Influence of surface and finite size effects on the structural and magnetic properties of nanocrystalline lanthanum strontium perovskite manganites
Résumé
Syntheses of nanocrystalline perovskite phases of the general formula La1−xSrxMnO3+δ were carried out employing sol-gel technique followed by thermal treatment at 700-900 °C under oxygen flow. The prepared samples exhibit a rhombohedral structure with space group View the MathML source in the whole investigated range of composition 0.20≤x≤0.45. The studies were aimed at the chemical composition including oxygen stoichiometry and extrinsic properties, i.e. size of the particles, both influencing the resulting structural and magnetic properties. The oxygen stoichiometry was determined by chemical analysis revealing oxygen excess in most of the studied phases. The excess was particularly high for the samples with the smallest crystallites (12-28 nm) while comparative bulk materials showed moderate non-stoichiometry. These differences are tentatively attributed to the surface effects in view of the volume fraction occupied by the upper layer whose atomic composition does not comply with the ideal bulk stoichiometry.