Search

In order to gain insight into how the addition of Cu element affects the crystallization mechanism of amorphous nanocrystalline alloys and soft magnetic properties, the crystallization behavior of (Fe 0.83 B 0.11 Si 0.02 P 0.03 C 0.01) 100-x Cu x (x = 0 and 0.5) amorphous ribbons was investigated based on kinetic and thermodynamic behavior under non-isothermal and isothermal annealing conditions. The results show that under non-isothermal annealing conditions, the Cu0.5 amorphous ribbon not only favors the formation of the amorphous structure, but also enlarges the temperature window for annealing and improves the thermal stability of the α-Fe(Si) phase. At the same time, the Cu0.5 amorphous ribbon shows slow kinetic and is insensitive to heating rate change during annealing treatment. Under isothermal conditions, the addition of Cu decreases the nucleation activation energy (E n) and increases the growth activation energy (E g). This further indicates that the nucleation of α-Fe(Si) grains is easier than the growth process, which is conducive to the formation of a homogeneous nanostructure and improves the soft magnetic properties of the alloy. Compared to Cu0 amorphous ribbon, it is also shown that the Cu0.5 amorphous ribbon changes the crystallization mechanism from diffusion-controlled one-dimensional to two-dimensional growth when the crystallization volume fraction x is 10–30 vol%. While three-dimensional growth become dominated when x is reaches 60 vol% for both ribbons. Therefore, the kinetics of crystallization as well as microstructure supports that the Cu0.5 ribbon is able to exhibit uniformly fine nanocrystalline structures. Further, the Cu0.5 nanocrystalline ribbon shows a higher B s of 1.85 T and a lower H c of 2.55 A/m, respectively, and the favorable (100) orientation of α-Fe(Si) grains formed after annealing is another factor to increase B s. • The Cu-containing alloy show kinetic insensitivity and is suitable for a high heating rate. • The addition of Cu changes the crystallization mechanism when x is between 10% and 30%. • When the applied magnetic field is ND, precipitation of (100) orientation α-Fe grains favors enhancing B s. • The Cu0.5 alloy show B s of 1.85 T, H c of 2.55 A/m. [ABSTRACT FROM AUTHOR]

Crystal and electronic structures, and magnetic properties of polycrystalline tantalum substituted manganites CaMn 1- x Ta x O 3 (x = 0.00, 0.03, 0.06, 0.09 and 0.12) were studied by x-ray diffraction, x-ray absorption near edge spectroscopy (XANES) at Mn K -edge, and by magnetization measurements. Large changes of cell volume and magnetic transition temperature, in addition to shift of Mn K -edge spectra and change of shape of XANES spectra, indicate the existence of Mn3+ as well as Mn2+ species induced by the substitution of Mn4+ by Ta5+. Cell parameters and cell volume increase with increasing x because the Mn3+, Mn2+ and Ta5+ ions are larger that substituted Mn4+ ion. According to XANES results, at least the x = 0.00 sample is oxygen deficient. The negative magnetization was observed in the CaMnO 3-δ sample, and a possible explanation of the phenomenon is given considering two canted (almost antiferro)magnetic sublattices and a shielding current, associated with the itinerant e g electrons, induced by the oxygen vacancies. • Negative magnetization (NM) and divalent manganese are observed in CaMn 1−x Ta x O 3-δ. • NM caused by canted antiferromagnetic (AFM) states and e g electron shielding current. • AFM state and shielding current originate from Ta- and/or oxygen vacancy- content. • Large decrease in T C and change in shape of XANES spectra due to Mn2+ are observed. [ABSTRACT FROM AUTHOR]

