S. Flandrois

Intercalation compounds of graphite with nickel chloride: synthesis, structure, and mechanism of intercalation

Abstract The intercalation of nickel chloride into graphite in presence of chlorine gas has been studied in the temperature range 390 – 750 °C with an apparatus allowing the measurement of the chlorine pressure during intercalation. The results indicate that chlorine takes part in the reaction with a 600 mmHg threshold pressure below which no intercalation occurs. Between 495 and 690 °C, a second stage compound C 11.3 NiCl 2.13 , is obtained with the apparent activation energy of the intercalation being about 50 kcal/mole. X-ray investigations show that intercalated nickel chloride has a structure very close to the nickel chloride sandwich in free metal halide. However, intercalant layers are not complete, with the filling coefficient being at most 0.71. All of the data are consistent with an islandic nature of nickel chloride: islands of diameter 100 A allow explanation of the non integer stoichiometric coefficients given by chemical analyses and the amount of charge transferred from graphite to nickel, which is, moreover, consistent with a decrease of CC bond lengths as observed by X-ray diffraction.

Physical Properties of One Dimensional Conductors

Abstract In the course of investigations of organic metals we have investigated the cation-radical series TMTTF2-X′ with X′ = BF4, ClO4, PF6, SCN and Br. On this isomorphous series a large range of physical properties have been studied: electrical conductivity, magnetic susceptibility, EPR, optical reflectivity and specific heat. In correlation with crystallographic results, which indicate the existence of TMTTF diads, the dominant interactions are analyzed. It results that the metallic behavior at high temperatures and the occurrence of a Peierls distorsion below 100 K arise mainly from a competition between electron-electron and electron-phonon coupling inside the cation-radical chains

Synthesis, structure and preliminary results on electrical and magnetic properties of (Perylene)2 [Pt(mnt)2]

Abstract In this paper we report the preparation, crystal structure and some physical properties of the conducting molecular (Perylene)2 [Pt(S4C4(CN)4)]. The crystal structure consists of segregated stacks of perylene and Pt S4C4 (CN)4 units, with a spacing of 3.3 A between the carbon atoms in the perylenes. The temperature dependence of the electrical conductivity is metallic with a maximum at approximately 15 K. At this temperature a sharp transition to an insulating state occurs. Magnetic suceptibility measurements confirm the existence of a transition in this temperature range.

Effect of Graphite Crystal Structure on Lithium Electrochemical Intercalation

The electrochemical intercalation of lithium into various graphite materials has been examined in LiPF{sub 6} solutions of ethylene carbonate (EC)/dimethyl carbonate (DMC) or EC/DMC/propylene carbonate (PC). When the graphite powder samples contained at least 30% of the rhombohedral form, no exfoliation was observed, even with electrolytes containing a large amount (80%) of PC. However, when the graphites were heat-treated at temperatures above 1,000 C, the faradaic losses due to the exfoliation reappeared, even though the rhombohedral phase content was unchanged. From Raman spectroscopy measurements, a correlation was found between the irreversible capacity due to the exfoliation and the ratio, R, of the integrated intensity of the disorder-induced line at 1,350 cm{sup {minus}1} to the Raman-allowed line at 1,580 cm{sup {minus}1}. This suggests that structure defects, probably localized in grain boundaries between rhombohedral and hexagonal domains, hinder the layer opening necessary for the intercalation of solvated lithium species at the beginning of the first electrochemical cycle.

Charge transfer and islands in metal halides-graphite intercalation compounds: New evidence from x-ray diffraction of intercalated Mn Cl2

Abstract Single crystal structure studies at room temperature have been made for the first stage Mn Cl 2 intercalated graphite. The nominal composition was C 5·6 Mn Cl 2·4 , as deduced from chemical analyses and X-ray diffraction intensities. The data are in agreement with the island model, already proposed for Ni Cl 2 intercalation. From the decrease in C-C bond length and comparison with As F 5 compound, it is shown that the charge transfer is determined by chlorine in excess with respect to free metal halide.

One-, two- and three-electron reduction of C60 using the electron-reservoir complex [FeI(C5H5)(C6Me6)]

The reaction between the 19-electron complex (FeIC5H5)(C6Me6)]1 and C60 in toluene gives the paramagnetic salts (1+)C60–, (1+)2C602– and (1+)3C603– depending on the stoichiometry of the reactants

Boronated carbons: structural characterization and low temperature physical properties of disordered solids

BxC1–xcompounds (x≤0.25) have been prepared by the thermal CVD technique. The aim of this paper is to better characterize some specific boron rich compositions that are not yet satisfactorily described. Both structural and physical properties have been investigated; including low temperature direct current resistivity, dynamic and static magnetic susceptibilities, specific heat and thermal conductivity. The final purpose is to correlate the structural disorder, both positional and substitutional, with particular electronic and vibrational properties deduced from low temperature experiments.

Neutron diffraction and small-angle scattering studies of graphite-nickel chloride intercalation compounds

Abstract Intercalation of graphite with metal chlorides leads to compounds for which chemical analyses give non-integer stoichiometric coefficients. In particular, an excess of chlorine is observed with respect to free metal chlorides. For NiCl 2 intercalated graphite, the composition of the second-stage compound corresponds to the formula: C 11.3 NiCl 2.13 . This chlorine excess was accounted for by assuming the existence of small islands of intercalated chloride. As NiCl 2 -graphite compounds are known to undergo a magnetic phase transition at about 20K, neutron scattering and diffraction experiments were carried out in order to provide evidence for the islands and to specify the magnetic ordering at low temperature. From the small-angle scattering data collected below and above the magnetic transition, the first experimental evidence for the presence of intercalated islands has been obtained. The mean size of the islands is about 150 A, as previously assumed. From diffraction experiments, it has been shown that the spins of Ni 2+ ions in the magnetic phase are aligned ferromagnetically within the intercalant layer.

Etude par diffraction es rayons x et microscopie electronique a haute resolution de quelques composes d'insertion graphite-chlorure metallique

Resume X-ray diffraction and high resolution electron microscopy studies have been carried out on single crystals of Madagascar natural graphite intercalated with several metal halides: NiCl 2 , MnCl 2 and CuCl 2 . The structure of the second stage CuCl 2 compound is reported. Then the results obtained for the three metal chlorides are compared.

On the Structure and Properties of TMTTF and TMTSF Salts: Experimental Evidence for the Importance of Interchain Couplings

Abstract The structure and physical properties of tetramethyl-tetrathiofulvalene (TMTTF) salts are reviewed. New results are given about (TMTTF)2 PF6, (TMTTF)2 ClO4 and the selenium analog (TMTSF)2 ClO4. An experimental relationship is shown between the electrical and magnetic properties and the closest contacts S-S or Se-Se of neighbouring stacks.