Influence of Mo on the Fe:Mo:C nanocatalyst thermodynamics for single-walled carbon nanotube growth

Curtarolo, Stefano; Awasthi, Neha; Jiang, Aiqin; Bolton, Kim; Tokune, Toshio; Harutyunyan, Avetik R.

doi:10.1103/physrevb.78.054105

Cited by 30 publications

(35 citation statements)

References 62 publications

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“…8 Thermodynamic calculations suggested that Mo 2 C enhances the activity of Fe-Mo NPCs by releasing free iron atoms while the formation of Fe carbides such as Fe 3 C and (Fe,Mo) 23 C 6 interferes with the growth of single-walled CNTs (SWNTs). 33 Contrary to these arguments, our ETEM study on Mo-added Fe-catalyzed CVD has shown that molybdenum leads to (Fe,Mo) 23 C 6 -type carbide NPCs and that Mo 2 C is not observed in our CVD condition. On the other hand, several authors suggested that molybdenum inhibits the diffusion of metal species such as Co on substrates, keeping the size of NPCs suitable for the growth of SWNTs.…”

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confidence: 69%

Atomic-Scale Analysis on the Role of Molybdenum in Iron-Catalyzed Carbon Nanotube Growth

et al. 2009

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We have elucidated the synergetic role played by molybdenum in iron-catalyzed chemical vapor deposition growth of carbon nanotubes (CNTs) by in situ environmental transmission electron microscopy. Molybdenum can be well accommodated by Fe-based carbide nanoparticle catalysts of M(23)C(6)-type structure (M = Fe and Mo). We have also shown that molybdenum suppresses the nucleation of iron compounds that are known to exhibit no catalytic activity for the growth of CNTs.

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confidence: 69%

Atomic-Scale Analysis on the Role of Molybdenum in Iron-Catalyzed Carbon Nanotube Growth

et al. 2009

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“…Size-induced stabilization present at the nanoscale 44,45 may promote stability at higher temperature for nanodispersed precipitates. Although the mechanical properties would not modify the solidsolution Mg-Li appreciably, the overall effect in thermal and electric transport can be dramatic, as it has been shown for nanoprecipitates in semiconducting materials.…”

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confidence: 99%

Ordered magnesium-lithium alloys: First-principles predictions

2010

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Magnesium-lithium ͑Mg-Li͒ alloys are among the lightest structural materials. Although considerable work has been done on the Mg-Li system, little is known regarding potential ordered phases. A first and rapid analysis of the system with the high-throughput method reveals an unexpected wealth of potentially stable low-temperature phases. Subsequent cluster expansions constructed for bcc and hcp superstructures extend the analysis and verify our high-throughput results. Of particular interest are those structures with greater than 13 at. % lithium, as they exhibit either partial or complete formation as a cubic structure. Order-disorder transition temperatures are predicted by Monte Carlo simulations to be in the range 200-500 K. I. MOTIVATION AND BACKGROUNDEmerging technologies increasingly depend on the production of ultralight-weight materials. Magnesium-lithium ͑Mg-Li͒ alloys are the lightest metallic alloys, having densities near that of plastics, 1-3 and are strong enough to be used in a variety of high-performance applications. In particular, Mg-Li alloys are good candidates for material applications in industries such as aerospace and automotive manufacturing. 4 As an alloying agent in magnesium, lithium is advantageous principally because of its low density and cubic crystal structure. The addition of lithium converts the hexagonalclose-packed ͑hcp͒ structure of natural magnesium to a more ductile and formable body-centered-cubic ͑bcc͒ alloy. Addition of 13 at. % Li partially converts the alloy to a cubic structure and content exceeding 33 at. % results in total conversion. 5 Although the Mg-Li system has been studied extensively, 5-11 evidence suggesting the formation of ordered phases is notably sparse. Diffusionless transformations of the martensitic type have been observed in pure Li, and similar transformations occur in low-temperature magnesium alloyed lithium at certain concentrations. 11,12 Binary ordered phases have not been conclusively identified, however, and any instances contained in the literature are indeterminate. 6,9,13,14 The results of high-throughput ͑HT͒ ab initio calculations performed with the AFLOW package ͑described later͒ show, however, that the heat of formation is negative for a large number of potential structure types, implying the existence of at least one thermodynamically stable ordered phase ͑Fig. 1͒. II. FIRST-PRINCIPLES METHODFollowing the HT results, we have made predictions of Mg-Li ordered phases using the cluster-expansion ͑CE͒ method-a first-principles-based approach in which input data is mapped to a truncated Ising-type Hamiltonian. The configurational Hamiltonian allows for a fast ground-state search ͑GSS͒ over many derivative superstructures. 16 The CE method was applied to the Mg and Li lattice configurations ͑bcc and hcp, respectively͒. Although minimum-energy configurations may exist outside those considered, superstructures derived from the parent lattices of the alloy constituents generally include the lowest-energy configurations. This assumption is ...

