M. Lelaurain

X-ray investigation of highly saturated Li-graphite intercalation compound

Abstract Highly saturated lithium-graphite intercalation compounds (of a composition LiC2LiC4) synthesized under high-pressure conditions were investigated using X-ray diffraction. It was shown that these compounds present the structure with hexagonal unit cell with a parameter 8.63 A , c = 3I c = 3 · 3.7 = 11.1 A . The most probable stoichiometry for this unit cell is LiC2.67, as deduced from the comparison of the calculated and observed intensities of (hkl) reflections. It is supposed that this structure is the most “stable” step in decomposition of LiC2 compound obtained under pressure.

Insertion du chlore dans le graphite

Abstract The action of liquid chlorine on graphite has been studied by gravimetric, dilatometric and radiocrystallographic means. Around −20°C and according to the nature of the graphite, the compounds C12Cl and C16Cl corresponding to stages 3 and 4 respectively, were obtained. The interplanar distance is practically double that of pure graphite or 6.70 A. The intercalation involves a decrease in electrical resistivity in the direction parallel to the layers comparable to that observed for bromine. It was not possible to prepare compounds richer in chlorine by cooling to −40 and −78°C.

Synthesis, characterization and electrical resistivity of graphite bi-intercalation compounds G-FeCl3-MCl3 (M=Al, Ga, In) and the related binaries

Abstract We present new chemical, crystallographic and electrical conductivity data concerning the title compounds. It is found that the c axis repeat distances of the bi-intercalation compounds (GBC) are almost identical to the sum of the interplanar distances of the associated binary compounds. The basal plane resistivity ρ a decreases upon intercalation of the second halide into the stage two, binary host: ρ a ∼ 5 ± 1 μΩ cm at 295 K and ρ 295 ρ 4.2 for the GaCl 3− and AlCl 3 -containing GBC. The c axis resistivity possesses a positive temperature coefficient for all compounds examined except the 4th stage FeCl 3 GIC. The room temperature anisotropy is ∼10 6 for 1st and 4th stage GaCl 3 GIC as for low stage AsF 5 materials. Chemically determined values of the charge transfer are about twice as great as those evaluated from analysis of the C-C bond distances.

Some aspects of carbonization of mixtures containing coal tar pitch and graphite FeCl3 compounds

Abstract Pyrolysis of coal tar pitch has been carried out with new added species: a first-stage FeCl 3 graphite intercalation compound (GIC). Small particles of graphite were used (average diameter ≈ 5 μm) with the aim of obtaining a good distribution of the particles within the pitch matrix. Contrary to many works described in the literature, FeCl 3 intercalation in such small particles does not need stringent conditions for first-stage synthesis. Many hk0 reflexions of the FeCl 3 lattice are observed by X-ray diffraction; the incommensurability of the two macromolecular lattices (graphite and intercalated FeCl 3 ) is well characterized. The coal tar pitch-GIC mixture (4% in volume) presents a good distribution of the particles, as confirmed by scanning electronic microscopy (SEM). X-ray measurements show that the GIC particles are not deintercalated during the thermal treatment of mixing. Pyrolysis was carried out at 550°C with a heating rate equal to 20°C/min. The green coke yield obtained after this treatment is higher than in the case of a pure coal tar pitch pyrolysis, and new species containing iron are characterized in the green coke matrix. A partial diffusion of this element out of GIC particles occurs during the thermal treatment, and the released iron is reduced to oxidation degrees 2 and 0.

Evolution of the tridimensional organization of alkali metal doped polyacetylene complexes (MyCH)x with the doping level for M=Na,K,Rb,Cs

Abstract The evolution of the tridimensional organization of (M y CH) x complexes with M=Na,K,Rb,Cs has been examined as a function of the doping level y. The highly crystalline starting polyacetylene, synthesized according to the Akagi procedure, was stretched to realize an elongation of 600 %. Such an orientation which allows the separation of the different families of X-ray reflections (001, hk0 and hkl) is necessary to appreciate the 3D order of the materials studied. For samples doped with heavy alkali metals, it appears that for molar doping levels y≤0.125, the polymer and the alkali metal lattices are commensurate : along the c-axis one alkaline atom is always associated with 4(CH) units (4.96A) ; for y = 0.0625, a short distance order in (a,b) direction agrees however with a tetragonal system corresponding to Cmm or P 2 symmetries for the projection of the unit cell along the chain axis - the ideal formula for a stage 2 compound would be [M(C 4 H 4 ) 4 ] x - for y = 0.125, polymer and alkali metal networks are commensurate and describe a centred tetragonal lattice corresponding to the formula [M(C 4 H 4 ) 2 ] x . For doping levels higher than 0.125 the commensurability disappears. The periodicities of the alkaline species along the c-axis which depend on the size of the inserted counterion are 3.98, 4.02 and 4.07 A for K, Rb and Cs respectively in saturated compounds. At the same time, the periodicity along the polymer chain is 1.250 A. These data show that the formula [M(C 3 H 3 ) 3 ] x is never obtained. For sodium doped compounds, an hexagonal symmetry is found according to other authors. We found that the periodicities of the sodium atoms along the c-direction are 4.96 A (1 Na for 4(CH) units) and 4.20 A respectively for lightly and heavily doped materials. It must be also noticed that the alkali metal doping improves the coherence lengths and decreases the mosaic along the fiber axis at least for heavily doped samples.

