Application of molten flux sintering for half-heusler thermoelectric materials Jan-Willem Bos and Blair Kennedy Heriot-Watt University, UK Half Heusler alloys are a key family of compounds for thermoelectric waste heat recovery. The alloys possess good electrical properties, wide operating temperature ranges and abundant, low toxicity precursors. The significant issue facing these alloys is the inherently high thermal conductivity that lowers the thermoelectric performance (zT = (S 2 σ/κ)T). The reduction of κ has been the focus of the last two decades of Half-Heusler alloy research. 1 Isovalent alloying of these compounds, resulting in mass and bond disorder, is the primary strategy for reducing κ. Atomic size mismatch and high enthalpy of mixing, however, result in a non-ideal solid solution, with phase segregation reducing point defect disorder. In previous work, we have observed the effect of a Cu based mineralizer reducing this effect, with the best performance occurring with a Cu-Sn based phase present. 2 Here we present our findings from investigating this mineralizing flux in a prominent n-type Half-Heusler alloy composition Ti 0.5 Zr 0.5 NiCu y Sn (y = 0.025, 0.1). In a variable temperature study, the phase behaviour of these compositions are examined through a combination of X-ray powder diffraction and scanning electron microscopy, with complementary energy dispersive X-ray spectroscopy. This poster will discuss the observed phase behaviour of these Half-Heusler alloys in the presence of the Cu mineralizer, in comparison to models based on lattice solubility. Thermoelectric analysis shows a direct correlation between the phase behaviour and thermal
conductivity. References
1. R. J. Quinn and J. W. G. Bos, Mater. Adv. , 2021, 2 , 6246-6266 2. S. A. Barczak et al , J. Mater. Chem. A , 2019, 7 , 27124-27134
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© The Author(s), 2022
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