Investigation of Binary Metal (Ni,Co) Selenite as Li‐Ion Battery Anode Materials and Their Conversion Reaction Mechanism with Li Ions

Highly efficient anode materials with novel compositions for Li‐ion batteries are actively being researched. Multicomponent metal selenite is a promising candidate, capable of improving their electrochemical performance through the formation of metal oxide and selenide heterostructure nanocrystals during the first cycle. Here, the binary nickel–cobalt selenite derived from Ni–Co Prussian blue analogs (PBA) is chosen as the first target material: the Ni–Co PBA are selenized and partially oxidized in sequence, yielding (NiCo)SeO₃ phase with a small amount of metal selenate. The conversion mechanism of (NiCo)SeO₃ for Li‐ion storage is studied by cyclic voltammetry, in situ X‐ray diffraction, ex situ X‐ray photoelectron spectroscopy, in situ electrochemical impedance spectroscopy, and ex situ transmission electron microscopy. The reversible reaction mechanism of (NiCo)SeO₃ with the Li ions is described by the reaction: NiO + CoO + xSeO₂ + (1 ‐ x)Se + (4x + 6)Li⁺ + (4x + 6)e^? ? Ni + Co + (2x + 2)Li₂O + Li₂Se. To enhance electrochemical properties, polydopamine‐derived carbon is uniformly coated on (NiCo)SeO₃, resulting in excellent cycling and rate performances for Li‐ion storage. The discharge capacity of C‐coated (NiCo)SeO₃ is 680 mAh g^?1 for the 1500th cycle when cycled at a current density of 5 A g^?1.     

Phase-controlled synthesis of thermally stable nitrogen-doped carbon supported iron catalysts for highly efficient Fischer-Tropsch synthesis

Nano Research - Iron-based nanoparticles with uniform and high particle dispersion, which are supported on carbon structures, have been used for various applications. However, their preparation...     

Increased mobility of an <Emphasis Type="Italic">α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> grain boundary by electron-beam irradiation

When subjected to electron-beam irradiation in a transmission electron microscope, the grain boundary in an α-Al₂O₃ bicrystal is observed to migrate even at room temperature. The bicrystal is composed of grains with the same normal direction, and thus the difference in strain energy or surface energy between the two grains cannot explain the observed migration. We attribute this phenomenon to an increase in grain boundary mobility by electron-beam irradiation, especially by radiolysis effects.     

Accelerated precipitation behavior of cast Mg-Al-Zn alloy by grain refinement

This study demonstrates that the precipitation behavior of β-Mg₁₇Al₁₂ phase during aging and the resultant variation in hardness and mechanical properties of cast Mg-Al-Zn alloy are strongly dependent on initial grain size. Grain size reduction accelerates discontinuous precipitation at the early stage of aging treatment by increasing the area fraction of grain boundaries that can act as nucleation sites for discontinuous precipitates (DP), but it does not influence DP growth rate. Grain refinement also prematurely terminates continuous precipitation because the formation of a large number of DP reduces the amount of Al dissolved in the matrix, which is required for the formation of continuous precipitates (CP). This promotion of DP formation and early termination of CP formation significantly decrease the peak-aging time to one-third. The enhanced precipitation behavior also leads to an additional hardness improvement in the aged alloy, along with an increase in hardness owing to grain boundary strengthening by grain refinement. The amount of increase in hardness changes with aging time, which is determined by the variation of three variables with aging time: DP fraction difference between refined and nonrefined alloys, hardness difference between DP and matrix, and matrix hardness difference between the two alloys. Grain refinement improves both tensile strength and ductility of the homogenized alloy owing to grain boundary strengthening and suppression of twinning activation, respectively. However, the loss of ductility after peak-aging treatment is greater in the refined alloy because of the larger amount of DP acting as a crack source in this alloy.     

