Electrochemical Lithium Storage Performance of Molten Salt Derived V_(2)SnC MAX Phase

MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage.Here,we report the preparation of V_(2)SnC MAX phase by the molten salt method.V_(2)SnC is investigated as a lithium storage anode,showing a high gravimetric capacity of 490 mAh g−1 and volumetric capacity of 570 mAh cm^(−3) as well as superior rate performance of 95 mAh g^(−1)(110 mAh cm^(−3))at 50 C,surpassing the ever-reported performance of MAX phase anodes.Sup-ported by operando X-ray diffraction and density functional theory,a charge storage mechanism with dual redox reaction is proposed with a Sn-Li(de)alloying reaction that occurs at the edge sites of V_(2)SnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at V_(2)C layers with Li.This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.

Three-and two-dimensional calculations for the interface anisotropy dependence of magnetic properties of exchange-spring Nd2Fe(14)B/α-Fe multilayers with out-of-plane easy axes

Hysteresis loops,energy products and magnetic moment distributions of perpendicularly oriented Nd2Fe(14)B/α-Fe exchange-spring multilayers are studied systematically based on both three-dimensional(3D)and one-dimensional(1D)micromagnetic methods,focused on the influence of the interface anisotropy.The calculated results are carefully compared with each other.The interface anisotropy effect is very palpable on the nucleation,pinning and coercive fields when the soft layer is very thin.However,as the soft layer thickness increases,the pinning and coercive fields are almost unchanged with the increment of interface anisotropy though the nucleation field still monotonically rises.Negative interface anisotropy decreases the maximum energy products and increases slightly the angles between the magnetization and applied field.The magnetic moment distributions in the thickness direction at various applied fields demonstrate a progress of three-step magnetic reversal,i.e.,nucleation,evolution and irreversible motion of the domain wall.The above results calculated by two models are in good agreement with each other.Moreover,the in-plane magnetic moment orientations based on two models are different.The 3D calculation shows a progress of generation and disappearance of vortex state,however,the magnetization orientations within the film plane calculated by the 1D model are coherent.Simulation results suggest that negative interface anisotropy is necessarily avoided experimentally.

pH-dependent Synthesis of Octa-nuclear Uranyl-oxalate Network Mediated by U-shaped Linkers

In this work,we report a novel octa-nuclear uranyl(U8)motif[(UO2)8O4(μ3-OH)2(μ2-OH)2]4+embedded in a uranyl-oxalate coordination polymer(compound 1)based on a U-shaped linker with extra-long xylylene chains for stabilizing the resulting high-nuclear motif through additional cross-linking connectivity.A comparison with dimeric and monomeric uranyl compounds obtained at different pH value from the same hydrothermal system reveals that,solution pH plays a vital role in formation of this octa-nuclear uranyl motif by promoting hydrolysis of uranyl source.Since high similarity of eight uranium centers in this nearly planar U8 motif here,overlapping and broadening of signals in fluorescence,infra-red(IR)and Raman spectra can be found.

Electronic Properties of Defects Induced by H Irradiation in Tantalum Phosphide

Tantalum phosphide（TaP） is predicted to be a kind of topological semimetal. Several defects of TaP induced by H irradiation are studied by the density functional theory. Electronic dispersion curves and density of states of these defects are reported. Various defects have different impacts on the topological properties. Weyl point positions are not affected by most defects. The H atom can tune the Fermi level as an interstitial. The defect of substitutional H on P site does not affect the topological properties. P and Ta vacancies of concentration 1/64 as well as the defect of substitutional H on Ta site destruct part of the Weyl points.

Effects of Grain Boundary Characteristics on Its Capability to Trap Point Defects in Tungsten

As recombination centers of vacancies(Vs)and self-interstitial atoms(SIAs),firstly grain boundaries(GBs)should have strong capability of trapping point defects.In this study,abilities to trap Vs and SIAs of eight symmetric tilt GBs in tungsten are investigated through first-principles calculations.

