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The effect of film thickness on water uptake and structure in ultra-thin Nafion is probed via in situ neutron reflectometry for a series of 10 films with thicknesses ranging from 5 to 153 nm. Observed interfacial lamellae are used to understand anomalous transport limitations in such films. Results show three distinct thickness regimes: (i) in the truncated regime (

Carbon-based cryosorbers are generally synthesized in the form of powders, which compromises the volumetric capacity in gas storage applications. Here we report the synthesis of monolithic carbide-derived carbon (CDC) by chlorination of fully-dense ceramic titanium carbide plates. Volume change is minimal, consistent with conformal transformation from TiC to CDC, and the weight loss is consistent with nearly 100% conversion. The resulting materials have a microporous carbon structure with little or no macroporosity and exhibit enhanced volumetric gas storage capacity compared to powder equivalents. Optimized volume uptakes are 35 g L−1 at −196 °C and 60 bar for H2, 193 V(STP) v−1 at 35 bar and 219 V(STP) v−1 at 60 bar (25 °C) for CH4. Monolithic CDCs thus offer potential as gas storage media for on-board fuel-cells and other applications.

Development of high-capacity hydrogen-storage systems utilizing physisorption at high pressure and low temperature is hindered by poor understanding of the pore size/shape requirements for achieving the maximum hydrogen uptake. Tuning the carbon structure and pore size of carbide-derived carbons (CDCs) with high accuracy by using different starting carbides, chlorination temperatures and activation temperatures allows rational design of carbon materials with increased hydrogen-storage capacity. Systematic experimental investigation of a large number of CDCs with controlled pore size distributions and specific surface area (SSA) shows that pores larger than ∼1.5 nm contribute little to hydrogen storage. It has been experimentally demonstrated that, just as at ambient pressure, pores of 0.6–0.7 nm in diameter provide the largest H 2 uptake per unit SSA at elevated pressures and liquid nitrogen temperatures. The effect of pore size was stronger than the effect of surface chemistry on the hydrogen uptake.

Carbide-derived carbons (CDC) allow a precise control over the pore size through the selection of the carbide precursor and varying of the synthesis conditions. However, their pore volume is limited by the carbide stoichiometry. While activation of carbons derived from various organic precursors has been widely studied, this process may similarly be able to increase the pore volume and specific surface area of CDC. Oxidation of carbide-derived carbon in air and CO2 at different temperatures and times allows for significant increase in pore volume and specific surface area as well as control over average pore size with subnanometer accuracy. The effect of activation and associated changes in the pore volume and surface area on the hydrogen uptake are also discussed.

Carbide-derived carbons (CDCs) produced by chlorination of carbides offer great potential for precise pore size control at the atomic level, making them attractive candidates for energy storage media. CDCs activated with CO 2 or KOH possess distinct improvements in porosity, displaying specific surface areas above 3000 m 2 g −1 and pore volumes above 1.3 cm 3 g −1 . These correspond to gravimetric methane uptake of 16 wt% at 35 bar and 25 °C, close to the currently best reported material PCN-14, a metal-organic framework (MOF), at 35 bar and 17 °C or KOH activated anthracite at 35 bar and 25 °C. The best excess gravimetric methane uptake is obtained with a TiC-derived CDC activated with CO 2 at 975 °C for 2 h, namely a very large surface area of 3360 m 2 g −1 resulting in 18.5 wt% at 25 °C and 60 bar. To obtain realistic volumetric methane capacity, the packing density of completely dried CDC was measured, from which we obtain excess capacity of 145 v(STP) v −1 from CDC activated with CO 2 at 875 °C for 8 h, 81% of the DOE target (180 v(STP) v −1 ) at 35 bar and 25 °C. From small-angle X-ray scattering (SAXS) measurements, pore radii of gyration ( R g ) between 0.5 nm and 1 nm are determined. Temperature-dependent methane isotherms show that the isosteric heat of adsorption reaches 24 kJ mol −1 at the initial stage of low loading.

