Simulation of segregation to free surfaces in cubic oxides

Segregation of isovalent solute cations to (001) and (011) free surfaces in cubic metal oxides is investigated using atomistic computer simulations. Solute concentrations are represented by a mean-field approximation, and equilibrium distributions of solute are calculated by minimizing the free energy. Surface energy effects are found to dominate segregation behavior, even when in competition with misfit strain energy effects. Results are compared with a conventional Langmuir-McLean (LM) analysis. The two approaches are found to agree well in certain cases, but the LM treatment fails to reproduce important phenomena revealed using the free energy method (i.e., segregation to subsurface atomic layers).