Overpotential terms on the electrochemical permeability of Sr0.97(Ti,Fe)O3-γ materials

The transport properties of Sr-0.97(Ti,Fe)O3-y materials were reevaluated by a simple electrochemical permeability technique, comprising an electrochemical oxygen pump and a potentiometric oxygen sensor to measure the driving force. The rate of transport through single layer dense samples was significantly lower than through bilayered dense/porous samples with the porous layer in contact with the oxidizing atmosphere (air); this suggests that the overall resistance to oxygen transfer across the mixed conducting material includes terms related to surface exchange, and mixed (electronic + oxide ion) conduction. The dependence of permeability current on the driving-force also tends to a limiting current, which was attributed to concentration overpotentials due to limitations of transport in dilute gas phases. (C) 1999 Elsevier Science B.V. All rights reserved.