromagnetic (AFM) surface CuO has been investigated with the partially oxidized nanocomposites of Cu-CuCl, ~ 200 nm. The samples are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray-excited Auger electron spectroscopy, transmission electron microscope and magnetic measurements. The characterizations indicate that the composites have a core-shell structure. Before the oxidation, it is (Cu)core/(CuCl)shell, and after the oxidation, (Cu)core/(Cu2O+CuCl+minuteCuO)shell. The magnetic measurements have revealed that a ferromagnetic (FM) like open hysteresis exists at the temperature below the freezing point, TF. In the high field region, a paramagnetic (PM) response appears without showing a sign of saturation. Also, the field dependent magnetization (M-H) measurement is PM-like at T > TF. These interesting magnetic properties are evident to arise from the AFM CuO on the outer surface. They are attributed to the uncompensated surface spins of Cu2+ and the effect of surface random potential. More interestingly, the magnetic susceptibility is greatly enhanced in the presence of Cl- anions at T < TF, according to the field-cooled/zero-field-cooled (FC/ZFC) measurements. This further supports the point that the disorder or frustration effect of the impurity would reduce the AFM ordering of CuO and increase the level of uncompensated spins., 8 pages including 7 figures, Nanotechnology In Press

We fabricated several superconducting MgB2 thick films on stainless steel (SS) substrates by using hybrid physical-chemical vapor deposition (HPCVD) technique. The thickness was in the 10μm to 20μm range, and the onset critical transition temperature Tc (onset) and the width of the superconducting transition (ΔT) were about 37.8 and 1.2 K. They were dense and textured along (101) direction with high tenacity, despite the existence of a little amount of MgO and Mg. We bent the films at different degrees and studied the ductility and transport properties of these MgB2 thick films under applied force. The results demonstrated that the superconducting properties of these thick films, prepared by HPCVD, stay almost unaffected even with the films bent to a large degree with a curvature of 0.5 mm. This indicated that the superconducting wires or tapes of MgB2 with a core of SS had the advantages of avoiding rigidity and brittleness in industrial handling. The technique of HPCVD has, therefore, a high application potential.

The evolution of microstructure parameters (precipitate size and volume fraction) for an Al–8.0 Zn–2.05 Mg–1.76 Cu alloy during isothermal ageing has been studied by synchrotron-radiation small angle X-ray scattering (SAXS) combining transmission electron microscopy (TEM). The results show that the precipitates are only a few nanometers even at higher temperature 160 °C up to 72 h (5.82 nm). The precipitate volume fraction reaches a plateau except ageing at 120 °C and the maximum is about 0.052–0.054 in the range 140–160 °C. Models describing the evolution of these two parameters with ageing temperature and time have been constructed for our further predicting the precipitate hardening. The coarsening of precipitate is consistent with LSW (Lifshitz–Slyozov–Wagner) model even in the initial stage where volume fraction is still varying. The activation energy of coarsening regime has been determined to be about 1.25 ± 0.02 eV.

The precipitate size distribution and morphology in an AI-Zn-Mg-Cu-Li alloy have been studied by small angle X-ray scattering (SAXS). The results show that the precipitates belong to flat ellipsoids of revolution and their axis ratio range is between 0.2 and 0.4 aged at different conditions. To verify the validity, the results of SAXS have been compared with that of TEM. This study has also constructed the logarithm Gaussian distribution of effective size and the Maxwell distribution of particles mass with gyration radius by means of a prior assumed model of the size distribution. The geometric mean and distribution width for both type distribution curves increase with kinetic strength K-s, which indicates the characteristics of the size distribution in space during aging. (c) 2005 Elsevier Inc. All rights reserved.

Very thick, ~ 40 $\mu$m, clean, and highly textured MgB2 film was effectively grown on an Al2O3 substrate. The fabrication technique is by the hybrid physical-chemical vapor deposition (HPCVD) using B2H6 gas and Mg ingot as the sources. The X-ray diffraction (XRD) analysis shows a highly (101)-oriented MgB2 crystal structure without any impurity detected. There is no signal from the substrate in the XRD spectrum, indicating that the film thickness exceeds the X-ray penetration length. Scanning electron microscopy (SEM) reveals that the film is composed of highly-packed MgB2 micro-crystals with a uniform size distribution of about 2 $\mu$m in diameter and 0.2 $\mu$m in thickness. According to the compositional analysis of energy-dispersive X-ray spectroscopy (EDX), no oxygen, hence no MgO, exists in the textured film, consistent with the XRD result. Also, the transport properties are similar to those of a single crystal, indicating a clean film of good crystallite. The zero field transition temperatures are determined as TC(onset) = 39.2 K and TC(zero) = 38.4 K, giving a sharp transition typical of a clean sample. The residual resistivity ratio (RRR) is determined as 6.4 and the magnetoreisitance (MR) is about 28 % at 40 K under the applied field of 9 T, which are similar to those of a single crystal. The zero temperature upper critical field, HC2(0), is extrapolated as 19 T from the TC(onset) at applied field up to 9 T., Comment: 10 pages, 4 figures

The microstructures of 1.0% Li-containing A15.14Zn1.35Mg1.76Cu (wt.%) alloy have been studied by TEM in present paper. The precipitates of this alloy with peak hardness at two-step aging were fine η′(MgZn2), instead of δ′(Al3Li) phases. Narrow precipitation-free zones were observed as well.

With laser surface melting and conventional heat treatment, superplastic diffusion bonding of TiAl alloy samples was carried out. Three different microstructure, i.e. fully lamellar structure, fine dendritic structure and refined equiaxed structure are used and their effects on bonding quality were investigated, and the bond quality was assessed by shear test at room temperature. Sound bonds could be achieved at 900 °C by laser surface modification or by laser surface modification and pre-bond heat treatment at 1000 °C for 60 min, which is lower than conventional diffusion bonding temperature. The bonds were also post-bond heat treated at 1200 °C for 30 min, which improved the bond quality in all cases. The best shear strength of the bonds is greater than 80% of that of base metal.

Microcracks and their effect on the plastic deformation of γ-TiAl alloy with fully lamellar microstructure (FL) at relatively low strain rate (1 × 10−5/s) has been investigated. It is found that a large number of microcracks nucleate within the grains. The microcrack density increases with the increase of grain size. Most of the microcracks nucleate at the γ/α2 interfaces and gather at grains with soft-orientations. Based on the observation and analysis, a model of microcrack nucleation in FL γ-TiAl alloy is built up. The plastic elongation of γ-based TiAl alloys with FL microstructure changes non-monotonously with the increase of grain size, which results from cooperation of micro-deformations and microcracks.