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The intercalation of fluorine into graphite leads to graphite intercalation compounds (F-GICs) exhibiting potential properties such as the storage and transport of fluorine. Stage-1 compounds with C2.5F to C4F compositions are obtained by fluorination treatments at room temperature of ex-pitch, high-temperature treated carbon fibres under 10 bars F2 pressure in the presence of gaseous HF. The deintercalation process of fluorine species has been studied by evolved gas analysis: the F-GICs are decomposed using the Controlled transformation Rate Thermal Analysis (CRTA) method. The thermal analysis curve obtained for stage-1 F-GICs exhibits three decomposition steps. The first two steps correspond to a simultaneous deintercalation of atomic fluorine F and gaseous HF and the third step (above 460°C) to the degradation of the compound with formation of C2F4 and CF4 which further dissociate in the spectrometer to CFn (1 ≤ n ≤ 3) species.

The deintercalation process of fluorine species from fluorine-graphite intercalation compounds (F-GICs) has been investigated by evolved gas analysis. The controlled transformation rate thermal analysis method was used. In this way, the rate of production of the gaseous phase is permanently controlled at low pressure, so that both temperature and pressure gradients can be lowered at will, avoiding the overlap of the successive steps of the reaction. These experiments have been carried out on stage-1 F-GICs with C F ratios ranging from 3 to 4, which were obtained from high-temperature treated carbon fibres (ex-pitch) fluorinated at room temperature with P F 2 bar in the presence of gaseous HF. The thermal analysis exhibits three parts: the first two parts correspond to the deintercalation of fluorine and HF; and the third part (> 460 °C) to the degradation of the carbonaceous skeleton. The activation energies associated with the different parts have been determined by the rate-jump method. A kinetic study of the deintercalation/decomposition processes has been proposed. The first (deintercalation) part is apparently accompanied by a post-deintercalation reaction of evolving fluorine with carbon atoms of defects leading to the formation of covalent CF bonds. The deintercalation is achieved during the second part which can be described by a two-dimensional interfacial advancement process. The apparent activation energy of this deintercalation part has been evaluated to be 144 kJ mol−1. The degradation part, with 240 kJ mol−1 activation energy, can be ascribed to a two-dimensional nucleation and growth of nuclei mechanism.

Measurements of the heat capacity of the elpasolite Rb2KGaF6 and the solid solutions Rb2KGaxSc1−x F6 with a gallium content in the range x=0.6–0.95 are performed. The nature of the influence of the chemical composition of the compounds and the hydrostatic pressure on the temperature and entropy of the ferroelastic phase transitions is established.

The syntheses and crystal structures of two new fluoromanganese(III) complexes are reported; [MnF3(H2O)(2,2′-bipy)] 1 and 4,4′-bipyH2[MnF4(H2O)2]·2H2O 2, where 2,2′-bipy and 4,4′-bipy are 2,2′-bipyridyl and 4,4′-bipyridyl, respectively. Compound 1: monoclinic, space group P21/n, a = 1973.7(4), b = 749.0(2), c = 903.1(3) pm, β = 95.22(3)°, Z = 4, R1 = 0.051. Compound 2: monoclinic, space group P21, a = 516.4(2), b = 1851.9(4), c = 986.3(3) pm, β = 99.07(2)°, Z = 2, R1 = 0.028. The manganese co-ordination environment was found to be octahedral in both compounds, but strongly distorted by the Jahn–Teller effect as a result of the high-spin d4 configuration of Mn3+. A very extensive intermolecular hydrogen-bond framework is present in both compounds. For compound 1 the octahedra are linked through hydrogen bridges resulting in octahedral manganese chains. For compound 2, the octahedra [MnF4(H2O)2]– are associated via hydrogen bonds into chains, which in turn are connected by interchain hydrogen bridges. The polarized optical spectra of single crystals are presented and explained in terms of intraconfigurational d4 transitions split by ligand fields of nearly Cs and D4h symmetries for compounds 1 and 2, respectively. The results are compared with those available for other MnIII fluorides.