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“…Surface segregation may also change at small particle sizes ͑less than ϳ2 nm in diameter͒ as the surface energy changes 42 and surfacetension effects might become relevant. 43,44 These approximations could affect the equilibrium stability 45,46 if the magnitude of the segregation energies were not as strong as the ones we found ͑e.g., the smallest ͉ Fe ͑1͒ Cu ͉ / k B Ӎ 4677 K͒.…”

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First principles study of Ag, Au, and Cu surface segregation in FePt-L1

Chepulskii

Curtarolo

2010

Applied Physics Letters

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Doping FePt nanoparticles could be a possible approach to achieve high L1 0 order and magnetic anisotropy. To address stability, first-principles studies of surface segregation of dilute Ag/Au/Cu solutes at and near the ͑001͒/͑100͒/͑111͒ surfaces of FePt-L1 0 are performed. It is found that a strong surface segregation tendency at first outer layer is present in all the cases. For Cu, segregation is less than half of Ag and Au. Ag and Cu segregate to Fe sites at surfaces and preferentially substitute for Fe in the bulk, whereas Au substitutes for Fe at surfaces and for Fe and Pt in the bulk. © 2010 American Institute of Physics. ͓doi:10.1063/1.3522652͔In the past decade, FePt nanoparticles have been extensively investigated in view of possible future applications as an ultrahigh-density information-storage medium and highperformance permanent magnets. [1][2][3][4][5][6] The critical issue for information-storage application is the presence of magnetic anisotropy offering sufficiently large thermal stability. In FePt, a high magnetic anisotropy is guaranteed by an ordered L1 0 phase. However, experimental observations 4-6 have shown a difficulty in obtaining a high degree of L1 0 order in FePt nanoparticles annealed at T Շ 600°C with diameter less than ϳ4 nm. The phenomenon has been explained with size, kinetic, and surface segregation effects. [7][8][9][10][11][12][13] One of the possible approaches to achieve high L1 0 order and a correspondingly high magnetic anisotropy is by doping FePt nanoparticles with a third element. 1,3 Atomic species such as Ag, [14][15][16][17][18][19][20] Au,17,[19][20][21][22][23][24][25] and Cu 25-27 have been previously tested. To follow this approach, it is imperative to determine whether dopants concentrate inside the particle cores or segregate at the surfaces. In the latter case, the additional surface vacancies generated by the atoms rearranging on the surface during segregation upon annealing might increase Fe and Pt mobilities and help the particles to reach their L1 0 equilibrium. 16,21,27 Moreover, modeling and explaining surface segregation phenomena are important to understand catalysis, oxidation, and corrosion in nanostructured systems with high surface to volume ratio.In this letter, we study the segregation of dilute Ag, Au, and Cu solutes on and near the ͑001͒, ͑100͒, and ͑111͒ surfaces of FePt crystals with perfect L1 0 order ͑directions are defined with respect to Ref. 9͒. The results can also be used to draw conclusions regarding surface segregation in FePt nanocrystals with ͑001͒ and ͑111͒ facets such as cubes, tetrahedrons, octahedrons, cubeoctahedrons, truncated cubes, and the truncated octahedrons experimentally observed. [28][29][30] We consider ͑001͒, ͑100͒, and ͑111͒ slabs with perfect L1 0 order. For the ͑100͒ and ͑111͒ cases we choose the systems to have eight layers, while for the ͑001͒ slabs we consider nine layers ͑see Fig. 1 of Ref. 9͒. The vacuum thickness between the periodic replica of the slabs is fixed at ϳ12 Å. One substitutional impurity of ...

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Influence of Mo on the Fe:Mo:C nanocatalyst thermodynamics for single-walled carbon nanotube growth

Cited by 30 publications

References 62 publications

Atomic-Scale Analysis on the Role of Molybdenum in Iron-Catalyzed Carbon Nanotube Growth

Atomic-Scale Analysis on the Role of Molybdenum in Iron-Catalyzed Carbon Nanotube Growth

Ordered magnesium-lithium alloys: First-principles predictions

First principles study of Ag, Au, and Cu surface segregation in FePt-L1

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