Partial cationic order at the B site of the n = 3 Ruddlesden-Popper phases LaSr3(Fe,Co,Ga)3O10-δ studied by Neutron Powder Diffraction and X-ray Absorption Spectroscopy

Abstract

The crystal chemistry of the Ruddlesden-Popper phases LaSr3Fe1.5Co1.5O10-δ, LaSr3Fe1.35Co1.35Ga0.3O10−δ, LaSr3Fe1.8Co0.6Ga0.6O10−δ and LaSr3Fe2.4Ga0.6O10−δ with tetragonal symmetry has been studied by Neutron Powder Diffraction (NPD) and X-ray Absorption Spectroscopy (XAS) varying Fe, Co and Ga content. NPD data shows that oxygen vacancies are located at the O(2) and O(4) crystal sites at the central octahedra of the perovskite block. Furthermore, Fe, Co and Ga cations are not homogeneously distributed, showing certain preference for particular crystal sites in the perovskite block. For instance, Fe cations tend to accommodate in sites with a lower concentration of oxygen defects, i.e. the B(2) crystal sites of the perovskite layers next to the rock salt layer, while Ga cations noticeably prefer the B(1) sites at the central perovskite layer. This cationic distribution was confirmed by Extended X-ray Absorption Fine Structure (EXAFS) analysis, which shows the average coordination number of Fe is always higher than the coordination number obtained for Co and Ga, in agreement with the preferential location of the oxygen vacancies at the central perovskite layer where Ga cations are located according to NPD data. The combination of NPD and XAS data was found effective to describe the crystal chemistry and defect structure of the LaSr3FexCoyGa3−x−yO10−δ system.