Enhanced Thermoelectric Performance of Bi-Based Half-Heusler Compounds <i>XY</i>Bi (<i>X</i>: Ti, Zr, Hf; <i>Y</i>: Co, Rh, Ir)

Over the past few decades, Half-Heusler materials have garnered significant research attention for thermoelectric applications due to their cost-effectiveness, high thermal stability, mechanical strength, high power factor (PF), nontoxicity and moderate efficiency. Here, using first-principles density functional theory combined with the semiclassical Boltzmann transport equations, we systematically studied the thermoelectric properties of nine Bi-based Half-Heusler compounds, XYBi (where, X=Ti, Zr, Hf; Y=Co, Rh, Ir). We demonstrate that these compounds exhibit a moderate band gap (Eg) and an exceptionally high power factor (PF), outperforming many conventional thermoelectric materials. The high power factor primarily stems from the very high charge carrier concentration and high electrical conductivity. However, these Half-Heusler compounds show moderate thermal conductivity (κ). Based on our calculations, these Bi-based Half-Heusler compounds exhibit sufficiently high ZT values ranging from 0.56 to 1.98, with the highest values being 1.98 and 1.93 for n-type ZrRhBi and p-type HfRhBi, respectively. Our work reveals the inherent high ZT values in these previously less-explored Bi-based Half-Heusler compounds, indicating their strong potential for high-performance thermoelectric device applications.