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International audience; Boron/carbon/nitrogen (B/C/N) materials and boron/carbon (B/C) materials having graphite-like layered structures were synthesized by using chemical vapor deposition (CVD) method. Calcium (Ca) was intercalated into the B/C materials by the reaction of Ca vapor with the host B/C film to form an intercalation compound with a second stage structure as a main product. Ca was also co-intercalated with lithium (Li) into the B/C/N materials by using the liquid-alloy method to form an intercalation compound. These are the first examples of syntheses of Ca and Ca-Li intercalated B/C and B/C/N materials. The nuclear microprobe analysis (NMA) indicated the compositions of the original host B/C/N and B/C materials to be BC2.6N0.55 and BC6.4, and the Ca-Li intercalated compound to be Ca0.67Li0.42(BC3.3N0.50) and suggested the homogeneity of these materials and the compound. We also found that the NMA is one of the most accurate methods for determining the compositions of air and water sensitive intercalation compounds as well as complex systems like the B/C/N and B/C materials.

Graphene materials exhibit extraordinary properties, but are difficult to produce. The present work describes the possibility of using a plasma process to exfoliate and functionalize graphite flakes. An impulse plasma phase is generated at a liquid surface to produce chemical species and shock waves in order to modify the reactive liquid as well as the graphite flakes. With this process, industrial graphite was treated. 20% thickness diminution was observed, and the formation of a random turbostratic structure. The exfoliation occurs with small amount of functionalization of the surface. Even after treatment, the graphite flakes present a low defect density compared with other treated graphite obtained by more conventional chemical treatments. This process is a new way to exfoliate graphite and to produce functionalized graphenic materials.

The LiCl-KCl molten salts method has been used in order to intercalate strontium into graphite. Combination of X-Ray Diffraction (XRD) experiments and ion beam analyses attests the obtaining of a monophasic sample. Its chemical composition corresponds to the Li 0.2 K 0.6 Sr 0.4 C 6 formula, revealing the synthesis of a quaternary Graphite Intercalation Compound (GIC), in agreement with the high repeat distance of 640 pm determined from its 00 l XRD and with the 1D electronic density profile. The very high-quality data obtained by hk 0 diffraction and rotating crystal method lead to a 2D organization of the intercalated sheet described by a large hexagonal unit cell containing 78 carbon atoms. Such quaternary phase including simultaneously alkali and alkaline-earth metals is unique and can only be prepared from molten salts method, opening new perspectives concerning graphite-based two-dimensional materials.

Particularly large surface area and well-defined nanoparticles are both critical in the issue of nonporous carbons for challenging energy, catalyst and environmental fields. Therefore, following th...

International audience; The synthesis of a novel first stage GIC containing simultaneously lithium, potassium and barium through a solid–liquid reaction by molten salts method is described. Such a route has been largely developed in our laboratory for intercalation of metals into graphite. The interplanar distance of this quaternary compound reaches 950 pm and exhibits poly-layered intercalated sheets defined by X-ray measurements. The Li0.2K0.75Ba0.6C6 chemical formula of the compound is determined by ion beam analysis and this GIC is remarkably homogeneous. This GIC is the first poly-layered one containing barium.

International audience; A solid-liquid method is used to synthesize the first stage bulk BaC6 graphite intercalation compound (GIC). This way of synthesis allows the preparation of bulk and massive samples useful for crystal structure determination. Through an eutectic medium LiCl-KCl, and by submerging a graphite platelet in barium-molten solution at 450°C for several days, the bulk BaC6 compound is obtained and X-ray diffraction investigations allowed a complete structural study. The collected data certify that BaC6 crystallizes in the hexagonal P63/mmc space group with the following parameters a = b = 430.6 pm and c = 1058.2 pm.

International audience; The promising and extraordinary properties of graphene have attracted significant interest, making graphene an alternative to replace many traditional materials for many applications, particularly in conductive ink for the fabrication of flexible electronics. For the past 10 years, numerous studies have been reported on the synthesis of graphene conductive ink for printing on flexible substrates for various electronic applications. The development of graphene-based ink is reviewed, with the main focus on the types of graphene-like materials in conductive inks, and the compositions and important properties of those inks. Another intention behind this review is to compare the pros and cons of graphene-based ink with those using other common conductive materials, such as gold nanoparticles, silver nanoparticles, copper nanoparticles, conductive polymers and carbon nanotubes. Recent works on graphene hybrid-based ink containing other metallic nanoparticles as an alternative way to improve the electrical properties of the conductive inks are also reported. Brief comparisons between inkjet printing and other printing techniques for the fabrication of flexible electronics are discussed.

