Liquid-liquid transition (LLT) referring to a first-order transition from one liquid to another is an intriguing phenomenon in condensed-matter physics[1, 2]. The existence of LLT characterized by a calorimetric anomaly in some metallic glass (MG)-forming supercooled liquids have been reported recently but the explanation for this anomaly as a LLT remains controversial since alternatives like phase separation and nano-crystallization may exist, and more importantly, the underlying mechanism and order parameter of LLT remain unclear. We perform in-situ vitrification, annealing and heating of Pd42.5Ni42.5P15 glass-forming liquid via fast scanning calorimetry, revealing an annealing-induced and reversible LLT, and that the LLT mechanism can be both nucleation-growth (NG) and spinodal-decomposition (SD) types. After annealing, a two-step-like specific-heat increase of the glass transition is observed during reheating, reflecting the coexistence of two distinct liquids and thus confirming the first-order nature of the LLT. These findings coincide well with the LLT behaviors of the molecular liquids[3], however, the LLT in MG-forming liquid is unique in the sense that it can take place in a manner of glass-glass transition below the conventional glass-transition temperature, which is counterintuitive to our normal cognition that a first-order phase transition cannot proceed after the liquid being frozen by vitrification.

　　参考文献：

　　[1]H. Tanaka. Importance of many-body orientational correlations in the physical description of liquids.Faraday Discuss. 167, 9-76 (2013).

　　[2]J. Shen, Z. Lu, J. Q. Wang, S. Lan, F. Zhang, A. Hirata, M. W. Chen, X. L. Wang, P. Wen, Y. H. Sun, H. Y. Bai and W. H. Wang.Metallic glacial glass formation by a first-order liquid-liquid transition.J. Phys. Chem. Lett.