Novel, Oxygen-Deficient n = 3 RP-Member Sr₃NdFe₃O9-δ and 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, Sr 3 NdFe 3 O 9-δ . The structural analysis has revealed that this oxide crystallizes in an orthorhombic lattice ( a p √2 × a p √2 × 28 Å), distorted with regard to the ideal I -type symmetry of the RP-type structures. Interestingly, this oxygen-deficient n = 3 RP-member reacts at room temperature with ambient moisture to transform into a hydrated oxyhydroxide, Sr 3 NdFe 3 O 7.5 (OH) 2 ·H 2 O. This second phase can be dehydrated topotactically in two steps by heating to 400 °C, leading to Sr 3 NdFe 3 O 7.5 (OH) 2 and then Sr 3 NdFe 3 O 8.5+δ, respectively. The reversible character of these hydration/hydrolysis reactions is also demonstrated.