Intermetallic Nanowires Research Articles

Possible routes for the synthesis of nanowires of intermetallic compounds: The case of CeIn3

In this work, we investigated the role of different parameters in the synthesis of intermetallic nanowires of CeIn3 by the metallic-flux nanonucleation (MFNN) method such as template pore diameter, crystallization temperature, heat treatment temperature, and synthesis time. Depending on the growing parameters, we obtained CeIn3 nanowires (d ∼ 350 nm) or CeAlO3 nanotubes. For the nanowires, we observed a suppression of the CeIn3 antiferromagnetic transition from the bulk TN ∼ 10 K to the nanowire system TN ∼ 3 K, which may be associated with the dimensionality affecting the interplay between magnetic exchange interactions, crystalline electrical field, and Kondo effects. We assume that the CeAlO3 nanotubes may result from a reaction with the alumina template and consequent rare-earth oxidation. Our work shows that even it is a great challenge to find the correct growth path of a particular intermetallic compound, the MFNN method can be a promising route to obtain rare-earth based nanowires.

Ordered PtFeIr Intermetallic Nanowires Prepared through a Silica-Protection Strategy for the Oxygen Reduction Reaction.

Developing efficient and stable Pt-based oxygen reduction reaction (ORR) catalysts is a way to promote the large-scale application of fuel cells. Pt-based alloy nanowires are promising ORR catalysts, but their application is hampered by activity loss caused by structural destruction during long-term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face-centered tetragonal structure (fct-PtFeIr/C) is reported. A silica-protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as-prepared fct-PtFeIr/C exhibited superior mass activity for ORR (2.03 A mgPt -1 ) than disordered PtFeIr nanowires with face-centered cubic structure (1.11 A mgPt -1 ) and commercial Pt/C (0.21 A mgPt -1 ). Importantly, the structure and electrochemical performance of fct-PtFeIr/C were maintained after stability tests, showing the advantages of the ordered structure.

Ordered PtFeIr Intermetallic Nanowires Prepared through a Silica‐Protection Strategy for the Oxygen Reduction Reaction

AbstractDeveloping efficient and stable Pt‐based oxygen reduction reaction (ORR) catalysts is a way to promote the large‐scale application of fuel cells. Pt‐based alloy nanowires are promising ORR catalysts, but their application is hampered by activity loss caused by structural destruction during long‐term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face‐centered tetragonal structure (fct‐PtFeIr/C) is reported. A silica‐protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as‐prepared fct‐PtFeIr/C exhibited superior mass activity for ORR (2.03 A mgPt−1) than disordered PtFeIr nanowires with face‐centered cubic structure (1.11 A mgPt−1) and commercial Pt/C (0.21 A mgPt−1). Importantly, the structure and electrochemical performance of fct‐PtFeIr/C were maintained after stability tests, showing the advantages of the ordered structure.

Martensite transformation induced superplasticity and strengthening in single crystalline CoNiCrFeMn high entropy alloy nanowires: A molecular dynamics study

In this work, we report simultaneous superplasticity and strengthening in single crystalline face-centered cubic (FCC) CoNiCrFeMn high entropy alloy (HEA) nanowires through synergistic martensitic phase transformation and micro-twin nucleation as revealed by molecular dynamics simulations. Furthermore, in contrast to the irreversible martensite transformation that has been previously reported in bulk HEAs under high pressure, the martensitic transformation in HEA nanowires is found to be reversible upon reverse loading. Shape memory effects can thus be enabled in HEA nanowires, although such effects are found to be mitigated for some orientations due to stacking fault crossing. Those mechanisms are dramatically different from deformation twinning dominated superplasticity in conventional FCC metal and intermetallic nanowires. While deformation twinning is still observed in FCC HEA nanowires, three pathways are found and in particular. All the novel mechanical behaviors in FCC CoNiCrFeMn HEA nanowires reported in this study can be explained by their unique negative stacking fault and martensite energies, which may shed some light on understanding the mechanical behavior of general HEAs under more complicated loading conditions.

