Thomas Wågberg

High-pressure induced metastable phase in tetragonal 2D polymeric C60.

The structural stability of the tetragonal two-dimensional (2D) polymeric phase of C60 has been studied under pressure up to 24 GPa and room temperature by means of in situ Raman scattering. An irr ...

Electric resistance of single-walled carbon nanotubes under hydrostatic pressure

The electric resistance of single-walled nanotube mats has been studied systematically under both ambient and high hydrostatic pressures up to 1.5 GPa. Both the temperature dependence of the resistance and the magnetoresistance indicate that electrical transport occurs by variable range hopping, apparently in 2D. We suggest that this unexpected dimensionality arises from a fractal network of tubes and bundles. Under hydrostatic pressure (HP) the resistance still shows 2D variable range hopping and decreases with increasing HP. An irreversible increase in localization length and DOS is induced below 0.5 GPa. The behavior is reversible and due to strong interaction of tubes from 0.5 GPa up to 1.05 GPa. These results indicate that 2D variable range hopping occurs within bundles.

Structural evolution of low-pressure polymerised C60 with polymerisation conditions

We show in this paper that characteristic features in the Raman spectra, especially the frequency of the pentagonal pinch mode, can give information about the polymeric structure of pressure polymerised C60. High-pressure treatment at 1 GPa below 510 K for 3 h results in the formation of a low fraction of dimers only, while treatment at the same pressure and time above 540 K affords a fully polymerised material. In the latter case, different relative fractions of dimers and polymer chains are obtained depending on whether the final reaction conditions were reached by isobaric or isothermal path. We suggest that this difference results from different reaction dynamics in the two cases. The polymerisation rate depends on T and p and on the rotational and orientational states of the molecules. At 1 GPa no polymerisation is observed in sc C60, while in “hexagon” oriented sc C60 at 1.7 GPa dimers are already formed 175 K below the fcc–sc transition and a fully polymerised material is obtained just below the transition to the fcc phase.

Synthesis and Structural Characterization of C70H38

Reference LSMB-ARTICLE-2008-007doi:10.1002/anie.200705450View record in Web of Science Record created on 2008-11-03, modified on 2017-05-12

Raman study of bromine-doped single-walled carbon nanotubes under high pressure

Raman results for different single-walled carbon nanotube bundles doped with Br2 were studied both at ambient pressure and under high pressure up to 6 GPa. Our study indicates that bromine resides in the interstitial channel of nanotube bundles as a form of polymer.

Structural and physical properties of pressure polymerized C60

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 t ...

Reversible nano-scale phase separation of Rb4C60 under pressure

The alkali fulleride Rb4C60 has been investigated by studies of the resistance and by Raman spectroscopy under pressures up to 2 GPa and 13 GPa, respectively. Our data show a reversible phase separation into metallic Rb3C60 and Rb6C60 at pressures above 1 GPa. The reversibility indicates that the phase separation primarily occurs on the nanometer length scale. The data explain several puzzling results reported in the recent literature.

Chain orientation and layer stacking in the high-pressure polymers of C60: Single crystal studies

High-pressure polymerization of C60 leads to a variety of new crystalline or amorphous phases which display interesting physical properties. We have prepared one-dimensional (1D, C60 chains) and two-dimensional (2D, C60 layers) polymers from C60 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” 1D orthorhombic polymer had been characterized previously [1]. We have now determined the specific stacking of the C60 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.

The physical properties of high-pressure polymerized C60

We have studied the structural, thermophysical, and spectroscopic properties of polymeric C60 obtained by high pressure treatment at pressures and temperatures near 1 GPa and 600 K. We present here ...

2D POLYMERIZATION AND DOPING OF FULLERENES UNDER PRESSURE

Abstract Tetragonal polymeric C60 has been studied by Raman spectroscopy and other methods. Attempts have been made to transform samples from the tetragonal to the orthorhom-bic phase and vice versa. The results suggest that the transformation is direct with no intermediate stage with free molecules. Tetragonal C60 has also been intercalated by potassium metal.