Exploring the evolution of magnesium oxidation mechanisms by density functional theory

Magnesium (Mg) is an abundant metal which has been used in aviation, medicine, hydrogen energy storage, etc. However, Mg can be rather reactive, and therefore an improved understanding of corrosion and oxidation mechanisms can enhance the efficiency of these processes to control and widen applications. The study presented here investigates the mechanisms of oxidation from the initial to full monolayer stages, on two low-index Mg surfaces, Mg(0001) and Mg$\left(10\overline{1}0\right)$. By analysing the valence electron changes during the oxidation process, we reveal a connection between oxidation and electron properties, suggesting that oxygen (O) atoms preferentially adsorb in the regions of charge accumulation on the surfaces. After the adsorption of a first O atom, the charge distribution on the surface changes, and following O atoms are attracted to neighbouring charge-rich regions. In addition, the oxidized Mg-O units form geometric structures initially different from the rocksalt structure commonly reported for a fully oxidized surface. In Mg(0001), the Mg-O unit structure transitions from a wurtzite type to hexagonal, while on Mg$\left(10\overline{1}0\right)$ a more perfect Mg-O unit of wurtzite structure forms.