| 1. |
- Buga, Sergei G., et al.
(författare)
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Synthesis of superhard 3D-polymeric C60 fullerites from rhombohedral 2D-polymer by high-pressure-high-temperature treatment.
- 2003
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Ingår i: High Pressure Research vol. 23, issue 3. - London : Taylor & Francis. ; , s. 259-264
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Konferensbidrag (refereegranskat)abstract
- Rhombohedral C60 polymer was subjected to high-pressure-high-temperature treatment at P =13 GPa, T =620-1620 K. After quenching, crystalline and disordered structures with densities in the range of 2.1-2.9 g cm-1 were obtained. The structures of the samples have been investigated by powder X-ray diffraction and Raman scattering. DSC analysis showed a transformation of the polymeric structure into monomeric on annealing in the range 400-640 K. The temperature dependence of the electrical resistance of samples with disordered structure was measured in the range 2.5-300K. For different samples, the conductivity was proportional to T1/2, T3/2, T4 and exp(-1/T1/4).
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| 2. |
- Liu, Bingbing, et al.
(författare)
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Electric resistance of single-walled carbon nanotubes under hydrostatic pressure
- 2001
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Ingår i: Solid State Communications. - : Elsevier B.V.. - 0038-1098 .- 1879-2766. ; 118:1, s. 31-36
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Liu, Bingbing, et al.
(författare)
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Raman study of bromine-doped single-walled carbon nanotubes under high pressure
- 2002
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Ingår i: Journal of Physics: Condensed Matter vol. 14 issue no. 44. - Bristol : Institute of Physics. ; , s. 11255-11259
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Konferensbidrag (refereegranskat)abstract
- Raman results for different single-walled carbon nanotube bundles doped withBr2 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 nanotubebundles as a form of polymer.
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| 4. |
- Liu, Bingbing, et al.
(författare)
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Synthesis and characterization of single-walled nanotubes produced with Ce as catalyst
- 2000
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Ingår i: Molecular Materials: Molecular Crystals and Liquid Crystals Section C, vol. 13. - : Overseas Publishers Association N.V.. ; , s. 75-80
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Konferensbidrag (refereegranskat)abstract
- We have studied the effect of using rare-earth elements C (typically +4 oxide state) and Eu (typically +2 oxide state) together with nanometer Ni as catalysts to synthesize SWNT in high yield by arc evaporation. A black collar deposit containing mainly SWNT was formed in the presence of Ce/Ni while only nanometer carbon particles were formed using Eu/Ni, as identified by SEM, TEM and Raman spectra. The Raman spectra of our SWNT mats show difference from spectra shown in the literature in a low frequency range, indicating that our mats contain chiral tubes. The temperature dependent resistance of SWNT mats was also measured. A semiconducting behaviour was observed with a negative dR/dT and no resistance minimum from 2 to 350 K. The resistance follows a 2D variable range hopping behaviour.
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| 5. |
- Liu, Bingbing, et al.
(författare)
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Synthesis and characterization of single-walled nanotubes produced with Ce/Ni as catalysts.
- 2000
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Ingår i: Chemical Physics Letters. - : Elsevier B.V.. - 0009-2614 .- 1873-4448. ; 320:3-4, s. 365-372
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Tidskriftsartikel (refereegranskat)abstract
- SWNTs were synthesized in high yield in the presence of Ce/Ni as catalyst. Raman and SEM results show that a fraction of the tubes are chiral and have small diameters (the smallest one is 0.79 nm), indicating that Ce plays an important role in the formation. Acid treatment is effective in eliminating impurities but changes the morphology and the electric resistance of mats with increasing treatment time. The resistance of as-grown and short time acid-treated mats follow a 2D VRH behaviour while mats treated for a long time follow a 3D model. The results indicate that hopping conduction occurs on bundles or on tubes and that there are intrinsic links between tubes in as-grown mats.
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| 6. |
- Liu, Bingbing, et al.