Physisorption of hydrogen in microporous molybdenum carbide (Mo 2 C)-derived carbons has been studied as a function of synthesis conditions. Changes in local structure induced by varying the chlorination temperature afford controllable variations in average pore size and specific surface area. Optimal hydrogen storage capacity of 4.3 wt%, measured at −196 °C and 35 bar pressure, is obtained from a sample chlorinated at 660 °C for 3 h. This optimum correlates with the largest fraction of total pore volume having average pore sizes in the 0.6–0.8 nm range.

Hydrogen storage measurements on peels formed from powdered carbide-derived carbons (CDCs) mixed with 3–5 wt% PTFE binder are presented. Polymer interactions with adsorption sites are explored by examining CDCs derived from different precursors. The observed trends in loss of gravimetric capacity suggest that the detrimental effect of the polymer is greatest for large (>1.5 nm) pores and small ( 2 /L, respectively, at 77 K and 4 MPa hydrogen pressure.

Laser flash and self-heating 3 ω techniques were employed to determine the anisotropic thermal conductivity and thermal diffusivity of a highly oriented, free-standing multiwalled carbon nanotube (MWCNT) sheet and a yarn drawn from a sidewall of the MWCNT forest grown by chemical-vapor deposition. Normalized to ideal high density structure the thermal conductivity and the thermal diffusivity along the alignment are 50 ± 5 W/m K and 45 ± 5 mm 2 /s, respectively, and are mostly limited by dangling terminals of bundles, intrinsic defects of individual nanotubes and phonon scattering within the bundles, which form the supporting matrix of the MWCNT sheet. The high degree of tube–tube overlap substantially decreases the electrical and thermal interconnection resistance, which usually dominates in randomly deposited mat-like nanotube assemblies. The extremely high surface area of the MWCNT sheet leads to excessive radial heat radiation that does not allow transferring the heat energy along the MWCNT sheet by means of phonons to distances >2 mm. On the other hand, the high surface area and negligible heat capacitance make it a perfect material for bolometric sensing ( r = 38 V/W) and heat dissipation.

High surface area nanoporous carbon has been prepared by thermo-chemical etching of titanium carbide TiC in chlorine in the temperature range 200–1200 °C. Structural analysis showed that this carbide-derived carbon (CDC) was highly disordered at all synthesis temperatures. Higher temperature resulted in increasing ordering and formation of bent graphene sheets or thin graphitic ribbons. Soft X-ray absorption near-edge structure spectroscopy demonstrated that CDC consisted mostly of sp 2 bonded carbon. Small-angle X-ray scattering and argon sorption measurements showed that the uniform carbon-carbon distance in cubic TiC resulted in the formation of small pores with a narrow size distribution at low synthesis temperatures; synthesis temperatures above 800 °C resulted in larger pores. CDC produced at 600–800 °C show great potential for energy-related applications. Hydrogen sorption experiments at −195.8 °C and atmospheric pressure showed a maximum gravimetric capacity of ∼330 cm 3 /g (3.0 wt.%). Methane sorption at 25 °C demonstrated a maximum capacity above 46 cm 3 /g (45 vol/vol or 3.1 wt.%) at atmospheric pressure. When tested as electrodes for supercapacitors with an organic electrolyte, the hydrogen-treated CDC showed specific capacitance up to 130 F/g with no degradation after 10 000 cycles.

An interfacial polymerization method for nylon 6,6 was adapted to produce nanocomposites with single wall carbon nanotubes (SWNT) via in situ polymerization. SWNT were incorporated in purified, functionalized or surfactant stabilized forms. The functionalization of SWNT was characterized by FTIR, Raman spectroscopy and TGA and the SWNT dispersion was characterized by optical microscopy before and after the in situ polymerization. SWNT functionalization and surfactant stabilization improved the nanotube dispersion in solvents but only functionalized SWNT showed a good dispersion in composites, whereas purified and surfactant stabilized SWNT resulted in poor dispersion and nanotube agglomeration. Weak shear flow induced SWNT flocculation in these nanocomposites. The electrical and mechanical properties of the SWNT/nylon nanocomposites are briefly discussed in terms of SWNT loading, dispersion, length and type of functionalization.

