Transmission spectra of lithium intercalation complexes of some layered transition-metal dichalcogenides

Abstract

The room-temperature transmission spectra of the Group-IVA transition-metal dichalcogenides and the intercalation compounds they form with lithium have been measured in the energy range 0·5 to 6·0 eV. The changes in the spectra after intercalation can be interpreted in terms of a rigid-band model, charge transfer from the ionized lithium to the lowest d conduction band of the host resulting in metallic behaviour of all the intercalation complexes. However, the transmission spectra of the lithium complexes in the region of the Drude edge have been fitted by a theoretical model, from which the optical parameters appropiate to this edge have been obtained, and the values of certain of these parameters indicate that, in the Zr and Hf complexes, the rigid-band model should be modified to allow overlap of s-like conduction band states with the lowest d conduction band of the host material; this would give rise to two types of carrier in these metals.