查看更多>>摘要：We present the results of thermodynamic and optical spectroscopy measurements of the Pr_3CrGe_3Be_2O_(14) compound - a member of the recently discovered Be-subgroup of the langasite family. Despite the presence of both rare-earth and transition-metal subsystems in Pr_3CrGe_3Be_2O_(14), no long-range magnetic order has been found down to 0.4 K in terms of both magnetization M and specific heat C_p. These data are compared with those on Pr_3AlGe_3Be_2O_(14). Both compounds evidence the Schottky anomaly at low temperatures, most pronounced in the case of Pr_3CrGe_3Be_2O_(14).
查看更多>>摘要：In recent years, molybdenum disulfide (MoS_2) with sandwich structure has been widely studied as cathode material of aqueous rechargeable zinc-ion batteries (ARZIBs), but inherent low capacity and short cycle life limit its further development. Here, we synthesized a novel hydrophilic spherical 1T-MoS_2 through hexadecyl trimethyl ammonium bromide (CTAB) template-assisted hydrothermal reaction as cathode materials for ARZIBs and systematically study its mechanism of electrochemical enhancement. The results suggest that stable spherical MoS_2 was prepared by in-situ reduction of molybdate ion under the electrostatic absorption of CTAB template and 0 element introduced by ethylene glycol (oil-phase solvent) not only increases the hydrophilicity of the material and facilitates the intercalation of ammonium ions and water molecules, but also promotes the formation of the 1 T phase by changing the electronic structure. Consequently, this modified electrode exhibits a reversible capacity of 110 mAh g~(-1) at the current density of 1.0 A g~(-1), and the capacity retention rate is up to 90% after 500 cycles, showing excellent cycling stability and rate performance.
查看更多>>摘要：The uncontrollable dendritic behavior and volume expansion in alkali metal anodes have led to short-circuit issues and low Coulombic efficiency which significantly hamper the commercialization of alkali metal anodes. To address these issues, we report the fabrication of a novel functional host in which the alkaliphilic Cu(OH)_2 nanowires were uniformly grown on Cu foam (denoted as Cu(OH)_2-NWs@CF) for Li/Na anodes. The 3D network structure of Cu(OH)_2-NWs@CF with high specific surface area can not only effectively reduce local current density to guide homogeneous deposition of Li~+, leading to more controllable nucleation sites and dendrite-free Li deposition, but also minimize the volumetric strain during repeated Li/Na stripping/ plating processes, mitigating the volume change of the batteries. Benefitting from these advantages, the as-prepared Li/Na@CF composite anodes exhibit outstanding long-term cycle stability and structure maintaining ability. In particular, the Li@CF-based symmetric cells deliver elevated cycling performance under a moderate polarization voltage for nearly 1200 h at a current density of 1 mA cm~(-2). Similarly, the Na@CF-based symmetric cells can also cycle stably for 800 h at a current density of 0.5 mA cm~(-2). Furthermore, the Li@CF||LFP full cells show significantly improved rate capability and high cycle stability (97% capacity retention after 100 cycles). Our work demonstrates the effectiveness of the 3D copper foam framework with improved alkaliphilic ability for the development of safe and commercially viable alkali metal anodes.
查看更多>>摘要：The ductility of the Al alloys produced by additive manufacturing (AM) has become a critical property, as the AM Al alloys are increasingly used in the automotive industry. However, the ductility of as-built AM Al alloys is relatively low, even with optimized AM conditions. The post-annealing treatment provides an efficient way to improve ductility. Previous investigation has shown that the annealed AM AlSi3.5Mg2.5 alloy possesses superior ductility. However, the plastic deformation micro-mechanisms of the annealed AM AlSi3.5Mg2.5 alloy remain unclear. In this study, in-situ neutron diffraction was employed to explore the annealed AM AlSi3.5Mg2.5 alloy. The evolutions of phase stresses, dislocation density, and crystallite size in the annealed AM AlSi3.5Mg2.5 alloy during tensile deformation were analyzed. The experimental investigation reveals that the dislocation density in the Al matrix of the annealed AM AlSi3.5Mg2.5 alloy increases slowly in the early plastic deformation stage, and it reaches a saturated level upon the following uniform deformation. The crystallite size decreases quickly in the early deformation stage, and then it decreases slowly. The Kocks-Mecking model and the Voce model can capture the strain hardening behavior well. The determined physical constitutive equations can be applied in continuum mechanical computer simulations.