InGaN/GaN micro-crystals (μ-crystals) are self-contained and individually-addressable light emitting crystals that have unique potential in the development of ultra-small and ultra-high resolution pixels for next-generation displays. In this study, we explore the electrically-driven light emission behavior of vertically standing InGaN/GaN micro-crystals (μ-crystals) with well-defined crystal facets and tunable size. InGaN/GaN μ-crystals have hollow pedestals weakly bound to the substrate surface, thus enabling individual manipulation and/or collective transfer to other target surfaces. Cyclic bending tests and finite element analysis (FEA) of the strain distribution further highlight the excellent mechanical deformability of a device layout consisting of μ-crystal pixels embedded in a polymeric matrix. Light-emitting diodes (LEDs) with individual InGaN/GaN μ-crystals exhibit strong electroluminescence (EL) with unique features such as variations in emission spectra with respect to crystal diameter and driving voltage bias. Comparative analyses of photoluminescence, cathodoluminescence, and electric potential simulation indicate a strong correlation between the EL wavelengths and dominant emitting regions of InGaN/GaN polyhedral crystal planes. This is further supported by scanning transmission electron microscopy of quantum well structures, which strongly depend on both size and the crystal facets. • Self-contained InGaN/GaN MQW micro-crystal arrays are employed as light emitting pixels on a deformable substrate. • The μ-crystal LEDs exhibit a variation of emission spectra with respect to the crystal diameter and driving voltage bias. • Optoelectrical and structural analysis of InGaN/GaN μ-crystal LEDs reveals the multicolor emission mechanism. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy at Mn K - and L -edges, and at O K -edge, combined with the x-ray diffraction and magnetization measurements are performed to study the electron structure of La 0.7 Ca 0.3 Mn 1-x Sc x O 3 (x = 0.0; 0.03, and 0.05) perovskites. Substitution of manganese by scandium decreases Curie temperature, T c, and increases lattice parameters because of the different electron configuration and radii of trivalent manganese and scandium ions. The T c decrease is explained by the change of level of hybridization of O 2 p and Mn 3 d states. This is manifested by the parallel shift of O K -edge, change of intensity of 2 p 3/2 and 2 p 1/2 spectrum lines and T C with x increase. Fourier transform of the EXAFS spectra shows a change of local crystal structure caused by the larger Sc3+ than the Mn3+ ions. • Electron structure of La 0.7 Ca 0.3 Mn 1-x Sc x O 3 manganites is studied. • Change of electron hybridization of Mn 3 d and O 2 p states is observed. • Change of Mn L -edge spectra intensity and T C is parallel with x. • Shift of O K -edge and T C is parallel with x. • Fourier transform of EXAFS spectra shows a change of local crystal structure. [ABSTRACT FROM AUTHOR]

Compared to lead lanthanum zirconate titanate (PLZT), potassium-sodium niobate shows good advances because of its excellent photoelectric response frequency and holographic storage. However, its low transmittance limits its application in photoelectrical controllers. To address this issue, lanthanum was introduced as a dopant, and the properties of the resulting ceramics were evaluated using both experimental and theoretical approaches. The (1-x)(K 0.5 Na 0.5 )NbO 3 -xLa 2 O 3 (KNN-xL; x = 0.005, 0.010, 0.015, 0.020) transmittance ceramics were prepared by traditional low-pressure sintering process. Among the ceramics examined, KNN-0.015L achieved the widest band gap (Eg) of 3.108 eV and the highest transparency of 74%; both values are higher than those of PLZT (band gap = 3.10 eV, transparency = 70%) prepared by hot-press sintering. The transition rule was evaluated by density functional theory (DFT) to validate the experimental results obtained. Additionally, the related mechanism of transparency variation induced by electronic structure and grain size modulation was discussed thoroughly. [ABSTRACT FROM AUTHOR]

