Percolation dissipation of the α and β processes in metallic glasses

Abstract

Dynamic processes in glasses are crucial for unraveling fundamentals of the glass transition and material properties. A recent theoretical framework proposes a ‘double-percolation’ scenario for the α and β-relaxation processes. While supported by simulations, no experimental validation has so far been presented. We here conduct a comprehensive analysis of the relaxation dissipation of more than 300 mechanical spectra of metallic glass samples. Our study yields two key findings, both aligning with the double-percolation theory: (i) The α-relaxation has a damping factor of 0.6 ( ±0.05), independent of material composition, probing frequency, and thermal history—a signature that is consistent with the percolation of immobile atomic clusters proposed to characterize the α-relaxation. (ii) The β-relaxation dissipation, though of variable magnitude and dependent on external factors, can be rationalized as caused by the percolation of mobile atomic entities driving configurational rearrangements; thus for the β-relaxation we show that certain atomic motions are neither dissipative nor induce configurational changes. These results bridge theoretical predictions with experimental observations, suggesting a generally applicable picture of the atomic-scale mechanisms of relaxation dissipation in glass formers.