Oxygen diffusion and surface exchange in La0.8Sr0.2Fe0.8Cr0.2O3-δ under reducing conditions

Oxygen tracer diffusion (D*) and surface exchange (k) have been measured, using isotopic exchange and depth profiling by secondary ion mass spectrometry, in La0.8Sr0.2Fe0.8Cr0.2O3-delta as a function of temperature (700-1000 degreesC) in dry oxygen, in water vapour and in a water vapour/hydrogen/nitrogen mixture. The apparent activation energies for D* are 2.4 eV in oxygen, 2.6 eV in water vapour and 0.71 eV in the water vapour/hydrogen/nitrogen mixture. In these reducing conditions, D* is approximately 10(-6) cm(2) s(-1) at 1000 degreesC. At all temperatures, D* increases with reducing oxygen activity reflecting an increase in the concentration of oxygen vacancies. k remains high even under reducing conditions indicating that exchange with oxygen in the H2O molecule occurs at a similar rate to that with the O-2 molecule at normal atmospheric pressure of molecular oxygen. (C) 2001 Elsevier Science B.V. All rights reserved.