Dependence of the atomic dynamics of metallic glasses on quenched-in density fluctuations and on temperature

Results from two different series of neutron inelastic scattering experimen ts are presented. In the first series the dependence of the atomic dynamics of a metallic glass. NiPdP, on rapid quenching hits been Studied. The quen ched-in density fluctuations and especially the free volume lead to an incr ease of the low energy modes (LEMs) for energies between 2 and 20 meV for t his glass. This intensity increases in the low energy region is however, no t much more than was found for a rapidly quenched, i.e., highly defective f cc-Al lattice. The change of the calculated vibrational entropy due to thes e additional LEM is of the order of 3%. In search for anharmonic modes in m etallic glasses, it second series of experiments investigated the dependenc e of the atomic dynamics on temperature using it conventional metal-metal g lass, NiZr, and one of the more stable Zr-based glasses, ZrCuAl. Anharmonic effects in the form of a shift of the complete generalised vibrational den sity of states to lower energies on heating were in fact observed for the f irst time. However these effects can be attributed to the expansion of the glass, which for it metallic glass obviously proceeds by an increase of the atomic distances rather than by formation of additional free volume, or by anharmonic modes expected from the soft potential model. (C) 2001 Elsevier Science B.V. All rights reserved.