Reversible Iodine Intercalation into Tungsten Ditelluride.

The new compound WTeI was prepared by a reaction of WTe with iodine in a fused silica ampule at temperatures between 40 and 200 °C. Iodine atoms are intercalated into the van der Waals gap between tungsten ditelluride layers. As a result, the WTe layer separation is significantly increased. Iodine atoms form planar layers between each tungsten ditelluride layer. Due to oxidation by iodine the semimetallic nature of WTe is changed, as shown by comparative band structure calculations for WTe and WTeI based on density functional theory. The calculated phonon band structure of WTeI indicates the presence of phonon instabilities related to charge density waves, leading to an observed incommensurate modulation of the iodine position within the layers.