| 1. |
- Nagel, Peter, et al.
(författare)
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C60 one- and two-dimensional polymers, dimers, and hard fullerite: Thermal expansion, anharmonicity, and kinetics of depolymerization
- 1999
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 60:24, s. 16920-16927
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Tidskriftsartikel (refereegranskat)abstract
- We report on high-resolution thermal expansion measurements of high-temperature-pressure treated C60 [one-dimensional (1D) and (2D) polymers and “hard fullerite”], as well as of C60 dimers and single crystal monomer C60 between 10 and 500 K. Polymerization drastically reduces the thermal expansivity from the values of monomeric C60 due to the stronger and less anharmonic covalent bonds between molecules. The expansivity of the “hard” material approaches that of diamond. The large and irreversible volume change upon depolymerization between 400 and 500 K makes it possible to study the kinetics of depolymerization, which is described excellently by a simple activated process, with activation energies of 1.9±0.1 eV (1D and 2D polymers) and 1.75±0.05 eV (dimer). Although the activation energies are very similar for the different polymers, the depolymerization rates differ by up to four orders of magnitude at a given temperature, being fastest for the dimers. Preliminary kinetic data of C70 polymers are presented as well.
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| 2. |
- Nagel, Peter, et al.
(författare)
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High-resolution thermal expansion of high-pressure polymerized and 'normal' C60 from 10-500 K: Kinetics of depolymerization
- 1998
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Ingår i: Molecular Nanostructures. - Singapore : World Scientific. - 9810232616 ; , s. 365-368
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Konferensbidrag (refereegranskat)abstract
- High-resolution capacitance dilatometry was used to study the thermal expansion of both 'normal' and polymer phases of C60. The expansivity, alpha(T), of 'normal' C60 exhibits an unusual temperature dependence above the orientational disordering transition at 260 K; alpha(T) decreases by about 30% from 260 to 500 K and appears to reach a minimum near 500 K. Polymerized C60 has a much smaller expansivity than normal C60 due to the stronger covalent bonding between molecules. The polymerized state converts back to 'normal' C60 at temperatures between 450 and 500 K. We show that this is an activated process with a well-defined activation energy of 1.92 eV and a volume increase of about 2%.
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| 3. |
- Nagel, Peter, et al.
(författare)
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Intermolecular bond stability of C60 dimers and 2D pressure-polymerized C60
- 1998
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Ingår i: AIP Conference Proceedings Vol. 442. - Woodbury, NY : American Institute of Physics (AIP). - 1563968088 ; , s. 194-197
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Konferensbidrag (refereegranskat)abstract
- The thermal stability of C60 dimers and 2D pressure-polymerized C60 is studied using high-resolution capacitance dilatometry. The transformation of both the dimer and the polymer phases back to 'normal' C60 is excellently described by a simple thermally activated process with activation energies of 1.75 +/- 0.1 eV (dimer) and 1.9 +/- 0.2 eV (polymer). These results are compared to previous data for 1D-polymerized C60 and photo-polymerized C60. The thermal expansivity of the 2D-polymer phase is as much as a factor of ten smaller than that of pure C60 and approaches values for diamond.
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| 4. |
- Persson, Per-Axel, et al.
(författare)
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Physical properties of pressure polymerized C60
- 1996
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Ingår i: High Pressure Science and Technology. - Singapore : World Scientific. - 9810225474 ; , s. 716-718
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Konferensbidrag (refereegranskat)abstract
- The properties of C60 have been studied after treatment at high temperature and high pressure (1.1 GPa and 565 K for 2 h). The treated material is insoluble in organic solvents. We present results obtained in NMR and Raman studies and measured data for the specific heat and the thermal expansion. Our results show clearly that there are no covalent bonds and no molecular rotation, but suggest that the molecules are slightly deformed and held together by weak pi-type bonds.
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| 5. |
- Soldatov, Alexander, et al.
(författare)
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Polymeric fullerenes: from C60 to C70
- 1999
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Ingår i: AIP Conference Proceedings vol. 486. - Melville, NY : American Institute of Physics (AIP). - 1563969009 ; , s. 12-15
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Konferensbidrag (refereegranskat)abstract
- For the first time polymerization of both powder and single crystals of C70 fullerene was established after their subjection to high pressure (1.1 - 2 GPa) at elevated temperature (500 - 580 K). High-resolution capacitance dilatometry, FTIR/Raman spectroscopy and thermal conductivity were employed to characterise the polymeric phase of C70. The results demonstrate drastic changes in the physical properties of C70 on polymerization. We report on a reverse transformation to the monomeric state on heating the polymer to 500 K at ambient pressure. The activation energy of depolymerization was determined to be 1.8(1) eV. We discuss our results in terms of existing structural models for polymerization of C70 and compare the physical properties of C70 and C60 polymers.
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| 6. |
- Sundqvist, Bertil, et al.
(författare)
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Physical properties of pressure polymerized C60
- 1996
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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
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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.
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| 7. |
- Sundqvist, Bertil, et al.
(författare)
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Physical properties of two-dimensionally polymerized C60
- 1998
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Ingår i: Fullerenes: Recent Advances in the Chemistry and Physics of Fullerenes and Related Materials, vol. 6. - Pennington, NJ : The Electrochemical Society. - 1566772028 ; , s. 705-716
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Konferensbidrag (refereegranskat)abstract
- Preliminary data are reported for the thermal expansion, compressibility, and specific heat of two-dimensionally polymerized C60 obtained by treating fullerene samples at temperatures above 800 K under a pressure of 2 GPa. The samples have also been characterized by Raman spectroscopy and inelastic neutron scattering. The measured data for the thermophysical properties are strongly modified by the creation of strong covalent intermolecular bonds and we show that the results are compatible with the predictions of simple theories.
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