Alkali Metal Intercalation and Reduction of Layered WO2Cl2

Li, Na, K, Rb, and Cs have been intercalated into the two-dimensional (2D) van der Waals material WO 2 Cl 2, with K, Rb, and Cs intercalation being reported for the first time. The topochemical reaction of these alkali metals causes dramatic crystallographic, optical, and electronic changes to WO 2 Cl 2 . During the reaction with each of the alkali metals, WO 2 Cl 2 changes from a clear and transparent insulating phase to a blue partially intercalated species and finally to a lustrous bronze material. Upon intercalation, the host undergoes significant and systematic changes in interlayer spacing, as well as a 10 orders-of-magnitude change in resistivity from the base material to the intercalated bronze phase. Each of the alkali metals intercalates at a different rate and leads to specific changes in interlayer spacing and color of the bronze phase. This study provides a platform to study the electronic and optical properties of each of these new tungsten bronzes with a particular focus on lithium intercalation.