ATOMIC-LEVEL MECHANISMS OF FAST RELAXATION IN METALLIC GLASSES

Glasses are ubiquitous in daily life and have unique properties which are a consequence of the underlying disordered structure. By understanding the fundamental processes that govern these properties, we can modify glasses for desired applications. Key to understanding the structure-dynamics relationship in glasses is the variety of relaxation processes that exist below the glass transition temperature. Though these relaxations are well characterized with macroscopic experimental techniques, the microscopic nature of these relaxations is difficult to elucidate with experimental tools due to the requirements of timescale and spatial resolution. There remain many questions regarding the microscopic nature of relaxation in glass including the role of defects, determination of subsets of atoms that cause the relaxations, the time/space correlations and how low energy activations occur in the potential energy landscape (PEL). To give new insight into these questions we use classical molecular dynamics (MD) to mimic experimental techniques of mechanical perturbation by sinusoidally shearing a model Cu65Zr35 metallic glass. We then uniquely combine this technique with the concept of atomic-level stresses to identify the viscoelastic character of each atom during a cycle of sinusoidal straining. Using results from these techniques, we examine the microscopic nature of relaxation phenomena below the glass transition temperature, examining the transient nature, temperature dependence of said transience and spatial correlation of mechanical loss. We demonstrate the surprising transient nature of relaxation, the spatial correlation of mechanical loss and the low energy barriers on the order of 1meV that represent the ripples in the bottom of the PEL. These new insights into the microscopic nature of relaxation get us closer to being able to tune the properties of glass reliant on relaxation phenomena.