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

Abstract

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 NixAl1-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 NixAl1−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 NixAl1−x are stabilized by releasing O2(g). We neatly summarize the interface reactions using an Ellingham diagram.