Effects of ultrasonic assisted friction stir welding on flow behavior,microstructure and mechanical properties of 7N01-T4 aluminum alloy joints

Conventional friction stir welding(FSW)and ultrasonic assisted friction stir welding(UAFSW)were employed to weld 6-mm thick 7 N01-T4 aluminum alloy plates.Weld forming characteristics and material flow behavior in these two different welding processes were studied and compared.Ultrasonic vibration was applied directly on the weld in axial direction through the welding tool.Metal flow behavior,microstructure characteristics in the nugget zone(NZ)and evolution of the mechanical properties of naturally aged joints were studied.Results show that the ultrasonic vibration can significantly increase the welding speed of defect-free welded joint.At the rotation speed of 1200 rpm,the UAFSW can produce defect-free welded joints at a welding speed that is 50%higher than that of the conventional FSW.Ultrasonic vibrations can also improve surface quality of the joints and reduce axial force by 9%.Moreover,ultrasonic vibrations significantly increase the volume of the pin-driven zone(PDZ)and decrease the thickness of the transition zone(TZ).The number of subgrains and deformed grains resulting from the UAFSW is higher than that from the FSW.By increase the strain level and strain gradient in the NZ,the ultrasonic vibrations can refine the grains.Ultrasonic energy is the most at the top of the NZ,and gradually reduces along the thickness of the plate.The difference in strengths between the FSW and the UAFSW joints after post-weld natural aging(PWNA)is small.However,the elongation of the UAFSW is8.8%higher than that of the FSW(PWNA for 4320 h).Fracture surface observation demonstrates that all the specimens fail by ductile fracture,and the fracture position of the UAFSW joint changes from HAZ(PWNA for 120 h)to NZ(PWNA for 720 and 4320 h).

Magneto-Transport and Shubnikov–de Haas Oscillations in the Type-Ⅱ Weyl Semimetal Candidate NbIrTe4 Flake

We report on magnetoresistance, Hall effect, and quantum Shubnikov–de Haas oscillation(SdH) experiments in NbIrTe4 single crystals, which was recently predicted to be a type-II Weyl semimetal. NbIrTe4 manifests a non-saturating and parabolic magnetoresistance at low temperatures. The magneto-transport measurements show that NbIrTe4 is a multiband system. The analysis of the SdH oscillations reveals four distinct oscillation frequencies. Combined with the density-functional theory calculations, we show that they come from two types of Fermi surfaces: electron pocket E1 and hole pocket H2.

CH4 Gas Extraction by CO2: Substitution in Clathrate Hydrate through Bimolecular Iteration

Methane clathrate hydrate(MCH)is a promising energy resource,but controllable extraction of CH4 from MCH remains a challenge.Gradually replacing CH4 in MCH with CO2 is an attractive scheme,as it is cost efficient and mitigates the environmentally harmful effects of CO2 by sequestration.However,the practicable implementation of this method has not yet been achieved.In this study,using in situ neutron diffraction,we confirm that CH4 in the 51262 cages of bulk structure-I(si)MCH can be substituted by gaseous CO2 under high pressure and low temperature with a high substitution ratio(~44%)while conserving the structure of the hydrate framework.First-principles calculations indicate that CO2 binds more strongly to the 51262 cages than methane does,and that the diffusion barrier for CH4 is significantly lowered by an intermediate state in which one hydrate cage is doubly occupied by CH4 and CO2.Therefore,exchange of CO2 for CH4 in MCH is not only energetically favorable but also kinetically feasible.Experimental and theoretical studies of CH4/CO2 substitution elucidate a method to harness energy from these combustible ice resources.

Giant ultrafast dichroism and birefringence with active nonlocal metasurfaces

Switching of light polarization on the sub-picosecond timescale is a crucial functionality for applications in a variety of contexts,including telecommunications,biology and chemistry.The ability to control polarization at ultrafast speed would pave the way for the development of unprecedented free-space optical links and of novel techniques for probing dynamical processes in complex systems,as chiral molecules.Such high switching speeds can only be reached with an all-optical paradigm,i.e.,engineering active platforms capable of controlling light polarization via ultrashort laser pulses.Here we demonstrate giant modulation of dichroism and birefringence in an all-dielectric metasurface,achieved at low fluences of the optical control beam.This performance,which leverages the many degrees of freedom offered by all-dielectric active metasurfaces,is obtained by combining a high-quality factor nonlocal resonance with the giant third-order optical nonlinearity dictated by photogenerated hot carriers at the semiconductor band edge.