• The Cu 6 Sn 5 and Cu 3 Sn alloy interface layers are prepared through simple temperature control. • The key factors affecting the interface layer of Li metal in different Cu-Sn alloys have been summarized. • Cu 6 Sn 5 @Cu has a uniform surface structure and excellent electrolyte wettability. • The deposition mechanisms of Li metal on the Cu 6 Sn 5 and Cu 3 Sn alloy interface layer are proposed. [Display omitted] Lithium (Li) metal is one of the best anode candidates for high energy density battery because of the lowest electrode potential and high theoretical capacity. However, the unstable electrode/electrolyte interface will cause uneven Li deposition and induce the formation of Li dendrites. The Cu-Sn alloy interface layer has been proven to be an effective strategy to inhibit the growth of Li dendrites, but how the alloy type of Cu-Sn alloy affects the deposition/exfoliation behavior of Li metal is still unclear. Here, we used a simple and fast chemical plating method to prepared lithophilic Cu 3 Sn and Cu 6 Sn 5 pure phase interface layers on the surface of the Cu foil by controlling the temperature. Then, the effects of two different alloy types on the deposition/stripping behavior of Li metal anodes were studied. Compared with Cu 3 Sn@Cu, Cu 6 Sn 5 @Cu has a more uniform surface structure and higher surface free energy. Uniform electron distribution and fast reaction kinetics are conducive to the uniform deposition of Li metal. Meanwhile, Cu 6 Sn 5 @Cu also has higher electrolyte wettability. This helps to reduce the interphase impedance and polarization, thereby avoiding the growth of Li dendrites. These advantages make deposition mechanism of Li metal on the Cu 6 Sn 5 @Cu surface a unidirectional "Parallel-Deposition", while on the Cu 3 Sn@Cu surface it is a multi-directional "Preferred-Deposition". After being modified by Cu 6 Sn 5 , a more reasonable deposition mechanism reduces the overpotential of Li deposition on Cu foil by half. Even under the high deposition capacity of 10 mAh cm−2, Cu 6 Sn 5 @Cu can still cycle stably for more than 900 h. In addition, Li-Cu 6 Sn 5 @Cu has also been proved to have more stable rate performance and higher capacity retention rate than Li-Cu 3 Sn@Cu when it is used in full cell with LiFePO 4. [ABSTRACT FROM AUTHOR]

Abstract: TiO2 hollow nanospheres have been synthesized in agarose gels by a bio-inspired method for the first time in this study. Their outer and inner diameter are about 99.7 and 56.8nm, respectively, and their shell has bimodal mesopores about 3.8 and 5.5nm in size. These mesopores may be formed through removing the agarose gel fibers embedded in the shell of TiO2 hollow nanospheres during their nucleation and growth. It is inferred that a spherical composite formed by protamine and agarose molecules takes a key role in the formation of TiO2 hollow nanospheres. After calcined at high temperature (400–600°C) for 2h, these TiO2 materials exhibit higher photocatalytic activity for the methyl orange decoloration than Degussa P25 under artificial solar light irradiation. This study may provide a novel and facile approach for the synthesis of metal oxide hollow nanospheres under mild conditions. [Copyright &y& Elsevier]

• Aging treatments were performed for tailoring the precipitation behavior in the SLM-built Cu-Ni-Sn-P alloy. • Yield strength was significantly improved in the 2 h sample more than three times compared to that of as-homogenized sample. • Aged samples shows a higher thermal conductivities than as-homogenized sample. This study investigated ways to improve both the mechanical and thermal properties of a Cu-Ni-Sn-P alloy manufactured with selective laser melting (SLM) using aging treatment. Homogenization heat treatment was conducted to the alloy at 820 °C for 12 h, and aging heat treatment was applied at 400 °C for 0.25, 0.5, 1, 2 and 4 h. Initial microstructure analysis identified (Cu, Ni) 3 P phase precipitates of a few μm in size, and the size and fraction of precipitates increased as aging heat treatment time increased. Room temperature compressive tests on the homogenized sample identified a yield strength of 135.7 MPa. Meanwhile, the yield strength of the sample that underwent 2-hour aging treatment measured 454.5 MPa, indicating a three times greater improvement of the mechanical properties than the homogenized sample. This was confirmed to have been contributed by precipitation hardening from the increased precipitate size and fraction as a result of aging treatment. In addition, thermal conductivity also increased as aging treatment was performed. In particular, an aging time greater than 2 h achieved an approximately 30% increase in thermal conductivity compared to the homogenized sample. Through aging treatment, both the mechanical property and thermal conductivity of an SLM-built Cu-Ni-Sn-P alloy were improved. Based on these findings, this study also discussed the underlying mechanisms according to aging time with respect to microstructural changes. [ABSTRACT FROM AUTHOR]

