Crystallographic changes and thennal properties of lanthanum-strontium ferromanganites between RT and 700°C

X-ray powder diffraction was used to determine the crystallographic changes between room temperature (RT) and 700 degreesC of the (La0.8Sr0.2)(Mn1-yFey)O3+/-delta perovskites with y=0.2, 0.5, 0.8, 1 which can be considered as possible cathode materials for the ITSOFCs. For y=0.2, the rhombohedral symmetry was preserved in the whole temperature range. For y=1, a transition from orthorhombic to rhombohedral symmetry occurred at 290 degreesC. The compounds with y=0.5 and 0.8 were found to be diphasic at RT by combination of both rhombohedral and orthorhombic symmetries. They became only rhombohedral at 80 and 160 degreesC, respectively. This reversible transition is discussed in terms of iron concentration, vacancy diffusion and oxidation state. These results were corroborated by a dilatometric study. The thermal expansion coefficients of these materials show a good compatibility with YSZ, the usual yttria-stabilized zirconia electrolyte. (C) 2004 Elsevier B.V. All rights reserved.