Grain size effects on oxygen permeation in submicrometric CaTi0.8Fe0.2O3−δ ceramics obtained by mechanical activation

Ceramic samples of CaTi0.8Fe0.2O3−δ were obtained from mechanically activated mixtures of TiO2, Fe2O3 and CaCO3 sintered at 1150 °C for 2 h. The ceramics are dense with submicrometric grains with sizes in the order of 100–200 nm and 400–600 nm. X-ray diffraction analysis revealed a single perovskite phase structure indicating a high level of homogeneity, which was confirmed by transmission electron microscopy. The oxygen permeability through these samples, measured in the range 700–950 °C, is about 50% lower than for ceramics with considerably larger grains, close to 10 μm. The permeability increases linearly with the increase of the grain size in the range from ≈200 nm to ≈10 μm. Observations by results suggest that the grain boundaries have a negative impact on the high temperature ionic transport properties of CaTi0.8Fe0.2O3−δ ceramics.