Search

Copper-based materials with high electrical conductivity and high strength are strongly desired in energy and electric power fields. Unfortunately, it's almost impossible to obtain scalable and facile copper-based materials with the combined improvement of electrical conductivity and strength through traditional means. Here, by in-situ grown high quality graphene in copper through vacuum hot-press sintering the Cu powder and non-toxic, cheap liquid paraffin, high electrical conductivity and high strength are easily realized. Through further elaborate structure design and morphology control of graphene by altering the copper powder size, the liquid paraffin content and the sintering process parameters, the performance is improved. The uniformly-distributed 3D graphene plays a vital role, which acts as an electron transport channel and strengthens the matrix by grain refinement, dislocation strengthening and load transfer mechanisms. As a result, the cold drawn Cu/Graphene composite wire exhibits high electrical conductivity of 94.85% IACS and high tensile strength of 516 MPa, together with good softening resistance. This work provides a low cost and high-efficiency way to prepare high-performance graphene reinforced Cu matrix composite, and opens a new window for large-scale production of high-performance Cu/Graphene composites with different shapes.

Thermocatalytic decomposition of methane is proposed to be an economical and green method to produce COx-free hydrogen and carbon nanomaterials. In this work, the catalytic performance of Ni–Mn–Ru/Al2O3 catalyst under different reaction parameters (such as, pre-reduction temperature, reaction temperature, space velocity, etc.) were investigated to obtain optimum reaction conditions. The catalysts were characterized by N2 adsorption/desorption, X-ray diffraction, inductively coupled plasma optical emission spectrometer and hydrogen temperature programmed reduction. For the 60 wt% Ni-5 wt% Mn-10 wt% Ru/Al2O3 catalyst using Ru(NO)(NO3)x(OH)y(x + y = 3) as Ru precursor, the methane conversion rate obtained is high as 93.76% under optimum reaction conditions (reduction at 700 °C for 1 h, reaction at 750 °C, GSHV = 36,000 mL/gcat h). Carbon nanomaterials formed during the process of methane thermocatalytic decomposition were characterized by scanning electron microscopy, thermal gravimetric analyzer and Raman spectroscopy. Carbon nanofibers were formed over all the Ni–Mn–Ru/Al2O3 catalysts.

Carbon nanotubes (CNTs) have been proved a significant role as the reinforcement material in improving the mechanical and electrical properties of metal matrix composites due to their high mechanical properties, excellent electrical and thermal conductivity as well as unique atomic structure. In addition, the dispersion of CNTs has been a key factor in fabricating of metal-based complex especially for copper (Cu) with performance improvement. In the present paper, the well dispersion of functionalized CNTs (F-CNTs) is obtained at the first time, accompanied by using pulse reverse electrodeposition (PRED) technology, leading to formation of the ultrahigh electrical conductivity composite films of Cu/F-CNTs. These composite films exhibit an ultrahigh electrical conductivity of up to 6.1 × 107 S/m (increased by 105.4% of that international annealed copper standard, IACS), but maintain a high hardness of 82.3 HV and tensile strength of 297.1 MPa. It is believed that this work opens new perspectives to develop ultrahigh electrical conductivity composite materials and would role as electric wire for reducing energy loss.

A filtering capacitor is an important component for signal stabilization in renewable power generators. Portable ultrahigh-rate electrochemical capacitors with high area specific capacitance have b...

Cu-Ag alloy is widely used as conductive material for high-field pulsed magnets in electrical industry. The cryorolling technique is considered as the most applicable severe plastic deformation technique. Therefore, in this study, cryorolling and subsequent annealing process were used to prepare Cu-4Ag (in wt.%) alloy sheets. The strength, ductility and electrical conductivity of Cu-4Ag alloy sheets were investigated. Microstructure of Cu-4Ag alloy was also studied by OM, SEM, XRD and TEM. As a result, the cryorolling specimens after annealing at temperature of 300 °C display a good combination of tensile strength of 652.2 ± 6.0 MPa, moderate elongation of 12.5 ± 0.7% and electrical conductivity of 80.6 ± 0.2% IACS. This is due to the presence of dislocations, dislocation cells, nanograins and nanotwins in the non-recrystallized regions and fine nanoscaled silver precipitates. Besides, a good ductility is achieved in this condition due to its desirable ductile fracture characteristics.

