Synthesis and structural mechanisms of the 2201-type ferrites and polytypes: Fe 2(Sr 2 − xA x)FeO 6.5 − δ/2 (A = Ba, La, Tl, Pb and Bi)

Abstract

The Fe 2(Sr 2 − x A x )FeO 6.5 − δ/2 systems have been investigated, by doping the iron rich 2201-type parent structure with Ba 2+, La 3+ and 5d 10 post-transition cations. The syntheses have been carried out up to the limit of the 2201-type solid solutions, in order to test the role of the double iron layer Fe 2O 2.5 − δ/2 . The localisation of the charge carriers in these compounds is consistent with their strong antiferro-magnetism. The investigation was then carried out in the transition part of the diagram up to the formation of stable phases. The study of structural mechanisms was carried using high resolution electron microscopy (transmission and scanning transmission), electron diffraction and energy dispersive spectroscopy. Different non-stoichiometry mechanisms are observed, depending on the electronic structure and chemical properties of the doping elements. The specific behavior of the modulated double iron layer is discussed.