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The structural origin of the slow dynamics in glass formation remains to be understood owing to the subtle structural differences between the liquid and glass states. Even from simulations, where the positions of all atoms are deterministic, it is difficult to extract significant structural components for glass formation. In this study, we have extracted significant local atomic structures from a large number of metallic glass models with different cooling rates by utilising a computational persistent homology method combined with linear machine learning techniques. A drastic change in the extended range atomic structure consisting of 3–9 prism-type atomic clusters, rather than a change in individual atomic clusters, was found during the glass formation. The present method would be helpful towards understanding the hierarchical features of the unique static structure of the glass states. In glass formation, the dynamics of extended structures beyond atomic short-range order is yet to be understood. Here, persistent homology, combined with machine learning, reveals superstructures made of 3-to-9 prism-type atomic clusters which undergo drastic changes according to the glass cooling rate.

The broken symmetry in the atomic-scale ordering of glassy versus crystalline solids leads to a daunting challenge to provide suitable metrics for describing the order within disorder, especially on length scales beyond the nearest neighbor that are characterized by rich structural complexity. Here, we address this challenge for silica, a canonical network-forming glass, by using hot versus cold compression to (i) systematically increase the structural ordering after densification and (ii) prepare two glasses with the same high-density but contrasting structures. The structure was measured by high-energy X-ray and neutron diffraction, and atomistic models were generated that reproduce the experimental results. The vibrational and thermodynamic properties of the glasses were probed by using inelastic neutron scattering and calorimetry, respectively. Traditional measures of amorphous structures show relatively subtle changes upon compacting the glass. The method of persistent homology identifies, however, distinct features in the network topology that change as the initially open structure of the glass is collapsed. The results for the same high-density glasses show that the nature of structural disorder does impact the heat capacity and boson peak in the low-frequency dynamical spectra. Densification is discussed in terms of the loss of locally favored tetrahedral structures comprising oxygen-decorated SiSi4 tetrahedra., 世界一構造秩序のあるガラスの合成と構造解析に成功 --ガラスの一見無秩序な構造の中に潜む秩序を抽出--. 京都大学プレスリリース. 2021-12-25.

Although previous molecular dynamics studies proposed the existence of Zr-centered Frank-Kasper Z16 structures in Cu-Zr metallic glasses, it cannot be concluded yet, owing to the degeneracy problem of the Voronoi index and the artifact in sets of potentials for Cu-Zr systems. We solve both problems by combining a recently developed Finnis-Sinclair potentials to generate realistic atomic structures and the ${p}_{3}$ code to properly differentiate local structures. In previous studies, the Voronoi index $\ensuremath{\langle}0,0,12,4\ensuremath{\rangle}$ was typically associated with Frank-Kasper Z16 local structures. However, we demonstrate that this index includes two types of polyhedra, only one of which is associated with the Frank-Kasper Z16 structures. We reveal that the Z16 structures are more frequent than the other structures and that the two have different behaviors. The tendency of Zr-centered Z16 local structures to be neighbors of Cu-centered icosahedral local structures is also confirmed. Our findings illustrate the importance of properly differentiating local structures in order to elucidate the behavior of metallic glasses at the atomic scale.

This paper presents a new lattice pattern that can extend the pass band of 120-GHz-band split ring resonator (SRR) filter that was arranged close to the lattice pattern. We have already shown that the insertion loss of a 120-GHz-band SRR bandstop filter can be controlled by coupling another lattice pattern substrate. We designed a new lattice pattern that extends the pass bandwidth of the SRR filter when it was arranged close to the new lattice pattern. Simulation results indicate that the resonant peak split into two peaks whose frequency interval was 45.8 GHz, and the 3-dB pass bandwidth was 22.4 GHz (113.6–136.0 GHz), when new lattice pattern was arranged close to the SRR bandstop filter. S 21 of the prototyped SRR filter that was arranged with the new lattice pattern was − 1.5 dB at 125 GHz. 3-dB pass bandwidth of the SRR filter with new lattice pattern became over 20 GHz, which was over 3 dB larger than the 3-dB pass bandwidth of the SRR filter coupled with the conventional lattice pattern. The transmitter power of the 120-GHz-band wireless link necessary for achieving the BER of below 10−11 decreased by 3.3 dB by replacing the conventional lattice pattern with the new lattice pattern.

