Monte Carlo simulations of gadolinium doped ceria surfaces

Hybrid Monte Carlo and adaptive kinetic Monte Carlo calculations have been performed to examine the thermodynamic equilibrium and kinetic properties of a double sided {111} terminated 10 mol% gadolinium doped ceria system. Hybrid Monte Carlo simulations demonstrate that both the concentration of gadolinium ions and oxygen vacancies are enhanced at the surface compared to the bulk. We do not observe the formation of any domain structures at the surface by gadolinium ions. The calculated average activation energy for oxygen transitions from the surface layer is reduced to 0.36 eV, compared to the bulk value of 0.50 eV. Consequently, the ionic conductivity in the surface layers is approximately twice that of the bulk which can be attributed to the surface structure. The adaptive kinetic Monte Carlo simulations found numerous multi-atom concerted diffusion mechanisms spanning large distances which would not have been accounted for in a typical list based kinetic Monte Carlo approach. The taken combined approach is essential to fully understand these complex materials.