Morphology-controlled transformation of Cu@Au core-shell nanowires into thermally stable Cu3Au intermetallic nanowires

Multimetallic nanowires with long-range atomic ordering hold the promise of unique physicochemical properties in many applications. Here we demonstrate the synthesis and study the stability of Cu3Au intermetallic nanowires. The synthesis is achieved by using Cu@Au core-shell nanowires as precursors. With appropriate Cu/Au stoichiometry, the Cu@Au core-shell nanowires are transformed into fully ordered Cu3Au nanowires under thermal annealing. Thermally-driven atom diffusion accounts for this transformation as revealed by X-ray diffraction and electron microscopy studies. The twin boundaries abundant in the Cu@Au core-shell nanowires facilitate the ordering process. The resulting Cu3Au intermetallic nanowires have uniform and accurate atomic positioning in the crystal lattice, which enhances the nobility of Cu. No obvious copper oxides are observed in fully ordered Cu3Au nanowires after annealing in air at 200 °C, a temperature that is much higher than those observed in Cu@Au core-shell and pure Cu nanowires. This work opens up an opportunity for further research into the development and applications of intermetallic nanowires.

Disintegration of nanostructured metals with the formation of nanoparticles in electron microscope

In this paper we report on an explosive disintegration of metallic 3D samples with built-in nanoscaled hierarchical order under electron beam irradiation in a transmission electron microscope. The objects of our investigation are novel 3D mesostructures containing either FeNi3 intermetallic nanowires, or silver wafers of nanoscale thickness, or Pb–In nanorods. These structures were fabricated via a self-organization of metallic nanowires growing on templates during the pulsed electro-deposition process. The disintegration of 3D mesostructures yields an array of 2–50 nm metallic crystalline nanoparticles scattered on a holding substrate in the vicinity of the contact of the electron beam with samples. Direct atomic resolution images made in-situ reveal the monocrystalline structure of the nanoparticles. The observed rapid disintegration of 3D mesostructures in the electron beam is related to the internal energy significantly enhanced in the nanostructured samples. Possible applications of the phenomenon are discussed.

Graphene nanoribbon as an elastic damper

Heterostructures composed of dissimilar two-dimensional nanomaterials can have nontrivial physical and mechanical properties which are potentially useful in many applications. Interestingly, in some cases, it is possible to create heterostructures composed of weakly and strongly stretched domains with the same chemical composition, as has been demonstrated for some polymer chains, DNA, and intermetallic nanowires supporting this effect of two-phase stretching. These materials, at relatively strong tension forces, split into domains with smaller and larger tensile strains. Within this region, average strain increases at constant tensile force due to the growth of the domain with the larger strain, at the expense of the domain with smaller strain. Here, the two-phase stretching phenomenon is described for graphene nanoribbons with the help of molecular dynamics simulations. This unprecedented feature of graphene that is revealed in our study is related to the peculiarities of nucleation and the motion of the domain walls separating the domains of different elastic strain. It turns out that the loading–unloading curves exhibit a hysteresis-like behavior due to the energy dissipation during the domain wall nucleation and motion. Here, we put forward the idea of implementing graphene nanoribbons as elastic dampers, efficiently converting mechanical strain energy into heat during cyclic loading–unloading through elastic extension where domains with larger and smaller strains coexist. Furthermore, in the regime of two-phase stretching, graphene nanoribbon is a heterostructure for which the fraction of domains with larger and smaller strain, and consequently its physical and mechanical properties, can be tuned in a controllable manner by applying elastic strain and/or heat.

