Ru-doping effect on the thermopower and electrical transport properties of misfit-layered Ca3Co4O9+δ

We have studied Ru-doping effect on the thermopower and electrical transport properties of Ca3Co4O9+δ samples. A thermopower in Ca3Co4−xRuxO9+δ was enhanced by Ru doping. A clear field-induced suppression of thermopower implies a large spin entropy contribution. Magnetic results indicate that the spin entropy enhancement originates from the decrease of Co4+ concentration induced by Ru-doping. The increase of resistivity results from the decreases of carrier concentration and mobility. The electrical transport properties reveal that Ru-doping induces a metal-insulator transition at x≈0.2 and the thermally activated mechanism dominates the transport behavior at low temperature.