X-ray absorption spectroscopy studies of Fe-doped misfit-layered Ca3Co4-xFexO9+δ (x=0, 0.05, 0.1, and 0.15)

We have carried out O K- and Co L-2,L-3-edge x-ray absorption studies on misfit-layered oxides of polycrystalline Ca3Co4-xFexO9+delta (x=0,0.05,0.1,0.15). The analyses of integrated absorption intensity show that the number of Co 3d unoccupied states decreases upon partial substitution of Fe for Co, which correlates well the variation trend of the room-temperature resistivity with x. Nevertheless, the number of O 2p unoccupied states increases with x. Both Hall and thermopower measurements indicate that the majority carrier is of hole type for Ca3Co4-xFexO9+delta. Therefore, the decrease of O 2p occupancy should be responsible for the increase of the hole carrier concentration upon partial substitution of Fe for Co.