Tunning of microstructure and thermoelectric properties of Ca3Co4O9 ceramics by high-magnetic-field sintering

The structural, magnetic, electrical, and thermal transport properties of Ca3Co4O9 ceramics sintered under high magnetic field were investigated. Crystal grain texturing and densification were achieved through cold-pressing and high-magnetic-field sintering techniques. The c-axis of the layered crystal grain was partly oriented along the c-axis of the pressed samples via a cold-pressing technique, and the degree of orientation was further increased while applying the magnetic field in the sample sintering progress. The easy magnetization axis of Ca3Co4O9 polycrystalline ceramics was found to be the c-axis. The room-temperature resistivity along the ab-plane of the sample sintered under 8 T magnetic field was about 30% smaller than that of the sample sintered without magnetic field, and the Seebeck coefficient of the former reached 177.7 μV/K at the room temperature, which is about 50% larger than that of the latter. Consequently, for the sample sintered at 8 T magnetic field, the power factor along the ab-plane was enhanced by about 1.8 times compared to the sample without magnetic field sintering. The obtained result is suggested to originate from the variations of the carrier mobility and spin-orbital degeneracy due to high-magnetic-field sintering in the progress of the sample preparation.