V_(2)CT_(X) MXene Sphere for Aqueous Ion Storage

Despite the remarkable ion-hosting capability of MXenes,their electrochemical performance is restricted to the ion shuttle barrier stemming from the capacious surface and the sluggish chemical activity of intrinsic transition metal layers.Herein,we construct a vertically aligned array of V_(2)CT_(X) flakes utilizing a carbon sphere template(V_(2)CT_(X)@CS),with the interlayer galleries outward facing the external electrolyte,to shorten the diffusion length and mitigate the ion shuttle barrier.Moreover,we leverage the high sensitivity of V_(2)CT_(X) flakes to the water-oxygen environment,fully activating the masked active sites of transition metal layers in an aqueous environment via continuous electrochemical scanning.Aqueous V_(2)CT_(X)@CS/Zn battery delivers a novel capacity enhancement over 42,000 cycles at 10 A g^(−1).After activation,the capacity reaches up to 409 mAh g^(−1) V_(2)CT_(X) at 0.5 A g^(−1) and remains at 122 mAh g^(−1) V_(2)CT_(X) at 18 A g^(−1).With a 0.95-V voltage plateau,the energy density of 330.4 Wh kg^(−1) V_(2)CT_(X) surpasses previous records of aqueous MXene electrodes.

Polycation-functionalized gold nanodots with tunable near-infrared fluorescence for simultaneous gene delivery and cell imaging

Near-infrared （NIR） fluorescent metal nanodots may have significant advantages in biological detection and bioimaging. Herein, we introduce tunable near-infrared fluorescent gold nanodots （AuNDs） protected by branched polyethylenimine （PEI） modified by surface segmental attachment of sulfhydryl groups （PEI-SH）, abbreviated as PEI-SH-AuNDs, for simultaneous gene delivery and cell imaging. The modified PEI endows the resultant PEI-SH-AuNDs with the following excellent advantages. Sulfhydryl groups of PEI-SH anchor to the surface of AuNDs, and such polycations with amine groups give PEI-SH-AuNDs remarkable stability. The cationic polymer PEI-SH with positive charges enables PEI-SH-AuNDs to perform gene delivery, and the gene transfection efficiency can reach 22.8%. Moreover, the fluorescence of PEI-SH-AuNDs is tunable from visible red light （wavelength 609 nm） to NIR light （wavelength 811 run） via an increase in the size of AuNDs. PEI-SH-AuNDs yielded gene transfection efficiency similar to that of commercial PEI, but showed much lower cytotoxicity and much greater red-shift fluorescence. With excellent photoluminescent properties, such multifunctional fluorescent PEI-SH-AuNDs hold promise in applications to bioimaging and as ideal fluorescent probes for tracking gene transfection behavior.

Glycidyl methacrylate-compatibilized poly(lactic acid)/hemp hurd biocomposites： Processing, crystallization, and thermo-mechanical response

Poly（lactic acid）-based biocomposites were developed with hemp hurd （Cannabis sativa L.） with grafting-based interfacial compatibilization. Poly（lactic acid） was extruded with hemp hurd and glycidyl methacrylate as the polymer/hurd interfacial compatibilizer, and injection molded. Interfacial compatibility between poly（lactic acid） and hemp hurd increased with grafted glycidyl methacrylate in comparison to the non-compatibilized control, as corroborated by scanning electron microscopy fractog- raphy and mechanical analysis, which showed increases in the glycidyl methacrylate-grafted 20% （w/w） hemp hurd/poly（lactic acid） biocomposite, retaining 94% of the neat polymer strength, with increases in crystallinity, and showing a range of thermo-mechanical properties desirable for rigid biocomposite aoolications.

Asymmetric MXene/monolayer transition metal dichalcogenide heterostructures for functional applications

A versatile two-dimensional(2D)molecular bilayer heterostructure of asymmetric MXene/monolayer transition metal dichalcogenide(aMXene/mTMDC)with a high interfacial built-in electric field is here simulated,where aMXene is an aMXene with the top or bottom electronegative atom plane of MXene removed.The asymmetric structural design of aMXene leads to a high dipole moment perpendicular to the 2D molecular plane.Although the unpassivated metal atoms in the aMXene are unstable and electropositive,coupling them to the electronegative chalcogenide atoms in an aMXene/mTMDC bilayer resolves this deficiency.The dipole field tunable by the specific composition of aMXene/mTMDC is leveraged to engineer unusual band structures,band alignments,and charge redistribution/injection in the bilayer.The simulated design of several aMXene/mTMDC bilayers for possible use in spintronics,microelectronics/optoelectronics,and catalysis/photocatalysis are shown.