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Journal of Alloys and Compounds
Elsevier Science S.A.
Journal of Alloys and Compounds

Elsevier Science S.A.

0925-8388

Journal of Alloys and Compounds/Journal Journal of Alloys and CompoundsSCIISTPEI
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    (162761)Terahertz-infrared dielectric properties of lead-aluminum double-cation substituted single-crystalline barium hexaferrite

    Asmaa AhmedAnatoly S. ProkhorovVladimir Anzin
    14页
    查看更多>>摘要：Hexaferrite materials are highly demanded to develop and manufacture electronic devices operating at radio- and microwave frequencies. In the light of the prospects for their use in the forthcoming terahertz electronics, here, we present our results on the terahertz and infrared dielectric response of a typical representative of hexaferrites family, lead-substituted M-type barium hexaferrite doped with aluminum, Ba_(0.2)Pb_(0.8)Al_xFe_(12-x)O_(19), x(Al) = 0.0, 3.0, and 3.3. We studied uniquely large and high-quality single crystals of the compounds prepared by spontaneous crystallization growth technique. Our aim was to explore the effect of aluminum substitution on the dielectric response of the compounds. Systematic and detailed investigations of the dependences of terahertz-infrared (frequencies 8-8000 cm"1) spectra of complex dielectric permittivity on the temperature, 4-300 K, and on the chemical composition, x(Al) = 0.0,1.2,3.0, and 3.3, were performed for two principal polarizations of the electric field E-vector of the probing radiation relative to the crystallographic c-axis, namely E||c and E⊥c. Furthermore, infrared phonon resonances are recorded and discussed. In contrast to undoped BaFe_(12)O_(19), no softening of the lowest frequency A_(2u) phonon is observed, indicating suppression of a displacive phase transition in substituted compounds. A number of resonance absorption bands are discovered at terahertz frequencies and assigned to transitions between energy levels of the fine-structured ground state of Fe~(2+) (~5E) ions. The temperature and aluminum-doping dependences of the resonances are analyzed with an account taken of disorder introduced by aluminum. Basing on dielectric data and detailed X-ray experiments, we find that for all concentrations of Al~(3+) ions, x (Al) = 0.0,1.2,3.0, and 3.3, they mainly occupy the 2a and 12k octahedral site positions and that the degree of substitution of iron in tetrahedral positions is not substantial. Along with fundamental findings, the obtained data on broad-band dielectric properties of Ba_(0.2)Pb_(0.8)Al_xFe_(12-x)O_(19) crystals provides the information that can be used for development and manufacture of electronic devices with operating frequencies lying in the terahertz spectral band.
      原文链接:
    • NSTL
    • Elsevier

    (162895)Visible-light-active mesoporous ceria (CeO_2) nanospheres for improved photocatalytic performance

    Jie PanShirui WangAilian Chen
    12页
    查看更多>>摘要：As one of the most significant rare-earth oxides, cerium dioxide (ceria, CeO_2) has an enormous potential in a variety of materials science applications due to many excellent characteristics. In this work, cubic-phase mesoporous CeO_2 (mCeO_2) nanospheres with nanocrystalline frameworks, high Ce~(3+) and oxygen vacancy contents, large porosity and specific surface area, were fabricated via a facile solvothermal method using inorganic precursors and without surfactant as a template. The resulting products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, photoluminescence (PL) spectroscopy, and N_2 adsorption-desorption analyses. Raman and XPS results confirmed the presence of Ce~(4+), Ce~(3+) and Zr~(4+) ions and oxygen vacancies. By comparison with the undoped ones, Zr-doping in mCeO_2 nanospheres contributed to increased concentrations of Ce~(3+) (45.25% vs 32.64%) and oxygen vacancy (37.63% vs 27.53%), as well as decreased band gap energies (2.9 vs 3.1 eV). The photocatalytic activities of the pure and Zr-doped mCeO_2 nanospheres were evaluated with the degradation of methylene blue (MB) under visible-light irradiation. The Zr-doped mCeO_2 products exhibited a superior photodegradation rate of ca. 94% after 120 min visible-light illumination. A kinetic study suggested that the reaction followed pseudo-first order rate equation. The optimizations on Zr-doped mCeO_2 nanospheres against structural, optical, and physicochemical properties might be responsible for the enhanced visible-light-driven photocatalytic performance. The plausible photodegradation mechanism over MB dyes of mCeO_2 nanospheres were also proposed. This work is expected to provide an insight view into the design and synthesis of low-cost and high-efficiency CeO_2-based photocatalysts with improved visible photocatalytic activity.
      原文链接:
    • NSTL
    • Elsevier

