Thin films of 2 mol% Nb-doped cerium oxide are prepared via pulsed laser deposition and investigated using impedance spectroscopy. The electronic conductivity of various films having different microstructures is found to decrease with increasing grain boundary density. The defect chemistry is treated in terms of anti-Frenkel disorder, and possible origins of the blocking effect of the grain boundaries are discussed. (C) 2012 Elsevier B.V. All rights reserved.