| 1. |
- Chorro, Matthieu, et al.
(författare)
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Discriminated structural behaviour of C60 and C70 peapods under extreme conditions
- 2007
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 79:5, s. 56003-
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Tidskriftsartikel (refereegranskat)abstract
- We studied structural changes in C60 and C70 peapods—i.e. C60 and C70 chains inserted inside single-walled carbon nanotubes—when submitted to high pressure and temperature conditions. X-ray diffraction experiments showed that while C60 molecules polymerize inside nanotubes at pressures and temperatures consistent with polymerization in bulk C60 phases, no polymerization is observed in C70 peapods, even at pressures and temperatures above the threshold for polymerization in bulk C70. Tubular confinement in the nanotube container prevents the monomers to rearrange in the way needed for polymerization. This result testifies for the strong influence of confinement on the behaviour of C70.
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| 2. |
- Hou, Yuanyuan, et al.
(författare)
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Comparative study of pressure-induced polymerization of C60 nanorods and single crystals
- 2007
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Ingår i: Journal of Physics Condensed Matter. - Bristol : Institute of Physics. - 0953-8984 .- 1361-648X. ; 19:42, s. 425207-
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report a comparative study of pressure-induced polymerization in C60 nanorods and bulk single crystals, treated simultaneously under various pressures and temperatures in the same experiment. For both materials, orthorhombic, tetragonal and rhombohedral phases have been produced under high pressure and high temperature. The structures have been identified and compared between the two sample types by Raman and photoluminescence spectroscopy. There are differences between the Raman and photoluminescence spectra from the two types of materials for all polymeric phases, but especially for the tetragonal phase. From the comparison between nanorods and bulk samples, we tentatively assign photoluminescence peaks for various polymeric phases.
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| 3. |
- Iwasiewicz-Wabnig, Agnieszka, et al.
(författare)
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Absence of an insulator-metal transition in Rb4C60 up to 2 GPa
- 2008
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Ingår i: Physical Review B. - 0163-1829. ; 77:8, s. 085434-
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of direct resistance measurements on Rb4C60 under pressures up to 2 GPa. At all pressures covered by this study and over the temperature range of 90–450 K Rb4C60 is a semiconductor with a weakly pressure dependent band gap near 0.7 eV. We do not observe the insulator-to-metal transition previously reported to occur below 1.2 GPa, although we cannot rule out the possibility that such a transition might occur at some significantly higher pressure. The measured resistivity is surprisingly low and is dominated by carriers excited over a 0.1 eV gap. Because the corresponding conductivity increases with deformation of the sample, we assign these states to structural or orientational defects. The known structural transformation below 0.5 GPa leads to a decrease in resistivity under high pressure, but the material remains semiconducting. A Rb6C60 control sample showed a similar behavior, also being a semiconductor under all conditions studied. At temperatures above 460 K, Rb was partially lost from our samples, resulting in metallization by a transformation into Rb3C60.
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| 4. |
- Iwasiewicz-Wabnig, Agnieszka, et al.
(författare)
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Electrical resistance of Rb4C60 under pressure
- 2008
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Ingår i: The Journal of Physics and Chemistry of Solids, vol. 69, issues 5-6. - Amsterdam : Elsevier B.V.. ; , s. 1218-1220
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Konferensbidrag (refereegranskat)abstract
- We report the results of direct in situ resistance measurements of Rb4C60 under high pressure up to 2 GPa, in the temperature range 90–400 K. The resistance changes smoothly with pressure and temperature without sharp anomalies, and all data sets can be fitted to the same theoretical semiconductor model. We find no signs of the insulator-to-metal transition previously reported in this range, but the fitted band gap decreases with pressure and such a transition may possibly take place above 5 GPa.
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| 5. |
- Iwasiewicz-Wabnig, Agnieszka, et al.
