Investigation of the interstitial oxygen behaviors in vanadium alloy: A first-principles study

This study aims at characterizing the interstitial Oxygen (O) behaviors in the Vanadium (V) Alloy by means of the first-principles calculations. For this, the interations between vacancy (Vac) and O interstitil atom are studied in detail to obtain the binding energies and stable structures of the complexes. It can be seen that monovacancy binding with two O atoms occupied the opposing octahedral stie are particularly stable, and is liable to form VacO2 cluster in the V alloys. According to the mass action analysis, the predicted temperature dependence of the concentration for VacOn complexes are presented. Apart from monovacancy, we also consider the trapping behavior of vacancy cluster on the O atoms. The results also prove that one vacancy can trap two O atoms in the V alloys. Based the diffusion theory, we obtain the diffusion coefficients as a function of temperature with or without the vacancy effect in the V alloys. The predicted O diffusion coefficients in defect-free V alloys from our first-principles calculations are in excellent ageement with the experimental data, meanings that the vacancy-limited mechanism does not play the key role for O diffusion in V alloys. Regarding the interactions between vacancy, solutes and O atom, combining with the diffusion barriers of O affected by vacancy and solute, we infer the formation mechanism of the precipitates in the V alloys.