The fluorination of a furnace carbon black (N115 from Degussa) with gaseous F2, diluted in N2, at room temperature was studied by XPS. The influence of the reaction parameters (% of F2 in the gaseous mixture, duration of contact) and activation (O2 at 450 °C) of the carbon black on the amounts of fluorine fixed, in the bulk and at the surface and subsurface zone of the carbon particles has been investigated. By analyzing the C1s and F1s peaks, different forms of C and F were evidenced and their relative contributions in fluorinated black determined. Information concerning the nature of the CF bond formed and the effect of the fluorination on the structure of the pristine carbon black is given. It is shown that the fluorinated product obtained is of polyphasic nature. Fluorinated islands of limited thickness alternate with non-fluorinated zones that have kept their original structure. F is mainly covalently bonded to reactive C atoms of the surface and subsurface shell of the particles.

A critical review of the literature relative to the chemical characterisation of fluorinated carbon compounds by X-ray photoelectron spectroscopy is proposed. Guidelines for identification and assignation of the different components which are individualized by fitting of the C 1s and F 1s peaks are given. It is suggested that in fluorocarbons, the chemical shifts of the C and F core levels depend not only on the nature of the CF bond (ionic, semi-ionic or covalent), the number of F atoms linked to the C atom and the chemical environment of the CF group (β effect), but also on the structure and conformation of the C atom skeleton in the fluorinated material. The types of fluorinated structural unit that are formed vary as a function of the conditions of fluorination (temperature, eventual presence of traces of HF or fluoride acting as catalysts) and of the structure and graphitic character on the starting material. Since the experimental values of the binding energy of the different types of CF bonds proposed by the authors differ to a slight extent, some fluorinated polymers and fluorographites of known composition have been analysed by XPS. The binding energies of the components of the C 1s and F 1s peaks, the energy separation ΔCiCr of the former relative to the component (Cr) corresponding to hydrocarbon contamination and the energy separation ΔCiFi between the corresponding components of the C 1s and F 1s peak have been determined and correlated to the nature of the chemical and structural environment of the involved atom.

Fluorination processes of polymer surfaces are able to lead to drastic modifications of the surface properties without changing the bulk characteristics of the virgin material. In this paper, two types of polymers, i.e. ultrahigh molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE), are considered. The surface of these materials have been modified using two different fluorination routes, both carried out at room temperature: the direct fluorination with 10% F2 + 90% He gaseous mixtures and the radio-frequency plasma-enhanced fluorination (PEF) using either O2/CF4 mixtures or c-C4F8. The effect of these processes on the surface of the polymer samples are compared using mostly XPS results. The different components of the C1s spectra are assigned in term of CFx bonding, giving valuable information on the surface fluorination rate.

Single crystals of CsFe2F6 are obtained by solid state reaction of a stoichiometric mixture of CsF, FeF2, and FeF3 (sealed Pt crucible, 750 °C, controlled cooling).

This chapter deals with the description of the most important structural types of transition-element fluorides and oxide-fluorides, pointing out the relationships occurring between these networks. The peculiar nature of M–F bonds generally leads to outstanding physical behavior, such as ferri- and ferromagnetism, piezoconductivity, multiferroism, F-induced high-critical-temperature superconductivity, high ionic conductivity, and optical properties, and the knowledge of the precise structural characteristics of these phases appears to be essential for a better approach of these properties. Some new elaboration methods are described as far as they provide access to materials with specific features (nanosized particles, etc.) and significantly improved properties.

International audience; Fluorination processes of polymer surfaces are able to lead to drastic modifications of the surface properties without changing the bulk characteristics of the virgin material. In this paper, two types of polymers, i.e. ultrahigh molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE), are considered. The surface of these materials have been modified using two different fluorination routes, both carried out at room temperature: the direct fluorination with 10% F2 + 90% He gaseous mixtures and the radio-frequency plasma-enhanced fluorination (PEF) using either O2/CF4 mixtures or c-C4F8. The effect of these processes on the surface of the polymer samples are compared using mostly XPS results. The different components of the C1s spectra are assigned in term of CFx bonding, giving valuable information on the surface fluorination rate.

