Structural pathway of polyamorphous transition in metallic glasses

Polyamorphous transition refers to the transformation between two distinct amorphous states with identical composition. This phenomenon is intriguing in the field of physics and offers avenues for glass material design. Recently, polyamorphous transitions have been frequently observed in glassy materials. However, the transition pathway has yet to be established, which is essential for understanding its structural origins. Here, we present evidence from 12 different types of metallic glasses spanning 7 orders of magnitude in timescales, demonstrating that polyamorphous transitions consistently occur after the devitrification process, between two supercooled liquid phases (I and II). Notably, we observe a decrease in liquid fragility and heat capacity following the transition, suggesting that the polyamorphous transition is associated with the fragile-to-strong transition (FST) in liquids. These findings elucidate the detailed structural pathway of the polyamorphous transition, via glass I → devitrification → liquid I → fragile-strong transition → liquid II, and incorporate the FST into a cohesive framework for its understanding.