Abstract
Although layered cobaltites exhibit ′good′ thermoelectric properties, we need aligned polycrystals (or single crystals) to fabricate thermoelectric devices, because of large anisotropy of the cobaltites. Here, we report the preparation and characterization of the aligned Ca3Co4O9 polycrystals. At first, we synthesized Co(OH)2 platelets by a precipitation technique, then they were used as reactive templates for Ca3Co4O9. That is, the aligned Co(OH)2 platelets were reacted with CaCO3 at 920 °C to form Ca3Co4O9 polycrystals. The obtained polycrystals were almost perfectly aligned along the c axis and showed clear anisotropic properties; i.e., the thermoelectric power factor in the a-b plane was found to be one order higher than that along the c-axis. Therefore, the reactive templated grain growth (RTGG) technique employed here was confirmed to be a key technology for the preparation of large-sized thermoelectric materials with high thermoelectric performance.
