Unusual Structure and Electronic Behaviour of Lithium Intercalated Fullerides

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Unusual Structure and Electronic Behaviour of
Lithium Intercalated Fullerides
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• M. Riccò1, D. Pontiroli1, M. Belli1, T. Shiroka1,
  M. Pagliari1, S. Margadonna2, G. Ruani3,
  D. Palles3, D. Arcon4, M. Tomaselli5

1 Dip. di Fisica and CNISM, Univ. di Parma,
Parco A. delle Scienze 7/a, 43100 Parma,
Italy 2 School of Chemistry, University of
Edinburgh, West Mains Road, Edinburgh EH9
3JJ, UK 3 Istituto ISMN-CNR, Via P. Gobetti
101, 40129 Bologna, Italy 4 S. S. Physics
Department, J. Stefan Institute, Jamova 39,
SI-1000, Ljubljana,
Slovenia 5 Lab. of Physical Chemistry,
ETH-Hönggerberg, Pauli Strasse 10,
CH-8093, Zürich, Switzerland
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Outline
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• Polymerisation in fullerenes

• The LixC60 family

• Structure of Li4C60 a novel polymer

• Thermal evolution of Li4C60 a new metallic phase

• Conclusions

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Why Studying Lithium Intercalated Fullerides?
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• Lithium doped polymers present a good
  crystallinity

• The depolymerisation process could let
  non-zero spin states available

• The number of electrons transferred to C60 in
  doped systems can be tuned easily

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Polymerisation in C60 Compounds
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Photo-polymerised C60
C60 HP (1D, 2D, 3D)
Doped AC60 (AK, Rb)
Na2RbC60 slow cooling
Li3CsC60 HP
Na4C60 (2D single bonds)
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Polymerisation in C60 Compounds
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Energetically favoured in undoped or low-doped
systems (black markers)
Present in compounds with high charge transfer
(white markers)
Pekker et al., Synt. Met. 103, 1999, 2411
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The LixC60 Family
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Lithium doping
30
Li/C60
0
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Low-doped LixC60 (1?x?6)
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C60 x LiN3 ? LixC60 3/2 x N2 ?
Cu K?
LixC60 (1?x?6) was prepared
By mixing metallic Li and C60 powder
By thermal decomposition of LiN3
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High resolution diffraction of ?-Li4C60
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High resolution diffraction of ?-Li4C60
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High resolution diffraction of ?-Li4C60
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Rwp 5.12 Rexp 1.53
Novel 2D polymer with coexistence of single and
double c-c bonds
(Margadonna, Pontiroli, Belli, Shiroka, Riccò,
Brunelli, J. Am. Chem. Soc., 126, 2004, 15032)
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13C NMR ?-structure confirmations
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13C NMR MAS (8 kHz) on ?-Li4C60 at 20C
Two groups of peaks
sp2 carbons at ?150 ppm
sp3 carbons at ?60 ppm
Splitting of the sp3 peak
Int. Ratio 21
Absence of Knight shift
Insulating character
Riccò, Shiroka, Belli, Pontiroli, Pagliari,
Ruani, Palles, Margadonna, Tomaselli, Phys. Rev.
B, accepted
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Thermal evolution of Li4C60 structure
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Powder XRD at ESRF ID31
a parameter ?a4.410-6 K-1
fcc monomeric phase
The bonds break at the same time
b parameter ?b1.710-6 K-1
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Thermal evolution of Li4C60 structure
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CW ESR (9.6 GHz) on Li4C60
20C Narrow peak
presence of defects (C60-)
?Hpp0.27(3) G g2.0009(3)
350C (monomer) ESR signal is a dysonian
metallic behaviour!
?Hpp2.27(5) G g2.0036(3)
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Thermal evolution of Li4C60 structure
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CW ESR (9.6 GHz) on Li4C60
On cooling the metallic phase remains down to
200C
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Thermal evolution of Li4C60 structure
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Raman results on Li4C60
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Raman spectroscopy on Li4C60
20C measurements
lift of the degeneracy of Hg and Ag modes
resonance at ?980 cm-1
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Conclusions
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• New hybrid polymeric structure was found in
  ?-Li4C60

• 13C NMR confirms the diffraction results

• Thermal evolution monomer phase with
  metal-to-insulator transition (from ESR and Raman
  data)

• 4 e- charge transfer in the metallic state
  intriguing electronic behaviour!

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Thank you for your attention!