Ju Li

Xi'an Jiaotong University, Ch’ang-an, Shaanxi, China

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Publications (227)1490.9 Total impact

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    ABSTRACT: By using multi-scale simulation techniques, we probed the role of hydrogen-vacancy complexes on nucleation and growth of proto nano-voids upon dislocation plasticity in α-Fe. Our atomistic simulations reveal that, unlike a lattice vacancy, a hydrogen-vacancy complex is not absorbed by dislocations sweeping through the lattice. Additionally, this complex has lower lattice diffusivity; therefore, it has a lower probability of encountering and being absorbed by various lattice sinks. Hence, it can exist metastably for a rather long time. Our large-scale atomistic simulations show that when metals undergo plastic deformation in the presence of hydrogen at low homologous temperatures, the mechanically driven out-of-equilibrium dislocation processes can produce extremely high concentrations of hydrogen-vacancy complex (10-5∼10-3). Under such high concentrations, these complexes prefer to grow by absorbing additional vacancies and act as the embryos for the formation of proto nano-voids. The current work provides the possible route for the experimentally observed nano-void formation in the context of hydrogen-induced failure and also bridge the link from the atomic-scale events to the macroscopic failure.
    International Journal of Plasticity 06/2015; DOI:10.1016/j.ijplas.2015.05.017 · 5.97 Impact Factor
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    ABSTRACT: Spintronics involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. The fascinating spin-resolved properties of graphene motivate numerous researchers into the studies of spintronics in graphene and other two-dimensional (2D) materials. Silicene, silicon analog of graphene, is considered as a promising material for spintronics. Here, we present a review on the theoretical advances about the spin-dependent properties including the electric field and exchange field tunable topological properties of silicene and the corresponding spintronic device simulations.
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    ABSTRACT: At elevated temperatures, glasses crystallize via thermally activated diffusion. However, metallic glasses can also undergo deformation-induced crystallization at very low temperatures. Here we demonstrate the crystallization of Al50Fe50 metallic glasses under cyclic deformation at 50 K using molecular dynamics simulations and reveal the underlying atomic-scale processes. We demonstrate that stress-driven nonaffine atomic rearrangements, or shear diffusion transformation (SDT) events, lead to successive metabasin-to-metabasin transitions and long-range ordering. We also illustrate that the nucleation and growth of the crystal proceed via collective attachment of ordered clusters, advancing the amorphous/crystal interface in an intermittent manner. The cooperative nature of the steplike crystallization is attributed to the large activation volume of Eshelby transformations which generate as a by-product nonaffine diffusive atomic displacements that accumulate over loading cycles. The dual nature of shear (affine) and diffusion (nonaffine) in low-temperature stress-driven SDT events thus unifies inelasticity with crystallization.
    Physical Review B 06/2015; 91(21). DOI:10.1103/PhysRevB.91.214103 · 3.66 Impact Factor
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    ABSTRACT: Rejuvenation is the configurational excitation of amorphous materials and is one of the more promising approaches for improving the deformability of amorphous metals that usually exhibit macroscopic brittle fracture modes. Here, we propose a method to control the level of rejuvenation through systematic thermal processing and clarify the crucial feasibility conditions by means of molecular dynamics simulations of annealing and quenching. We also experimentally demonstrate rejuvenation level control in Zr 55 Al 10 Ni 5 Cu 30 bulk metallic glass. Our local heat-treatment recipe (rising temperature above 1.1T g , followed by a temperature quench rate exceeding the previous) opens avenue to modifying the glass properties after it has been cast and processed into near component shape, where a higher local cooling rate may be afforded by for example transient laser heating, adding spatial control and great flexibility to the processing.
