In-plane Stacking Disorder in Hard-Sphere Crystals (THESIS VERSION)

Abstract

In-plane stacking disorder is not only characterised by the discontinuous transitions through line-defects presented in the previous chapter, but also by continuous transitions through lattice deformations. We introduce an interplanar bond order criterion to distinguish AB and AC type transitions between two consecutive hexagonal layers. Many of these are found to be Shockley partial screw dislocations, with a characteristic deformation that is spread across two consecutive layers. How the deformation is spread between the layers varies from case to case, which decreases positional order even more strongly than the continuous transitions presented in the previous chapter. These deformations can be traced until far away from the dislocation, both in layers above and below. The relative deformation between two consecutive hexagonal layers does have a well defined width. The deformed layers act as templates for the consecutive layers, which are deformed as well. The transitions between lateral position therefore take place even far away from the dislocation core, but the transition between AB and AC stacking does not. The full island boundary usually consists of a complex combination of both discontinuous and continuous transitions. Furthermore, we show that the regions, in which the stacking changes, contain a much higher concentration of vacancies. These vacancies cause tiny lattice deformations themselves due to the osmotic pressure imbalance caused by the missing particle, pointing towards a mechanism for the stabilisation of lattice deformations through vacancies.