The A-Ni chemical bond in AIIINiSb (AIII=Sc, Y, Er) half-Heusler materials triggers the formation of anomalous vacancy defects

Defects exert a profound influence on thermoelectric materials by altering electronic band structures and significantly impacting their performance. Despite being a potentially promising thermoelectric material, the mechanism behind defect formation in half-Heusler (HH) compounds ABX remains unclear, impeding the enhancement of their thermoelectric properties. In this study, we investigated the intrinsic defect formation energies for A^ⅢNiSb (A^Ⅲ = Sc, Y, Er) and other 9 HH compounds, namely A^ⅣNiSn (A^Ⅳ = Ti, Zr, Hf), A^ⅤFeSb (A^Ⅴ = V, Nb, Ta), and A^ⅣCoSb (A^Ⅳ = Ti, Zr, Hf), using first-principles calculations and thermodynamics. The results reveal that A^ⅢNiSb (A^Ⅲ = Sc, Y, Er) exhibits anomalous B (Ni) vacancy defects, with their formation energies being significantly lower than those of the corresponding B vacancy defects in the other 9 HH compounds. This anomaly can be attributed to the strength of the A-B bonds, where a decrease in bond strength leads to a decrease in the formation energy of B vacancies. This approach of exploring the influence of interatomic bond strength on defect formation is not only insightful for HH compounds but also holds potential applications in defect studies across various materials, offering a broader perspective on the fundamental mechanisms governing defect formation and stability.