Effects of doping on electronic structure and thermoelectric properties of CoSb3

CoSb3 has been doped with Ni, Pd, and Pt as donor impurities, and the effects on the electronic structure and the electrical and thermoelectrical properties have been investigated so as to improve the thermoelectric figure of merit. It was found that the Hall mobility, the Seebeck coefficient, and the electrical conductivity depend strongly not only on the carrier concentration but also on the impurities. Our theoretical analysis of these results suggests that the electron effective mass and the conduction band deformation potential are significantly affected by doping. These doping effects in CoSb3 can be attributed to (1) the influence of doping on the electronic structure and (2) the specific nature of the conduction band structure, in particular, the nonparabolicity of the band, which can be explained in terms of a Kane model. On the other hand, the lattice thermal conductivity decreased to about 4 Wm(-1)K(-1) with increasing carrier concentration, almost independently of the impurities. Our analysis based on the Debye model indicates that the coupling of the point-defect (alloy) scattering with the electron-phonon scattering plays an important role in reducing the lattice thermal conductivity of heavily doped n-type CoSb3. A large value of the dimensionless thermoelectric figure of merit ZT= about 0.85 (at 800 K) could be obtained for Pd and Pt double doping. Therefore, the double doping with Pd and Pt is considered to be effective in optimizing the electronic properties and the carrier concentration of CoSb3.