The Cooperativity of Atomic Fluctuations in Highly Supercooled Glass-Forming Metallic Melts

The behavior of supercooled glass-forming metals depends on the cooperative atomic fluctuations caused by dynamic heterogeneities in the melt. These spatial and temporal heterogeneities form dynamic clusters, which are regions of cooperative rearrangement (CRR). In this study, the macroscopic kinetics and the correlation length ξ, of the CRR, are derived for Pt_57.4Cu_14.7Ni_5.3P_22.6 and Pd₄₃Cu₂₇Ni₁₀P₂₀ metallic glass-formers by fast differential scanning calorimetry near the glass transition. While the alloy composition influences the α-relaxation and vitrification kinetics, typically defined by the glass transition, as well as the limiting temperature of the Vogel-Fulcher-Tammann-Hesse equation and the fragility index, it has no significant influence on the correlation length of the cooperative atomic motions. In agreement with many other materials, ξ is about 3 nm at the glass transition for both metallic glasses. The temperature dependence of ξ correlates with the apparent activation energy of the α-relaxation and is the reason for its non-Arrhenius behavior.