| 1. |
- Chorro, Matthieu, et al.
(författare)
-
Discriminated structural behaviour of C60 and C70 peapods under extreme conditions
- 2007
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 79:5, s. 56003-
-
Tidskriftsartikel (refereegranskat)abstract
- We studied structural changes in C60 and C70 peapods—i.e. C60 and C70 chains inserted inside single-walled carbon nanotubes—when submitted to high pressure and temperature conditions. X-ray diffraction experiments showed that while C60 molecules polymerize inside nanotubes at pressures and temperatures consistent with polymerization in bulk C60 phases, no polymerization is observed in C70 peapods, even at pressures and temperatures above the threshold for polymerization in bulk C70. Tubular confinement in the nanotube container prevents the monomers to rearrange in the way needed for polymerization. This result testifies for the strong influence of confinement on the behaviour of C70.
|
|
| 2. |
- Launois, Pascale, et al.
(författare)
-
Pressure polymerized C60 single crystals: First x-ray diffraction results
- 1998
-
Ingår i: Molecular Nanostructures. - Singapore : World Scientific. - 9789810232610 ; , s. 348-352
-
Konferensbidrag (refereegranskat)abstract
- C60 single crystals compressed at approx. 1 GPa and heated at about 300 C are found to polymerize in one dimension without losing their crystalline order. The resulting structure is orthrhombic, with space group Pmnn and parameters a=9.14 Å, b=9.9 Å and c=14.66 Å. The X-ray single crystal results allow us to derive a polymerization mechanism, which may also, for instance, apply to one dimensional C60 polymers in the doped compounds. The new polymer phase is discussed with respect to the C60 pressure-temperature diagram. The comparison with the A1C60 polymers raises questions about the interchain and the alkali metal - fullerene interactins.
|
|
| 3. |
- Moret, Roger, et al.
(författare)
-
Chain orientation and layer stacking in the high-pressure polymers of C60: Single crystal studies
- 2000
-
Ingår i: Electronic Properties of Novel Materials: Science and Technology of Molecular nanostructures. - : American Institute of Physics (AIP). - 1563969734 ; , s. 81-84
-
Konferensbidrag (refereegranskat)abstract
- High-pressure polymerisation of C^o leads to a variety of new crystalline or amorphous phases which display interesting physical properties. We have prepared onedimensional (ID, C6o chains) and two-dimensional (2D, C60 layers) polymers from C6o single crystals. The resulting multi-domain crystals have been studied using x-ray diffraction and Raman spectroscopy. The relative orientations of the chains in the "low-pressure" ID orthorhombic polymer had been characterized previously [1]. We have now determined the specific stacking of the Ceo layers in the 2D tetragonal and rhombohedral polymers. Using these results we analyze the relations between the different polymers and the intermolecular environments which may play a role in stabilizing the observed polymer structures.
|
|
| 4. |
- Moret, Roger, et al.
(författare)
-
First X-ray diffraction analysis of pressure polymerized C60 single crystals
- 1997
-
Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 40:1, s. 55-60
-
Tidskriftsartikel (refereegranskat)abstract
- It is shown that C60 single crystals can be polymerized under relatively modest pressure-temperature conditions. The resulting single crystals exhibit long-range order and they are made up of 12 orientation variants. The structure is orthorhombic with a short intermolecular distance along the chains (9.14 Å), characteristic of covalent bonding. We propose a structural mechanism for the polymerization of fullerene-based compounds; it involves a shift of one of the (111) cubic planes together with a shortening of the (111) spacing. The configuration of the polymer chains presents interesting relations with that found in the A1C60 polymer compounds.
|
|
| 5. |
- Moret, Roger, et al.
(författare)
-
High-pressure synthesis, structural and Raman studies of a two-dimensional polymer crystal of C60.
- 2000
-
Ingår i: European Physical Journal B. - : Springer. - 1434-6028 .- 1434-6036. ; 15:2, s. 253-263
-
Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional polymerisation of a C60 single crystal has been obtained under high-pressure high temperature conditions (700 K - 2 GPa). Crystalline order is preserved but the crystal splits into variants (orientational domains). The analysis of X-ray diffraction and Raman spectroscopy data reveals that the polymer crystal is primarily tetragonal with some admixture of rhombohedral phase. Furthermore, Raman spectroscopy gives evidence for additional C60-C60 dimers, which are probably disordered. For the tetragonal phase, it is shown that successive polymer layers are rotated by about the stacking axis, according to the P42/mmc space group symmetry. The structure of the rhombohedral phase is also clarified. The role of the interlayer interactions in stabilising the two-dimensional polymer phases of C60 is discussed.
|
|
| 6. |
- Moret, Roger, et al.
