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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]

Ta-doped Ti1-xTaxCoSb (0≤x≤0.08) half-Heusler compounds were synthesized by melting and annealing process. Their thermoelectric properties were studied in the temperature range of 300–900 K. The Ti1-xTaxCoSb compounds exhibit negative Seebeck coefficients with considerably large absolute values. With increasing Ta substitution, the electrical conductivity was greatly increased, but the thermal conductivity was reduced. Because of the combined effects of increased electrical conductivity and reduced thermal conductivity, the thermoelectric performance of Ti1-xTaxCoSb alloys was apparently improved by doping Ta. The dimensionless figure of merit of 0.3 was obtained for Ti0.92Ta0.08CoSb compound at 900 K. This value is about ten times larger than that of the undoped TiCoSb compound. [ABSTRACT FROM AUTHOR]