To investigate multi-boson peaks (multi-BP), terahertz time-domain spectroscopy was performed on amorphous silicon monoxide (a-SiO), which exhibits unusual disproportion in the nanoscale region where the SiO 2 and Si regions are separated. In the resulting THz spectrum, the BP was observed at 2.4 THz, as a broad asymmetric peak, and the BP frequency was evidently higher than that of silica glass. The results suggest that the higher BP frequency of a-SiO in the infrared spectrum originates from the a-Si cluster region.

This paper presents non-destructive inspection of sub-millimeter wide concrete surface cracks covered by paper using near-field scattering. One of the problem for nondestructive imaging using near-field scattering is low millimeter-wave (MMW) image contrast at the surface crack, because the decrease of received power due to near-field scattering is about 1 dB. This paper presents the nondestructive inspection technologies that improve the MMW image contrast at the surface crack by using standing wave between the probe antenna and sample surface. We have found that the black and white of the MMW image pixels that correspond to the concrete cracks is inverted according to the paper thickness or antenna height, and the image contrast can be improved by calculating the difference of two MMW images obtained from different paper thickness. When we measured the frequency characteristics of the reflected MMW signal, a sharp spectral notch was observed in the reflected MMW signals, and the spectral notch frequency depends on the presence or absence of crack, paper thickness, and antenna height. We have achieved the improvement of MMW image contrast at surface crack by using these MMW spectroscopy technologies.

The glacial phase, with an apparently glassy structure, can be formed by a first-order transition in some molecular-glass-forming supercooled liquids. Here we report the formation of metallic glacial glass (MGG) from the precursor of a rare-earth-element-based metallic glass via the first-order phase transition in its supercooled liquid. The excellent glass-forming ability of the precursor ensures the MGG to be successfully fabricated into bulk samples (with a minimal critical diameter exceeding 3 mm). Distinct enthalpy, structure, and property changes are detected between MGG and metallic glass, and the reversed "melting-like" transition from the glacial phase to the supercooled liquid is observed in fast differential scanning calorimetry. The kinetics of MGG formation is reflected by a continuous heating transformation diagram, with the phase transition pathways measured at different heating rates taken into account. The finding supports the scenario of liquid-liquid transition in metallic-glass-forming liquids.

International audience; In this paper, we present a near-field pattern measurement based on an electro-optic sensing at 300 GHz band. The measurement system is based on a self-heterodyne technique and non-polarimetric frequency down-conversion technique. The far-field radiation pattern of a horn antenna calculated from the measured near-field pattern is compared with far-field pattern measured with a conventional measurement system using open-ended waveguide probe.

Understanding the formation and evolution of bicontinuous nanoporous structure during dealloying has been one of the most challenging subjects of dealloying research. However, previous

Glass forming ability (GFA) is critically important for large-scale applications of bulk metallic glasses with maximized functionalities at low costs in materials and processing. Traditionally, excellent glass formers usually have compositions in eutectic regions where liquid phases have high stability and low liquid temperatures while GFA of off-eutectic alloys is largely limited by primary crystallization. In this study we reported that the GFA of Ni-based off-eutectic alloys can be dramatically improved by manipulating the primary crystallization reaction through minor alloying. As a result, a novel Ni60Pd20P14Si2B4 metallic glass with excellent GFA is developed by substituting P in Ni60Pd20P14Si2B4 using 2 at.% Si and 4 at.% B. The minor alloying leads to the transition of the primary crystallization from a tetragonal (Ni, Pd)3P phase to a chemically modulated complex monoclinic phase. The enhanced GFA results in the largest achievable processing diameter (25 mm) of Ni-based bulk metallic glasses, which is more than four times larger than that of Ni60Pd20P14Si2B4 . The complex crystal structure of the primary crystalline phase with chemical modulation and a large unit cell leads to slow crystallization kinetics from high barrier energy for crystal nucleation and growth, and hence the improved glass forming ability.

