THERMAL-DECOMPOSITION STUDY OF SOME COMPLEXES, PRECURSORS OF MIXED OXIDES, WITH FORMULA MM'(L).NH2O (M, M' = BI, PB, SR, CA AND CU - L = EDTA-LIKE LIGANDS)

Five compounds of formula MM'(L).nH2O [L = ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA); M, M' = Bi, Pb, Sr, Ca or Cu, n = 3-5] have been synthesized and characterized by elemental analysis, spectroscopic techniques and X-ray diffraction. The thermal behaviour of these complexes has been studied by thermogravimetry and differential thermal analysis. The data set provided by the TG and DSC curves of the complexes shows the occurrence of three consecutive steps: dehydration, ligand pyrolysis and the formation of inorganic residues. The enthalpies of the corresponding dehydration process have been calculated. In considering the last-named stage, the compounds were heated at different temperatures. The final products of the pyrolysis, metallic and bimetallic oxides, were examined by X-ray powder diffraction. Note that the PbSrO3 phase is obtained under normal conditions of pressure.