Ab initio thermodynamic study of the structure and chemical bonding of a β -Ni 1 − x Al x / α -Al 2 O 3 interface

The properties of an interface between a metallic alloy and an oxide are computed by combining ab initio quantum mechanics with thermodynamics. Results for the stability, structures, and chemical compositions of the $\ensuremath{\beta}{\text{-Ni}}_{1\ensuremath{-}x}{\text{Al}}_{x}/\ensuremath{\alpha}{\text{-Al}}_{2}{\text{O}}_{3}$ interface are presented. We found that there are two types of stable structures for the interface. Type I is characterized by joining an Al-rich Ni-Al alloy with an Al-rich ${\text{Al}}_{2}{\text{O}}_{3}$ surface (terminated by two Al atomic layers). Type II is a junction of a Ni-rich Ni-Al alloy with an ${\text{Al}}_{2}{\text{O}}_{3}$ surface terminated by an oxygen atomic layer and with atomic migrations and interchanges within the interfacial region. Both types of interfaces exhibit Al accumulation on top of the oxide scale while an adjacent Ni-rich layer is found at the type-II interfaces. The atomic geometries, electronic structures, and chemical bonds of the two types of interfacial systems were analyzed. The calculated interfacial works of separation ${W}_{sep}$ agree reasonably well with experimental data and earlier calculations.