查看更多>>摘要：A comparative study on the structure and photocatalytic activity of halo-aggregated and differently connected ZrO_2@TiO_2 and TiO_2@ZrO_2 nanocomposites was investigated here towards photodegradation of Alizarin yellow GG model azo dye. The nanocomposites were synthesized by two-step sol-gel method with predominant monoclinic phase for ZrO_2, anatase phase for TiO_2, and characterized through different structural and spectroscopy tools. The photocatalysts with high adsorption capability were however differing in their photodegradation efficiency attributed to varying preferential binding at their interfaces and Zr~(4+) substitution in the TiO_2 lattice. Between the two nanocomposites, superior photocatalytic property was shown by ZrO_2@TiO_2 exhibiting 90-93% degradation efficiency with reproducibility. The growth of titania over zirconia in ZrO_2@TiO_2 reduced the surface states and defects of the core nanocrystal (NC) through strong Zr-O-Ti binding, besides providing shallow traps in smaller TiO_2 NCs that enhanced the separation of photogenerated carriers. The process was also assisted through trapping of holes by surface OH groups on ZrO_2 reducing the carrier migration to TiO_2. The type I heterojunction had favorable positive and negative potentials for valence and conduction bands in ZrO_2 and TiO_2 compared to intermediate superoxide anion and hydroxyl radical generation potentials that catapulted the dye degradation. The interfacial contact in TiO_2@ZrO_2 nanocomposite on the other hand, has been very weak as understood from their absorption and photoluminescence spectra resulting in poorer degradation efficiency. Alizarin yellow GG being a prominent textile azo dye and there are not many reports on its photodegradation, the study also assumes significance in the context of sunlight driven photocatalysis and environmental remediation.
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.
查看更多>>摘要：This work focuses on the electrical properties of Ni/n-GaN Schottky barrier diodes (SBDs) fabricated on GaN bulk substrates with different crystal orientations. For the SBDs on a-plane, m-plane, and s5-plane GaN, the Schottky barrier heights (SBHs) exhibited magnitudes of 0.65 eV, 0.69 eV, and 0.75 eV, respectively. The relatively small SBH of a-plane devices results in a relatively larger reverse leakage current than that of m-plane and s5-plane. In addition, the carrier concentrations extracted by C-V characteristics are comparable for the GaN substrates with different crystal orientations. The temperature-dependent I-V characteristics indicate how the barrier inhomogeneity of the Ni/GaN Schottky contacts on the a-plane GaN is smaller than the others. Based on the XPS spectra results, the discrepancy in Schottky contact characteristics stems from the different polarization charges and/or surface oxides of the different crystal planes. The low GaOx density on a-plane GaN surface contributes to the minimum barrier inhomogeneity of the corresponding SBD devices.
查看更多>>摘要：Substantial attention for dielectric ceramic capacitors toward lead-free has been driven by the enhanced awareness of environmental protection. However, the unsatisfying breakdown strength (E_b) and comparatively low efficiency (η) becomes an obstacle for their widespread application. Here, environment-friendly lead-free relaxor ferroelectric (1-x) (0.67BiFeO_3-0.33Ba_(0.8)Sr_(0.2)TiO_3) -xSr_(0.7)La_(0.2)TiO_3 + 0.1 wt% MnO_2 (BFO-BST-SLT) ceramic is reported as an efficient route to possess excellent E_b and high r\ simultaneously. The doping of SLT can significantly suppress the grain growth, improve the relaxation behavior, and thus increasing the E_b and η of the ceramics. Consequently, the corresponding ceramics with x = 0.3 achieves good discharged energy density of -2.55 J/cm~3 and ultrahigh η of -92%. Notably, it presents outstanding charging/discharging performances with fast charging/discharging time (-0.0266 μs), power density (-28.11 MW/cm~3) along with current density (-468.5 A/cm~2). Together with great temperature stability, frequency stability and cycle stability, this contributes provides a crucial way to prepare lead-free dielectrics for next-generation pulsed power capacitor applications.
查看更多>>摘要：Hybrid materials composed of inorganic magnetic cobalt-manganese mixed nanoferrites and PMMA polymeric shell have been fabricated by applying an in-situ polymerization process using pre-prepared inorganic core particles (8-9 nm). The ability of the hybrid heating under action of alternating magnetic field and laser radiation (in a separate and synergy mode) was evaluated and compared with stock nano-particles. It was found that hybrid materials show a high response to both stimulants and the highest temperature was achieved by using both AMF and laser exposure under synergic mode (twice the value for the AMF alone). The specific absorption rate of composite material was around 30 W/g for the optimized field parameters and both laser wavelengths (808 and 1122 nm). The great response of the hybrid material for contactless action of AMF and NIR radiation makes the proposed material very interesting for future biomedical and EMI shielding applications.
查看更多>>摘要：Bismuth (Bi)-doped glasses have the potential to be applied in tunable photonic devices owing to their broadband near-infrared (NIR) luminescence. However, it is still challenging to develop Bi-doped glasses with luminescence performance at desirable emission wavelength since it is hard to stabilize the specific luminescent Bi centers. In this work, a structural model describing the negatively charged local environments is proposed to stabilize the activated Bi centers by adding Ta_2O_5 and/or Al_2O_3 in Bi-doped silicate glasses. The results show that the structural model leads to great enhancement of the NIR emission, the broadening of the emission bandwidth and the blueshift of the emission peak, compared to the samples without Ta_2O_5/Al_2O_3 doping. The change in NIR emission performances could originate from the generation of active Bi~+ centers. The latter arises from oxidation of Bi° induced by the negatively charged local environments around Bi. Moreover, the intensity of the Bi NIR emission is enhanced, and this is attributed both to the suppression of phase separation by adding Ta_2O_5 and to the dispersing effect of alumina.
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Elsevier