Electron-hole conduction in Pr-doped Ce(Gd)O2-δ by faradaic efficiency and emf measurements

Non-negligible electrode polarisation in faradaic efficiency and emf electrochemical cells used for transport number determination results in apparent ion transference numbers which are lower than the true values. However, appropriate modifications of these techniques combined with use of electrodes having a high polarisation resistance, enable a precise determination of even minor electronic contributions to the total conductivity of solid electrolytes. Experimental modification of the faradaic efficiency method, taking into account the electrode polarisation resistance, is proposed and verified using Ce0.80Gd0.18Pr0.02O2-delta ceramics. Substitution of 2% gadolinium cations in the lattice of Ce0.80Gd0.20O2-delta solid electrolyte with praseodymium was found to increase the p-type electronic conductivity by 2.5-4 times, while the activation energy for the electron-hole transport decreases from 145 to 125 kJ mol(-1). The oxygen ion transference numbers of Ce0.80Gd0.18Pr0.02O2-delta in air vary in the range 0.996-0.970 at 873-1223 K, decreasing with increasing temperature. No significant effect of co-doping with praseodymium on the ionic conductivity, crystal lattice and thermal expansion of ceria solid electrolyte was found. (C) 2001 Elsevier Science Ltd. All rights reserved.