Low temperature synthesis, structural characterization, and zero-field resistivity of nanocrystalline La_(1-x)Sr_xMnO_(3+δ) (0.0 ≤ x ≤ 0.3) manganites

摘要

This paper reports the synthesis of nanocrystalline strontium doped manganites by a simple and instantaneous solution combustion method, which is a low temperature initiated route to prepare fine-grained oxide powders with good surface area. Rietveld refinement of X-ray data indicates that the as-formed manganites exhibit a cubic phase with space group Pm3m. However calcined (900 ℃, 6 h) samples transform into rhombohedral phase with space group R-3c. The scanning electron micrographs of the powders reveal that the sizes of very fine primary particles which are in an agglomerated form, decrease as strontium content increases. The infrared spectra of lanthanum manganites show two active modes at 400 and 600 cm~(-1). From zero-field resistivity measurements, it is found that all the samples exhibit metal-insulator transition (T_(M-I)) in the range of 219-252 K, which is low as compared to the samples prepared by ceramic route. The lower (T_(M-I)) values might be due to smaller particle sizes in the range of 25-45 nm.