Structural and magnetic properties in the self-doped perovskite manganites with nominal composition La0.7Sr0.3−xMnO3−δ

Perovskite manganites with nominal composition La0.7Sr0.3−xMnO3−δ (0.00≤x≤0.20) have been prepared by the sol–gel method with the highest heat treatment temperature being 1073 K. The XRD patterns indicate that when the doping level is x≤0.10 the samples have only a single phase, with the R3̄c perovskite structure, while for x>0.10, the samples have two phases with the R3̄c perovskite being the dominant phase and Mn3O4 being the second phase. A quantitative analysis and Rietveld fitting of the X-ray powder diffraction data indicate that on the basis of the thermal equilibrium theory of crystal defects there are Mn2+ ions at the A sites and Mn3+ plus Mn4+ ions at the B sites in the ABO3 perovskite phase. The curves of magnetization versus applied magnetic field at 10 K showed that the magnetic moments of the Mn2+ ions at the A sites are antiparallel to those of the Mn3+ and Mn4+ ions at the B sites.

Research highlights
► There are Mn2+ ions at the A sites and Mn3+ plus Mn4+ ions at the B sites.
► Magnetic moments of Mn2+ ions are antiparallel to those of Mn3+ and Mn4+ ions.
► The assumption that there are vacancies at the A sites is not supported by the data.
► Powder samples prepared by the sol–gel method is nanocrystalline materials.