Abstract: Using CaCO3 as blowing agent and via melt foaming method, Mg foams with closed-cells have been fabricated successfully. It has been proved that the blowing gas to foam melted Mg is not CO2 but CO, which is released from the liquid–solid reaction between Mg and CaCO3. The releasing temperature of CO is more than 100°C lower than the decomposition temperature of CaCO3, which leads to melted Mg being foamed much more easily and the foaming process can be accomplished in a temperature range of 665–750°C. [Copyright &y& Elsevier]

In this study, the effects of transverse magnetic field annealing and mixing fine powder on the soft magnetic properties of FeSiBC soft magnetic powder cores (SMPCs) are investigated. The results show that with the increase of transverse magnetic field intensity, the core loss of FeSiBC SMPCs decreases and then increases with a continuous increase in permeability compared to the zero magnetic field treatment. Wherein, the effective permeability of the powder cores is increased from 58.07 to 59.63 after transverse magnetic field annealing at a magnetic field intensity of 900 Gs and annealing temperature of 430 ℃. It shows that mixing the FeSiBC amorphous crushed powder with fine powder and transverse magnetic field annealing are effective ways to further promote amorphous SMPCs to meet the requirements of the development of electronic devices, and the prepared high-performance SMPCs also have a certain prospect of industrial application. • The effect of transverse magnetic field applied during annealing on the magnetic properties of FeSiBC cores was investigated. • The mechanism of transverse magnetic field annealing to enhance the properties of FeSiBC cores was analysed. • Further enhancement of DC bias property of FeSiBC magnetic powder cores by mixing carbonyl iron powder. [ABSTRACT FROM AUTHOR]

Abstract: This study examined the hydrogen storage and electrochemical characteristics of bcc type Ti0.32Cr0.43− x V0.25Fe x (x =0–0.08) alloys and their ball-milled composites with AB5 type LmNi41Al0.25Mn0.3Co0.65 alloy. With increasing Fe content in the bcc alloy, the hydrogen storage capacity decreased and the plateau pressure increased due to the decreased lattice volume. In addition, the plateau pressure of the bcc alloys decreased with decrease in its temperature. The discharge capacity of the composite alloys of bcc and AB5 alloy decreased with increasing Fe content in the bcc alloy at 25°C, attributed to the increased plateau pressure. On the other hand, at low temperatures, the discharge capacity of the Fe-doped composite alloys was higher than that of the un-doped alloy due to the catalytic effect of Fe. In addition, with increasing discharge rate, the Fe-doped composite alloys with improved surface catalytic activity showed better discharge capacity. [Copyright &y& Elsevier]

Abstract Nanostructured Fe 3 O 4 , as a typical transition metal oxide material, has been widely used as high capacity anode in lithium ion batteries (LIBs). In order to further exerting its Li storage capacity, herein, we reported a rationally designed dual carbon shells coated Fe 3 O 4 nanoparticle (NP) superlattices with mesoporous carbon (MC) and N-doped carbon (NC) as the dual shells. The inner mesoporous carbon shell could effectively buffer the volume change and promote the conductivity of Fe 3 O 4 NP superlattices, and the outside N-doped carbon shell can ease the structure pulverization. N-doped carbon@mesoporous carbon@Fe 3 O 4 NP superlattices (NC@MC@Fe 3 O 4 NP superlattice) showed superior electrochemical performance, including high specific capacity (838 mAh/g at 0.5 A/g after 150 cycles), unique rate capacity (322 mAh/g at 5 A/g) and ultrahigh cycling capacity (576 mAh/g at 2 A/g after 500 cycles). Highlights • Dual carbon layers coating Fe 3 O 4 nanoparticle superlattices. • N-doped carbon layer and mesoporous carbon layer was prepared by one facile step reaction. • NC@MC@Fe 3 O 4 nanoparticle superlattices show high specific capacity and rate performance. [ABSTRACT FROM AUTHOR]

