Kinetics and Evolution of Magnetism in Soft-Chemical Synthesis of CrSe₂from KCrSe₂

Cation deintercalation with soft-chemical methods provides a route to synthesize new layered compounds with emergent physical and chemical properties that are inaccessible by conventional high-temperature solid-state synthesis methods. One example is CrSe2, a van der Waals (vdW) material that is promising as an air-stable two-dimensional (2D) magnet. Cation deintercalation has rarely been studied mechanistically, and optimized reaction pathways to yield high-quality materials are often poorly understood. In this work, we perform a detailed study of the oxidative deintercalation process of KCrSe2. We prove for the first time using high-resolution scanning transmission electron microscopy (STEM) that even though CrSe2 indeed exists in a true vdW-layered structure, K-intercalated crystalline defects exist in the final product, even when an excess of oxidizing agent was used. We then study the kinetics of the oxidative deintercalation process, showing that it is a zeroth-order reaction with an activation energy of 0.27(6) eV, where the solid-state diffusion of K+ cations in the potassium deintercalation process is the rate-limiting step. Finally, we study the relationship between Cr-Cr distances and the change in magnetic order by tracking how the properties change as a function of varying potassium content due to deintercalation. These data suggest that it might be possible to switch between magnetic states in CrSe2 monolayers by varying its lattice parameters with methods, such as applying strain. Our study also provides a deeper understanding of the cation deintercalation process from a mechanistic perspective that will be helpful for the future development of synthetic methodology that can lead to other new layered materials.