The need for high data rates of several Gbit/s in 5G and beyond wireless networks will require capacities of 100 Gbit/s in the backhaul and fronthaul links. 300 GHz wireless links are promising candidates to provide these links. The paper describes the ongoing activities in the EUJapan project ThoR towards suitable propagation and channel models applicable for the simulation and planning of such links. The corresponding modelling activities are based on ray tracing models, which are enhanced by taking into account atmospheric propagation effects, measured characteristic of building materials and the effect of wind to the poles, where the antennas are mounted. First results applied to realistic simulation scenarios are presented.

This contribution describes and assesses the outcome of WRC 2019 w.r.t. THz communications. WRC 2019 has included a new footnote to the radio regulations, which describes the conditions for the use of the spectrum between 275 and 450 GHz by land mobile and fixed service. Totally, 160 GHz of spectrum are now available for THz communications, where no specific conditions are necessary to protect EESS. This provides a sound basis for the future implementation of THz communications. Furthermore, the paper identifies a couple of future regulatory and standardization activities.

The deformation microstructure of an interdendritic18 R long-period stacking ordered (LPSO) phase in an Mg-Zn-Y alloy subjected to shock loading was investigated by transmission electron microscopy. It was found that kink banding, the key deformation mode of LPSO phases under quasi-static loading, is suppressed by shock loading. Instead, second-order pyramidal slip by dislocations, which has not been observed in LPSO before, contributes to the plastic deformation of LPSO, in addition to the dislocations. The rate-dependent deformation modes of LPSO have an important implication in understanding the mechanical behaviour of LPSO strengthened Mg alloys under extreme loading conditions.

An aprotic lithium–oxygen battery with an ultrahigh theoretical energy density has attracted significant attention as the next-generation electrochemical energy device demanded by all-electric vehicles and other high-energy devices. Extensive effort has recently been devoted to improving the performances of cathodes, anodes, and electrolytes. However, as an integrated system, the overall battery properties are not determined by the individual components but by the synergy of all components. Despite important progress in the development of cathodes, anodes, and electrolytes, the system-level design and assembly of lithium–oxygen batteries have not benefited from these recent advances. Here, we report a graphene-based quasi-solid-state lithium–oxygen battery consisting of a rationally designed 3D porous graphene cathode, redox mediator-modified gel polymer electrolyte, and porous graphene/Li anode. This integrated prototype battery simultaneously addresses the major challenges of lithium–oxygen batteries and achieves stable cycling at a large capacity, low charge overpotential and high rate in both coin-type and large-scale pouch-type batteries. For the first time, these lithium–oxygen batteries as a whole device deliver gravimetric and volumetric energy densities higher than those of a commercial Li-ion polymer battery. This study represents important progress toward the practical implementation of full-performance lithium–oxygen batteries. An experimental lithium battery ideal for powering electric vehicles is one step closer to commercialization thanks to graphene technology. While lithium–oxygen batteries offer extremely high energy storage in a low-weight package, they often fail prematurely due to irreversible formation of precipitates during recharging. To overcome these issues, Mingwei Chen from Tohoku University in Sendai, Japan, and co-workers have constructed battery cathodes and anodes from a new porous form of graphene. The team’s approach sandwiches a conductive gel between a bare 3D nanoporous graphene film and one loaded with lithium ions. The abundant active sites for oxygen reduction in the device, coupled with a gel design that facilitates ion transport, inhibited precipitation reactions for up to 100 charge cycles. A prototype ‘pouch’-type battery produced more energy per square centimeter than conventional lithium-ion cells. A graphene based quasi-solid state rechargeable Li-O2 battery is developed by utilizing 3D nanoporous graphene cathode, TTF modified quasi-solid state GPE and porous graphene/Li anode. This integrated prototype battery simultaneously addresses the major challenges of Li-O2 batteries in energy efficiency, lifetime and safety and present an important progress in practical implementation of full performance Li-O2 battery.

