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Abstract: Very thick, ∼40μm, clean, and highly textured MgB2 film was effectively grown on an Al2O3 substrate. The fabrication technique was 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 has exceeded 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 2μm in diameter and 0.2μm 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)=39.2K and TC(zero)=38.4K, giving a sharp transition typical of a clean sample. The residual resistivity ratio (RRR) is determined as 6.4 and the magnetoresistance (MR) is about 28% at 40K under the applied field of 9T, 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 9T. [Copyright &y& Elsevier]

Careful investigations on a series of the MgB2 phases quenched at different sintering temperatures during fabrication process have been carried out, and important information is obtained, by the X-ray diffraction (XRD), the scanning electron microscopy (SEM) images, and the temperature dependent magnetization (M–T) measurements. The particle sizes of the raw magnesium and boron powders are on the order of 0.1 mm and 1 μm, respectively. Three stages in the formation of the polycrystalline MgB2 phase are identified in different sintering temperature ranges according to the corresponding superconducting properties and the crystallization conditions. The MgB2 phase first appears in a microscopic scale at about 530 °C according to the M–T measurement. Then, the MgB2 phase forms macroscopically within a narrow temperature range from 653 to 660 °C, while the residual raw materials of the magnesium and boron components persist to the temperature of 700 °C. The optimum sintering temperature range for the MgB2 phase to form is determined from 750 to 900 °C. [Copyright &y& Elsevier]

The MgB2 superconductor synthesized in a flowing argon atmosphere using nanometer magnesium powder as the raw materials, denoted as Nano-MgB2, has been studied by the technique of in situ high temperature resistance measurement (HT-RT measurement). The MgB2 phase is identified to form within the temperature range of 430–490 °C, which is much lower than that with the MgB2 sample fabricated in the same gas environment using the micron size magnesium powder, denoted as Micro-MgB2 and reported previously. The sample density of the Nano-MgB2 reaches 1.7 g/cm3 with a crystal porosity structure less than a μm, as determined by the scanning electron microscope (SEM) images, while the Micro-MgB2 has a much more porous structure with corresponding density of 1.0 g/cm3. This indicates that the Mg raw particle size, beside the sintering temperature, is a crucial factor for the formation of high density MgB2 sample, even at the temperature much lower than that of the Mg melting, ∼650 °C. The X-ray diffraction (XRD) pattern shows a good MgB2 phase with small amount of MgO and Mg and the transition temperature, TC, of the Nano-MgB2 was determined to be 39 K by temperature dependent magnetization measurements (M–T), indicating good superconducting properties. [Copyright &y& Elsevier]

Abstract: Co-based (Co and Co3O4) nanoparticles were self-integrated into SiO2 nanotubes with a methodology based on the use of a Co salt as a template structure for the formation of SiO2 nanotubes. Within the confinement of tubular matrix of SiO2, the nanofibres of cobalt precursor, i.e., [Co(NH3)6](HCO3)(CO3)·2H2O, were treated in a H2 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 SiO2 nanotubes. With an insufficient reduction, platelet-like Co-based nanoparticles are formed, being arranged in a random manner inside the SiO2 nanotubes. The sufficiently reduced Co–SiO2 nanocomposite exhibits an open hysteresis loop in the low field region (<3kOe) and a paramagnetic response in high field (>3kOe) at 300K. 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. SiO2 nanotubes. [Copyright &y& Elsevier]

Abstract Ultrathin single crystalline nanoplates of Ni 12 P 5 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 Ni 12 P 5 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. Graphical abstract Image 1 Highlights • Single-crystalline Ni 12 P 5 nanoplates by a facile, template-free wet chemical route. • Nanoplate surface is of { 2 ¯ 11 } crystal plane, and its thickness, about 7 nm. • The growth mechanism is by Kirkendall effect. • High specific capacity is 697 C/g at the current density of 1 A/g. • Surface term accounts for about 2/3 of the specific capacity, and the bulk, 1/3. [ABSTRACT FROM AUTHOR]

