Aging effects of large-size n-type CoSb3 prepared by spark plasma sintering

We prepared large-size CoSb3 specimens using spark plasma sintering (SPS) in order to assemble practical thermoelectric modules. The effects of aging on the thermoelectric properties were also investigated. The density of the obtained disc-shaped compacts of size phi50 X 10 mm(3) was up to 98% larger than the theoretical density. The electrical resistivity p and Seebeck coefficient a were measured as a function of temperature over the range from room temperature to 800 K, and the thermal conductivity K was also estimated. The figure of merit Z defined as alpha(2)/rhokappa reached 90% for the smaller specimen with size phi20 X 5 mm(3) at 800 K. It was found that the large-size specimen obtained had sufficiently good performance for thermoelectric application. After heating at 873 K in ambient air, the surface of the specimen was found to be covered with a thin film with a double layered structure. The first layer consisted of beta-Sb2O4, Sb2O4 and Sb2O3, and the second of CoSb2O6, CoSb2O4, Sb2O3 and beta-Sb2O4. The thickness of the film was estimated to be approximately 370 mum after aging at 873 K for 10 years in atmospheric air. (C) 2002 Elsevier Science B.V. All rights reserved.