3d transition metal intercalates of the niobium and trantalum dichalcogenides

Abstract

Optical reflectivity spectra of the first-row transition metal intercalation complexes, M_1/3NbS₂ and M_1/3TaS₂ (M = V, Cr, Mn, Fe, Co, Ni), Mn_1/4 TaS₂ and Fe_1/4 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.