Preparation and annealing effects of large sized ingot of n-type CoSb/sub 3/

We prepared large sized ingot of CoSb/sub 3/ using spark plasma sintering in order to assemble the actual modules. The annealing effects on the thermoelectrical properties were also investigated. The apparent density ratio of obtained ingot with size of /spl phi/50/spl times/10 mm was larger than 98%. The electrical resistivity /spl rho/ and Seebeck coefficient a were measured as functions of temperature over the range from room temperature to 800 K. The values of /spl alpha/ and /spl rho/ were 90% to those of the smaller sized ingot with /spl phi/20/spl times/5 mm. They suggest that the obtained large ingot has enough performance for application. It was found that the surface of the specimen was covered with a thin film with double layered structure after heating above 923 K in ambient air. This was identified as an antimony oxide-based material. It can be estimated that the thickness of the inner layer will be approximately 370 /spl mu/m after annealing at 873 K for ten years in air atmosphere.