STRUCTURAL RELAXATION IN SUPERCOOLED GLASS-FORMING SOLUTIONS - A NEUTRON SPIN-ECHO STUDY OF LICL, 6D2O

We have performed neutron spin-echo measurements on the supercooled gl ass-forming system (LiCl)-Li-7, 6D2O above its glass transition temper ature (T(g) = 135 K). This investigation has permitted us to determine the time dependence of the density correlation function phi(Q,t) betw een 2 ps and 2 ns at the maximum of the structure factor(Q = 1.9 angst rom-1). We have shown for the viscosity, the existence of two temperat ure domains limited by two critical temperatures (fixed points). This crossover from the stable liquid to the metastable liquid might be rel ated to a change in the multiplicity of the microscopic interactions. In this study we show that the dynamics of the structural relaxation i s consistent with the two scaling laws of the viscosity. Both the aver age relaxation time and the stretched exponential behaviour indicate a crossover regime around 210 K. However, the scaling of the density co rrelation function differs, in the lower-temperature regime, from the scaling of the shear viscosity. For the supercooled liquid dynamics, t he results are more or less correlated to the mode-coupling theory.