effects of b-site substituents on oxygen permeability and phase transformation of Sr_(0.9)Ca_(0.1)Co_(1-x)B'_xO_(2.5+) system

摘要

Oxygen permeation properties and phase transformation of A-and B-site partially substituted strontium cobaltites, Sr_(0.9)Ca_(0.1)Co_(1-x)B'_xO_(2.5+&) (B'=Mn, Co, Ni, In, Fe or Al), were examined. These oxides were found to have either 2H-BaNiO_3-type structure (B'=Mn, Ni or Co) or orthorhombic brownmillerite-type one (B'=Fe or Al) at room temperature. As revealed by high-temperature XRD analysis, all of these oxides transformed into perovskite-type structure at elecvated temperatures. The transformation temperatures tended to be lower for the latter group (B'=Fe or Al) than for the former one. TG-DTA analysis revealed that the transformation was accompanied by an appreciable amounts of oxygen absorption. Noticeably, the phase transformation temperature coincided with the temperature at which oxygen permeation switched on. The lowest switching-on temperature (750 deg C) was observed with the Fe-substituted oxide among the above oxides. Further investigations of the Fe-substituted system showed that the switching-on temperature was lowered down to about 720 deg C with increasing Fe-substitution of B-site up to 20percent.