Thermoelectric power and transport properties of pure and Al-doped MgB2

We have measured the thermoelectric power, S, and resistivity, rho, of pure and Al-doped MgB2. S is positive and increases linearly with temperature above the superconducting transition temperature, Tc. Deviations from the linear dependence appear at higher temperature, T>T0 approx 160 K. Tc and T0 both decrease with Al doping whereas the slope of S(T) in the linear range increases with the Al content. The data are discussed in terms of doping induced changes of the Fermi surface and the density of states at the Fermi level.