First-principles computational study of Ni/α-Al₂O₃ hybrid interface reactions under extreme thermodynamic conditions

Atomic-level understanding of hybrid interface reactions for metal and oxide plays an important role in innovative design of multifunctional materials. We apply first-principles calculations to thin layers of metallic Ni and oxide α-Al₂O₃ (Ni/α-Al₂O₃) and unveil reaction mechanism under extreme thermodynamic conditions (T > 2500 K and pressure P ∼ 40 GPa). In such thermally shocked state, we track interface reaction scenario by calculations of thermodynamically feasible structures and energy convex hull: (i) chemical-bond break of α-Al₂O₃ enabling fast diffusion of O into Ni atomic layers, (ii) formation of NiO, (iii) formation of intermetallic compounds Ni_xAl_{1- x} and followed by (iv) evolution of O₂ gas. The NiO is formed locally at around the interface for short time period at the beginning of the interface reactions. Intermetallic compounds Ni_xAl_{1− x} are thermodynamically unstable against the decomposition into Al₂O₃ and Ni. It is also elucidated that abrupt mechanical shock to the interface by such a high pressure adiabatically raise interface temperature extremely high, in which mixtures of Ni_xAl_{1− x} are stabilized by releasing O₂(g). We neatly summarize the interface reactions using an Ellingham diagram.