Formation of two glass phases in binary Cu-Ag liquid
Q An and WL Johnson and K Samwer and SL Corona and WA Goddard, ACTA MATERIALIA, 195, 274-281 (2020).
The glass transition is alternatively described as either a dynamic transition in which there is a dramatic slowing down of the kinetics, or as a thermodynamic phase transition. To examine the physical origin of the glass transition in fragile Cu-Ag liquids, we employed molecular dynamics (MD) simulations on systems in the range of 32,000 to 2,048,000 atoms. Surprisingly, we identified a 1st order freezing transition from liquid (L) to metastable heterogenous solid-like phase, denoted as the G-glass, when a supercooled liquid evolves isothermally below its melting temperature at deep undercooling. In contrast, a more homogenous liquidlike glass, denoted as the L-glass, is achieved when the liquid is quenched continuously to room temperature with a fast cooling rate of similar to 10(11) K/sec. We report a thermodynamic description of the L-G transition and characterize the correlation length of the heterogenous structure in the G-glass. The shear modulus of the G-glass is significantly higher than the L-glass, suggesting that the first order L-G transition is linked fundamentally to long-range elasticity involving elementary configurational excitations in the G-glass. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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