Hydrothermal synthesis of LaMnO3+δ: F.T.I.R. and W.A.X.S. investigations of the evolution from amorphous to crystallized powder

Pseudo-cubic LaMnO3+δ powders were obtained by pyrolysis of the amorphous residue of the hydrothermal treatment, at 150°C under autogeneous pressure, of lanthanum and manganese nitrates in presence of citric acid. The pyrolysis steps are identified by coupled T.G.A.-D.T.A. determining also the carbon content evolution. From F.T.I.R. and W.A.X.S. investigation of the amorphous powders calcined at various temperatures in the 200–1000°C range, it is shown that the crystallization occurs slowly in the 550–700°C range and that the perovskite skeleton already exists in the amorphous citrate precursors formed by the hydrothermal treatment.