Enhanced\nThermoelectric\nPerformance of Bi-Based Half-Heusler\nCompounds <i>XY</i>Bi (<i>X</i>: Ti, Zr, Hf; <i>Y</i>: Co, Rh, Ir)

Over the past few decades, Half-Heusler\nmaterials have\ngarnered\nsignificant research attention for thermoelectric applications due\nto their cost-effectiveness, high thermal stability, mechanical strength,\nhigh power factor (<i>PF</i>), nontoxicity and moderate\nefficiency. Here, using first-principles density functional theory\ncombined with the semiclassical Boltzmann transport equations, we\nsystematically studied the thermoelectric properties of nine Bi-based\nHalf-Heusler compounds, <i>XY</i>Bi (where, <i>X</i>=Ti, Zr, Hf; <i>Y</i>=Co, Rh, Ir). We demonstrate that\nthese compounds exhibit a moderate band gap (<i>E</i><sub><i>g</i></sub>) and an exceptionally high power factor\n(<i>PF</i>), outperforming many conventional thermoelectric\nmaterials. The high power factor primarily stems from the very high\ncharge carrier concentration and high electrical conductivity. However,\nthese Half-Heusler compounds show moderate thermal conductivity (κ).\nBased on our calculations, these Bi-based Half-Heusler compounds exhibit\nsufficiently high <i>ZT</i> values ranging from 0.56 to\n1.98, with the highest values being 1.98 and 1.93 for n-type ZrRhBi\nand p-type HfRhBi, respectively. Our work reveals the inherent high <i>ZT</i> values in these previously less-explored Bi-based Half-Heusler\ncompounds, indicating their strong potential for high-performance\nthermoelectric device applications.