Highly Oriented Pyrolytic Graphite was exfoliated via pulsed discharge plasma in liquid nitrogen. The potential mechanisms involved were investigated by observing the treated surface of the graphitic material and the obtained particles. Non-exfoliating defects from the plasma treatment were observed and experimental parameter were modified to counteract those. One experiment was performed without exposing the HOPG directly to the discharges so as to better understand the plasma role. The exfoliated particles were observed via TEM and SEM to evaluate the defects, the size, the purity and the crystallinity but no quantitative characterization of their thickness was possible so the actual number of layer of each particle is unknown. Nonetheless, few layers graphene (FLG) was successfully exfoliated through this process. The proposed mechanisms were extrapolated from the observation of the damaged HOPG surface and the obtained particles but the correlation found does not prove causation., Comment: 14 pages, 21 figures

First stage strontium-graphite intercalation compound (GIC) is successfully synthesized using a recent method based on eutectic medium LiCl–KCl. The bulk compound is obtained after immersing a graphite platelet in strontium-molten salt solution at 450 °C for several days. Using such bulk GIC, an accurate structural study is performed by applying X-ray diffraction techniques (00l, hk0 and rotating crystal method). It is validated that SrC6, similarly to most MC6 compounds, crystallizes in a hexagonal P63/mmc space group with subsequent parameters a = b = 431 p.m. and c = 988 p.m.

For the purpose of synthetizing 3-dimensional nitrogen-doped graphenic materials, which could be used as oxygen reduction catalysts in membrane fuel cells, a solvothermal-based route was successfully carried out. However, the solvothermal reaction between metallic sodium and 1-(2-hydroxyethyl)piperidine (HEP), with the latter as the source of both carbon and nitrogen, is still little understood. The present work was aimed at investigating the solvothermal process under different conditions of temperature and pressure and with different amounts of sodium. Use of in situ mass spectroscopy during the three-day reaction revealed the early formation of dihydrogen, as well as carbon oxides, methane and ammonia, in addition to fragments of ethylpiperidine alkoxide (EP-ONa). XRD measurements evidenced the formation of sodium-based compounds, e.g. hydride, carbonate, hydroxide, and cyanide. Interestingly, Raman spectroscopy revealed the significant presence of large aromatic molecules as well as an sp2 carbon network, an early precursor of graphene. Analysis of the overpressures and reaction yields suggests that the primary compound from the reaction of HEP with sodium is a large sp2 carbon-based network entrapping numerous sodium-based molecules as well as a volatile liquid phase. The suggested reaction mechanism provides information to better tailor the solvothermal products, whose pyrolysis at 850 °C led to very high specific area nitrogen-doped carbon materials.

International audience; Extraordinary properties of graphenic materials no longer need to be demonstrated. Nitrogen doping has been known to broaden the graphene application fields, especially for catalysis purposes. The present work reports a solvothermal-based process for the synthesis of a nitrogen-doped graphenic foam with up to 2.6 at.% nitrogen, exhibiting the inherent properties of graphenic materials with high textural properties and surface areas as high as 2243 m².g-1. This study aims to give a better understanding of the influence of the pyrolysis treatment on the properties of the produced material for optimization of the synthesis in view to fuel cell applications. Several cross-linked techniques such as transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy, nitrogen physisorption at 77 K and X-ray photoelectron spectroscopy have been employed to give a complete, precise characterization of the elaborated N-doped graphenic foams, leading to optimized conditions for the pyrolysis step. Pyrolysis at 850 °C has been found to allow the best compromise in terms of purity, homogeneity and crystallinity, with high fractions of pyrrolic, pyridinic and graphitic N-substitution that are known to greatly enhance the material catalytic properties. An oxidative degradation process was also evidenced for temperatures above 875 °C, leading to far lower graphene amounts.

In the current work, carbon nanospheres (CNSs) were prepared via pyrolysis of gas condensate in N2 at 1273 K and atmospheric pressure for 2 h using ferric chloride as a catalyst precursor. X-ray di...

