Pure and Ca-doped LaCoO 3 Nanopowders: Sol-Gel Synthesis, Characterization and Magnetic Properties
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Pure and Ca-doped LaCoO3 Nanopowders: Sol-Gel Synthesis, Characterization and Magnetic Properties
Lidia Armelao1, Davide Barreca1, Gregorio Bottaro1, Andrea Caneschi2, Claudio Sangregorio2, Alberto Gasparotto3, Stefano Gialanella4, Cinzia Maragno3, Eugenio Tondello3 1 ISTM-CNR and INSTM - Department of Chemistry - University of Padova - Italy 2 Department of Chemistry and INSTM - University of Firenze - Italy 3 Department of Chemistry and INSTM - University of Padova - Italy 4 Department of Engineering and Industrial Technologies - University of Trento - Italy
ABSTRACT This work is focused on the sol-gel synthesis of pure and Ca-doped LaCoO3 nanopowders. The samples were prepared starting from methanolic solutions of cobalt (II) acetate (Co(CH3COO)2.4H2O), lanthanum (III) nitrate (La(NO3)3.6H2O) and calcium (II) acetate (Ca(CH3COO)2.H2O). After solvent evaporation, the obtained powders were dried under vacuum and subsequently treated in air up to 1273 K. The system evolution under thermal annealing was studied by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM), while the chemical composition was analyzed by X-ray Photoelectron (XPS) and X-ray Excited Auger electron (XE-AES) spectroscopies. The temperature and field dependence of the magnetic properties of the Ca-doped samples were investigated, and compared to those of the corresponding pure LaCoO3 powders.
INTRODUCTION Perovskite-type oxides of rare-earth and transition metals (LaMO3, M = Co, Mn, Fe…) are being increasingly investigated due to their potential applications in heterogeneous catalysis, oxygen sensing and Solid Oxide Fuel Cells (SOFCs) [1]. Among them, lanthanum cobaltite is particularly promising, thanks to the accessibility for cobalt of the II and III oxidation states. Furthermore, the partial substitution of lanthanum by strontium and calcium improves the material functional properties, i.e., ionic conductivity and thermal characteristics, especially important for the utilization in SOFCs [2]. The growing interest in such mixed oxides relies on a detailed investigation of their structureproperty relationships on the nano dimensional scale, where the inherent synergy of large surface area and high defect content is expected to result in a significantly different behavior with respect to the bulk counterpart. The possibility to tailor these features as a function of synthesis procedures appears thus as a powerful tool in order to optimize the material performances. In this context, the sol-gel technique plays an outstanding role as a soft bottom-up approach to achieve a good control over the system composition and microstructure.
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In this work, particular attention is focused on the chemical and microstructural evolution of lanthanum cobaltite-based nanosystems as a function of composition and processing conditions as well as on their influence on the magnetic properties.
EXPERIMENTAL DETAILS Pure and Ca-doped LaCoO3 nanopowders were synthesized by a non-alkoxidic route. The samples were prepared starting fro
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