Impact of Bonding on the Stacking Defects in Layered Chalcogenides

Phase-change materials for high-density data storage traditionally exploit the amorphous-to-crystalline phase transition. A number of these compounds are organized in blocks, separated by van der Waals-like gaps. Such layered chalcogenides are attracting interest due to their unique material properties and the possibility to change their properties upon local rearrangements at the gap, giving rise to novel applications. To better understand the behavior of layered chalcogenides, the connection between structural defects, physical properties, and the bonding situation is highlighted here using electron microscopy, X-ray diffraction, and density functional theory. In particular, stacking defects in hexagonal Ge4Se3Te, GaSe, and Sb2Te3 are characterized experimentally, followed by an investigation of the influence of observed and hypothetical stacking defects on optical and electronic properties by theoretical means. Then, a connection between observed defects and the bonding situation in these materials is drawn and related to the presence of van der Waals and metavalent bonding in chalcogenides. Finally, additional experiments are performed to validate the conclusions for other metavalently bonded layered chalcogenides. Transmission electron microscopy provides a powerful tool for direct detection of defects and, when combined with diffraction experiments and ab initio theory, it facilitates the precise investigation of the bonding mechanisms in layered chalcogenides.