Electron-doping through La-III-for-Sr-II substitution in (Sr1-xLax)(2)FeTaO6: Effects on the valences and ordering of the B-site cations, Fe and Ta

摘要

We have employed aliovalent A-site cation substitution, La-III-for-Sr-II, to dope the Sr(Fe0.5Ta0.5)03 perovskite oxide with electrons. Essentially single-phase samples of (Sr1-xLax)(Fe0.5Ta0.5)O-3 were successfully synthesized up to x approximate to 0.3 in a vacuum furnace at 1400 degrees C. The samples were found to crystallize (rather than with orthorhombic symmetry) in monoclinic space group P2(1) that accounts for the partial ordering of the B-site cations, Fe and Ta. With increasing La-substitution level, x. the degree of Fe/Ta order was found to increase such that the La-richest compositions are best described by the B-site ordered double-perovskite formula, (Sr,La)(2)FeTaO6. From Fe L-3 and Ta L-3 XANES spectra it was revealed that upon electron doping the two B-site cations, Fe-III and Ta-V. are both prone to reduction. Magnetic susceptibility measurements showed spin-glass type behaviour for all the samples with a transition temperature slightly increasing with increasing x. (c) 2005 Elsevier Inc. All rights reserved.