Universal amorphous-amorphous transition in GexSe1-x glasses under pressure

TL;DR

This study reveals a universal amorphous-amorphous transition in GexSe1-x glasses under pressure, showing consistent structural changes and a metallization event across different compositions up to 42 GPa.

Contribution

It demonstrates a universal pressure-induced structural transition in GexSe1-x glasses, combining experimental and simulation data to reveal consistent densification mechanisms.

Findings

All compositions remain amorphous up to 42 GPa.

Ge-Se distances show a two-step response to pressure.

Metallization occurs around 15-20 GPa, indicated by spectral shifts.

Abstract

Pressure induced structural modifications in vitreous Ge$_{x}$Se$_{100-x}$ (where 10 $\leq$ x $\leq$ 25)are investigated using X-ray absorption spectroscopy (XAS) along with supplementary X-ray diffraction (XRD) experiments and ab initio molecular dynamics (AIMD) simulations. Universal changes in distances and angle distributions are observed when scaled to reduced densities. All compositions are observed to remain amorphous under pressure values up to 42 GPa. The Ge-Se interatomic distances extracted from XAS data show a two-step response to the applied pressure; a gradual decrease followed by an increase at around 15-20 GPa, depending on the composition. This increase is attributed to the metallization event that can be traced with the red shift in Ge K edge energy which is also identified by the principal peak position of the structure factor. The densification mechanisms are studied in details by means of AIMD simulations and compared to the experimental results. The evolution of bond angle distributions, interatomic distances and coordination numbers are examined and lead to similar pressure-induced structural changes for any composition.