Low-temperature thermoelectric power of CaB₆

We report the results of measurements of the thermoelectric power S of stoichiometric CaB 6 and vacancy-doped Ca 1-δ B 6 between 5 and 300 K. The thermopower for both materials is surprisingly large at room temperature. Across the whole temperature range covered, S is negative and the temperature dependence is most probably dictated by band-structure effects. The phenomenological interpretation of our data involves a calculation of S ( T ), using the Boltzmann equation in the relaxation time approximation and assuming a band of defect states in proximity to the lower edge of the conduction band. Good agreement with our data is found by considering acoustic phonon and ionized impurity scattering for the electrons in the conduction band, which is well separated from the valence band.