We demonstrate herein the possibility to prepare carbon anodes for Li-ion batteries using simple carbonized polymeric precursors such as cotton and phenolic cloths. Activation by controlled oxidation forms highly porous carbons whose electrochemical activity in Li salt solutions is mostly an irreversible reduction of solution species and double layer charging. Treating these porous carbons by chemical vapor deposition (CVD) of carbon on their surfaces, closes the pores in a way that they can insert Li-ions, but not solution species. These general carbon engineering processes form new carbons with nanoscopic, selectively closed pores, which can serve as highly reversible anode materials for Li-ion batteries, with relatively low irreversible capacity. The capacity of these electrodes depends on the nature of the carbon CVD process. This paper describes the scheme for carbon engineering, gas adsorption measurements that demonstrate the impact of the carbon CVD process, and the relevant changes in the structure of the pores and some preliminary electrochemical measurements in non-aqueous Li salt solutions.

Low T oxidation followed by brief sonication in hot HCl has been optimized to remove Fe catalyst residues from HiPco material with minimal loss of tubes. One pass reduces Fe from 6–10 to 0.6–1.6 at.% with 60% yield, most of the loss being Fe. Raman scattering reveals a broad diameter distribution with a mean of 1.0–1.1 nm. After purification we find excellent correlation between oxidation temperature and Raman spectra whereby the oxidation rate varies inversely with tube diameter. This can be explained by the larger strain associated with greater curvature of small tubes.

This work relates to a rigorous study of the correlation among surface chemistry (FTIR, XPS), 3D structure (X-ray and neutron scattering), morphology (SEM, AFM), and electrochemical and impedance behavior of lithiated carbon electrodes in commonly used liquid electrolyte solutions. Four different types of carbons were explored in a single study. These included, for comparison, two types of disordered carbons, single-wall carbon nanotubes (SWNT), and synthetic graphite powder as a reference system. All four types of carbons develop a similar surface chemistry in alkyl carbonate solutions which is dominated by solvent reduction. The differences in the 3D structure of these carbons leads to pronounced differences in the mechanisms of Li-insertion into them. The effect of the carbons’ 3D structure on the solid-state diffusion of Li-ions is demonstrated and discussed.

Electrochemical doping and in situ Raman scattering were used to study charge transfer in K- and Li-doped single wall carbon nanotubes (SWNT) as a function of alkali concentration. An 8 cm ˇ1 downshift was observed for the tangential phonon mode of SWNT doped to stoichiometries of KC24 and Li1:25C6. The shift in both systems is reversible upon de-doping despite an irreversible loss of crystallinity. These results indicate that the tangential mode shifts result from electron transfer from alkali dopants to the SWNT, and that these modes are only weakly aAected by long-range order within the ropes. ” 2001 Elsevier Science B.V. All rights reserved.

Electrochemical impedance spectroscopy (EIS) was used to study the kinetics and insertion mechanism of alkali metals in single wall carbon nanotubes (SWNT). Three distinct processes with very different time constants were identified: charge transfer across the macroscopic electrolyte/electrode interface, diffusion through the mesoscale porosity of the SWNT electrode, and nanoscale diffusion in individual SWNT ropes. Electrode resistance and capacitance from EIS compare well with direct dc measurements. We propose that alkalis decorate the internal and external surfaces of the SWNT ropes.

This Letter describes the production of single-wall carbon nanotube (SWNT) – polymer composites with enhanced mechanical and electrical properties and exceptional nanotube alignment. A combination of solvent casting and melt mixing was used to disperse SWNT materials in poly(methyl methacrylate) (PMMA). Composite films showed higher conductivity along the flow direction than perpendicular to it. Composite fibers were melt spun to achieve draw ratios between 20 and 3600. The elastic modulus and yield strength of SWNT–PMMA composite fibers increased with nanotube loading and draw ratio. Polarized resonant Raman spectroscopy indicates that the nanotubes in the fibers are well aligned, with mosaic distribution FWHMs as small as 4°.

