Thesis (M.Sc.)--Chulalongkorn University, 2009

The chemical compatibilities of the candidates, La1-xSrxCo1-yAlyO3 perovskites and La2-xSrxCo1-yAlyO4 K2NiF4-typed, of cathode material for solid oxide fuel cell with the commercial solid electrolyte, 8 mol % yttria stabilized zirconia (8-YSZ), were studied. Firstly, perovskite and K2NiF4-typed oxides with 0.0 < x, y < 1.0 and 0.0 < x < 2.0, 0.0 ≤ y ≤ 1.0 respectively were prepared by modified nitric citrate method, and characterized by XRD. It was found that the single-phased perovskites were synthesized successfully at 900 – 1000oC for 5h. When x is 0.0 - 1.0 (except x = 0.5 – 0.7), y ≤ 0.2, the crystal structure is cubic. The lattice constants, the volume per formula unit and density decrease with the increase of Al content. The single-phased K2NiF4-typed oxides were achieved when x = 0.8 – 1.2 (except x = 1.1), y = 0.1 and when x = 1.0, y = 0.0 – 0.6 after calcination at 900 – 1100oC. The crystal structure of K2NiF4-typed oxides is tetragonal. Monitored by XRD and SEM/EDX, the La0.6Sr0.4Co1-yAlyO3 with y = 0.05, 0.1 and 0.2 and LaSrCo1-yAlyO4, y = 0.05, 0.2, 0.4 and 0.6 have a good chemical compatibility with 8-YSZ from room temperature up to 850oC and 800°C respectively. In addition the thermal expansion coefficients of La0.6Sr0.4Co1-yAlyO3 (y = 0.0, 0.05 and 0.2) decrease with the increase of Al content and the thermal expansion coefficients of LaSrCo1-yAlyO4 (y = 0.0, 0.05 and 0.2) increase with the increase of Al content.