Samples of PrBaCo 2 O 5.50+ δ ( δ = −0.15–0.14), synthesized by solid-state reactions, were investigated to ascertain oxygen compositional effects on transport/magnetic properties. Resistivity decreases with increasing oxygen content, indicative of p -type conduction. A metal-insulator transition was observed at 330 K only for sample PrBaCo 2 O 5.52 , coinciding with phase transition and spin-state transition of Co 3+ . When δ deviates from zero, samples show insulator–insulator transitions, although for sample δ = 0.14, no transition occurs but only semi-conductive behavior appears. Electronic transport is governed by the hopping mechanism at lower temperatures and thermal activation at higher temperatures. All samples underwent paramagnetic–ferromagnetic–antiferromagnetic transitions, except PrBaCo 2 O 5.64 , which only went through a paramagnetic–ferromagnetic transition. The ferromagnetic state for δ < 0 originates with the Co 3+ /Co 2+ super-exchange interaction; for δ > 0, it stems from the Co 3+ /Co 4+ double exchange interaction. [ABSTRACT FROM AUTHOR]

Abstract: Nearly monodispersed hollow nanospheres of bimetallic NiPt have been synthesized by a one-pot wet chemical method at room temperature with a precursor Ni nanocompound as a sacrificial template. The size control is carried out via the sacrificial template, from about 35nm to nearly 100nm in diameter. The shell thickness of the NiPt hollow sphere reaches down to as thin as 2–3nm slightly larger than a single layer of alloyed NiPt nanocrystallites. The product with the citric acid as surfactant exhibits enhanced oxygen reduction activities compared to a commercial Pt/C catalyst and the hollow nanospheres coated with PVP. It has potential applications in fuel cells, biotechnology and environmental chemistry with the facile synthesis, low cost and excellent electrocatalytic activity. [Copyright &y& Elsevier]

Abstract: Co-doped ZnO single-crystalline nanorods with 80–100nm in diameter and 1.5–2μm 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− x Co x O 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 380K. The high-temperature ferromagnetic properties allow this Zn1− x Co x O nanorods potential applications in future spintronic devices. [Copyright &y& Elsevier]

Abstract: 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 4.6torr, and specified respective partial pressures for the oxidizing agents, O2 and N2O at 1.7torr and 1.1torr, 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 3min. 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 90K and 1.32MA/cm2 (77K, 0Oe) 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. [Copyright &y& Elsevier]

Abstract: Superconducting YBa2Cu3O7− x thin films were deposited on LaAlO3 (100) substrates by a photo-assisted metal-organic chemical vapor deposition (MOCVD) technique. In our experiment, growth temperature, chamber pressure and growth time were all fixed; the only process variable was the susceptor inclination angle (Φ) between the axis of gas inlet and the susceptor surface. It was found that the growth rate of YBCO films increases monotonically as Φ increases, whereas the superconducting critical current density (J c) has a maximum (1.2×106 A/cm2) near Φ =22.5°. The experimental results were found to be well correlated with the three-dimensional simulations of gas flow inside the MOCVD reactor, with Φ being the only process variable. [Copyright &y& Elsevier]

Abstract: A novel Co complex [Co(NH3)6Cl3] nanorods with diameters of 150–200nm and 2–2.5μm 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. [Copyright &y& Elsevier]

Abstract: We have made a progress in fabricating MgB2 films, ∼25μm, on the stainless steel substrate by hybrid physical–chemical vapor deposition. The superconducting transition temperature is, T C (onset)=39.6K with a transition width, ΔT =0.5K. The characterization by scanning electron microscope and X-ray diffraction indicates that its structure is polycrystalline. At T =0K, the upper critical field H C2 is determined as 15.2T 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 3.74MA/cm2 at T =15K by a magnetic measurement according to the Bean model. [Copyright &y& Elsevier]