Thermoelectric properties of p-type Fe-doped TiCoSb half-Heusler compounds.

TiFe_xCo_1-xSb half-Heusler materials with randomly distributed TiO₂ particles have been synthesized by arc melting and annealing. Thermoelectric properties were measured in the temperature range of ∼300–850 K. TiCoSb shows n-type conduction, while TiFe_xCo_1-xSb transfers to p-type conduction when x≥0.01. The electrical conductivity of p-type TiFe_xCo_1-xSb increased with increasing Fe content. The maximum Seebeck coefficient reached about 300 μV/K at 850 K for x=0.15. Since Fe powder contained a trace of Fe₂O₃, a small amount of TiO₂ particles formed during the synthesis process. The lattice thermal conductivity dramatically decreased with increasing Fe content, which was mostly caused by the introduction of in situ formed TiO₂ particles, as well as the effects of mass fluctuation and strain field fluctuation due to the substitution of Fe to the Co site. The dimensionless figure of merit (ZT=S²σT/κ) was significantly improved over the whole temperature region, and a maximum ZT value of 0.45 has been obtained for the composition of TiFe_0.15Co_0.85Sb at 850 K. [ABSTRACT FROM AUTHOR]