Thermoelectric and thermophysical properties of ErPdX (X=Sb and Bi) half-Heusler compounds

Half-Heusler compounds ErPdX (X=Sb and Bi) were prepared by a spark plasma sintering technique. Their thermoelectric properties at high temperature and thermophysical properties at room temperature were measured. The electrical resistivity rho and thermoelectric power S of ErPdSb are larger than those of ErPdBi, and both compounds indicate semiconductorlike characteristics at high temperature. ErPdSb has the large power factor (=S-2/rho)> 10 mu W/K-2 cm above room temperature. From the ln rho-1/T plot, the band gap energies E-g were estimated to be 0.28 and 0.05 eV for ErPdSb and ErPdBi, respectively. The S-T and S-ln rho plots indicate that the conduction mechanism of the carriers is an intrinsic conduction at high temperature. The differences of rho and S between both compounds are caused by the difference of the carrier concentration, whose magnitude originated in the difference of E-g and the deviation from the stoichiometric composition. The total thermal conductivity kappa of ErPdBi exceeds that of ErPdSb because of the large carrier thermal conductivity kappa(C). The maximum values of the dimensionless figure of merit ZT (=(ST)-T-2/rho kappa) of ErPdSb and ErPdBi are 0.16 around 699 K and 0.075 at 495 K, respectively. (c) 2006 American Institute of Physics.