Besides the well-known research concerning graphene, great attention has more recently been paid to three-dimensional graphene structures, motivated by the combination of the properties of graphene and the development of porosity and large specific surface areas. The most current methods of obtaining for this kind of structure start from graphite oxide, which can be thermally treated or assembled in liquid-phase. This work is focused on a little-known and bottom-up method of elaboration, which consists in a solvothermal reaction between metallic sodium and an alcohol, followed by a thermal treatment. The as-obtained graphene foams exhibit very large specific surface areas. More specifically, the length of the carbon chain of the precursor alcohol employed for the solvothermal reaction is found to have a strong influence on the adsorptive properties of the foams, especially on their pore size distribution. The mechanism of formation of such porous structures is discussed through the exploration of the compounds of the carbon-sodium-oxygen system.

The lithium-ion batteries are widely used in rechargeable electronic devices. The current challenges are to improve the capacity and safety of these systems in view of their development to a larger scale, such as for their application in electric and hybrid vehicles. Lithium-ion batteries use organic solvents because of the wide operating voltage. The corresponding electrolytes are usually based on combinations of linear, cyclic alkyl carbonates and a lithium salt such as LiPF 6 . It has been reported that in abusive thermal conditions, a catalytic effect of the cathode materials lead to the formation fluoro-organics compounds. In order to understand the degradation phenomenon, the study at 240 °C of the interaction between positive electrode materials (LiCoO 2 , LiNi 1/3 Mn 1/3 Co 1/3 O 2 , LiMn 2 O 4 and LiFePO 4 ) and electrolyte in dry and wet conditions has been realized by an original method which consists in analyzing by mass spectrometry in real time the volatile molecules produced. The evolution of specific gases channels coupled to the NMR reveal the formation of rarely discussed species such as 2-fluoroethanol and 1,4-dioxane. Furthermore, it appears that the presence of water or other protic impurities greatly influence their formation.

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International audience; The main aim of the present study is to develop graphene-based ink and graphene hybrid-based ink with excellent stability, physical and electrical properties for flexible electronics. Graphene foam (GF) was used as the graphene-like material and inkjet printing technique was utilized in the fabrication of the conductive patterns. GF ink, GF/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) hybrid ink and GF/silver nanoparticles (AgNPs) hybrid ink were prepared by using new mixed solvents of 2-propanol (IPA) and ethylene glycol (EG) at ratio of 1:1. Results showed that GF/PEDOT:PSS hybrid ink presented better stability and surface conductivity than those of GF ink and GF/AgNPs hybrid ink, in which the ink exhibited only 30% decrement from the initial concentration after a month and 100% improvement in the surface conductivity at 50 printed layers. Besides that, the conductive pattern made of GF/PEDOT:PSS hybrid ink exhibited gauge factor with the value of 4.3 which is capable to be used for low strain sensor application.

International audience; Conductive inks made of graphene-like materials have attracted significant attention due to their extraordinary electrical properties. In this study, three different types of graphene-like materials, namely, graphene foam (GF), graphite nanoplatelets (GNPs) and synthetic graphite (SG), are utilized to fabricate conductive inks for printable flexible electronics applications. The results show that GF exhibits the highest surface area and pore volume, while GNPs and SG display large lateral sizes, highly crystalline structures and high-quality particles. In addition, the quality of the sprayed patterns are mainly influenced by the properties of graphene-based inks. The properties of conductive inks made from various graphene-like materials, including the viscosity, contact angle and surface energy, are investigated. The viscosity and contact angle of the conductive inks increase markedly with increasing filler loadings in a polyester varnish (PV) binder. Based on the electrical conductivity of unfilled PV, the conductive ink made of GNPs exhibits a 186% improvement in electrical conductivity at 10 vol% filler loading compared to those of 40% and 10% shown by SG and GF, respectively.

International audience; A new synthesis method using molten salts has been achieved allowing the intercalation of metals (e.g europium) into graphite. This method consists in dissolving various metals in a LiCl-KCl medium intended to be intercalated. In this work, many reactions are carried out by dissolving metals of first and second columns of the periodic table (Li, Na, K, Mg, Ca, Sr, Ba) in the molten salts before performing intercalation reactions for periods ranging from few minutes to several days and for temperatures included between 400 and 450 °C. The obtained compounds are then characterized by X-ray diffraction. Three different behaviors have been observed. With alkali metals, the obtained GIC is systematically LiC6 GIC. Magnesium leads to a sample of pure graphite remaining pristine. In case of alkaline earth metals, calcium, strontium and barium, the intercalation of the metal is systematically observed. The method presented in this paper reports for the first time the synthesis of a bulk SrC6 GIC. Finally, the intercalation mechanism using this medium has been deduced from these results and thanks to a study performed by ex situ X-ray diffraction in the case of the formation of the EuC6 GIC.