application/pdf, Article, Journal of Applied Crystallography. 2018, 51 (5), p.1467-1473

In comparison to conventional supercapacitors that commonly fall short of energy densities, the intercalation pseudocapacitors have combined high charge-storage capacity and fast charge/discharge rates from their unique charge storage mechanism of fast kinetics without the limitation of diffusion. Nevertheless, only very limited crystalline materials have a structure that can fulfill the strict demands of fast ion transport pathways and insignificant structural variation upon ion insertion and extraction for the intercalation pseudocapacitance. Here we report that amorphous titanium dioxide, grown on highly conductive nanoporous graphene frameworks by atomic layer deposition, is capable of storing and delivering a large capacity at high rates by pseudocapacitive and bulk-form Li+ intercalation/de-intercalation reactions. Different from intercalation pseudocapacitive crystals, amorphous TiO2 experiences local structure changes during Li+ insertion and extraction which essentially only lead to insignificant constraints on the overall kinetics as a result of loose packing and structure disorder of amorphous materials. This study paves a new way to develop high-energy capacitive materials in a wide spectrum of amorphous materials and may promote the practical implementation of high-rate and large-capacity energy storage.

RuO2 displays excellent bifunctional catalysis towards the oxygen reduction and evolution reactions of Li-O2 battery. Nevertheless, how the solid catalyst successively catalyzes solid Li2O2 formation and decomposition, confronting passivation and loss of RuO2/Li2O2 contact, during discharging and charging remains a mystery. Here we report operando observations of RuO2 catalyzed oxygen reduction and evolution reactions of Li2O2 by utilizing a liquid cell scanning transmission electron microscope. Upon discharging, RuO2 obviously accelerates formation of soluble LiO2 intermediates and acts as preferential sites of Li2O2 precipitation. During charging, the catalytic activation of RuO2 takes place at electrolyte-RuO2-Li2O2 triple-phase interfaces. Importantly, RuO2 not only catalyzes the decomposition of directly contacted Li2O2, but also promotes oxidation of soluble LiO2 for rapid dissolution of isolated Li2O2 nanoparticles by a chemical comproportionation reaction. The observation unveils how RuO2 catalyzes the formation and decomposition of Li2O2 during discharging and charging and provides nanoscale insights into cathodic reactions of Li-O2 batteries with solid catalysts.

Developing advanced lithium-ion batteries that afford both high energy density and high power density has been one of the crucial research targets in the field of electrochemical energy storage. Realization of fast Li+ storage would require a smart electrode design that enables simultaneous enhancements in ion and electron transports as well as a fast and facile bulk-form solid-state reaction. Here we report a high-performance 3D bilayered composite electrode constructed by bicontinuous nanoporous graphene and thin molybdenum oxide stacking films. The novel electrode offers fast kinetics of Li+ diffusion and reactions and, consequently, delivers a large specific capacity of 710 mAh g-1, the excellent rate performance of charging within seconds and an ultra-long lifetime over 13,000 discharge-charge cycles. High and stable volumetric capacities up to 900 mAh cm-3 have also been achieved with the squeezed composite electrodes. This study shines light into the realization of a high-performance graphene-based porous electrode for advanced lithium-ion batteries and will inspire the development of new 3D hybrid materials for high-rate and large-capacity electrochemical energy storage.

Structural characterization of dislocations and dislocation reactions in a face-centered cubic high entropy alloy was conducted using the state-of-the-art spherical aberration corrected transmission electron microscopy. We experimentally measured the stacking fault energy of the high entropy alloy from the atomic images and diffraction contrast of dislocation cores. The low stacking fault energy results in widely dissociated dislocations and extensive dislocation reactions, which leads to the formation of immobile Lomer and Lomer-Cottrell dislocation locks. These dislocation locks act as both dislocation barriers and sources and are responsible for the significant work hardening with a large hardening rate in the alloy. Based on the atomic-scale characterization and classical dislocation theory, a simple equation was derived to describe the work hardening behavior of the high entropy alloy in the early-stage of plastic deformation.

