Numéro |
J. Phys. IV France
Volume 114, April 2004
|
|
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Page(s) | 81 - 85 | |
DOI | https://doi.org/10.1051/jp4:2004114015 |
J. Phys. IV France 114 (2004) 81
DOI: 10.1051/jp4:2004114015
Structural instability and electronic localization in the 2:1 salts: The case of the Fabre and the (DMtTTF) 2CIO 4salts
S. Ravy1, 1, P. Foury-Leylekian1, D. Le Bolloc'h1, J.-P. Pouget1, J.M. Fabre2, R.J. Prado3 and P. Lagarde31 Laboratoire de Physique des Solides (CNRS UMR 8502), Bât. 510, Université Paris-Sud, 91405 Orsay Cedex, France
2 Laboratoire de Chimie Structurale Organique, Université de Montpellier, 34095 Montpellier Cedex 5, France
3 LURE (CNRS UMR 130), Bât. 209D, Université Paris-XI, BP. 34, 91898 Orsay Cedex, France
Abstract
The charge ordering observed in the (TMTTF)
2X family
has been studied by X-ray absorption spectroscopy. XANES measurements at the
Sulfur K-edge show no evidence of charge disproportionation larger than 0.5
e, and EXAFS at the Phosphorus K-edge indicate no displacements of the
PF
6 anion larger than 0.05 Å. The difficulty to observe a
structural signature of this charge ordering is due to the triclinic
symmetry of these salts. By contrast, in the monoclinic charge transfer salt
(DMtTTF)
2ClO
4, a screw axis symmetry constrains the molecular
stacks to be uniform. In this real
-filled
system, charge localization is observed at about 150 K. We show that around
this temperature an incommensurate modulation of reduced wave vector
(0.58,0,-0.275) is stabilized. The transition is strongly hysteretic, but no
long range order is established. We suggest that this modulation, which has
the 4k
F periodicity in the chain direction, stabilizes a local
antiferroelectric state similar to the one previously observed in
(TMTTF)
2SCN.
Key words. Charge ordering, Structural phase transition.
© EDP Sciences 2004