The effects of vacancies in oxygen sites on physical properties of the lanthanum manganites

The non-stoichiometric solution Ln(1-x)Sr(x)MnO(3-delta rectangle delta) wa s prepared by the classic ceramic method. The physical properties as crysta llographic, magnetic and electrical properties were studied. A structural p hase transition from rhombohedral to orthorhombic was observed at a concent ration of Mn4+ between 10% and 15% 6 per Mn atom in the unit formula. The m agnetic properties are very sensitive to the presence of vacancies at the o xygen sites. The non-stoichiometric, samples change from metallic to insula ting behaviour depending on their vacancy concentration. In the semiconduct or phase, the activation energy value changes with the structural phase, in creasing in the rhombohedral phase and decreasing in the orthorhombic phase .