International audience; The precise quantification of catalyst residues in purified carbon nanotubes is often a major issue in view of any fundamental and/or applicative studies. More importantly, since the best CNTs are successfully grown with magnetic catalysts, their quantification becomes strictly necessary to better understand intrinsic properties of CNT. For these reasons, we have deeply analyzed the catalyst content remained in nickel-yttrium arc-discharge single walled carbon nanotubes purified by both a chlorine-gas phase and a standard acid-based treatment. The study focuses on Ni analysis which has been investigated by transmission electron microscopy, X-ray diffraction, thermogravimetry analysis, and magnetic measurements. In the case of the acid-based treatment, all quantifications result in a decrease of the nanocrystallized Ni by a factor of two. In the case of the halogen gas treatment, analysis and quantification of Ni content is less straightforward: a huge difference appears between X-ray diffraction and thermogravimetry results. Thanks to magnetic measurements, this disagreement is explained by the presence of ions, belonging to NiCl2 formed during the Cl-based purification process. In particular, NiCl2 compound appears under different magnetic/crystalline phases: paramagnetic or diamagnetic, or well intercalated in between carbon sheets with an ordered magnetic phase at low temperature.

Intercalation reaction occurs when an excess of a liquid heavy alkali metal-arsenic alloy is contacted with a graphite sample under vacuum. This leads to the formation of several novel ternary phases. X-ray structural analysis was conducted to determine how intercalated metallic alloy is arranged between the graphitic layers. The results have shown that these phases are composed of poly6layered sheets alternately stacked with carbon layers along the c-axis. In addition, these layers are perfectly ordered with respect to the adjacent carbon planes. Two-dimensional super-lattices have been recorded and analyzed. The electrical conductivity has been studied both parallel and perpendicular to the basal planes, between 4.2 and 295 K. The basal-plane behavior is metallic, but the c-axis resistivity displays very high resistivity. The room temperature anisotropy is of the order of 104, which increases for some phases, by more than one order of magnitude at 4.2 K.

International audience; Most of alkali metals are well-known to easily intercalate into graphite to form stage-1 graphite intercalation compounds (GIC) whose structure and physical properties have been extensively studied. This work is focused on the intercalation of potassium, sodium and cesium into graphenic foams prepared by a solvothermal-based process. The as-obtained samples are analyzed by means of X-ray diffraction and Raman spectroscopy, and reveal a double phenomenon: the intercalation of alkali metals between the interplanar spaces of the multi-layer graphene stackings, and their sorption into the porosity of the host sample. This kind of behavior has already been reported when studying the reactivity of alkali metals with disordered carbon. Interestingly, our study shows a low stage intercalation in the case of sodium. Moreover, the dispersion of the potassium-intercalated samples into a polar solvent leads to a few-layer graphene dispersion stable for months.

International audience; The intercalation of gold into graphite has been achieved thanks to a solid-liquid method using potassium metal-based molten alloys. Numerous syntheses have been performed varying the reactive alloy composition, the reaction temperature and the reaction time. The optimization of these parameters allowed to synthesize three novel ternary graphite intercalation compounds (GIC) containing poly-layered intercalated sheets, called alpha, beta and gamma. Thanks to a specific X-Ray diffraction study, the c-axis stacking sequence of the three compounds was determined. The a-GIC, which is a metastable compound, contains mixed potassium and gold two-layered intercalated sheets. The b-GIC and g-GIC contain very thick well ordered threelayered and five-layered sheets respectively. The very high repeat distances of the latter compounds are clearly explained by the amount of intercalated metals, precisely determined using nuclear microprobe analyses.

International audience; A ternary graphite-potassium-gold compound K1.3Au1.5C4 was synthesized by immersing a pyrographite platelet in various potassium metal-based molten alloys. Numerous reaction parameters were investigated (duration, temperature, composition of the alloy) in order to determine the stability conditions of the ternary compound. Using complementary X-ray diffraction and ion beam analysis experiments, the optimal conditions of preparation of this compound have been pointed out. The composition and homogeneity were evidenced by ion beam analysis and X-ray diffraction allowed to determine its repeat distance (1311pm) and its c-axis stacking sequence (K-Au-Au-Au-K). The 2D unit cell observed thanks to Transmission Electron Microscopy (TEM) is square with a = 1192pm, no-commensurate with that of graphite.

