Abstract
We applied an efficient methodology to separate vibrational and configurational entropies in bulk metallic glasses by means of molecular dynamics simulation based on a combination of non-equilibrium adiabatic switching and reversible scaling methods. This approach involves calculating the vibrational free energy using the Einstein crystal as a reference for the solid phase and the recently proposed Uhlenbeck-Ford model for the fluid phase. This methodology has the advantage that it does not require a crystalline solid phase for separating the entropies. Therefore, in principle, it is applicable to any material, regardless of whether or not it has a crystalline phase. Using this methodology, we separate the vibrational and configurational entropies of two metallic glasses with different fragilities at zero external pressure, namely, Cu$_{50}$Zr$_{50}$ and Cu$_{46}$Zr$_{46}$Al$_{8}$. We find that the results for the former alloy are in quite reasonable agreement with recent experimental work by Smith \textit{et al.}[H. L. Smith \textit{et al.}, Nat. Phys. \textbf{13}, 900 (2017)]. We also find the configurational entropy of the glass containing Al to be 70\% larger than that of the other glass. Our results suggest that, although other factors may be at play, the configurational entropy can be used to investigate the effect of the addition of a minor-alloying element on the glass-forming ability of bulk metallic glasses.
Highlights
The excess entropy in glass-forming liquids in relation to the crystalline phase is a phenomenon studied since the early 1900s
Our results suggest that other factors may be at play, configurational entropy can be helpful to understand the effect of the addition of a minor-alloying element on the glass-forming ability (GFA) of bulk metallic glasses (BMGs)
We employed in our calculations a robust methodology, whose qualities are evidenced by the good agreement between the results of our simulations and the experimental available data [31] for the vibrational and configurational entropies of the Cu50Zr50 metallic glass
Summary
The excess entropy in glass-forming liquids in relation to the crystalline phase is a phenomenon studied since the early 1900s. It started with measurements of the caloric properties of glass-forming substances done by Nernst in order to verify whether or not the third law of thermodynamics was applicable to all forms of condensed matter [1], which was followed by the publication in 1926 by Simon and Lange of their results about finite values of entropy for T = 0 K in glasses of glycerol and silica [2].
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