International audience; For the first time, structural phase transitions induced by the temperature were found in AxMxIIM(1−x)IIIF3 fluorides with the defect pyrochlore structure (FdView the MathML sourcem, Z=8). The room temperature structure of CsFe2F6 was determined using X-ray powder diffraction technique. This phase was found to be ordered with the Pnma space group. The study of the temperature stability of orthorhombic structure by differential scanning calorimeter between 100 K and 700 K has shown a succession of phase transitions. The Pnma (Z=4)→Imma (Z=4)→I41/amd (Z=4)→FdView the MathML sourcem (Z=8) structural sequence was proposed to occur within a rather narrow temperature range 500-560 K. The mechanism of structural transition has been mainly associated with the rotation of (MF6) octahedra and small displacements of some Fe atoms. This assumption is in good agreement with the low experimental entropy value, which is characteristic for displacive transformations.

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Boron-substituted carbons have been synthesized by chemical vapor deposition from acetylene and boron chloride. The highest boron concentration corresponded to BC 3 formulation as shown by electron probe microanalysis. The intercalation behavior of these materials has been investigated with electron donors (alkali metals) and electron acceptors (fluorine, bromine). Of particular interest is the intercalation of lithium from the vapor phase: whereas lithium carbide is formed with pristine graphite at temperatures above 450 °C, such a reaction does not occur with BC 3 , even at 700 °C. Very high Li contents corresponding to compositions such as (B 0.25 C 0.75 ) 3 Li can be obtained at 600 °C. On the other hand, halogens do not react with BC 3 , but bromine is intercalated in products with lower boron contents. Preliminary results are also presented on the intercalation in nitrogen- and boron-substituted carbons.

The different types of CF interactions have been evidenced from XPS investigations on fluorinated carbonaceous materials. The respective amount of the C1s and F1s components depends on several factors, including the nature of the host material, the thermal treatments which increase the graphitization level and the fluorination conditions. TEM images and corresponding Fourier transforms of high temperature-treated pitch-based and PAN-based fibres have shown that only stage-1 compounds and graphitic-type domains are detectable in the experimental conditions. In particular, no interlayer spacing corresponding to higher stage materials has been noticed. The observed results can be correlated to the ratio of semi-ionic to covalent FC bonding determined by XPS.

The compounds Rb 2 KYF 6 , Rb 2 KInF 6 and Tl 2 KInF 6 undergo structural phase transitions from low-temperature distorted forms to a cubic high-temperature elpasolite-type structure. The thermal evolution of the 19 F NMR signal observed in these three fluorides allows correlation of the structural phase transitions with atomic motions of fluorine. The type of motion involved, however, differs for each compound: they can be correlated to rotational motions or isotropic reorientation of (MF 6 ) 3− octahedra.

An enhancement of the in-plane thermal conductivity in the superconducting state is observed in most high-T-c superconductors. Here the observation of a similar enhancement of the thermal conductivity in copper-oxide compounds, which is not related to the superconducting transition, is reported. Since this anomaly is also accompanied by a significant variation of the electrical conductivity it indicates that a strong electron-phonon coupling exists and that thermal-conductivity enhancements in copper-oxide compounds should be attributed to an increase of its lattice component.

A new elpasolite Tl2KInF6 has been synthesized. This compound undergoes at 228 K a ferroelastic phase transition from a room-temperature Fm3m variety to a monoclinic variety. X-ray, optical, calorimetric and DTA studies under hydrostatic pressure have been performed and compared with other elpasolite-type fluorides.

