Oxygen permeation of perovskite-type ceramics consists of three elementary processes: oxygen absorption, bulk oxygen diffusion, and oxygen desorption. In most cases, the rate-determining step is the oxygen diffusion step, and the use of thin films improves the oxygen permeation rate of perovskite-type ceramics. Polymer-brushmodification is a useful technique to produce thin films. Grafted PMMA-brushes exhibit a screening effect for attractive interactions between core ceramic particles, thereby inducing repulsive forces on them. This results in the formation of a densely packed ordered array. Modification of the polymerization-initiator and polymerbrushes should affect the oxygen permeation properties of the ceramic particles, especially surface oxygen adsorption and desorption. In this paper, it is demonstrated that these modifications change the cation chemical states and lower the oxygen desorption rate, while increasing the desorption peak temperature. The surface of La-Sr-Co-Fe perovskite-type oxides was modified only with the polymerization initiator,(2-bromo-2-methyl)propionyloxyhexyltriethoxysilane (BHE) because there is no direct interaction between the polymer-brush and the substrate, while the initiator is directly modified to the substrate. The oxygen desorption behavior of BHE-modified oxides indicates that its oxygen desorption property is impeded without modification with PMMA. The investigation of BHE-modified oxide cation chemical states and oxygen desorption behaviors imply that the BHE-modifying site and change in chemical states have selectivity depending on cation species. Although sintering causes the formation of silicate and ceramic decomposition, this step can eliminate the harmful effects of BHE-modification in total. When conventional La-Sr-Co-Fe perovskitetype ceramics are used, sintering is preferable for the recovery of thin-film surface reactions. However, if we utilize site selectivity of BHE-modification, the harmful effects of those modifications can be avoided by modifying BHE onto sites that hardly participate in surface reactions.

The oxygen non-stoichiometry (¤) and structural properties of a brownmillerite-type oxide of La 0.1 Sr 0.9 Co 0.9-Fe 0.1 O 3¤ (LSCF1991) during oxygen sorption/desorption were investigated by simultaneously applying a temperature-programmed technique and high-temperature X-ray diffraction. The structural changes of perovskite-type (P-type) to brownmillerite-type (B-type) and B-type to P-type occurred within limited p(O 2) ranges, and a B-type phase-stable region was observed in the presence of oxygen at high temperature. Moreover, P-type LSCF1991 changed into B-type LSCF1991 through tetragonal P-type LSCF1991 as an intermediate phase. B-type LSCF1991 showed repeating structural changes with a certain limited p(O 2), which is 0.5% < p(O 2) < 1.0%, whereas such changes could not be observed at p(O 2) > 1.0%. These behaviors correspond with the temperature programmed desorption of oxygen profiles, as well as the amount of lattice oxygen (3¤). The p(O 2) dependence of the structural change will provide a basis for a further investigation into the durability of an oxygen-permeated membrane by predicting the strain across the membrane under practical conditions.