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

CUELLO GABRIEL; FERNANDO PRADO; JESÚS E. VEGA CASTILLO

Campinas

Encuentro; 30th LNLS Annual Users? Meeting (RAU); 2020

Brazilian Center for Research in Energy and Materials (CNPEM)

We have studied the crystal chemistry of the Ruddlesden-Popper (RP) phases LaSr3(Fe,Co,Ga)3O10- with tetragonal symmetry by Neutron Powder Diffraction (NPD) and X-ray Absorption Spectroscopy (XAS) with bdifferent contents of Fe, Co and Ga. NPD data shows the oxygen vacancies are located at the oxygen crystal sites at the central octahedra of the perovskite block in the RP structure. Fe, Co and Ga cations are not homogeneously distributed, showing a sort of preference for particular crystal sites in the perovskite block. For instance, Fe cation tends to accommodate rather at sites with a lower concentration of oxygen vacancies, i.e. at the crystal sites of the perovskite layers next the rock salt layer, whereas Co and more markedly Ga prefer the 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. X-rays Absorption Near Edge Structure (XANES) analysis suggests that the average valence of Fe is always higher than Co and both are higher than 3+ of Ga cations.The results of both EXAFS and XANES analyses are in agreement with the preferential location of the oxygen vacancies at the central perovskite layer where Co and Ga cations are majorly located according to NPD data. The combination of NPD and XAS has been proven effective to assess the crystal chemistry and defect structure of the LaSr3FexCoyGa3−x−yO10− system.