    (162789)The serration behavior and mechanical properties of Al_(0.1)CoCrFeNi high-entropy alloy under coupled electron-heat field

    Yafei WangLiu XiaHongjie Zhang
    10页
    查看更多>>摘要：Ever-harsher service environments in the future will call for systematic studies on service behaviors of high-entropy alloys (HEAs) under multi-field coupling. Instead of focusing solely on service behaviors under conventional conditions, the promoted serration behavior of Al_(0.1)CoCrFeNi HEA, commonly known as Portevin-Le Chatelier (PLC) effect, under coupled electron-heat field was quantitatively analyzed in terms of several characteristic parameters in this work. The obvious PLC phenomenon with severe serration can boost the decrease of tensile strength and elongation in the service environment of coupled electron-heat. Our results indicate that this macroscopic serrated behavior can be rationalized by defect-level micro-structural interaction, namely the enhanced repetitive pinning and de-pinning effect of solute atoms on mobile dislocations, according to the mechanism of dynamic strain aging. This was proved by the increased kinking and bowing morphologies of dislocations, as well as abundant stacking faults under coupled electron-heat field.
      原文链接:
    • NSTL
    • Elsevier

    (162893)Scalable synthesis of Li_2GeO_3/expanded graphite as a high-performance anode for Li-ion batteries

    Fangkun LiXinyi WangWeixin He
    8页
    查看更多>>摘要：A simple, economical, and easily scalable high-energy ball-milling method for the synthesis of Li_2GeO_3/ expanded graphite (LGO/EG) as a high-performance anode for lithium-ion batteries is reported. The LGO/EG exhibits a unique architecture with expanded graphite (EG) uniformly coating Li_2GeO_3 (LGO) particles, which effectively inhibited the agglomeration of LGO particles. The LGO/7 wt%EG anode delivers a discharge capacity of 800.6 mA h g~(-1) at 5.0 A g~(-1) with an outstanding capacity retention of 75.9% after 300 cycles at 1.0 A g~(-1) which is 8.3% higher than that of the uncoated LGO anode. This is attributed to the introduction of EG which improves the electronic conductivity of LGO, and the uniformly coated EG can effectively inhibit the volume change of LGO particles during the charging-discharging process. As a result, LGO/EG has outstanding high-rate performance and long-term cycle stability.
      原文链接:
    • NSTL
    • Elsevier

    (162967)Structural, conductivity and dielectric properties of europium trioxide doped lead boro-tellurite glasses

    C DevarajaG. V. Jagadeesha GowdaB. Eraiah
    7页
    查看更多>>摘要：A very rare set of glasses having chemical compositions of B_2O_3-TeO_2-Na_2O-PbO, doped with europium trioxide were obtained by the conventional melt quenching procedure. An X-ray diffractometer was run to confirm the non-crystalline nature of the structural studies. The AC conductivity and dielectric properties of glasses were studied in the temperature range 343-483 K with a 40 Hz to 6 MHz frequency range. The Almond-West model of power-law suggests, the well-fitting of found AC conductivity values and conductivity is due to translational motions of carriers. AC conductivity decreases with increasing concentration of Eu_2O_3. The non-Debye type of relaxations was predicted by AC conductivity plots. The dielectric constant and dielectric loss of complex permittivity was measured and obtained values suggested that the phenomenon of dielectric relaxation is mainly subjected to the frequency-dependent polarization mechanism. The obtained power-law exponent values indicate the AC conductivity mechanism and follow the CBH model.
      原文链接:
    • NSTL
    • Elsevier

