J. Phys. I France
Volume 2, Numéro 6, June 1992
Page(s) 813 - 827
DOI: 10.1051/jp1:1992181
J. Phys. I France 2 (1992) 813-827

The implication of the lattice in the non-equilibrium behaviour of a glassy crystal

M. Descamps1, J. F. Willart1, G. Odou1 and K. Eichhorn2

1  Laboratoire de Dynamique et Structure des Matériaux Moléculaires UA CNRS 801, Université de Lille 1, Bât P5, F 59655 Villeneuve d'Ascq, France
2  DESY - F 41, Hasylab, Notkestr. 85, D 2000 Hamburg 52, Germany

(Received 5 February 1992, accepted in final form 17 March 1992)

Time resolved X-ray measurements on single crystals of the mixed system (cyanoadamantane) 1-x (chloroadamantane) x, for $x\cong 0.25$, have been made. Special attention has been paid to the underlying lattice in the glassy state. The rotational glass transition is signalled by a jump of the expansivity at $T_{\rm g}$ as in conventional glasses. There is no signature of the freezing on the peak profiles after a deep quench below $T_{\rm g}$. In the neighbourhood of $T_{\rm g}$, there is evidence of a slow correlated amplification of antiferroelectric and ferroelastic fluctuations respectively observed at the X and $\Gamma$ points of the Brillouin zone. In this quasi static ordering process the average underlying lattice is preserved but the mean square displacements are considerably increased.

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