A new transition phase has been observed in the copper complex fluoride, Tl 2 CuF 4 , with the K 2 NiF 4 -derived structure. A Rietveld refinement of the room-temperature X-ray powder pattern in the I 4/ mmm space group [ a = 4.206(2) A; c = 13.673(5) A] has confirmed the antiferrodistortive arrangement of the e g orbitals of Cu 2+ . Around 200 K a structural phase transition to a low-temperature monoclinic phase has been evidenced by DSC and X-ray diffraction [space group I 2/ m , a = 4.182(2) A, b = 4.183(2) A, c = 13.492(6) A; β = 94.564(4)°]. Tl 2 CuF 4 exhibits ferromagnetic properties below T c = 10 K. The dependence of the magnetization on the applied field is characterized at 1.7 K by a coercive field of 2.5 × 10 −2 T and a remanent magnetization of 0.6 μ B . The phase sequence has been compared with those found in La 2 CuO 4 -type compounds.

New elpasolites like A2KMF6 doped with Cr3+ have been investigated by means of optical and EPR techniques. It is shown that though the structural phase transition undergone by Rb2KGaF6 at T = 129 K is much stronger than that corresponding to Rb2KInF6, the emission band at 10 K of the latter is much broader than that for the former. This inhomogeneous broadening is correlated with the increase experienced by the EPR bandwidth below 150 K reflecting only local changes around Cr3+. An analysis of zero phonon lines through the fluoroelpasolite series reveals that they are very sensitive to changes of the Cr3+-F− distance, R. It is shown that changes δRo in the perfect lattice induce changes on R given by δR = fRo where f is only 0.15. At variance with the findings for MnF6 4-, the present results indicate that an increase of R tends to decrease the Stokes shift. The origin of this fact is discussed. Finally, the present results indicate that R increases (about 0.2 pm) in the phase transition of Rb2KG...

The structure of CsPd2F5 has been confirmed from neutron diffraction data on powdered sample. CsPd2F5 crystallizes in the orthorhombic Imma space group. At 100 K, the unit-cell constants are a = 6.473(2) A, b = 7.853(5) A, c = 10.718(3) A and the calculation carried out using the Rietveld method leads to R1 = 0.020. The network is formed of PdF6 octahedra chains containing half of Pd in high-spin configuration, connected one to each other by square planes containing the other half of Pd in low-spin configuration. CsPd2F5 orders antiferromagnetically below TN = 38 K. In the ordered state a weak ferromagnetic component occurs (σ0 = 0.098 μB at 2 K). The magnetic structure determined at 4 K is consistent with the magnetization data and can be described in the Im′m′a′ magnetic group without any doubling of the unit-cell parameters. Within the chains, Pd2+ are coupled antiparallel. The magnetic moments are located in the (x0z) plane, the angle between the moments and the z axis being 18°. Magnetische Struktur von CsPd2F5 Die Struktur von CsPd2F5 wird durch Neutronenbeugungsdaten an Pulverproben bestatigt. CsPd2F5 kristallisiert in der orthorhombischen Raumgruppe Imma. Die Gitterkonstanten bei 100 K sind a = 6,473(2), b = 7,853(5), c = 10,718(3) A, und mit der Rietveld-Methode wird ein R1 = 0,020 erhalten. Die Struktur wird aus Ketten von PdF6-Oktaedern gebildet, die die eine Halfte des Palladiums in high-spin-Konfiguration enthalten und miteinander uber Quadrate verbunden sind, in denen die andere Halfte des Palladiums in low-spin-Konfiguration vorliegt. CsPd2F5 ist unter TN = 38 K antiferromagnetisch. Im geordneten Zustand zeigt sich eine schwache ferromagnetische Komponente (σ0 = 0,098 μB bei 2 K). Die bei 4 K bestimmte magnetische Struktur ist mit den magnetischen Daten vereinbar und kann in der magnetischen Gruppe Im′m′a′ ohne eine Verdoppelung der Gitterparameter beschrieben werden. In den Ketten sind die Pd2+ antiparallel gepaart. Die magnetischen Momente sind in der (x0z)-Ebene lokalisiert, der Winkel zwischen den Momenten und der z-Achse betragt 18°.

