Large effect of polydispersity on defect concentrations in colloidal crystals

Area of Science:

• Condensed matter physics
• Materials science
• Colloidal science

Background:

• Understanding crystal defects is crucial for material properties.
• Hard-sphere crystals are model systems for studying defects.
• Polydispersity (variation in particle size) can significantly alter crystal behavior.

Purpose of the Study:

• To compute equilibrium defect concentrations in polydisperse hard-sphere crystals.
• To compare defect concentrations in polydisperse versus monodisperse systems.
• To identify the impact of particle size distribution on defect formation.

Main Methods:

• Thermodynamic calculations of equilibrium defect concentrations.
• Analysis of stacking faults, vacancies, and interstitials.
• Modeling of hard-sphere interactions with varying size distributions.

Main Results:

• Stacking fault concentrations are comparable between polydisperse and monodisperse crystals.
• Vacancy concentrations are reduced by approximately 50% in polydisperse crystals.
• Interstitial concentrations in maximally polydisperse crystals are up to 10^6 times higher than in monodisperse crystals.

Conclusions:

• The increased probability of finding small particles drives the high interstitial concentration in polydisperse systems.
• The tail of the small-particle size distribution is a critical factor for interstitial concentration.
• Findings highlight the importance of polydispersity in colloidal crystal defect physics.