Decoupling structural and bonding effects on ferroelectric switching in ScAlN via molecular dynamics under an applied electric field

TL;DR

This study uses molecular dynamics simulations to decouple and analyze the individual structural and bonding effects influencing ferroelectric switching in ScAlN, revealing that polarization is solely structurally determined while coercive field depends on both effects.

Contribution

The paper introduces a method to separate structural and bonding effects on ferroelectric switching using machine-learning MD simulations, providing new insights into their individual roles.

Findings

Remanent polarization depends only on structural effects.

Coercive field is influenced by both structural and bonding effects.

Static switching barrier depends solely on the structural parameter u.

Abstract

ScxAl1-xN has emerged as a promising wurtzite-type ferroelectric material, where increasing the Sc composition reduces both the coercive field (Ec) and remanent polarization (Pr). This composition-dependent behavior is physically attributed to two simultaneous changes: the increase in the internal structural parameter u (structural effect) and the weakening of bond strength (bonding effect). Because these factors are strongly coupled in experiments, their individual contributions to ferroelectric switching remain unclear. In this study, we systematically decoupled these effects using machine-learning force field-based molecular dynamics (MD) simulations under an applied electric field. By artificially tuning u via in-plane strain at a fixed composition, we demonstrated that Pr is determined exclusively by the structural effect, exhibiting a universal linear dependence regardless of the composition. In contrast, Ec deviated from this structural trend, implying an additional compositional contribution. To isolate this, we evaluated configurations with identical u but varying Sc compositions; Pr remained constant, whereas Ec systematically decreased due to bond weakening. Furthermore, static nudged elastic band (NEB) calculations revealed that the static switching barrier depends solely on u, failing to explicitly capture the bonding effect on Ec. These results establish that while Pr is governed strictly by the structural effect, Ec is determined by a superposition of structural and bonding effects. Our findings highlight the necessity of dynamic MD simulations for fully understanding ferroelectric switching in compositionally tunable materials.