Point Defects and Surface Diffusion in Iron Oxide and Nickel Oxide

Diffusion of the ⁵⁷Co isotope on Fe₃O₄ (110) and NiO (100) surfaces was investigated by the edge-source method. The surface diffusion parameter, α D _sδ, where α is the segregation factor, D _s the surface diffusion coefficient, and δ the thickness of the high-diffusivity layer, was determined at 750°C for different partial pressures of oxygen. In both cases point defects strongly influenced surface diffusion. For Fe₃O₄ the vacancy mechanism is dominant at high oxygen activities and interstitial (or interstitialcy) mechanism dominates at low oxygen activities. For NiO the surface diffusion at low oxygen activities is influenced by aliovalent impurities and at high oxygen activities the strong influence of the intrinsic defects, nickel vacancies, on surface diffusion was observed. It was concluded that similar mechanisms operate during surface diffusion in the near surface layer and during diffusion in the lattice.