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The presence of a van der Waals gap within layered materials enables the intercalation of guest species, which can be used for tuning properties. The introduction of intercalant species may also lead to structural transformations across a range of temperatures and use conditions, but we have a limited understanding of the high-temperature evolution of intercalated layered materials. Here, we use in situtransmission electron microscopy to investigate temperature-dependent structural evolution of Bi2Te3, a layered material with well-known application as a thermoelectric, which contains intercalated Cu. As temperature is increased, the initially disordered Cu undergoes local ordering within the van der Waals gap, along with anisotropic sublimation behavior of the crystals. As the temperature is raised further, layered Cu2Te crystals nucleate and grow with a crystallographic relationship to the Bi2Te3lattice. Notably, the presence of Cu decreases the thermal stability of the Bi2Te3and substantially alters the transformation pathways during heating.

MoS2has important applications in (electro)catalysis and as a semiconductor for electronic devices. Other chemical species are commonly added to MoS2to increase catalytic activity or to alter electronic properties through substitutional or adsorption-based doping. While groundbreaking work has been devoted to determining the atomic-scale structure of MoS2and other layered transition-metal dichalcogenides (TMDCs), there is a lack of understanding of the dynamic processes that govern the evolution of these materials during synthesis. Here, in situtransmission electron microscopy (TEM) heating, in combination with larger length scale ex situexperiments, is used to investigate the effects of added Ni on the growth of MoS2during the thermolysis of the solid-state (NH4)2MoS4precursor. Low concentrations of Ni are observed to cause significant differences in the MoS2crystallization and growth process, leading to an increase in MoS2crystal size. This is likely a result of the altered mobility of interfaces between crystals during growth. These findings demonstrate the important role of additional elements in controlling the evolution of TMDCs during synthesis, which should be considered when designing these materials for a variety of applications.