Interplay between elastic fields due to gravity and a partial dislocation for a hard-sphere crystal coherently grown under gravity: driving force for defect disappearance

TL;DR

This study combines Monte Carlo simulations and elastic energy calculations to show how gravity influences defect reduction in colloidal crystals by driving partial dislocations toward the upper boundary, promoting defect disappearance.

Contribution

It introduces a calculation of the elastic energy cross-coupling term between gravity and dislocation fields, explaining defect reduction mechanisms in colloidal crystals under gravity.

Findings

Gravity induces a driving force for partial dislocation movement.

Elastic energy cross term increases with system size.

Dislocation glide leads to stacking fault shrinkage.

Abstract

We previously observed that an intrinsic staking fault shrunk through a glide of a Shockley partial dislocation terminating its lower end in a hard-sphere crystal under gravity coherently grown in <001> by Monte Carlo simulations [Mori et al., Molec. Phys. 105, 1377 (2007)]; it was an answer to a one-decade long standing question why the stacking disorder in colloidal crystals reduced under gravity [Zhu et al., Nature 387, 883 (1997)]. Here, we present an elastic energy calculation; in addition to the self-energy of the partial dislocation [Mori et al., Prog. Theor. Phys. Suppl. 178, 33 (2009)] we calculate the cross-coupling term between elastic field due to gravity and that due to a Shockley partial dislocation. The cross term is a increasing function of the linear dimension R over which the elastic field expands, showing that a driving force arises for the partial dislocation moving toward the upper boundary of a grain.