The effects of lanthanide co-dopants on oxygen diffusion in yttria-stabilized zirconia were studied using a combined first-principles density functional theory and kinetic Monte Carlo modeling approach. Density functional theory methods were used to calculate barrier energies for oxygen migration in various local cation environments, which were then input to kinetic Monte Carlo simulations to obtain long-term oxygen diffusivities and activation energies. Simulation results revealed a substantial increase in the maximum value of the oxygen diffusivity upon co-doping, and in the dopant content at which this value was obtained for Lu co-doped material; while relatively little change was seen for Gd co-doped material. Examination of the density functional theory barrier energies revealed a linear scaling of barrier height with the size of cations at the diffusion transition state. Using this strong correlation, oxygen diffusivity was examined in material co-doped with several lanthanide elements. The oxygen diffusivity decreased with dopant atomic number (and decreasing dopant ion size) for co-dopants smaller than Y, and changed relatively little when Y was replaced by larger co-dopants. These results were largely consistent with experiment, and were explained in terms of cation-dopant and vacancy concentration-dependent correlation effects, using a simple analytical model.

Effects of Lanthanide Dopants on Oxygen Diffusion in Yttria-Stabilized Zirconia. R.Krishnamurthy, D.J.Srolovitz, K.N.Kudin, R.Car: Journal of the American Ceramic Society, 2005, 88[8], 2143-51