Jingxue Sun

Bulk metallic glasses: Smaller is softer

The authors report on the dramatic effect of sample size on the plastic deformation capability of a Ti-based bulk metallic glass. Compared with the larger one, the smaller size glassy alloy with the same chemical composition exhibits significantly enhanced plasticity, suggesting a “smaller is softer” trend of metallic glasses. The phenomenon is attributed to the fact that the smaller size alloy, which experienced a faster cooling rate during solidification, contains a larger amount of heats of relaxation and crystallization, favoring the preferential nucleation of shear bands and thus allowing enhanced plasticity upon compressive loading.

Excellent magnetocaloric properties of melt-extracted Gd-based amorphous microwires

We report upon the excellent magnetocaloric properties of Gd53Al24Co20Zr3 amorphous microwires. In addition to obtaining the large magnetic entropy change (−ΔSM ∼ 10.3 J/kg K at TC ∼ 95 K), an extremely large value of refrigerant capacity (RC ∼ 733.4 J/kg) has been achieved for a field change of 5 T in an array of forty microwires arranged in parallel. This value of RC is about 79% and 103% larger than those of Gd (∼410 J/kg) and Gd5Si2Ge1.9Fe0.1 (∼360 J/kg) regardless of their magnetic ordering temperatures. The design and fabrication of a magnetic bed made of these parallel-arranged microwires would thus be a very promising approach for active magnetic refrigeration for nitrogen liquefaction. Since these microwires can easily be assembled as laminate structures, they have potential applications as a cooling device for micro electro mechanical systems and nano electro mechanical systems.

Binary eutectic clusters and glass formation in ideal glass-forming liquids

In this letter, a physical concept of binary eutectic clusters in “ideal” glass-forming liquids is proposed based on the characteristics of most well-known bulk metallic glasses (BMGs). The authors approach also includes the treatment of binary eutectic clusters as basic units, which leads to the development of a simple but reliable method for designing BMGs more efficiently and effectively in these unique glass-forming liquids. As an example, bulk glass formers with superior glass-forming ability in the Zr–Ni–Cu–Al and Zr–Fe–Cu–Al systems were identified with the use of the strategy.

Plasticity of a TiCu-based bulk metallic glass: Effect of cooling rate

Compressive deformation was experimentally investigated for Ti 41.5 Cu 42.5 Zr 2.5 Hf 5 Ni 7.5 Si 1 bulk metallic glass (BMG) fabricated at different cooling rates. It was found that the ductility of the BMG alloy increased with increasing of the cooling rate in solidification. The alloy with a monolithic amorphous structure exhibited a large ductility, up to 12%. The effect of cooling rate on the ductility of the BMG alloy is interpreted in terms of the variation in amorphous nature and free volume of the as-cast materials.

A Novel Mesoporous Single-Crystal-Like Bi2WO6 with Enhanced Photocatalytic Activity for Pollutants Degradation and Oxygen Production

The porous single-crystal-like micro/nanomaterials exhibited splendid intrinsic performance in photocatalysts, dye-sensitized solar cells, gas sensors, lithium cells, and many other application fields. Here, a novel mesoporous single-crystal-like Bi2WO6 tetragonal architecture was first achieved in the mixed molten salt system. Its crystal construction mechanism originated from the oriented attachment of nanosheet units accompanied by Ostwald ripening process. Additionally, the synergistic effect of mixed alkali metal nitrates and electrostatic attraction caused by internal electric field in crystal played a pivotal role in oriented attachment process of nanosheet units. The obtained sample displayed superior photocatalytic activity of both organic dye degradation and O2 evolution from water under visible light. We gained an insight into this unique architectures impact on the physical properties, light absorption, photoelectricity, and luminescent decay, etc., that significantly influenced photocatalytic activity.

Formation of nanowaves in compressive fracture of a less-brittle bulk metallic glass

Formation of periodical fracture surface marks in the dynamic fracture can only be observed, mainly in ideally brittle amorphous materials and under mode I loading conditions. Here the authors report on the observation of elastic-wave patterns on nanoscale that form in the compressive fracture process of a Ni-based alloy which is a less-brittle amorphous metal with an appreciable compressive ductility. The formation of nanowaves is evidenced via the creation of microbranching instability as well as the interaction of a crack front with the material inhomogeneities, i.e., microcracks.

