First-principles study of the interfacial adhesion between SiO₂ and MoSi₂

Upon oxidation, a silica scale forms on MoSi₂, a potential high-temperature coating material for metals. This silica scale protects MoSi₂ against high-temperature corrosive gases or liquids. We use periodic density functional theory to examine the interface between SiO₂ and MoSi₂. The interfacial bonding is localized, as evidenced by an adhesion energy that changes only slightly with the thickness of the SiO₂ layer. Moreover, the adhesion energy displays a relatively large (0.40 J∕m²) variation with the relative lateral position of the SiO₂ and MoSi₂ lattices due to changes in Si-O bonding across the interface. The most stable interfacial structure yields an ideal work of adhesion of 5.75 J∕m² within the local density approximation (5.02 J∕m² within the generalized-gradient approximation) to electron exchange and correlation, indicating extremely strong adhesion. Local densities of states and electron density difference plots demonstrate that the interfacial Si-O bonds are covalent in character. Mo-O interactions are not found in the SiO₂∕MoSi₂ interface investigated here. Our work predicts that the SiO₂ scale strongly adheres to MoSi₂, and further supports the potential of MoSi₂ as a high-temperature structural material and coating.