Superionic conduction of oxygen ions in 10mol% ytterbia-stabilized zirconia was studied at various temperatures via molecular dynamics simulation (table 24). Although discrete hopping of one or two oxygen ions began at about 675K, the onset of superionic conduction occurred at about 1200K, where almost all of the oxygen ions participated in hopping. The activation energy for oxygen ion diffusion was 53.25kJ/mol. At this temperature and above, the oxygen ionic conductivity exceeded 0.1S/cm. At 675 to 1200K, the material acted as a normal ionic conductor. The ionic conductivity values obtained via simulation compared well with experimental results. The activation energy for oxygen ion conduction, found from the Arrhenius plot of the simulation, was however 52.71kJ/mol; which was 35% less than the experimental value. Radial distribution functions, g(r), showed that there was no sharp structural phase transition and no oxygen-ion sub-lattice melting at the superionic transition. The lowering, broadening and shifting of the peaks in g(r) for all ionic pairs at higher temperatures indicated volume expansion of the crystal.

Molecular Dynamics Simulations of Oxygen Ion Diffusion and Superionic Conduction in Ytterbia-Stabilized Zirconia. Pramananda Perumal, T., Sridhar, V., Murthy, K.P.N., Easwarakumar, K.S., Ramasamy, S.: Computational Materials Science, 2007, 38[4], 865-72

Table 24

Diffusivity and Conductivity of 10mol%Ytterbia-stabilized Zirconia