Studies on nanocrystalline La1-x CaxMnO3 (0.0 \leq x \leq 0.5) manganites

Nanocrystalline CMR materials La1-x Ca xMnO3 (0.0 \leq x \leq 0.5) have been prepared by a low temperature solution combustion (LCS) method. Powder X-ray diffraction patterns of the as made phase – pure powders reveals that undoped and doped manganites are cubic in phase. The stabilization of cubic phases in doped La-manganites is due to substitution of Ca2+ in La3+ sites, resulting in higher Mn4+ content . The Mn4+ present in the samples was determined by iodometric titration as function of calcium doping. The homogeneity, microstructure and particle size of the compounds were examined by SEM. Both undoped and doped lanthanum manganites show two active IR vibrational modes at 400 and 600 cm-1. Metal – insulator transition temperature (TM-I) is observed in the range 235-117 K for calcium doped samples. These values are low compared to the samples prepared by ceramic route. This difference in transition temperature may be due to smaller particle size in the range 30-50 nm