Nanoscale-to-Mesoscale Heterogeneity and Percolating Favored Clusters Govern Ultrastability of Metallic Glasses.

Comprehending and controlling the stability of glasses is one of the most challenging issues in glass science. Here we explore the microscopic origin of the ultrastability of a Cu-Zr-Al metallic glass (MG). It is revealed that the ultrastable window (0.7-0.8 T g ) of MGs correlates with the enhanced degree of nanoscale-to-mesoscale structural/mechanical heterogeneity and the connection of stability-favored clusters. On one side, the increased fraction of stability-favored clusters promotes the formation of a stable percolating network through a critical percolation transition, which is essential to form ultrastable MG. On the other side, the enhanced heterogeneity arising from an increased distribution in local clusters may promote synergistically a more efficient and frustrated packing of amorphous structure, contributing to the ultrastability. The present work sheds new light on the stability of MGs and provides a step toward next-generation MGs with superior stability and performances.