Novel, Oxygen-Deficient n = 3 RP-Member Sr3NdFe3O9and Its Topotactic Derivatives

The stabilization of the n = 3 member of the Ruddlesden-Popper series has been investigated in the Sr-Nd-Fe-O system. A new series of phases closely derived from RP-type structures has been synthesized and characterized by X-ray diffraction and electron microscopy. The control of the oxygen stoichiometry first allowed us to isolate a new highly oxygen deficient, layered oxide, Sr3NdFe3O9-. The structural analysis has revealed that this oxide crystallizes in an orthorhombic lattice (ap2 × ap2 × 28), distorted with regard to the ideal I-type symmetry of the RPtype structures. Interestingly, this oxygen-deficient n = 3 RP-member reacts at room temperature with ambient moisture to transform into a hydrated oxyhydroxide, Sr3NdFe3O7.5(OH)2·H2O. This second phase can be dehydrated topotactically in two steps by heating to 400 C, leading to Sr3NdFe3O7.5(OH)2 and then Sr3NdFe3O8.5+, respectively. The reversible character of these hydration/hydrolysis reactions is also demonstrated.