Dynamics of glasses and undercooled melts of Zr-Cu

Molecular dynamics simulations are used to study the metallic binary alloy ZrCu, mainly Zr_6_7Cu_3_3, 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 separate 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 a 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. (orig.)87 refs.SIGLEAvailable from TIB Hannover: RA 831(3556) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman