Electrical and Seebeck effect measurements in Nb doped VO2

The resistance of pure and Nb doped VO2 and the Seebeck coefficient of Nb doped VO2 have been measured in the temperature range of 78 to 360 K. A simple analysis of the results shows that above 140 K and below the transition temperature the effective density of states in the conduction band of VO2 is of the order of (but larger than) one state per vanadium atom. This high effective density of states is consistent with the large effective mass (and low mobility) of electrons in this material. It is shown also that in this range, the temperature dependence of the electronic mobility in VO2 is Tsup(-γ) where γ > approximately 2. Additional results are discussed in the text. (author)