The basic expressions which governed conductivity in fast ion conductors were considered with particular regard to doped oxides which exhibited such conduction. The role of dopant-vacancy interactions in determining the concentration of mobile vacancies was assessed for selected materials. A comparison of experimental data with the results of atomistic lattice simulations led to the conclusion that, for acceptor dopants where the effective charge on the substitutional ion was –1, a minimum was observed in the concentration dependence of the activation energy for O-ion conduction. This minimum was a characteristic feature and could be used as an indicator of dopant-vacancy interaction. The activation energy for conduction also depended upon the size of the dopant, via a size-dependence of the association enthalpy of the dopant-vacancy pairs. The activation energy was minimized when the dopant was close, in size, to the host cation. One example of materials where this situation was optimum was that of the SrLa substitution which was found in many mixed conducting perovskites. This partly explained the very high O diffusivities which were found in these materials.

Fast Oxygen Transport in Acceptor Doped Oxides. J.A.Kilner: Solid State Ionics, 2000, 129[1-4], 13-23