    (162790)Enhanced mechanical properties of tungsten alloy by synergistic strengthening of flaky Ni_3Al and Al_2O_3 nano-particles

    Ruipeng MaoZhishuai FanDaoping Xiang
    8页
    查看更多>>摘要：Tungsten alloys are extensively applied in kinetic energy penetrators but these alloys exhibit poor self-sharping properties-connected with high thermal conductivity, large grain size, and low hardness-which limit their application. Ni_3Al is one of the most promising candidates as a binder phase for tungsten alloys used as kinetic energy penetrators because of its high hardness, low thermal conductivity, and low solubility of tungsten, which can refine the tungsten grain. In this study, a simple and scalable methodology, termed 'synergistic strengthening with flaky binder phase and ceramic nano-particles', has been developed to fabricate high-performing W-Ni_3Al alloys. The flaky Ni_3Al binder phase acted as a ductile layer to improve the mechanical properties of the alloy by crack deflection and tip blunting. The in-situ formed nano Al_2O_3 particles on the interface between the W and Ni_3Al phase inhibited the dislocation motion and restrained the dissolution and re-precipitation of the tungsten grain, leading to grain refining of the tungsten and alloy strengthening. As a result, a unique structural W-Ni_3Al alloy was prepared with an approximately 2 um tungsten grain size, and its bending strength was improved by 24.3% in comparison to conventional W-Ni_3Al alloys, and the hardness of greater than 70 HRA remained constant. Moreover, it was exciting that the higher bending strength could be obtained by regulating the W-Ni_3Al alloy microstructure. In short, we demonstrated that this structural design strategy was an effective method to fabricate refractory alloys, such as tungsten alloys, with good overall mechanical performance.
      原文链接:
    • NSTL
    • Elsevier

    (162855)Boost the cyclability and Na~+ diffusion kinetics of Sb_2S_3 anode by CNTs cross-linking N-doped carbon matrix

    Qimeng PengJu FuGang Chen
    10页
    查看更多>>摘要：Antimony sulfides exhibit a tremendous potential owing to the high theoretical specific capacity from multiple redox storage mechanisms for sodium-ion batteries (SIBs). However, these bottlenecks, including low electrical conductivity, poor ionic diffusion kinetics, and severe volume expansion, still restrict the development of antimony sulfide as SIBs anodes. Meanwhile, in view of long-term interests and practical application, the cost-efficient preparation methods become an imminent challenge to the advancement of high-performance SIBs anodes. Here, a novel three-step strategy, composed of co-precipitation, heat reduction processes, and sulfation conversion, was utilized to construct a "reinforced concrete" architecture, in which Sb_2S_3 nanoparticles embedded in N-doped carbon matrix (NC) modified by carbon nanotubes (CNTs), denoted as Sb_2S_3/CNTs/NC. As the "cement block", the N-doped 3D carbon matrix can promote the electron migration and reduce the aggregation of active materials upon cycling. In terms of "rebars" (i.e., 1D CNTs) for ensuring the anode integrality during incessant sodiation/de-sodiation processes, they function as binders and stabilizers, which intimately cross-link with Sb_2S_3 nanoparticles and carbon matrix, accommodate the volume change, and maintain the fast transfer of electron transfer inside the whole composite. Benefiting from these merits of the hierarchical structure (i.e., 3D NC and 1D CNTs), as an anode for SIBs, Sb_2S_3/CNTs/NC demonstrates an improved sodium storage capability with an initial specific capacity of 770.80 mAh g~(-1) at 0.1 A g~(-1) and a superior initial coulombic efficiency (ICE) of 79.90%. Moreover, even at a high current density of 1.0 A g~(-1) a reversible capacity of 313.54 mAh g~(-1) can be delivered after 350 long cycles, indicating the stable cyclicity. The Sb_2S_3/CNTs/NC with designed construction and enhanced electrochemical performance could provide a new perspective on low-cost, time-saving, and exercisable synthesis approach for high-performance sulfide-based anodes.
      原文链接:
    • NSTL
    • Elsevier

