Abstract
Thermal expansion of LaCoO3 perovskite in air and 4% H2/96% Ar reducing atmosphere has been studied by Thermal Mechanical Analysis (TMA). The thermal behavior of LaCoO3 in air exhibits a non-linear expansion in 100 � 400�C temperature range. A significant increase of CTE measured in air both during heating and cooling experiments occurs in the 200 � 250�C temperature range, corresponding to a known spin state transition. LaCoO3 is found to be unstable in a reducing atmosphere. It undergoes a series of expansion and contractions due to phase transformations beginning around 500�C with very intensive chemical/phase changes at 850oC and above. These expansions and contractions are directly related to the formation of La3Co3O8, La2CoO4, La4Co3O10, La2O3, CoO, and other Co compounds due to the reducing atmosphere. Although LaCoO3 is a good ionic and electronic conductor and catalyst, its high thermal expansion as well structural instability in reducing environments presents a serious restriction for its application in solid oxide fuel cells, sensors or gas separation membranes.
