Change of dynamical cooperativity in the glass-transition regime: computer modelling results for Ni0.5Zr0.5

Abstract Results are reported of molecular dynamics simulations for an amorphous Ni0.5Zr0.5 model. Presented are the mean squares displacements of the atoms on the μs-scale at 700, 785 and 900 K, well below the dynamical glass temperature Tc=1120 K. According to the data, the dynamical cooperativity characteristic for dense melts around Tc, that is irreversible motion of individual chains of atoms, becomes ineffective at low temperatures. Here a new type of higher organised dynamical cooperativity seems to take over, characterised by the occurrence of avalanches of mutually triggered transitions of chain of atoms separated by periods of calmness.