Doug L. Medlin, N Yang, Catalin D. Spataru,
Tetradymite-structured chalcogenides, such as the bismuth telluride Bi2Te3, present signifi cant interest as technological materials for thermoelectric energy conversion, and as examples of topological insulators. Dislocations in such materials play a critical role during synthesis and processing and can strongly affect their functional properties. The dislocations existing between quintuple layers present special interest as their core structure is controlled by the van der Waals interactions between the layers. Although the discovery of such dislocations by electron microscopy in the early 1960s was one of the fi rst direct observations of dislocations in non-metallic materials, their atomic-level core structure has remained elusive for decades. In this work, we have finally resolved the dislocation core structure in Bi2Te3 and quanti fied the disregistry of the atomic planes across the dislocation core by atomic-resolution electron microscopy. We show that, in spite of the existence of a stable stacking fault, the dislocation core spreading is not caused by dissociation in two discrete partials as one would expect. Instead, the wide spreading of the core is mainly due to the weak bonding between the layers, leading to a relatively small energy penalty for layer sliding parallel to the van der Waals gap. The experimental fi ndings are supported by calculations within a semidiscrete variational Peierls-Nabarro model with input from first-principles calculations, showing excellent agreement with experiment. The methodology and conclusions of this work can be extended to other quasi-2D materials with van der Waals bonding between layers.
dislocation, bismuth telluride, HRTEM, DFT