Intermittent cluster dynamics and temporal fractional diffusion in a bulk metallic glass

• Published in: Nature communications 2024-08, Vol.15 (1), p.6595-9, Article 6595
• Main Authors: Riechers, Birte, Das, Amlan, Dufresne, Eric, Derlet, Peter M., Maaß, Robert
• Format: Article
• Language: English
• Subjects: 639/166/988; 639/301/1023/218; Aging; Aging (metallurgy); Amorphous materials; Diffusion; Dynamic structural analysis; Heterogeneity; Humanities and Social Sciences; Material properties; Metallic glasses; multidisciplinary; Power law; Science; Science & Technology - Other Topics; Science (multidisciplinary); Time dependence; X-ray scattering
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-50758-3

Glassy solids evolve towards lower-energy structural states by physical aging. This can be characterized by structural relaxation times, the assessment of which is essential for understanding the glass’ time-dependent property changes. Conducted over short times, a continuous increase of relaxation times with time is seen, suggesting a time-dependent dissipative transport mechanism. By focusing on micro-structural rearrangements at the atomic-scale, we demonstrate the emergence of sub-diffusive anomalous transport and therefore temporal fractional diffusion in a metallic glass, which we track via coherent x-ray scattering conducted over more than 300,000 s. At the longest probed decorrelation times, a transition from classical stretched exponential to a power-law behavior occurs, which in concert with atomistic simulations reveals collective and intermittent atomic motion. Our observations give a physical basis for classical stretched exponential relaxation behavior, uncover a new power-law governed collective transport regime for metallic glasses at long and practically relevant time-scales, and demonstrate a rich and highly non-monotonous aging response in a glassy solid, thereby challenging the common framework of homogeneous aging and atomic scale diffusion. In metallic glasses, atomic-scale transport strongly affects the materials properties and thus performance in applications. Here the authors present the intermittent character of structural relaxation connected to microstructural heterogeneity, and power-law behavior at long time scales resulting from collective and correlated atomic motion.