The effect of grain size upon the ionic conductivity of yttria-stabilized zirconia samples synthesized by ball milling was reported. Complex impedance measurements were performed on 10mol%yttria-stabilized zirconia nanocrystalline samples, with grain sizes ranging from 900 to 17nm, as a function of temperature and frequency. It was noted that the bulk ionic conductivity decreased dramatically for grain sizes below 100nm; although the activation energy was essentially independent of grain size. The results were interpreted in terms of a space-charge layer resulting from segregation of mobile oxygen vacancies to the grain-boundary core. The thickness of this space-charge layer formed at the grain boundaries was on the order of 1nm for large micron-sized grains but extends up to 7nm when decreasing the grain size down to 17nm. This gave rise to oxygen vacancies depletion over a large volume fraction of the grain and consequently to a significant decrease in oxide-ion conductivity.

Ionic Conductivity of Nanocrystalline Yttria-Stabilized Zirconia: Grain Boundary and Size Effects. O.J.Durá, M.A.López de la Torre, L.Vázquez, J.Chaboy, R.Boada, A.Rivera-Calzada, J.Santamaria, C.Leon: Physical Review B, 2010, 81[18], 184301