The microscopic pathway to crystallization in supercooled liquids

TL;DR

This study uses computer simulations to reveal that bond orientational order fluctuations, rather than density fluctuations, initiate crystallization in supercooled liquids, influencing polymorph selection and glass formation.

Contribution

It demonstrates that bond orientational fluctuations, not density, trigger nucleation and determine polymorphs, providing new microscopic insights into crystallization mechanisms.

Findings

Bond orientational order fluctuations trigger nucleation.

These fluctuations influence polymorph selection.

High-density fluctuations favor fivefold structures that hinder crystallization.

Abstract

Despite its fundamental and technological importance, a microscopic understanding of the crystallization process is still elusive. By computer simulations of the hard-sphere model we reveal the mechanism by which thermal fluctuations drive the transition from the supercooled liquid state to the crystal state. In particular we show that fluctuations in bond orientational order trigger the nucleation process, contrary to the common belief that the transition is initiated by density fluctuations. Moreover, the analysis of bond orientational fluctuations shows that these not only act as seeds of the nucleation process, but also i) determine the particular polymorph which is to be nucleated from them and ii) at high density favour the formation of fivefold structures which can frustrate the formation of crystals. These results can shed new light on our understanding of the relationship between crystallization and vitrification.