Determination of manganese valence in complex La-Mn perovskites

We describe a chemical method for determining the manganese concentration and average oxidation state in mixed-valence compounds, and in particular in complex La-Mn perovskites. The method is based on two independent iodometric titrations, with amperometric dead-stop end-point detection. The oxygen stoichiometry and the molecular weight of the compounds can also be evaluated if secondary phases or multi-valent elements different from manganese are not present. The method was applied to the analysis of La-Mn perovskites with the same cation stoichiometry but synthesized under different conditions. Significant variations of the Mn average valence were measured, which corresponded to different physical and structural properties of the materials.