Cation vacancy diffusion on the NiO(001) surface by molecular dynamics simulations

We present results concerning the cation vacancy diffusion mechanisms occurring on the NiO(001) surface along with their corresponding migration energies. Using a rigid ion potential and molecular dynamics simulations we found that the cation vacancy diffusion is the main diffusion process in this surface employing the simple and two different double hopping mechanisms. Although the hopping rates of the latter are about two times lower than that of simple jumps, at high temperatures their contribution to the total vacancy diffusion coefficient is comparable with that of simple jumps. In addition, for all mechanisms saturation is found in the Arrhenius diagrams above a temperature T-s = 2850 K. We attributed this behavior to collective and correlated movements of the surface atoms that are activated from multi-phonon processes taking place above T-s. Similar behavior was found recently in the case of metals. (C) 1999 Published by Elsevier Science B.V. All rights reserved.