(författare)
-
Single-crystal structural study of the pressure-temperature induced dimerization of C60
- 2004
-
Ingår i: European Physics Journal B. - Berlin : Springer. - 1434-6028 .- 1434-6036. ; 37:1, s. 25-37
-
Tidskriftsartikel (refereegranskat)abstract
- We present a study by Raman spectroscopy and X-ray diffraction/diffuse scattering of C60 single-crystals treated at high-pressure and high-temperature. This allowed us to obtain structural information on the C60 dimer state which can be considered as an intermediate state in the polymerization process. In the 1-6 GPa pressure range the crystals are primarily formed of dimers with additional minor fractions of monomers, 1D and 2D polymers, as shown by the analysis of the Raman spectra. The dimers are disordered within an average cubic lattice derived from that of the monomer. Single-crystal diffraction patterns reveal a characteristic diffuse scattering intensity distribution which has been simulated by calculating the diffuse scattering produced by dimer and trimer model structures. Satisfactory agreement is obtained for random positional and orientational disorder of the C60-C60 dimers although a small concentration of similarly disordered trimers is likely. In a first approximation the dimer/trimer disorder can be considered as random but various inter-dimer correlations are probably present, as discussed.
|
|
| 7. |
|
|
| 8. |
- Sundqvist, Bertil, et al.
(författare)
-
Physical properties of pressure polymerized C60
- 1996
-
Ingår i: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, volume 3. - Pennington, NJ : The Electrochemical Society. - 1566771625 ; , s. 1014-1028
-
Konferensbidrag (refereegranskat)abstract
- We present in this paper an overview of the physical properties of the high pressure polymerized C60 phase commonly known as "soft fcc". This phase has been studied by several methods over wide ranges in temperature T and/or pressure, p. We present here experimental information about the specific heat capacity, the thermal expansion coefficient, the lattice structure, and the thermal conductivity, and we also show results obtained by NMR and Raman spectroscopy. All data presented agree with the accepted model that the individual molecules in this phase are covalently bound to form linear molecular chains. In particular, the NMR data show clearly the presence of covalent bonds, and the Raman data exhibit several new lines at very low energies connected with chain vibrations. Thermal conductivity data obtained during polymerization show both the time dependence of the process and that polymerization occurs at lower p and T than observed previously for this phase.
|
|
| 9. |
- Sundqvist, Bertil, et al.
(författare)
-
Polymerization of C60 under hydrostatic and non-hydrostatic conditions
- 1997
-
Ingår i: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 5. - Pennington, NJ : The Electrochemical Society. - 1566771927 ; , s. 439-449
-
Konferensbidrag (refereegranskat)abstract
- We have submitted both powder and single crystal C60 to pressures in the range 1 - 2 GPa at temperatures between 300 and 900 K in order to study pressure polymerization. Reaction conditions varied, from non-hydrostatic conditions with powder samples in steel capsules treated in solid pressure media, to hydrostatic experiments using silicone oils, N2 or He gas. The reacted samples were characterized by Raman spectroscopy and x-ray diffraction. Depending on experimental conditions, their structures varied from orthorhombic (single crystals) to more or less disordered face centered cubic lattices, and the observed Raman spectra could usually be correlated with the observed structures. The results are used to refine and update the pressure-temperature phase diagram of C60.
|
|
| 10. |
- Sundqvist, Bertil, et al.
(författare)
-
Structural and physical properties of pressure polymerized C60
- 1998
-
Ingår i: Carbon, vol. 36 issue 5-6. - : Elsevier B.V.. ; 36:5-6, s. 657-660
-
Konferensbidrag (refereegranskat)abstract
- We discuss the structural and dynamic properties of C60 polymerized under low-P, low-T conditions, and suggest that the disordered mixed orthorhombic-tetragonal-rhombohedral phases produced under these conditions arise from nucleation of molecular chains in random directions because of the quasi-free molecular rotation under standard reaction conditions in the fcc phase of C60. Polymerization in He gives results qualitatively different from those obtained in other media.
|
|
