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

Abstract

The formation mechanisms for a series of n = 2 Ruddlesden-Popper phases Ln₂SrFe₂O₇ (Ln = La, Nd, Gd, Dy) in the Ln₂O₃-SrO-Fe₂O₃ systems were determined. The solid-state synthesis of Ln₂SrFe₂O₇ (Ln = La, Nd) proceeds by a mechanism involving the stage of formation of LnFeO₃ and LnSrFeO₄ 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 + Gd_0.5Sr_0.5FeO_3-α interaction stages. The limiting stage of the Dy₂SrFe₂O₇ formation is the reaction between Dy₂O₃ and Dy_0.5Sr_0.5FeO_3-α.