X.-P. Tang

Electrochemical intercalation of single-walled carbon nanotubes with lithium

Abstract Single-walled carbon nanotubes (SWNT) synthesized by laser ablation were electrochemically intercalated with lithium. As-grown SWNTs showed a reversible saturation composition of Li 1.2 C 6 (450 mAh g −1 ). After removing the impurity phases by filtration, the reversible saturation composition increased to Li 1.6 C 6 (600 mAh g −1 ), significantly higher than the ideal value of LiC 6 (372 mAh g −1 ) for graphite. All the SWNT materials showed large irreversible capacities and voltage hysteresis. Upon processing the nanotubes by ball-milling, the reversible Li capacity increased to 1000 mAh g −1 (Li 2.7 C 6 ) while the irreversible capacity decreased to 650 mAh g −1 .

Enhanced saturation lithium composition in ball-milled single-walled carbon nanotubes

Abstract The effects of processing on the structure and morphology of single-walled carbon nanotubes (SWNT) and their electrochemical intercalation with lithium were investigated. Purified SWNTs were processed by impact ball-milling and were electrochemically intercalated with lithium. The reversible saturation Li composition increased from Li 1.7 C 6 in purified SWNTs to Li 2.7 C 6 after 10 min of milling. The irreversible capacity decreased from Li 3.2 C 6 to Li 1.3 C 6 . Electron microscopy, Raman and X-ray diffraction measurements indicated that ball-milling induced disorder within the bundles and fractured the nanotubes.

Diffusion mechanisms in metallic supercooled liquids and glasses

The mechanisms of atomic transport in supercooled liquids and the nature of the glass transition are long-standing problems. Collective atomic motion is thought to play an important role in both phenomena. A metallic supercooled liquid represents an ideal system for studying intrinsic collective motions because of its structural similarity to the “dense random packing of spheres” model, which is conceptually simple. Unlike polymeric and network glasses, metallic supercooled liquids have only recently become experimentally accessible, following the discovery of bulk metallic glasses. Here we report a 9Be nuclear magnetic resonance study of Zr-based bulk metallic glasses in which we investigate microscopic transport in supercooled liquids around the glass transition regime. Combining our results with diffusion measurements, we demonstrate that two distinct processes contribute to long-range transport in the supercooled liquid state: single-atom hopping and collective motion, the latter being the dominant process. The effect of the glass transition is clearly visible in the observed diffusion behaviour of the Be atoms.

Lithium intercalation into etched single-wall carbon nanotubes

Abstract The effects of structure and morphology on lithium storage in single-wall carbon nanotubes (SWNTs) were studied by electrochemistry. SWNTs were chemically etched and were intercalated with Li. The reversible Li storage capacity increased from LiC6 in close-end SWNTs to LiC3 after etching, which is twice the value observed in Li intercalated graphite. The enhanced capacity is attributed to Li diffusion into the interior of the SWNTs through the opened ends and sidewall defects.

Devitrification of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass studied by XRD, SANS, and NMR

Abstract The crystallization process of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 bulk metallic glass was investigated by X-ray diffraction (XRD), small-angle neutron scattering, and 9 Be nuclear magnetic resonance. Upon annealing near the glass transition and up to a temperature near 673 K, a Be-containing crystalline phase forms after sufficient decomposition of the supercooled liquid. The XRD pattern of this Be-containing phase is consistent with icosahedral symmetry. The small length scale of the decomposed supercooled liquid structure limits the grain size of this phase, which gives rise to broad XRD peaks. Above 673 K, annealing produces Be 2 Zr and Zr 2 Cu, along with other crystalline phases.

Lithium storage in single wall carbon nanotubes

The effects of structure and morphology on lithium storage in single wall carbon nanotubes (SWNTs) were studied by electrochemistry, x-ray diffraction and nuclear magnetic resonance (NMR) techniques. Purified SWNT bundles were chemically etched to variable lengths and were reacted with Li via the electrochemical and solid state routes. The reversible Li storage capacity increased from LiC6 in close-end SWNTs to LiC3 after etching. The increase is attributed to diffusion of the Li ions into the interior space of the individual SWNTs through the open ends and defects on the sidewalls.

Probing Slow Atomic Motions in Metallic Glasses using NMR

We report a nuclear magnetic resonance (NMR) study of slow atomic motions in Zr-Ti-Cu- Ni-Be bulk metallic glasses. The employed 9 Be spin alignment echo technique is able to probe Be motions with jump rate below 0.1 Hz. It was found that the Be motion is spatially homogeneous. The jump rate follows a perfect Arrhenius temperature dependence. The measured activation enthalpy of 1.2 eV is nearly identical to that obtained by Be diffusivity measurement using elastic backscattering (EBS); this indicates that energy barriers are the same for short and long range Be motions. The present work provides direct experimental evidences that exclude vacancy-assisted and interstitial diffusion mechanisms for Be motions in these systems. The result is interpreted in terms of the spread-out free volume fluctuation mechanism.