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

Abstract

Results from two different series of neutron inelastic scattering experiments are presented. In the first series the dependence of the atomic dynamics of a metallic glass, NiPdP, on rapid quenching has been studied. The quenched-in density fluctuations and especially the free volume lead to an increase of the low energy modes (LEMs) for energies between 2 and 20 meV for this glass. This intensity increases in the low energy region is however, not much more than was found for a rapidly quenched, i.e., highly defective fcc-Al lattice. The change of the calculated vibrational entropy due to these additional LEM is of the order of 3%. In search for anharmonic modes in metallic glasses, a second series of experiments investigated the dependence of the atomic dynamics on temperature using a conventional metal–metal glass, NiZr, and one of the more stable Zr-based glasses, ZrCuAl. Anharmonic effects in the form of a shift of the complete generalised vibrational density of states to lower energies on heating were in fact observed for the first time. However these effects can be attributed to the expansion of the glass, which for a 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.