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In order to prepare self-standing and flexible slow neutron reflectors made of graphite fluoride (GF) with high contents of (C2F)n structural phase, graphite foils of different thicknesses were used as starting materials for gas (F2)/solid fluorination. The maximal interlayer distance of GF was obtained with this phase thanks to the stacking sequence FCCF/FCCF; this is mandatory for the efficient reflection of slow neutrons. 71 and 77% of the (C2F)n phase were achieved for graphite foils with thicknesses of 1.0 and 0.1 mm, respectively. The interlayer distances were 8.6 Å as expected. The fluorination conditions (static mode, a long duration of 24 h, annealing in pure F2 gas for 24 h, and temperatures in the 390–460 °C range) were adapted to large pieces of graphite foils (7 × 7 cm2) in order to both avoid exfoliation and achieve a homogeneous dispersion of fluorine atoms. This process was also efficient for thinner (0.01 mm thick) graphitized graphene oxide foil. 56% of the (C2F)n phase and an interlayer of 8.6 Å were achieved for this foil when fluorination was performed at 430 °C. Whatever the nature and the thickness of the foil, their flexibilities are maintained. [ABSTRACT FROM AUTHOR]

Pressure and temperature phase transitions of nanomaterials often differ significantly from those of their bulk parents, offering novel approaches for the engineering of original materials. The importance or even the dominance of surface atoms in the nanoworld enhances the effects of environment, geometry, and intercalation. In the present article, we explore the current knowledge of these effects, as evidenced in the high pressure phase diagrams of nanomaterials such as nanocrystals, carbon nanotubes, fullerites, graphene, and other 2D systems, as well as nanoporous structures like clathrates or zeolites. Recent advances and future challenges in the use of extreme thermodynamic conditions to develop new functional nanomaterials, composites, or devices will be reviewed, along with the specificities of the experimental environment required for these investigations. [ABSTRACT FROM AUTHOR]

Fluorine‐based chemistry is widely used in commercial battery technology, from primary batteries consisting of Li/CFx to binders for electrodes in secondary lithium‐ion batteries. Fluorine‐based compounds are also formed during operation for both battery configurations as discharge products such as LiF or as components of the solid electrolyte interface (SEI) layers on electrodes. Herein, the fluorinated carbons or CFx detailing the commercialization of the first Li/CFx cells are discussed‐ the understanding of how performance is correlated to composition or x, the various methods to synthesize CFx compounds, the correlation between the nature of the CF bonds and electrochemical performance, the role of theoretical studies in such endeavors, the use of CFx in alternative battery chemistries and the wide range of techniques available to probe either CFx compounds individually or CFx compounds in devices under electrochemical conditions. A picture of the field from which future directions can be derived is provided. [ABSTRACT FROM AUTHOR]

Abstract: Combined XRD and Mössbauer effect spectroscopy studies to high pressures of ∼30GPa of vacancy ordered maghemite are presented. The vacancy ordered superstructure is robust and remains intact up to the pressure-induced onset transition to hematite at 13–16GPa. The pressure transformed hematite is shown to be crystallographically textured, unlike the randomised low pressure maghemite phase. This arises out of a pressure or stress instigated topotactic transformation of the cubic-spinel to hexagonal-corundum structure. The textured sample permits us to obtain information on the spin reorientation behavior of the pressure transformed hematite in compression and decompression sequences. Spin reorientation is restricted to ∼15° over wide pressure ranges, attributable to the effect of entrapped vacancies in the high pressure structure. Thus there are structural and magnetic peculiarities specific to pressure transformed hematite not evident in pressurized hematite starting material. These are triggered by the maghemite→hematite transformation. [Copyright &y& Elsevier]

In this article the alkali metal-intercalated two-dimensional (2D) polymer Na4C60 is studied under pressure up to 41 GPa at room temperature by Raman spectroscopy and x-ray diffraction (XRD) measurements. Two transitions are identified in the studied pressure range. The first one is observed at ~3 GPa by both diffraction and Raman scattering. A kink in the pressure slope of the cell parameters (especially along the c axis) shows the appearance of a less compressible phase. The decrease in the C60-C60 distance and the Na-C distance, combined with the frequency softening of the Raman modes, leads to a picture of higher electron hopping. The second transition occurs at around 15 GPa, where the distinct Raman peaks of 2D-Na4C60 disappear and become very broad and diffuse. New bands at 200-800 cm-1, 1590 cm-1, and ~1800 cm-1 exhibit similar features to those of a reported 3D-C60 polymeric structure. The XRD data show that the cell parameters a, b, and c deviate from their early pressure evolution and become almost pressure independent, accompanied by the formation of amorphous material. Both the evolution of the Raman features of Na4C60 at pressures above 15 GPa and the Raman measurements of the samples on decompression indicate that most C60 molecules in the material are preserved after such a high pressure cycle. Our findings are discussed in terms of the formation of the first high-pressure intercalated C60 3D-polymer structure through the random creation of new polymeric bonds between fullerene molecules. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate that laser irradiation on the narrow-gap insulator Li4C60 and Na4C60 polymers results in metallic monomeric structures, having the same Raman features as metallic fcc K3C60 and Rb3C60, with orientationally disordered anions stable at ambient conditions. The Raman Ag(2) mode indicates that a single phase was obtained. Additionally, a monomeric A4C60-type phase (A=K, Rb) is observed in Na4C60 after irradiation. The electron–phonon coupling constants derived from Raman modes of fullerides is found to be higher than that of fullerides, agreeing with the trend found in heavy alkali fullerides. We propose possible structures of the metallic phases. [Copyright &y& Elsevier]

In order to prepare self-standing and flexible slow neutron reflectors made of graphite fluoride (GF) with high contents of (C 2 F) n structural phase, graphite foils of different thicknesses were used as starting materials for gas (F 2 )/solid fluorination. The maximal interlayer distance of GF was obtained with this phase thanks to the stacking sequence FCCF/FCCF; this is mandatory for the efficient reflection of slow neutrons. 71 and 77% of the (C 2 F) n phase were achieved for graphite foils with thicknesses of 1.0 and 0.1 mm, respectively. The interlayer distances were 8.6 Å as expected. The fluorination conditions (static mode, a long duration of 24 h, annealing in pure F 2 gas for 24 h, and temperatures in the 390-460 °C range) were adapted to large pieces of graphite foils (7 × 7 cm 2 ) in order to both avoid exfoliation and achieve a homogeneous dispersion of fluorine atoms. This process was also efficient for thinner (0.01 mm thick) graphitized graphene oxide foil. 56% of the (C 2 F) n phase and an interlayer of 8.6 Å were achieved for this foil when fluorination was performed at 430 °C. Whatever the nature and the thickness of the foil, their flexibilities are maintained.