Permanganometric determination of oxygen nonstoichiometry in manganites

Strontium and lanthanum manganites are nowadays the subject of extensive research because of their promising electrical and magnetic properties. Strontium manganite, SrMnO3, was successfully prepared by citrate-nitrate autocombustion (CNA) and by the coprecipitation method. These methods were then applied to synthesis of strontium doped lanthanum manganites, La1-xSrxMnO3 (x ​= ​0, 0.1, 0.2 and 0.3). The optimal phase formation conditions were determined by thermogravimetry and differential scanning calorimetry. Crystallization of precursors and calcined powders was studied by X-ray diffraction. Powders, in which pure manganite phase was obtained, were also analyzed by permanganate titration with Mohr's salt in order to determine oxygen nonstoichiometry. Oxygen stoichiometry was achieved in SrMnO3 powders obtained by the CNA method and calcined at 1000 ​°C as well as in powders obtained by the coprecipitation method and calcined at 1200 ​°C. La1-xSrxMnO3 phase was oxygen stoichiometric for x ​= ​0.3 while decreasing of x resulted in cation deficiency, i.e. oxygen excess. Oxygen deficit was achieved for x ​= ​0.09 upon calcination at 1200 ​°C. The obtained results were confirmed by thermogravimetry and the Rietveld refinement analysis.