The electrical conductivity of [(ZrO2)(1-x)(CeO2)(x)](Y2O3)(0.08) (x = 0, 0.1, 0.2, and 0.3) was measured between 850 and 1000 degreesC in a wide P-O2 range. The P-O2 independent ionic conductivity at high P-O2 was replaced by the electronic conductivity at reducing atmosphere for x = 0.2 and 0.3 and a conductivity maximum was shown above the ionic plateau. The observation was explained by an equation accommodating the proposed defect model. The rapid decrease of conductivity at low P-O2 was attributed to the combined effect of the decrease of both the ionic and the electronic conductivity. The decrease of electronic conductivity was also contributed by both the decrease of concentration of hopping carriers and the accompanied decrease of the electron mobility. The electronic transference number (t(e1)) was calculated from the fitted data and was shown to increase with increasing Ce content. The t(e1) decreased after a maximum with decreasing P-O2 for fixed Ce content. (C) 2000 Elsevier Science B.V. All rights reserved.