(författare)
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Transport properties of single-walled nanotube mats under hydrostatic pressure
- 2000
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Ingår i: Electronic Properties of Novel Materials: Science and Technology of Molecular nanostructures. - Melville : American Institute of Physics (AIP). - 1563969734 ; , s. 344-348
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Konferensbidrag (refereegranskat)abstract
- The study of electrical transport properties of bulk single-walled carbon nanotube (SWNT) materials attracts a lot of attention. However, the transport results differ from sample to sample[l]. Some results show semiconducting behavior with different laws and whether the behavior is dominated by on-tube or on-bundle effects or by interbundle contacts is still unknown. Therefore, further investigation is still meaningful. The effect of hydrostatic pressure(HP), which is expected to significantly change the interaction between tubes or bundles, gives us a further possibility to understand the characteristic properties. Under HP, Raman spectra and electric resistance show pronounced changes at 1.5GPa[2]. In this study, we systematically studied the electric resistance up to 1.5 GPa, giving a different image of the transport behavior.
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| 7. |
- Makarova, Tatiana L, et al.
(författare)
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Conductivity of two-dimensional C60 polymers
- 2000
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Ingår i: Proceedings of the 4th International Workshop on Fullerenes and Atomic Clusters (IWFAC'99), St. Petersburg 1999. - : Overseas Publishers Association N.V.. ; , s. 151-156
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Konferensbidrag (refereegranskat)abstract
- The general trend in the shift of electronic properties as the result of polymerization has been studied with the aid of temperature dependences of conductivity. Samples representing the pure rhombohedral phase exhibit great anisotropy in their electrical properties. The main features of the behaviour of these samples are: (i) in the z-direction the resistivity is of the order of several kOhm cm and decreases with temperature; (ii) in the x-y direction resistivity is less than 1 Ohm cm and shows a minimum at a certain temperature.
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| 8. |
- McRae, Edward, et al.
(författare)
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Raman light scattering and c-axis resistivity evidence for a pressure-induced stage transformation in PdAl2Cl8 intercalated graphite.
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 62:20, s. 13757-13766
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Tidskriftsartikel (refereegranskat)abstract
- We have examined several samples of first- to third-stage PdAl2Cl8-intercalated graphite under hydrostatic pressures up to 1 GPa. In stage-1 highly oriented pyrolytic graphite–(HOPG) and single-crystal-graphite-based materials, the c-axis resistivity decreases sharply above a few kilobars; pressure release induces a reversible return to the initial value only in the case of the latter sample. Raman spectra taken in situ under pressure on a HOPG-based material show similarly irreversible effects. Analysis of the spectra taken on higher-stage samples leads to the conclusion that hydrostatic pressure beyond a few kilobars increases the density of the intercalate within the graphitic galleries, transforming the initial sample to a higher-stage material. Since there is no loss of intercalate, the overall intercalate-to-host charge transfer remains constant so that the Raman frequency is approximately the same for both first- and second-stage products. This is an unusual situation in which there is thus an apparent lack of Raman signature in spite of the stage change.
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| 9. |
- Meletov, Kostas P., et al.
(författare)
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High-pressure induced metastable phase in tetragonal 2D polymeric C60.
- 2001
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Ingår i: Chemical Physics Letters. - : Elsevier B.V.. - 0009-2614 .- 1873-4448. ; 341:5-6, s. 435-441
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Tidskriftsartikel (refereegranskat)abstract
- 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 irreversible transformation of the material to a new phase was observed at pressure 20 GPa. The phonon spectrum of the high-pressure phase provides a strong indication that the fullerene molecular cage is retained and therefore this phase may be related to a three-dimensional (3D) network of C60 cages. The new phase remains stable upon slow release of pressure to ambient conditions. The recovered material is metastable and transforms in air by detonation under laser irradiation to partially dimerized C60.,
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| 10. |
- Moret, Roger, et al.
(författare)
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Chain orientation and layer stacking in the high-pressure polymers of C60: Single crystal studies
- 2000
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Ingår i: Electronic Properties of Novel Materials: Science and Technology of Molecular nanostructures. - : American Institute of Physics (AIP). - 1563969734 ; , s. 81-84
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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.
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