Irreversible expansion behavior of Mn3O4+δ spinel and shrinkage behavior of La0.6Sr0.4MnO3 composites with the spinel during thermal cycling in O2 atmosphere

The thermal expansion behaviors of the porous and dense Mn3O4+delta spinel bodies, and the La0.6Sr0.4MnO3 cathode with the spinel in high temperature solid oxide fuel cells have been investigated during a thermal cycle measurement in an O-2 atmosphere. The porous Mn3O4+delta body with relative density of 81% showed a large expansion at temperatures between 1018 and 1064degreesC during the heating cycle and its expansion continued irreversibly every heating cycle. The first large expansion value of this sample showed 1.56% and the expansion had a tendency to decrease with thermal cycles. On the other hand, the dense Mn3O4+delta body with relative density of 98% showed no anomalous expansion. From the results of thermogravimetry and high temperature X-ray diffractometry, the irreversible expansion of the porous body relates to the phase change from beta-Mn2O3-delta into Mn3O4+delta by the oxygen release, and no phase change during the thermal cycle measurement was observed for the dense body. Although the porous body of La0.6Sr0.4MnO3 showed no shrinkage behavior during the thermal cycle measurement, the one of La0.6Sr0.4MnO3 composite with 20 vol % Mn3O4+delta spinel shrank. (C) 2002 The Electrochemical Society.