Liquid-to-liquid transition around the glass-transition temperature in a glass-forming metallic liquid

Liquid-to-liquid transition (LLT) refers to a first-order phase transition between two liquid states. Here, the relationship between the liquid dynamics and LLT is studied by performing in-situ vitrification, annealing, and heating of Pd _42.5Ni _42.5P ₁₅ metallic-glass-forming liquid via fast scanning calorimetry. Unlike isokinetic LLTs reported in metallic liquids, here isothermal-annealing induced forward and heating-initiated reversible LLT are detected, and the LLT mechanisms of both nucleation-growth and spinodal-decomposition types are revealed by controlling the annealing temperature. A two-step-like increase in the specific heat of the glass transition is observed upon reheating reflecting the coexistence of two distinct liquids. The detected transition conforms to LLT behavior observed in molecular liquids; however, it can also proceed as a glass-to-glass transition below the conventional glass-transition temperature. This work not only provides a complementary understanding of the nature of LLTs in both metallic and molecular liquids but also reveals a unique first-order glass-to-glass transition in the multi-component metallic system.