(författare)
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Investigations of N@C60 and N@C70 stability under high pressure and high temperature conditions
- 2009
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Ingår i: Physica Status Solidi B vol. 246, issue 11-12. - : Wiley. ; , s. 2767-2770
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Konferensbidrag (refereegranskat)abstract
- Endohedral fullerenes encapsulating single nitrogen atoms (N@C60 and N@C70) are spin active, due to the presence of unpaired nitrogen electron spins. High reactivity of nitrogen leads to a poor stability of these molecules at elevated temperatures, drastically restricting possibilities of their chemical treatment. In this study, N@C60 and N@C70 in toluene solutions were subjected to high pressure (HP) up to 0.8 GPa and annealed for 1, 2, 10 or 24 h, at either room or elevated temperatures. In each case the number of surviving molecules was evaluated based on the relative spin counts of ex situ EPR spectra obtained before and after the treatment. The enhanced thermal stability of N@C60 and N@C70 under HP conditions is attributed to inhibited formation of azabridges, which under normal pressure facilitate the escape of nitrogen from the fullerene cage.
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| 6. |
- Iwasiewicz-Wabnig, Agnieszka, et al.
(författare)
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Low-temperature optical studies of C60-cubane rotor-stator compound
- 2008
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Ingår i: Journal of Physics: Conference Series, vol. 100, part 5. - : Institute of Physics (IOP). ; , s. 052091-
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Konferensbidrag (refereegranskat)abstract
- We present here low-temperature Raman and photoluminescence spectra of the C60-cubane rotor-stator compound. We show the continuous evolution of Raman spectra between 77 K and room temperature, with no sharp transition visible at 140 K, the orientational ordering temperature. Low-temperature luminescence spectra of C60 in C60-cubane compound are found to be shifted and better resolved then spectra for pristine C60 at the corresponding temperatures, showing relatively weaker intermolecular interactions. In fact, the solid-state luminescence of C60-cubane is similar to free-molecule C60 luminescence spectra.
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| 7. |
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| 8. |
- Iwasiewicz-Wabnig, Agnieszka, et al.
(författare)
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Polymerization of the rotor-stator compound C60-cubane under pressure.
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:2, s. 024114-
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Tidskriftsartikel (refereegranskat)abstract
- Cubane, C8H8, can be inserted into the octahedral voids of fullerene lattices to create a family of rotor-stator compounds. We have investigated the structural phase behavior of C60 center dot C8H8 by annealing a number of samples for up to 3 h at selected temperatures in the range 380-870 K under pressures up to 2 GPa. The high-pressure treated materials were then investigated under ambient conditions using Raman spectroscopy and x-ray diffraction. C60 center dot C8H8 is found to have at least five different structural phases depending on treatment conditions. In addition to the known cubic and orthorhombic structures observed at atmospheric pressure, we find two polymeric states with pseudocubic and pseudoorthorhombic structures, respectively, based on the two original lattices and created by heating in different pressure ranges. These materials are believed to be copolymers of C60 and decomposition products of cubane. In contrast to the polymeric states of C60 the present polymer structures are determined by the topology of the original lattices rather than by the molecular structure. Above 700 K we find a carbon-rich amorphous state created when the cubane finally decomposes, releasing its hydrogen content in the form of hydrocarbons.
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| 9. |
- Iwasiewicz-Wabnig, Agnieszka, et al.
(författare)
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Pressure-temperature phase diagram of the rotor-stator compound C60-cubane
- 2007
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 143:4-5, s. 208-212
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Tidskriftsartikel (refereegranskat)abstract
- When the rotor–stator compound C60·C8H8 is treated at temperatures above about 450 K under high-pressure conditions, fullerene-based copolymers are formed. Earlier results have shown the existence of two types of polymers, a “low-pressure” pseudo-cubic copolymer similar to that formed at atmospheric pressure, and a “high-pressure” phase tentatively identified as a pseudo-orthorhombic copolymer structurally based on the known low-temperature phase. In this communication we show that the reaction boundary between the polymers occurs at pressures near 1 GPa. From this result it follows that the slope of the cubic–orthorhombic phase line in the pristine material is 305 K GPa−1, significantly larger than the slope observed for the corresponding rotational transition in pure C60.
