Effect of Mn doping on the physical properties of misfit-layered Ca3Co4O9+δ

We have carried out an x-ray absorption near-edge structure (XANES) study on a series of misfit-layered cobaltites Ca3Co4-xMnxO9+delta (x = 0, 0.05, 0.1, 0.15). In this system, the average valences of Co and Mn, according to Co and Mn K-edge measurements are about 3.50+ and 3+, respectively. Both the trivalent and tetravalent Co are of low-spin configurations as confirmed by our magnetization measurements. The variations of absorption intensities of Co L-2,L-3-edge and O K-edge XANES with respect to the Mn doping concentration (x) are analysed. Co L-2,L-3-edge results show that the Co 3d unoccupied states decrease with x, which correlate well with the trend of variation of thermoelectric power. O K-edge results indicate that the number of O 2p unoccupied states decreases with x, which implies a decrease in the majority charge carriers (hole) concentration upon partial substitution of Mn for Co.