Real-Time Observations of Electrochemical Reactions in Rechargeable Energy Storage Systems

Electrodes in rechargeable batteries undergo complex electrochemically-driven phase transformations upon driving Li ions into their structure. Such phase transitions in turn affect the reversibility and stability of the battery. This presentation gives an overview of the PI’s research program on in-situ transmission electron microscopy (TEM) of battery materials. In-situ TEM has been shown to be a very powerful technique in shedding light to some of the mysteries in electrochemical performance of new materials. Various anode materials including SnO2, MnO2, ZnSb were subjected to lithiation process and the transport of Li ions was visualized within their atomic structure. For SnO2 nanowires, it was observed that the Li ion transport results in local strain development preferably along (200) or (020) plans and [001] crystallographic directions. The lithiation behavior in the presence of twin boundary defects was completely different compared to pristine state with no twin boundary defect. We showed that twin boundaries in general provide a more accessible pathway for Li ion transport. Anisotropic plastic deformation was also observed along [010] directions of MnO2 nanowires. Sb-based intermetallics, such as Zn-Sb system, which have been proved to be promising anode materials for Li-ion batteries, are also capable of storing of sodium ions. We investigated the microstructural changes and phase evolution of the Zn-Sb intermetallic nanowires using in-situ TEM. Zn-Sb alloys also exhibit a new cubic alloying phase Li2ZnSb that form by intermixing of the ABAB atomic ordering in hexagonal LiZnSb due to Li inclusion in their lattices. Our results indicate that the reaction between Zn-Sb and sodium proceeds through a different pathway during the first compared to the subsequent cycles. Atomic resolution imaging shows that NaZnSb has a layered structure, which provides channels for fast Na+ diffusion.

Ultrafast and Highly Reversible Sodium Storage in Zinc‐Antimony Intermetallic Nanomaterials

The progress on sodium‐ion battery technology faces many grand challenges, one of which is the considerably lower rate of sodium insertion/deinsertion in electrode materials due to the larger size of sodium (Na) ions and complicated redox reactions compared to the lithium‐ion systems. Here, it is demonstrated that sodium ions can be reversibly stored in Zn‐Sb intermetallic nanowires at speeds that can exceed 295 nm s−1. Remarkably, these values are one to three orders of magnitude higher than the sodiation rate of other nanowires electrochemically tested with in situ transmission electron micro­scopy. It is found that the nanowires display about 161% volume expansion after the first sodiation and then cycle with an 83% reversible volume expansion. Despite their massive expansion, the nanowires can be cycled without any cracking or facture during the ultrafast sodiation/desodiation process. In addition, most of the phases involved in the sodiation/desodiation process possess high electrical conductivity. More specifically, the NaZnSb exhibits a layered structure, which provides channels for fast Na+ diffusion. This observation indicates that Zn‐Sb intermetallic nanomaterials offer great promise as high rate and good cycling stability anodic materials for the next generation of sodium‐ion batteries.

One-Step, Facile and Ultrafast Synthesis of Phase- and Size-Controlled Pt-Bi Intermetallic Nanocatalysts through Continuous-Flow Microfluidics.

Ordered intermetallic nanomaterials are of considerable interest for fuel cell applications because of their unique electronic and structural properties. The synthesis of intermetallic compounds generally requires the use of high temperatures and multiple-step processes. The development of techniques for rapid phase- and size-controlled synthesis remains a formidable challenge. The intermetallic compound Pt1Bi2 is a promising candidate catalyst for direct methanol fuel cells because of its high catalytic activity and excellent methanol tolerance. In this work, we explored a one-step, facile and ultrafast phase- and size-controlled process for synthesizing ordered Pt-Bi intermetallic nanoparticles (NPs) within seconds in microfluidic reactors. Single-phase Pt1Bi1 and Pt1Bi2 intermetallic NPs were prepared by tuning the reaction temperature, and size control was achieved by modifying the solvents and the length of the reaction channel. The as-prepared Pt-Bi intermetallic NPs exhibited excellent methanol tolerance capacity and high electrocatalytic activity. Other intermetallic nanomaterials, such as Pt3Fe intermetallic nanowires with a diameter of 8.6 nm and Pt1Sn1 intermetallic nanowires with a diameter of 6.3 nm, were also successfully synthesized using this method, thus demonstrating its feasibility and generality.

Lithiation-induced shuffling of atomic stacks.

