Preparation and characterization of nano-polycrystalline lanthanum-based manganite (La1-yKy)0.7Ca0.3MnO3(La1-yKy)0.7Ca0.3MnO3

A series of nano-polycrystalline alkali metal doped in La-based manganites (La1-yKy)0.7Ca0.3MnO3(La1-yKy)0.7Ca0.3MnO3 samples (y=0.0y=0.0, 0.1, 0.2, and 0.3) were synthesized using the polymerical complex sol–gel method. The structural properties are studied via the X-ray diffraction experiments, and results are refined by the Rietveld method. The electrical transport properties of the polycrystalline samples have been investigated in the temperature range 50–300 K and a magnetic field up to 10 kOe. The metal–insulator transition temperature (Tp)(Tp) changes with doping due to the difference between the electron configuration and ionic radius of the dopants and manganese trivalent ions. Characteristic grain boundary defects, such as low-field magnetoresistance, which is absent in the single-crystalline perovskite, were observed. The samples with low potassium content showed colossal magnetoresistance (CMR) of about ∼10–25%∼10–25% under H=10kOe, and increases at low temperatures. The resistivity data were analyzed using various models, and it has been concluded that the electrical resistivity data in the high temperature regime (T>Tp)(T>Tp) can be explained by the small polaron hopping model.