Effect of samarium content on onset of minor p-type conductivity in ceria-based electrolytes

Abstract

Ce1-xSmxO2-delta powders (x = 0.1, 0.2, 0.3) were prepared by a freeze-drying method, preserving monophasic fluorites when precursors were annealed between 375 and 1600 degrees C. Dried precursor powders were calcined at 375 degrees C for 4 h and sintered at 1600 degrees C for 10 h yielding gas-tight ceramics with densifications >95%. The oxygen-electrochemical permeability measurements were employed to study the oxygen flux under moderate oxidizing conditions which was directly related to the onset of residual electronic conductivity. In the experimental process the charge transport through the membrane was due to the ambipolar conductivity, which was controlled by the minor electronic conductivity in Ce1-xSmxO2-delta. The electronic properties of the pellets were analysed between pO(2) approximate to 10(-3)-0.21 atm in the range 750-900 degrees C. The estimated ionic transport number, obtained by combination of the electronic conductivity by oxygen permeability and total conductivity by impedance spectroscopy, remained higher than 0.99 in the studied conditions. The electronic conductivity was found dominated by p-type carriers and dependent on the content of Sm in the ceria lattice. Although the overall electrical conductivity under oxidizing conditions is governed by the ionic behaviour, an increased Sm-doping improved the p-type conductivity. (C) 2012 Elsevier B.V. All rights reserved.