MICROSTRUCTURE AND THERMOELECTRIC PROPERTIES OF (Zr,Hf)NiSn-BASED HALF-HEUSLER ALLOYS BY MELT SPINNING AND SPARK PLASMA SINTERING

(Zr,Hf)NiSn-based half-Heusler thermoelectric materials have been prepared by melt spinning and spark plasma sintering to refine the grain size. The grain sizes of the melt-spun thin ribbons varied from ~500 nm to ~3 μm and no significant grain growth were found for the bulk samples compacted by spark plasma sintering. Nanoscale precipitates dispersed in the matrix were observed, which should be more metallic due to the increase of the electrical conductivity. The reduction of lattice thermal conductivity was observed due to the refined grain sizes.