| 1. |
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| 2. |
- Buga, Sergei G., et al.
(författare)
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Semimetallic and semiconductor properties of some superhard and ultrahard fullerites in the range 300-2 K
- 2000
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Ingår i: Proceedings of the 5th IUMRS International Conference on Advanced Materials, Beijing 1999. - : Elsevier B.V.. ; , s. 1009-1015
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Konferensbidrag (refereegranskat)abstract
- Electrical resistivity and magnetoresistance were measured on samples with disordered structures synthesized from pure C60 and C70 at pressures in the range 8–12.5 GPa and temperatures of 900–1500 K. Different types of behaviour were observed: semimetallic, VRH and semiconducting, depending on the degree of disorder and the particular short-range order of the samples. A negative magnetoresistance was observed at T<10 K on samples with a semimetallic type of conductivity synthesized at 8 GPa pressure. The temperature dependence of resistivity in the sample with a disordered crystalline structure based on 3D-polymerized C60 molecules fits Mott's law for hopping conductivity. T3/2, T2 and T4 dependencies of conductivity are observed for samples with densities of 2.8 and 3.05 g/cm3 synthesized at a pressure of 12.5 GPa. The effect of hydrostatic pressure on the resistivity of cross-linked layered carbon structures obtained from C60 at P=8 GPa, T=1600 K was investigated up to 0.6 GPa at room temperature. An approximately linear decrease of resistivity was observed with a very small value of the derivative d ln ρ/dp=0.06 /GPa, which correlates with a very low compressibility of the material.
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| 3. |
- 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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| 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. |
- 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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| 6. |
- Zhu, Xiaomei, et al.
(författare)
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Measurement of the total transverse force on moving vortices in YBCO films
- 1996
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Ingår i: Proceedings of 10th Anniversary HTS Workshop on Physics, Materials, and Applications, Houston 1996. - Singapore : World Scientific. - 9810227159 ; , s. 417-418
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Konferensbidrag (refereegranskat)abstract
- We have designed a mechanical experiment to measure the total transverse force on moving vortices in type II superconductors. The vortices are driven into motion by the vibration of a permanent magnet above a relatively large superconductor. The transverse force is measured by monitoring the motion of the superconducting film mounted on a quartz plate.
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| 7. |
- Zhu, Xiaomei, et al.
(författare)
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Mechanical measurement of the transverse force on the moving vortices in superconductors
- 1996
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Ingår i: Czechoslovak Journal of Physics volume 46, Supplement S3. - Praha : CZECHOSLOVAK JOURNAL OF PHYSICS. ; , s. 1727-1728
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Konferensbidrag (refereegranskat)abstract
- We have designed a mechanical experiment to measure the total transverse force on moving vortices in a type II superconductor. The transverse force is measured by monitoring the motion of the superconductor while the vortices are driven into motion by a moving magnet. The advantage of this direct force measurement is that it is free from complications due to vortex interactions.
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| 8. |
- Zhu, Xiaomei, et al.
(författare)
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Observation of the transverse force on moving vortices in YBCO films
- 1997
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 78:1, s. 122-125
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Tidskriftsartikel (refereegranskat)abstract
- We have designed a mechanical experiment to measure the total transverse force on moving vortices in a type II superconductor. The vortices are driven into motion by the vibration of a magnet above a superconducting YBCO film. The transverse force is measured by monitoring the motion of the superconductor in response. The advantage of this direct force measurement is that it is free from complications due to the vortex interaction. Our results are consistent with the Ao-Thouless theory.
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