International audience; Three-dimensional graphene structures have attracted a great interest these last years. The combination of well-known graphene properties and a large specific surface area developed by their intrinsic porosity is especially interesting for challenging applications such as energy storage and conversion or catalysis. This work is focused on the elaboration of graphene foams by pyrolysis of sodium ethoxide. Whereas the literature mentions the possible elaboration of graphene foams by combustion of sodium ethoxide synthesized by a quite heavy solvothermal-based process, we propose here a thermal treatment consisting in a pyrolysis under a nitrogen flow. Using commercial sodium ethoxide, we show that this treatment leads to the preparation of graphene foams with great structural quality and high specific surface area. This original result is supported by a compared characterization of solvothermal and commercial sodium ethoxide and the proposition of a formation mechanism of the three-dimensional graphene network during the pyrolysis is proposed. This new graphene foam elaboration route is extremely interesting in order to consider a large-scale fabrication of such materials.

Carbon materials including carbon nanoparticles, such as nanographite, graphene and graphenic materials, and carbon nanotubes are known to be highly hydrophobic. Oxidation treatments are widely used as the best methods to improve their affinity in a liquid medium or a polymer matrix so that they can be dispersed, handled and processed. Here, we have applied eight different oxidation treatments in order to graft oxygen-containing functional groups at the surface of polyhedral graphitic particles synthesized by arc discharge from graphite, also called astralenes. The used functionalization approaches include both standard chemical attack by strong oxidants and radical functionalization of the sp2 network by direct CC bond opening. Commonly efficient functionalization methods were unsuccessful to functionalize astralenes while radicals generated from arylhydrazine could lead to functionalization of the outer surface of astralenes. The occurrence of functionalization could be shown by TGA coupled with MS and XPS. The reported method represents the first example of functionalization of astralenes. The efficiency of the applied functionalization methods is discussed considering the chemical reactivity of different carbon nanomaterials including graphene and carbon nanotubes.

International audience; Carbon nanotubes (CNTs) are difficult to process, and their assembly in macroscopic materials that allow us to benefit from the exceptional properties of the nanotubes is of crucial interest for applications. The developed CNT processing procedures usually involve additives that remain in the final product and are known to diminish the properties of the CNT-based material. Here, we propose a multistep approach to process single-walled carbon nanotubes (SWNTs) and obtain macroscopic additive-free SWNT materials. High-quality dispersion purified SWNTs is first induced in polar solvent due to their preceding reduction reaction with an alkali metal. The partial debundling process occurring at this stage leads to ramified SWNTs. They can then be self-assembled by attractive intermolecular forces through a controlled destabilization of the dispersions by a simple oxidation. Swollen gels of SWNTs are formed at an air/solvent interface. After freeze-drying, the additive-free SWNT material shows a hierarchical structure with highly interconnected SWNTs. Thanks to the obtained ramification of the SWNTs, these latter are able to well entangle what guarantees the robustness of the obtained additive-free SWNT material. Moreover, this integrated process offers an increase of the accessible surface compared to that of the raw bundled SWNTs. The obtained assembled SWNTs show an improved adsorption capacity.

Graphene-based materials are extensively studied, due to their excellent properties and their wide range of possible applications. Attention has recently been paid to three-dimensional-like graphenic structures, such as crumpled graphene sheets and graphenic foams: these kinds of materials can combine the properties of graphene associating high surface area and porosity, what is particularly interesting for energy or catalysis applications. Most of the synthesis methods leading to such structures are based on graphite oxide exfoliation and re-assembly, but in this work we focus on the preparation of graphenic foams by a solvothermal-based process. We performed a solvothermal reaction between ethanol and sodium at 220°C, during 72 h, under 200 bar, followed by a pyrolysis under nitrogen flow. An extended study of the influence of the temperature (800°C–900°C) of pyrolysis evidences an unexpected strong effect of this parameter on the characteristics of the materials. The optimal conditions provide multi-layer graphene (10 layers) foam with a surface area of 2000 m2·g−1. This work is an important step for the understanding of the mechanisms of the thermal treatment. Post-treatments in different experimental conditions are performed in order to modulate the structure and properties of the graphenic foams.

