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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.

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.

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.

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.

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.

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.

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.

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.

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.

Lithium is able to intercalate into graphite leading to various binary graphite intercalation compounds, that are well defined by their stage. Concerning the ternaries, there is little literature on the subject. Thermodynamical and structural data, that differ largely from those of the other alkali metals, lead one to foresee some serious difficulties in synthesising such ternary compounds. Many experiments have attempted to synthesise ternary graphite intercalation compounds with lithium, using successively very electronegative elements, then fairly electronegative species and lastly electropositive metals. Numerous results, that are wholly negative, are described in this paper. The calcium–lithium system only allows one to prepare a novel intercalation compound, that is a first stage ternary phase exhibiting a large interplanar distance. This latter suggests that the intercalated sheets consist of several superimposed atomic layers. The synthesis of this ternary is not easy, because it needs reagents of very high purity. It possesses the brightness of metals and its strong hardness is very unusual among graphite intercalation compounds. On the other hand, the charge transfer between the graphene planes and the intercalated sheets, that just allows the intercalation, is especially high, and much higher than the LiC 6 compound.

The influence of dihydrogen gas on the reactions between graphite and liquid potassium containing a very small amount of a chalcogen (O, S, Se, Te) was studied. The reactions were carried out under a pure argon atmosphere in a stainless steel reactor, between 400 and 600°C. Controlled amounts of dihydrogen gas can be added in this reactor. When dihydrogen is strictly absent, the co-intercalation of potassium and chalcogen does not take place at 400°C: only potassium intercalates, leading to the KC8 binary compound. The same experiments carried out with controlled amounts of dihydrogen at the same temperature lead to various ternary compounds with oxygen, sulphur, selenium and tellurium. However, at 600°C, and strictly without dihydrogen, co-intercalation occurs, but only for S, Se and Te, allowing the preparation of new well-defined ternary graphite intercalation compounds. The co-intercalation of potassium and oxygen is possible only in the presence of dihydrogen, at any temperature.

Graphite and fullerite C60 exhibit low dimensionality crystal structures, which allow to observe numerous intercalation reactions. These latter are always accompanied with an electron transfer. When the graphene sheet or the fullerene molecule have been reduced, we obtain generally strongly reactive anionic species. However, their reducing character can disappear in several cases.

Potassium-phosphorus binaries are able to intercalate into graphite as potassium-oxygen or potassium-sulphur binaries, so that phosphorus behave as a classical electronegative element. But, it is able, on the other hand, to behave as a metal such as mercury, so that potassium-phosphorus and potassium-mercury binaries intercalate into graphite by very close synthesis routes. Phosphorus appears thus as a linking element between strongly and fairly electronegative species.

New first stage ternary graphite-potassium-chalcogen compounds were synthesized. They are very rich in alkali metal : their chemical formulas are close to KC3AX (A = sulphur or selenium). We studie...

New first stage ternary compounds associating potassium and phosphorous were synthesized in liquid potassium containing a few atomic percent of red phosphorous. The structural arrangement of these alkali metal rich phases was studied by X-Ray diffraction. Electrical measurements parallel and perpendicular to the c-axis were carried out between room temperature and 4.2 K.

Intercalation into graphite of electron donors is discussed, regarding the nature of the chemical species to be intercalated. In the binary compounds, the intercalated sheets are always mono-layere...

A new second stage blue phase of donor-type with an interplanar distance of 745 pm has been synthesized by reaction of graphite with partly oxidized sodium. It contains oxygen in form of peroxide ions.

The ternary graphite-potassium-thallium and graphite-rubidium-thallium systems were systematically studied. New compounds were observed, and the c-axis and 2D structures of all the ternary phases were determined and compared.