Thermoelectric properties of semimetallic (Zr, Hf)CoSb half-Heusler phases

Unlike semiconducting TiCoSb, ZrCoSb and HfCoSb half-Heusler phases are sem imetallic below room temperature and exhibit small Seebeck coefficients of similar to-10 mu V/K at 300 K. However, upon substituting (doping) the Co a nd Sb sites with Pt and Sn, respectively, much larger thermopowers (S) are obtained. For ZrCoSb, S reaches -110 and +130 mu V/K while resistivity rho decreases from similar to 5x10(4) mu Omega cm in the undoped phase to 1-2x1 0(3) mu Omega cm in the substituted phases at 300 K. The lowest thermal con ductivity obtained in the substituted alloys is similar to 3.0 W/m K at 300 K, which is among the lowest reported for this class of structural phases. There are indications that the thermoelectric properties have not been opt imized in these multinary alloys. (C) 2000 American Institute of Physics. [ S0021-8979(00)02316-1].