Molecular dynamics simulation of the ferroelectric phase transition in GeTe: displacive or order-disorder?

TL;DR

This study uses machine learning-enhanced molecular dynamics to investigate the nature of the phase transition in GeTe, revealing evidence for both displacive and order-disorder characteristics.

Contribution

It provides a detailed simulation-based analysis clarifying the conflicting interpretations of GeTe's phase transition.

Findings

Radial distribution function shape above critical temperature matches previous studies.

Large anharmonicity can cause asymmetric radial distribution without order-disorder transition.

Evidence of both order-disorder and displacive transition features near the critical point.

Abstract

Experimental investigations of the phase transition in GeTe provide contradictory conclusions regarding the nature of the phase transition. Considering growing interest in technological applications of GeTe, settling these disputes is of great importance. To that end, we present a molecular dynamics study of the structural phase transition in GeTe using a machine-learned interatomic potential with ab-initio accuracy. First, we calculate the asymmetric shape of the radial distribution function of the nearest-neighbor bonds above the critical temperature, in agreement with previous studies. However, we show that this effect is not necessarily linked with the order-disorder phase transition and can occur as a result of large anharmonicity. Next, we study in detail the static and dynamic properties of the order parameter in the vicinity of the phase transition and find fingerprints of both order-disorder and displacive phase transition.