Structural relaxation in PdGe metallic glass

Abstract

We have measured small reversible changes of electrical resistance which occur following a small temperature change applied to an amorphous Pd 78Ge 22 alloy. Reversibility of this relaxation was demonstrated by the resistance returning (nearly) to the original value after repeated temperature cycling and equilibration. The reversible characteristic of the relaxation suggests that the mechanism is the change in chemical short-range order (CSRO) with temperature. Thus the measurements provide information on atomic mobility in this metallic glass. The relaxation kinetics indicate a spectrum of relaxation times which is best described as log-normal but skewed towards longer times. Parameters describing the breadth and shift in this spectrum with temperature are described. We also observe an irreversible resistance change superimposed on the reversible changes. The kinetics of the irreversible change are found to obey the equation for free volume relaxation proposed by van den Beukel. However, this model fails to describe the slowing of the CSRO kinetics that occurs relatively early in the annealing process.