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TiCoSb-based half-Heusler compounds have been prepared and their thermoelectric properties are studied. By isoelectronic alloying on the Ti site with Zr, although both the thermal conductivity and electrical conductivity are suppressed, the Seebeck coefficient is improved remarkably with a highest value of -420 μV/K for Ti0.5Zr0.5CoSb at 600 K, which provides a larger space to optimize the thermoelectric performance. To further improve the performance of the TiCoSb-based isoelectronic alloy, doping Ni on the Co site was explored. It is found that small amount of Ni doping results in a great increase in the electrical conductivity, still with a relative large Seebeck coefficient. Ti0.6Hf0.4Co0.87Ni0.13Sb sample exhibits a peak power factor of 23.4 μW/cm K2, which is the highest value for n-type TiCoSb-based half-Heusler compounds reported so far. As a result, a maximum dimensionless figure of merit of 0.70 has been achieved at 900 K for Ti0.6Hf0.4Co0.87Ni0.13Sb. [ABSTRACT FROM AUTHOR]

TiFexCo1-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 TiFexCo1-xSb transfers to p-type conduction when x≥0.01. The electrical conductivity of p-type TiFexCo1-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 TiFe0.15Co0.85Sb at 850 K. [ABSTRACT FROM AUTHOR]