Modelling of point defect migration in proton conducting ceramics

Numerical simulations of the diffusion of protons, oxygen vacancies, electrons and holes in SrCe0.95Yb0.05O3-alpha were performed for conditions where external fluxes were not allowed and where they were allowed. With no external fluxes and the application of an electrical field, the concentration profiles approached that expected from the Gouy-Chapman/Debye-Huckel theories. When the profiles were sharper than the Debye length, the particle migrations are not linked. However, for longer times their migrations became linked due to the generation of large electrostatic fields. This yielded the answer expected from chemical diffusion. Similar analysis resulted from cases with enhanced surface concentrations with no external fields. The approach to these conditions, however, was not as expected from simplified equations, and independent diffusion can occur for a time much longer than expected.