Electronic structure and chemistry of iron-based metal oxide nanostructured materials: A NEXAFS investigation of BiFeO₃, Bi₂Fe ₄O₉, α-Fe₂O₃, γ-Fe ₂O₃, and Fe/Fe₃O₄

We present a systematic and detailed near edge X-ray absorption fine structure (NEXAFS) experimental investigation of the electronic structure and chemistry of iron-based metal oxide nanostructured (FeMONS) materials including BiFeO₃, Bi₂Fe₄O₉, a-Fe ₂O₃, y-Fe₂O₃, and Fe/Fe ₃O₄. Correlations of the electronic structure and structural chemistry of these intriguing nanomaterials are presented, ranging from the nano to the bulk scale. In this work, variations in the shape, position, and intensity of the O K-edge and Fe L-edge NEXAFS spectra have been analyzed in terms of electronic structure and surface chemistry of the FeMONS materials as compared with that of the bulk. We hypothesize that surface imperfection and surface strain anisotropies in nanoparticles induce distortion and site inequivalency of the oxygen O_h sites around the Fe ion located close to the surface, resulting in an increase in the degree of multiplicity as well as in nonstoichiometric effects in FeMONS materials.