CHEMICAL DIFFUSION AND OXYGEN-EXCHANGE OF LA0.6SR0.4CO0.6FE0.4O3-DELTA

The transport parameters of La0.6Sr0.4Co0.6Fe0.4O3-delta were determin ed by electrical conductivity relaxation and high temperature coulomet ric titration experiments. The experimental response curves were analy zed in the frequency domain. The results obtained by both methods were in good agreement. The chemical diffusion coefficients measured at te mperatures of 923-1255 K and oxygen partial pressures of 0.03-1 bar O- 2, vary between 10(-6) -5 x 10(-5) cm(2) s(-1). The experimental activ ation energies are in the range 95-117 kJ mol(-1). At oxygen partial p ressures below 0.03 bar O-2 the re-equilibration process is completely governed by the rate of oxygen exchange at the interface. The surface exchange coefficients were determined by conductivity relaxation expe riments at temperatures of 1000-1285 K and oxygen pressures of 10(-4) -0.1 bar O-2. The activation energy is about 60-70 kJ mol(-1). The exc hange coefficients are almost proportional to the oxygen pressure. Tre atment of the surface in a nitric acid solution for several hours incr eases the surface exchange rates by factors of 3-5.