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| 10. |
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| 11. |
- Iwasiewicz-Wabnig, Agnieszka, 1979-
(författare)
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Studies of carbon nanomaterials based on fullerenes and carbon nanotubes
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Materials based on fullerenes and carbon nanotubes are very much different from most “traditional” materials, primarily because they are built from nanosized molecules with highly symmetry-dependent properties. Being the subject of a very active research field over the last twenty years, carbon nanostructures proved to be indeed extraordinary. Their splendid mechanical properties attract a great interest among material scientists. Their wide range of electrical properties, from ballistic conductors to insulators, makes them ideal candidates for future, better electronics. The possibilities seem to be nearly unlimited, with proposed applications ranging from quantum computing to medicine. However, in order to make it all happen one day, we first need to explore and understand the physics and chemistry of carbon nanomaterials. This work focuses on production and characterization of materials and structures in which fullerenes and/or carbon nanotubes are the main ingredients, and which can be produced or modified under high-pressure – high-temperature (hp-hT) conditions. Raman and photoluminescence spectroscopy, X-ray diffraction and scanning probe microscopy were employed for characterization of the samples. The research presented in this thesis is spread over a rather wide range of carbon nanomaterials. To highlight some of the main results – the first hp-hT polymerization of C60 nanorods and the C60-cubane compound is reported. The polymerization mechanism in the latter case was identified to be radically different from that in pure C60. The pressure-temperature diagram of C60-cubane is presented. A comparative study of C60 and C70 peapods under extreme p-T conditions reveals how the confinement affects the fullerenes’ ability for polymerization. Finally, in situ resistance measurements on Rb4C60 under high pressure show that the semiconducting character of this material persists at least up to 2 GPa, contradicting earlier reports on the existence of an insulator-to-metal transition and providing an insight into conduction mechanisms in this anomalous intercalated compound.
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| 12. |
- Liu, Bingbing, et al.
(författare)
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High pressure and high temperature induced polymeric C60 nanocrystal
- 2008
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Ingår i: Diamond and related materials, vol. 17, issue 4-5. - Amsterdam : Elsevier B.V.. ; , s. 620-623
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Konferensbidrag (refereegranskat)abstract
- In this paper, C60 nanosheets with polymeric phases have been obtained under various high pressures and high temperatures, including orthorhombic and tetragonal polymeric phases. The structures have been identified and compared with those of nanorods by photoluminescence and Raman spectroscopies. The main fluorescence band shifted from 1.70 eV in the monomeric phase to near infrared in the polymeric phase when pressure and temperature were increased. The difference of photoluminescence and Raman spectra between nanosheets and nanorods samples treated under the same conditions is probably caused by different polymerization degree in these samples because of different shapes.
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| 13. |
- Sundqvist, Bertil, et al.
(författare)
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High pressure studies of the rotor-stator compound C60-cubane.
- 2007
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Ingår i: Materials Research at High Pressure. - Warrendale : Materials Research Society. - 9781558999442 ; , s. 0987-PP03
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Konferensbidrag (refereegranskat)abstract
- Insertion of cubane (C8H8) into the octahedral voids of the C60 lattice leads to the formation of an interesting rotor-stator compound which can be converted into a C60 co-polymer by heating. We have treated a number of C60C8H8 samples for up to 3 h each in the range 380-875 K under pressures up to 2 GPa. The resulting materials were investigated by Raman spectroscopy and X-ray diffraction. Depending on treatment conditions, at least five different structural phases can be found. In addition to the four structural phases observed at atmospheric pressure and different temperatures we find that a new polymeric state is created at pressures above 1 GPa, and we tentatively identify its structure as pseudo-orthorhombic. The cubic-orthorhombic phase transition line is found to have a slope of 295 K GPa-1, much larger than the slope of the fcc-sc line in pure C60.
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| 14. |
- Yao, Mingguang, et al.
(författare)
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Reversible nano-scale phase separation of Rb4C60 under pressure
- 2010
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Ingår i: Journal of physics: conference series. - Bristol : Institute of Physics (IOP). ; , s. 012020-
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Konferensbidrag (refereegranskat)abstract
- 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.
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