The effect of grain size distribution in perovskite-type (Ba0.5Sr0.5)(Fe0.8Zn0.2)O3−δ

ceramics upon their oxygen permeation behaviour was investigated via variation of

the calcination temperature in powder production and in the sintering time for the

ceramics. The membranes were examined via scanning electron microscopy,

transmission electron microscopy and oxygen permeation experiments. It was

found that the dwell-time during sintering had an important influence upon the

microstructure of the ceramic. The longer the dwell-time, the further graincoarsening

proceeded; which affected the oxygen permeation in a positive way and

led to enhanced permeation. Supplementary decreasing of the calcination

temperature in perovskite powder synthesis gave fine powders with grain sizes less

than one micrometer and thus smaller grains in the ceramic. Unfortunately, the

grain size distribution in sintered membranes was not constant through membrane

cross-sections since grains in the bulk were smaller when compared to those at the

surface; which was not favorable to oxygen permeation of the ceramics. The

activation energy was determined to be 51 to 53kJ/mol and its variation did not

exhibit a dependence of grain size change. High-resolution transmission electron microscopy proved that grain boundaries were atomically thin without any

interfacial phases. It was concluded that the transport rate of oxygen permeation

was limited mainly by bulk diffusion. Due to the fact that the grain boundaries

acted as barriers to bulk diffusion, the material was a high-mobility one.

Influence of Grain Size on the Oxygen Permeation Performance of Perovskite-Type

(Ba0.5Sr0.5)(Fe0.8Zn0.2)O3−δ Membranes. J.Martynczuk, M.Arnold, A.Feldhoff:

Journal of Membrane Science, 2008, 322[2], 375-82