Microscopic dynamics of enhanced glass-forming ability with minor oxygen addition in bulk metallic glasses

Minor oxygen addition has been proposed as a promising strategy to enhance the performance of metallic glasses, particularly their glass-forming ability. In this work, we investigate the microscopic dynamics of a CuZr glass former with oxygen content up to 2 at. % using molecular dynamics simulations based on specially developed neural network interatomic potentials. Our findings indicate a gradual increase in the glass transition temperature with oxygen addition, with an anomalous peak at 0.4 at. % O. We reveal an anti-correlation of kinetic fragility and dynamic heterogeneity behind this unusual rise, where the system exhibits reduced kinetic fragility alongside more significant dynamic heterogeneity. Using the continuous time random walk method, we show that at 0.4 at. % O, a highly mobile Cu atomic layer forms around O-Zr clusters, resulting in notable dynamic heterogeneity. This dynamic behavior is closely linked to the bonding pattern within the O-Zr network, particularly favoring the configuration with edge and surface sharing. In addition, such structures contribute to a more compact O-Zr network, leading to lower kinetic fragility. These findings provide detailed insights into the microscopic dynamics behind the effects of minor oxygen additions.