| 51. |
- Sundqvist, Bertil
(författare)
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Polymeric phases of fullerenes
- 2004
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Ingår i: Fullerene-Based Materials. - Berlin/Heidelberg : Springer. - 9783540201069 ; , s. 85-106
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Fullerenes, in particular C60, can form covalent intermolecular bonds ("polymerize") when treated at high temperature under high pressure. This contribution briefly reviews some recent advances in this field. Short overviews are given of the pressure-temperature phase diagrams of pristine C60 and C70 and of their physical properties under high pressure. The paper has its main emphasis on the structures and properties of the one- and two-dimensional (chains and planes) polymeric phases of C60 created in the range 1–9 GPa (10–90 kbar) and up to 1100 K. Their structures, as obtained from studies on polymerized single crystals, the treatment conditions used to obtain well-defined structures, and some selected physical properties, including the surprising discovery of ferromagnetism, are discussed. The paper presents the results of both ex situ and in situ structural studies. Three-dimensional polymers, and the possibility to create well-defined three-dimensional structures by high-pressure treatment of low-dimensional polymers, are also discussed. Finally, a short section devoted to higher fullerenes discusses the polymeric forms of C70, including the ordered zigzag chain phase recently created under hydrostatic pressure conditions.
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| 52. |
- Sundqvist, Bertil
(författare)
-
Senaste nytt om fullerener
- 2001
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Ingår i: Fysikaktuellt. - : Svenska Fysikersamfundet. - 0283-9148. ; :4, s. 19-22
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 53. |
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| 54. |
- Sundqvist, Bertil, et al.
(författare)
-
Structure and stability of pressure polymerized C60
- 2000
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Ingår i: Molecular Materials: Molecular Crystals and Liquid Crystals Section C, vol. 13. - : Overseas Publishers Association N.V.. ; 13:1-4, s. 117-122
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Konferensbidrag (refereegranskat)abstract
- We discuss the bond energy of the orthorhombic C60 polymer and the structure of the two-dimensional C60 polymers. For the orthorhombic polymer, measurements of the dissociation energy by different methods give results that differ by a factor of two. We show that optical excitations lead to a temporary weakening of the intermolecular bonds and optical measurements thus show a low apparent bond energy. We have also polymerized a single crystal of C60 into two-dimensional phases. X-ray diffraction studies of this crystal have enabled us to determine the stacking sequences of both the tetragonal and the rhombohedral structures.
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| 55. |
- Talyzin, Alexandr, et al.
(författare)
-
Gentle fragmentation of C60 by strong hydrogenation: a route to synthesizing new materials
- 2004
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Ingår i: Chemical Physics Letters. - Amsterdam : Elsevier B.V.. - 0009-2614 .- 1873-4448. ; 400:1-3, s. 112-116
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Tidskriftsartikel (refereegranskat)abstract
- A large number of small hydrogenated fullerenes and unusual polycyclic aromatic hydrocarbons were detected by mass-spectrometry in samples obtained by C60 reaction with hydrogen gas at 673 K. A synthesis of a large number of sequential breakdown products instead of fast formation of amorphous carbon was found due to immediate termination of dangling bonds by hydrogen atoms during the C60 fragmentation process. This opens a possibility to synthesize these unusual materials in bulk amounts. Investigation of breakdown products could also help to select building blocks for synthesis of cage structures by purely chemical methods.
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| 56. |
- Talyzin, Alexandr, et al.
(författare)
-
Reversible phase transition in LiAlH4 under high pressure conditions.
- 2004
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:18, s. 180101(R)-
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Tidskriftsartikel (refereegranskat)abstract
- The structural stability of the hydrogen storage compound LiAlH4 was studied by Raman spectroscopy in the pressure interval 0–6 GPa. A slow phase transition from a-LiAlH4 to a b phase was observed to occur between 2.2 and 3.5 GPa. The phase transition is reversible and a reverse transformation to a-LiAlH4 was observed below 1.4 GPa. Analysis of Raman spectra from b-LiAlH4 shows that they cannot be explained by the theoretically predicted a-NaAlH4-type structure with I41 /a symmetry.
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| 57. |
- Ulyanov, A.N., et al.
