Mechanical versus thermodynamical melting in pressure-induced amorphization: the role of defects

TL;DR

This study uses numerical simulations to compare mechanical and thermodynamical mechanisms of pressure-induced amorphization, highlighting the influence of defects on the transition process and reconciling conflicting theories.

Contribution

It demonstrates how defects alter the amorphization mechanism, showing a transition close to melting conditions without phonon softening, thus clarifying previous debates.

Findings

Perfect crystals undergo transition via phonon softening.

Defects reduce nucleation barriers, leading to transition near melting line.

Transition mechanisms differ with defect presence, unifying prior conflicting views.

Abstract

We study numerically an atomistic model which is shown to exhibit a one--step crystal--to--amorphous transition upon decompression. The amorphous phase cannot be distinguished from the one obtained by quenching from the melt. For a perfectly crystalline starting sample, the transition occurs at a pressure at which a shear phonon mode destabilizes, and triggers a cascade process leading to the amorphous state. When defects are present, the nucleation barrier is greatly reduced and the transformation occurs very close to the extrapolation of the melting line to low temperatures. In this last case, the transition is not anticipated by the softening of any phonon mode. Our observations reconcile different claims in the literature about the underlying mechanism of pressure amorphization.