High performance half-Heusler thermoelectric materials with refined grains and nanoscale precipitates

(Zr, Hf)NiSn-based half-Heusler alloys with refined grains were prepared by melt spinning and spark plasma sintering. The grain size of the melt-spun (MS) thin ribbons varied from similar to 500 nm to similar to 3 mu m. X-ray diffraction analysis showed that single phased alloys were obtained. Nanoscale precipitates dispersed in the matrix could be observed in both the MS ribbons and sintered bulk samples, which increased the carrier concentration and electrical conductivity. The lattice thermal conductivity decreased by more than 20% below 100 K and 5-20% from 200 to 1000 K, compared with the levitation melted counterparts, due to the refined grain sizes. The maximum dimensionless figure of merit ZT value reached similar to 0.9 for the MS Hf0.6Zr0.4NiSn0.98Sb0.02 sample.