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Synthesis and Characterization of Nanocrystalline Manganese Oxide and Rare-Earth Manganites

Since the discovery of colossal magnetoresistance (CMR) phenomenon, the great attention of scientists was directed to the study of manganite perovskites T1-xDxMnO3, where T is a trivalent rare-earth cation (e.g. La, Pr, Nd, Sm) and D is a divalent alkaline-earth cation (e.g. Ca, Sr, Ba). In a certain range of doping, x≈ 0.2-0.4, the ground state is ferromagnetic, and the paramagnetic to ferromagnetic transition is accompanied by a sharp drop in resistivity. Here, we report the preliminary results of the first part of our study concerning synthesis and characterization of nanocrystalline manganese oxide and rare-earth manganites. We used nonaqueous sol-gel route in order to prepare pure, stoichiometric, homogeneous, highly-crystalline nanosized manganite perovskites with controlled crystallite size and morphology. The Rietveld refinement of XRD powder patterns, combined high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) analysis were employed for structural characterization of as-synthesized compounds. The particle morphology, crystallinity, structure and microstructure were related to the synthesis conditions: precursors, type of solvent, reaction temperature, duration of the reaction, reaction atmosphere in order to find out the optimal conditions for successful synthesis of manganese oxide and rare-earth CMR manganite perovskites.

Nanocrystalline; Nonaqueous sol-gel

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