Preparation and characterization of La_(1-x)Sr_xMnO_(3+δ) (0 ≤ x ≤ 0.6) powder by sol-gel processing

摘要

La_(1-x)Sr_xMnO_(3+δ) (0 ≤ x ≤ 0.6) were synthesized via sol-gel route (Pechini process). The gel decomposition was studied by several thermal analysis methods. After calcination at 1000 ℃ of the dried gels, the oxides were characterized by X-ray diffraction, thermal analyses, transmission and scanning electron microscopies and chemical analyses. In order to correlate the Mn~(4+)/Mn~(3+) ratio with the symmetry of the structure and the particle size, the nonstoichiometry level at room temperature, δ, was determined by two methods: chemical titration and temperature programmed reduction. It is shown that a negative correlation exists between the strontium content and the nonstoichiometry level, i.e., at low Sr content the oxygen content is higher. To define the best material composition for use as a solid oxide fuel cell (SOFC) cathode, a comparison was made between δ values at room temperature and SOFC operating temperature (1000 ℃).