Giant magneto-resistive (GMR)-superconducting mixed magnetic sensors are expected to be widely used because of their excellent sensitivity, stability, band characteristics, and low cost. If a tunnel magnetoresistance (TMR)-superconducting mixed magnetic sensor is prepared using a higher sensitivity and lower power TMR instead of GMR, the performance of the device will be further improved. We have fabricated a TMR-superconducting mixed sensor by a bonding process, and the feasibility was verified. The sensitivity was 21 times higher than that of the TMR device alone, reaching 18.1%/Oe. The noise level reached 6.6 pT/Hz1/2 at 77 K. At the same time, the influence of different constriction width of the superconducting magnetic flux concentrator on the device performance was compared at 4.5–77 K.

Measuring the electron-transport properties of substrate-supported nanomaterials with the traditional two-point comparison method is difficult at electron energies below 50 eV, where core-level signals are too feeble to be detected against the strong secondary-electron background. Herein, a data-driven spectral analysis technique is used to study the low-energy electron-transport properties of substrate-supported target nanomaterials, while eliminating the influence of the substrate signal. Applying this technique, the electron-transport properties of the effective attenuation length and the inelastic mean free path (IMFP) can be determined with extremely high efficiency over the entire measured energy range of 6--600 eV. Further, these results show excellent agreement with other experimental and theoretical results. Significant differences are observed between monolayer graphene and the bulk graphite IMFP, which illustrates the importance of the nanometer effect in the electron-transport properties of the material. Furthermore, this technique is readily applicable to any ultrathin material that can be transferred onto a polycrystalline gold substrate.

Abstract A Monte Carlo calculation of the secondary electron emission from a SiO2 macro-capillary in the backward direction induced by electron irradiation is presented with the aim to understand transmission guiding of a scanning electron beam through a borosilicate glass macro-capillary. The theoretical modeling of electron transport in SiO2 capillary incorporates the elastic, inelastic and phonon scatterings, resulting, respectively, from the interactions with nucleus, electrons and phonons. The influence on electron inelastic scattering by the insulator bandgap is also considered. In this work a simplified approach has been employed to deal with the charging of the internal wall of the capillary and it is found that at a glancing incident angle, the secondary electrons are mostly originated from the top surface. Graphical abstract

Graphene-based materials that can spontaneously response to external stimulations have triggered rapidly increasing research interest for developing smart devices due to their excellent electrical, mechanical and thermal properties. The specific behaviors as bending, curling, and swing are benefit for designing and fabricating the smart actuation system. In this minireview, we overview and summarize some of the recent advancements of stimuli-responsive actuators based on graphene materials. The external stimulus usually is as electrical, electrochemical, humid, photonic, and thermal. The advancement and industrialization of graphene preparation technology would push forward the rapid progress of graphene-based actuators and broaden their application including smart sensors, robots, artificial muscles, intelligent switch, and so on.

Pure ZnO precursor films were prepared by a sol-gel spin coating method. The films were directly annealed by the electron beam (EB) for 5 min. The structural, optical and electrical properties were investigated by means of SEM, AFM, XRD, UV–vis spectrophotometer and Hall-effect measurement. SEM and AFM studies revealed smooth, dense film microstructure with some holes. The average grain size ranged from 10 nm to 60 nm and the surface RMS roughness of the films is less than 3 nm. X-rays diffraction patterns showed (002) preferential growth in all annealed films. From optical transmittance spectra, the absorption edge of the films was determined to be at ∼380 nm with > 85% transmittance in visible region. ZnO film annealed with beam current 0.7 mA was found to exhibit minimum resistivity value of 1.57 × 10 −2 Ωcm and carrier concentration as high as 6.37 × 10 19 cm −3 , which is 2 ∼ 3 orders better than that of the typical pure ZnO thin films using sol-gel method.

