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

Abstract

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 ρ 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 (=S2∕ρ)>10μW∕K2cm above room temperature. From the lnρ-1∕T plot, the band gap energies Eg were estimated to be 0.28 and 0.05eV for ErPdSb and ErPdBi, respectively. The S-T and S-lnρ plots indicate that the conduction mechanism of the carriers is an intrinsic conduction at high temperature. The differences of ρ and S between both compounds are caused by the difference of the carrier concentration, whose magnitude originated in the difference of Eg and the deviation from the stoichiometric composition. The total thermal conductivity κ of ErPdBi exceeds that of ErPdSb because of the large carrier thermal conductivity κC. The maximum values of the dimensionless figure of merit ZT (=S2T∕ρκ) of ErPdSb and ErPdBi are 0.16 around 699K and 0.075 at 495K, respectively.