In rechargeable lithium-ion batteries, understanding the atomic-scale mechanism of Li-induced structural evolution occurring at the host electrode materials provides essential knowledge for design of new high performance electrodes. Here, we report a new crystalline-crystalline phase transition mechanism in single-crystal Zn-Sb intermetallic nanowires upon lithiation. Using in situ transmission electron microscopy, we observed that stacks of atomic planes in an intermediate hexagonal (h-)LiZnSb phase are "shuffled" to accommodate the geometrical confinement stress arising from lamellar nanodomains intercalated by lithium ions. Such atomic rearrangement arises from the anisotropic lithium diffusion and is accompanied by appearance of partial dislocations. This transient structure mediates further phase transition from h-LiZnSb to cubic (c-)Li2ZnSb, which is associated with a nearly "zero-strain" coherent interface viewed along the [001]h/[111]c directions. This study provides new mechanistic insights into complex electrochemically driven crystalline-crystalline phase transitions in lithium-ion battery electrodes and represents a noble example of atomic-level structural and interfacial rearrangements.

Exploring the effects of dimensionality on the magnetic properties of intermetallic nanowires

Correlated electron intermetallic bulk systems exhibit exciting phenomena, such as unconventional superconductivity, heavy fermion behavior, magnetic ordering, and quantum criticality. However, such exciting properties in related systems with reduced dimensionality are rather unexplored and unpredictable. In this work, we explore the routes for synthesizing nanowires of the intermetallic antiferromagnet compound GdIn3 by an innovative method: the metallic-flux nanonucleation (MFNN). This technique allows the simultaneous synthesis of bulk GdIn3 single crystals (TN3D=45K) and their low-dimensional (LD) analogs, which nucleate with diameter d≈200nm and length l≈30μm inside pores of an Al2O3 template. Both systems were studied by means of Energy Dispersive Spectroscopy (EDS), magnetic susceptibility, heat capacity and electron spin resonance (ESR) measurements. Interestingly, the metallic nanowires show a drastic suppression of the antiferromagnetic ordering to TNLD=4K. These observations suggest the presence of LD magnetic frustration in this compound and possibly open a new route to explore the role of low-dimensionality in strongly correlated materials.

Selective synthesis and superconductivity of In–Sn intermetallic nanowires sheathed in carbon nanotubes

We demonstrate a simple and reproducible technique to synthesize crystalline and superconducting In–Sn intermetallic nanowires sheathed in carbon nanotubes (CNTs). The method is based on the catalytic reaction of C2H2 over a mixture of both SnO2 and In2O3 particles. Importantly, tetragonal β-In3Sn and hexagonal γ-InSn4 nanowires with diameters of less than 100 nm are selectively synthesized at different SnO2 to In2O3 weight ratios. CNTs may serve as cylindrical nanocontainers for continuous growth of liquid-phased In1−xSnx nanowires during growth process as well as for their solidification into In–Sn intermetallic nanowires during the cooling process. Microscopic and spectroscopic analyses clearly reveal evidence of a core–shell structure of the CNT-sheathed In–Sn intermetallic nanowires. Magnetization measurements show that the superconducting In–Sn nanowires have a critical magnetic field higher than the value of their bulk intermetallic compounds. Our method can be adopted to the nanofabrication of analogous binary and ternary alloys.

Analytical model and molecular dynamics simulations of the size dependence of flow stress in amorphous intermetallic nanowires at temperatures near the glass transition

Molecular dynamics (MD) simulations are used to compute the flow stress of amorphous metallic nanowires that are deformed at temperatures near the glass transition. The simulations predict a strong size dependence of flow stress and predict the existence of a critical wire radius that minimizes the flow stress. Examination of the cross sections of the wires shows evidence of significant free-volume nucleation and diffusion during straining. The MD results are interpreted using a simple analytical model that assumes that the wire deforms by a combination of viscous flow, together with a diffusional deformation process in which free volume is continuously nucleated in the interior of the wire, and subsequently diffuses to the surface. The predictions of the model are in good qualitative agreement with simulation results. The analytical model is used to estimate the critical wire dimensions where this diffusional mechanism is likely to replace viscous creep at time scales that are inaccessible using MD simulations.