Entropy Stabilized ZrHfCoNiSnSb Half-Heusler Alloy for Thermoelectric Applications: A Theoretical Prediction

Abstract

Half-Heusler (HH) alloys are potential thermoelectric materials for use at elevated temperatures due to their high Seebeck coefficient and superior mechanical and thermal stability. However, their enhanced lattice thermal conductivity is detrimental to thermoelectric applications. One way to circumvent this problem is to introduce mass disorder at lattice sites by mixing the components of two or more alloys. Such systems are typically stabilized by the entropy of mixing. In this work, using computational tools, we propose a mixed HH, namely, ZrHfCoNiSnSb, which can be formed by the elemental compositions of the parent half-Heuslers ZrNiSn/HfNiSn and HfCoSb/ZrCoSb. We propose that this new compound can be synthesized at elevated temperatures, as its Gibbs free energy is reduced due to higher configurational entropy, making it more thermodynamically stable than the parent compounds under such conditions. Our calculations indicate that it is a dynamically stable semiconductor with a band gap of 0.61 eV. Its lattice thermal conductivity at room temperature is $5.39~\text{Wm}^{-1}\text{K}^{-1}$, which is significantly lower than those of the parent compounds. The peak value of this alloy's figure of merit (ZT) is 1.00 for the n-type carriers at 1100 K, which is 27% more than the best figure of merit obtained for the parent compounds.