Molecular dynamics simulations were used to examine the relationship between oxide ion conductivity and dopant content in systems having the general formula, Ba1−xSrxCo1−yFeyO2.5, where x and y varied from 0 to 1, and all of the B-site cations were assumed to be in the +3 state. Doping Ba-rich systems with Fe initially caused a decrease in the ionic conductivity; reaching a minimum at around 50at%Fe. Above this concentration, the conductivity again increased to a maximum for y = 1. In Sr-rich systems (x = 1.0), the conductivity increased continuously as y was increased. Simulations using a mean-field approximation for short-range Co3+/Fe3+ interactions were also performed. A comparison with the discrete ion model results showed that a parabolic variation in the ionic conductivity was due to a mixing effect caused by a random distribution of dopant ions in the perovskite structure. A calculation of the coordination numbers for each cationic species showed that anion vacancies tended to be strongly associated with Co3+ ions, and that the strongest bonding occurred when y = 0.5. Doping with Sr2+ was found to increase the conductivity. These results showed that compositional changes had a strong effect upon the oxide ion conductivity when the concentration of O vacancies was held constant.

Oxide Ion Diffusion in Perovskite-Structured Ba1−xSrxCo1−yFeyO2.5 - a Molecular Dynamics Study. C.A.J.Fisher, M.Yoshiya, Y.Iwamoto, J.Ishii, M.Asanuma, K.Yabuta: Solid State Ionics, 2007, 177[39-40], 3425-31