The tracer diffusion of O was measured, by using isotopic exchange and depth-profiling via secondary ion mass spectrometry, in La0.8Sr0.2Fe0.8Cr0.2O3 as a function of temperature (700-1000C) in dry O, water vapour or a vapour-H-N mixture. The apparent activation energies for tracer diffusion were 2.4eV in O, 2.6eV in water vapour and 0.71eV in vapour-H-N mixture. Under these reducing conditions, the tracer diffusivity was approximately equal to 10-6cm2/s at 1000C. At all temperatures, the tracer diffusivity increased with decreasing O activity. This reflected an increase in the concentration of O vacancies. The surface exchange coefficient remained high, even under reducing conditions, thus indicating that exchange with O in the H2O molecule occurred at a similar rate to that with the O2 molecule at normal atmospheric pressures of molecular O.

Oxygen Diffusion and Surface Exchange in La0.8Sr0.2Fe0.8Cr0.2O3 under Reducing Conditions. A.Atkinson, R.J.Chater, R.Rudkin: Solid State Ionics, 2001, 139[3-4], 233-40