CHEMICAL-REACTIVITY AND INTERDIFFUSION OF (LA, SR) MNO3 AND (ZR, Y) O2, SOLID OXIDE FUEL-CELL CATHODE AND ELECTROLYTE MATERIALS

The chemical reactivity and interdiffusion of (La, Sr) MnO3 and (Zr, Y)O2 were studied from 1110 to 1755 K. Reaction of LaMnO3 with (Zr, Y)O2 was already observed at 1170 K, whereas reactions between (La, Sr) MnO3 with 30 at.% Sr and (Zr, Y)O2 with 8 at.% Y were not observed at 1365 K. The reaction products observed in the experiments are La2Zr2O7 and/or SrZrO3. It is proposed that reaction layers are formed by diffusion of La and/or Sr into (Zr, Y)O2 via a vacancy diffusion mechanism. The composition of the layers depends on the La2O3 and SrO activities in (La, Sr)MnO3. The activation energy for the formation of a La2Zr2O7 reaction layer was determined to be 17.5 +/- 1.8 kJ-mol-1, the activation energy for the formation of a SrZrO3 reaction layer was determined to be 18.8 +/- 1.9 kJ.mol-1. On the basis of the experiments it was calculated that at 1273 K it would take about 29100 h to grow a reaction layer of SrZrO3 from (La0.5Sr0.5)MnO3 and (Zr0.97Y0.03)O1.985, and about 82000 h to grow a reaction layer of La2Zr2O7 from LaMnO3 and (Zr0.92Y0.08)O1.96, with a thickness of 1-mu-m for both layers. It is proposed that the reaction layers might result in both ohmic and polarization losses of the SOFC.