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Solid State Ionics, Vol.180, No.40, 1702-1709, 2010
Synthesis and electrical properties of nanocrystalline Ca1-xEuxMn3 +/-delta (0.1 <= x <= 0.4) powders prepared at low temperature using citrate gel method
Nanopowders of Ca1-xEuxMnO3 (0.1 <= x <= 0.4) manganites were synthesized as a single phase using the auto gel-combustion method. The citrate method shows to be simple and appropriate to obtain single phases avoiding segregation or contamination. The Ca(1-x)Eu(x)Mno(3) system has been synthesized at 800 degrees C during 18 h, against the conventional method of mixing oxides used to obtain these materials at higher temperatures of synthesis. The formation reaction was monitored by X-ray diffraction (XRD) analysis and an infrared absorption technique (FTIR). The polycrystalline powders are characterised by nanometric particle size, similar to 48 nm as determined from X-ray line broadening analysis using the Scherrer equation. Morphological analysis of the powders, using the scanning electron microscope (SEM), revealed that all phases are homogeneous and the europium-substituted samples exhibit a significant decrease in the grain size when compared with the undoped samples. The structure refinement by using the Rietveld method indicates that the partial calcium substitution by europium (for x >= 0.3) modifies the orthorhombic structure of the CaMnO3 perovskite towards a monoclinic phase. All manganites show two active IR vibrational modes around 400 and 600 cm(-1). The high temperature dependence of electrical resistivity (between 25 and 600 degrees C) allows us to conclude that all the samples exhibit a semiconductor behaviour and the europium causes a decrease in the electrical resistivity by more than one order of magnitude. The results can be well attributed to the Mn4+/Mn3+ ratio. (C) 2009 Elsevier B.V. All rights reserved.
Keywords:Nanocrystalline manganites;Electron-doped manganites;Citrate gel method;Europium doping;Electrical properties