We report inelastic neutron scattering results on hydrogen adsorbed onto samples containing single-wall carbon nanotubes. These materials have attracted considerable interest recently due to reports of high density hydrogen storage at room temperature. Inelastic neutron scattering clearly shows the ortho‐para conversion of physisorbed hydrogen in a nanotube containing soot loaded with hydrogen. From the rotational Ja 0! 1 transition, no indication of a significant barrier to quantum rotation is seen. ” 2000 Elsevier Science B.V. All rights reserved.

Disordered carbons offer promise of performance gains relative to graphite as the anode host material in Li ion batteries. They also present major challenges in determining structure-property relationships, in particular the location, density and properties of the site (or sites) at which reversible Li uptake occurs. Our understanding of graphite anodes is built on 35 years of research on the crystal compound LiC6. Here we review our efforts to obtain similar understanding of disordered carbons, using local structure determination via radial distribution function analysis, quantum chemical simulations and neutron vibrational spectroscopy. The ultimate goals are to understand the origin of the very high capacity for Li uptake exhibited by some of these materials, and to establish a scientific basis for optimizing their performance in real batteries. Two illustrative examples will be discussed in detail: the effect of residual hydrogen and ‘edge sites’ on Li binding, and the detailed evolution from long-range to short-range order in ball-milled graphite.

Spherical objects (presumably C60 molecules) have been observed inside ∼14 A diameter single-wall carbon nanotubes. We applied acid etching to access the interior of the tubes, and leaching in toluene to dissolve liberated C60. Quantitative UV–Vis of the 335 nm C60 transition establishes beyond doubt that these are indeed C60, and that their relative abundance in a macroscopic sample can be as high as 5.4% (expressed as the filled fraction of total tube length). Variations in abundance with growth and processing conditions provide clues as to how they form.

The structures of the lamellar selenodiphosphates CuMP2Se6 (M=Cr, In) are reexamined using powder diffraction and auxiliary techniques. Antiferromagnetic behavior observed in CuCrP2Se6 below 40 K is shown to be consistent with the existence of separate, triangular Cu and Cr sublattices rather than a random cation distribution. Analyses of neutron powder diffraction patterns recorded at various temperatures for CuCrP2Se6 confirm this as well as reveal partial occupation by copper of equivalent sites shifted away from the layer midplane. Diffraction evidence is also given for site disorder involving off-center positions in the copper sublattice of CuInP2Se6 at room temperature. The deduced off-center shift for copper in CuCrP2Se6 is less than in CuInP2Se6; moreover, these displacements are significantly smaller than in the thiophosphates CuMP2S6 (M=Cr, In). No indication of dipole ordering within the copper sublattice of CuCrP2Se6 was found down to T=10 K, in contrast with the appearance of antipolar copper order in CuCrP2S6 below 150 K. On the other hand, calorimetry detected a transition in CuInP2Se6 between T=200 and 240 K, a range much lower and broader than for the ferro-paraelectric transition in CuInP2S6 (Tc=315 K). The possible nature of the low T-phase of CuInP2Se6 is discussed based on preliminary diffraction data and the known thermal behavior of CuInP2S6.

Single-wall carbon nanotubes exhibit many properties analogous to quantum dots and wires at very low temperatures: Coulomb blockade and single-electron charging. These and other phenomena may be exploited in constructing active electronic devices of unprecedentedly small size. Bulk material may be chemically doped to yield mass-normalized electrical conductivity higher than that of copper.

Co-evaporation of carbon, in the presence of helium with some other element as catalyst, yields interesting new molecules of the fullerene family which have tubular morphologies with a cross-section at the nanoscale but lengths at the macroscale. In particular, using Ni or Co based mixtures as catalyst with the electric arc technique, one obtains single wall carbon nanotubes in large quantities, with an average diameter of 1.4 nm and which assemble themselves in highly crystalline bundles containing a few tens of elements. These nanotubes have been observed, characterized and studied using high resolution microscopy techniques. X-ray and electron diffraction have been used to characterize the crystalline nature of individual bundles. The diameter dispersion has been studied in detail using Raman spectroscopy which shows impressively well-resolved structures of the observed modes. A majority of (10, 10) armchair tubes is observed, but some other configurations are also present with slightly different diameters.

