Electron-doping through LaIII-for-SrII substitution in (Sr1−xLax)2FeTaO6: Effects on the valences and ordering of the B-site cations, Fe and Ta

We have employed aliovalent A-site cation substitution, LaIII-for-SrII, to dope the Sr(Fe0.5Ta0.5)O3 perovskite oxide with electrons. Essentially single-phase samples of (Sr1−xLax)(Fe0.5Ta0.5)O3 were successfully synthesized up to x≈0.3 in a vacuum furnace at 1400 °C. The samples were found to crystallize (rather than with orthorhombic symmetry) in monoclinic space group P21/n 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)2FeTaO6. From Fe L3 and Ta L3 XANES spectra it was revealed that upon electron doping the two B-site cations, FeIII and TaV, 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.