Nanoscale Effect on the Ionic Conductivity of Highly Doped Bulk Nanometric Cerium Oxide

Dense (> 99%) samaria-doped cerium oxide show a conductivity dependence on grain size, as measured by AC impedance spectroscopy. With a grain size less than 20 nm, only one semicircle pertaining to bulk conductivity is observed, as indicated in the figure. The absence of the grain-boundary blocking effect has been reported before, but not in bulk materials with pure ionic conductivity. The observations are explained in terms of a space-charge model