On the Role of Atomic Mobility in the Polyamorphism of Metallic Glasses

Abstract

Understanding the microscopic mechanisms underlying polyamorphic transitions requires simultaneous knowledge of thermodynamic and structural evolution, which has remained experimentally inaccessible. Here, we combine chip-based fast differential scanning calorimetry with high-energy synchrotron X-ray diffraction to simultaneously probe the thermodynamic and structural evolution during the polyamorphic transition of a Pd-Ni-P metallic glass. Correlating heat-flow signals with the corresponding structural evolution during both heating and cooling reveals a direct relationship between thermodynamic evolution and medium-range structural ordering. Based on this relationship, we identify two distinct transition mechanisms. In the glassy state, the transition proceeds continuously through progressive medium-range ordering, accompanied by enhanced thermal stability and strongly temperature-dependent kinetics. In contrast, in the equilibrium supercooled liquid, the transition proceeds through the coexistence of distinct amorphous states, with only a weak temperature dependence of the kinetics. These findings show that atomic mobility governs the transformation pathway by coupling thermodynamic evolution to structural ordering, providing new insights into polyamorphic transitions in nonequilibrium amorphous systems.