Liquid–liquid transition, a phase transition of one liquid phase to another with the same composition, provides a key opportunity for investigating the relationship between liquid structures and dynamics. Here we report experimental evidences of a liquid–liquid transition in glass-forming La50Al35Ni15 melt above its liquidus temperature by 27Al nuclear magnetic resonance including the temperature dependence of cage volume fluctuations and atomic diffusion. The observed dependence of the incubation time on the degree of undercooling is consistent with a first-order phase transition. Simulation results indicate that such transition is accompanied by the change of bond-orientational order without noticeable change in density. The temperature dependence of atomic diffusion revealed by simulations is also in agreement with experiments. These observations indicate the need of two-order parameters in describing phase transitions of liquids.
We report the values of steps of heat capacity (ΔCp) during the glass transition in a variety of metallic glasses (MGs). It is found that ΔCp is around 13.69 J mol−1 K−1 and almost invariable for the MGs. Based on the Eyring’s theory [N. Hirai and H. Eyring, J. Polym. Sci. 37, 51 (1959)], the phenomenon corresponds to a critical reduced free volume value. This exhibits that the glass transition takes place when the reduced free volume approaches to ∼2.35% in the MG systems. The value, consistent with that of the yielding of MGs, confirms that temperature and stress are equivalent for fluidizing MGs. Our results give an implication to understanding the glass transition in MGs as a Lindemann-type melting behavior [F. A. Lindemann, Z. Phys. 11, 609 (1910)].
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