    Scientific Reports 05/2015; 5. DOI:10.1038/srep10545 · 5.58 Impact Factor
  • Proceedings of the National Academy of Sciences 05/2015; 112(19):6068-6073. DOI:10.1073/pnas.1505584112 · 9.81 Impact Factor
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    ABSTRACT: Magnetic exchange driven proximity effect at a magnetic insulator / topological insulator (MI/TI) interface provides a rich playground for novel phenomena as well as a way to realize low energy dissipation quantum devices. Here we report a dramatic enhancement of proximity exchange coupling in the MI / magnetic-TI EuS / Sb$_{2-x}$V$_x$Te$_3$ hybrid heterostructure, where V doping is used to drive the TI (Sb$_{2}$Te$_3$) magnetic. We observe an artificial antiferromagnetic-like structure near the MI/TI interface, which may account for the enhanced proximity coupling. The interplay between the proximity effect and doping provides insights into controllable engineering of magnetic order using a hybrid heterostructure.
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    ABSTRACT: The trend from "smaller is stronger" to "size-independent strength plateau" is observed in the compression of spherical iron nanoparticles. When the diameter of iron nanospheres is less than a critical value, the maximum contact pressure saturates at 10.7 GPa, corresponds to a local shear stress of ≈9.4 GPa, which is comparable to the theoretical shear strength of iron. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Advanced Materials 04/2015; 27(22). DOI:10.1002/adma.201500377 · 15.41 Impact Factor
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    ABSTRACT: By prescribing asymmetric ligaments with different arrangements in elastomeric porous membranes of pre-twisted kagome lattices, the buckling instability is avoided, allowing for smooth and homogenous structural reconfiguration in a deterministic fashion. The stress-strain behaviors and negative Poisson's ratios can be tuned by the pre-twisting angles. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Advanced Materials 03/2015; 27(17). DOI:10.1002/adma.201500716 · 15.41 Impact Factor
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    ABSTRACT: The mechanical properties of a Sc75Fe25 nanoglass and monolithic metallic glass (MG) with identical chemical composition were investigated by means of nanoindentation tests and quantitative in situ compression tests and tensile tests in a transmission electron microscope. The nanoglass exhibits excellent plastic deformation ability relative to the monolithic MG. It is particularly interesting to find that the 400 nm Sc75Fe25 nanoglass exhibits a 15% plastic strain under uniaxial tension. Such a nearly uniform tensile plasticity is unprecedented among MGs of similar sample sizes. The enhanced plasticity of the nanoglass can be attributed to its unique microstructure.
    Scripta Materialia 03/2015; 98. DOI:10.1016/j.scriptamat.2014.11.010 · 2.97 Impact Factor
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    ABSTRACT: We report a combined experimental and simulation study of deformation-induced diffusion in compacted two-dimensional amorphous granular pillars, in which thermal fluctuations play negligible role. The pillars, consisting of bidisperse cylindrical acetal plastic particles standing upright on a substrate, are deformed uniaxially and quasistatically by a rigid bar moving at a constant speed. The plastic flow and particle rearrangements in the pillars are characterized by computing the best-fit affine transformation strain and non-affine displacement associated with each particle between two stages of deformation. The non-affine displacement exhibits exponential crossover from ballistic to diffusive behavior with respect to the cumulative deviatoric strain, indicating that in athermal granular packings, the cumulative deviatoric strain plays the role of time in thermal systems and drives effective particle diffusion. We further study the size-dependent deformation of the granular pillars by simulation, and find that different-sized pillars follow self-similar shape evolution during deformation. In addition, the yield stress of the pillars increases linearly with pillar size. Formation of transient shear lines in the pillars during deformation becomes more evident as pillar size increases. The width of these elementary shear bands is about twice the diameter of a particle, and does not vary with pillar size.