The thermal stability of fluorine-intercalated carbon fibres has been studied using differential thermal analysis and thermogravimetry. The selected host fibres were polyacrylonitrile-based and pitch-based carbon fibres, either as-received or heat-treated at 3000 °C. Fluorination performed at room temperature in the presence of hydrogen fluoride led to stage-1 compounds for the most graphitized samples. The thermal stability was found to depend on the host structure and on the amount of intercalated fluorine.

New exotic phenomena have recently been discovered in oxides of paramagnetic Ir(4+) ions, widely known as 'iridates'. Their remarkable properties originate from concerted effects of the crystal field, magnetic interactions and strong spin-orbit coupling, characteristic of 5d metal ions. Despite numerous experimental reports, the electronic structure of these materials is still challenging to elucidate, and not attainable in the isolated, but chemically inaccessible, [IrO6](8-) species (the simplest molecular analogue of the elementary {IrO6}(8-) fragment present in all iridates). Here, we introduce an alternative approach to circumvent this problem by substituting the oxide ions in [IrO6](8-) by isoelectronic fluorides to form the fluorido-iridate: [IrF6](2-). This molecular species has the same electronic ground state as the {IrO6}(8-) fragment, and thus emerges as an ideal model for iridates. These results may open perspectives for using fluorido-iridates as building-blocks for electronic and magnetic quantum materials synthesized by soft chemistry routes.

The structure of BaBiO 2 Cl has been determined from single crystal X-ray diffraction data. It crystallizes in the orthorhombic space group Cmcm with a = 5.880(4), b = 12.945(18), c = 5.677(3) A, V = 432.0(3) A 3 , and Z = 4. BaBiO 2 Cl is related to a family of bismuth oxyhalides which can be viewed as separate oxygen and chlorine layers stacked along the b axis, with bismuth and barium cations located between the layers. The structure differs from other bismuth oxyhalides in that the barium and bismuth cations are found to be ordered in two distinct coordination environments. The cation ordering and fourfold coordination environment of bismuth is seen as a structural expression of the stereochemically active bismuth 6s lone pair of electrons.

The heat capacities of Rb2KHoF6 and Rb2KErF6 have been investigated over a wide temperature range 150-430 K including the temperatures at which the phase transitions Fm3m → P21/n occur. The pressure dependence of phase transition temperatures, studied up to 0.6 GPa was found to be nonlinear. Effect of B3+ ion size both on entropy of structural transformation and dT0dp is discussed for Rb2KB3+F6 series.

The effect of fluorination on the transport properties of three classes of materials is presented. The intercalation of fluorine in graphitized carbon fibres drastically modifies their electrical behaviour. A wide range of conductivities is observed from sigma(300K) similar to 1.5 X 10(5) S cm(-1) for Csimilar to 14F to sigma(300K) similar to 10(2) S cm(-1) for C

The X-ray photoelectron spectroscopy study of fluorine-intercalated carbon fibers has shown the formation of semi-ionic bonding between carbon and intercalated fluorine species, leading to an increase in the positive charge on the involved carbon atoms and a subsequent increase in C 1s binding energy. Covalent CF bonding is present at the external surface of the fibers. The relative amounts of these species are dependent on the intercalation rate and on the nature of the host fibers: polyacrylonitrile or pitch based, either as received or high temperature treated.

A high resolution transmission electron microscopy study of fluorine-intercalated carbon fibers has been carried out on two types of host materials: high-temperature treated pitch-based and PAN-based fibers. TEM images and corresponding Fourier transforms have shown that only stage-1 compounds and graphitic-type domains are detected in the experiment conditions. In particular, no interlayer spacing corresponding to higher staged materials have been noticed. The observed results can be correlated to the ratio of semi-ionic to covalent FC bonding previously determined by XPS. The disorder mostly depends on the nature of the host fiber and on the amount of mobile species that may react with the graphene layers during the deintercalation process, which is favored by the high-vacuum conditions.

