Atomic-scale expressions for viscosity and fragile-strong behavior in metal alloys based on the Zwanzig-Mountain formula

TL;DR

This paper introduces a semi-analytical model linking atomic-scale interactions to viscosity and fragile-strong behavior in metal alloys, combining the shoving model with the Zwanzig-Mountain formula and MD simulation data.

Contribution

It develops a novel three-parameter model that connects atomic-scale physical quantities to macroscopic viscosity and fragility in metal alloys.

Findings

Steeper interatomic repulsion results in fragile liquids.

Soft atoms are associated with strong liquids.

The model accurately fits experimental viscosity data.

Abstract

We combine the shoving model of $T$-dependent viscosity of supercooled liquids with the Zwanzig-Mountain formula for the high-frequency shear modulus, using the $g(r)$ of MD simulations of metal alloys as the input. This scheme leads to a semi-analytical expression for the viscosity as a function of temperature, which provides a three-parameter model fitting of experimental data of viscosity for the same alloy for which $g(r)$ was calculated. The model provides direct access to the influence of atomic-scale physical quantities such as the interatomic potential $\phi(r)$, on the viscosity and fragile-strong behavior. In particular, it is established that a steeper interatomic repulsion leads to fragile liquids, or, conversely, that "soft atoms make strong liquids".