    (162831)Graphitic carbon nanochambers interweaved porous yolk-shell skeleton for long-lifespan lithium-ion batteries

    Huinan GuoKai ChenWeiqin Li
    9页
    查看更多>>摘要：The synergistic integration of compositional and structural advantages for anode material provides a feasible avenue toward high-performance lithium-ion batteries (LIBs). Here, a tailored Co/N-doped yolk-shell porous carbon skeleton is fabricated by graphitic carbon nanochambers and amorphous carbon to effectively enhance the electrochemical performances of LIBs. Benefitting from the exquisite composition and structure, the designed anode material delivers a desirable discharge capacity of 440.3 mA h g~(-1) after 2500 cycles at a current density of 4 A g~(-1) with the Coulombic efficiency of 99.5%. The assembled lithium full battery with LiFePO_4 cathode achieves 288 Wh kg~(-1) after 200 cycles. The present strategy expands the direction of advanced material preparations for long-lifespan battery applications.
      原文链接:
    • NSTL
    • Elsevier

    (162889)9Improvement of thermoelectric properties of flexible Bi_2Te_3 thin films in bent states during sputtering deposition and post-thermal annealing

    Oga NorimasaTomoyuki ChibaMasataka Hase
    6页
    查看更多>>摘要：High-quality thermoelectric thin films formed on flexible substrates are important for the development of flexible thermoelectric generators as power supplies for wireless sensors and wearable devices. However, the thermoelectric properties of the films formed on flexible substrates are inferior to those of films formed on rigid substrates because flexible substates shrink during the processes of film deposition and post-thermal annealing. To overcome this problem, we propose a modification during these processes. Bismuth telluride thin films were deposited on polyimide substrates using radio-frequency magnetron sputtering. The substrates were bent to a convex or concave shape, followed by thermal annealing under the same bending conditions. The crystallite size and crystal orientation improved when the films were set to a concave shape during the film deposition and post-thermal annealing processes. This phenomenon occurred presumably because the substrate shrinkage was counteracted by the stretching of the substrate, and the strains did not accumulate much in the films, resulting in improved crystal growth. Consequently, the electrical conductivity was increased, and the resulting power factor of 16.1 μW/(cm K_2) is 1.4 times higher than that of the Bi_2Te_3 film formed on a flat substrate.
      原文链接:
    • NSTL
    • Elsevier

    (162946)The effect of graphene on structure and optical properties of CdSe nanoparticles for optoelectronic application

    Ahmed I. Abdel-SalamM.M. AwadT.S. Soliman
    9页
    查看更多>>摘要：CdSe-reduced Graphene Oxide (CdSe-rGO) nanocomposite was synthesized using a facile hot injection method with excellent control over the size and morphology. The superb distribution of the CdSe quantum dots (CdSe QPs) and the tightly anchoring to the graphene sheets enhance their optical properties. Therefore, the effect of reduced Graphene oxide (rGO) on the structure and optical properties of CdSe nanoparticles is studied by X-ray diffraction (XRD), UV-visible spectroscopy, and transmission electron microscopy (TEM). As well as Effective mass approximation model (EMA) and Polynomial Fitting Functions (PFF) were used to calculate the sizes of nanoparticles, yielding particle sizes ranging from 4.64 to 5.46 nm and 2.74-3.72 nm, respectively. These values were comparable to those obtained by TEM and XRD. Furthermore, the data revealed that the direct energy gap of the CdSe QDs was reduced from 2.33 eV for the smallest size to 2.17 eV for the largest size. The optical parameters of CdSe-rGO nanocomposite such as the refractive index and extinction coefficient were increased with the particle size growth. As well, optical dielectric constant and optical conductivity were improved due to the increase of the particle size of CdSe Q_Ds in the CdSe-rGO nanocomposite. So, the capability of CdSe-rGO nanocomposite to tune the optical parameters makes it a suitable candidate for a wide range of applications, specifically optoelectronics.
      原文链接:
    • NSTL
    • Elsevier