Abstract
In this research, homogeneous (R0.5A0.5)MnO3 (R = Gd, Yb; A = Ca, Sr) and (R0.5A0.5)NiO3 (A = Ce, Th) compounds with perovskite structure were synthesized by a polymeric citrate precursor method. (R0.5A0.5)TiO3 (A = Ca, Sr) was synthesized by a solid state method. (R0.5A0.5)MnO3 series samples have orthorhombic symmetry and (R0.5A0.5)NiO3 have monoclinic symmetry. The samples prepared by the polymeric citrate precursor method has a better homogeneity and the grain size is smaller than that prepared by the solid state method. Mn and Ti samples have M3+ and M4+ mixed valence state observed by XANES. The (R0.5A0.5)MnO3 samples are insulator, they has a spin-glass like property and the FC and ZFC susceptibility is irreversible. The (R0.5A0.5)NiO3 samples are paramagnetic metal. At 1 T magnetic field, both (R0.5A0.5)MnO3 and (R0.5A0.5)NiO3 have negative magnetoresistance (MR) ratio. The maximum MR ratio of (Gd0.5Ca0.5)MnO3 sample is found at 80-100 K,with a range of 60-65%. The maximum MR ratio of (R0.5A0.5)NiO3 sample is found at 180-200 K, with a range of 50- 60%. The (R0.5A0.5)TiO3 samples are paramagnetic Mott insulator.
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