Kinetic phase diagram for nucleation and growth of competing crystal polymorphs in charged colloidal suspensions

TL;DR

This study maps the kinetic phase diagram of nucleation and growth in charged colloids, revealing how different crystal structures form under various conditions and identifying regimes where metastable phases dominate.

Contribution

It provides the first comprehensive kinetic phase diagram for charged colloid crystallization, including nucleation barriers and the conditions favoring different polymorphs.

Findings

Metastable bcc can nucleate due to lower barriers near the triple point.

Multiple crystal structures (hcp, fcc, bcc) coexist at high supersaturation.

Nucleation barriers vary with screening length and supersaturation.

Abstract

We determine the full kinetic phase diagram for nucleation and growth of crystal phases in a suspension of charged colloids. We calculate nucleation barrier heights for face-centered cubic (fcc) and body-centered cubic (bcc) crystal phases for varying screening lengths and supersaturations using the seeding approach in extensive simulations. Using classical nucleation theory, we determine for the entire metastable fluid region the crystal polymorph with the lowest nucleation barrier. Surprisingly, we find a regime close to the triple point where metastable bcc can form due to a lower nucleation barrier, even though fcc is the stable phase. For higher supersaturation, we find that the difference in barrier heights decreases and we observe a mix of hexagonal close-packed (hcp), fcc and bcc structures in the growth of crystalline seeds as well as in spontaneously formed crystals.