Tailoring magnetic behavior by composition and annealing is an effective way. The phase transition from the face-centered-cubic (FCC) to B2 structure influenced by the Al content on the CoFeMnNiAlx alloys leads to the enhanced magnetization. However, the excessive Al addition in the B2-structured alloys impairs the magnetization. The phase transformation caused by annealing also indicates that the saturation magnetization of the alloy depends on the volume fraction of the B2 phase, and a higher content of the B2 phase is beneficial to the large saturation magnetization. Ab initio calculations are used to explain the magnetic behavior of the present HEAs and the effects of phase structures on magnetic characteristics. The phase stability of the CoFeMnNiAlx alloy is thoroughly studied by both the existing phase-formation empirical criteria and annealing. The existing empirical criteria used to predict the phase formation are not universal. However, combining the ΔHmix-δ relation and the φ value, whether the single disordered solid-solution phase is formed can be preliminarily predicted.

A bulk Cu/Graphene composite with high electrical conductivity (98.2%IACS) and high hardness (61.2 HV) was fabricated by vacuum hot-press sintering. Cu powder with in-situ grown graphene was prepared by non-toxic, cheap liquid paraffin at lower temperature. The in-situ grown 3D graphene act as an electron transport channel and hinder the movement of the grain boundary. After cold rolling and annealing, the Cu/Graphene composite maintained a high tensile strength of 369.4 MPa, high electrical conductivity of 96.1%IACS and good ductility (6%). Comparing with the pure Cu, the existence of Graphene raised the recrystallization temperature of the composite, and made the composite possess excellent softening resistance.

Interface control is an important method to improve the properties of Copper/Carbon Nanotubes composite. In this work, different kinds of carbide formation elements like Nb, Zr, Mo, Ti, or W is mechanically added into Cu to form composite with Carbon Nanotubes. The element doping leads carbides formed at the interface and makes the composite achieve simultaneously high electrical conductivity and high hardness by improving the wettability and interface bonding force between Cu and Carbon Nanotubes. The sintered composite doping with W possesses the optimal performance with the electrical conductivity about 96.6%IACS, the hardness about 68.54 HV. The nano sized W2C phase formed at the interface contributes to the high performance.

Acquiring high electrical conductivity and good mechanical property is a key issue for Cu/CNTs composites, which affects their potential applications in electrical material field. In this study, Cr was induced in the Cu matrix to enhance the interfacial bonding. Different amounts of Cr were chosen to thoroughly investigate their effect on the interface structure, the electrical conductivity and the mechanical property. By tailoring the combined effects of good densification, uniform dispersion of CNTs, moderate amount of carbide at the Cu/CNTs interface, strong interfacial bonding force and suitable Cu matrix microstructure, the good overall performance was obtained in a (Cu-0.07 wt.%Cr)-0.5 wt.%CNTs composite. The addition of trace amounts of Cr leads to in-situ formation of an appropriate amount of nano chromium carbide (Cr3C2) at the Cu/CNTs interface, which improves the interface wettability and benefits the current transfer and load transfer, and hence improves the conductivity while increasing the hardness.

Black phosphorus nanobelts are fabricated with a one-step solid-liquid-solid reaction method under ambient pressure, where red phosphorus is used as the precursor instead of white phosphorus. The thickness of the as-fabricated nanobelts ranges from micrometers to tens of nanometers as studied by scanning electron microscopy. Energy dispersive X-ray spectroscopy and X-ray diffraction indicate that the nanobelts have the composition and the structure of black phosphorus, transmission electron microscopy reveals a typical layered structure stacked along the b-axis, and scanning transmission electron microscopy with energy dispersive X-ray spectroscopy analysis demonstrates the doping of bismuth into the black phosphorus structure. The nanobelt can be directly measured in scanning tunneling microscopy in ambient conditions.