1T–1H metal–semiconductor interfaces in two-dimensional (2D) transition-metal dichalcogenides (TMDs) play a crucial role in utilizing the band gaps of TMDs for applications in electronic devices. Although the 1T–1H two-phase structure has been observed in exfoliated 2D nanosheets and chemically or physically treated TMDs, it cannot in principle be achieved in large-scale TMD monolayers grown by chemical vapor deposition (CVD), which is a fabrication method for electronic device applications, because of the metastable nature of the 1T phase. In this study we report CVD growth of 1T–1H two phase TMD monolayers by controlling thermal strains and alloy compositions. It was found that in-plane thermal strains arising from the difference in thermal expansion coefficients between TMD monolayers and substrates can drive the 1H to 1T transition during cooling after CVD growth. Moreover, grain boundaries in the 2D crystals act as the nucleation sites of the 1T phase and the lattice strain perturbations from alloyin...

Dr. Robert Tournier and Dr. Michael Ojovan found that the liquidus temperatures Tl of Ni60Pd20P20-y-xSiyBx glass formers, recently reported by us, are equal or close to the disappearance temperatures Tn+ of liquid medium-range order. In this letter we presented the repeated heating/cooling differential scanning calorimetry (DSC) results of the alloys and demonstrated that the liquidus temperatures Tl of the off-eutectic alloys are closely related to the melting of the primary crystalline phases that have the highest melting temperatures in the alloys systems.

A series of boron-rich boron carbides are investigated to explore the effect of boron/carbon ratios on the microstructure and mechanical properties of the complex material. It has been found that excess boron substitution gives rise to expanded lattice constants, orientational asymmetry of the chain structure and distortion of the icosahedra of rhombohedra B 4 C units in comparison with conventional carbon-rich boron carbides. Microstructure characterization reveals a high density of stacking faults and growth twins in boron-rich boron carbides. Nanoindentation measurements demonstrate that the hardness and modulus of boron-rich boron carbides decrease with the increase of boron content while the B 10.2 C sample with the highest boron substitution shows relatively high hardness and modulus. This study suggests that the structure of single-phase covalent materials could be tailored by self-alloying for improved mechanical properties.

Vapor phase dealloying (VPD) is an environmentally-friendly method for fabricating nanoporous materials by utilizing the saturated vapor pressure difference of elements to selectively drive sublimation of one or more components from an alloy. VPD kinetics has not been explored and rate-controlling factors of the solid-gas transformation within complex nanostructure remain unknown. Using manganese-zinc alloys as a prototype system, we systematically investigated the dependence of dealloying velocity on temperature and pressure and presented a model to quantitatively describe the dealloying kinetics. We found that the dealloying velocity exhibits a linear to power law transition at a critical dealloying depth, resulting from the interplay between the kinetic process of dealloying and dealloyed microstructure. This transition bridges ballistic evaporation at early time to Knudsen diffusion of Zn vapor in developed pore channels where the Zn partial pressure at the dealloying front reaches the local equilibrium between the solid and vapor phases. By comparing activation energies for VPD and bulk zinc sublimation, the entire energy landscape of VPD is measured. The fundamental understanding of VPD kinetics paves an effective way to design dealloyable precursor alloys and to optimize dealloyed microstructure of VPD materials for a wide range of applications.

One central material issue in spintronics is the search for high temperature (above room temperature) magnetic semiconductors. We report on the formation of a transparent magnetic semiconductor with embedded ferromagnetic metallic glass nano-granules, showing a Curie temperature of ~600 K. Soft X-ray magnetic circular dichroism data verify its intrinsic room-temperature ferromagnetism. Owing to the unique structure of ferromagnetic nano-granules embedded in the host magnetic semiconductor, additional interfacial exchange anisotropy emerges and stabilizes the ferromagnetism. The magnetotransport measurements of the amorphous nanocomposite indicate that its anomalous Hall effect is dominated by the extrinsic mechanism of the side-jump due to the spin-dependent impurity. Keywords: Metallic glasses, Magnetic semiconductor, Nano-granules

