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 R3-bar c perovskite structure, while for x>0.10, the samples have two phases with the R3-bar c 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.