A facile solvothermal synthesis of hierarchical Sb2Se3 nanostructures with high electrochemical hydrogen storage ability

Sb2Se3 carpenterworm-like hierarchical structures composed of numerous sheet-like crystals with a diameter of ca.1 μm and a thickness of ca.40 nm have been fabricated by a simple glucose assisted solvothermal approach in a mixture of solvents. The factors influencing the formation of the hierarchical Sb2Se3 nanostructures are monitored by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) characterization. Based on the time dependent experiments, the aggregation-based process and anisotropic growth mechanism are reasonably proposed to understand the formation mechanism of Sb2Se3 hierarchical architectures. The electrochemical hydrogen storage behavior of the as-prepared products is studied in detail. It is found that the morphology plays a key role in the hydrogen storage capacity of such nanomaterials. The carpenterworm-like of Sb2Se3 presents a much higher discharging capacity (248 mA h g−1) than that of Sb2Se3 microspheres (196 mA h g−1) at room temperature.

Novel (Na, K)TaO3 single crystal nanocubes: Molten salt synthesis, invariable energy level doping and excellent photocatalytic performance

Without any surfactants or special equipments, a novel series of efficient photocatalysts (Na, K)TaO3 (NKT) is successfully synthesized via a simple and convenient molten-salt process. The synthesized NKT is determined to be highly crystallized single crystal nanocubes with a diameter of 100 nm. A detailed time-resolved TEM kinetic study of the formation of the structure is carried out to investigate the growth mechanism of nanocubes. Photocatalytic activity of NKT is found to be especially high without any co-catalysts. However, stability of NKT is unsatisfied due to the forming of peroxidation phases. Doping tetravalent Zr4+ and Hf4+ (NKZT and NKHT) efficiently improves both activity and stability of catalyst without changing energy level. Uniform and nearly-monodispersed nanocubes with a size of about 50 nm are observed on NKZT and NKHT. Without co-catalyst, photocatalytic activity achieves 4.65 and 2.31 mmol h−1 for H2 and O2 generation, respectively. The reason of especially high activity of this series is believed to be the prolongation of lifetime for photo-excited charges.

A simple approach to strontium sodium tantalite mesocrystals with ultra-high photocatalytic properties for water splitting

A novel kind of strontium sodium tantalite (SNT) mesocrystal has been synthesized via a simple molten salt process without using any organic additives. The SNT mesocrystals are characterized as built from nanocubes (20–60 nm) via a non-classical crystallization process. The obtained 3D architectures show high crystallinity and a preferred orientation growth. Formation of SNT mesocrystals strongly depends on the weight ratio (W) of salt to starting materials. An inappropriate value of W will restrain the orientation attachment and promote the process of classic crystallization. The SNT mesocrystals exhibit an outstanding photocatalytic performance due to their nanosteps, high porosity and preferred oriented direction. Rates of hydrogen generation reach values of 27.5 and 4.89 mmol h−1 for aqueous methanol and pure water splitting, respectively. Besides, the molten salt method is suggested to be beneficial for large scale applications of catalysts due to its nontoxicity, recyclability, cheapness and high efficiency.

Facile synthesis of Li4Ti5O12 nanosheets stacked by ultrathin nanoflakes for high performance lithium ion batteries

Li4Ti5O12 nanosheets stacked by ultrathin nanoflakes derived from the interlayer splitting and exfoliation of the layered orthorhombic Li1.81H0.19Ti2O5·xH2O precursors are obtained by a facile method. The precursors are synthesized through a one-step, low-temperature hydrothermal method with a mixed solvent of ethanol and water. The surfactants and templates are free during the fabrication process. The ultrathin nanoflakes are interconnected and their thicknesses are only ∼3 nm. Possible morphology formation and crystal structure transition mechanisms are proposed through time-dependent experiments. As an anode material for rechargeable lithium-ion batteries, the Li4Ti5O12 nanosheets with a stacked structure delivered an initial discharge capacity of 175.9 mA h g−1, together with a discharge capacity of 166.8 mA h g−1 after 100 cycles at 0.5 C. The discharge capacity could reach up to 100.2 mA h g−1 even at 20 C. We infer that except for the self advantages of nanosheets as nanomaterials, the delicate structure consisted of stacks of interconnected ultrathin nanoflakes and can promote the kinetic property of lithium ions and electrons diffusion through offering more transporting channels, which is favorable for high-rate performance.