On the origin of enhanced thermoelectricity in Fe doped Ca3Co4O9

摘要

Resistivity and Seebeck coefficient measurements on Ca3Co_(4-x)Fe_xO9 (x = 0, 0.05, 0.1, 0.2 and 0.25) reveal enhanced thermoelectric performance with an optimalx value of 0.2. X-ray diffraction measurements show continuous Fe doping into the host lattice, while X-ray absorption experiments reveal that Fe substitutes for Co in the Ca2CoO3 (rock salt) block. The Fe substitution for Co produces electron doping. The local structure around Fe in the Ca2CoO3 block becomes disordered, while the structure in the conducting CoO2 layer becomes more ordered. The structural change in the CoO2 layer plays the key role to enhance the electron transport. The highest ordered structure is achieved at x = 0.2 with the lowest resistivity. Soft X-ray absorption measurements find no Co site spin-state change with Fe doping. Thermoelectric property enhancement associated with doping induced structural change points to a new approach for creating materials with improved ZT in complex oxide systems.