(författare)
-
Crystal symmetry and pressure effects on the properties of mixed-valence manganites
- 2003
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Ingår i: Journal of Magnetism and Magnetic Materials vol. 258-259, Special Issue SI. - Amsterdam : Elsevier B.V.. ; , s. 312-314
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Konferensbidrag (refereegranskat)abstract
- A lattice structure effect on the magnetic and magnetotransport properties of La0.7Ca(0.3-x)SrxMnO3 lanthanum manganites have been studied. The Curie temperature pressure coefficient increased almost linearly under an applied pressure as dTc/dP=14K/GPa and as dTc/dP=7.5K/GPa in the orthorhombic and rhombohedral structures,respectively. This is caused by the different pressure effect on the Mn–O bond distances and on the Mn–O–Mn bond angles in those phases. The anomalous low value of dTc/dP(=3.5K/GPa) for La0.7Ca0.15Sr0.15MnO3 composition and a jump of the magnetoresistance maximum value at the concentrational Pbnm2R%3c phase transition were observed and discussed.
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| 58. |
- Ulyanov, A.N., et al.
(författare)
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La0.7Ca0.3-xSrxMnO3 manganites: Effect of structure on the magnetic and transport properties.
- 2002
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Ingår i: Journal of the Physical Society of Japan. - : The Physical Society of Japan. - 0031-9015 .- 1347-4073. ; 71:3, s. 927-929
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Tidskriftsartikel (refereegranskat)abstract
- The effect of lattice structure on the magnetic and transport properties of La0.7Ca0.3-xSrxMnO3 (x= 0; 0.03; 0.06; ...; 0.3) lanthanum manganites have been studied. Curie temperature pressure coefficient, dTc/dP, showed the dependence on x value. Temperature Tc increased almost linearly under applied pressure as dTc/dP≈14 K/GPa and as dTc/dP≈7.5 K/GPa in the orthorhombic (Pbnm) and rhombohedral (R3c) phases, respectively. The value of dTc/dP(≈3.5 K/GPa) showed a minimum and a temperature of the resistance maximum, Tp(x), showed a change of slope at x=0.15, corresponding to the concentration structural phase transition. Differences between the values of dTc/dP and slopes of Tp versus x in Pbnm and R3c phases are explained by the different effect of external pressure on the Mn–O bond length and Mn–O–Mn bond angle, and by the different internal pressure effect in those phases, respectively
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| 59. |
- Ulyanov, A. N., et al.
(författare)
-
Structure and pressure effects on the properties of La0.7Ca0.3-xSrxMnO3 manganites.
- 2002
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Ingår i: Journal of Applied Physics vol. 91. - : American Institute of Physics. ; , s. 7739-7741
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Konferensbidrag (refereegranskat)abstract
- We report a study of the structure and pressure effects on magnetic and transport properties of a lanthanum manganite, La0.7Ca0.3–xSrxMnO3 (0<=x<=0.3, Deltax = 0.03). The pressure coefficient of the Curie temperature (Tc), dTc/dP, is shown to depend on x. The temperature Tc increases approximately linearly under applied pressure as dTc/dP[approximate]14 K/GPa in the orthorhombic (Pbnm) phase and as dTc/dP[approximate]7.5 K/GPa in the rhombohedral (R3-bar c). The value of dTc/dP shows a minimum ([approximate]3.5 K/GPa) and the temperature of the resistance maximum, Tp(x), shows a change of slope at x = 0.15, corresponding to a concentration structural phase transition. Differences between the values of dTc/dP and the slopes of Tp vs x in Pbnm and R3-bar c phases are explained by the different effect of external pressure on the Mn–O bond length and the Mn–O–Mn bond angle, and by the different internal pressure effect (depending on the value of x) in those phases, respectively.
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| 60. |
- Wågberg, Thomas, et al.
(författare)
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13C NMR on intercalated 2D-polymerised C60 and modified peapods.
- 2004
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Ingår i: Electronic Properties of Synthetic Nanostructures. - Melville, NY : American Institute of Physics (AIP). - 0735402043 ; , s. 238-41
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Konferensbidrag (refereegranskat)abstract
- We present 13C NMR results on the intercalated 2D C60-polymers Li4-xNaxC60 (x=0-4 with half integer steps) showing that while Li4C60 forms a tetragonal polymer with double polymer bonds between the molecules, Na4C60 form a monoclinic polymer with single polymer bonds. The chemical shift is much larger for Li-rich samples than for Na-rich samples, indicating perhaps a different type of interaction with the C60 molecules. The crossover between the two structures appears to be at the composition Li2.5Na1.5C60 . We also show NMR data on SWNT filled with C60 molecules, so called peapods, showing that the NMR line of C60 can not be observed when the C60 is inside the tubes. Weinterpret this as resulting from a very long relaxation time, indicating that the dynamics of the C60 molecule is hindered by the nanotube walls.
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