Inter- and intra-layer disorder in a representative hard carbon derived from epoxy novolac resin at 1000°C have been investigated by comparing both the elastic structure factor S(Q) and radial distribution function obtained from pulsed neutron time-of-flight measurements with calculations from simple hypothetic systems with specific disorder characteristics. The spatial relationship between these building blocks, planar graphene fragments with length scale of 1 nm, is probed in terms of inter-layer alignment and intra-layer connectivity. Coupled with the density of dangling bonds obtained from ESR and residual hydrogen concentration, these simulations provide sufficient information to construct an overall model of the carbon structure. Of special interest is the physical origin of the ubiquitous broad (002)-like reflection frequently interpreted as that from layers with a uniform interlay spacing (d002) It is found to be directly related to the misalignment between layers with an average interlayer spacing as that in crystalline graphite (3.35 A).

The superconducting properties of fullerene intercalation compounds can be rationalized fairly well in the context of standard theories. In contrast, our understanding of correlations between properties and chemical composition, crystal structure, molecular orientations and valency remains rudimentary. Key features which were believed to be well understood have been called into question by recent experiments while others remain unexplained.

The local structure of several disordered carbons, obtained from radial distribution function analysis of elastic neutron scattering data, consists of small isolated graphene fragments. The effect of residual hydrogen which presumably saturates the dangling bonds in low-temperature pyrolyzed materials was studied by inelastic neutron vibrational spectroscopy and computer modelling of lithiated polyaromatic hydrocarbons. We discuss the possibility of exploiting the high-pressure crystal phase LiC2 in primary batteries, by demonstrating that trace boron substitition greatly enhances the (meta) stability of this phase at atmospheric pressure.

Three different natural graphite powders (MPG, SPG and HPG) were used to make anode films of lithium-ion batteries by rolling technique. It was found that particle size and particle distribution of graphite, as well as particle orientation in the foil, show great influence on the electrochemical performance of graphite foil anodes. Different X-ray experiments were performed to study the mosaic distributions and coherence lengths of graphite crystallites. This study of the morphology and texture characteristics of anode foils reveals results that pertain to the understanding of electrochemical performance of cells.

We report the result of 13 C nuclear magnetic resonance (NMR) measurements on A 6 C 60 ( A =K, Rb, Cs) and Ba 3 C 60 . By using high-resolution magic angle spinning, we were able to identify an isotropic line around 156 ppm for all investigated compounds. NMR spectra of the saturated alkali compounds are quite similar. The corresponding isotropic lines show three narrow components consistent with orientationally ordered C 60 molecules leading to three non-equivalent carbon sites in these compounds as reported by x-ray studies. No line splitting was observed for the Ba 3 C 60 isotropic line.

The splitting of the tetrahedral Rb - and K - N M R lines in Rb 3 C 60 and K 3 C 60 is analyzed in terms of the mechanism of alkali-cation vacancies. The calculations indicate the presence of vacancies only in the tetrahedral positions, and the inter-atomic potentials between the alkali cations and the fullerene molecules account satisfactorily for the temperature dependence of the position of the distorted line.

Pair distribution functions (PDFs), obtained from powder neutron diffraction measurements have been used to construct structural models for the body centered orthorhombic (bco) and fcc phases of RbC 60 . The PDF exhibits small differences, primarily due to the shortened inter-fullerene distance in the bco phase. The bco-RbC 60 system is well fit to a model derived from first-principles quantum molecular dynamics in which the C-C interfullerene distance is 1.57 A. While the geometry of the interfullerene linkages is similar to a previously proposed model, the present results imply less distortion of the C 60 molecules and larger interfullerene distances. The PDF analysis also indicates significant orientational disorder between chains of linked molecules.