Tuning surface structures by bottom-up synthesis has been demonstrated as an effective strategy to improve the catalytic performances of nanoparticle catalysts. Nevertheless, the surface modification of three-dimensional nanoporous metals, fabricated by a top-down dealloying approach, has not been achieved despite great efforts devoted to improving the catalytic performance of three-dimensional nanoporous catalysts. Here we report a surfactant-modified dealloying method to tailor the surface structure of nanoporous gold for amplified electrocatalysis toward methanol oxidation and oxygen reduction reactions. With the assistance of surfactants, {111} or {100} faceted internal surfaces of nanoporous gold can be realized in a controllable manner by optimizing dealloying conditions. The surface modified nanoporous gold exhibits significantly enhanced electrocatalytic activities in comparison with conventional nanoporous gold. This study paves the way to develop high-performance three-dimensional nanoporous catalysts with a tunable surface structure by top-down dealloying for efficient chemical and electrochemical reactions., Tuning the ratio of facets in materials can affect catalytic activity but methods to achieve this can be difficult to control. Here, using surfactants during dealloying, the authors prepare nanoporous gold with controlled facet ratios and show how it can significantly improve electrocatalytic activity.

Two-dimensional (2D) materials are promising for applications in a wide range of fields because of their unique properties. Hydrogen boride sheets, a new 2D material recently predicted from theory, exhibit intriguing electronic and mechanical properties as well as hydrogen storage capacity. Here, we report the experimental realization of 2D hydrogen boride sheets with an empirical formula of H1B1, produced by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride (MgB2) with an average yield of 42.3% at room temperature. The sheets feature an sp2-bonded boron planar structure without any long-range order. A hexagonal boron network with bridge hydrogens is suggested as the possible local structure, where the absence of long-range order was ascribed to the presence of three different anisotropic domains originating from the 2-fold symmetry of the hydrogen positions against the 6-fold symmetry of the boron networks, based on X-ray diffraction, X-ray atomic pair dist...

Grain boundaries (GBs) are unavoidable crystal defects in polycrystalline materials and significantly influence their properties. However, the structure and chemistry of GBs in 2D transition metal dichalcogenide alloys have not been well established. Here we report significant chemical selectivity of transition metal atoms at GB dislocation cores in Mo1-xWxS2 monolayers. Different from classical elastic field-driven dislocation segregation in bulk crystals, the chemical selectivity in the 2D crystals originates prominently from variation of atomic coordination numbers at dislocation cores. This observation provides atomic insights into the topological effect on the chemistry of crystal defects in 2D materials.

Realizing a large specific area in disordered metallic glasses is of great scientific and technological importance. Here we report a nanoporous multicomponent metallic glass fabricated by the combination of selective phase dissolution and passivation of a spinodally decomposed glassy precursor. The nanoporous metallic glass shows superior hydrogen uptake performance by taking advantage of the large specific surface area of the nanoporous structure and the high diffusivity of hydrogen in metallic glasses. The facile route of selective corrosion and passivation, decoupling the galvanic corrosion and alloy stability, opens a new avenue for functionalizing metallic glasses as a large-surface area and lightweight material for various structural and functional applications.

This paper presents non-destructive millimeter-wave (MMW) imaging of sub-millimeter wide cracks on concrete surface that are covered by paper. Measurement of near-field scattering of 76.5-GHz-MMW signal at cracks enables the detection of sub-millimeter wide cracks. The decrease of received power due to near-field scattering is small, therefore the MMW image contrast of fine surface concrete cracks is not clear. We found that standing wave occurs between the sample surface and the antenna, and received power increases by the near-field scattering caused by the surface crack in case the antenna locates around the node of the standing wave. The MMW image contrast of the cracks improved by up to 3 dB by calculating the difference of two MMW images that are obtained with different paper thickness or different antenna height.