Numéro spécial de : Journal of Fluorine Chemistry 2012, vol. 134, 188 p.; International audience; Fluorine is an omnipresent chemical element in our everydaylife. The last two decades have witnessed a spectacular growth ofinterest in selectively fluorinated molecular compounds. Nowadays,several hundreds of thousands molecules contain at least onefluorine atom. These molecules found essential applications in lifesciences, medicine, pharmacology, medical imaging, agriculturalchemistry, materials, etc. The manifold facets of fluorinatedbiomaterials and drugs are illustrated by examples ranging frominorganic ceramics to perfluorinated organic molecules. Theapplications include neuroleptics, anti-cancer, antibiotics, PETimaging for an early detection of tumors, etc. In the cornerstonefield of energy storage and conversion, fluorine constitutes a keyelementbecause most devices devoted to the storage of the energy(lithium-ion batteries, fuel cells) use fluoride materials aselectrodes, electrolytes containing a fluoride salt, fluoromembranes,etc. Another illustration is the impact of this element in thenuclear cycle via the synthesis of uranium hexafluoride which is anunavoidable step toward uranium enrichment. Through theseexamples, it is clear that whatever its state, fluorine has asignificant societal impact.

International audience; Surface properties of nanosized silica, synthesized using fluoridation technologies, have been modified by direct fluorination using F2-gas or by plasma radio frequency. The modifications of the physicochemical characteristics of the surface have been characterized by spectrometry of photoelectrons (XPS), infrared and high resolution transmission electronic microscopy and compared with those of pristine silica.

International audience; Several nanosized fluoro-compounds have been prepared by microwave-assisted solvothermal routes: Al3+-, Fe3+- and Ti4+-based oxyfluorides with the hexagonal tungsten bronze (HTB) framework, Ti4+-based fluorinated anatase, and rutile MgF2. The structural features have been determined using XRD and TEM analyses. The presence of OH− groups substituted for F− ions has been demonstrated for all of these nanofluorides. In Al- and Mg-based nanofluorides, the OH rate can be reduced by F2-direct fluorination. Furthermore, the higher the polarizing power of the cation, the higher the oxygen content. For cation with high formal charge, such as Ti4+ stabilized in a distorted octahedral site, the occurrence of O2−/OH−/F− anions in its vicinity as well as vacancies have to be mentioned. Finally coupling the microwave-assisted solvothermal route with the F2-direct fluorination allow preparing high surface area metal fluorides where the amount of oxygen is noticeable and contribute to create under-coordinated cationic species at the surface which can induce high Lewis acidity.

The chain Mn(III) fluoride Na 2 MnF 5 has been studied by means of neutron powder diffraction. Below T N = 11.1(5) K, a 3D intrachain antiferromagnetic coupling is observed: this is the first time that a 3D ordering is unambigously found in anhydrous A 2 MnF 5 series. Additionally a magnetic frustration phenomenon is found for the interchain ordering. At 1.5 K the magnetic structure is colinear, with the manganese magnetic moments (3.3(1) μ B ) parallel to the a axis. Structural and magnetic data of Na 2 MnF 5 are compared with those of other related compounds.

Precise photoluminescence measurements have been carried out on RbCdF3:Mn2+ in the 9-300 K range to explore the structural phase transition of the host lattice at Tc=124 K using the first (M1) and second (M2) moments of the emission band together with the lifetime tau as probes. Aside from showing a sensitivity of M2(T) and tau (T) to the phase transition, the present data reveal that the curve M1(T) experiences a small but observable change of slope in the vicinity of Tc. It is demonstrated that this jump, Delta t( delta M1/ delta T)P=0.22 cm-1 K-1, is mainly associated with the increase experienced by the local thermal expansion coefficient below Tc. The importance of both the implicit and explicit contributions to M1(T) is analysed throughout this work. Neither the luminescence nor the excitation spectrum shows any evidence of tetragonal distortion in the MnF64- complex. This fact is explained through the Rax-Req=0 2 pm value (where Rax and Req are the axial and equatorial Mn2+-F- distances) at 30 K, and the coupling coefficient VE=66 cm-1 pm-1 with the Eg Jahn-Teller mode of MnF64-. Finally, we have found that this crystal exhibits photochemical reactions under UV light irradiation, leading to the formation of centres that transfer easily to Mn2+ ions. These centres give rise to an intense absorption band at 310 nm, analogously to those previously formed under x-irradiation.

