Overpotential terms on the electrochemical permeability of Sr-0.97(Ti,Fe)O3-gamma materials

The transport properties of Sr-0.97(Ti,Fe)O3-y materials were reevaluated b y a simple electrochemical permeability technique, comprising an electroche mical oxygen pump and a potentiometric oxygen sensor to measure the driving force. The rate of transport through single layer dense samples was signif icantly lower than through bilayered dense/porous samples with the porous l ayer 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-forc e also tends to a limiting current, which was attributed to concentration o verpotentials due to limitations of transport in dilute gas phases. (C) 199 9 Elsevier Science B.V. All rights reserved.