The real capacity of graphene and the lithium-storage process in graphite are two currently perplexing problems in the field of lithium ion batteries. Here we demonstrate a three-dimensional bilayer graphene foam with few defects and a predominant Bernal stacking configuration, and systematically investigate its lithium-storage capacity, process, kinetics, and resistances. We clarify that lithium atoms can be stored only in the graphene interlayer and propose the first ever planar lithium-intercalation model for graphenic carbons. Corroborated by theoretical calculations, various physiochemical characterizations of the staged lithium bilayer graphene products further reveal the regular lithium-intercalation phenomena and thus fully illustrate this elementary lithium storage pattern of two-dimension. These findings not only make the commercial graphite the first electrode with clear lithium-storage process, but also guide the development of graphene materials in lithium ion batteries., The mechanism of lithium storage in graphenic carbon remains a fundamental question to be addressed. Here the authors employ suitable bilayer graphene foam to investigate various physiochemical phenomena of lithium intercalation and propose a storage model.

Although ionic conductors have been thoroughly investigated, topological features of these materials' nanotextures have been surprisingly overlooked. Here, we report fabrication of a metal-oxide nanocomposite consisting of intertwined phases of platinum (Pt) metal and oxygen-ion conductive cerium oxide (CeO2), i.e., Pt#CeO2. Sectional TEM observations coupled with topological analysis demonstrated that Pt#CeO2 composites having different nanostructures can be classified with a topological measure that corresponds to the phase connectivity of CeO2, namely, the Betti number β 0, and another that corresponds to holes of the Pt phase, namely, the Betti number β 1. The samples' oxygen ionic conductivity Pt#CeO2 was measured at elevated temperatures in air by alternating current impedance spectroscopy. It was found that the nanostructure changed from a striped appearance to a maze-like appearance as the value of β 1 / β 0 decreased. Both the activation energy E and the pre-exponential factor σ 0 for the oxygen ionic conductivity were found to be independent of β 1 and exhibited linear, negative correlations with β 0. The topological connectivity of the ion-conductive CeO2 phase, which was quantified with the Betti number β 0, was suitable as a descriptor to correlate the image data of nanostructures with their ionic transport properties.

This article proposes a topological method that extracts hierarchical structures of various amorphous solids. The method is based on the persistence diagram (PD), a mathematical tool for capturing shapes of multiscale data. The input to the PDs is given by an atomic configuration and the output is expressed as 2D histograms. Then, specific distributions such as curves and islands in the PDs identify meaningful shape characteristics of the atomic configuration. Although the method can be applied to a wide variety of disordered systems, it is applied here to silica glass, the Lennard-Jones system, and Cu-Zr metallic glass as standard examples of continuous random network and random packing structures. In silica glass, the method classified the atomic rings as short-range and medium-range orders and unveiled hierarchical ring structures among them. These detailed geometric characterizations clarified a real space origin of the first sharp diffraction peak and also indicated that PDs contain information on elastic response. Even in the Lennard-Jones system and Cu-Zr metallic glass, the hierarchical structures in the atomic configurations were derived in a similar way using PDs, although the glass structures and properties substantially differ from silica glass. These results suggest that the PDs provide a unified method that extracts greater depth of geometric information in amorphous solids than conventional methods., Comment: 8 pages, 14 figures

In this study, we report that the supercapacitor performance of polypyrrole (PPy) in non-aqueous electrolytes can be dramatically improved by highly conductive nanoporous gold which acts as both the support of active PPy and the current collector of supercapacitors. The excellent electronic conductivity, rich porous structure and large surface area of the nanoporous electrodes give rise to a high specific capacitance and low internal resistance in non-aqueous electrolytes. Combining with a wide working potential window of ~ 2 V, the non-aqueous PPy-based supercapacitors show an extraordinary energy density and power density.

Li−O2 batteries are a promising electrochemical energy-storage system with a sufficient energy density for all electric vehicles, with a one-charge driving distance comparable to conventional petrol cars. However, the practical implementations of Li−O2 batteries face many scientific and technological challenges. Among these is the development of high-performance cathode materials that can provide high capacity, low charge/discharge overpotentials and stable cycling stability. Here, we report a nanoporous Ni cathode covered by N-doped graphene and self-grown catalyst for rechargeable Li−O2 batteries. The novel hybrid cathode shows relatively low charge/discharge overpotentials, high volumetric capacity and long cycling lifetime, which may pave a new way for practical implementation of economic nanoporous metals as binder-free cathodes for high-performance Li−O2 batteries.