Synchrotron-based X-ray powder diffraction has proved indispensable in the study of fullerene solids, their alkali metal intercalation compounds and chemical derivatives. Here we review some recent developments to which David E. Cox has made important material and intellectual contributions, not only in advancing the field of fullerenes but in helping to train a new generation of young scientists. Topics covered include finite vacancy concentrations in superconducting phases, estimates of the vacancy formation energies from temperature-dependent phase analysis, and the effects of alkali metal intercalation on orientational states, order-disorder transitions and superconductivity.

We have measured the time decay of the magnetization for a well characterized superconducting fullerene Rb 3 C 60 . The temperature dependence of the magnetic relaxation rate dM(t)/dln(t) exhibits a maximum at a characteristic temperature T max , which decreases with increasing field. At low temperatures a nonlinear logarithmic time decay of the magnetization is observable only after several hours, but is clearly observable after much shorter times at high temperatures. This nonlinear behavior suggests the existence of a vortex glass state in Rb 3 C 60 and is consistent with the collective creep model. PACS #: 74.30.Ci, 74.60.Ge, 74.70.Wz

A review is given of crystal structures and order/disorder phenomena in the fullerene solids C 60 , C 60 O and C 70 and in the alkali metal intercalation compounds of C 60 . Recent results on orientational melting and quenched orientational disorder in the pristine solids are summarized, and the effect of small perturbations on the quasi-spherical molecular shape are described. The intercalation properties of C 60 are discussed in the context of other host lattices such as graphite. The variety of orientational correlations in fullerenes and fullerides is rationalized in terms of competing contributions to the orientational potentials. Structural properties of alkali fullerides are correlated with electronic properties and superconductivity, and an updated binary phase diagram is described.

The thermal behavior of solid C70 has been studied by synchroton X-ray powder diffraction and differential scanning calorimetry. The equilibrium solid state structures formed by C70 were solved by full profile refinement techniques in which orientational and packing disorder were explicitly accounted for. Above 345 K, C70 forms a plastic crystal, with an equilibrium face-centered cubic structure. At lower temperatures, orientational freezing occurs in two stages. Between 295 and 345 K, disorder persists only about the long axis of the molecule, and the lattice undergoes a rhombohedral distortion. Below 295 K, the rhombohedral lattice undergoes a further distortion, resulting in a previously unobserved monoclinic structure, in which the molecules are presumed to be essentially static. At all temperatures, however, the structure of C70 retains an ABC packing sequence.

AC impedance and x-ray diffraction measurements versus temperature and pressure on several ternary fullerene intercalation compounds are reported. The results support our previously established empirical correlation between superconducting onset temperature and 300K fcc lattice constant. Compounds which do not follow this correlation either phase separate or are otherwise unstable at low T and/or high P.

Rietveld refinements of x-ray powder profiles show that the C 60 molecules in Na 2 RbC 60 are orientationally ordered in a manner essentially the same as in pure C 60 , the only fullerene-based superconductor thus far to do so. Fits to data at both 300 K and 27 K are significantly better in space group Pa 3 (simple cubic) than in Fm 3 m (merohedral disorder) or by assuming uniform spherical shells of charge (complete disorder). The anomalously low T c of this compound cannot be attributed to excess orientational disorder, and therefore remains a mystery.

Structural and dynamical features of the fullerene solids C 60 and C 70 are reviewed. X-ray-derived crystal structures of C 60 intercalation compounds with sodium, potassium, rubidium, cesium and iodine are described, and aspects of alkali-C 60 phase equilibria are discussed. Efforts to establish structure-property relationships are presented.

The growth of thin C 60 films on GaSe(0001) has been studied by infrared High Resolution Electron Energy Loss Spectroscopy (HREELS) in specular reflection geometry. In contrast to previously studied disordered films on Si(100), it was found that deposition on a GaSe substrate heated to 120°C leads to well-ordered, epitaxial C 60 films. The structural order, manifested by a sharp LEED pattern, was confirmed by the clear detection in the specular beam of all four T lu dipole-active vibrations of the C 60 molecule. Several other infrared inactive modes, which were prominent in the C 60 /Si HREELS spectrum, are still seen in C 60 /GaSe but with reduced intensities. Application of the dielectric theory of reflection EELS allows a quantitative determination of the contribution of the dipole-active modes to the total spectrum. Although the relative oscillator strengths of the four infrared modes are in good agreement with optical absorption measurements, their absolute values, as determined by theoretical simulation, are found to be three times larger than the optical results.

