Study of La_1−xMnO_3−δ non-stoichiometry and defect structure using ESR and iodometry

Abstract

The oxidation states of manganese in the La_1−xMnO_3−δ (x = 0.09–0.11) were investigated by electron spin resonance (ESR) and iodometry. The ESR analysis carried out at room temperature for the samples prepared in air revealed the presence of broad peaks at g = 2.0, considered to be relevant to Mn²⁺. It was also found that the intensity of the peak increased as lanthanum vacancy content increased. The average valence state of manganese, determined by iodometry, was approximately 3.2, and decreased by 1 as the lanthanum vacancy increased by 1. Similar trends were observed with the samples prepared at P _{o 2} = 1×10⁻⁷. The results indicated that Mn²⁺ is stably present in the La_1−xMnO_3−δ having an average valence number exceeding 3.0. A series of experimental results with respect to the non-stoichiometry of La_1−xMnO_3−δ can be explained by assuming that Mn²⁺ is stabilized after forming a complex with a lanthanum vacancy and two oxygen vacancies.