High-performance half-Heusler thermoelectric materials Hf 1−x Zr xNiSn 1−ySb y prepared by levitation melting and spark plasma sintering

Abstract

Half-Heusler thermoelectric materials Hf 1− x Zr x NiSn 1− y Sb y ( x = 0, 0.25, 0.4, 0.5; y = 0.02, 0.04, 0.06) have been prepared by levitation melting followed by spark plasma sintering or hot pressing. X-ray diffraction analysis and scanning electron microscopy observation show that single-phased half-Heusler compounds without compositional segregations have been obtained by levitation melting in a time-efficient manner. A small amount of Sb doping can improve the electrical power factor but undesirably increases the thermal conductivity due to the increased carrier thermal conductivity. The isoelectronic substitution of Zr for Hf substantially decreased the lattice thermal conductivity. A state-of-the-art ZT value of 1.0 has been attained at 1000 K for the levitation-melted and spark-plasma-sintered Hf 0.6Zr 0.4NiSn 0.98Sb 0.02, which is one of the highest achieved ZT values for half-Heusler thermoelectric alloys.