Abstract
XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS) on the phase distributions and thermoelectric properties of Ti0.5Zr0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m−1·K−1 at 350 K and 3 W·m−1·K−1 at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti0.5Zr0.5NiSn composition.
Highlights
Half-Heusler alloys are of significant interest in the field of thermoelectrics, where they can be used in the recovery of waste heat [1,2,3]
This is largely due to naturally high Seebeck coefficients (S) and relatively large electrical conductivity values (σ), which are both key components in determining the thermoelectric efficiency (ZT) of a material
A significant amount of research has been directed at improving the thermoelectric efficiencies of half-Heuslers. κlat is often the limiting factor in achieving high ZT values, its minimisation is of key concern
Summary
Half-Heusler alloys are of significant interest in the field of thermoelectrics, where they can be used in the recovery of waste heat [1,2,3]. This is largely due to naturally high Seebeck coefficients (S) and relatively large electrical conductivity values (σ), which are both key components in determining the thermoelectric efficiency (ZT) of a material. The most widely employed strategy to achieving this is isovalent substitution on the X-site in the XNiSn-based compositions In this case, κlat is expected to decrease by introducing mass and size fluctuations leading to a disrupted phonon flow. The best performing samples generally contain either, Zr and Hf on the X site, or a mixture of
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