Ab initio study of decohesion properties in oxide/metal systems

Several studies of the decohesion properties of various oxide/metal systems have been performed recently by ab initio calculations. However, the use of different computational methods, which involve diverse approximations, energy functionals, or calculation conditions, makes the identification of general trends difficult. In the present work, a broad range of interfaces between an ionic oxide (Al_(2)O_(3), ZrO_(2), HfO_(2), and MgO) and a metal [either transition metal (TM) or Na], has been investigated systematically in order to find correlations among the work of separation (Wsep) and the intrinsic properties of the interface, such as the crystal structure, the strain conditions, or the electronic properties of both constituents. Our main result is that the calculated Wsep adjusts very accurately to a parabolic dependence on the summed surface energies of the metal and the oxide, regardless of the oxide and metal components, crystal lattices, interface orientations, and atomic terminations. Furthermore, Wsep is mostly determined by the surface energies although for interfaces involving nonpolar oxide surfaces the contribution of the interfacial energy is not negligible. The strongest adhesion is found for interfaces formed by polar surfaces and bcc TM, e.g., the Wsep of ZrO_(2)(001)_(O)/TM interfaces changes almost by a factor of 2 depending on whether the TM has bcc or fcc structure. In addition, a correlation between the strain conditions of the equilibrium interface structure and the adhesion properties has been obtained. Finally, in order to predict metal/oxide systems whose mechanical properties are reinforced by the plastic deformation of the metal, we examine the expected behavior of the system beyond the elastic regime in the light of the calculated adherence at the interface. The comparison with the scarcely available experimental data provides good agreement for both the Wsep and the qualitative prediction of mechanical reinforcement.