Selective oxidation of thermoelectric TiNiSn

Multiscale modelling, involving thermodynamic assessment and molecular dynamics based on density functionaltheory, was employed to unravel oxidation mechanisms pertinent to half-Heusler TiNiSn (space group F-43m), inparticular counterintuitive Ni inertness. O2 molecules dissociate and chemisorb onto TiNiSn(001) and TiNiSn(110), which is followed by ingress of O. Both Ti and Sn egress, while Ni is less mobile. Such diffusion processesyield point defects (vacancies and interstitials) and give rise to Ti and Sn binary oxide formation, while Ni isinert, which may be corelated to its relatively low mobility. Based on the Mulliken analysis and thermodynamicsat 900 K, the Ti oxide formation sequence is suggested to be Ti2O3 → Ti3O5 → TiO2 → TiO. These data explain theexperimental observations on the Ni inertness during oxidation of TiNiSn