On the stability of metadislocations with 16 associated phason planes

High-resolution scanning transmission electron microscopy was used to investigate the core structure of a metadislocation in a plastically deformed sample of the complex metallic alloy ε6-Al-Pd-Mn. The atomic-level characterization of a metadislocation with 16 associated phason planes showed dissociation into metadislocations with 6 and 10 phason planes. A structural model of the dissociated core region was developed. The Burgers vector of the dislocation b→16 = −0.07 nm [001] splits up into b→6 = −0.183 nm [001] and b→10 = 0.113 nm [001] increasing the strain at the metadislocation cores. Although unfavourable with respect to an increasing elastic strain energy the dissociation is realized due to a decrease in fault-plane energy. The latter arises from a size reduction of the ξ-phase area that is required to accommodate the metadislocation in the structure. A careful inspection of several exemplary metadislocations with 16 phason planes using electron microscopy indicates their dissociated structure which casts doubt on the stability of elementary metadislocations with 16 phason planes. The study includes a detailed analysis of the structure of a metadislocation core with 6 associated phason planes.