  • ChemInform 02/2015; 46(7). DOI:10.1002/chin.201507001
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    ABSTRACT: Lithium sulfide (Li2S) is a promising cathode material for Li-S batteries with high capacity (theoretically 1166 mAh g-1), and can be paired with non-lithium-metal anodes to avoid potential safety issues. However, the cycle life of coarse Li2S particles suffers from poor electronic conductivity and polysulfide shuttling. Here we develop a flexible slurryless nano-Li2S/reduced graphene oxide cathode paper (Li2S/rGO paper) by simple drop-coating. The Li2S/rGO paper can be directly used as a free-standing and binder-free cathode without metal substrate, which leads to significant weight savings. It shows excellent rate capability (up to 7 C) and cycle life in coin cell tests, due to the high electron conductivity, flexibility and strong solvent absorbency of rGO paper. The Li2S particles that precipitate out of the solvent on rGO have diameters 25-50nm, in contrast to the 3-5 μm coarse Li2S particles without rGO.
    Nano Letters 01/2015; 15(3). DOI:10.1021/acs.nanolett.5b00112 · 12.94 Impact Factor
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    ABSTRACT: Nanoparticle electrodes in lithium-ion batteries have both near-surface and interior contributions to their redox capacity, each with distinct rate capabilities. Using combined electron microscopy, synchrotron X-ray methods and ab initio calculations, we have investigated the lithiation pathways that occur in NiO electrodes. We find that the near-surface electroactive (Ni2+→Ni0) sites saturated very quickly, and then encounter unexpected difficulty in propagating the phase transition into the electrode (referred to as a "shrinking-core" mode). However, the interior capacity for Ni2+→Ni0 can be accessed efficiently following the nucleation of lithiation "fingers" which propagate into the sample bulk, but only after a certain incubation time. Our microstructural observations of the transition from a slow shrinking-core mode to a faster lithiation finger mode corroborate with synchrotron characterization of large-format batteries, and can be rationalized by stress effects on transport at high-rate discharge. The finite incubation time of the lithiation fingers sets the intrinsic limitation for the rate capability (and thus the power) of NiO for electrochemical energy storage devices. The present work unravels the link between the nanoscale reaction pathways and the C-rate-dependent capacity loss, and provides guidance for the further design of battery materials that favors high C-rate charging.
    Nano Letters 01/2015; 15(2). DOI:10.1021/nl5049884 · 12.94 Impact Factor
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    ABSTRACT: Through in situ scanning electron microscope microcompression tests, we demonstrated that the strain-rate sensitivity of body-centered cubic single crystal iron pillars will be reduced by one order when the pillar size was reduced from 1000 to about 200 nm. In addition, size-strengthening exponent exhibited obvious strain-rate dependence. We propose that the observed behavior is a result of the high stresses required to induce curvature bowout of dislocation arms at small sample or grain sizes, which overwhelms the lattice friction stress contribution and diminishes the role played by the mobility difference between edge and screw dislocations.
    Materials Research Letters 01/2015; 3(3):1-7. DOI:10.1080/21663831.2014.999953
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    ABSTRACT: Dislocations are topological line defects in 3D crystals. Same-sign dislocations repel according to Frank's rule |b1+b2|2>|b1|2+|b2|2. This rule is broken for dislocations in van der Waals (vdW) layers, which possess crystallographic Burgers vector as ordinary dislocations, but feature "surface ripples" due to the ease of bending and weak vdW adhesion of the atomic layers. We term these line defects "ripplocations" in accordance to their dual "surface ripple" and "crystallographic dislocation" characters. Unlike conventional ripples on non-crystalline (vacuum, amorphous or fluid) substrates, ripplocations tend to be very straight, narrow, and crystallographically oriented. The self-energy of surface ripplocations scales sublinearly with , indicating that same-sign ripplocations attract and tend to merge, opposite to conventional dislocations. Using in situ transmission electron microscopy (TEM), we directly observed ripplocation generation and motion when few-layer MoS2 films were lithiated or mechanically processed. Being a new subclass of elementary defects, ripplocations are expected to be important in the processing and defect engineering of vdW layers.