Alloying is an important approach to improving catalytic activities and realizing new functions of heterogeneous catalysts, which has extensively been employed in fabricating noble metal based bimetallic catalysts. However, it is technically unviable in the synthesis of alloyed transition metal compounds, which are emerging as important catalysts for water splitting, in a controllable manner using conventional wet chemical methods. Here we report nanoporous bimetallic (Co1−xFex)2P phosphides with controllable compositions and tuneable porosity, which are fabricated by the combination of metallurgical alloy design and electrochemical etching. By tailoring the Co/Fe ratios and nanoporosity, the bimetallic phosphides exhibit versatile catalytic activities towards HER and OER in acidic and basic electrolytes. As both the cathode and the anode of an electrolyser, nanoporous (Co0.52Fe0.48)2P shows an outstanding performance in water electrolysis, comparable to the commercial electrolyser with paired Pt/C and IrO2 catalysts.

Graphene with a large specific surface area and high conductivity has a large specific capacitance. However, its volumetric capacitance is usually very low because the restacking of 2D graphene sheets leads to the loss of the large ion-accessible surface area. Here we report squeezable bicontinuous nanoporous nitrogen-doped graphene, which is extremely flexible and can tolerate large volume contraction by mechanical compression without the face-to-face restacking occurring. The compressed nanoporous N-doped graphene with a large ion accessible surface area and high conductivity shows an ultrahigh volumetric capacitance of ∼300 F cm−3 together with excellent cycling stability and high rate performance.

Conductive polymers, particularly polypyrrole (PPy), are emerging as promising electrode materials for flexible supercapacitors because of their high pseudocapacitance, low density, high mechanical flexibility and low material costs. However, the practical implementations of PPy based supercapacitors have been prevented by the poor charge/discharge rate capability and low cycle stability. In this study we report a novel three dimensional interconnected nanotubular graphene–PPy (nt-GPPy) hybrid by incorporating PPy into highly conductive and stable nanoporous graphene. The bicontinuous nanotubular hybrid material with a large specific surface area and high conductivity demonstrates significant enhancement in supercapacitance performance of PPy in terms of high specific capacitance, excellent cycling stability and high rate capability.

The intricate 3D geometric shape and surface atomic structure of nanoporous gold catalysts are investigated using aberration-corrected scanning transmission electron microscopy in combination with discrete tomography. The real-space 3D atomic configurations illustrate geometrically necessary surface defects on the curved surface of the NPG, offering atomic insights into the catalysis of the nanoporous catalyst.

This paper presents the terahertz absorber technologies for a close-proximity wireless system. We have proposed slot ring resonator (SRR) absorber integrated planar slot array antenna for a 120-GHz-band close proximity wireless system, and we have already shown that the SRR absorber formed on quartz substrate suppresses multiple reflection between Tx-Rx antennas by simulation. We have evaluated the alignment margin of the close proximity wireless system using the SRR absorber integrated planar slot array antenna. We simulated the transmission characteristics of the close proximity wireless system using the SRR absorber integrated planar slot antennas. The received power decreases by more than 30 dB when Rx antenna moves from the position directly above Tx antenna by 4.9 mm in the plane parallel to Tx antenna in case a single waveguide slot antenna is used for both of Tx and Rx antenna. When the SRR absorber integrated planar slot antennas are used for both of Tx and Rx, $\mathbf{S}_{\pmb{21}}$ becomes −17.5 dB and its fluctuation becomes below 3.6 dB in case Rx antenna deviates from the position directly above Tx antenna by 4.9 mm.

This paper presents the progress of the plate-laminated waveguide slot array antennas by diffusion bonding in 60GHz, 120GHz and 350GHz bands. The large-size 60GHz-band antenna reduces the weight by using aluminum-alloy plates. The 120GHz-band antenna achieves wideband characteristic by adding a layer of exciting slots. The 350GHz-band antenna introduces gold-coating silicon wafers for high precision in the fabrication.