Fe3+ to Fe2+ Partial Reduction in the Monoclinic Double Perovskite Ba2-xLaxFeSbO6

BLANCO, M. CECILIA; GUIMPEL, J. J.; PAESANO, A.; CARBONIO, R. E.

Praga. República Checa.

Conferencia; 9th Conference on Solid State Chemistry; 2010

  Double perovskites design is a very interesting area when the classic A2BB’O6 structure is accompanied by a rock salt type ordering for B cations, because of their diverse potential technological applications [1].  In this work the successful synthesis of the Ba2-xLaxFeSbO6 series, with x = ¼, 1/3, ½ and ¾, is presented. Here, electron doping through substitution of La(III) by Ba(II) in Ba2FeSbO6 is studied. Also, structural, magnetic and Mössbauer spectroscopy characterization is performed. All compounds were synthesised through traditional solid state ceramic method. Ba7/4La1/4FeSbO6 compound was prepared in air, while the remaining perovskites were synthesised under Argon inert atmosphere. Corresponding heat treatments were performed at 1350 ºC. Structural characterization by Rietveld Analysis showed a monoclinic P 21/n structure for all compounds. Powder neutron diffraction data confirmed the final stoichiometry. Partial ordering for Fe2+/3+ and Sb5+ ions over two different crystallographic octahedral sites could be established. Unit cell parameters showed the expected decrease with the corresponding increase of La3+ content, due to its lower ionic radii compared with Ba2+.   In the figure we show the Mössbauer spectra for x=1/2. We observed three doublets, one assigned to pure Fe3+, another to a mixed valence Fe3+/2+ and the third to pure Fe2+. As x increases, there is a gradual increase in Fe2+ and a decrease in the Fe3+ doublet, which finally disappears for x= ¾. This is expected since Fe2+ content should increase as La3+ replaces Ba2+. Magnetization versus Temperature measurements for x = ¼ material showed predominating ferromagnetic interactions. Magnetization versus Applied Magnetic Field showed a hysteresis loop with a slight curvature of the magnetization and saturation values not been reached. Complete magnetic and structural studies will be presented.     [1] T. K. Mandal et al, Chem. Mater. 2008, 20, 4653-4660.