Low temperature synthesis and structural characterization of over-stoichiometric LaMnO3+δ perovskites

Powders of perovskite LaMnO3+δ with large over-stoichiometry coefficient δ up to δ=0.29 have been synthetized by two different soft chemistry routes using hydrothermal treatment at 150 °C and sol–gel process. Structural and morphological properties were examined by thermal analysis, X-ray diffraction and transmission electron microscopy. Rietveld refinement led to rhombohedral distorted perovskite for all the over-stoichiometric LaMnO3+δ with 0.10<δ<0.29. These studies confirm from structural parameters analysis the solubility limit of cationic vacancies previously evidenced by Maurin et al. by X-ray absorption spectroscopy. Special attention was devoted to the correlation between grain size, synthesis pathways, calcination temperature and the formal MnIV content.