Effects of Ge doping on the thermoelectric properties of TiCoSb-based p-type half-Heusler compounds

Abstract

Ge-doped TiCoSb-based half-Heusler compounds, TiCoGexSb1−x (x = 0–0.2), were prepared by arc melting and spark plasma sintering (SPS). The electrical conductivity, Seebeck coefficient and thermal conductivity were measured from room temperature to 850 K. The Seebeck coefficient changed from negative to positive by Ge doping, and the electrical conductivity increased with increasing Ge content. The lattice thermal conductivity for TiCoGexSb1−x is considerably reduced, because the point defects induced by Ge substitution for Sb intensively scatter the thermal phonons. The mass fluctuation part Γmass and strain field fluctuation part Γstra were estimated, and it was found that the reduction of lattice thermal conductivity is mainly attributed to the strain field fluctuation. Ge doping improved the thermoelectric figure of merit ZT of TiCoSb and the maximum ZT value of 0.16 was obtained for TiCoGe0.15Sb0.85 sample at 850 K.