Hf-doped Ni - Al ₂ O ₃ interfaces at equilibrium

In this study, a series of solid-state dewetting experiments of pure and Hf-doped Ni films on sapphire and HfO₂ substrates were conducted in order to measure the change in interfacial energy of the Ni-Al₂O ₃ interface in the presence of Hf, and to study Hf interfacial segregation. It was found that Hf oxidizes under the conditions of the experiment (P(O₂)=10^-20 atm), Hf does not segregate to the Ni-Al₂O₃ interface, and that the interface energy of Ni-HfO₂ is 2.7 ± 0.4 J/m² vs 2.16 ± 0.2 J/m² for the Ni-Al₂O₃ interface. This contradicts several theoretical studies that predict that Hf segregates to the interface to stabilize it thermodynamically. The solubility of Hf in bulk Ni was found to be significantly lower than the value reported in the equilibrium phase diagram.