Thermal decomposition of Ce-Sm and Ce-Lu mixed oxalates: Influence of the Sm- and Lu-doped ceria structure

The thermal decomposition of the (Ce1 - xREx)2(C2O4)3nH2O oxalates (RE [tbnd] Sm, Lu) has been studied over the whole compositional range by differential thermal analysis coupled to thermogravimetry. The temperature of the anhydrous oxalate -> oxide transition results to be driven by two main factors, namely the mean cationic radius of the oxalate, which affects the RE[sbnd]O distances, and the crystal structure of the resulting oxides; the decomposition process is then discussed by taking into account the crystal properties of both compounds. In the Ce-Sm system a slope change appears in the trend of the oxide formation temperature vs. the Sm content at the composition corresponding to the upper limit of the fluorite structure. In the Ce-Lu system the oxalate decomposition of samples with x ranging between 0.4 and 0.8 occurs through a number of steps, in agreement with the polyphasicity of the resulting oxides.