Interface Control of Ferroelectricity in an SrRuO3/BaTiO3/SrRuO3 Capacitor and its Critical Thickness

The atomic‐scale synthesis of artificial oxide heterostructures offers new opportunities to create novel states that do not occur in nature. The main challenge related to synthesizing these structures is obtaining atomically sharp interfaces with designed termination sequences. In this study, it is demonstrated that the oxygen pressure during growth plays an important role in controlling the interfacial terminations of SrRuO₃/BaTiO₃/SrRuO₃ (SRO/BTO/SRO) ferroelectric (FE) capacitors. The SRO/BTO/SRO heterostructures are grown by a pulsed laser deposition method. The top SRO/BTO interface, grown at high (around 150 mTorr), usually exhibits a mixture of RuO₂–BaO and SrO–TiO₂ terminations. By reducing , the authors obtain atomically sharp SRO/BTO top interfaces with uniform SrO–TiO₂ termination. Using capacitor devices with symmetric and uniform interfacial termination, it is demonstrated for the first time that the FE critical thickness can reach the theoretical limit of 3.5 unit cells.     

Brain‐Inspired Photonic Neuromorphic Devices using Photodynamic Amorphous Oxide Semiconductors and their Persistent Photoconductivity

The combination of a neuromorphic architecture and photonic computing may open up a new era for computational systems owing to the possibility of attaining high bandwidths and the low‐computation‐power requirements. Here, the demonstration of photonic neuromorphic devices based on amorphous oxide semiconductors (AOSs) that mimic major synaptic functions, such as short‐term memory/long‐term memory, spike‐timing‐dependent plasticity, and neural facilitation, is reported. The synaptic functions are successfully emulated using the inherent persistent photoconductivity (PPC) characteristic of AOSs. Systematic analysis of the dynamics of photogenerated carriers for various AOSs is carried out to understand the fundamental mechanisms underlying the photoinduced carrier‐generation and relaxation behaviors, and to search for a proper channel material for photonic neuromorphic devices. It is found that the activation energy for the neutralization of ionized oxygen vacancies has a significant influence on the photocarrier‐generation and time‐variant recovery behaviors of AOSs, affecting the PPC behavior.     

Fabrication of Millimeter‐Long Carbon Tubular Nanostructures Using the Self‐Rolling Process Inherent in Elastic Protein Layers

Millimeter‐long conducting fibers can be fabricated from carbon nanomaterials via a simple method involving the release of a prestrained protein layer. This study shows how a self‐rolling process initiated by polymerization of a micropatterned layer of fibronectin (FN) results in the production of carbon nanomaterial‐based microtubular fibers. The process begins with deposition of carbon nanotube (CNT) or graphene oxide (GO) particles on the FN layer. Before polymerization, particles are discrete and nonconducting, but after polymerization the carbon materials become entangled to form an interconnected conducting network clad by FN. Selective removal of FN using high‐temperature combustion yields freestanding CNT or reduced GO microtubular fibers. The properties of these fibers are characterized using atomic force microscopy and Raman spectroscopy. The data suggest that this method may provide a ready route to rapid design and fabrication of aligned biohybrid nanomaterials potentially useful for future electronic applications.     

Direct Observation of Inherent Atomic‐Scale Defect Disorders responsible for High‐Performance Ti1−xHfxNiSn1−ySby Half‐Heusler Thermoelectric Alloys

Structural defects often dominate the electronic‐ and thermal‐transport properties of thermoelectric (TE) materials and are thus a central ingredient for improving their performance. However, understanding the relationship between TE performance and the disordered atomic defects that are generally inherent in nanostructured alloys remains a challenge. Herein, the use of scanning transmission electron microscopy to visualize atomic defects directly is described and disordered atomic‐scale defects are demonstrated to be responsible for the enhancement of TE performance in nanostructured Ti_1?x Hf_x NiSn_1?y Sb_y half‐Heusler alloys. The disordered defects at all atomic sites induce a local composition fluctuation, effectively scattering phonons and improving the power factor. It is observed that the Ni interstitial and Ti,Hf/Sn antisite defects are collectively formed, leading to significant atomic disorder that causes the additional reduction of lattice thermal conductivity. The Ti_1?x Hf_x NiSn_1?y Sb_y alloys containing inherent atomic‐scale defect disorders are produced in one hour by a newly developed process of temperature‐regulated rapid solidification followed by sintering. The collective atomic‐scale defect disorder improves the zT to 1.09 ± 0.12 at 800 K for the Ti_0.5Hf_0.5NiSn_0.98Sb_0.02 alloy. These results provide a promising avenue for improving the TE performance of state‐of‐the‐art materials.