Mechanisms of the Solid-State Synthesis of Ln2SrFe2O7 (Ln = La, Nd, Gd, Dy) Layered Perovskite-Related Phases

The formation mechanisms for a series of n = 2 Ruddlesden-Popper phases Ln(2)SrFe(2)O(7) (Ln = La, Nd, Gd, Dy) in the Ln(2)O(3)-SrO-Fe2O3 systems were determined. The solid-state synthesis of Ln(2)SrFe(2)O(7) (Ln = La, Nd) proceeds by a mechanism involving the stage of formation of LnFeO(3) and LnSrFeO(4) intermediates with their subsequent interaction to form the target product. In the case of Gd2SrFe2O7 formation, two mechanisms are realized, namely, those going through the GdFeO3 + GdSrFeO4 and Gd2O3 + Gd0.5Sr0.5FeO3-alpha interaction stages. The limiting stage of the Dy2SrFe2O7 formation is the reaction between Dy2O3 and Dy0.5Sr0.5FeO3-alpha.