3d transition metal intercalates of the niobium and trantalum dichalcogenides

Abstract Optical reflectivity spectra of the first-row transition metal intercalation complexes, M1/3NbS2 and M1/3TaS2 (M = V, Cr, Mn, Fe, Co, Ni), Mn1/4 TaS2 and Fe1/4 NbSe2 have been measured at room temperature and compared with those for the host compounds, 2H NbS2, 2H TaS2 and 2H NbSe2. It is found that a simple rigid-band model is inconsistent with the data and that it is necessary to include both broadening of the valence and the lowest conduction band through increased interlayer interactions and broadening of the 3d energy levels on the intercalate ions through interaction with the Nb or Ta d-band conduction electrons. Quantitative analysis of the free-carrier reflectivity edge is performed by fitting to a simple Drude model from which the free-carrier effective mass and scattering time can be deduced.