Characterization techniques available for bulk or thin-film solid-state materials have been extended to substrate-supported nanomaterials, but generally non-quantitatively. This is because the nanomaterial signals are inevitably buried in the signals from the underlying substrate in common reflection-configuration techniques. Here, we propose a virtual substrate method, inspired by the four-point probe technique for resistance measurement as well as the chop-nod method in infrared astronomy, to characterize nanomaterials without the influence of underlying substrate signals from four interrelated measurements. By implementing this method in secondary electron (SE) microscopy, a SE spectrum (white electrons) associated with the reflectivity difference between two different substrates can be tracked and controlled. The SE spectrum is used to quantitatively investigate the covering nanomaterial based on subtle changes in the transmission of the nanomaterial with high efficiency rivalling that of conventional core-level electrons. The virtual substrate method represents a benchmark for surface analysis to provide ‘free-standing' information about supported nanomaterials., Quantitative characterization of supported nanomaterials is challenging, because the nanomaterial signals cannot easily be deconvoluted from those of the substrate. Here, the authors introduce an inventive approach to overcome this problem for electron-based surface analysis techniques.

Root morphological characteristics are important parameters for the evaluation of plant adaptation to stress environment. In this study, a pot experiment was conducted to investigate changes in the root morphology of Bothriochloa ischaemum intercropped with Lespedeza davurica under three soil water regimes and two phosphorus (P) fertilizer treatments. Results showed that root biomass (RB) per B. ischaemum plant decreased as its proportion increased in the mixtures. There were no significant differences in root:shoot ratio (RSR) among the mixture ratios, and P application did have consistent effects on the RSR. Bothriochloa ischaemum tended to have smaller root surface area (RSA), root average diameter (RAD), specific root length (SRL), and specific root area (SRA) under water stress conditions. There was a negative linear relationship between RB and RSA under each water and P treatment. Negative and positive linear relationships were found between RB and TRL (total root length), TRL and RSA, respectively,...

The c-axis textured Sr1-xKxFe2As2 tapes produced by cold rolling and post-annealing, could carry a high super-current over 2*104 A/cm2. However, the magnitude is far from its maximum, because of the current obstacles associated with various defects in the material. To predict the maximal transport critical current density, we modeled the current paths in a c-axis textured polycrystal as a three-dimensional flow network, and calculated the maximum flow with the Ford-Fulkerson algorithm. It indicates that a much higher super-current of about 2*105 A/cm2 could be achieved in an ideal c-axis textured K-doped 122 polycrystal. The dependences of transport Jc on density, content of invalid boundary and grain size and shape were also studied. The results imply that, over 30% of the grain boundaries in the reported c-axis textured Sr1-xKxFe2As2 tapes may act as current obstacles, and the large ratio of width to thickness was expected to be the most favorable grain shape for high transport Jc in c-axis textured 122 superconducting tapes., Comment: 17 pages, 7 figures