    Nano Letters 01/2015; 15(2). DOI:10.1021/nl5045082 · 12.94 Impact Factor
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    ABSTRACT: The isolation of the two-dimensional semiconductor molybdenum disulphide introduced a new optically active material possessing a band gap that can be facilely tuned via elastic strain. As an atomically thin membrane with exceptional strength, monolayer molybdenum disulphide subjected to biaxial strain can embed wide band gap variations overlapping the visible light spectrum, with calculations showing the modified electronic potential emanating from point-induced tensile strain perturbations mimics the Coulomb potential in a mesoscopic atom. Here we realize and confirm this 'artificial atom' concept via capillary-pressure-induced nanoindentation of monolayer molybdenum disulphide from a tailored nanopattern, and demonstrate that a synthetic superlattice of these building blocks forms an optoelectronic crystal capable of broadband light absorption and efficient funnelling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei. Such two-dimensional semiconductors with spatially textured band gaps represent a new class of materials, which may find applications in next-generation optoelectronics or photovoltaics.
    Nature Communications 01/2015; 6:7381. DOI:10.1038/ncomms8381 · 10.74 Impact Factor
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    ABSTRACT: Stress-driven grain boundary (GB) migration has been evident as a dominant mechanism accounting for plastic deformation in crystalline solids. Using molecular dynamics (MD) simulations on a Ti bicrystal model, we show that a uniaxial stress-driven coupling is associated with the recently observed 90° GB reorientation in shock simulations and nanopillar compression measurements. This is not consistent with the theory of shear-induced coupled GB migration. In situ atomic configuration analysis reveals that this GB motion is accompanied by the glide of two sets of parallel dislocation arrays, and the uniaxial stress-driven coupling is explained through a composite action of symmetrically distributed dislocations and deformation twins. In addition, the coupling factor is calculated from MD simulations over a wide range of temperatures. We find that the coupled motion can be thermally damped (i.e., not thermally activated), probably due to the absence of the collective action of interface dislocations. This uniaxial coupled mechanism is believed to apply to other hexagonal close-packed metals.
    Acta Materialia 01/2015; 82:295–303. DOI:10.1016/j.actamat.2014.09.010 · 3.94 Impact Factor
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    ABSTRACT: Quantum spin Hall (QSH) effect materials feature edge states that are topologically protected from backscattering. However, the small band gap in materials that have been identified as QSH insulators limits applications. We use first-principles calculations to predict a class of large-gap QSH insulators in two-dimensional transition metal dichalcogenides with 1T' structure, namely, 1T'-MX2 with M = (tungsten or molybdenum) and X = (tellurium, selenium, or sulfur). A structural distortion causes an intrinsic band inversion between chalcogenide-p and metal-d bands. Additionally, spin-orbit coupling opens a gap that is tunable by vertical electric field and strain. We propose a topological field effect transistor made of van der Waals heterostructures of 1T'-MX2 and two-dimensional dielectric layers that can be rapidly switched off by electric field through a topological phase transition instead of carrier depletion. Copyright © 2014, American Association for the Advancement of Science.
    Science 12/2014; 346(6215):1344-1347. DOI:10.1126/science.1256815 · 31.48 Impact Factor
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Publication Stats

7k Citations
1,490.90 Total Impact Points

Institutions

  • 2010–2015
    • Xi'an Jiaotong University
      • State Key Laboratory for Mechanical Behavior of Materials
      Ch’ang-an, Shaanxi, China
  • 1995–2015
    • Massachusetts Institute of Technology
      • • Department of Materials Science and Engineering
      • • Department of Nuclear Science and Engineering
      Cambridge, Massachusetts, United States
  • 2008–2013
    • University of Pennsylvania
      • • Department of Chemistry
      • • Department of Materials Science and Engineering
      Philadelphia, Pennsylvania, United States
    • Iowa State University
      • Department of Physics and Astronomy
      Ames, Iowa, United States
  • 2008–2012
    • William Penn University
      Filadelfia, Pennsylvania, United States
  • 2011
    • Georgia Institute of Technology
      Atlanta, Georgia, United States
  • 2003–2008
    • The Ohio State University
      • Department of Materials Science and Engineering
      Columbus, Ohio, United States