Double Peak Behavior of Resistivity-Temperature Curves in (Nd / Pr)(0.67)Sr0.33MnO3 Manganites

We have reported the synthesis of polycrystalline samples of R0.67Sr0.33MnO3 (R = Pr, Nd) from the precursors of PrMnO3, NdMnO3 and SrMnO3 by using solid state reaction method. These samples were sintered at 1200 degrees C and 1400 degrees C. Some of samples were also undergone oxygen annealing at 950 degrees C for 6 h. All the synthesized samples were characterized by X-Ray diffraction (XRD) technique, scanning electron microscopy (SEM) and low temperature resistivity versus temperature (R-T) measurement. The XRD patterns show the monophasic nature of the sintered and annealed samples. The sintered samples of Nd0.67Sr0.33MnO3 has metal-insulator transition at 250 K, while the sample annealed in oxygen shows two peaks, one sharp peak at 250 K and other broad peak at 200 K. The sintered samples of Pr0.67Sr0.33MnO3 has only one peak at 290 K, while the sample annealed in oxygen shows two peaks, one sharp peak at 290 K and another broad peak at 225 K. The two peak behavior in the annealed samples has been explained by inhomogeneous diffusion of oxygen in the core of the grain and at the grain boundaries region.