The radiofrequency plasma technique involving mixtures of CF4+O2 gases has been applied to the surface treatment of high Tc superconducting oxides (YBa2Cu3O7−δ). Investigation of the various experimental parameters of the process has shown that the improvement of the critical current density, Jc, mainly depends on the inlet precursor composition CF4+τ%O2, on the total pressure and on the reaction time. The presence of fluorine in the bulk of the ceramics has been observed from electron microprobe analysis, together with an increase of the “Cu3+” content. The plasma-enhanced fluorination (PEF) treatment improves the superconducting properties of the materials: both values of the resistivity in the normal state and of the superconducting transition width are reduced and the critical transition temperature is improved by about 1 K.

Mechanisms of interaction between the reactive species of a (CF 4 +O 2 ) plasma and YBa 2 Cu 3 O 7-δ ceramics have been proposed through detailed angle-resolved X-ray photoelectron spectroscopic analyses. At the surface of the outer grains, the plasma treatment removes (OH) - and (CO 3 ) 2- species contained in the degradation layer and gives rise to a fluoride-rich layer, whereas in the bulk of the material the occurrence of metal-fluorine bonds in the superconducting phase has been assumed. An increase of the oxidation state of copper has been also detected, confirming the oxidizing effect of the plasma treatment. A comparison with the oxidation mechanisms obtained by fluorine gas treatment is proposed

The peculiar reactivity of fluorine with graphite can be related to some characteristic parameters of this element. The competition between strong C-F bonds in covalent graphite fluorides and weak semi-ionic bonds in graphite intercalation compounds is pointed out. The different experimental routes for the intercalation of fluorine and metal fluorides into graphite are reviewed. The oxidation state, the environment of the metal and the nature of the bonding between the intercalated species and carbon can be approached by various techniques, including XANES, EXAFS, and XPS spectroscopies. The structural relationships between the graphene sublattice and the intercalate sublattice can be pointed out on the basis of single crystal data. Concerning the transport properties, acceptor-GICs have proved to be very appropriate to investigate the effects of disorder and reduced dimensionality. The charge transfer which accompanies the insertion of fluorinated species between the graphene layers can be evalu...

The influence of a halogen-gas (Cl-2 or F-2) treatment on both structural and physical properties of La2CuO4 has been studied. In ail cases, the resulting product contains an excess of anionic species and shows superconducting properties below 32K and 40K respectively for the chlorine- or fluorine-treated sample. But these treatments have a different influence on the evolution of the: structural properties comparatively to those observed for the starting oxide : after chlorination a decrease of the orthorhombic distortion is detected, whereas an opposite trend is shown after fluorination. The Cl-2-gas treatment leads to an oxygen-excess phase La2CuO4.08, whereas the fluorination yields an oxyfluoride La2Cu(O,F)(4.17).

The ionic conductivity properties of Bi 1-x 3+ (A 0,5 2+ B 0,5 5+ ) x O 1,5 + 0,25x (A  Pb, Mg; B  Nb, Ta) solid solutions with the fluorite-type structure have been studied between 298 and 623 K. Good electrical performances have been obtained. Correlations have been established between the electrical and structural properties.

The intercalation of fluorine in various types of carbon fibers (PAN-based or pitch-based, asreceived or high-temperature treated) has been investigated at room temperature in the presence of gaseous HF. Stage-1 compounds with C2.5F to C4F compositions are obtained for 10 bar F2 pressures, whereas lower pressures (1 bar F2) lead to stage-2 compounds. Although in higher stages (≥2) the electrical conductivity is generally larger than in the pristine fiber, in stage-1 compounds a drastic increase of resistivity is observed, ρ being more than one order of magnitude larger than that of the starting material. Finally, fluorine-intercalated GICs have been found appropriate to investigate the effects of disorder and reduced dimensionality.

