We report on the effects of partial substitution of nickel by palladium on the thermoelectric properties of ZrNiSn-based half-Heusler compounds. It is shown that the substitution of palladium for nickel results in a significant, beneficial reduction of the thermal conductivity. The Seebeck coefficient also decreases, but only by a small amount. In the Hf 0.5 Zr 0.5 Ni 0.8 Pd 0.2 Sn 0.99 Sb 0.01 compound, a power factor of 22.1 W K Ϫ2 cm Ϫ1 and a thermal conductivity as low as 4.5 W/m K are measured at room temperature. The dimensionless figure of merit ZT increases with increasing temperature and reaches a maximum value of 0.7 at about 800 K.

Barium-filled skutterudites BayCo4Sb12 with an anomalously large filling fraction of up to y=0.44 have been synthesized. The lattice parameters increase linearly with Ba content. Magnetic susceptibility data show that Ba0.44Co4Sb12 is paramagnetic, which implies that some of the Co atoms in BayCo4Sb12 have acquired a magnetic moment. The presence of the two different valence states of Co (Co3+ and Co2+) leads to the anomalously large barium filling fraction even without extra charge compensation. All samples show n-type conduction. The electrical conductivity increases with increasing the Ba filling fraction. The lattice thermal conductivity of BayCo4Sb12 is significantly depressed as compared to unfilled Co4Sb12. The dimensionless thermoelectric figure of merit, ZT, increases with increasing temperature reaching a maximum value of 1.1 for Ba0.24Co4Sb12 at 850 K.

No abstract

Synthesis and electrical and thermal transport properties are reported for several filled skutterudite compounds doped with Ni: Ba 0.3 Ni x Co 4Ϫx Sb 12 with 0ϽxϽ0.2. Divalent Ba readily fills the cages of the skutterudite structure and is effective in reducing the thermal conductivity of the structure. The presence of a small amount of Ni increases the electron concentration, further reduces the thermal conductivity, and enhances the thermoelectric power factor. Hall mobility studies indicate that the addition of Ni to the system has the effect of increasing the relative strength of ionized impurity scattering as compared to acoustic phonon scattering. These results suggest that doping with Ni is an attractive avenue to optimization of filled skutterudites. The dimensionless thermoelectric figure of merit ZT was observed to increase from a value of 0.8 at 800 K for Ba 0.3 Co 4 Sb 12 to a value of 1.2 for the sample with xϭ0.05. These materials show considerable potential as n-type legs in thermoelectric power generation at elevated temperatures.

No abstract