Crystallographic and transport studies on AsF 5 intercalated graphite from 4.2 to 295 K. I. Structural ordering and phase separation

A study of the (00 l ), ( hk 0), and ( hkl ) reflections of stage 1 AsF 5 intercalated graphite between 4.2 and 295 K has been done using synchrotron radiation for single-crystal samples and a linear detector setup for those based on highly oriented pyrographite (HOPG). The nature and temperature dependence of the structural ordering allow the materials to be classified into (at least) two types related to the degree to which the AsF 5 has been converted into AsF − 6 and AsF 3 . At 295 K a small amount of in-plane order is detected within the essentially two-dimensional (2-D) liquid intercalate attributed to small quantities of AsF 5 and AsF − 6 − AsF 5 -ordered phases. Lowering the temperature leads to increased phase separation through crystallization and to changes in the in-plane unit cells associated with each. The most marked structural change is an incommensurate-to-commensurate ( I⇉C ) transformation within the AsF 5 phase, which starts at 215 ± 5 K. No new structural order is detected below 180 K. The (00 l ) studies give clear confirmation of the existence of separate phases with different values of interplanar distance. A smaller number of stage 2 compounds were examined. The most clearly different feature is that the I⇉C transformation is downshifted by ∼ 70 K. At room temperature, the stacking sequences are A/A/A … for stage 1 and A/AB/BC/CA … for stage 2.

Conductivity anisotropy in AsF5 — intercalated graphite

Abstract The electrical resistivity from 295 to 4.2 K both parallel (ρ a ) and perpendicular (ρ c ) to the basal planes has been examined in 1st and 2nd stage AsF 5 -intercalated graphite. The room temperature value of the anisotropy (ρ c /ρ a ) is greater than 10 6 in all cases; it decreases slightly for stage 1 and increases for stage 2 at liquid helium temperature. The anomalous changes in ρ a ( T ) and ρ c ( T ) are shown to be related to phase segregation into AsF 5 and AsF − 6 rich regions.

A study of temperature and pressure induced structural and electronic changes in SbCl5 intercalated graphite. Part II: Experimental data for c-axis resistivity

We present experimental data for the c-axis resistivity ?c of stage s = 2, 3, 4, 5, and 8, SbCl5 intercalated graphite, over the temperature range 40 to 300 K and the pressure range 0 to 0.8 GPa (0 ...

A study of temperature and pressure induced structural and electronic changes in SbCl5 intercalated graphite : Part I: Structural aspects

We have studied the effects of temperature (10 ≤ T ≤ 295 K) and pressure (0 ≤ p ≤ 0.8 GPa) on the state of intercalate layer crystallization in SbCl 5 graphite intercalation compounds of stages 2, 4, and 8. At room temperature (RT), the intercalate layer may in some second stage compounds be fully crystallized and lowering the temperature creates no further modifications. In all other cases, i.e., those in which the intercalate layer has only partial crystallization at RT, lowering T leads to the formation of new in-plane unit cells, the final state depending on the kinetics. Applying pressure to above 0.3–0.5 GPa results in crystallization in all cases, different from that induced simply by lowering of the temperature. We discuss the unit cells observed and the relationships they bear to each other in the light of other works on similar compounds.

Structural variations of oriented polyacetylene upon intercalation with selected electron donating and accepting species

Abstract Unaligned and highly oriented polyacetylene (HOPA) have been doped with a heavy alkali metal M in the vapour phase. The evolution of the crystallographic structure of these polyacetylenes during the progress of the intercalation has been studied by X-ray diffraction. Different ordered and partially ordered phases have been characterized depending on the dopant concentration. Our results support the channel intercalation model and allow the description of the mechanisms of (CH) x doping. First, at the beginning of doping the alkaline ions enter into the channels; their separation distance in the chain direction is equal to 4 (CH) units; only a short-range 2-D order perpendicular to the chains corresponds to the selective filling of one channel among the two possible available ones, which leads to the tetragonal lattice of the ideal (M(C 4 H 4 ) 4 ) x compound in agreement with the corresponding slope observed in potential versus composition curves. Secondly, upon higher doping there is the apperance of a 3-D order where the columns of alkaline ions separated by 4 (CH) units fill up equally the available channels in a centred tetragonal cell; the formula of this commensurate compound is represented by (M(C 4 H 4 ) 2 ) x . Finally, more extended doping results in loss of the commensurability of the alkaline ion and polymer lattices, in the chain direction; at this time the distance between the alkaline ions becomes near to 3 (CH) units leading to the limiting formula (M(C 3 H 3 ) 2 ) x . These two latest formulae agree with the limiting richest compositions of the slope region observed in the potential versus composition curves. Preliminary structural data are also reported on the incommensurate GaCl 4 − −(CH) x products synthesized electrochemically in LiGaCl 4 CH 3 NO 2 electrolyte.