Grain Boundary Pinning in Doped Hard-Sphere Crystals (AGGREGATION CH 6)

Abstract

We report on how grain boundaries are pinned in between large spherical impurities in hard sphere colloidal crystals, studied by confocal microscopy. We introduce a frustration length ξ, connected to the extent to which the orientational order of a crystal is reduced in the vicinity of impurities. Initially, ξ increases with the impurity size ratio due to fluid particles near the impurity, but it reduces again later when particles form layers on the impurity surface. If two impurities are separated by a distance smaller than their combined frustration lengths, straight, strongly pinned grain boundaries directly form in between the impurities. At larger separations the grain boundaries can still form in between the impurities due to the enhanced stability of the fluid phase in between the impurities during crystallization, but the pinning is much weaker. Our results indicate that in between impurities, strongly pinned grain boundaries form in a well defined region in the parameter space of impurity volume fractions and impurity-to-particle size ratio.