ISBN 978-0-444-72002-3; The surface characteristics of materials dominate the performance of the final products in many applications. For instance the mechanical behavior of composite materials are strongly dependent on the nature of the fiber/matrix interface, the lubricant properties are influenced by surface tribological effects, the success of bio-implants is mostly determined by biocompatibility, etc.

Many structural networks of transition metal fluorides and oxide fluorides may be derived from simple units of octahedral MF6 units, connected by common corners, generally in a 3D way: e.g., perovskite, ReO3, elpasolite, HTB, TTB, pyrochlore, etc. The accurate knowledge of these structures, together with the stabilities of these phases vs. temperature, allows deeper interpretation and fitting of many of their physical properties. Among the numerous fluoro-compounds which derive from these structural arrangements, several fluorinated and oxyfluorinated series have been chosen to illustrate the great range of outstanding physical properties, including ferromagnetism, piezoconductivity, ferroelasticity, high TC superconductivity, surface functionalization, that can be better understood with the help of structural considerations. The concept of nanometric particles in materials science has also drastically changed the investigations in solid state fluorine chemistry, not only for finding original synthetic routes, but also new characterization tools. As an example, in nanostructured M(OH,F)3 metal hydroxyfluorides that can be used as acidic heterogeneous catalysts, the morphological nature and specific area of the materials can be tuned by changing the experimental parameters of synthesis. In particular, the number and strength of Bronsted/Lewis acidic sites and the thermal stability can be correlated to the structural arrangements.

International audience; The electrochemical reaction of lithium with a vacancy-containing titanium hydroxyfluoride was studied. On the basis of pair distribution function analysis, NMR, and X-ray photoelectron spectroscopy, we propose that the material undergoes partitioning upon initial discharge to form a nanostructured composite containing crystalline Li(x)TiO(2), surrounded by a Ti(0) and LiF layer. The Ti(0) is reoxidized upon reversible charging to an amorphous TiF(3) phase via a conversion reaction. The crystalline Li(x)TiO(2) is involved in an insertion reaction. The resulting composite electrode, Ti(0)-LiF/Li(x)TiO(2) ⇔ TiF(3)/ Li(y)TiO(2), allows reaction of more than one Li per Ti, providing a route to higher capacities while improving the energy efficiency compared to pure conversion chemistries.

An analysis of the effect that chemical and hydrostatic pressures have on the thermodynamic properties of perovskite-like fluorine-oxygen compounds A 2 A′MeO x F6 − x has revealed that materials under-going order-disorder transitions and having significant external-pressure compliance have the highest caloric efficiency. Some of the fluorides and oxyfluorides under study can be considered promising solid coolants.

International audience; Treatments involving fluorinated gases and radio-frequency plasma-enhanced fluorination (PEF) constitute exceptional tools for modifying at low temperature the surface properties of materials. These techniques are adapted to yield nanosized functionalized materials and will be illustrated by several examples, including carbon-based electrode materials, functionalized silica and silicates, switchable hydrophobic-hydrophilic porous alumina. X-ray photoelectron spectroscopy is a preferred method for characterizing the resulting surface modifications.

Samples of stage-2 fluorine graphite intercalation compounds (GIC) were studied by scanning tunneling microscope (STM) from submicrometer to atomic scale. From the STM view point, the most striking observation concerns the topographic modifications of the ( a , b ) sample surface induced by the intercalation process. Our STM images of a C 6 F compound are the first direct visualization of the fluorine atoms organization in the van der Waals gap.

The influence of fluorination on ceramic samples of La1.85-xNdxSr0.15CuO4 solid solutions has been studied. The presence of small amounts of fluorine species in the interior of the grains which has been evidenced by Auger electron spectroscopy significantly influences the structural and transport properties. It has been shown that the intercalation of fluorine into the structure reinforces the metallic-like behaviour and superconducting properties by hindering the tendency to the low-temperature structural transition and by increasing the charge carrier density.