Microstructure and thermoelectric properties of doped p-type CoSb₃ under TGZM effect

The Co-96.9 wt% Sb hypoeutectic alloy doped by 0.12 wt% YbFe was solidified in a Bridgman-type furnace based on temperature gradient zone melting (TGZM) effect. A mushy zone was observed between the complete liquid zone and the solid zone at different thermal stabilization time ranging from 15 min to 40 h. The mushy-zone solidified microstructures of the alloy only consist of CoSb₃ and Sb phase. After 40 h thermal stabilization time, the volume fraction of CoSb₃ in the mushy zone increases significantly up to 99.6% close to the solid-liquid interface. The hardness and fracture toughness of doped CoSb₃ can reach 7.01 ± 0.69 GPa and 0.78 ± 0.08 MPa·m^1/2, respectively. Meanwhile, the thermoelectric properties of the alloy were measured ranging from room temperature (RT) to 850 K. The Seebeck coefficient of the specimen prepared by TGZM effect after 40 h could reach 155 μV/K and the ZT value is 0.47 at 660 K, showing that it is feasible to prepare CoSb₃ bulk material via TGZM effect. As a simple and one-step solidification method, the TGZM technique could be applied in the preparation of skutterudite compounds.