Crystal Nucleation and Growth in Liquids: Cooperative Atom Attachment and Detachment

TL;DR

This paper challenges classical crystal growth theories by showing that atoms attach cooperatively and match crystal order parameters rather than diffusing individually, based on molecular dynamics studies of supercooled metals.

Contribution

It introduces a new understanding of atom attachment in crystal growth, emphasizing cooperative behavior and order parameter matching over diffusion-based mechanisms.

Findings

Atoms join the crystal by matching orientational order.

Multiple atoms attach cooperatively, increasing with decreasing temperature.

Contradicts classical diffusion-based attachment models.

Abstract

Classical theories of crystal nucleation and growth from the liquid assume activated processes that are interface limited, with the atoms individually joining the growing interface by jumps that occur at a rate that is determined by the diffusion coefficient in the liquid phase. These assumptions are in contradiction with the results of molecular dynamics studies that are presented here for supercooled Ni and Al20Ni60Zr20. Instead of diffusion-based attachment across the interface, atoms join the interface by making small changes so as to match the orientational order parameter of the nucleating crystal. Further, instead of joining individually multiple atoms join cooperatively, with the number of cooperative atoms increasing with decreasing temperature.