Abstract
A series of nano-polycrystalline alkali metal doped in La-based manganites ( La 1 - y K y ) 0.7 Ca 0.3 MnO 3 samples ( y = 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 ( T p ) 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 % under H = 10 kOe , 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 > T p ) can be explained by the small polaron hopping model.
Published Version
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