AC susceptibilities (real χ ′ and imaginary χ ″) of Sr 0.6 K 0.4 Fe 2 As 2 (122 type) polycrystalline with Ag addition are analysed by the grained Bean model. A variety of characteristics, double peak in χ ″ and shoulder transition in χ ′, appear in the model simulation. Comparing the measured χ ′ and χ ″ with the model allows more clear insight on the polycrystalline structure. Estimated critical current densities J cg and J cl of the grain and the link in the iron-based pnictides show that the addition of 20 wt.% Ag increases J cl 9 times larger. Improvement of intergrain characteristics with Ag addition is clearly indicated.

```  Abstract-- In this review paper, we report the characteristics of the critical current density in FeAs based superconductors which is newly discovered by Hosono group of Tokyo Institute of Technology on 2008. Since the many specimens in present stage are not single crystals, there are two kinds of critical current density observed in the specimens which are so-called local and global critical current densities. Therefore, it is necessary to evaluate both kinds of critical current densities. The history effect in which the global critical current density shows different values in increasing and decreasing magnetic field is also observed when the specimens have the local and the global critical current densities. The wire which critical current is 180 A is successfully developed with using the knowledge of abovementioned characteristics of two kinds of critical current densities and the history effect. kinds of critical current density in the specimens. They are so-called local and global critical currents. That is, the connection between the grains in specimen is too week to carry large current, and the global critical current density is far lower than the local critical current density which flows only inside the grain. They are also called intra- and inter-grain shielding current density. It is essential to measure both local and global critical current densities, because the local critical current density will be achieved when the specimen will be prepared as single crystalline in near future which is already done in RE-123 (RE: Rare Earth) superconducting coated wire. Moreover, the global critical current is corresponding to transport critical current density which is usually measured by four probe method. In the present study, the local and the global critical current

The doping effect of different carbon source on the properties of MgB 2 tapes was compared using three typical dopants, nano-C, C 60 , and C 9 H 11 NO. It is found that C 60 doped samples showed the highest carbon substitution ratio and resistivity, with the lowest T c . For the nano-C doped samples, T c did not drop so significant, which is only 2 K lower than that of the pure ones. Compared to C 60 and C 9 H 11 NO doped samples, the nano-C doped samples show a lower J c value at 5 K. On the other hand, the C 9 H 11 NO doped samples show a high J c value at both 5 K and 20 K. This is a representative demonstration to the complex affecting factors on the J c – H property of MgB 2 tapes. Detailed mechanism for the property difference in MgB 2 induced by different chemical doping is discussed based on the systematically examined results.

Sub-micron scale BiFeO 3 has been fabricated by annealing precursor powders prepared through microwave-assisted sol–gel self-combustion method. It is found that the content of glacial acetic acid is crucial to particle morphologies and magnetic properties. The average particle size for the final products increases from tens to hundreds of nanometers with increasing glacial acetic acid content. With the increase of particle size, room temperature ferromagnetic hysteresis loops along with remarkable improvement of saturation magnetizations have been observed in sub-micron (tens to hundreds of nanometers) BiFeO 3 , which in bulk form exhibits an antiferromagnetic order. These features may suggest that the magnetic properties of BiFeO 3 , at the sub-micron level, increase with increasing particle size.

Persistent current (PC) operating magnet with bore diameter of about 32 mm was design and developed based on multi- and mono-filament MgB2 wires. The magnet was in a multi-solenoid structure. One pilot coil was wound and joints were fabricated at both ends, connecting it to a superconducting switch for PC operation tests. The magnet was to demonstrate the high field and high temperature performance at different temperatures. Numerical and experimental results demonstrated a promising future of MgB2 wires in low cost magnetic resonance imaging (MRI) systems and high field scientific magnets.

The superconducting properties of polycrystalline Sr0.6K0.4Fe2As2 were strongly influenced by Ag doping (Supercond. Sci. Technol. 23 (2010) 025027). Ag addition is mainly dominated by silver diffusing, so the annealing process is one of the essential factors to achieve high quality Ag doped Sr0.6K0.4Fe2As2. In this paper, the optimal annealing conditions were studied for Ag doped Sr0.6K0.4Fe2As2 bulks prepared by a one-step solid reaction method. It is found that the annealing temperature has a strong influence on the superconducting properties, especially on the critical current density Jc. As a result, higher heat treatment temperature (∼900°C) is helpful in diffusing Ag and reducing the impurity phase gathered together to improve the grain connectivity. In contrast, low-temperature sintering is counterproductive for Ag doped samples. These results clearly suggest that annealing at ∼900°C is necessary for obtaining high Jc Ag-doped samples.

