Short- and medium-range orders in Al90Tb10 glass and their relation to the structures of competing crystalline phases

TL;DR

This study uses neural network-based molecular dynamics to analyze the local and medium-range order in Al90Tb10 metallic glass, revealing specific cluster arrangements and their relation to crystalline phases.

Contribution

It introduces a neural network interatomic potential for detailed structural analysis and identifies low-energy crystalline structures related to the glass's local order.

Findings

Over 80% of Tb-centered clusters have specific short-range orders ('3661' or '15551').

Medium-range order extends to second and third coordination shells, forming Bergman-type packing.

Crystalline structures with similar local order exhibit different atomic packings in outer shells.

Abstract

Molecular dynamics simulations using an interatomic potential developed by artificial neural network deep machine learning are performed to study the local structural order in Al90Tb10 metallic glass. We show that more than 80% of the Tb-centered clusters in Al90Tb10 glass have short-range order (SRO) with their 17 first coordination shell atoms stacked in a '3661' or '15551' sequence. Medium-range order (MRO) in Bergman-type packing extended out to the second and third coordination shells is also clearly observed. Analysis of the network formed by the '3661' and '15551' clusters show that ~82% of such SRO units share their faces or vertexes, while only ~6% of neighboring SRO pairs are interpenetrating. Such a network topology is consistent with the Bergman-type MRO around the Tb-centers. Moreover, crystal structure searches using genetic algorithm and the neural network interatomic potential reveal several low-energy metastable crystalline structures in the composition range close to Al90Tb10. Some of these crystalline structures have the '3661' SRO while others have the '15551' SRO. While the crystalline structures with the '3661' SRO also exhibit the MRO very similar to that observed in the glass, the ones with the '15551' SRO have very different atomic packing in the second and third shells around the Tb centers from that of the Bergman-type MRO observed in the glassy phase.