Photoelectron spectra and transport properties of intercalates of Nb and Ta dichalcogenides with Sn and Pb

The electrical resistivity, Hall effect and Seebeck effect of the intercalation compounds MxTX2 (M = Sn, Pb; T = Nb, Ta; X = S, Se; x= 13, 1 are reported. The number of charge carriers for the x=13 compounds, deduced from the Hall effect, agree quite well with a model in which each Pb or Sn atom donates two electrons to the narrow Nb or Ta d-band. The electrical conductivity in the x = 1 compounds is attributed to electrons in overlapping px,ySn(Pb) orbitals. Photoelectron spectra of core electrons and of the valence band are presented. The valence band region shows a narrow d-band slightly above a broad band corresponding to S(3p) or Se(4p) orbitals. The data clearly show the increased filling of the d-band with increasing intercalation. The Sn and Pb core lines in the x = 1 compounds show a splitting into two components, which is attributed to a rapid valence fluctuation Sn0=Sn2+.