Chemical Intercalations in Layered Transition Metal Chalcogenides: Syntheses, Structures, and Related Properties

Transition metal chalcogenides (TMChs) have recently attracted a great deal of interest in the chemical and physical research fields. These compounds have a common crystal structure: they usually consist of two-dimensional or quasi two-dimensional layers stacked along the direction perpendicular to the layers. The combination between layers is generally by van der Waals interaction or weak chemical bonding, making the layered chalcogenides potential hosts for intercalation. Alkali metals, alkaline earths, rare earths, and organic groups or compounds can be intercalated into the structure as spacing layers, resulting in a variety of new compounds and exhibiting interesting physical and chemical properties. In this review, we introduce and summarize the latest advances in chemical intercalation and the role of these spacing layers in TMChs, and their relation to relevant properties. Especially, we focus on the developments of chemical intercalation in Fe chalcogenide superconductors to understand the effect from intercalation on formation, structure, and property, in the hope to provide some new insights for novel material design. Finally, perspectives on the challenge and opportunity for future exploration on this topic are also discussed.