| 1. |
- Inaba, Akira, et al.
(författare)
-
Lattice vibrations and thermodynamic stability of polymerized C60 deduced from heat capacities
- 1999
-
Ingår i: Journal of Chemical Physics. - : American Institute of Physics. - 0021-9606 .- 1089-7690. ; 110:24, s. 12226-12232
-
Tidskriftsartikel (refereegranskat)abstract
- Heat capacities of 1D and 2D pressure polymerized C60 as well as the thermally depolymerized C60 have been measured at temperatures between 4 and 350 K and the results analyzed for the lattice vibrations and the thermodynamic stability. It was found from the low-temperature heat capacity (T < 100 K) that on polymerization (1) the lattice vibrations, both translational and rotational, stiffen substantially, (2) an anisotropic nature emerges in response to the lower dimensionality, and (3) an anharmonicity still remains as in pristine C60. The normal C60 has an excess entropy of 67.8 and 99.4 J K – 1 mol – 1 at 300 K relative to the 1D and 2D polymerized C60, respectively. The thermodynamic stability is considered with two possible phase diagrams.
|
|
| 2. |
- Nagel, Peter, et al.
(författare)
-
C60 one- and two-dimensional polymers, dimers, and hard fullerite: Thermal expansion, anharmonicity, and kinetics of depolymerization
- 1999
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 60:24, s. 16920-16927
-
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.
|
|
