| Issue |
Europhys. Lett.
Volume 53, Number 5, March 2001
|
|
|---|---|---|
| Page(s) | 611 - 617 | |
| Section | Condensed matter: structure, mechanical and thermal properties | |
| DOI | https://doi.org/10.1209/epl/i2001-00196-9 | |
| Published online | 01 December 2003 | |
Experimental and numerical signatures of dynamical crossover in orientationally disordered crystals
Laboratoire de Dynamique et Structure des Matériaux Moléculaires,
CNRS ESA 8024,
Université Lille I -
59655 Villeneuve d'Ascq Cedex, France
Received:
25
October
2000
Accepted:
22
December
2000
By means of NMR experiment and MD computer simulation
we investigate the dynamical properties of a
chloroadamantane orientationally
disordered crystal.
We find a plastic-plastic dynamical
transition at 
K in the pico-nanosecond regime.
It is interpreted
as the rotational
analogue of the Goldstein
crossing temperature between quasi-free diffusion and activated regime
predicted in liquids. Below Tx, NMR experimental
data are well described by a Frenkel model corresponding to
a strongly anisotropic motion. At higher temperatures,
a drastic deviation is observed
toward quasi-isotropic rotational diffusion.
We show also that two-step relaxations
emerge close to Tx which probably does not
correspond to the 
of the Mode Coupling Theory.
An interpretation which is based on the present study
of a specific heat anomaly detected
by a recent calorimetric experiment is proposed.
PACS: 64.70.Pf – Glass transitions / 76.60.-k – Nuclear magnetic resonance and relaxation / 61.43.-j – Disordered solids
© EDP Sciences, 2001
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