Fe/Ti, Nb, and Ta sheathed SmO 0.7 F 0.3 FeAs wires were manufactured using the powder-in-tube method. A comparative study was made of the effect of sheath material on the microstructure and superconducting properties of the SmO 0.7 F 0.3 FeAs wires. Among these sheath materials, the penetration depth of Ta into the superconducting core is the largest. There was nearly no difference in the critical transition temperature of the SmO 0.7 F 0.3 FeAs wires sheathed with different materials, and the upper critical fields were approximately the same. On the other hand, it was found that Nb-sheathed wires had a higher superconducting current density than the others. Impurities existing in the superconducting core were thought to be one of the most important factors that affected the critical current density of the SmO 0.7 F 0.3 FeAs wires.

We present herein a comparison of the magnetic properties of bulk ceramics and thin films of the ferrimagnetic ErCo0.50Mn0.50O3 compound. Epitaxial thin films were deposited onto (1 0 0) SrTiO3 substrates by pulsed-laser ablation while bulk ceramics were prepared by solid state reaction. When cooling under low applied fields, a spin reversal is observed in both thin film and bulk due to the competition between two magnetic sublattices (Co/Mn and Er) coupled by a negative exchange interaction. Original features are observed in the M(H) loops for bulk materials: abrupt jumps at 4 T due to a reorientation of domains, while in the low field region, the increasing and decreasing branches of the magnetization intersect each other. In the thin film, the ordering temperature increased from 69 to 75 K, and the ZFC anomaly (AF transition) became sharper, compared to the bulk specimen. The oxygen content and the microstructure are crucial to observe the intersection of the magnetization branches.

MgB2 was thought as a promising superconductor used at temperatures around 20 K for cryogen-free magnet. Nanostructure materials were often selected as MgB2 additives due to their high chemical reactivity. In this paper, the mixture of nano-C and nano-SiC was doped to MgB2 bulks and tapes. The co-doping effect of C and SiC on the phase formation, microstructure, and critical current density of MgB2 bulks and tapes were systematically investigated. The mechanisms for the superconducting properties improvement in co-doped MgB2 superconductor was analyzed based on the characterization and measuring results.

The recent discovery of superconductivity in the iron based superconductors with very high upper critical fields presents a new possibility for practical applications, but fabricating fine-wire is a challenge because of mechanically hard and brittle powders and the toxicity and volatility of arsenic. In this paper, we report the synthesis and the physical characterization of iron pnictide wires and bulks prepared by the powder-in-tube method (PIT). A new class of high-Tc iron pnictide composite wires, such as LaFeAsO1-xFx, SmFeAsO1-xFx and Sr1-xKxFeAs, has been fabricated by the in situ PIT technique using Fe, Ta and Nb tubes. Microscopy and x-ray analysis show that the superconducting core is continuous, and retains phase composition after wire drawing and heat treatment. Furthermore, the wires exhibit a very weak Jc-field dependence behavior even at high temperatures. The upper critical field Hc2(0) value can exceed 100 T, surpassing those of MgB2 and all the low temperature superconductors and indicating a strong potential for applications requiring very high field. These results demonstrate the feasibility of producing superconducting pnictide composite wire. We also applied the one step PIT method to synthesize the iron-based bulks, due to its convenience and safety. In fact, by using this technique, we have successfully discovered superconductivity at 35 K and 15 K in Eu0.7Na0.3Fe2As2 and SmCoFeAsO compounds, respectively. These clearly suggest that the one-step PIT technique is unique and versatile and hence can be tailored easily for other rare earth derivatives of novel iron-based superconductors., Review for the special issue of Physica C on iron-based pnictide superconductors

In order to investigate the effect of fabrication process on the superconducting properties of MgB 2 tapes, several types of MgB 2 tapes were fabricated using different techniques, such as different deformation ratio, different precursor process, etc. It is found that the higher rotary–swage ratio, the better J c – B properties. For example, at 4.2 K and 10 T, J c value for the samples swaged to 4 mm was five times higher than that for the samples swaged to 6 mm. On the other hand, the J c values were significantly improved when the staring powder was homogenized by ball milling. For instance, at 10 T (4.2 K), the J c value was improved from 2.2 × 10 3 A/cm 2 to 3.5 × 10 3 A/cm 2 for undoped samples sintered at 800 °C, while it was improved from 1.3 × 10 4 A/cm 2 to 1.8 × 10 4 A/cm 2 for 5 at% carbon doped ones. Detailed mechanism of the J c – B property difference induced by different deformation ratio or different staring material process is discussed based on the systematically examined results.