Polymorph selection during crystallization of a model colloidal fluid with a free energy landscape containing a metastable solid

TL;DR

This study investigates how the complex free energy landscape influences polymorph selection during crystallization in a colloidal system modeled by Yukawa interactions, revealing a switch from FCC to BCC phases driven by local order fluctuations.

Contribution

It demonstrates the impact of free energy landscape features on polymorph selection and the role of local order fluctuations in a Yukawa colloidal model.

Findings

Crystallization can switch from FCC to BCC phase despite FCC being thermodynamically stable.

Local bond-orientational order fluctuations influence polymorph selection.

The composition of critical clusters depends on the free energy landscape.

Abstract

The free energy landscape responsible for crystallization can be complex even for relatively simple systems like hard sphere and charged stabilized colloids. In this work, using hard-core repulsive Yukawa model, which is known to show complex phase behavior consisting of fluid, FCC and BCC phases, we studied the interplay between the free energy landscape and polymorph selection during crystallization. When the stability of the BCC phase with respect to the fluid phase is gradually increased by changing the temperature and pressure at a fixed fluid-FCC stability, the final phase formed by crystallization is found to undergo a switch from the FCC to the BCC phase, even though FCC remains thermodynamically the most stable phase. We further show that the nature of local bond-orientational order parameter fluctuations in the metastable fluid phase as well as the composition of the critical cluster depend delicately on the free energy landscape, and play a decisive role in the polymorph selection during crystallization.