Silicon is a potential next generation anode material for lithium-ion battery, however, its commercial application was hindered by its poor electronic conductivity and huge volume change upon lithiation. Herein, Si@N-doped carbon nanoparticles with commercial Si nanoparticle as the core and N-doped carbon as the shell were prepared by a facial, low-cost and scalable one-step method using ionic liquid (3-cyanopyridine/H 2 SO 4 ) as both of the N and C sources. While using as anode material for lithium-ion batteries, Si@N-doped carbon exhibited a high reversible capacity of 725 mAh/g after 100 discharge/charge cycles at a current density of 420 mA/g, about twice higher than that of Si@C, a control sample prepared by a similar process using sucrose as the carbon precursor, which showed a capacity of 360 mAh/g after 100 cycles at 420 mA/g. The improved electrochemical performance could be ascribed to the stable core-shell structure of the nanocomposite and more importantly the doping of N element into the carbon shell. Furthermore, this work also provides a versatile strategy for preparation of core-shell N-doped carbon coated nanoparticles. [ABSTRACT FROM AUTHOR]

A series of superconducting tapes were prepared by growing MgB 2 film on Hastelloy tapes buffered with SiC buffer layers. When the SiC buffer layer increases in thickness, the superconducting transition temperature ( T c ) of MgB 2 tapes show slight increment with no depression detected. This T c behavior may have been originated from the changes occurred in the local structure of MgB 2. From EXAFS analysis, the ordering of the Mg–Mg bonds was systematically increased when the thicknesses of SiC buffer layers were decreased. We also found that unlike the relatively random bond lengths of Mg–B bond, the Mg–Mg bond lengths are expanding when SiC adds its thickness, inferring the clear effect of SiC to the Mg–Mg bond lengths. On the basis of the results shown in this letter we argue that SiC buffer layers have significant effects on the local structure of MgB 2 which contributes to the fundamentals of superconducting properties of MgB 2 tapes. [ABSTRACT FROM AUTHOR]

Abstract: ZnO interconnected network nanostructures are grown on cracked GaN substrate using aqueous solution method in this paper. ZnO nanostructures nucleate in the sidewall of crack and selectively grow along the crack direction on the GaN substrate. Due to the diversity of the crack, the nanostructures show interconnected network structures. Time-dependent of ZnO nanostructure morphology evolution shows the network nanostructures are formed by self-organized growth by interconnection of nanorods. The average diameter of the nanorods is around 500–600nm. Micro-Raman spectroscopy shows the nanostructures are under tensile stress. Meanwhile, the nanostructures also show good optical quality. The interconnecting structure characteristics, high degree of networking make them potential applications in ultra-sensitive gas sensing, exciton based photonic devices. [ABSTRACT FROM AUTHOR]

Electronic structure of niobium doped CaMn 1- x Nb x O 3 (x = 0.02, 0.04, 0.06 and 0.08) powder and fresh chip manganites was studied by x-ray absorption near edge spectroscopy (XANES) at Mn K -edge, and by x-ray photoelectron spectroscopy (XPS) of Mn 3 s -, Mn 2 p -, O 1 s -, Ca 2 p - and Nb 3 d -core levels. These XPS spectra for all the studied perovskites are very similar. The O 1 s and Ca 2 p spectra for powders differ from those for fresh chips because of the quick oxidation and carbonization of powder surface. The Mn 3 s , Mn 2 p and Nb 3 d spectra for the powders and fresh chips are almost the same. According to Mn 3 s spectra the formal valence of surface manganese ions is 3.82 for all studied oxides indicating the presence of oxygen vacancies in the samples. Niobium is in pentavalent state as evidenced by XPS measurements, but the negative chemical shift of the Nb 3 d 5 / 2 core level with respect to Nb 2 O 5 oxide is observed. High similarity of the XPS spectra of the samples with different Nb doping is probably a result of the self-organization of terminal layers. • Niobium doping decreases manganese valence and introduces oxygen vacancies. • Pentavalent state of niobium is evidenced by position and shape of Nb 3 d lines. • Negative chemical shift of Nb 3 d 5 / 2 line with respect to Nb 2 O 5 oxide is observed. • Effect of oxidation and carbonization of surface is underlined. • Self-organization of terminal layers is revealed. [ABSTRACT FROM AUTHOR]