Quasi-localized modes in crystalline high entropy alloys

TL;DR

This study uses molecular dynamics to explore how disorder affects vibrational properties in high entropy alloys, revealing quasi-localized modes persist even in crystalline states, influencing their mechanical behavior.

Contribution

It provides new insights into vibrational modes in crystalline and amorphous HEAs, linking disorder to vibrational density of states and mechanical properties.

Findings

Density of states follows $D()\u223c^4$ in amorphous HEAs

Quasi-localized vibrations are present in crystalline HEAs

Degree of crystallization affects vibrational deviations

Abstract

High Entropy Alloys (HEAs) are designed by mixing multiple metallic species in nearly the same amount to obtain crystalline or amorphous materials with exceptional mechanical properties. Here we use molecular dynamics simulations to investigate the role of positional and compositional disorder in determining the low-frequency vibrational properties of CrMnFeCoNi HEAs. Our results show that the expected dependence of the density of states on the frequency as $D(\omega)\sim\omega^4$ is recovered for amorphous HEAs and is also observed for partially crystallized alloys with deviations that depend on the degree of crystallization. We find that the quasi-localized vibrations are still visible in crystalline HEAs, albeit suppressed compared to the corresponding amorphous alloys. Our work offers a unified perspective to describe HEA mechanical properties in terms of their vibrational density of states.