Nanoparticles of tungsten and tungsten carbide have been prepared using solid-state chemistry methods. After the vapor phase impregnation of a tungsten hexachloride precursor on a carbon support, a temperature-programmed reduction/carburization was performed. Several parameters were investigated and the evolution of obtained samples was followed by XRD and TEM. The optimization of the reaction parameters led to the preparation of W, W2C and WC particles well dispersed on the support. WC phase however could not be obtained alone with less than 10 nm mean size. This could be explained by the carburization mechanism and the carbon diffusion on the support.

International audience; The magnetic ground state of EuC 6 , a first-stage graphite intercalation compound, was investigated by means of zero-field muon spectroscopy. Below the Néel an-tiferromagnetic temperature (42 K), the highly damped oscillations in the muon asymmetry could be modelled with a Bessel line shape, indicative of an incom-mensurate magnetic order. The internal magnetic field, as probed by the implanted muons, lies in the plane of the europium ions, has an average intensity of 150(22) mT, and seems to arise from a strong contact hyperfine interaction. The latter partially cancels out the dipolar contribution to the local field, in turn due to the localized Eu spins arranged in an antiferromagnetic triangular lattice (frustrated spin lattice) with negligible inter-layer couplings.

A first stage binary graphite intercalation compound was synthesised in the lithium–europium–graphite system by direct immersion of a pyrolytic graphite platelet in a molten lithium-based alloy with a well chosen Li/Eu ratio at 350 °C. The as-obtained bulk EuC 6 compound exhibits mono-layered intercalated sheets of europium surrounded by two graphene sheets with a repeat distance equal to 487 pm. The three dimensional study of the EuC 6 crystal structure shows a hexagonal symmetry for this compound that crystallises in a P 6 3 / mmc space group with the following unit cell parameters: a = 430 pm and c = 974 pm.

International audience; The purification of single-walled carbon nanotube (SWCNT) samples was analysed using a multi-technique approach, with structural as well as spectroscopic probes, in order to characterize the samples and to identify important factors for improvement of SWCNT sample quality. The first dry oxidation step (air at 365 degrees C) is shown to have only a weak selectivity for the removal of the amorphous carbon or weakly organized graphitic species as well as resulting in a partial consumption of the SWCNTs. The functionalization of the SWCNTs is highly specific with formation of carboxyl, hydroxyl and carbonyl groups. On the other hand this oxidation step is highly efficient for the oxidation of the catalytic impurities (Ni, Y) which can be easily removed by subsequent acid treatment. A final high temperature treatment indicates some incomplete restoration of the quality of the SWCNT surface. (C) 2009 Elsevier Ltd. All rights reserved.

The description and understanding of the intercalation mechanism of electron donors or acceptors in single-walled carbon nanotube (SWNT) bundles are of critical interest for optimization and improvement of transport properties for future applications of SWNTs in electronics or energy storage. Here, we propose a novel approach based on the analysis of the state of debundling for SWNT bundles, used as a feedback for occupation sites of alkali metal atoms within the SWNT host material. Heterogeneity of the structure might be the origin of the complexity of the intercalation process in SWNTs.

In the lithium–europium–graphite system, a novel ternary compound was synthesised by direct immersion of a pyrolytic graphite platelet in a molten lithium-based alloy with a well chosen Li/Eu ratio at 400 °C. The ternary compound exhibits poly-layered intercalated sheets mainly constituted of two europium planes. Its chemical formula can be written LixEuC4, since the amount of lithium is still not determined. The 151Eu Mossbauer spectra clearly indicate a +II valence for europium. The magnetic susceptibility and the magnetisation versus temperature reveal a complex behaviour which is qualitatively described thanks to structural hypothesis and analogies with the magnetic properties of the binary EuC6 compound. A first ferromagnetic transition occurring at 225 K is attributed to interactions between both intercalated europium planes. The lower temperature susceptibility behaviour can be interpreted by antiferromagnetic interactions between in-plane neighbours and ferromagnetic interactions along the c-axis.

Lithium intercalates easily into graphite either by chemical way or by electrochemical way. This well-known reaction leads to the first stage LiC 6 binary compound. However, it is more difficult to prepare a ternary compound by intercalation of a lithium alloy. This is mainly due to thermodynamical causes. Nevertheless, it has been observed that a few well-chosen alloys (Ca–Li and Eu–Li) are able to intercalate into graphite. Calcium and europium have been used for well defined reasons. Although in these alloys both metals present are able to intercalate by themselves, the intercalated sheets are poly-layered. This observation is entirely original, but it can be easily explained. On the other hand, it has been established that, using well-chosen lithium alloys, calcium and europium can also intercalate alone into graphite, leading to the corresponding binary phases. In these occasions, lithium appears essentially as a factor able to promote the melting of the second metal and its intercalation by a preliminary spreading of the graphene planes.

