Characterization of La_0.67Ca_0.33MnO_3±δ particles prepared by the sol–gel route

Abstract

We report in this work the characterization of La_0.67Ca_0.33MnO_3±δparticles synthesizedvia sol–gel technology starting from an aqueous solution of the metallic nitrates and using urea as gelificant agent. The gelification is assumed to happen through the formation of polynuclear species by condensation reactions between hydroxo complexes. Gels were decomposed at 250 °C and calcined for 3 h at temperatures ranging from 300 to 1000 °C. Complete crystallization takes place at ca. 600 °C. The powders were structurally characterized by X-ray diffraction and their structural parameters were calculated using the Rietveld method. The Mn^IV content of the several samples was determined to be higher than the stoichiometric 33%. TEM micrographs show elongated particles of which the polar (long) axis size increases from 40 to 300 nm as the calcination temperature increases. Magnetization and magnetoresistance studies are reported showing that the particles smaller than 80 nm behave as single magnetic domains while the large ones behave as multidomains. A magnetoresistance of 12% at 1 kOe was observed for all the particles synthesized by this sol–gel method.

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