Sol-gel synthesis of neodymium-barium manganites utilizing microwave irradiation
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Sol-gel synthesis of neodymium-barium manganites utilizing microwave irradiation A. E. Chekanova1, A.S. Vanetsev2, E.A. Eremina3, Yu. D. Tretyakov3 1
Lomonosov Moscow State Academy of Fine Chemical Technology, Russian
Federation, Moscow, 119571, Vernadskii ave. 86. E-mail: [email protected] 2
Kurnakov Institute of General and Inorganic Chemistry RAS, Russian
Federation, Moscow, 119991, Leninskii ave. 31. 3
Department of Chemistry, Lomonosov Moscow State University, Russian
Federation, Moscow, 119992, Leninskie Gory.
INTRODUCTION Discovery of the effect of colossal magnetoresistance (CMR) in doped manganites R1-xAxMnO3 (where R- La, Pr, Nd, Sm; A- Ca, Sr, Ba, Pb) has attracted large interest (MR of the colossal magnetoresistance materials could be very large, 100%) due to their potential applications as electrode materials in solid oxide fuel cell, chemical sensors, catalysts, and magnetic sensors [1-3]. It is worthy to note that the functional properties of R1-xAxMnO3 manganites depend on their composition, microstructure, chemical and thermal prehistory. One of the methods for improvement of functional properties of materials consist in application of method of chemical homogenization, particularly sol-gel method. Recently this method appears to be one of the most attractive synthetic paths due to its simplicity, scalability, and low cost. The most commonly used modification of solgel technique is citrate method [6, 7] in which citric acid and ethylene glycol are used as co-polymerization agents and product of polyetherification is combusted and annealed to form desired oxide product (Pechini method). The main disadvantages of common Pechini-type approach consist in agglomeration of resulting oxide powders as well as comparatively high
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temperature and long duration of calcination required for decomposition of intermediate gel phase [8]. In this work we tried to overcome these demerits of Pechini technique using possibilities of microwave irradiation. Microwave heating provides significant peculiars comparing with conventional heating methods, namely, volumetric and non-contact heating, direct energy transfer, and possibility of selective heating of reaction mixture components [9]. These advantages appear to be extremely useful in solid state synthesis of complex functional materials allowing to decrease energy consumption and duration of process significantly. Present work is dedicated to optimization of Nd0.7Ba0.3MnO3 synthesis by application of sol-gel technique with subsequent microwave treatment of intermediate product.
EXPERIMENTAL Sol-gel process: suitable amount of citric acid was added to the nitrates solution in distilled water. After that ammonium hydroxide solution was added until pH=6. Then solution was heated to evaporate the excess of water. Then suitable amount of coordinating agent (ethylene glycol) was added and heating was continued until transparent gel was formed.[6] Obtained gel was divided in two parts one of which was thermally decomposed in
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