Ju Li

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

Are you Ju Li?

Claim your profile

Publications (220)1454.14 Total impact

  • [Show abstract] [Hide abstract]
    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; DOI:10.1002/adma.201500377 · 15.41 Impact Factor
  • [Show abstract] [Hide abstract]
    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; DOI:10.1002/adma.201500716 · 15.41 Impact Factor
  • Scripta Materialia 03/2015; 98. DOI:10.1016/j.scriptamat.2014.11.010 · 2.97 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • [Show abstract] [Hide abstract]
    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
  • Source
  • Materials Research Letters 01/2015; DOI:10.1080/21663831.2014.999953
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate by high resolution low temperature electron energy loss spectroscopy (EELS) measurements that the long range ferromagnetic (FM) order in vanadium (V)-doped topological insulator Sb$_2$Te$_3$ has the nature of van Vleck-type ferromagnetism. The positions and the relative amplitudes of two core-level peaks (L$_3$ and L$_2$) of the V EELS spectrum show unambiguous change when the sample is cooled from room temperature to T=10K. Magnetotransport and comparison of the measured and simulated EELS spectra confirm that these changes originate from onset of FM order. Crystal field analysis indicates that in V-doped Sb$_2$Te$_3$, partially filled core states contribute to the FM order. Since van Vleck magnetism is a result of summing over all states, this magnetization of core level verifies the van Vleck-type ferromagnetism in a direct manner.
    Physical Review Letters 12/2014; 114(14). DOI:10.1103/PhysRevLett.114.146802 · 7.73 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we discuss the transformation of a sheet of material into a wide range of desired shapes and patterns by introducing a set of simple cuts in a multilevel hierarchy with different motifs. Each choice of hierarchical cut motif and cut level allows the material to expand into a unique structure with a unique set of properties. We can reverse-engineer the desired expanded geometries to find the requisite cut pattern to produce it without changing the physical properties of the initial material. The concept was experimentally realized and applied to create an electrode that expands to >800% the original area with only very minor stretching of the underlying material. The generality of our approach greatly expands the design space for materials so that they can be tuned for diverse applications.
    Proceedings of the National Academy of Sciences 11/2014; 111(49). DOI:10.1073/pnas.1417276111 · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We develop a new envelope-function formalism to describe electrons in slowly-varying inhomogeneously strained semiconductor crystals. A coordinate transformation is used to map a deformed crystal back to geometrically undeformed structure with deformed crystal potential. The single-particle Schr\"{o}dinger equation is solved in the undeformed coordinates using envelope function expansion, wherein electronic wavefunctions are written in terms of strain-parametrized Bloch functions modulated by slowly varying envelope functions. Adopting local approximation of electronic structure, the unknown crystal potential in Schr\"{o}dinger equation can be replaced by the strain-parametrized Bloch functions and the associated strain-parametrized energy eigenvalues, which can be constructed from unit-cell level ab initio or semi-empirical calculations of homogeneously deformed crystals at a chosen crystal momentum. The Schr\"{o}dinger equation is then transformed into a coupled differential equation for the envelope functions and solved as a generalized matrix eigenvector problem. As the envelope functions are slowly varying, coarse spatial or Fourier grid can be used to represent the envelope functions, enabling the method to treat relatively large systems. We demonstrate the effectiveness of this method using a one-dimensional model, where we show that the method can achieve high accuracy in the calculation of energy eigenstates with relatively low cost compared to direct diagonalization of Hamiltonian. We further derive envelope function equations that allow the method to be used empirically, in which case certain parameters in the envelope function equations will be fitted to experimental data.
    Journal of Physics Condensed Matter 10/2014; 26(45). DOI:10.1088/0953-8984/26/45/455801 · 2.22 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In nanotechnology, small-volume metals with large surface area are used as electrodes, catalysts, interconnects and antennae. Their shape stability at room temperature has, however, been questioned. Using in situ high-resolution transmission electron microscopy, we find that Ag nanoparticles can be deformed like a liquid droplet but remain highly crystalline in the interior, with no sign of dislocation activity during deformation. Surface-diffusion-mediated pseudoelastic deformation is evident at room temperature, which can be driven by either an external force or capillary-energy minimization. Atomistic simulations confirm that such highly unusual Coble pseudoelasticity can indeed happen for sub-10-nm Ag particles at room temperature and at timescales from seconds to months.
    Nature Material 10/2014; DOI:10.1038/nmat4105 · 36.43 Impact Factor
  • Source
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ammonia (NH3) nitridation on an Fe surface was studied by combining density functional theory (DFT) and kinetic Monte Carlo (kMC) calculations. A DFT calculation was performed to obtain the energy barriers (Eb) of the relevant elementary processes. The full mechanism of the exact reaction path was divided into five steps (adsorption, dissociation, surface migration, penetration, and diffusion) on an Fe (100) surface pre-covered with nitrogen. The energy barrier (Eb) depended on the N surface coverage. The DFT results were subsequently employed as a database for the kMC simulations. We then evaluated the NH3 nitridation rate on the N pre-covered Fe surface. To determine the conditions necessary for a rapid NH3 nitridation rate, the eight reaction events were considered in the kMC simulations: adsorption, desorption, dissociation, reverse dissociation, surface migration, penetration, reverse penetration, and diffusion. This study provides a real-time-scale simulation of NH3 nitridation influenced by nitrogen surface coverage that allowed us to theoretically determine a nitrogen coverage (0.56 ML) suitable for rapid NH3 nitridation. In this way, we were able to reveal the coverage dependence of the nitridation reaction using the combined DFT and kMC simulations.
    The Journal of Chemical Physics 10/2014; 141(13):134108. DOI:10.1063/1.4896610 · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Although lithium-sulfur batteries exhibit a high initial capacity, production cost and lack of cyclability are major limitations. Here we report a liquid-based, low-cost and reliable synthesis method of lithium-sulfur composite cathode with improved cyclability. An open network of Conductive Carbon Black nanoparticles (Cnet) is infused with sulfur (Snet) to form sponge-like networks (Cnet + Snet). Initially, Snet is open to the outside, allowing liquid electrolyte to infiltrate and impart Snet Li+ conductivity. During lithiation, Cnet could accommodate the volume expansion of Snet without largely losing electrical contact. During delithiation, the carbon nanoparticles would preferably flocculate on outer surface due to polysulfide dissolution an depletion of sulfur, to form a passivation layer that still allows Li+ exchange, but preventing more polysulfides from getting out, thus slowing the leaching of polysulfides into bulk electrolyte liquid. The plausibility of carbonaceous passivation layer was checked using an extra carbon deposition layer to achieve an improved performance of ~400 mAh/g after 250 cycles under a high rate 2.0 C. A 763 mAh/g discharge specific capacity of this sulfur nanosponge cathode (abbreviated as “SULFUN”) was obtained after 100 cycles under a rate of 0.2 C. 520 mAh/g and 290 mAh/g discharge capacities were attained after 300 and 500 cycles, respectively, making this cathode material attractive for powering portable electronics.
    10/2014; 2(46). DOI:10.1039/C4TA04759A

Publication Stats

7k Citations
1,454.14 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
  • 2013
    • Korea University
      • Department of Materials Science and Engineering
      Sŏul, Seoul, South Korea
  • 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
  • 2011
    • Georgia Institute of Technology
      Atlanta, Georgia, United States
  • 2008–2011
    • William Penn University
      Filadelfia, Pennsylvania, United States
  • 2003–2008
    • The Ohio State University
      • Department of Materials Science and Engineering
      Columbus, Ohio, United States