Verlag des Forschungszentrums Jülich
JUEL-3556
Gaukel, Christoph
Dynamics of glasses and undercooled melts of Zr-Cu
135 S., 1998
Molecular dynamics simulations are used to study the metallic binary alloy ZrCu, mainly
Zr67Cu33, in a temperature range stretching from deep in the glassy state to the
melt well above the melting and glass transition temperatures. To describe the interatomic
interactions a modified embeded atom potential was developped. The configurations are
analyzed by a number of complementary techniques: coherent and incoherent intermediate
scattering functions, different combinations of structure factors, instantaneous mode
spectra, monitoring of single relaxations etc.
The dynamics of the system changes qualitatively with the temperature and we seperate
three different temperature ranges, the normal diffusive behaviour in the hot melt, the
hopping dominated dynamics in the undercooled melt and increasingly reversible motion
without measurable diffusion in the glassy state. In the undercooled melt o collective
motion is observed which coexists with the single atom hopping motion. For the latter a
semiquantitative three shell model is introduced, where the deviation from the Arrhenius
law, the Kohlrausch-Williams-Watts behaviour, results from a change in the back-jump-rate.
Fitting this model to the results of the simulations shows that, whereas the hopping rate
obeys an Arrhenius law, with decreasing temperature the reversibility of the jumps
increases strongly. In the glassy state the single relaxations form chain-like structures
where both, the number of participating atoms and the jump lengths of the atoms increase
with temperature.
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