Cation deintercalation with soft-chemical methods is an elegant way to synthesize new layered compounds with exotic physical and chemical properties that are inaccessible by conventional high-temperature solid-state synthesis methods. One example is CrSe2, a van der Waals material that is promising as an air stable two-dimensional magnet. Cation deintercalation has however rarely been studied mechanistically, and often it is poorly understood how to best carry out these reactions to obtain high quality materials. In this work, we perform a detailed study of KCrSe2's oxidative deintercalation process. First, we proof for the first time using high-resolution scanning transmission electron microscopy, that even though CrSe2 indeed exits in a true vdW layered structure, K-intercalated crystalline defects exist in the final product, even an excess of oxidizing agent was used. We then study the kinetics of the oxidative deintercalation process, revealing it to be a zeroth-order reaction with an activation energy of 0.27(6) eV, where potassium deintercalation is the rate-limiting step. Finally, we track the magnetic properties during the deintercalation process by studying samples with varying potassium content. We use this data to construct a phase diagram that links the type of magnetic order to the Cr-Cr distance in the materials. While in KCrSe2 and the products of early stage oxidation, a relatively large nearest intralayer Cr-Cr distance leads to dominant ferromagnetic super exchange within the plane, further oxidation results in reduced in-plane lattices parameters and antiferromagnetic coupling within the plane. These results suggest that it might be possible to switch between magnetic states in CrSe2 monolayers by applying strain. Our study also provides a deeper understanding of the cation deintercalation process from a chemical prospective that will be helpful for the future development of synthesis methods that can lead to further new layered compounds.

Deintercalation reaction to synthesize van der Waals materials: Detailed study on the reaction, as well as property change upon deintercalating KCrSe2 to CrSe2

ACS Fall 2021

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