A liquid–solid synthesis method to prepare high quality bulk samples of MC6 binary graphite intercalation compounds (with M = Ca, Ba and Eu) is described. Liquid Li–M alloys are used to synthesize such compounds for two reasons: first, lithium spreads apart the graphene sheets and second, it allows the intercalation reactions to be carried out at temperatures sufficiently low to avoid the formation of carbides. The intercalation reactions were investigated precisely, that reveal the existence of a two-steps mechanisms. Several attempts performed in order to synthesise SrC6 failed. However, all the possible conditions were not tried, so that the synthesis of pure SrC6 using this liquid–solid synthesis route is still unsolved.

Équipe 103 : Composés intermétalliques et matériaux hybrides; International audience; HiPco single-walled carbon nanotube samples contain a non-negligible amount (about 30 wt.%) of metal-based impurities. These impurities are prejudicial to the development of CNT-based applications. In the literature, there is no agreement for their nature and their relative content. Consequently, the standard purification treatments could not be selective enough and they lead to damage the carbon nanotubes. In this work, we have deeply investigated the mineral impurities of a raw HiPco SWCNT sample by means of several techniques. We were able to identify and quantify at least six iron-based phases that coexist in the HiPco SWCNT samples. The raw SWCNTs were submitted to a selective purification treatment involving a high temperature treatment under chlorine. The results show that the efficiency of the metal removal is improved by increasing the temperature of treatment leading to a purification yield of 95.4%, while preserving the structural quality of the SWCNTs. The analysis of the mineral residues in the purified and annealed SWCNT samples allows to propose the chemical mechanisms involved during the chemical treatments.

The electronic structure of the ternary intercalated graphite beta-KS(0.25)C3 is studied by means of a first-principles density functional theory approach. The nature of the partially filled bands is analyzed, and the K sublayers of the intercalate are shown to have an important contribution to the Fermi surface. This K-based contribution confers a sizable three-dimensional character to the conductivity even if considerably less than that for the related binary KC8. The electronic structure of beta-KS(0.25)C3 differs noticeably from that of the related ternary compound, KH(x)C4. The charge transfer is analyzed, and a way to evaluate it, which can be used in general for intercalated graphites, is proposed. The charge transfer per C atom in this ternary material is shown to be smaller than that in the KC8 binary compound despite a more favorable stoichiometry ratio between K and C.

It is possible to synthesise easily the first stage LiC 6 compound by immersing a pyrographite platelet in liquid lithium. The same experiments carried out using liquid lithium–calcium alloys with a Li/Ca atomic ratio, respectively, of 1 and 2, at 350 °C for ten days give two first stage ternary graphite intercalation compounds containing five- and seven-layered intercalated sheets, respectively. The experiments carried out with a liquid alloy rich in lithium (Li/Ca atomic ratio of 3) at 350 °C for ten days, in order to be sure that the thermodynamical equilibrium is reached, show that the reaction product is the CaC 6 binary compound, and not LiC 6 . This very unexpected result can be partially explained by kinetical and thermodynamical argumentation. Before the equilibrium, the experiments show that lithium intercalates first, leading to a mixture of several stages of graphite–lithium compounds with an increasing enrichment in LiC 6 . This compound disappears gradually to the benefit of CaC 6 , which remains alone in the system. In these conditions, it appears that CaC 6 is more stable than LiC 6 . This particular situation in these systems is observed for the first time. The temperature has a strong influence on the reaction. The ternary compounds are mainly obtained at the lowest temperatures whereas the binary ones are obtained for higher values.

