Relaxations in glasses

Relaxations in soft-sphere- and ZrCu-glasses are studied by molecular dynamics. We observe local jumps where groups of ten or more atoms move collectively forming chain-like structures. At the lowest temperatures the total jump length is of the order of the nearest neighbor distance whereas a single atom moves only a fraction of this distance. Both the displacements and the numbers of participating atoms increase with temperature. Successive jumps tend to involve the same atoms. These relaxations are correlated with soft quasi-localized vibrations. Similar to the vibrations the collectivity of the relaxation is also observed in their contribution to the dynamic structure factor. In the binary metallic ZrCu glass we observe additional 'collective local' jump processes at temperatures above 400 K (approximate to 0.5T(g)) jumps of single Cu-atoms into nearest neighbour sites. (C) 1999 Elsevier Science B.V. All rights reserved.