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The authors recently reported that undercooled liquid Ag and Ag–Cu alloys both exhibit a first order phase transition from the homogeneous liquid (L-phase) to a heterogeneous solid-like G-phase under isothermal evolution. Here, we report a similar L–G transition and heterogenous G-phase in simulations of liquid Cu–Zr bulk glass. The thermodynamic description and kinetic features (viscosity) of the L-G-phase transition in Cu–Zr simulations suggest it corresponds to experimentally reported liquid–liquid phase transitions in Vitreloy 1 (Vit1) and other Cu–Zr-bearing bulk glass forming alloys. The Cu–Zr G-phase has icosahedrally ordered cores versus fcc/hcp core structures in Ag and Ag–Cu with a notably smaller heterogeneity length scale Λ . We propose the L–G transition is a phenomenon in metallic liquids associated with the emergence of elastic rigidity. The heterogeneous core–shell nano-composite structure likely results from accommodating strain mismatch of stiff core regions by more compliant intervening liquid-like medium.
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First-Order Phase Transition in Liquid Ag to the Heterogenous G-Phase
A molten metal is an atomic liquid that lacks directional bonding and is free from chemical ordering effects. Experimentally, liquid metals can be undercooled by up to ∼20% of their melting temperature but crystallize rapidly in subnanosecond time scales at deeper undercooling. To address this limited metastability with respect to crystallization, we employed molecular dynamics simulations to study the thermodynamics and kinetics of the glass transition and crystallization in deeply undercooled liquid Ag. We present direct evidence that undercooled liquid Ag undergoes a first-order configurational freezing transition from the high-temperature homogeneous disordered liquid phase (L) to a metastable, heterogeneous, configura-tionally ordered state that displays elastic rigidity with a persistent and finite shear modulus, μ. We designate this ordered state as the G-phase and conclude it is a metastable non-crystalline phase. We show that the L−G transition occurs by nucleation of the G-phase from the L-phase. Both te L- and G-phases are metastable because both ultimately crystallize. The observed first-order transition is reversible: the G-phase displays a first-order melting transition to the L-phase at a coexistence temperature, TG,M. We develop a thermodynamic description of the two phases and their coexistence boundary.
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- Award ID(s):
- 1710744
- PAR ID:
- 10139158
- Date Published:
- Journal Name:
- The journal of physical chemistry letters
- Volume:
- 11
- ISSN:
- 1948-7185
- Page Range / eLocation ID:
- 632-645
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021
