The aim of this work was the determination of the total, the electronic and the ionic conductivity of gadolinia-doped ceria (GDC), Gd0.1Ce0.9O1.95-delta, as a function of oxygen partial pressure at 700 degrees C. Two complementary techniques (impedance spectroscopy and a galvanostatic dc polarization method) were applied to samples with different thicknesses. From the dc measurements only the electronic conductivity could be extracted, while impedance spectroscopy delivered data for both the electronic and ionic conductivity of the mixed ionic-electronic conductor under reducing conditions, p(O-2)<10(-15) bar. Furthermore, the two methods enabled the determination of the chemical diffusion coefficient in reducing atmospheres with typical values around 10(-4) cm(2) s(-1) at 700 degrees C. (C) 2012 Elsevier B.V. All rights reserved.