In this letter, we report the discovery of superconductivity in Li3Ca2C6. Several graphite intercalation compounds (GICs) with electron donors, are well known as superconductors. It is probably not astonishing, since it is generally admitted that low dimensionality promotes high superconducting transition temperatures. Superconductivity is lacking in pristine graphite, but after charging the graphene planes by intercalation, its electronic properties change considerably and superconducting behaviour can appear. Li3Ca2C6 is a ternary GIC, for which the intercalated sheets are very thick and poly-layered (five lithium layers and two calcium ones). It contains a great amount of metal (five metallic atoms for six carbon ones). Its critical temperature of 11.15 K is very close to that of CaC6 GIC (11.5 K). Both CaC6 and Li3Ca2C6 GICs possess currently the highest transition temperatures among all the GICs., 5 pages, 3 figures

A novel and efficient synthesis method concerning the preparation of the first stage calcium graphite intercalation compound is provided. It makes use of a reaction between liquid metallic alloy and pyrolytic graphite. From now on it is especially easy to obtain bulk CaC6 samples. Thanks to such samples, it was possible to study in detail the crystal structure of this binary intercalation compound. It has been entirely specified, so that we know that CaC6 crystal is rhombohedral and belongs to the R 3 ¯ m space group with the following parameters: a = 517 pm and α = 49.55 ° . The elemental unit cell contains one calcium atom and six carbon atoms. In this paper, we show also how the various MC6 structures evolve according to the size of the intercalated element and to the bond nature that appears in the final compound. CaC6 is unique, since all the other MC6 compounds exhibit a hexagonal symmetry.

Three new layered compounds were synthesised by immersing a pyrographite platelet in a molten Ca−Li alloy creating a new graphite intercalation compound family. The samples were studied by X-ray and neutron diffraction, revealing that the intercalated sheets are polylayered. The study of the 00l reflections allowed us to establish the c-axis stacking of these three phases. The α-phase exhibits a five-layered intercalated sheet which has something in common with a Li−Ca−Li−Ca−Li slice cut in the CaLi2 structure (ThMn2 Laves phase type). The β-phase, which is richer in metallic elements and with a greater repeat distance, possesses seven-layered intercalated sheets due to the splitting of the middle lithium plane in three. The third phase is a pseudo-binary compound, containing monolayered sheets and with a formula close to CaC6. Electron microdiffraction allowed us to determine the 2D unit cell for each compound, all of which were commensurate with that of graphite. Charge transfer from the intercalate to the host lattice was evaluated for the three phases from hk0 data, leading to high values. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Lithium can intercalate easily into graphite leading to the LiC 6 compound but the synthesis of a ternary compound associating lithium with a second element seems to be difficult. Recently, graphite–lithium–calcium compounds were obtained by reaction of a pyrographite platelet in a molten Ca–Li alloy at 350 °C. Chemical analyses, electron microprobe, SEM and TEM give the C/Ca ratio but do not allow to determine the lithium concentration and its distribution in these compounds. Therefore, the nuclear microprobe was used to characterise more precisely these ternary intercalation compounds. Using a 3.1 MeV proton beam, the three elements can be quantified simultaneously from the 7 Li(p,α) 4 He nuclear reaction for lithium and from elastic scattering for calcium and carbon. Among the three synthesised compounds, one of them (α phase) opposes great heterogeneities in lithium and the amount of lithium in the β phase is very high (C/Li ratio approaches 2).

Ternary graphite intercalation compounds associating an alkali metal and an electronegative element are described. The synthesis is more often realized in molten alkali metal media containing the associate electronegative element or radical in the adequate concentration. The intercalated sheets are systematically polylayered. The arrangement along c-axis and the in-plane structures are described. The physical properties of the compounds are precised.

After a short overview on the co-intercalation into graphite of light alkali metals––lithium and sodium––with a third element, novel results concerning the co-intercalation of these alkali metals with an alkaline earth metal are given. The intercalation into graphite of lithium together with magnesium, calcium, strontium and barium is investigated, and the reaction products are described and characterised by X-ray diffraction. Ternary intercalation compounds were synthesised only in the graphite–lithium–calcium system. In the other systems, binary compounds were obtained. The co-intercalation of sodium and the alkaline earth metals calcium, strontium and barium is studied too. No ternary compounds were obtained. However, in the case of the sodium–barium system, a discussion on ternary graphite–sodium–barium compounds previously published is opened. Several data are in favour of a graphite–sodium–oxygen compound instead of a graphite–sodium–barium one.

Resume Le graphite, structure d’accueil amphotere, reagit aisement avec les elements electropositifs et, en particulier, avec les metaux alcalins, pour conduire a des composes d’intercalation binaires graphite–metal. Les metaux alcalins servent egalement de reactifs vecteurs pour permettre l’intercalation d’elements qui ne peuvent s’intercaler seuls dans le graphite. On obtient alors des composes d’intercalation ternaires par diverses methodes de synthese. Pour citer cet article : C. Herold, P. Lagrange, C. R. Chimie 6 (2003).