Effects of post-annealing on thermoelectric properties of p-type CoSb3 grown by the vertical Bridgman method

Crystals of CoSb3, a peritectic skutterudite compound, were grown by the vertical Bridgman method at various growth speeds ranging from 0.4 to 2.8 mm/h. Changes in the growth parameters resulted in the formation of polycrystalline p-type CoSb3 grains surrounded by Sb metal. To remove the excess Sb in the as-grown crystals, post-annealing was performed. Removing the residual Sb through the post-annealing process caused reconstruction of CoSb3 grain externals and formation of voids in the crystals, resulting in an increase in the Seebeck coefficient from around 40 μV/K (in as-grown samples) to 250-500 μV/K. The increased Seebeck coefficient values of the post-annealed samples are higher than that of single-crystal bulk CoSb3 with the corresponding carrier concentration.