  In this work we introduce a metal-oxide bond-energy model for alloy oxides
based on pure-phase bond energies and bond synergy factors that describe the
effect of alloying on the bond energy between cations and oxygen, an important
quantity to understand formation and stability of passive films. This model is
parameterized for binary cation-alloy oxides using density-functional theory
energies and is shown to be directly transferable to multi-component alloy
oxides. We parameterized the model for alloy oxide energies with metal cations
that form the basis of corrosion resistant alloys, including Fe, Ni, Cr, Mo,
Mn, W, Co, and Ru. We find that isoelectronic solutes allow quantification of
pure-phase bond energies in oxides and that the calculated bond energy values
give sensible results compared to common experience, including the role of Cr
as the passive-layer former in Fe-Ni-Cr alloys for corrosion applications.
Additionally, the bond synergy factors give insights into the mutual
strengthening and weakening effects of alloying on cation-oxygen bonds and can
be related to enthalpy of mixing and charge neutrality constraints. We
demonstrate how charge neutrality can be identified and achieved by the
oxidation states that the different cations assume depending on alloy
composition and the presence of defects.
