Computer Simulation of Surface Segregation

Computer simulation techniques can now reliably model the surface structure and energies of inorganic solids. We present recent work which has been directed at modelling the segregation of impurities. The techniques are based on energy minimisation where the forces between the atoms are described by the Born model of solids. We initially show that magnesium and calcium segregation to the prism surfaces of alumina reproduce the available experimental data within the uncertainties of the experimental technique. However, reliable experimental data is not always available, and hence we show using the examples of calcium segregation to zirconia surfaces can give insights to the surface structure and provide predictions for experiment to test. Secondly, the simulations can be verified by comparison with morphologies. This is illustrated by comparison of the experimentally determined morphology of calcite with magnesium and lithium impurities with those calculated. Next extensions to the energy minimisation methods are described using dynamical techniques based on lattice and molecular dynamics. Finally, we describe the situation where there is phase separation and the structure and stability of the interface is governed by the epitaxial relations between the underlying oxide and the impurity oxide.