Point Defects in Crystals of Charged Colloids

TL;DR

This study uses simulations and free-energy calculations to analyze point defects in charged colloidal crystals, revealing higher defect prevalence in BCC phases and identifying crowdions as interstitials, thus enabling experimental observation.

Contribution

It provides the first detailed characterization of vacancies and interstitials in colloidal BCC and FCC crystals, highlighting the prominence of crowdions in BCC phases.

Findings

Defects are more common in BCC than FCC colloidal crystals.

Interstitials in BCC manifest as crowdions, a one-dimensional defect.

Results suggest potential for experimental detection of these defects.

Abstract

Charged colloidal particles - both on the nano and micron scales - have been instrumental in enhancing our understanding of both atomic and colloidal crystals. These systems can be straightforwardly realized in the lab, and tuned to self-assemble into body-centered cubic (BCC) and face-centered cubic (FCC) crystals. While these crystals will always exhibit a finite number of point defects, including vacancies and interstitials - which can dramatically impact their material properties - their existence is usually ignored in scientific studies. Here, we use computer simulations and free-energy calculations to characterize vacancies and interstitials in both FCC and BCC crystals of point-Yukawa particles. We show that, in the BCC phase, defects are surprisingly more common than in the FCC phase, and the interstitials manifest as so-called crowdions: an exotic one-dimensional defect proposed to exist in atomic BCC crystals. Our results open the door to directly observing these elusive defects in the lab.