The evolution with hydrostatic pressure (0 < P < 8.1 kbar) of the interchain ordering in trans-polyacetylene was measured using 4-circle synchrotron x-ray diffractometry and a Merrill-Bassett diamond anvil cell. The P-dependence of (HK0) reflections signify a lowering of the two-dimensional space group symmetry from pgg to p2 with a threshold P < 0.5 kbar, with an angle γ between the a and b axes of about 92° throughout the entire P range. The interchain compressibility is large and highly anisotropic. Below 6 kbar, Δa/a and Δb/b are 8.3 × 10−3/kbar and 3.8 × 10−3/kbar respectively. Both a and b stiffen above 6 kbar as the system approaches true close-packing.

We present new x-ray diffraction data on trans-(CH)x which shows that the blond alteration is out of phase on adjacent chains, and therefore the correct space group is P2 1 n . Previous attempts to resolve this question by analyzing only the (00L) intensities have yielded ambiguous results; all experiments show some (001) intensity which is not allowed P2 1 n . By analyzing indidual off-axis peak intensities, we show unambiguously that the bulk 3-D structure is inconsistent with P2 1 a (in-phase bond alternation), and therefore the weak, sample-dependent (001) intensity probably results from uncorrelated local defect regions with in-phase bond alternation on adjacent chains.

High-pressure reaction of Li metal and graphite yields LiC 2 , three times as dense in Li as the usual LiC 6 . LiC 6 decomposes rapidly but incompletely into LiC 6 + Li upon releasing pressure. A dramatic enhancement is observed in the metastability of the high Li density when the graphite contains 0.5 at.% substitutional boron. Average compositions from X-ray (OOL) intensities, determined several months after releasing the pressure, are LiC 2.2 and LiC 3.8 with and without boron respectively. The Li “layer” is split along c by 0.5 A suggesting a puckering which reduces the repulsive interactions.

The high-temperature f.c.c. phase of KC 60 is unstable upon cooling and transforms into the orthorhombic polymer (OP). We show in this paper that the polymeric phase is also unstable above room temperature and separates into the thermodynamically stable K 3 C 60 + α-C 60 phases. The analysis of the lifetime of both f.c.c. and polymeric phases, probed by ESR as a function of temperature, allows the determination of activation energies of both f.c.c. → polymeric and polymeric → K 3 C 60 + α-C 60 phase transformations, as being 0.17 and 1.1 eV, respectively.

We have measured the bulk modulus K for C61D2 up to 1 GPa in the temperature range 175–343 K. For face-centered cubic C61D2 above 290 K, we find an anomalously low value for K below about 0.15 GPa, ...

Powder profiles have been obtained from unoriented films of (CH) x and (CD) x solution-doped with lithium by using x-ray and neutron diffraction respectively. Detailed intensity analyses show improved fits with a lower symmetry R3 model for the two-dimensional interchain packing, as compared to the previously proposed high-symmetry R3C space group. The R3-based structure is derived from the R3C one by a local distortion of the interchain packing motif, in a very similar way to the symmetry breaking observed in the tetragonal phases for larger alkali metals.

A simple model explains both the Bragg peaks and the diffuse scattering observed in neutron diffraction measurements on Solid C 60 at 295 and 14 K. Neutron inelastic scattering measurements reveal dynamic orientational disorder above the order-disorder transition temperature. An analysis of the diffraction results shows that significant disorder remains at 14 K.

Neutron and gamma diffraction (00L) rocking curves of stage-1 AsF5-graphite intercalation compounds have been performed. The intrinsic c-axis mosaic FWHM is 0.8°, significantly less than the value typical of donor compounds. This suggests that intercalation with large molecules may provide new options for the development of long-wavelength neutron monochromators and filters.